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ABSTRACT: Tectonic and Eustatic Controls on Sedimentary Successions at Passive Continental Margins

Nicholas Christie-Blick

The configuration and internal characteristics of sedimentary successions at passive continental margins are controlled largely by patterns of tectonically driven subsidence and deformation, by eustasy, by the character and flux of available terrigenous sediment, and by the rate of in-situ production of carbonate and other chemical sediments. Rates of subsidence and sediment accumulation are also influenced by the effects of sediment loading and deformation, and by the manner in which sediments become lithified through compaction and diagenesis. The purpose of this presentation is to explore, with reference to passive margins of Mesozoic and Cenozoic age, some of the complex interconnections and feedbacks between these controls, their characteristic time scales and rates, and the leads and lags that may be involved. In particular, we draw attention to the controversy concerning the roles of tectonics and eustasy in the development of unconformities. A practical application of this ongoing research is the promise of new concepts and tools for the exploration and production of oil and gas. An inherent difficulty is that none of the important variables can be isolated completely, and simplifying assumptions, although necessary for analysis, unfortunately tend to take on the aura of established fact. Models have already outstripped the data available to test them, and at best we can place bounds only on what is possible. The apparent success of a stratigraphic simulation is no guarantee that all (or even any) of the important variables are included within the starting assumptions.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990