SHEET VOIDS AND RADIAXIAL FIBROUS CALCITE CEMENT FILLS FROM UPPER JURASSIC BEACHROCK, CALCAIRES-BLANCS-DE-PROVENCE, SOUTHEAST FRANCE

Extensive bedding-parallel cement and sediment-filled voids occur in p eritidal carbonate sediments of the Upper Jurassic, St. Croix Formatio n of the Calcaires Blanc de Provence, southeast France. Sheet voids ar e present in both grainstones and in stromatolitic sediments and are f ormed by different processes in each lithology. The best-developed she et voids occur in fenestral grainstones, often between layers of diffe rent grain size, where they are up to a meter long and 5mm high. In co ntrast to previously- described examples of bedding-parallel voids in peritidal carbonates, these sheet voids are not linked to vertical des iccation cracks nor are they linked to separation of layers during tep ee formation. Sheet voids described here were formed by winnowing/eros ion of unconsolidated or lightly-cemented sediment from between early- cemented grainstone layers deposited in a beach and very shallow subti dal environment. Erosion and winnowing were probably initiated in the swash zone, and may have continued in the subtidal together with some sediment deposition in parts of the voids. The dominant fill is vadose /phreatic marine radiaxial fibrous calcite cement, the first-reported occurrence of this type of cement in beachrock. Remaining pore space i s occluded by probable meteoric phreatic cements which were precipitat ed during later subaerial exposure associated with extensive pedogenes is of the overlying carbonate mud-dominated succession. Examples of an cient beachrock sediments are not common, and we suggest that sheet ce ments of this type may be diagnostic.