Abstract: Paleokarst
and Sequence
Boundaries in L.-M. Ordovician Dolomites South of the Las
Vegas Valley Shear Zone, California and Nevada
COOPER, JOHN D., MARTIN KELLER and OLIVER LEHNERT
Lithoclast breccias
within the dolomitic Lower to Middle Ordovician Pogonip Group in the Nopah
Range, eastern California, previously interpreted as Ordovician debris
flows or as post-Ordovician colluvial or tectonic deposits, are reinterpreted
as Ordovician karst breccias. These include solution collapse breccias,
cave roof crackle breccias, and doline and cave-fill breccias, commonly
with reddish quartz sand and detrital dolomite matrix. These breccias also
occur in association with solution karren, terra rossa sediment, and quark
sand-filled grike systems. As such they define a succession of exposure
surfaces that are disconformities and thus sequence
boundaries. This is
somewhat of a departure from conventional
sequence
stratigraphic studies
in platform carbonates where parasequence stacking patterns are employed
in the search for subtle
sequence
boundaries.
With the Nopah Range section
serving as an anchor, these karst- and hardground-expressed sequence
boundaries/disconformities
provide a high-resolution chronostratigraphic framework that can be correlated
to craton-margin sections to the east in the Spring Mountains of southern
Nevada, and more distal platform sections to the west. Systems tract and
other
sequence
architectural element
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Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California