DIMENSIONAL AND SPATIAL PATTERNS OF DISRUPTED BLOCKS OF MESSINIAN GYPSUM, WESTERN CALTANISSETTA BASIN, SICILY
Evaporites associated with the Messinian Salinity Crisis are widespread throughout the Mediterranean region. The Sicilian Messinian stratigraphy is composed of two evaporitic units. The lower of these, (Lower Gypsum (LG)), includes both shallow-water, Primary Lower Gypsum (PLG) and deep-water, Resedimented Lower Gypsum (RLG). In the western Caltanissetta Basin, the RLG includes chaotic, non-bedded bodies containing disarticulated cm- to km-blocks of massive selenite gypsum, bedded gypsum mass-flows, and gypsum turbidites. The resedimented components were derived from the dismantlement of PLG along basin margins. Previous studies suggest that major sections of the PLG, both in the northern Apennines and Sicily, underwent large-scale mass-wasting processes and that the chaotic bodies in the RLG are gravitationally driven mass-flow deposits (olistostromes). The olistoliths within the RLG have a well-defined stratigraphy that can be correlated back to in-place sections. We investigated the distribution of these blocks to reveal the deposit’s internal structure and possible block emplacement mechanisms. Field mapping and satellite imagery were used to map the size, shape, and block distribution in order to establish dimensional and spatial patterns of block disruption. The stratigraphy and orientation of each major block was also determined to estimate dispersal patterns and possible temporal or stratigraphic sub-groupings. On the basis of work to date, we hypothesize that the blocks slid out onto the basin floor and were buried by younger, deep-water sediments, which are now being eroded to exhume original seafloor topography created by the emplaced blocks.