Kendall, Christopher George St. Clement¹ 
(1) University of South Carolina, Columbia, SC

ABSTRACT: Critical Accidents in Paleo-geography and Oceanography Induced by Abrupt Changes in Base Level, Signaled by Hard or Firm Grounds in Shallow Water Clastics and Carbonates

Sequence stratigraphic interpretations of shallow water clastic and carbonates are largely based on subdivision of stratigraphic sections by sequence boundaries, maximum flooding surfaces and transgressive surfaces. Each surface may be represented by firm or cemented hardgrounds, the product of definable accidents of paleogeography and/or oceanography induced by changes in base level and so abrupt changes in wave energy, local currents, temperature, salinity, nutrient level, light penetration and suspended materials. These initiate critical changes in local carbonate production and lead to substrate cementation. The eclectic origins of the surfaces are deciphered from their associated system tract determined from their patterns of stacking (progradational, retrogradational and aggradational), trajectory (falling, aggrading or climbing seaward or landward at different angles) and facies. While clastics tend to maintain generally similar lateral facies patterns through a sequence, carbonate facies tend to differ as system tracts track changes in base level. Both sedimentary systems are subject to the effects of wave action and long shore drift but if transported clastics are sequestered immediately following their transportation they tend to fine up. Both clastics and in situ carbonates are reworked by waves following deposition tend to coarsen up till the depositional setting is too wide and shallow for wave reworking and then finer sediment accumulates. Major facies differences occur when carbonate accumulation and cementation rates are inhibited or enhanced by accidents of paleogeography, and oceanography, particularly in late LST and TST. The signal of these events is strong and is repeated vertically in many shallow water sedimentary sections.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.