SEPIOLITE-PALYGORSKITE FROM THE HEKIMHAN REGION (TURKEY)

Abstract--Upper C etaceous-Tertiary marine clayey-calcareous rocks of the Hekimhan basin contain fibrous clay minerals in significant amounts. Ophiolitic rocks in the provenance area have contributed the elements to form the clay minerals. XRD, SEM, major, trace and REE analyses were applied to samples taken from several stratigraphic sections. Diagenetic minerals uch as smectite, dolomite, calcite, gypsum, celestite and quartz/chalcedony areassociated with sepiolite-palygorskite group days. Trace and rare earth elements (REE) are more abundant in palygorskite han sepiolite. REE abundances in the sepiolite-palygorskite are characterized bynegative Eu and positive Nd anomalies when normalized with respect to chondrite and shale. Sepiolites with sharp XRD peaks are formed by diagenetic replacement of dolomite and diagenetic transformation f palygnrskite, orby direct crystallization from solution. The average structural formula of the sepiolite is: (MgT.l sAloA 3Feo.3 ~ Cro.06Nio.04)(Si H.gsAlo.02)O30(OH)4(OH2)4Cao.03Nao.o2Ko.02.8H20 Palygorskite appears to be authigenic by direct precipitation from solution. It exists in both monodinic and orthorhombic forms with the mean structural formula given below: (Mg2.22A~Ti~.~4Fe~.7~Cr~.~Ni~.~2)(Si7.68Al~.32)~2~(~H)2(~H2)4Ca~.~7Na~.~5K~.~.4H2