Abstract: Sequence Stratigraphic Architecture and Cycle Stacking Patterns of Platform Carbonates--An Evaluation of Autocyclic, Deterministic, and Stochastic Controls
Robert K. Goldhammer
Regardless of geologic age and tectonic setting, virtually all shallow-marine, shelf, and ramp carbonates in the geologic record exhibit composite stratigraphic cyclicity whereby higher frequency fifth-order (0.01-0.10 m.y.) and fourth-order (0.1-1 m.y.) depositional cycles are grouped to define third-order (1-10 m.y.) depositional sequences. The building block of this hierarchy is the meter-scale, fifth-order/fourth-order, aggradational and/or progradational depositional cycle, which shoals upward and is bounded by a subaerial or submarine diastem. In the next level of the hierarchy, the lower frequency, typically third-order, sequences are described by the vertical and lateral stacking patterns (systematic variation in the thickness, facies makeup, and early diagenetic features) of the fifth-order and/or fourth-order cycles.
Different models proposed to explain meter-scale, fifth-order and/or fourth-order, shallowing-upward cycles include allocyclic glacio-eustatic phenomena, allocyclic random sea level fluctuations, allocyclic tectonics, and/or autocyclic progradation. After evaluating various mechanisms for generating high-frequency cyclicity, one can use the concepts of composite eustasy and the hierarchy of stratigraphic forcing to interpret composite stratigraphic cyclicity of carbonate platforms, and to determine third-order systems tracts and depositional sequences. Order within the hierarchy is maintained by systematic control of high-frequency cycle characteristics by longer term changes in accommodation.
The plausibility of composite eustatic control on development of high-frequency cycles and third-order sequences is demonstrated by one-dimensional and two-dimensional computer simulations under a variety of geologically reasonable conditions. These simulations provide the link in integrating classic facies stratigraphy with cyclic stratigraphy and the evolving concepts of sequence stratigraphy. An appreciation of these concepts will provide the link between kilometer-scale seismic stratigraphy and meter-scale cyclic stratigraphy, and will lead to a better understanding of the vertical and lateral distribution of subfacies and facies within platform carbonate sequences.
AAPG Search and Discovery Article #90985©1994-1995 AAPG Distinguished Lecture