Irene Antonenko, Ph.D. Thesis: Chapter 3

Abstract
An analysis of 24 low resolution and 4 higher resolution Clementine images from the region surrounding Schickard crater was undertaken to assess the applicability of Clementine data to the identification and examination of cryptomafic deposits. These investigations have shown that Clementine data can be used to effectively identify buried basalt materials. To a first order, RGB ratio composites are found to be effective indicators of mafic and feldspathic materials. Clementine 5-band UVVIS spot spectra can be used to confirm the basaltic or highland natures of fresh lunar materials. Such spectra are shown to be effective in distinguishing the presence of basalt materials in the halos of immature craters. Also, spectral data, when obtained from the slopes of fresh craters, can be used to distinguish subsurface layers, allowing cryptomafic deposits to be identified and stratigraphy to be determined. The diameters of such craters can be measured and used to estimate thicknesses of the stratigraphic layers. On the basis of these data, the following stratigraphy of the study region is proposed. At the top can be found a surface mare layer, on the order of 450 meters thick or less. Below is found a thin ejecta layer (<85 meters), which is underlain by a shallow cryptomafic deposit, approximately 400 meters thick. This cryptomafic layer is underlain by a unit of highland material, which is at least 400 meters thick. The existence of deeply buried cryptomafic materials is speculated in several areas. This entire stratigraphic column is expected to be present in only a few regions of the study area, and some of the proposed layers may be absent in most places.

Introduction

Hidden mafic deposits, termed cryptomaria by Head and Wilson [1992], have long been known to be of great importance to lunar studies because they provide evidence of ancient volcanism [Schultz and Spudis, 1979, 1983; Hawke and Bell, 1981; Bell and Hawke, 1984; Mustard et al., 1992, 1994]. Because of their hidden or obscured nature, the identification of cryptomare deposits has had to rely on indirect methods, such as the presence of dark-haloed craters [Schultz and Spudis, 1979, 1983], which penetrate through the obscuring layer and excavate the underlying mafic material. Such indirect methods cannot be used to confirm the mare nature of these hidden volcanic materials, thus the term cryptomafic deposits is preferable to describe these ancient volcanic units. Previously, criteria for the identification and classification of cryptomafic deposits have been presented by Antonenko et al. [1995]. In Chapters 1 and 2, techniques were developed for determining the geometries of cryptomafic bodies, through the use of dark-haloed impact craters, and applied to a study area on the western limb of the Moon. Volume estimates, totaling approximately 5 x 10⁵ km³, were obtained for the cryptomafic deposits that are found in this region, representing an increase of 5% to the total known volume of volcanic deposits on the lunar surface.
These early studies, however, used Earth-based telescopic images of the Moon [Kuiper et al., 1967; Whitaker et al., 1963], which are limited by their low resolution and lack of global lunar coverage. Consequently, the smallest dark-haloed craters in the study area may not have been identified and estimates of cryptomafic materials may be too low. Motivated by this concern, attention was turned to the Clementine data set [Nozette et al., 1994] that, with its higher resolution, affords an opportunity to study basalt excavation using smaller craters. Furthermore, the multispectral capabilities of the Clementine data set provide additional tools for identifying buried basalts. Visual identification of dark-haloed craters requires that the soils, which make up the crater ejecta, be optically mature. Spectral identification of basaltic halos does not require that the halo material be optically mature, thus allowing less mature craters to be analyzed for basalt excavation. Also, spectral identification of basalts on the fresh slopes of crater walls does not require an understanding of dark halo formation and obscuration for the presence of buried mafic material to be inferred. These considerations allow cryptomafic deposits to be studied in greater detail than with just dark-haloed craters alone.
Inspired by these possibilities, we began an analysis of multispectral Clementine UVVIS data for the area encompassing Schickard crater and its surroundings (Figure 1), where numerous dark-haloed craters have been identified and much previous work has been done [Lucey et al., 1991; Hawke et al., 1993; Mustard et al., 1992, 1994; Head et al., 1993; Greeley et al., 1993; Blewett et al., 1995]. The dark-haloed craters identify a cryptomafic deposit beneath a light plains unit that crosses Schickard. Ejecta from the Orientale basin is clearly visible here in the form of striations oriented radially from Orientale [Karlstrom, 1974]. Previous studies (Chapter 1) have suggested that Orientale ejecta corresponds to the cryptomafic-obscuring light plains unit in Schickard. Two post-Orientale mare patches, that embay the light plains unit, are found within Schickard crater, indicating that extrusive volcanism also occurred at a later date in this region.

Data Processing and Collection

Working with 5 UVVIS bands, Clementine data was compiled for an area of approximately 40,000 km², encompassing all of the crater Schickard and adjacent regions (Figure 1). The data set consists of 24 Clementine UVVIS image cubes that have a resolution of ~ 0.23 - 0.25 km/pixel, and a strip of 4 UVVIS cubes in the eastern edge of the Schickard crater (location is shown in Figure 1) that have a higher resolution of ~0.12 km/pixel. For each image cube, the data was calibrated as described by Pieters et al., 1994, 1996] and all filters were registered to the 750 nm filter frame, in order to allow point spectra to be obtained. Ratios of the 415 nm, 750 nm, and 950 nm filters were then calculated and stretched, to be displayed in the standard RGB color composite from Galileo lunar image analysis [Belton et al., 1992]. Mosaics of the color composite images and the 750 nm filters from the 24 lower resolution image cubes were compiled for display purposes (Figure 2). Wavelength dependent photometric corrections, which accommodate the change of color with phase angle, were not performed on the data set. However, since the phase angle at which this data was acquired only ranges from 41 to 49 degrees, the usefulness of the data, with regards to the identification of basalt vs. highland materials, is not expected to be dependent on this small correction [McEwen et al., 1998].
Spectra were obtained from the individual image cubes, using a 3x3 pixel-averaging kernel to minimize on spectra irregularities. Spectra were sampled at locations where steep slopes maintained a fresh, unweathered surface, such as on the slopes of crater walls and on scarp surfaces, since fresh materials have stronger spectral features and so are more easily distinguishable. The color composites, which highlight the presence of fresh materials, were used to help in spectra site selection.
Measurements of crater diameters were obtained from the individual 750 nm image frames. Diameters for craters were estimated by measuring the pixel distance from rim-crest to rim-crest for each crater, and then converting this distance to kilometers by comparison to other craters, of known diameter, in the same image frame. The overlap between frames, and an abundance of known crater diameters in this area (from Chapter 1), allowed for substantial double-checking to take place, giving us confidence in this method. A comparison of the meter per pixel resolutions obtained in this manner and those found in the Clementine data headers further shows that these crater diameter measurements are valid to within ±0.5 km for the largest craters considered, and have much lower discrepancies for the smallest craters.

Data Interpretation

Image Analysis
The goal of this study is to locate hidden basalts, which is accomplished by identifying the presence of mafic components in craters from the study area and determining whether they are basaltic in composition. The detection of mafic components can be accomplished quickly and easily by visual inspection of the color composite image (Figure 2b). In the color composite, the 750/950 nm ratio is shown in green, the 750/415 nm ration is shown in red, and the 415/750 nm ratio is shown in blue. The 415/750 nm ratio measures the steepness of the continuum slope in the visible wavelengths. Since soil maturation processes on the Moon tend to redden continuum slopes, mature materials will appear red in the color composite image. Flatter continuum slopes, which appear blue in the composite, generally indicate fresh or feldspathic materials [Adams and McCord, 1971; Pieters et al., 1993; Fischer and Pieters, 1995]. Therefore, these tend to show up as blue in the color composite image. The 750/950 nm ratio is sensitive to the strength of the ferrous absorption feature, which is centered near 1痠, in pyroxenes. Strong absorption features indicate the presence of abundant mafic minerals or fresh materials [Adams and McCord, 1971; Pieters et al., 1993; Fischer and Pieters, 1995], so these will appear green in the color composite. Thus, fresh materials will have both a strong green and blue component in the color composite, but less fresh mafic materials will only have a green component. Mafic materials can, therefore, be located by their bright green color on the composite image.
Comparing Figures 2a and 2b, it can be seen that many of the important characteristics of this region show up clearly in the color composite image. The rim of Schickard crater can be clearly seen as a bright blue annulus, indicating that the rim of Schickard is highly feldspathic. The mature light plains in and around Schickard crater appear red and are distinguishable from the more yellow regions of the mare patches inside Schickard. Several of the dark-haloed craters, indicated in Figure 1, are seen to have distinct yellow halos in the color composite image. This is consistent with the interpretation that these craters have excavated mafic material, which has matured to produce a mare-like signature. Finally, many craters in the red-colored plains areas are seen to have interior walls that are bright green, implying that buried mafic materials are abundant here. Clearly, to a first order, the RGB color composite image of Figure 2b can be used to assess the composition of the surface, and in some cases the subsurface, units in this region.

Spectra Analysis
The image analysis of Figure 2b can only indicate the presence of mafic materials. It cannot be used to identify basalts in these areas. To confirm the presence of basaltic materials, spectra must be obtained. The analysis of this region was, therefore, extended by considering 5-channel UVVIS spectra, taken from key areas in the image. Averaged 3x3 pixel spectra were obtained from various locations (Figure 3), with the search being generally confined to the fresh slopes of craters or high relief topography, because of the inherently stronger differences between fresh basalt and highland spectra. A total of 357 spectra was collected in the study area, with some repetition of spectra location occurring. The resulting spectra were plotted (Appendix 2) and analyzed on the basis of the strength of their 1um absorption feature. The results can be classified into three basic types; basaltic, highland and ambiguous spectra (Figure 4). Spectra that exhibit a strong ferrous absorption feature near 1 um are interpreted to represent a high-Ca pyroxene-rich material, and these are classified as basalt spectra (Figure 5a). Those spectra that exhibit very weak, or no, absorption features near 1 um are interpreted to represent feldspathic or anorthositic materials, and these are classified as highland spectra (Figure 5b). A number of spectra have characteristics that cannot be classified as definitely basaltic or highland. Some of these spectra exhibit features that may still contain artifacts from the calibration process (Figure 5d). Others may indicate that mixing is occurring at this location (Figure 5c), with highland, mare, or other lunar lithologies, either fresh or mature, representing potential endmembers. The exact nature of the spectral endmembers, however, cannot be confirmed without spectral mixing analysis, which is beyond the scope of this study. Even if basalt endmember could be identified in some ambiguous spectra, it is not possible to resolve whether this indicates the presence of basalt layers or the presence of mixed layers emplaced by ballistic sedementation processes [Oberbeck, 1975]. All of the unclassified spectra are defined as ambiguous and are not considered in further analysis. Of the 357 spectra obtained, it was possible to classify 198 spectra as being clearly basaltic or highland. The results of this spectral study are presented in Table 1.
The spectral results are shown plotted on the 750 nm mosaic image in Figure 6. Basaltic spectra are plotted as black dots. Highland spectra are plotted as white dots. Ambiguous spectra are not plotted. Using the spatial distribution of the distinct basaltic and highland spectra, as well as topographical cues such as crater rims, the boundaries of cryptomafic deposits in this area were then estimated (Figure 6). As expected, craters and flow scarps in the mare area (low albedo patches) all have basaltic spectra. The rim of Schickard crater (hatched boundary) exhibits only highland spectra. Everywhere else, basalt spectra appear to predominate, suggesting that buried basalts may be present here, and indicating that volcanism in this region was considerably more significant than indicated by the visible mare patches. One exception is the region just south of Schickard (cross-hatched boundary). This area is beyond the rim of Schickard crater, but here highland spectra predominate. The presence of one large, previously identified, dark-haloed crater, however, suggests that mafic units may be buried very deeply in this region.

Stratigraphic Analysis
On the basis of spectra, color composite images, and cryptomafic boundary determinations from this study, as well as prior knowledge of this area from previous studies (Chapter 1), a map of the study region was compiled (Figure 7). Here, the distribution of different stratigraphic columns or sequences, which are suspected to occur in the various mapped areas, are illustrated. Several types of distinct stratigraphic sequences are proposed. Their characteristic features and the basis for their determinations is discussed below.

Highland Column
The unit corresponding to the Schickard crater rim (hatched boundary in Figure 6, Highland Column in Figure 7) appears to consist of a thick sequence of predominantly highland material. As can be seen from the color composite of the three ratios (Figure 2b), the Schickard crater rim contains very little mafic material (very little green) and craters here tend to have no mafic materials on their slopes. All spectra in this unit, from large and small craters alike, indicate the presence of only highland materials. The predominant surface feature here seems to be the rough topography of the fresh highland slopes along the crater rim. These observations seem to indicate that no basaltic material lies buried anywhere beneath the upper layers here. Therefore, this unit is interpreted to have a "Highland" stratigraphy, meaning that the entire stratigraphic column can be represented solely by highland materials. It would seem that the Schickard crater excavated primarily highland material and so must have impacted into a predominantly highland substrate, such as the ancient highland crust.

Deep Cryptomafic Column
To the south of Schickard crater, a unique unit (cross-hatched boundary in Figure 6, Deep Cryptomafic Column in Figure 7) has been mapped, which is suspected to contain a very deeply buried cryptomafic deposit. On the surface, this unit seems to be very similar in appearance to the rim of Schickard crater, which has been mapped as having a "Highland" stratigraphic column (Figure 7). The topography here is rough in comparison to the adjacent plains, although not as rough as on the Schickard rim. The color composite of Figure 2b shows little evidence of abundant mafic materials. And almost all of the spectra identified in this unit, from both large and small craters, are highland spectra, indicating a predominantly highland lithology here. However, the presence of a deeply buried mafic deposit is suggested for this area by a single, large dark-haloed crater (21.4 km diameter), which is found in this unit. This dark-haloed crater (#15 in Figure 8) is so prominent that its halo can clearly be seen in the 750 nm filter image of Figure 2a and is also identifiable in the color composite of Figure 2b as a distinct yellow halo surrounding the crater. However, all efforts to obtain a clear basaltic spectrum from anywhere along the steep interior slopes of this crater were unsuccessful (Figure 6). The lack of any fresh basaltic spectra suggests that the dark halo surrounding this crater may have been formed by other processes. For example, impact melts have been known to produce low albedo ejecta deposits around craters [Schultz and Spudis, 1979; Howard and Wilshire, 1975]. However, the presence of basaltic materials in the halo of this crater has been identified by the spectral mixing analysis of Head et al. [1993]. Using Galileo SSI data, they determined mare abundances in the Schiller-Schickard area and found a significant mare component (>25%) in the ejecta of this particular crater. Such significant abundances argue that this mare material must originate from deep within the crater, otherwise the excavation of deep highland materials should have diminished the mare signature. Evidence of slumping, in the form of slump terraces, can clearly be seen in the interior of this large crater. Therefore, it is reasonable to expect that slumping of great thicknesses of surface highland material may have covered over and obscured deep mafic deposits further down the crater slopes. Also, this sampling method is biased towards the upper stratigraphic layers, since only the spectra of fresh materials are considered. Thus, the presence of mafic materials may not be detectable by this analysis if the basalt layer is located at a depth where the crater slopes are too shallow to produce a fresh surface. All of these considerations are consistent with the hypothesis that the mafic layer here is buried particularly deeply, and that mass wasting from the very thick overlying layers has filled the bottom of the crater with highland material, obscuring any mafic signature.
The presence of one basaltic spectra (Figure 6, #104 in Figure 3 and Table 1) in this unit presents an anomaly. It is possible that the crater (#104 in Figure 8) represented by this spectra is tapping into a small, shallow cryptomafic pond. However, it can also be proposed that this crater is tapping into fresh mafic materials that have been excavated and emplaced by the large dark-haloed crater (#15 in Figure 8) in this unit. Effectively, this anomalous basaltic spectra may be sampling immature dark halo material that has been exposed by the emplacement of crater #104 (Figure 8). Crater #104 is located within 2 crater diameters of the nearby dark-haloed crater (#15 in Figure 8), thus, approximately 14 meters [McGetchin et al., 1973; Schultz et al., 1981] of ejecta materials from the dark-haloed crater should be present at this location and it is reasonable to expect that some of this ejecta material could be tapped by subsequent cratering (i.e., by crater #104). Therefore, the following hypothesis is proposed; the crater associated with the anomalous basaltic spectra (#104) has tapped into the dark halo layer from crater #15 (Figure 8) and the freshly exposed basaltic materials have been serendipitously sampled by the spot spectra. This hypothesis is consistent with the suggestion that the proposed cryptomafic deposit here is buried very deeply; only large craters are expected to tap the deep cryptomafic layer and small craters are only expected to display basaltic spectra if they, by chance, impact into the dark halo materials. This hypothesis, however, is still speculative.
On the basis of the discussions presented above, the following interpretation for this unit is proposed. One potential cryptomafic deposit may be located in this region, a deeply buried basaltic unit that is overlain by a thick column of highland ejecta materials. This "Deep Cryptomafic" stratigraphy is suggested on the basis of one, large, single dark-haloed crater, and the deep burial of the cryptomafic layer is invoked to explain the lack of other basaltic signatures in this area. It should be noted that other interpretations for the stratigraphy of this unit are possible on the basis of the data. For example, this area may contain only one small, shallow cryptomafic pond that is underlain by a thick column of highland materials.

Shallow Cryptomafic Column
The remainder of the non-mare areas in the study region (Shallow Cryptomafic Column in Figure 7) are mapped as a distinct unit, and are believed to contain extensive shallow cryptomafic deposits. The areas of this unit are characterized by predominantly smooth topography at the surface, a multitude of small craters that have strong mafic signatures in the color composite image (Figure 2b), and abundant basaltic spectra (Figure 6), all of which indicate that basalt deposits are buried at very shallow depths here. The light plains materials [Karlstrom, 1974], which cover the cryptomaria in these areas, must therefore be very thin.
The presence of several highland spectra, scattered throughout this unit, suggests that the shallow cryptomafic deposit does not extend to great depths. This interpretation is supported by several sets of spectra (#6/7, 20/21, 30/31), which are obtained from the walls of larger craters (#6, 20, and 30 in Figure 8), 6 - 13 km in diameter. These spectra show that basaltic materials are present, but only near the crater rims. Further down slope in these craters, highland spectra can be found, indicating that the cryptomafic layer does not extend to great depths. None of these three craters have been identified as dark-haloed craters (Figure 1). It would appear, therefore, that the dark haloes surrounding these craters may have been obscured, supporting the theory presented in Chapter 1 that large craters will excavated sufficient mafic material to obscure a dark halo.
The presence of several dark-haloed craters (#12 and 25 in Figure 8), which are 13 - 14 km in diameter, suggests that another basalt layer may be found at greater depths here. As was indicated above, obscuration of dark-haloed craters has been indicated for craters slightly smaller than this size. Thus, the presence of visible dark halos around these large craters suggests that additional mafic material is possibly being excavated from deeper levels. Additionally, the presence of a deeply buried basalt layer is suggested by the identification of a basaltic spectra (#14) near the bottom of crater #12. This dark-haloed crater, in the southwest quadrant of Schickard, displays a series of spectra that progress from basaltic to highland to basaltic (#12, 13, 14 respectively), beginning at the crater rim and moving closer to the bottom (Figure 6). We suspect it is unlikely that the lower basaltic spectra was produced as a result of mass wasting and slumping of the upper basalt layer, since no evidence of slumping is seen on the crater walls (Figure 9) and mass wasting is expected to produce mixed or ambiguous spectra. Therefore, the presence of a deep cryptomafic layer is suggested.
Several large craters (#8, 28, 46) are identified for which no basalt spectra could be found on their slopes. If these craters penetrate through basalt layers, as is suggested by their size and the identification of basalts in nearby craters, then our failure to find basaltic spectra needs to be explained. First it must be pointed out that the data may not always permit all the layers present to be identified. Calibration and registration artifacts within the data may produce only ambiguous spectra at a given location. This is believed to be the case for crater #8, where an ambiguous spectra (spectra #8) that clearly shows calibration artifacts is identified near the crater rim. Thus, absence of a basalt (or highland) spectra does not necessarily indicate absence of a basalt (or highland) layer. This should have no affect on our assumption that stratigraphic layering is preserved with the crater wall and can be determined spectrally, since identification of a specific spectra is still expected to indicate the presence of a layer of the determined composition at that location. Second, Figure 1 shows that crater #28 is located on the rim of a large degraded crater. Therefore, the shallow cryptomafic layer may not be present at this location and crater #28 may only be excavating thick highland deposits associated with the crater rim. Conversely, the lack of basalt spectra at this location may also be related to calibration or registration artifacts (see spectra #28 in Appendix 2). Finally, crater #46 is a complex crater, which shows signs of slumping (Figure 8). Therefore, it is possible that, as was suggested for crater #12, slumping may have obscured the basaltic layers. Also, no ejecta deposit is visible around this crater and Karlstrom [1974] has mapped this crater as having subdued rims. This suggests that this crater may pre-date the emplacement of the basalt-emplacement event, thus the presence of a shallow basalt layer on the crater rim would not be expected.
From the evidence presented above, a shallow cryptomafic layer, underlain by highland materials is identified in this area. The existence of a speculative, deep cryptomafic layer is inferred beneath the highland unit. This suggested "Shallow Cryptomafic" stratigraphy is illustrated by the column in Figure 7. Two possible cryptomafic layers are suggested for the areas mapped with this column type, indicating that volcanism in this region may have occurred over an extended period of time. A total of three distinct highland layers are suspected to be present in the stratigraphy of these areas. The potential deep cryptomafic deposit is expected to be underlain by ancient highland crustal material. The upper cryptomafic layer is overlain by a deposit of highland ejecta material, which is suspected to be very thin. The third highland layer is speculative, representing the ejecta deposit that separates the two proposed cryptomafic layers.

Surface Mare Column
The two low albedo units of Figure 6 (Surface Mare Column in Figure 7) have been previously mapped as mare units [Karlstrom, 1974]. The surface topography of these mare units is very smooth, although a few flow lobe features can be distinguished in the Clementine 750 nm filter images. There are very few craters of any kind found on these mare units. All of the craters that do occur are small and have strong mafic signatures in the color composite image (Figure 2b). Only basaltic spectra are identified in these areas (Figure 6), but this could be due to a paucity of large craters, which would be required if penetration to any underlying highland units is to occur. Thus, there are no craters large enough to determine conclusively the stratigraphy below these mare units. However, crater dating studies indicate that these mare patches are younger than the adjacent light plains units [Greeley et al., 1993], an interpretation that is supported by onlap and embayment relations (Figure 2a). This relationship suggests that the maria were probably emplaced on top of material corresponding to the adjacent light plains unit. Thus, the layers suggested for the "Shallow Cryptomafic" stratigraphy, associated with the light plains unit, may also lie beneath the surface maria in these regions. A speculative "Surface Mare" stratigraphy is proposed for these mare units, as illustrated by the column in Figure 7. A total of three mafic layers are proposed for the stratigraphy of these units, one mare layer at the surface and two speculative cryptomafic layers at depth. This interpretation is consistent with the earlier suggestion that volcanism occurred over an extended period of time in the Schickard crater region.

Crater Diameter Analysis
In an effort to estimate the thicknesses of these cryptomafic units and their overlying deposits, the diameters of all craters that have distinct basaltic or highland spectra were measured (Table 1). These diameters were converted to a depth of excavation, using the relations developed in Chapter 1. It is reasoned that the presence of basaltic materials on the walls of a crater indicates that the crater has tapped into a basaltic layer. If this is the case, then the crater must be, at the very least, beginning to excavate basaltic materials. Thus, the excavation depths of craters with basaltic spectra can be used to provide a maximum estimate for the thickness of the overlying ejecta layer.
This assumption works fairly well for small craters, where only one or two layers are involved. However, for larger craters, where deeper layers may also be tapped, a more sophisticated analysis of the data is required. For example, the greater importance of mass wasting and slumping for larger craters means that material from the various layers may be transported downwards, obscuring the layers below or causing their spectra to be ambiguous. Taken to an extreme, this implies that the walls of a crater may only reflect the spectral characteristics of the uppermost layer (i.e., the dark-haloed crater #15 in Figure 8). Despite these considerations, the layering of the pre-impact surface appears to be preserved in the slopes of the crater walls. In the previous section, several cases were highlighted where different distinct highland and basaltic spectra were obtained at different depths along the crater walls (Figure 6; #6, 12, 20, and 30 in Figure 8). These spectra were obtained along a direct line from the crater rim to the crater center; thus the vertical placement of these different spectra is effectively one on top of the other. Clearly, if mass wasting is transporting the materials responsible for these spectra over great vertical distances, then some unit integrity is being maintained. In this case, materials originating from a specific unit do not appear to be mixing with materials from the other various units, which would result in ambiguous spectra, so transport is being affected by slumping (i.e., the dark-haloed crater #15 in Figure 8) or creep processes rather than the movement of individual blocks or particles. Another possibility is that not enough material is being transported to affect the spectra of the underlying layers. More likely is the possibility that the crater walls, at the location these spectra were taken, are still steep enough so that no significant accumulation from the upper layers occurs. In general, we are relatively confident that these spectra are sampling different layers of the pre-impact stratigraphy, depending on the vertical position of the spectra location along the crater wall.
In the case of the largest craters, the deepest spectra that was obtained for a specific crater, and that was definitively identified as either basaltic or highland, can be used to approximate the composition of the deepest layer that the crater is tapping. The depth of excavation can be used to estimate the maximum thickness of the units that overly that layer. However, it must be remembered that this estimate may not consider the deepest layer that the crater is tapping. Since spectra were only obtained from the steepest sections of the crater slopes, a significant portion of the crater depth will not be sampled by this method. Towards the bottom of the crater, the slopes are gentle enough to allow materials from the upper layers to accumulate, and for the soils to mature, generally resulting in ambiguous spectra. Thus, any layers, which are located within this shallow slope region, will not be detected.
In this analysis of crater diameters, any craters that are severely degraded, which show signs of flooding or the obscuration of their slopes, should be eliminated from consideration. For these craters, the crater walls may not show the full sequence of the underlying layers, since some layers may have been emplaced after these craters were formed. Only fresh craters that have excavated through the full range of the upper stratigraphy of this region should be considered. During the process of spectra collection, the nature of each spectral feature was noted and catalogued (Table 1). Features were identified as craters, mounds, flow lobes, or crater ejecta. The craters were further subdivided into fresh craters (Crater in Table 1), dark-haloed craters (DHC), degraded craters, and flat floor craters. Fresh craters have relatively crisp crater rims and are generally bowl-shaped. Flat floor craters tend to have relatively crisp rims, but have very flat floors that do not appear to have formed by lava flooding. Degraded craters tend to have heavily degraded rims and are often partially filled with later materials. Dark-haloed craters were generally found to be fresh, but are distinguished on the basis of their halos, which were identified in Chapter 1. Complex craters, identified on the basis of morphology, are indicated with an asterisk. For the purposes of this diameter analysis, craters that are catalogued as degraded (Table 1) are not considered.
This analysis of crater diameters can be supplemented with knowledge of the dark-haloed craters in this region (Chapter 1), to help further constrain layer thickness estimates. Using the equations derived in Chapter 2, estimates of the depth to a cryptomafic layer boundary can be obtained. Recalling that

t_m ~ 0.066 D_r for simple craters (1)

t_m ~ 0.12 D_r^0.85 for complex craters (2)

and

t_h < 0.053 D_r for simple craters (3)

t_h < 0.095 D_r^0.85 for complex craters (4)

where t_m is the thickness of the layers which overly a cryptomafic body, or the depth to the top of the cryptomafic deposit, t_h is the depth to the base of the cryptomafic deposit, and D_r is the rim-crest diameter of a crater with a barely visible dark halo (Chapter 2), estimates of layer thicknesses can be obtained. The error associated with these equations is ±15%, the same as the error for depth of excavation equations. If a crater has excavated enough mafic material to form a dark halo that is just beginning to be visible, then t_m gives an approximate estimate for the depth to the top of the cryptomafic layer. However, if a crater has a substantial dark halo, then t_m can still be used, but only to give a maximum estimate of the depth to the top of the cryptomafic deposit. The value t_h estimates the depth to the bottom of the cryptomafic layer only for craters where the dark halo is almost completely obscured by the excavation of underlying highland materials. If a crater is suspected of excavating a highland layer, but still displays a substantial dark halo, then t_h can be used to give a minimum estimate for the depth to the base of the cryptomafic deposit. In this manner, the dark-haloed craters in this study area can be used to help constrain the thicknesses of the stratigraphic layers.

Highland Column
No dark-haloed craters or basaltic spectra were identified in the Schickard crater rim unit, which is mapped as having a "Highland" stratigraphy. The largest craters in this unit can, therefore, be used to estimate the minimum thickness of the highland column. Craters with diameters as large as 12.5 - 14.7 km (#23, 180, 111 in Figure 8) are found here, with excavation depths that correspond to 1.0 - 1.2 km (Table 1). Thus, if basaltic materials are present in these areas, they are buried at depths that exceed 1.0 km.
The stratigraphy of the "Highland" column is interpreted to represent only pure highland material, and it is expected that the two mafic-obscuring highland layers suggested in the "Shallow Cryptomafic" column are also be present here, to some degree. Thus, the areas comprising the rim of Schickard crater, which are mapped as having a "Highland" stratigraphy, consist solely of highland material. It is, therefore, proposed that the projectile that formed the Schickard crater impacted into predominantly highland material and excavated ancient highland crust.

Deep Cryptomafic Column
As mentioned previously, only one basaltic spectra (#104) was identified in the regions mapped as having a "Deep Cryptomafic" stratigraphy, and it is suspected that this spectra represents a small, shallow cryptomafic patch or the excavation of fresh dark halo material. The depth to the proposed deeply buried cryptomafic layer, however, can be estimated from the dark-haloed crater, and further constrained by the largest craters found here. The dark-haloed crater in question (#15 in Figure 8) has a substantial halo, which can clearly be seen in both Figures 2a and 2b. Thus, using equation (2) and the diameter of this crater (21.4 km), the maximum depth to the top of the suggested cryptomafic unit can be estimated as 1.6 km. The other large craters in the region (#22, 32 in Figure 8) have diameters as large as 13.1 - 16.6 km, which correspond to excavation depths of 1.1 - 1.4 km. Therefore, the top of the suggested cryptomafic unit should be located at a depth of 1.4 - 1.6 km.
Analysis of the crater diameters, in the areas mapped as having a "Deep Cryptomafic" stratigraphy, is consistent with the earlier hypothesis that a cryptomafic layer may be located here at great depth. The suggested mafic unit would be buried by 1.4-1.6 km of overlying highland material, which is exceedingly thick. In comparison, Orientale ejecta, which is know to be emplaced in this area, should have thicknesses of only 110 - 300 meters at this distance from Orientale [McGetchin et al., 1973; Schultz et al., 1981]. While it is possible that this thickness can be explained by the presence of a particularly thick lobe of Orientale ejecta, identified in this region by Wilhelms [1987], it is likely that ejecta from the deposits of other basins and nearby large craters, such as Imbrium, Humorum, Hausen, and Zucchius, may contribute to the thickness of the overlying layer.

Shallow Cryptomafic Column
The presence of many small craters, which exhibit basaltic spectra on their inside slopes, confirms the presence of shallow cryptomafic deposits in the regions mapped as having a "Shallow Cryptomafic" stratigraphy. The smallest of these have diameters of 0.9 - 1.0 km, corresponding to an excavation depth of 76 - 84 meters. The thickness of the light plains units, which overly the shallow cryptomafic deposits in these areas, should therefore be less than 85 meters. Such small craters are found both inside and outside of Schickard crater, indicating that this thin light plains layer is relatively regional in nature. Estimates of the thin overlying layer can be confirmed by the presence of two small craters (#24, E70 in Figure 8), which appear extremely bright in the 750 nm image of Figure 2a, but whose ejecta have spectra (#221, E71) that are strongly basaltic in nature. These craters are clearly excavating sufficient quantities of mafic material for it to be spectrally detected around the crater rim, but the ejecta from these craters has not yet matured and still appears visually bright. The diameters of these craters (1.6 - 1.7 km), along with equation (1), are used to estimate that the top of the cryptomafic deposit should be significantly less than 110 meters deep. This is consistent with the estimates from depths of excavation.
Several small craters in these cryptomafic areas exhibit highland spectra. The smallest of these (#E26, E51) have depths of excavation that are 84 - 92 meters, and probably represent a thickening of the overlying layer due to mass wasting from the nearby rim of Schickard crater. A few larger craters (#222, E17, E61, E75) have depths of excavation ranging from 120 - 175 meters, suggesting that the cryptomafic deposit may be unusually thin. More likely, these craters have tapped into kipukas or irregularities in the pre-fill topography, which have made the mafic deposit particularly thin in some, isolated areas. The presence of several larger, degraded craters (#149, 213, 217, 218, E57), whose rims protrude through the underlying layers and exhibit highland spectra, attest to the rough topography of the underlying highland unit.
Earlier, three craters (#6, 20, 30), were shown to have basalt spectra on their rims and highland spectra further down slope. These were interpreted to be excavating highland materials, which may have obscured the dark haloes of these craters. These craters have depths of excavation that range from ~500 meters to 1.1 km, suggesting that the bottom of the shallow cryptomafic layer should be located at depths of less than 500 meters. This estimate can be further constrained by a medium-sized dark-haloed crater (#8), which contains a highland spectra (#9) on its lower slopes. The dark halo surrounding the crater is quite distinct, showing up in both Figures 2a and 2b, so it has not been obscured. Thus, the diameter (9.0 km) of this crater and equation (3) can be used to give a minimum estimate of ~500 meters for the depth to the bottom of the cryptomafic deposit. The base of the shallow cryptomafic layer is therefore fairly well constrained to a depth of roughly 500 meters.
Crater #12 (Figure 9), with its progression of basalt and highland spectra, has been interpreted as excavating a potential second layer of basalt material at depth. If this interpretation is correct, the excavation depth of this crater can be used to provide a speculative estimate for the thickness of the proposed intermediate highland layer. The depth to the base of this speculative highland layer may be roughly 1.1 km. The presence of visible dark halos around the craters #12 and #25 (Figure 8) has also been interpreted to suggest that additional mafic material is being excavated from deeper levels. If this interpretation is correct, the diameters of these craters (13.3 and 14.4 km ) and equation (1) can be used to give 900 meters as a rough estimate for the depth to the top of the suspected lower cryptomafic deposit. This value can be further constrained by considering the other large craters in this area (#6, 20 in Figure 8). These craters have no dark haloes, so their depths of excavation give a rough estimate of 1.1 for the depth to the base of the suspected intermediate highland unit. The highland unit, which has been identified beneath the shallow cryptomafic layer, should therefore, extend to a depth of at least roughly 900 meters.
On the basis of this analysis, the positions of the various stratigraphic layers in the "Shallow Cryptomafic" column are suggested as follows. The top of the shallow cryptomafic deposit should be located at a depth of less than 85 meters. The bottom of this layer should be found at depths of approximately 500 meters. The underlying highland layer extends to depths of at least 900 km. A potential cryptomafic layer, of unknown extent, may be located beneath the highland layer. From these determinations, the thicknesses of the stratigraphic layers can be estimated.
The upper light plains layer, which overlies the shallow cryptomafic deposits, is estimated to have a thickness of less than 85 meters, however it may be locally thicker near the eastern rim of Schickard crater. It has already been noted that Orientale ejecta is expected to have a thickness of 110 - 300 meters at this distance from the Orientale basin [McGetchin et al., 1973; Schultz et al., 1981]. Even considering the ±15% error that is associated with the depth of excavation equations, the top-most highland layer still appears to be too thin in comparison to the expected Oriental ejecta thickness. Thus, an Orientale origin for this highland layer cannot be confirmed. It is possible that this unit consists of many thin ejecta layers from a variety of young craters in the surrounding region. Candidate craters include Hausen and Zucchius to the south of this region, and numerous fresh craters from the Schickard crater rim, such as Schickard F, Schickard X, and Inghirami M. In addition, some craters in the cryptomafic areas may be excavating materials from either of the underlying highland layers and emplacing them onto the surface. This process may be occurring for such craters as Schickard B, Lehmann D, and Drebbel.
The obscuration of near-surface mafic deposits by a thin covering of crater ejecta has been identified by Antonenko et al. [1995] as one of the possible ways that cryptomafic deposits may occur. Whitford-Stark [1979] has shown that small craters can have a significant cumulative effect on the total thicknesses of surface ejecta materials. He calculated the total ejecta contribution, from all nearby basins and craters, that is present in the center of Australe basin. These calculations show that craters less than 200 km in diameter, which are found within a radius of 2000 km, together contribute ~100 meters of ejecta fill to the center of Australe [Whitford-Stark, 1979]. Pieters et al. [1985] have shown that highland rays from Copernicus crater are capable of altering the albedo of surrounding maria, even in places where the total ray deposit is on the order of 10-15 meters thick. Thus, extensive basin deposits are not required for the albedo of a mafic unit to be altered. Even a small change in albedo can be enough to call into question the mafic nature of the unit, thereby effectively obscuring it. Therefore, cumulative ejecta from small nearby craters can be enough to affect the albedo of mafic materials and form cryptomafic deposits. Furthermore, Pieters et al. [1985] have shown that a component of only 20-25% highland materials mixed into a mare surface is capable of raising mature mare albedos. Thus, the reworking of surface units by subsequent impacts should not remove the albedo-changing effects of this highland material for some time [Pieters et al., 1985]. This interpretation is not consistent with the popular belief that lateral transport is an inefficient process, where the enduring sharpness of mare and highland contacts is often cited as proof of this belief. However, Mustard and Head [1996] have shown that mare/highland contacts can be very complex regions, containing convolved geologic records. From spectral mixing analyses of Galileo SSI data, they conclude that narrow mixing zones may be common for the boundaries of large mare deposits such as Oceanus Procellarum, where obscuring material is only transported in one direction from the adjacent shore, but for smaller mare deposits, material transport effectively occurs from all directions because of the shorter distances that need to be covered. Thus, for smaller mafic deposits, the cumulative effects of ejecta from craters that surround the deposit on all side may be sufficient to obscure the mafic signature. The existence of such cryptomafic deposits has been previously proposed in the Balmer basin region on the eastern limb of the Moon [Hawke and Spudis, 1980]. Also, the Schiller-Zucchius plains, which are located to the south of Schickard crater, are known to have been obscured in this manner [Head et al., 1993; Greeley et al., 1993]. Thus, the obscuration of mafic deposits in the Schickard crater area by ejecta from nearby craters is a reasonable possibility.
The shallow cryptomafic layer, which underlies the thin highland unit, is estimated to be approximately 400 meters thick. However, the thickness of this layer is suspected to be extremely variable. At some locations, the basalt unit may be as thin as 40 meters or less, where irregularities in the pre-fill topography protrude into the cryptomafic layer and are tapped by small young craters. In other places, the entire rims of craters, which have been filled by volcanic flooding, can be seen protruding above the surface. The pre-fill topography beneath the shallow cryptomafic layer is, therefore, extremely rough.
The highland layer, which lies beneath the shallow cryptomafic layer, is estimated to be at least 400 meters. However, as noted above, highland crater rims are seen to protrude through the upper layers to the surface, thus suggesting that this highland layer can vary greatly in thickness because of irregularities in its upper boundary.
A potential cryptomafic layer, of unknown thickness, may be located beneath the highland layer. The relationship between this speculative cryptomafic layer, which may be located at a depth of roughly 900 meters, and the speculative layer identified in the "Deep Cryptomafic" column, which may be located at a depth of at least 1.4 km, is not clear. The thickness of overlying highland materials in the "Deep Cryptomafic" column may be greater than in the "Shallow Cryptomafic" column due to the presence of a thickened lobe of Orientale ejecta [Wilhelms, 1987], suggesting that the proposed layers may be connected at depth. However, no conclusions can be drawn regarding this possibility at this time.

Surface Mare Column
In the regions mapped as having a Surface Mare stratigraphy, only basaltic spectra were identified on the slopes of craters. All craters here are relatively small, ranging from 0.8 - 5.2 km in the northern mare unit and 1.1 - 2.1 km in the southern mare unit. These sizes correspond to excavation depths of roughly 70 - 440 meters and 90 - 175 meters respectively. We use these to estimate the minimum thickness of the surface mare layer, giving a thickness of <450 meters for the northern mare and <200 meters for the southern mare.
It is likely that the thicknesses of the surface mare units are actually much less than calculated above. The presence of several kipukas suggests that the mare layer may, in fact, be relatively thin. It is possible that the top highland ejecta layer, which was identified from the "Shallow Cryptomafic" column and is thought to underlie the surface mare units, is so thin that it may be difficult to detect on the crater slopes when interleaved between two basalt units. If this is true, larger craters could be penetrating through to the shallow cryptomare layer without registering the presence of the thin highland layer. This interpretation is consistent with the mare thickness estimates of Yingst and Head [1997]. Using a variety of techniques, they estimate the mare thicknesses here to be 165 meters for the northern mare unit and 80 meters for the southern mare unit. It would, therefore, appear that my thickness estimates are greatly exaggerated and it is highly likely that the larger craters in the surface mare areas are penetrating through to the shallow cryptomafic layer without registering the presence of the upper highland layer. This finding is consistent with the earlier interpretation that the upper highland unit is particularly thin.
On the basis of embayment and age relationships between the surface mare and the light plains units, as well as the above discussion, it is suggested that layers corresponding to those identified in the "Shallow Cryptomafic" column, and having similar thicknesses, are found at depth below these mare patches. .

Geologic History
On the basis of all the analyses in this area, a geologic history for the Schickard crater region of the Moon is proposed (Figure 10). At some time early in the history of the Moon, the Schickard impact event occurred, impacting into what is believed to be predominantly highland material, excavating the ancient highland crust, and forming a 227 km diameter [Wilhelms 1987] impact crater.
The impact event was possibly followed by an episode of volcanic flooding, which may have occurred both inside and outside of the Schickard crater, flooding the crater interior and the surrounding regions. This episode of volcanism, if it occurred, would have taken place prior to the Orientale impact event, since Orientale ejecta is thought to cover much of this area (Chapter 1). Since the age of the Orientale event is recognized to be 3.8 b.y. [Wilhelms, 1987], these basalt units would, therefore, be dated as older than 3.8 b.y.
At some time after flooding, an intermediate layer of highland material may have been emplaced on top of these possible early volcanics. Following this, an episode of known volcanic flooding occurred. Some areas around the Schickard crater did not experience this second episode flooding. These areas may be overlain by a particularly thick lobe of Orientale ejecta [Wilhelms, 1987], perhaps concentrated by the presence of the rim of Schickard crater, and so do not provide a topographic low where the lava flows could pond.
Subsequent impacts, including possibly the Orientale event as well as numerous craters in the nearby highland units, emplaced a very thin covering of highland ejecta material, which obscured the upper mafic layer. Contributions from craters that impacted into the rim of Schickard crater or that excavated highland units from below the cryptomafic layer may have added to the obscuration of mafic materials. This highland layer is exposed as a light plains unit in the center of the Schickard, and has been dated as roughly 3.8 b.y. old [Greeley et al., 1993]. The underlying shallow cryptomafic units can, therefore, be dated as older than 3.8 b.y.
One last episode of volcanic flooding occurred in selected areas within the crater Schickard, creating the two mare patches that can be seen today. Subsequent impacting produced many small craters, which were used in this study to determine this sequence of events.

Summary

Previous studies of cryptomafic deposits have used dark-haloed craters to determine the volumes of hidden mafic deposits (Chapter 1). However, the low resolution of the data sets used in these early studies presents a question as to the accuracy of these determinations. Motivated by this concern, attention was turned to the Clementine data set that, with its higher resolution, presents the possibility of improving our understanding of cryptomafic deposits and the stratigraphy of the lunar subsurface in general.
A total of 28 Clementine 5-band UVVIS image cubes from the region surrounding Schickard crater were calibrated and registered. Ratios were obtained and displayed in the standard RGB color composite format, developed for Galileo lunar image analysis [Belton et al., 1992]. Spectra were collected from a variety of fresh craters and scarp surfaces. And measurements of crater diameters were obtained from the 750 nm filter images and converted to depths of excavation using the equations developed in Chapter 1.
To a first order, the color composite image was found to be useful for inferring the compositions of both surface and subsurface materials. Confirmation of the composition could be obtained from the spectral data. A total of 357 spectra were collected in the study region, of which 198 could be identified as distinctly basaltic or highland in nature. These were used, along with topographic cues, to determine the boundaries of the cryptomafic deposit in this area.
On the basis of spectral data, color composites, and previous studies in this area, the stratigraphy of the various regions, identified in this area, was determined. Four distinct types of stratigraphic sequence or column were recognized. The simplest is the "Highland" column, consisting of the ancient highland crust, which is possibly overlain by additional deposits of predominantly highland ejecta. The rim of Schickard crater is represented by this type of column. A "Deep Cryptomafic" column was identified, which strongly resembles the "Highland" column, except for the suspected presence of a deeply buried cryptomafic deposit. Areas to the south of Schickard crater rim are represented by this column type. Areas within and around Schickard crater are represented by the "Shallow Cryptomafic" column type. This column consists of a known shallow cryptomafic deposit, which is covered by a thin unit of highland ejecta material. The shallow cryptomafic layer may be underlain by another ejecta unit, which overlies a speculative, deep cryptomafic unit. The final column type, the "Surface Mare" column, is characterized by the presence of mare deposits at the surface. It is suggested that these mare patches may be underlain by the full stratigraphic sequence of the "Shallow Cryptomafic" column, potentially producing the most complex stratigraphic sequence in this study.
Crater diameter measurements were used to give estimates of the different layer thicknesses. For small craters, the presence of basalt spectra on the crater slopes allows the crater's depth of excavation to be used as a maximum estimate for the depth to the top of the cryptomafic layer. For larger craters, spectra obtained from the deepest regions along the crater wall can be used to estimate the composition of the deepest layer the crater is tapping. The depth of excavation for these craters gives a maximum estimate for the thickness of the overlying layers. Dark-haloed craters can be used to further constrain layer depths. Using these values, the thicknesses of the various layers were estimated. In this manner, the surface mare layer is estimated to be <450 meters thick, but may be much thinner. The top highland unit is found to be very thin, <85 meters, and may be too thin to represent Orientale ejecta, which should be covering this region. Instead, this unit may represent an accumulation of ejecta materials from nearby highland craters. The shallow cryptomafic layer is estimated to be approximately 400 meters thick. This cryptomafic layer is underlain by a highland unit, which is at least 400 meters thick. The existence of deep, cryptomafic materials is speculated for parts of this region, suggesting that volcanism may have occurred over an extended period of time. The thicknesses of these potential cryptomafic units is undetermined, but they are expected to be underlain by materials of the ancient highland crust.
These results suggest the following geologic history for the Schickard crater area of the Moon. An impact into highland crustal material produced the Schickard crater. Some time prior to 3.8 b.y., lava may have flooded the regions in and around Schickard, partially filling the crater with basalt units. Ejecta from undetermined basins and large craters may have been deposited on top of these speculative basalts, obscuring their mafic signature. A known episode of volcanic flooding, some time prior to 3.8 b.y., covered large sections of the region. Subsequent impacts into the surrounding highlands, including possibly the Orientale impact event, deposited a thin layer of highland ejecta, effectively obscuring the cryptomafic layer. A final episode of volcanic flooding in selected areas of Schickard crater created the mare patches that are seen today. Subsequent impacting produced many small, fresh craters.

References

Adams, J.B. and T.B. McCord, Alteration of lunar optical properties; Age and composition effects, Science, 171, 567, 1971

Antonenko, I., J.W. Head, J.F. Mustard, and B.R. Hawke, Criteria for the detection of lunar cryptomaria, Earth, Moon, Planets, 69, 141-172, 1995.

Bell, J.F., and B.R. Hawke, Lunar Dark-haloed impact craters: Origins and implications for early mare volcanism, J. Geophys. Res., 89, 6899-6910, 1984.

Belton, M.S., J.W.III Head, C.M. Pieters, R. Greeley, A.S. McEwen, G. Neukum, K.P. Klaasen, C.D. Anger, M.H. Carr, C.R. Chapman, M.E. Davies, F.P. Fanale, P.J. Gierasch, R. Greenberg, A.P. Ingersoll, T. Johnson, B. Paczkowski, C.B. Pilcher, J. Veverka, Lunar impact basins and crustal heterogeneity: New western limb and far side data from Galileo, Science, 255, 570-576, 1992

Blewett, D.T., B.R. Hawke, P.G. Lucey, G.J. Taylor, R. Jaumann, and P.D. Spudis, Remote sensing and geologic studies of the Schiller-Schickard region of the Moon, J. Geophys. Res., 100, 16,959-16,978, 1995.

Fischer, E.M. and C.M. Pieters, Lunar Surface Aluminum and Iron Concentration from Galileo Solid State Imaging Data, and the Mixing of Mare and Highland Materials, J. Geophys. Res., E11, 23,279-23,290, 1995.

Greeley, R., S.D. Kadel, D.A. Williams, L.R. Gaddis, J.W. Head, A.S. McEwen, S.L. Murchie, E. Nagel, G. Neukum, C.M. Pieters, J.M. Sunshine, R. Wagner, and M.J.S. Belton, Galileo Imaging Observations of Lunar Maria and Related Deposits, J. Geophys. Res. 98, 17,183-17,205, 1993.

Hawke, B.R., and J.F. Bell, Remote sensing studies of lunar dark-halo impact craters: Preliminary results and implications for early volcanism, Proc. Lunar Planet. Sci. Conf., 12th, 665-678, 1981.

Hawke, B.R. and P.D. Spudis, Geochemical anomalies on the eastern limb and farside of the Moon, in Proc. Conf. Lunar Highlands Crust, J.J. Papike and R.B. Merrill (eds.), Pergamon, New York, N.Y., 467-481, 1980.

Hawke, B.R., C.A. Peterson, P.G. Lucey, G.J. Taylor, D.T. Blewett, B.A. Campbell, C.R. Coombs, and P.D. Spudis, Remote sensing studies of the terrain northwest of Humorum basin, Geophys. Res. Lett., 20, 419-422, 1993.

Head, J.W., and L. Wilson, Lunar mare volcanism: Stratigraphy, eruption conditions, and the evolution of secondary crusts, Geochim. et Cosmochim. Acta, 56, 2144-2175, 1992.

Head, J.W., S.M. Murchie, J.F. Mustard, C.M. Pieters, G. Neukum, A.S. McEwen, R.F. Greeley, E. Nagel, and M.J.S. Belton, Lunar impact basins: New data for the western limb and far side (Orientale and South Pole-Aitken basins) from the first Galileo flyby, J. Geophys. Res., 98, 17,149-17,181, 1993.

Howard, K,A. and H.G. Wilshire, Flows of impact melt at lunar craters, J. Res. U. S. Geol. Survey, 3, 237-251, 1975.

Karlstrom, T.N.V., Geologic map of the Schickard quadrangle of the Moon, scale 1:1,000,000, Map I-823, USGS, Department of the Interior, Washington, DC, 1974.

Kuiper, G.P., E.A. Whitaker, R.G. Strom, J.W. Fountain, and S.M. Larson, Consolidated Lunar Atlas, University of Arizona Press, Tucson, AZ, 1967.

Lucey, P.G., B.C. Bruno, and B.R. Hawke, Preliminary results of imaging spectroscopy of the Humorum basin region of the Moon, Proc. Lunar Planet. Sci. Conf. , 21, 391-403, 1991.

McEwen, A., E. Eliason, P. Lucey, E. Malaret, C. Pieters, M. Robinson, T. Sucharski, Summary of radiometric calibration and photometric normalization steps for the Clementine UVVIS images, Lunar and Planet. Sci. Conf. , 29, Abstract #1466, Lunar and Planetary Institute, Houston (CD-Rom), 1998.

McGetchin, T.R., M. Settle, and J.W. Head, Radial thickness variation in impact crater ejecta: implications for lunar basin deposits, Earth Planet. Sci. Letters, 20, 226-236, 1973.

Mustard, J.F., and J.W. Head, Buried stratigraphic relationships along the southwestern shores of Oceanus Procellarum: Implications for early lunar volcanism, J. Geophys. Res. , 101, 18,913-18,925, 1996.

Mustard, J.F., J.W. Head, and I. Antonenko, Mare-highland mixing relationships along the southwestern shores of Oceanus Procellarum, Lunar and Planet. Sci. Conf. , 24, 963-964, 1994.

Mustard, J.F., J.W. Head, S.M. Murchie, C.M. Pieters, M.S. Belton, and A.S. McEwen, Schickard Cryptomare: Interaction between Orientale ejecta and pre-basin mare from spectral mixture analysis of Galileo SSI data, Lunar and Planet. Sci. Conf. , 23, 957-958, 1992.

Nozette, S., P. Rustan, L.P. Pleasance, D.M. Horan, P. Regeon, E.M. Shoemaker, P.D. Spudis, C.H. Acton, D.N. Daker, J.E. Blamont, B.J. Buratti, M.P. Corson, M.E. Davies, T.C. Buxbury, E.M. Elaison, B.M. Jakosky, J.F. Kordas, I.T. Lewis, C.L. Kichtenberg, P.G. Lucey, E. Malaret, M.A. Massie, J.H. Resnick, C.J. Rollins, H.S. Park, A.S. McEwen, R.E. Priest, C.M. Pieters, R.A. Reisse, M.S. Tocingson, D.E. Smith, T.C. Sorenson, R.W. Vorder Breugge, and M.T. Zuber, The Clementine mission to the Moon: Scientific overview, Science, 266, 1835-1839, 1994.

Oberbeck, V.R., The role of ballistic erosion and sedimentation in lunar stratigraphy, Rev. Geophys. Space Phys. , 13, 337-362, 1975.

Pieters, C.M., J.B. Adams, P.J. Mouginis-Mark, S.H. Zisk, M.O. Smith, J.W. Head, and T.B. McCord, The Nature of Crater Rays: The Copernicus Example, J. Geophys. Res., 90 (B14), 12,393-12,413, 1985.

Pieters, C.M., J.W. Head, J.M. Sunshine, E.M. Fischer, S.L. Murchie, M. Belton, A. McEwen, L. Gaddis, R. Greeley, G. Neukum, R. Jaumann, and H. Hoffmann, Crustal Diversity of the Moon: Compositional Analyses of Galileo SSI Data, J. Geophys. Res., 98, No. E9, 17,127-17,148, 1993.

Pieters, C.M., M.I. Staid, E.M. Fischer, S. Tompkins, and G. He, A Sharper View of Impact Craters from Clementine Data, Science, 266, 1844-1848, 1994.

Pieters C.M., G. He, M. Staid, S. Tompkins, E. M. Fischer, Clementine UVVIS Data Calibration and Processing, http//:www.planetary.brown.edu/clementine/calibration.html, 1996.

Schultz, P.H., and P.D. Spudis, Evidence for ancient mare volcanism, Proc. Lunar Planet. Sci. Conf., 10th, 2899-2918, 1979.

Schultz, P.H., and P.D. Spudis, Beginning and end of lunar mare volcanism, Nature, 302, 233-236, 1983.

Schultz, P.H., D. Orphal, B. Miller, W.F. Borden, and S.A. Larson, Multi-ring basin formation: Possible clues from impact cratering calculations, in Multi-ring Basins, Proc. Lunar Planet. Sci., 12A, P.H. Schultz and R.B. Merrill (eds.), 181-195, 1981.

Whitaker, E.A., G.P. Kuiper, W.K. Hartmann, and L.H. Spradley, Rectified Lunar Atlas, University of Arizona Press, Tucson, AZ, 1963.

Whitford-Stark, J.L., Charting the Southern Seas: The Evolution of the Lunar Mare Australe, Proc. Lunar Planet. Sci. Conf. 10th, 2975-2994, 1979.

Wilhelms, D.E., The geologic history of the Moon, USGS Professional Paper 1348 United States Government Printing Office, Washington, DC, 1987.

Yingst, R. A. and J.W. Head, Volumes of lunar lava ponds in South Pole-Aitken and Orientale basins: Implications for eruption conditions, transport mechanisms and magma source regions, J. Geophys. Res. Planets, 102, 10,909-10,931, 1997.

Tables

Table 1. List of spectra that were obtained. Spectra #: Label used to designate the spectra. These spectra numbers correspond to those in Figure 3a. A prefix of E indicates that the spectra was obtained from the high resolution strip and its location is shown in Figure 3b. Type : The spectra were identified as highland, basaltic, or ambiguous (referred to by "? "). Feature : Spectra were obtained from mounds, flow lobes, craters, and crater ejecta. The craters are further subdivided into flat floor craters, degraded craters, dark-haloed craters (DHC) from the Chapter 1 study, and fresh craters (Crater). The definitions of the different crater types are discussed in the text. Complex craters are indicated with an asterisk. Column : The stratigraphic column type, as mapped in Figure 7, is identified for the area in which the crater is located. Highland refers to a Highland Column. Deep and Shallow refer to Deep and Shallow Cryptomafic Columns, respectively. An asterisk beside Shallow indicates that the spectra is located in the Shallow column unit outside of Schickard crater. Mare refers to Surface Mare Column. An asterisk indicates that the spectra is located in the southern mare patch in Schickard crater. D_r (km): The rim-crest diameter (in km) of craters with distinct highland or basaltic spectra was measured from Clementine images, as discussed in the text. d_e (m): The depth of excavation for craters whose diameters where measured was calculated from equations developed in Chapter 1, and presented in meters. Comments : Comments generally indicate crater names, if they are known, or any other useful information not included elsewhere.

Spectra # Type Feature Column D_r (km) d_e (m) Comments

1 Basalt DHC Shallow 5.6 470 Schickard R

2 ? DHC Shallow 5.6 470 Schickard R

3 Basalt Crater Shallow 6.2 521

4 ? Crater Shallow 6.2 521

5 Basalt Crater Mare 3.4 286

6 Basalt Flat Floor Shallow* 12.7 1067 Drebbel J

7 Highland Flat Floor Shallow* 12.7 1067 Drebbel J

8 ? DHC Shallow* 9.0 756 Drebbel N

9 Highland DHC Shallow* 9.0 756 Drebbel N

10 ? Flat Floor Shallow Schickard A

11 ? Flat Floor Shallow Schickard A

12 Basalt DHC Shallow 13.3 1117 Schickard C

13 Highland DHC Shallow 13.3 1117 Schickard C

14 Basalt DHC Shallow 13.3 1117 Schickard C

15 ? DHC* Deep 21.4 2027 Wargentin A

16 Highland DHC* Deep 21.4 2027 Wargentin A

17 ? DHC* Deep 21.4 2027 Wargentin A

18 Highland DHC* Deep 21.4 2027 Wargentin A

19 Highland DHC* Deep 21.4 2027 Wargentin A

20 Basalt Crater Shallow* 13.3 1117 Wargentin C

21 Highland Crater Shallow* 13.3 1117 Wargentin C

22 Highland Crater Deep 16.6 1394 Inghirami M

23 Highland Crater Highland 12.5 1050 Schickard G

24 Basalt Crater Shallow* 1.6 134 Basalt in ejecta #221

25 Basalt DHC Shallow* 14.4 1210 Lehmann H

26 Highland DHC Shallow* 14.4 1210 Lehmann H

27 ? DHC Shallow* 14.4 1210 Lehmann H

28 Highland Crater Shallow* 15.2 1277 Lehmann D

29 Highland Crater Shallow* 15.2 1277 Lehmann D

30 Basalt Crater Shallow* 5.7 479

31 Highland Crater Shallow* 5.7 479

32 Highland Crater Deep 13.1 1110 Nasmyth D

33 ? Crater Deep 13.1 1110 Nasmyth D

34 ? Crater Shallow*

35 ? Crater Shallow*

36 Basalt Crater Shallow* 2.7 227

37 Basalt Crater Shallow* 2.2 185

38 Basalt Crater Shallow* 5.4 454

39 Basalt Crater Shallow* 5.4 454

40 Basalt Crater Shallow* 2.0 168

41 ? Crater Shallow* 9.0 756 Drebbel L

42 Basalt Crater Shallow* 6.1 512 Drebbel K

43 ? Crater Shallow* 6.1 512 Drebbel K

44 Basalt Crater Shallow* 2.0 168

45 Basalt Crater Shallow* 1.7 143

46 Highland Flat Floor* Shallow* 32.0 2854 Drebbel

47 ? Crater Shallow*

48 ? Crater Shallow*

49 Basalt Crater Shallow* 4.9 412

50 ? Crater Shallow*

51 ? Crater Highland

52 ? Crater Highland

53 ? Degraded Shallow*

54 Basalt Crater Shallow 2.9 244

55 Highland Degraded Highland 5.5 462

56 Highland Crater Highland 6.0 504

57 Highland Crater Highland 3.1 260

58 Highland Crater Highland 8.7 731 Schickard X

59 Highland Crater Highland 6.0 504

60 Highland Degraded Highland 7.7 647

61 Basalt Crater Shallow 1.9 160

62 Basalt Crater Shallow 1.9 160

63 Highland Crater Highland 5.3 445 Schickard T

64 ? Crater Highland

65 Highland Crater Highland 6.2 521

66 Highland Crater Highland 3.3 277

67 Highland Crater Highland 2.4 202

68 Basalt Crater Shallow 2.0 168

69 Basalt Crater Mare* 2.1 176

70 ? Crater Mare*

71 Highland Degraded Highland 3.4 286

72 ? Crater Highland

73 Basalt Crater Shallow* 1.3 109

74 ? Crater Shallow*

75 Basalt Crater Shallow* 1.3 109

76 ? Crater Shallow*

77 Basalt Crater Shallow* 1.0 84

78 Basalt Crater Shallow* 2.9 244

79 ? Degraded* Highland 34.6 2906 Schickard E

80 Basalt Crater Shallow* 2.6 218

81 Basalt Crater Shallow* 2.1 176

82 ? Crater Shallow*

83 ? Crater Shallow*

84 ? Crater Highland

85 Highland Crater Highland 2.6 218

86 ? Crater Shallow*

87 ? Crater Shallow*

88 ? Crater Shallow*

89 Basalt Crater Shallow* 2.9 244

90 ? Degraded Shallow*

91 ? Crater Shallow*

92 Basalt Crater Shallow* 2.1 176

93 ? Crater Shallow*

94 ? Crater Shallow*

95 Highland Crater Deep 4.2 353

96 Highland Crater Deep 3.7 311

97 ? Crater Deep

98 Basalt Crater Shallow* 4.9 412

99 Highland Crater Deep 7.4 622

100 Highland Crater Deep 10.9 916

101 Highland Crater Deep 4.2 353

102 ? Crater Deep Wargentin K

103 Highland Crater Deep 11.6 974 Wargentin L

104 Basalt Crater Deep 3.7 311

105 ? Degraded Highland

106 ? Crater Deep

107 Highland Crater Highland 6.2 521 Schickard Y

108 ? Crater Highland

109 Highland Crater Highland 8.7 731

110 Highland Crater Highland 4.9 412

111 Highland Crater Highland 14.7 1235 Schickard S

112 Basalt Crater Shallow 2.5 210

113 Basalt Crater Shallow 2.7 227

114 ? Degraded Shallow

115 Basalt Degraded Shallow 11.5 996 Schickard D

116 ? Crater Shallow

117 Basalt Degraded Shallow 8.7 731 Schickard W

118 ? Flat Floor Shallow

119 Basalt Crater Shallow 5.2 437 Schickard V

120 ? Crater Shallow

121 ? Crater Shallow

122 Basalt Crater Shallow 3.1 260

123 Basalt Crater Shallow 2.3 193

124 Basalt Crater Mare 2.3 193

125 Basalt Crater Mare 2.9 244

126 ? Crater Mare 5.2 437

127 Basalt Crater Mare 2.3 193

128 Basalt Crater Mare 3.6 302

129 ? Crater Mare

130 ? Crater Shallow

131 Basalt Crater Mare 1.3 109

132 Basalt Crater Mare 4.2 353

133 Basalt Crater Mare 1.8 151

134 Highland Crater Highland 1.4 114

135 Basalt Crater Mare 1.3 109

136 Basalt Crater Mare 3.4 286

137 ? Crater Highland

138 Basalt Crater Mare 1.3 109

139 Basalt Crater Mare 5.2 437

140 Basalt Crater Mare 2.9 244

141 Highland Crater Highland 6.0 504

142 Highland Crater Highland 1.1 92

143 ? Crater Highland

144 ? Crater Shallow*

145 Basalt Crater Shallow* 3.5 294

146 Basalt Crater Shallow* 1.5 126

147 Basalt Crater Shallow* 1.7 143

148 ? DHC Shallow* 5.2 437

149 Highland Degraded Shallow* 6.9 580

150 Basalt Crater Shallow* 1.0 84

151 Basalt Crater Shallow* 1.4 118

152 ? Degraded Shallow*

153 Highland Degraded Highland 4.1 344

154 Highland Mound Highland

155 Basalt Crater Mare 1.8 151

156 ? Crater Mare

157 Basalt Degraded Mare 4.3 361

158 Basalt Crater Mare 1.9 160

159 ? Crater Shallow 1.9 160

160 Basalt Crater Shallow 2.4 202

161 Basalt Crater Shallow 1.6 134

162 Basalt Crater Shallow 1.6 134

163 ? Crater Shallow

164 Basalt DHC Shallow 2.9 244

165 Basalt Crater Shallow 2.1 176

166 Basalt DHC Shallow 4.7 395

167 ? Crater Shallow

168 Basalt Crater Shallow 1.0 84

169 Basalt Crater Shallow 2.9 244

170 Basalt Crater Shallow 2.3 193

171 ? Crater Shallow

172 Basalt Crater Shallow 1.3 109

173 Basalt Crater Shallow 1.3 109

174 ? Crater Shallow

175 ? Degraded Shallow

176 Basalt Crater Shallow 3.7 311

177 Basalt Flow Lobe Shallow

178 Highland Crater Highland 3.4 286

179 Basalt Crater Shallow 1.3 109

180 Highland Crater Highland 14.3 1201 Schickard F

181 Highland Crater Deep 2.6 218

182 ? Degraded Deep

183 ? Mound Deep

184 ? Degraded Deep

185 Basalt Crater Shallow* 2.7 227

186 Highland Crater Deep 1.9 160

187 Highland Crater Deep 4.3 361

188 ? Crater Shallow*

189 Basalt Crater Shallow* 3.2 269

190 Highland Crater Deep 4.7 395

191 Highland Degraded Deep 10.4 874 Wargentin H

192 Highland Crater Deep 3.1 260

193 ? Crater Deep

194 ? Crater Deep

195 Highland Crater Deep 5.0 420

196 Basalt Mound Shallow*

197 Basalt Degraded Shallow* 2.1 176

198 Highland Crater Deep 2.6 218

199 Highland Mound Highland

200 Basalt Crater Shallow 2.1 176

201 ? Crater Shallow

202 Highland Degraded Deep 5.8 487

203 ? Crater Shallow*

204 ? Degraded Deep

205 Highland Degraded Highland 10.1 848 Schickard L

206 Basalt Crater Shallow* 2.2 185

207 Highland Mound Highland

208 Highland Degraded Highland 3.4 286

209 Highland Crater Highland 2.4 202

210 Basalt Crater Shallow* 1.2 101

211 Highland Degraded Shallow* 1.5 126

212 Basalt Crater Shallow* 1.2 101

213 Highland Degraded Shallow* 7.3 613

214 Highland Degraded Highland 2.9 244

215 Highland Crater Highland 2.2 185

216 Highland Crater Highland 2.6 218

217 Highland Degraded Shallow* 4.0 336

218 Highland Degraded Shallow* 7.3 613

219 ? Ejecta Shallow* from crater #25-27

220 Basalt Crater Shallow* 1.4 118

221 Basalt Ejecta Shallow* from crater #24

222 Highland Crater Shallow* 2.1 176

166-E1 Basalt Crater Shallow 4.7 395

E2 ? Crater Shallow

E3 Basalt Crater Shallow 1.3 109

E4 Basalt Crater Shallow 0.9 76

E5 Basalt Crater Shallow 1.4 118

E6 Basalt Crater Shallow 1.7 143

E7 ? Crater Shallow

E8 ? Crater Shallow

E9 Basalt Crater Shallow 1.7 143

E10 Basalt Crater Shallow 1.8 151

E11 Basalt Degraded Shallow 4.3 361

E12 Basalt Crater Shallow 1.5 126

E13 ? Crater Shallow

E14 ? Crater Shallow

E15 ? Degraded Shallow

E16 Highland Crater Shallow 1.1 92

E17 Highland Crater Shallow 1.5 126

E18 ? Crater Shallow

E19 Basalt Crater Shallow 1.8 151

E20 Basalt Degraded Shallow 1.8 151

E21 ? Crater Shallow

E22 ? Crater Shallow

E23 ? Crater Shallow

E24 ? Mound Highland

E25 Basalt Crater Shallow 2.5 210

E26 Highland Crater Shallow 1.0 84

E27 Highland Flat Floor Shallow 14.7 1235 Schickard B

E28 Basalt Flat Floor Shallow 14.7 1235 Schickard B

E29 Highland Flat Floor Shallow 14.7 1235 Schickard B

E30 Highland Flat Floor Shallow 14.7 1235 Schickard B

E31 ? Flat Floor Shallow Schickard B

E32 ? Flat Floor Shallow Schickard B

E33 Highland Flat Floor Shallow 14.7 1235 Schickard B

E34 ? Flat Floor Shallow Schickard B

E35 Basalt Flat Floor Shallow 14.7 1235 Schickard B

E36 Basalt Flat Floor Shallow 14.7 1235 Schickard B

E37 Highland Flat Floor Shallow 14.7 1235 Schickard B

E38 ? Flat Floor Shallow Schickard B

E39 Highland Flat Floor Shallow 14.7 1235 Schickard B

E40 Highland Flat Floor Shallow 14.7 1235 Schickard B

E41 Basalt Flat Floor Shallow 14.7 1235 Schickard B

E42 Highland Flat Floor Shallow 14.7 1235 Schickard B

E45 Basalt Crater Shallow 1.5 126

E46 ? Crater Shallow

E47 ? Crater Shallow

E48 Basalt Crater Shallow 2.0 168

E50 Highland Degraded Shallow 2.2 185

E51 Highland Crater Shallow 1.1 92

E52 Highland Crater Shallow 1.4 118

E53 Highland Mound Highland

E54 Highland Mound Highland

E55 ? Crater Shallow

E56 ? Crater Shallow 9.5 798 Schickard Q

E57 Highland Degraded Shallow 9.5 798 Schickard Q

3-E58 ? Crater Shallow

E59 ? Mound Shallow

E60 ? Crater Shallow

E61 Highland Crater Shallow 1.4 118

E62 ? Crater Shallow

E63 ? Crater Shallow

E64 ? Crater Shallow

61-E65 Basalt Crater Shallow 1.9 160

E66 Basalt Crater Mare* 2.0 168

E67 ? Crater Shallow

62-E68 Basalt Crater Shallow 2.0 168

E69 Highland Mound Shallow

E70 Basalt Crater Shallow 1.7 143 basalt in ejecta #71

E71 Basalt Ejecta Shallow from crater #E70

E72 Basalt Crater Shallow 1.5 126

E73 ? Crater Shallow

E74 ? Crater Shallow

E75 Highland Crater Shallow 1.8 151 near kipuka #E69

E76 Basalt Crater Mare* 1.3 109

E77 ? Crater Shallow

E78 Basalt Crater Mare* 1.4 118

E79 Basalt Crater Mare* 1.1 92

E80 Basalt Crater Mare* 0.8 67

68-E81 ? Crater Shallow 2.0 168

E82 ? Crater Shallow

E83 ? Crater Shallow

Figures

Figure 1. Lunar Orbiter IV (160-H) image of Schickard crater and the surrounding areas. The arrows indicate dark-haloed craters that were identified in the Chapter 1 study. The rectangle shows the location of the high resolution strip of Clementine data (Figure 3b). Spectra obtained from this region are designated with a prefix E in Table 1, for east side of Schickard.

Figure 2. a) Mosaic of the low resolution Clementine data for the study area, complied from 24 separate image cubes, covering 4 different orbits, 750 nm filter images. Note how some of the dark-haloed craters, indicated in Figure 1, can be clearly seen in these high sun-angle images.

Figure 2. b) Mosaic of the low resolution Clementine RGB color composite images, displaying ratios. The red channel displays the 750/415 nm ratio. The green channel displays the 750/950 nm ratio. And the blue channel displays the 415/750 nm ratio. Note how some of the dark-haloed craters, indicated in Figure 1, can also be distinguished in this color mosaic.

Figure 3. a) Mosaic of the 24 lower resolution 750 nm filter images, with spectra locations and labels superimposed on top. The numbers here correspond to the number labels in Table 1.

Figure 3 b) Mosaic strip of the 4 higher resolution 750nm filter Clementine frames. The numbers here correspond to those number labels in Table 1 that are prefixed with an E.

Figure 4. Plot illustrating the differences between the three spectral types that were identified. Basalt spectra are identified by a strong absorption near 1um. Highland spectra are distinguished by the lack of a strong absorption near 1 um. Ambiguous spectra tend to be intermediate between highland and basaltic spectra, and sometimes may display irregular features.

Figure 5. Sample spectra of the different spectral types identified. The full set of spectra that were obtained is presented in Appendix 2. a) Basaltic spectra are distinguished by the presence of a strong ferrous absorption feature near 1 um. b) Highland spectra are identified by a very weak or no ferrous absorption feature near 1 um. c) Some spectra have an absorption feature whose strength is intermediate between highland and basaltic spectra. Several of these ambiguous spectra may represent mixing between highland and basalt materials. d) Other ambiguous spectra contain very unusual features, which may be artifacts from the calibration process.

Figure 6. The results of the spectral analysis are shown here, superimposed on top of the 750 nm filter mosaic. Spectra that were definitely identified as highland (white dots) or basaltic (black dots) are plotted at their appropriate locations. Those spectra that were classified as ambiguous are not plotted. Black lines indicate the boundaries of cryptomafic deposits, as determined from spectral results and from topographic cues. Hatched boundary lines distinguish the Schickard crater rim and cross-hatched boundary lines distinguish the unique region south of Schickard crater.

Figure 7. Map of the study area illustrating the distribution of different stratigraphic columns or sequences, which are suspected to occur in this region. Determination of the stratigraphic columns and their assignment to the various areas on the map is based on the spectral results, color composite images, cryptomafic boundary determinations, and prior knowledge of the region from studies in Chapter 1. The different stratigraphic columns are discussed in the text. Question marks within the column indicate proposed or suspected units.

Figure 8. Annotated 750 nm filter mosaic showing the locations of key craters that are discussed in detail in the text. The numbers correspond to the spectra identifications from Figure 3 and Table 1. Area boundaries from Figures 6 and 7 are included for reference. Again, black lines indicate boundaries of cryptomafic deposits. Hatched lines distinguish the Schickard crater rim and cross-hatched lines distinguish the unique region, possibly containing a deeply-buried cryptomafic unit, to the south of Schickard.

Figure 9. Close up view of crater #12 from Figure 8, showing the locations where spectra were taken. Basalt spectra are indicated by black circles, highland spectra by white circles. No ambiguous spectra were identified in this crater.

Figure 10. Block diagram illustrating the stratigraphy and geologic sequence of events for this region of the Moon. Impact into the highland crust produced the Schickard crater. Lava flooding may have emplaced a layer of mafic material within Schickard and the surrounding regions. This mafic unit would have been covered by a layer of Orientale ejecta. A known episode of basalt emplacement then flooded many of the areas affected by the proposed earlier episode. Continued cratering emplaced a thin layer of highland ejecta material on top of this region, obscuring the upper mafic layer. A final episode of volcanic flooding emplaced the two mare patches that are seen today.

Spectra #	Type	Feature	Column	D_r (km)	d_e (m)	Comments
1	Basalt	DHC	Shallow	5.6	470	Schickard R
2	?	DHC	Shallow	5.6	470	Schickard R
3	Basalt	Crater	Shallow	6.2	521
4	?	Crater	Shallow	6.2	521
5	Basalt	Crater	Mare	3.4	286
6	Basalt	Flat Floor	Shallow*	12.7	1067	Drebbel J
7	Highland	Flat Floor	Shallow*	12.7	1067	Drebbel J
8	?	DHC	Shallow*	9.0	756	Drebbel N
9	Highland	DHC	Shallow*	9.0	756	Drebbel N
10	?	Flat Floor	Shallow			Schickard A
11	?	Flat Floor	Shallow			Schickard A
12	Basalt	DHC	Shallow	13.3	1117	Schickard C
13	Highland	DHC	Shallow	13.3	1117	Schickard C
14	Basalt	DHC	Shallow	13.3	1117	Schickard C
15	?	DHC*	Deep	21.4	2027	Wargentin A
16	Highland	DHC*	Deep	21.4	2027	Wargentin A
17	?	DHC*	Deep	21.4	2027	Wargentin A
18	Highland	DHC*	Deep	21.4	2027	Wargentin A
19	Highland	DHC*	Deep	21.4	2027	Wargentin A
20	Basalt	Crater	Shallow*	13.3	1117	Wargentin C
21	Highland	Crater	Shallow*	13.3	1117	Wargentin C
22	Highland	Crater	Deep	16.6	1394	Inghirami M
23	Highland	Crater	Highland	12.5	1050	Schickard G
24	Basalt	Crater	Shallow*	1.6	134	Basalt in ejecta #221
25	Basalt	DHC	Shallow*	14.4	1210	Lehmann H
26	Highland	DHC	Shallow*	14.4	1210	Lehmann H
27	?	DHC	Shallow*	14.4	1210	Lehmann H
28	Highland	Crater	Shallow*	15.2	1277	Lehmann D
29	Highland	Crater	Shallow*	15.2	1277	Lehmann D
30	Basalt	Crater	Shallow*	5.7	479
31	Highland	Crater	Shallow*	5.7	479
32	Highland	Crater	Deep	13.1	1110	Nasmyth D
33	?	Crater	Deep	13.1	1110	Nasmyth D
34	?	Crater	Shallow*
35	?	Crater	Shallow*
36	Basalt	Crater	Shallow*	2.7	227
37	Basalt	Crater	Shallow*	2.2	185
38	Basalt	Crater	Shallow*	5.4	454
39	Basalt	Crater	Shallow*	5.4	454
40	Basalt	Crater	Shallow*	2.0	168
41	?	Crater	Shallow*	9.0	756	Drebbel L
42	Basalt	Crater	Shallow*	6.1	512	Drebbel K
43	?	Crater	Shallow*	6.1	512	Drebbel K
44	Basalt	Crater	Shallow*	2.0	168
45	Basalt	Crater	Shallow*	1.7	143
46	Highland	Flat Floor*	Shallow*	32.0	2854	Drebbel
47	?	Crater	Shallow*
48	?	Crater	Shallow*
49	Basalt	Crater	Shallow*	4.9	412
50	?	Crater	Shallow*
51	?	Crater	Highland
52	?	Crater	Highland
53	?	Degraded	Shallow*
54	Basalt	Crater	Shallow	2.9	244
55	Highland	Degraded	Highland	5.5	462
56	Highland	Crater	Highland	6.0	504
57	Highland	Crater	Highland	3.1	260
58	Highland	Crater	Highland	8.7	731	Schickard X
59	Highland	Crater	Highland	6.0	504
60	Highland	Degraded	Highland	7.7	647
61	Basalt	Crater	Shallow	1.9	160
62	Basalt	Crater	Shallow	1.9	160
63	Highland	Crater	Highland	5.3	445	Schickard T
64	?	Crater	Highland
65	Highland	Crater	Highland	6.2	521
66	Highland	Crater	Highland	3.3	277
67	Highland	Crater	Highland	2.4	202
68	Basalt	Crater	Shallow	2.0	168
69	Basalt	Crater	Mare*	2.1	176
70	?	Crater	Mare*
71	Highland	Degraded	Highland	3.4	286
72	?	Crater	Highland
73	Basalt	Crater	Shallow*	1.3	109
74	?	Crater	Shallow*
75	Basalt	Crater	Shallow*	1.3	109
76	?	Crater	Shallow*
77	Basalt	Crater	Shallow*	1.0	84
78	Basalt	Crater	Shallow*	2.9	244
79	?	Degraded*	Highland	34.6	2906	Schickard E
80	Basalt	Crater	Shallow*	2.6	218
81	Basalt	Crater	Shallow*	2.1	176
82	?	Crater	Shallow*
83	?	Crater	Shallow*
84	?	Crater	Highland
85	Highland	Crater	Highland	2.6	218
86	?	Crater	Shallow*
87	?	Crater	Shallow*
88	?	Crater	Shallow*
89	Basalt	Crater	Shallow*	2.9	244
90	?	Degraded	Shallow*
91	?	Crater	Shallow*
92	Basalt	Crater	Shallow*	2.1	176
93	?	Crater	Shallow*
94	?	Crater	Shallow*
95	Highland	Crater	Deep	4.2	353
96	Highland	Crater	Deep	3.7	311
97	?	Crater	Deep
98	Basalt	Crater	Shallow*	4.9	412
99	Highland	Crater	Deep	7.4	622
100	Highland	Crater	Deep	10.9	916
101	Highland	Crater	Deep	4.2	353
102	?	Crater	Deep			Wargentin K
103	Highland	Crater	Deep	11.6	974	Wargentin L
104	Basalt	Crater	Deep	3.7	311
105	?	Degraded	Highland
106	?	Crater	Deep
107	Highland	Crater	Highland	6.2	521	Schickard Y
108	?	Crater	Highland
109	Highland	Crater	Highland	8.7	731
110	Highland	Crater	Highland	4.9	412
111	Highland	Crater	Highland	14.7	1235	Schickard S
112	Basalt	Crater	Shallow	2.5	210
113	Basalt	Crater	Shallow	2.7	227
114	?	Degraded	Shallow
115	Basalt	Degraded	Shallow	11.5	996	Schickard D
116	?	Crater	Shallow
117	Basalt	Degraded	Shallow	8.7	731	Schickard W
118	?	Flat Floor	Shallow
119	Basalt	Crater	Shallow	5.2	437	Schickard V
120	?	Crater	Shallow
121	?	Crater	Shallow
122	Basalt	Crater	Shallow	3.1	260
123	Basalt	Crater	Shallow	2.3	193
124	Basalt	Crater	Mare	2.3	193
125	Basalt	Crater	Mare	2.9	244
126	?	Crater	Mare	5.2	437
127	Basalt	Crater	Mare	2.3	193
128	Basalt	Crater	Mare	3.6	302
129	?	Crater	Mare
130	?	Crater	Shallow
131	Basalt	Crater	Mare	1.3	109
132	Basalt	Crater	Mare	4.2	353
133	Basalt	Crater	Mare	1.8	151
134	Highland	Crater	Highland	1.4	114
135	Basalt	Crater	Mare	1.3	109
136	Basalt	Crater	Mare	3.4	286
137	?	Crater	Highland
138	Basalt	Crater	Mare	1.3	109
139	Basalt	Crater	Mare	5.2	437
140	Basalt	Crater	Mare	2.9	244
141	Highland	Crater	Highland	6.0	504
142	Highland	Crater	Highland	1.1	92
143	?	Crater	Highland
144	?	Crater	Shallow*
145	Basalt	Crater	Shallow*	3.5	294
146	Basalt	Crater	Shallow*	1.5	126
147	Basalt	Crater	Shallow*	1.7	143
148	?	DHC	Shallow*	5.2	437
149	Highland	Degraded	Shallow*	6.9	580
150	Basalt	Crater	Shallow*	1.0	84
151	Basalt	Crater	Shallow*	1.4	118
152	?	Degraded	Shallow*
153	Highland	Degraded	Highland	4.1	344
154	Highland	Mound	Highland
155	Basalt	Crater	Mare	1.8	151
156	?	Crater	Mare
157	Basalt	Degraded	Mare	4.3	361
158	Basalt	Crater	Mare	1.9	160
159	?	Crater	Shallow	1.9	160
160	Basalt	Crater	Shallow	2.4	202
161	Basalt	Crater	Shallow	1.6	134
162	Basalt	Crater	Shallow	1.6	134
163	?	Crater	Shallow
164	Basalt	DHC	Shallow	2.9	244
165	Basalt	Crater	Shallow	2.1	176
166	Basalt	DHC	Shallow	4.7	395
167	?	Crater	Shallow
168	Basalt	Crater	Shallow	1.0	84
169	Basalt	Crater	Shallow	2.9	244
170	Basalt	Crater	Shallow	2.3	193
171	?	Crater	Shallow
172	Basalt	Crater	Shallow	1.3	109
173	Basalt	Crater	Shallow	1.3	109
174	?	Crater	Shallow
175	?	Degraded	Shallow
176	Basalt	Crater	Shallow	3.7	311
177	Basalt	Flow Lobe	Shallow
178	Highland	Crater	Highland	3.4	286
179	Basalt	Crater	Shallow	1.3	109
180	Highland	Crater	Highland	14.3	1201	Schickard F
181	Highland	Crater	Deep	2.6	218
182	?	Degraded	Deep
183	?	Mound	Deep
184	?	Degraded	Deep
185	Basalt	Crater	Shallow*	2.7	227
186	Highland	Crater	Deep	1.9	160
187	Highland	Crater	Deep	4.3	361
188	?	Crater	Shallow*
189	Basalt	Crater	Shallow*	3.2	269
190	Highland	Crater	Deep	4.7	395
191	Highland	Degraded	Deep	10.4	874	Wargentin H
192	Highland	Crater	Deep	3.1	260
193	?	Crater	Deep
194	?	Crater	Deep
195	Highland	Crater	Deep	5.0	420
196	Basalt	Mound	Shallow*
197	Basalt	Degraded	Shallow*	2.1	176
198	Highland	Crater	Deep	2.6	218
199	Highland	Mound	Highland
200	Basalt	Crater	Shallow	2.1	176
201	?	Crater	Shallow
202	Highland	Degraded	Deep	5.8	487
203	?	Crater	Shallow*
204	?	Degraded	Deep
205	Highland	Degraded	Highland	10.1	848	Schickard L
206	Basalt	Crater	Shallow*	2.2	185
207	Highland	Mound	Highland
208	Highland	Degraded	Highland	3.4	286
209	Highland	Crater	Highland	2.4	202
210	Basalt	Crater	Shallow*	1.2	101
211	Highland	Degraded	Shallow*	1.5	126
212	Basalt	Crater	Shallow*	1.2	101
213	Highland	Degraded	Shallow*	7.3	613
214	Highland	Degraded	Highland	2.9	244
215	Highland	Crater	Highland	2.2	185
216	Highland	Crater	Highland	2.6	218
217	Highland	Degraded	Shallow*	4.0	336
218	Highland	Degraded	Shallow*	7.3	613
219	?	Ejecta	Shallow*			from crater #25-27
220	Basalt	Crater	Shallow*	1.4	118
221	Basalt	Ejecta	Shallow*			from crater #24
222	Highland	Crater	Shallow*	2.1	176
166-E1	Basalt	Crater	Shallow	4.7	395
E2	?	Crater	Shallow
E3	Basalt	Crater	Shallow	1.3	109
E4	Basalt	Crater	Shallow	0.9	76
E5	Basalt	Crater	Shallow	1.4	118
E6	Basalt	Crater	Shallow	1.7	143
E7	?	Crater	Shallow
E8	?	Crater	Shallow
E9	Basalt	Crater	Shallow	1.7	143
E10	Basalt	Crater	Shallow	1.8	151
E11	Basalt	Degraded	Shallow	4.3	361
E12	Basalt	Crater	Shallow	1.5	126
E13	?	Crater	Shallow
E14	?	Crater	Shallow
E15	?	Degraded	Shallow
E16	Highland	Crater	Shallow	1.1	92
E17	Highland	Crater	Shallow	1.5	126
E18	?	Crater	Shallow
E19	Basalt	Crater	Shallow	1.8	151
E20	Basalt	Degraded	Shallow	1.8	151
E21	?	Crater	Shallow
E22	?	Crater	Shallow
E23	?	Crater	Shallow
E24	?	Mound	Highland
E25	Basalt	Crater	Shallow	2.5	210
E26	Highland	Crater	Shallow	1.0	84
E27	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E28	Basalt	Flat Floor	Shallow	14.7	1235	Schickard B
E29	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E30	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E31	?	Flat Floor	Shallow			Schickard B
E32	?	Flat Floor	Shallow			Schickard B
E33	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E34	?	Flat Floor	Shallow			Schickard B
E35	Basalt	Flat Floor	Shallow	14.7	1235	Schickard B
E36	Basalt	Flat Floor	Shallow	14.7	1235	Schickard B
E37	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E38	?	Flat Floor	Shallow			Schickard B
E39	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E40	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E41	Basalt	Flat Floor	Shallow	14.7	1235	Schickard B
E42	Highland	Flat Floor	Shallow	14.7	1235	Schickard B
E45	Basalt	Crater	Shallow	1.5	126
E46	?	Crater	Shallow
E47	?	Crater	Shallow
E48	Basalt	Crater	Shallow	2.0	168
E50	Highland	Degraded	Shallow	2.2	185
E51	Highland	Crater	Shallow	1.1	92
E52	Highland	Crater	Shallow	1.4	118
E53	Highland	Mound	Highland
E54	Highland	Mound	Highland
E55	?	Crater	Shallow
E56	?	Crater	Shallow	9.5	798	Schickard Q
E57	Highland	Degraded	Shallow	9.5	798	Schickard Q
3-E58	?	Crater	Shallow
E59	?	Mound	Shallow
E60	?	Crater	Shallow
E61	Highland	Crater	Shallow	1.4	118
E62	?	Crater	Shallow
E63	?	Crater	Shallow
E64	?	Crater	Shallow
61-E65	Basalt	Crater	Shallow	1.9	160
E66	Basalt	Crater	Mare*	2.0	168
E67	?	Crater	Shallow
62-E68	Basalt	Crater	Shallow	2.0	168
E69	Highland	Mound	Shallow
E70	Basalt	Crater	Shallow	1.7	143	basalt in ejecta #71
E71	Basalt	Ejecta	Shallow			from crater #E70
E72	Basalt	Crater	Shallow	1.5	126
E73	?	Crater	Shallow
E74	?	Crater	Shallow
E75	Highland	Crater	Shallow	1.8	151	near kipuka #E69
E76	Basalt	Crater	Mare*	1.3	109
E77	?	Crater	Shallow
E78	Basalt	Crater	Mare*	1.4	118
E79	Basalt	Crater	Mare*	1.1	92
E80	Basalt	Crater	Mare*	0.8	67
68-E81	?	Crater	Shallow	2.0	168
E82	?	Crater	Shallow
E83	?	Crater	Shallow

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