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Earl E. Brabb

Publications and source records attributed to Earl E. Brabb.

At least 55 records · Page 3Linked to original sources
USGS1973

Petrography and structural relations of granitic basement rocks in the Monterey Bay area, California

In the past, the granitic basement of the Coast Ranges has been thought to be dominantly quartz diorite and low in K-feldspar. However, a study of outcrops around Monterey Bay, basement well samples, and dredge samples from Monterey Bay shows that the granitic basement averages about 15 to 20 percent K-feldspar. Therefore, as a sedimentary provenance, the basement around Monterey Bay could have contributed abundant K-feldspar to the Cenozoic sedimentary deposits of the region; that is, in the Monterey Bay area the local basement is an adequate source for the abundant K-feldspar in the sedimentary units. The distribution of basement rocks and mapped faults, coupled with gravity-geophysical data, suggests that the area between the San Andreas and Sur-Nacimiento fault zones (the Salinian block) near Monterey Bay is broken into several discrete structural blocks. Some of these blocks juxtapose not only different basement rocks, but also different contour patterns on the buried basement surface. These features suggest large strike-slip movements along some faults within the Salinian block in the Monterey Bay area.

California↗
USGS1973

Current slope-stability studies in the San Francisco Bay region

An extensive program of slope-stability studies is presently underway in the San Francisco Bay region, California. Work to date has resulted in the publication of estimates of landslide damage, an estimated-landslide-abundance map of the region, new slope maps prepared by photomechanical processes, photointerpretive maps of landslide, colluvial, and other surficial deposits, and maps of relative slope stability. These studies indicate that landsliding is a major slope-erosion process in the region, that the damage resulting from landsliding is very great, and that additional development in the upland parts of the region should not be undertaken without careful evaluation of slope stability.

California↗
USGS1972

Landslide susceptibility in San Mateo County, California

Information on areas susceptible to failure by landsliding is available in many general geologic maps and reports. However, it is commonly presented in complex, technical language, together with data not connected with slope stability. This derivative map is intended to convey such information in nontechnical form so that it will be intelligible to the non-geologist. It portrays only those geologic factors that bear directly on the susceptibility of specific areas to landsliding.

California↗
USGS1970

Geologic interpretation of reconnaissance aeromagnetic survey of northeastern Alaska

Aeromagnetic reconnaissance of northeastern Alaska in 1965 covered approximately 100,000 square miles, from lat 64° N. to the Arctic Ocean and from the Alaska-Yukon boundary to long 148°30' W. A magnetic contour map was compiled from data from the 1965 survey and earlier surveys. On the basis of these data, northeastern Alaska may be divided into five areas, each having a distinct magnetic character. A study of specific anomalies within these areas led to the tracing of such features as the Tintina fault zone, Ruby uplift, and Kobuk trench for more than 100 miles. Other features, such as inferred north-trending faults and serpentine belts, had not been identified previously by surface geologic methods. The probable extension of volcanic rocks beneath the Yukon Flats limits the size of a possible Tertiary petroleum basin. Discovery of large magnetic anomalies in the Yukon-Tanana Upland provides new possibilities for exploration for mineral deposits associated with ultramafic rocks.

Alaska↗
USGS1967

Devonian rocks of the Yukon-Porcupine Rivers area and their tectonic relation to other Devonian sequences in Alaska

Devonian rocks along the Yukon River near the Alaska-Yukon boundary comprise 250 feet of limestone and shale and 800 feet of chert and siliceous shale, all referred to the McCann Hill Chert of Early to Late Devonian age; about 3,000 feet of non-marine chert-pebble conglomerate, graywacke, and shale of the Nation River Formation (Late Devonian); and about 3,000 feet of an unnamed chert and siliceous shale formation, of Late Devonian to Early or Late Mississippian age. The McCann Hill Chert apparently rests disconformably on graptolitic shale of the Road River Formation that has a succession of graptolite zones ranging in age from Ordovician to possibly Early Devonian. The Devonian succession along the Porcupine River, 170 miles north of the Yukon River locality, consists of 600 feet of Salmon-trout Limestone, overlain by 200 feet of unnamed shale and about 500 feet of unnamed dolomite. The Salmontrout Limestone rests accordantly and probably conformably on graptolitic shale with Monograptus hercynicus of Late Silurian or Early Devonian age, and the dolomite is overlain unconformably by limestone and shale of Carboniferous age. Tentaculitid faunas from the top of the Salmontrout Limestone and from the basal limestone and shale member of the McCann Hill Chert are similar and indicate that the units are partly correlative. These faunas and others throughout the Salmontrout resemble those from the Lower Devonian of Bohemia, indicating that the Salmontrout Limestone and the limestone and shale member of the McCann Hill Chert are somewhat older than previously reported. The faunas, and those from the underlying graptolitic shales, also suggest that sedimentation in this area of Alaska was nearly continuous from Late Silurian into the Earliest Devonian, and that there is little record of Caledonian earth movements. The stratigraphy of the Porcupine River area is not as yet well enough established to determine if rocks equivalent in age to the Nation River Formation are present, were once present and have since been eroded, or were never deposited. Pillow basalt and andesitic breccia, although closely associated with Devonian limestone in the western part of the Yukon-Porcupine Rivers area, seem only structurally related and of different age. Devonian rocks in southern and southeastern Alaska consist of several thousand feet of graywacke, shale and volcanic rocks deposited in the northern Cordilleran geosyncline. A combination of strike-slip and thrust faults of Tertiary and Mesozoic age may have since displaced the Devonian geosynclinal rocks relatively northward into central Alaska.

Alaska↗