Sequence Stratigraphy and Paleokarst Evolution of the Ordovician Pogonip Group near Beatty, NV
Robert Kervin
California State University, Fullerton, Department of Geosciences
Fullerton, CA
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