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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↗
USGS1985

Aeromagnetic maps of the Latir Peak and Wheeler Peak Wildernesses and the Columbine-Hondo Wilderness Study Area, Taos County, New Mexico

This report interprets data from a helicopter-borne magnetic survey to help delineate subsurface geology. Such data, acquired near the ground, reflect greater magnetic detail than do data acquired at higher altitude. Data from a high-altitude reconnaissance aeromagnetic survey (U.S. Geological Survey, 1976) are used selectively to assist in the interpretation of the helicopter data. Interpretations are chiefly empirical, wherein magnetic anomalies characterizing known geologic features in the region are used as interpretive criteria for identifying such features where they are concealed. Identifying geologic environments favorable for mineral deposits is a primary objective of this report. Geophysical interpretations of a broader and more general scope are made from other geophysical data by Cordell and Jones (in press).

New Mexico↗
USGS1985

Aeromagnetic maps of the Mazatzal Wilderness and contiguous roadless areas, Gila, Maricopa, and Yavapai counties, Arizona

The Mazatzal Wilderness and contiguous roadless areas are located in Tonto and Coconino National Forests, west and southwest of Payson, and are almost exactly in the geographic center of Arizona. This is a region of relatively small mining districts and few mines, but occurrences of many different metals are widespread. The Mazatzal Mountains constitute the dominant physiographic feature of the wilderness. The eastern slopes of these mountains rise steeply from about 3,500 ft in altitude along the valley of Rye Creek east of the range, to 7,903 ft at Mazatzal Peak. To the west, the range slopes steeply from the crest then more gently along the lower flanks to the Werde River, one of the main drainage channels of Arizona. In the northern part of the wilderness, the East Werde River, a tributary of the Verde, occupies a deep canyon that separates the Mazatzal Mountains from mesas to the north. The lowest parts of the wilderness have altitudes of about 2,200 ft and are located near Bartlett Reservoir in the southwestern part of the area studied. Two aeromagnetic surveys were flown and interpreted to aid in the delineation of subsurface lithology and structure: one survey was flown at a low level (1,000 ft above ground) and the other at a high level (9,000 ft above sea level). In addition, the results of a small-scale electromagnetic (EM) survey are briefly discussed; the surface EM survey took place in an area of copper concentrations and past exploration activity to look for evidence of massive sulfide mineralization. Studies of the geology, geochemistry (Marsh and others, 1983a, b, Erickson, 1984), mines and prospects (Ellis, 1982), and mineral resource potential (Wrucke and others, 1983) of the Mazatzal Wilderness and contiguous roadless areas have been published elsewhere.

Arizona↗