Paleozoic Carbonate Gravity-Flow Deposits, and Relationships to Changes of Relative Sea Level, Southernmost Appalachians

Oscar E. Gilbert, Jr.

The Jumbo Dolomite, deposited during a sea level fall at the end of the Early Ordovician, consists of lenticular carbonate masses embedded in the Mount Zion Formation, basinal shales deposited seaward of a Cambrian-Early Ordovician carbonate shelf. Stacked gravity-flow deposits include: (1) early massive debris-flow beds, with allogenic carbonate, chert, and sandstone clasts in a micritic matrix; (2) thick to massive debris-flow beds, with authigenic clasts in an argillaceous micritic matrix; and (3) late, fine-grained carbonate turbidites with partial Bouma sequences. Interbedded basinal shales (Bouma E) are more numerous in the upper part of this third unit.

Gravity-flow deposits in the Athens (Middle Ordovician) and Floyd (mid-Mississippian) Shales were deposited during sea level rises. Argillaceous micrite turbidites in the Athens were derived from shallower bathymetric levels of a carbonate ramp. Gravity-flow deposits in the Floyd are individual tabular debris flows of skeletal debris and authigenic shale clasts in a micritic argillaceous matrix.

Discrete gravity-flow beds deposited during sea level rises may be attributed to platform margin collapses. Stacking of flow deposits in the Jumbo indicates point-sourced flows localized by channels. The succession in the Jumbo represents stages in the fall, stabilization, and rise of sea level relative to the shelf; unit 1 represents early exposure and erosion of the shelf, and units 2 and 3 indicate the cessation of coarse debris input as a low-relief subaerial surface developed and sea level stabilized. Interbedded shales near the top of unit 3 represent sediment starvation associated with the subsequent rise of relative sea level.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.