Large-Scale Tectonostratigraphic Controls on Source Rock Development in Extensional Basins
MACGREGOR, DUNCAN S., DAVID J. MOORE, and PETER R. SHARLAND, BP Exploration, London, U.K.
A study of some 180 of the world's source systems indicates the dominant control to be the prevailing tectonic regime. A limited number of favorable tectonostratigraphic settings can be identified in which source rocks most frequently occur. Source facies development is thus usually a regional phenomenon, with source rocks discontinually deposited and preserved over large-scale tectonically controlled "fairways."The majority of significant source rocks occur within post-rift megasequences in extensional basins. Favorable tectonostratigraphic levels in the post-rift include those tied to the passive infill stage following rifting, and to later stages of thermal sagging. These usually correspond to surfaces of transgression. Examples are given and reasons for the apparent favorability o these levels speculated upon.
Good examples of large-scale tectonic control are shown within post-rift megasequences in passive margin basins. Oceanic circulation is controlled by the influence of plate movements on the geometry of the developing ocean. Oceanic anoxia often controls source rock development in the early stages of spreading while upwelling is of greater relative importance in the later stages of ocean development.
The post-rift conditions favorable for source rock development are, on a global scale, somewhat concentrated in the late Paleozoic and middle Mesozoic, following the Wilson Cycle of Plate Tectonics. The observed concentrations of source rocks in these two episodes is thus easily explained.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)