System Tract Bounding Surfaces, Lithofacies, Geometric Hierarchies and Stacking Patterns: Keys to Shallow Water Carbonate Interpretation

Christopher G. St. C. Kendall¹ and Luis Pomar^2
1 Department of Geological Sciences, University of South Carolina, Columbia, SC
² Universitat de les Illes Balears, Palma de Mallorca, Spain

Stratigraphic evolution and origins of shallow water platform margin and shelf carbonates can be analyzed by considering them combined products of base level change and so using: bounding surfaces to system tracts; component lithofacies; hierarchies expressed by the geometries of the strata; and their stacking patterns. This approach recognizes that position of base level, coupled with ecological accommodation, is responsible for differences in shallow-water depositional settings of carbonate platforms so that, in conjunction with paleo-oceanography, they in part control the processes responsible for carbonate accumulation. Additionally increases in accommodation (subsidence) affect the potential for preservation of accretional units (basic sequences versus parasequences) while topsets of a platform contain either cycles and/or parasequences. This kind of analysis implicitly assumes connection between subdividing surfaces and base level change, and is sequence stratigraphic, whereas when subdivision is by surfaces unconnected with base level change it is allostratigraphic. Carbonate production rates are linked to photo-synthesis, so depth dependent. Thus carbonate facies and their fabrics are clear indicators of changing relative sea level position. Additionally carbonate sediments often have a biochemical origin influenced by the chemistry of the water they precipitated from. Thus the character of carbonate sediment can change as paleo-climate changes, or as paleogeography of a basin changes in response to isolation or access to open sea. This means that carbonates are environmental indicators, which combined with sequence stratigraphy and allostratigraphy make carbonate facies analysis a powerful tool for interpretation of the geological section and lithofacies prediction away from data rich areas.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005