Sequence Stratigraphy and Paleokarst Evolution of the Ordovician Pogonip Group near Beatty, NV
California State University, Fullerton, Department of Geosciences
The lower to mid-Ordovician Pogonip Group (Upper Ibexian-Lower Whiterockian) of southwestern Nevada contains an abundance of dolostone breccias that have been interpreted throughout southern Nevada and east-central California as the result of paleokarstification. The breccias appear within conduit-like cavities ranging in width from centimeters to tens of meters wide and centimeters to nearly one hundred meters thick. Repeated vertical facies successions, each capped by paleokarst, are indicative of transgressive-regressive eustatic cycles. For this study the breccias of the Ordovician Pogonip Group are being closely examined in the field and in thin section to determine the evolution of paleokarst development within parasequences. Initial results found within a single paleokarst package display four distinct sets of paleokarst that may be a result of fifth-order transgressive-regressive cycles. Furthermore, petrographic examination of fifty previously collected samples within the above mentioned section yield preliminary observations of cave collapse, platform exposure, and deep burial. Ongoing work will involve (1) further petrographic and cathodoluminesce examination of samples from the above mentioned paleokarst package; and, (2) creation of a sequence-stratigraphic framework for the study area that will enhance the resolution of the relative sea-level history of the Cordilleran margin of Laurentia. Collectively, these paleokarst breccias not only testify to the complex history of the early Paleozoic Cordilleran margin of Laurentia, but they also may lead to a better understanding of karst sequences and reservoir prediction.
AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid