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At least 1,657 records · Page 92Linked to original sources
USGS1994

Geologic maps of the southwestern Puerto Rico Parguera to Guanica insular shelf

These maps describe the sediments and sedimentary environment of the southwestern Puerto Rico shelf (index). In addition to presenting new data, the maps summarize earlier geological investigations. There are two morphological zones separated along a line extending southward from Punta Jorobaflo. The Parguera shelf extends from this line to the western boundary of the study area, and the Guanica shelf extends from Punta Jorobado to the eastern study limit (fig. 1). The age and character of the underlying limestone bedrock, the depositional environment, the history of subaerial erosion, and the intensity of modem physical processes differ in each of these shelf areas. However, the bedrock surface of both the Parquera and Guanica shelves is primarily karst; the limestone surface was modified by reef growth and sediment deposition after the last glacial lowstand. Although several anticlines and faults that trend parallel to the shoreline have been mapped on the adjacent land areas (Volckmann, 1984), no evidence was found to suggest major structural features on the shelf.

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USGS1994

Geologic map of the MTM -85080 quadrangle (revised), Planum Australe region of Mars

Published geologic maps of south polar region of Mars have been based on either Mariner 9 (Condit Soderblom, 1978; Scott and Carr, 1978) or Viking Orbiter (Tanaka and Scott, 1987) images. The mapped extent of the southern layered deposits differs in many places on these maps and on our maps. These differences reflect the difficulty in accurately determining the location of the contact between the layered deposits and subjacent units. The polar layered deposit gradually thin toward their margin in many places, and the smooth surface features that characterize the layered deposits are also found on other sedimentary blankets in the south polar region (Murray and others, 1972; Sharp, 1973). Previous workers have also reached different conclusions regarding the origin of the lower member of the Dorsa Argentea Formation, which was named by Tanaka and Scott (1987) and interpreted by them as volcanic in origin (based on observation of flow fronts in areas far outside this quadrangle). The lower member, previously called pitted material, and other sedimentary, and other sedimentary units were recognized in Mariner 9 images and described by Murray and others (1972), Sharp (1973), and Cutts (1973b). Sharp (1973) argued for exhumation of pits by wind, perhaps aided by sublimation of volatiles. He concluded that the massive pitted sediments of the lower member unconformably overlie older massive units. We have mapped one of these older units ridged and knobby material. Condit and Soderblom (1978) found some layered deposits within pits, which indicates that erosion of the pits was completed before accumulation of the layered deposits commenced. Howard’s (1981) suggestion that the pits may be formed by basal melting of ground ice is consistent with either a volcanic or sedimentary origin for the lower (pitted) member. Plaut and others (1988) mapped the extent of the pitted material and found that it overlies volcanic plains wherever the contact is visible. They concluded that the pitted material is no more than 1 km thick and is about 3.3 billion years old (Late Hesperian).

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USGS1994

Geologic map of the eastern part of the Challis National Forest and vicinity, Idaho

The paper version of the Geologic Map of the eastern part of the Challis National Forest and vicinity, Idaho was compiled by Anna Wilson and Betty Skipp in 1994. The geology was compiled on a 1:250,000 scale topographic base map. TechniGraphic System, Inc. of Fort Collins Colorado digitized this map under contract for N.Shock. G.Green edited and prepared the digital version for publication as a GIS database. The digital geologic map database can be queried in many ways to produce a variety of geologic maps.

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USGS1995

Geologic and topographic maps of the Elysium Paleolake basin, Mars

These geologic and topographic maps show a basin in the Elysium region of Mars that is thought to have been the site of a large paleolake during the most recent period (Amazonian) in Mars’ history (Scott and Chapman, 1991b). The basin, referred to as the Elysium basin, extends for more than 2,000 km across the lowland plains (fig. 1). It is important, not only geologically, but because the amount, location, and duration of liquid water that it may have contained would have been critical factors governing the possible origin and survival of life on Mars. The Elysium basin is the only large depositional basin on Mars where direct evidence, both geologic and topographic, of former water levels and spillways has been found. However, indications of possible paleoshorelines have been observed in several other areas along the highland-lowland boundary (described under Geologic and Physiographic Setting; Parker and others, 1989; De Hon and Pani, 1992; Scott and others, 1992). Our study of the Elysium basin had two objectives, to determine (1) the maximum extent of the basin and (2) the former volume of water in the basin and the sources of this water. To fulfill these objectives, we have compiled this sets of maps. The geologic maps shows the source channels and circumbasin materials, and the topographic map of the paleolake, on a new topographic base, shows former shorelines and drainage channels.

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