DEPOSITIONAL ENVIRONMENTS AND SEQUENCE STRATIGRAPHY OF GLAUCONITES OF WESTERN BLACK SEA REGION

Abstract

Glauconitic sediments which are subject to this study, have been deposited with different age and facies characteristics around Devrek-Zonguldak and Kastamonu regions. Glauconies within Lower Cretaceous sequence of Western Black sea region, developed in siliciclastic units which had been deposited in outer shelf by transgressive conditions. Typical occurrences, are found in Sapca formation of Zonguldak region. Glauconitic sandstones have preferably been accumulated in sand bars during sea level changes controlled by eustatic and tectonic factors. These sediments are characterised by large and small scale cross beddings, sheet sands with parallel lamination, and bioturbation. Glaucony grains within the sandstones have autochthon and allocton characteristics according to their depositional environments. The movements within the environment of glaucony formation had been accomplished by long and short distance displacements. In consequence limestone, quartz, feldspar and mafic rock grains which had been subjected to different degrees of glauconitisation were concentrated in off shore sand bars. The glauconies have been cemented by argillaceous matrix that shows different degree of glauconitisation or rarely cemented by carbonate within the silicislastics. The glauconitisation in Kastamonu region is observed within Lower Eocene units. This mineralisation had been developed in carbonate facies which differs from Zonguldak region. The areas where Lower Eocene limestones of reefal characteristics laterally pass to open sea facies, have prepared suitable environmental conditions for the glaucony formations. Fossil, intraclast and pellet type carbonate grains in this level have been glauconitised by different degrees and exhibit hard ground and complete authocthon properties. Glaucony occurrences of the region have widely been controlled by sea level changes. Autochthon glauconies of silisiclastics of Zonguldak region which had especially been formed in periods of maximum transgression, were transported to the lower system tracts by regression of the sea. Glaucony formation of Kastamonu region occurred in hard grounds which marked upper surface of reefs when they had been drowned by rapid rising of sea level.