Paper No. 40-10
Presentation Time: 9:00 AM-6:30 PM
SYNDEPOSITIONAL FAULTING, SHALLOWING AND INTRAFORMATIONAL CONGLOMERATES IN THE MISHASH FORMATION (UPPER CRETACEOUS, CAMPANIAN) AT WADI HAWARIM, SOUTHERN ISRAEL
The Mishash Formation (Mount Scopus Group; Upper Cretaceous, Campanian) in Israel contains significant amounts of phosphorite important to industry. It is stratigraphically divided into two parts: a lower Chert Member and an upper Phosphate Member. We found evidence in exposures of the formation in Wadi Hawarim, southern Israel, that a significant east-west trending steeply dipping normal fault was active during the early deposition of the Phosphate Member. This faulting was synchronous with the Syrian Arc compressional structures active at the time that produced a series of anticlinal ridges and synclinal basins in the region. The fault, with a displacement of at least 50 meters, produced a drag fold against the footwall composed of the underlying Menuha Formation chalks. The hanging wall is composed of the Chert Member that is folded nearly 90 degrees along the fault plane. The Phosphate Member begins with 2-3 meters of phosphorite and is followed by a meter-thick marly bed rich with the crustacean burrow trace fossil Thalassinoides. Immediately above the trace fossils is a siliciclastic layer composed of chert fragments. This layer is a very coarse conglomerate near the fault that thins down-dip for several hundred meters, grading into discontinuous sandstone layers less than a centimeter thick. Our hypothesis is that the fault was active during the late Campanian after the deposition of the Chert Member and the lower part of the Phosphate Member of the Mishash Formation. The Chert Member had considerable ductility and was folded along the fault scarp. Soon afterwards relative sea level dropped, produced an oxygen-rich interval that enabled shrimp burrowing. The drop in relative sea level also brought the chert-rich fault scarp into a high-energy zone of erosion, producing a clastic wedge of cherty debris to spread seaward over the sediments, including the shrimp burrows. Relative sea levels then rose again, terminating the supply of siliciclastics and returning the sedimentation regime to dysoxic phosphorite. The trace fossils and this intraformational clastic wedge indicate a regional sea level fall and rise. Moreover, the occurrence of clastic wedges within the Mishash Formation demonstrates that shallow sea conditions prevailed in the vicinity of the Syrian Arc structures during the late Campanian.