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Integrated gravity and seismic interpretation of duplex structures and imbricate thrust systems in the southeastern Pyrenees (NE Spain)

1997; Elsevier BV; Volume: 282; Issue: 1-4 Linguagem: Inglês

10.1016/s0040-1951(97)00223-0

1879-3266

A. Martínez, L. Rivero, A. Casas,

Geological formations and processes

Combined surface, subsurface and gravity data were used to determine the deep structure of the thrust belt in the southeastern Pyrenees. The Ripollès and La Garrotxa areas are part of the Cardona oil exploration permit. Hydrocarbons pervade the concession with numerous oil seeps, abandoned oil wells, and gas or condensate are in these two wells associated with the overthrust belt. The source rocks, the Armàncies formation (upper Cuisian-lower Lutetian), consist of alternating layers of organic-rich shales and thin limestones; this formation outcrops in the Cadí thrust sheet. In the Ripollès area, the Cadí unit overlies the Serrat unit with a hanging-wall ramp geometry, as deduced from the Serrat-1 well. The structure of the Garrotxa area is more complex. It consists of a duplex structure folded by antiformal stack structures with basement rocks in their cores. The northern boundary of these antiformal stacks represents an inversion of pre-existent extensional faults. The basement rocks involved in the structure represent shortcuts formed in the footwall of the extensional faults. A negative anomaly is shown in these antiformal stacks. These anomalies are interpreted as a combination of salt accumulation, evaporites and sedimentary rocks, under the antiformal stacks. In the Serrat-1 well, the Serrat unit is made up of a thick Middle Eocene evaporitic sequence. But the gravity and seismic data evidence the presence of non-evaporitic sedimentary rocks in the northern part of the Serrat unit. These sediments correspond to the footwall of the Cadí series, so the probable existence of the Armàncies formation in the Serrat unit is a very good target for oil prospecting. The existence of the previous extensional faults only in the Garrotxa area, determines the difference in the deep structure between the Ripollès and Garrotxa areas.