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G. A. Abrams

Publications and source records attributed to G. A. Abrams.

At least 19 recordsLinked to original sources
USGS1991

Late Laramide thrust-related and evaporite-domed anticlines in the southern Piceance Basin, northeastern Colorado Plateau

New seismic and gravity data across the hydrocarbon-producing Divide Creek and Wolf Creek anticlines in the southern Piceance basin reveal contrasting styles of deformation within two widely separated time frames. Seismic data indicate that prebasin Paleozoic deformation resulted in block faulting of the Precambrian crystalline basement rocks and overlying Cambrian through Middle Pennsylvanian strata. Movement along these block faults throughout much of Pennsylvanian time, during northeast-southwest crustal extension, likely influenced distribution of the Middle Pennsylvanian (Desmoinesian) evaporite-rich facies. Younger rocks, including the thick succession of Cenozoic basin strata, then buried the Paleozoic structures. Tectonic reconfiguration of the basin's eastern margin occurred during late Laramide northeast-southwest compression, when a basement-involved thrust block, whose surface expression is the Grand Hogback monocline, moved into the Piceance basin. A decollement developed in front of the thrust block within the mechanically weak Desmoinesian evaporites and splayed out basinward as small-scale imbricate thrusts in the Upper Cretaceous Mancos Shale. The Divide Creek anticline formed above these splays as thrusting locally overthickened the shale and repeated the sandstone units between it and the evaporites. The Wolf Creek anticline to the east, however, is due to both depositional and tectonic thickening of the evaporite section along the decollement. Gravity data confirm that excess mater al of relatively low density exists beneath the Wolf Creek structure, whereas material of relatively higher density (overthickened shale) is found beneath the Divide Creek anticline. Thrust-related basin margins and intrabasin folds structurally analogous to the Divide Creek and Wolf Creek anticlines may be more common than presently recognized in the Rocky Mountain foreland. One well-documented example is the Pinedale anticline in the northern Green River basin, Wyoming, which, like the Divide Creek anticline, developed above a zone of splay faults from a decollement in front of a large thrust block.

Colorado↗
USGS1986

Geophysical maps of the Dos Cabezas Mountains Wilderness Study Area, Cochise County, Arizona

The Dos Cabezas Mountains Wilderness Study Area, Arizona, lies along part of the crest and northeast flank of the Dos Cabezas Mountains, Cochise County, near the southeast corner of Arizona (fig. 1). The U.S. Bureau of Land Management requested mineral surveys of about 11,921 acres of the approximately 15,000 acre wilderness study area. In this report "wilderness study area" refers to the 11,921 acres that were studied. The Dos Cabezas Mountains are in many ways a typical mountain range of the Basin-and-Range physiographic province. They are a northwest-trending block-faulted range separated from adjacent ranges by broad valleys. The range is about 22 mi long and 8 mi wide, and it reaches an elevation of 8,354 ft at Dos Cabezas Peaks, located about 2 mi west of the study area. The terrain of the area is rugged. Roadheads and trails provide adequate access for foot traverses. In the Dos Cabezas Mountains the Apache Pass fault zone is the major structural feature, barely skirting the southwest side of the study area. It extends several miles to the northwest and tens of miles to the southeast, across the Chiricahua Mountains beyond Apache Pass. It is typically made up of a pair of bounding faults and some anastomosing faults between them. The study area is underlain by a variety of sedimentary, igneous, and metamorphic rocks that provide only a fragmentary record of geologic events between Precambrian and Holocene times. A suite of metamorphic and igneous (primarily crystalline) rocks forms the basement terrain. Paleozoic and Mesozoic sedimentary rocks and also Paleozoic and Mesozoic volcanic rocks overlie the basement rocks but are extensively eroded away and may be covered. A pile of volcanic rocks of Late Cretaceous and Paleocene age caps the older rocks in much of the study area. Mid-Tertiary intrusive rocks underlie the eastern part of the study area as well as some very small, widely scattered additional localities. Quaternary gravel deposits occur in the major valleys and along the mountain front.

Arizona↗