Abstract: Variability of Third-Order Sequences within the Second-Order Sequence Stratigraphic Framework of the Paris Basin

T. Jacquin, C. Durlet, J. P. Garcia, V. Goggin, Cnrs, P. Ch. de Graciansky, G. Rusciadelli, P. R. Vail

The stratigraphic expression of third-order sequences are closely dependent on their position within second-order cycles. Sequences may be either infilling or forestepping during the regressive phase and either aggrading or backstepping during the transgressive phase. Three sets of examples are presented.

1. Norian forestepping and Rhaetian backstepping sequences develop within a continental to marginal-marine clastic setting. Emphasis is placed on the tectonically enhanced sequence boundary that limits at the top of the Norian regressive clastics. Rhaetian backstepping sequences form a major change in the paleogeography of the basin due to the onset of the marine transgression.

2. Aalenian forestepping sequences are not well developed on the central horst of the Paris basin, because they are merged as a major subaerial unconformity (first-order boundary). In contrast, they develop on both sides of this central horst as big lowstand deposits. The following Bajocian transgressive phase displays aggrading to backstepping sequences comprising mostly shallow-water carbonates. The Bj5 sequence boundary prior to the peak transgression implies, however, a major downward shift of coastal onlap at a third-order scale.

3. Callovian backstepping sequences may be good shallow-water carbonate reservoirs. Here also some sequence boundaries imply major relative sea level drops, whereas the long-term trend is transgressive. The proceeding Oxfordian infilling to forestepping sequences indicate the re-establishment of carbonate factories over the previously drowned Bathonian-Callovian platform.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994