Comparative Development of the Western United States and Southern Kazakhstan, Soviet Union--Two Early Paleozoic Carbonate Passive Margins

COOK, HARRY E., U.S. Geological Survey, Menlo Park, CA, MICHAEL E. TAYLOR, U.S. Geological Survey, Denver, CO, S. V. ZHEMCHUZHNIKOV, M. K. APOLLONOV, G. KH. ERGALIEV, Z. S. SARGASKAEV, Institute of Geological Sciences, Academy of Sciences Kazakh SSR, Alma-Ata, Soviet Union, and S. V. DUBININA, Geological Institute, Academy of Sciences USSR, Moscow, Soviet Union

Early Paleozoic passive continental margins of the Western United States and southern Kazakhstan evolved at low latitudes on rifted Precambrian continental crust adjacent to the proto-Pacific Ocean. In the Western United States, early Paleozoic carbonate submarine fans and slides formed on continental slopes in central Nevada. Coeval shoal-water carbonate sediments occurred to the east, in Utah, where they interfingered with siliciclastic sediments and onlapped the craton. In contrast, early Paleozoic carbonate sediments of the Malyi Karatau, southern Kazakhstan, were deposited on isolated microcontinental blocks that developed during Late Proterozoic rifting of the continental crust. Carbonate sediment accumulated on one isolated block which was the site of the 40-km-wide Aisha-Bibi eamount. This shoal-water seamount was flanked by deeper water carbonate submarine fans and slides.

Comparison of stratigraphic sections from Nevada and Malyi Karatau indicate a similar upward-shallowing and seaward-prograding evolution. The Hot Creek Range section in Nevada consists of the Upper Cambrian Swarbrick Formation and Tybo Shale, and Upper Cambrian and lowest Ordovician Hales Limestone. These depositional facies include basin plain (about 500 m), carbonate submarine fan and slides (200 m), upper slope (150 m), and platform margin (150 m). The Kyrshabakty and Batyrbay sections in the Malyi Karatau consist of Cambrian and lowest Ordovician rocks of the Shabakty Suite. Middle and Late Cambrian and Early Ordovician facies include basin plain (100 m), carbonate submarine fan and slides (425 m), upper slope (125 m), and shoal-water carbonate seamount (375+ m).

Stratigraphic sections in both the Western United States and Malyi Karatau record three coeval episodes of sea level lowstands. These lowstands, which we interpret to be eustatic, are recognized by times of seaward collapse of large segments of the platform margins and deeper water slopes and by solution breccias and faunal discontinuities in shoal-water platform-interior sites.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)