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Abstract: Controls Over Cyclic Development of Rudist Biostromes in the Upper Cretaceous Maiella Platform-Margin, Italy

Iwan Stoessel, Maria Mutti, Daniel Bernoulli

In the Maiella platform-margin, spectacular km-scale outcrops reveal the three-dimensional organization of 250 metres of cyclic Cenomanian-Campanian shallow-water limestones. The platform is a pure carbonate system characterized by a non-rimmed shelf, bounded by a non-depositional, by-pass escarpment. Approximately 950 metres of age-equivalent megabreccias, calcareous turbidites and periplatform oozes onlap the escarpment and aggrade in the basin.

Sedimentation on the inner shelf consists of peritidal cycles made up mainly by mudstones and packstones. They show shoaling upward trends and are often capped by subaerial exposure surfaces. Thicker subtidal cycles of several meters to a few tens of meters thickness were deposited in the outer shelf and consist of cross-bedded grainstones, rudist biostromes and subordinate peritidal mudstones and packstones. These cycles also show a shoaling upward trend. Outcrops parallel and perpendicular to the platform margin document the distribution of peritidal cycles, biostromes and sandwaves in three dimensions and reveal the existence of a complex interplay between depositional dynamics and paleoecological controls. Rudists as the major producers of carbonate sediment in the system have the efore a major effect on the internal organisation of the cycles.

The integration of depositional geometries and facies associations with the downslope extent of subaerial exposure events allows to establish a detailed sequence stratigraphic framework and to split the strata into depositional sequences of different hierarchies. However no apparent relationship can be found between rudist biostrome type and systems tracts, suggesting that cyclic deposition at a local scale was mainly controlled by environment-related factors. The stacking pattern of the inner shelf shoaling upward cycles shows an overall increasing proportion of subtidal facies which indicates that deposition at a larger scale was controlled by relative sea-level rise.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France