SEQUENCE STRATIGRAPHY AND PALEOKARST EVOLUTION OF THE ORDOVICIAN ANTELOPE VALLEY LIMESTONE NEAR BEATTY, NV

The mid-Ordovician Antelope Valley Limestone of southwestern Nevada contains an abundance of dolostone breccias that have been interpreted throughout southern Nevada and east-central California to have formed as the result of paleokarstification (Cooper and Keller, 2001). The breccias appear within infilled cavities ranging in width from centimeters to tens of meters wide and centimeters to approximately seventy meters thick. Repeated vertical facies successions, each capped by paleokarst, are thought to be indicative of transgressive-regressive eustatic cycles; this study is closely examining paleokarst-derived breccias in the field and in thin section to determine the evolution of paleokarst within parasequences. Initial results found within a single large paleokarst package display four distinct sets of breccias with an overall regressive signature. The breccia sets range between 7 and 18 meters thick separated by conformable to possibly paraconformable boundaries that may be the result of fifth-order transgressive-regressive cycles. Future work will involve (1) petrographic and cathodoluminesce examination of fifty previously collected samples from the above mentioned paleokarst package; (2) the 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; and (3) further refinement of the paleogeographic/paleotectonic model for the Cordilleran margin of Laurentia during the Lower to Middle Ordovician of Cooper and Keller (2001). Collectively, these paleokarst breccias not only testify to the complex history of the early Paleozoic Cordilleran margin of Laurentia, but they may also lead to enhanced reservoir characterization within similar subsurface lithofacies.