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The AAPG/Datapages Combined Publications Database
Journal of Sedimentary Research (SEPM)
Abstract
Sequence Stratigraphy and Depositional Facies of Lower Ordovician Cyclic Carbonate Rocks, Southern Missouri, U.S.A.
ABSTRACT
Lower Ordovician cyclic carbonate strata of southern Missouri were deposited in a warm, shallow, epeiric sea
on a fully aggraded carbonate platform. Sedimentological characteristics distinguish the Jefferson City and Cotter dolomites from the underlying Gasconade and Roubidoux formations. Mixed carbonate-siliciclastic sedimentation characterizes the Roubidoux Formation, with sandstones accounting for up to 60% of sedimentation. The Gasconade, Jefferson City, and Cotter dolomites exhibit an increased occurrence of chalcedonic chert nodules in very similar shape and texture to the gypsum and anhydrite nodules common on modern sabkha supratidal flats. Casts of halite and ghosts of gypsum laths also exist in the Jefferson City and Cotter strata but are rarely found in the underlying units.
Facies analysis from drill cores and outcrop sections provides the basis for identifying two major meter-scale cycle
types. Type I cycles consist of algal stromatolites, tidal-flat laminites (mechanical and algal), ooid grainstones, wavy peloidal wackestones, and quartz sandstones interpreted as peritidal facies. They are the dominant components of the Roubidoux Formation, Jefferson City Dolomite, and Cotter Dolomite. Type II cycles consist mostly of subtidal facies such as strongly burrowed mudstone, thrombolite boundstone, and stromatolites. Type I cycles are thinner and represent highstand
systems
tracts
, whereas the thicker type II cycles represent transgressive
systems
tracts
and are dominant in the Gasconade Dolomite. The
cycle
stacking patterns, facies changes, and the intrabasinal correlatability of Fischer plots made from the widely spaced sections argue for a eustatic control on
sea
-
level
fluctuation on the platform.
Interbasinal correlation with other North American basins is possible using biostratigraphic information and comparison of Fischer plots. Five Missouri sequences correlate with those described for other regions. The continent-wide uniformity in cycle
stacking patterns indicates a primarily eustatic control on Lower Ordovician meter-scale
cycle
development. Regional tectonic and autocyclic controls probably account for general differences in sedimentation pattern among the correlated basins.
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