SEA LEVEL CONTROL ON FACIES ARCHITECTURE AND STRATAL GEOMETRIES OF THE APTIAN VILLARROYA DE LOS PINARES CARBONATE PLATFORM, IBERIAN RANGE, SPAIN

The Cretaceous Villarroya de los Pinares Formation (Iberian Range, Northeastern Spain) provides an ideal setting for investigating sea level control on carbonate stratigraphic architecture. The platform developed on the margin of the Aptian Galve sub-basin during a phase of rifting, and consists of five main facies. The inner platform is composed of bedded (1-3m) skeletal packstone, wackestone and grainstone. Toucasid rudists are common. The margin is composed of 4-10m thick Polyconites floatstone to rudstone beds, with some Polyconites rudists in life position. The slope beds dip ~30^o and are composed of skeletal wackestone and packstone with coral and debris from the Polyconites facies. Deeper water facies consist of skeletal wackestone containing scattered coral. In addition coarse, cross-bedded skeletal grainstone (up to 5m thick) occurs at the toe of the slope.

Facies distribution and stratal geometries were used to recognize system tracks representing one cycle of sea level fall and rise. A highstand system track (HST1) contains prograding beds of skeletal wackestone, packstone and grainstone that transition down-dip into deeper facies. A forced regression system track (FRST) composed of a thin wedge of coarse skeletal grainstone is restricted to the toe of the HST1 slope. It onlaps HST1, and thins down dip. The FRST was deposited under high energy conditions when sea level fell. The top of the FRST is a sequence boundary. The lowstand system track (LST) contains small prograding platform units with distinct margins (Polyconites floatstone to rudstones), slope and the inner platform facies. They downlap the FRST and contain internal onlapping geometries. A transgressive system track contains facies similar to the LST, but backsteps and onlaps HST1. A second HST (HST2) reestablished bedded skeletal wackestone to packstone with Toucasids across the platform.

Facies distribution and architecture were primarily controlled by relative sea level fall (HST1 to LST) and rise (LST to HST2). Sea level fell to the position of the HST1 margin, and deposited the coarse grainstone of the FRST. While sea level was low, shallow water Polyconites floatstone was deposited and prograded into the basin. As sea level rose, shallow facies retreated landward, and skeletal wackestone and packstone were reestablished in the area.