--> Abstract: Sequence Stratigraphy of the Jurassic: New Data from the Paris-London Basin Compiled on Well Logs, by C. M. Ponsot and P. R. Vail; #91004 (1991)

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Sequence Stratigraphy of the Jurassic: New Data from the Paris-London Basin Compiled on Well Logs

PONSOT, C. M., and P. R. VAIL, Rice University, Houston, TX

A sequence stratigraphic analysis of the Jurassic sedimentary succession in Paris basin is derived from an integration of subsurface log correlations, field observations, and reinterpretations of field descriptions. The analysis is presented on two log sections, one crossing the basin from northeast to southwest and the other from northwest to southeast (approximately 80 logs).

A vast quantity of field data, collected all around the Paris basin (English Dorset, French Normandy, Manche, Ardennes, Lorraine, Bourgogne) allowed the sequences and system tracts boundaries to be traced and dated at the same time or prior to being recognized on well log data.

The Lias period (210-179 m.y.) includes 14 interpreted sequences boundaries: Hettangian: 211,202; Sinemurian: 199, 198, 194.5; Pliensbachian: 190.5, 188.5, 188.3, 188, 186.5; and Toarcian: 184?, 182.5, 181, 179.5. We consider the 211 m.y. sequence boundary to fall within the Jurassic even if it is of Late Rheatian age. Frequently the Toarcian sediments experienced partial erosion in the study areas; some depositional sequences of that time may have been missed.

Fourteen sequence boundaries recognized during Dogger time (179-152 m.y.) include: Aalenian: Aal, 177, 175; Bajocian: 169, 168, 165.3; Bathonian: 163, 161.8, 160.8, 159.5, 158.5; and Callovian: 156, 154.3, 152.5. As the producing reservoirs of the Paris basin were deposited during Dogger time, the sedimentary column is well documented and well dated on outcrops and well logs. The sole exceptions are the Aalenian/Bajocian sediments that were either partly eroded or deposited as condensed intervals.

The eighteen sequence boundaries interpreted for the Malm period (152-131 m.y.) include: Oxfordian: 151.5, 150.2, 149.5, 149, 148, 147.5, 146.5, 145.2?; Kimmeridgian: 144, 143, 142, 140, 139, 138.5; and Portlandian: 136, 134.5, 133.8, 131. The sedimentary column for this period is relatively well documented.

In comparison with the Haq et al. 1987 cycle chart, 16 new sequences have been added: three for the Lias, seven for the Dogger, and six for the Malm. Occasionally, ages of some of the already recognized sequences boundaries have been slightly modified to fit new biostratal data. These biostratal data were usually at the scale of the ammonite sub-zone and the actual given ages all tie with the 1987 Haq et al. chart time scale.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)