RECONSTRUCTING CRETACEOUS SEAFLOOR TOPOGRAPHY BASED ON FACIES DISTRIBUTIONS: SANTONIAN SANT CORNELI FORMATION, SOUTHCENTRAL PYRENEES, SPAIN

The Santonian Sant Corneli Formation, southcentral Pyrenees, Spain, contains numerous distinct facies that were deposited within a relatively small area in response to actively changing seafloor topography. Upper Cretaceous strata in the southern Pyrenees comprise a regional set of northward prograding carbonate platforms that developed on the southern margin of the Pyrenean Basin prior to Alpine convergence. This regional trend is recorded in strata immediately below the Sant Corneli Formation across the field area. In the western part of the field area, the Sant Corneli Formation records continuation of this regional trend. Here, it is composed of skeletal grainstone that contains rudist, coral, and echinoderm fragments, benthic foraminifera, and 10-15% quartz sand. Large clinoforms define northward migrating sand bodies in a shallow shoreface environment.

In the eastern part of the field area, however, the Sant Corneli Formation contains rudist biostromes that are restricted to the crest of a structural high (the Boixols Anticline), suggesting the anticline was active during deposition and provided a shallow environment that localized the biostromes. This is supported by the occurrence of coeval deeper water marl containing syndepositional slumps on the anticline flanks, and a lack of quartz sand indicating this area was isolated from the regional depositional system. The rudist-rich facies intertongue with the skeletal grainstone just west of the Boixols Anticline.

The Sant Corneli Formation was deposited prior to the onset of Alpine convergence. A Santonian-aged origin of the Boixols Anticline recognized through facies analysis supports the growing recognition of an episode of halokinesis in the southcentral Pyrenees prior to convergence. Salt movement created the structural high that promoted rudist biostrome growth, and salt withdrawal to the north and south of the anticline created deeper environments as well as steeper slopes, both of which influenced deposition. At the same time, the western part of the field area did not appear to be influenced by the anticline during deposition of the Sant Corneli Formation. Understanding the distribution of contemporaneous facies was essential for identifying syndepositional changes to seafloor topography that influenced local sedimentation.