Sedimentray Petrography and Origin of Phosphate Peloids of the Mazıdağ-Derik Area (Mardin, Southeast Turkey)

Abstract

The Mazıdağ phosphate beds of the Upper Cretaceous carbonate sequence were deposited in an area of upwelling water which supplied phosphorous was deposited on the sea bottom as biogenic detritus of zoo— and phytoplankton, fish bones and scales. The biogenic accumulation with high content of organic matter and phosphorous was a prime source of the phosphate which formed the phosphate deposits of the Mazıdağ—Derik area. Commonly, currents transported the phosphatic sediments laterally, forming parallel and low angle cross laminations. In some cases, the sea floor was uplifted after upwelling periods. Consequently, some phosphate beds underwent karstification, giving rise to phoscretes and silcretes. Ground water percoalating into the karstic realm caused phosphate replacement of many carbonate grains of the shallow water limestone facies. These complex events resulted in the formation of three basic phosphate peloid types in the Mazıdağ-Derik phosphate sequence, which are classified to the following origin of peloids : (1) in situ precipitation; (2) abrasion of phosphatized intraclast and bioclast and (3) phosphate micritization of fish bones. The phosphate peloids show the following different microstructures under the electron microscopy : (1) amorphous; (2) microglobular; (3) semi-crystallized; (4) microcrystallized and (5) cementing.