Sedimentary Facies Analysis, Reservoir Characteristics and Paleogeography Significance of the Early Jurassic to Eocene Carbonates in Epirus (Ionian Zone, Western Greece)

Abstract

Sedimentological, micropalaeontological, and marine geological results from the Early Jurassic to Eocene carbonate formations of the Ionian zone, from six localities of Epirus, provide new insights into the basin palaeogeographic evolution and better correlation with coeval analogous tectono-stratigraphic successions along the southern margin of the Neo-Tethys Ocean. Facies analysis allowed the recognition of several microfacies types and their depositional characteristics. During the Early Jurassic, autochthonous carbonates (Pantokrator Limestones) were deposited in shallow-water environment. The overlying (hemi)pelagic Siniais or their lateral equivalent Louros Limestones were deposited to the basin borders and mark the general deepening of the Ionian domain. During Toarcian to Tithonian, the Ionian Basin was characterized by an internal differentiation in small sub-basins with half-graben geometry presenting abrupt thickness and facies changes. The deeper parts were characterized by continuous sedimentation, while the elevated parts were marked by unconformities. The Early Cretaceous marks the homogenization of sedimentation by the deposition of the pelagic Vigla Limestones all over the Ionian zone. The transition from the Early to Late Cretaceous records a significant carbonate diversification in terms of biota assemblages, and related mineralogy due to intense tectonic activity in the region. From Late Cretaceous to Paleogene, allochthonous carbonates were transported to the outer shelf by turbidity currents (calciturbidites) and/or debris flows (limestones with breccia) formed by the gravitational collapse of the platform margin. Additional porosity and bulk density measurements showed that petrophysical behavior of these carbonates are controlled by the depositional environment and further influenced by diagenetic processes. The partly dolomitized neritic Jurassic carbonates, but mainly the Senonian calciturbidites and the microbrecciated Paleocene/Eocene limestones display the higher average porosity values, and therefore present enhanced carbonate reservoir quality.