William C. Parcell¹

(1) University of Alabama, Tuscaloosa, AL

ABSTRACT: Local, Regional, and Global Controls on the Distribution of Upper Jurassic Reefs in the Eastern Gulf Coast, U.S.A. and Eastern Paris Basin, France

Controls on the development of Upper Jurassic reefs in the eastern Gulf Coast and the eastern Paris Basin were investigated through outcrop analyses, subsurface examinations, and computer modeling. The Late Jurassic was one of the major periods of reef development in the geologic record. It is unclear from field and subsurface examinations if reef development was due solely to local environmental conditions or can be attributed to regional and global-scale factors. To examine this problem, a fuzzy logic-based computer model (FUZZYREEF) was developed that simulates the response of the carbonate system to interdependent local, regional, and global scale variables.

To examine the effects of local controls on reef distribution, local variables were isolated from relative sea level and climate change. These simulations indicate that background sedimentation rates, substrate conditions, and hydrodynamic energy were the principal local factors controlling reef development. Changes in sea level and climate were then superimposed onto the simulation to examine the effects of changing regional and global variables. It was discovered that rate of relative sea level rise is critical to the development of reefs because the rate of sea level rise strongly controls the background sedimentation rate. With rapid rises in sea level, background productivity drops quickly and takes long to recover. It is during this recovery period that reefs have a window of opportunity to develop. The largest reefs develop during 3rd-order sea level rise between deposition of the latest transgressive systems tract and early highstand systems tract.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado