ABSTRACT

The Late Jurassic was a major period of reef expansion. Many Jurassic reefs are potential hydrocarbon reservoirs, but their stratigraphic distribution has been difficult to predict. Examination of the stratigraphic architecture of Oxfordian reefs in the northeast U.S. Gulf Coast and the eastern Paris Basin, France affords a comparison of mixed coral-algal sponge reefs versus microbial-dominated reefs.

The Smackover Formation in the northeastern Gulf Coast contains microbial-dominated reefs. The Smackover represents deposition during a major transgression and reefs occur within late transgressive system tract (TST) deposits.

Reefs of mixed coral, algae, and sponges characterize the Oxfordian of the eastern Paris Basin. In the Ardennes-Lorraine, reefs appear after the maximum flooding event of a stratigraphic sequence and are maintained through the highstand systems tract (HST) deposition and into the overlying stratigraphic sequence. In Burgundy, reefs occur in association with the maximum flooding event of the upper stratigraphic sequence. Dominated by platy microsolenids, reef growth begins in the TST. This interval is traditionally called the lower reef complex. More diverse reef growth (the upper reef complex) continues above the maximum flooding event through the early HST. Reef growth ceases by deposition of the late HST with the introduction of grainstones and other high-energy lithologies.

All reefs in this examination, regardless of biota, are associated with maximum flooding events. The sequence stratigraphy of the Oxfordian reefs in France and the Gulf Coast provides a framework for studying Jurassic reefs of both mixed and microbial-dominated assemblages.