Third-Order Underfilling-Overfilling Foreland Basin Sequences

M. Marzo, J. Verges, M. Lopez-Blanco, J. A. Munoz, T. Santaeularia, and D. W. Burbank

The Eocene deposits forming the marine hemicycle of the Tertiary infill of the Eastern Pyrenean foreland basin (NE Spain) consist of four, 3rd order (~3.5-5 my), underfilling-overfilling sequences which cannot be correlated with global eustatic cycles. The most complete of such sequences comprises: (1) a basal, basin-wide, shallow-marine unit sharply resting on top of subaerial deposits; (2) a southward-onlapping carbonate platform which rims the southern, passive margin of the foreland and merges toward the basin depocenter into deep-water mudstones; (3) a southward-prograding, turbiditic and/or deltaic terrigenous wedge derived from the growing orogen. The progradation of this clastic wedge is accompanied by both a southward shift in the location of the depocenter and o the coeval southern carbonate-platform towards the passive margin, causing a clear downlap over the previous deposited carbonates and mudstones; (4) a late stage of basin infill by continental deposits and/or an evaporitic plug.

The development of each sequence occurs under continuous shortening (~2 to 4.5 mm/yr) and homogeneous subsidence rates so that the passage from underfilling to overfilling conditions cannot be related with an alternation of periods of quiescence and tectonic activity but with the continuous growth of the orogenic wedge. Underfilling reflects low topography and low clastic delivery rate in the hinterland. Overfilling points to an increasing topography and clastic sediment supply. The repetitive (cyclic) nature of these sequences is linked to renewed flexural loading due to the emplacement of successive thrust sheets.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California