Mineralogic and organic responses to stratigraphic irregularities: An example from the Lower Paleozoic very low-grade metamorphic units of the Eastern Taurus Autochthon, Turkey

Abstract

The paleogeographic and diagenetic-metamorphic evolution of Lower Paleozoic (meta-) sedimentary rocks in the Eastern Taurus Autochthon were studied by means of petrographic and XRD methods. Parameters such as illite crystallinity index, b0 and % 2M1 proportion of K-white micas are characterized by an increase in grade from diagenesis at the top to epizone at the bottom. Organic data show a good correlation with phyllosilicate crystal chemical parameters. Three main zones and five sub-zones with distinct breaks at boundaries were distinguished throughout the Lower Paleozoic series. These boundaries seem to correspond to stratigraphic gaps, unconformities and/or irregularities that may have important implications regarding as yet unknown deformation events. The data indicate that the Eastern Taurus Autochthonous Unit was initially not only affected by typical sedimentary burial, but also preserved vestiges of an earlier regional thermal and/or deformational history. Alpine tectonic movements and related deformations caused but limited textural changes, thus did not completely erase some fingerprints of the Paleozoic mineralogic and organic transformations. The metamorphic evolution and relationships between the mineralogic, textural and organic properties and stratigraphic/metamorphic discontinuities in the Lower Paleozoic succession are controlled by diagenetic-metamorphic reactions and detrital input related to orogenic activity in the hinterland.