Sylvie Bourquin¹, Cécile Robin², François Guillocheau³, Jean-Michel Gaulier⁴

(1) CNRS, Rennes, France
(2) University, Paris, France
(3) Géosciences Rennes, Université de Rennes-1, Rennes, France
(4) IFP, Rueil-Malmaison, France

ABSTRACT: 3-D accommodation measurement of a continental intracratonic basin (Triassic, Paris Basin, France): discrimination between tectonic and sediment supply on the stratigraphic record

During Upper Triassic time, the Paris Basin is an intracratonic basin, mainly filled by continental deposits going from sabkha, lacustrine to braided alluvial fan. The 3D accommodation has been measured at the scale of half baselevel cycle (1 to 4 Ma) in order to quantify the relative influence of tectonics and sediment supply on the stratigraphic record. The accommodation rate varies in space at two scales: a short wavelength and a long wavelength (>150 km). The baselevel rise half-cycles show systematic space creation with orientation different of those observed during baselevel fall half-cycles. Both the spatial lateral changes in accommodation rates, for each half-cycle, and the orientation of depocentre from baselevel rise to fall periods imply that these sequences are partly of tectonic origin.

Our data suggest a subsidence pattern along two directions during this period: E-W for the Carnian (N-S extension) and NNE-SSW for the Norian and Rhaetian (E-W extension). Thus, the Paris Basin accurately records the different phases of the opening of the Ligurian Tethys Ocean associated with the rotation of the extension direction. The Norian records the transitional period between Triassic and Liassic tectonic pattern.

The Carnian and Norian baselevel fall half-cycles are characterised by accommodation space creation in the western part of the basin. This means that siliciclastic supply is larger than the accommodation space creation. This could be explained by large amount of sediment induced (1) by climate variations, for the Carnian cycle and (2) by local tectonic activity, for the Norian cycle.

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