ABSTRACT

The three-dimensional aspects of thick carbonate sequences can best be explained as a sequence of upward-shoaling cycles. A simple upward-shoaling cycle results in the building up of the sea floor by sedimentary processes, followed by progradation. Such sedimentary cycles can explain the mechanism of deposition of relatively thin (less than 60 feet) carbonate beds.

The stretched upward-shoaling cycle, which develops in response to contemporaneous subsidence, can be used to interpret the three-dimensional geometry of thick carbonate sequences. The stretched and simple upward-shoaling cycles are the building blocks which comprise the transgressive or regressive carbonate sequences. Both simple and stretched upward-shoaling cycles can be recognized in the Mesozoic section of the Gulf Coast region.

Eustatic sea level fluctuations which can be related to the spreading rate of lithospheric blocks in the context of plate tectonics are probably controlling factors for some major transgressive episodes. Most of the repetitive cycles, however, are believed to be related to the tensional and shear stresses developed within the upper brittle layer of crust as consequences of vertical movements within lithospheric plates. This mechanism was probably operative in the sedimentary basins whose origins were related to divergent, convergent, and transform motions of plates.