The Porosity Evolution of Eocene Limestones in the Preapulian Zone, Zakynthos Island, Western Greece

Marianna Kati¹ and Peter A. Scholle^2
1University of Athens, Athens, Greece
²New Mexico Bureau of Geology, NM Tech, Socorro, NM

The Eocene pelagic and redeposited carbonate sediments on Zakynthos Island were deposited at the base-of-slope between the Preapulian platform and Ionian basin. The resedimented facies are represented primarily by very coarse-grained reefal debris flow deposits as well as bioclastic turbidites (mostly low-density flows). Detailed facies analysis, in association with porosity and permeability measurements in many selected samples, allowed definition of two main paths of porosity modification. The primary porosity of reefal debris flows was mainly destroyed by synsedimentary cements although subsequent dissolution of their originally metastable constituents led to extensive moldic porosity and minor vuggy porosity. However, most of this secondary porosity was occluded with sparry blocky/equant cements and only in a later diagenetic stage did some leaching increased the size of some vugs and preserved intergranular pore spaces. In contrast, the reduction of porosity in turbiditic and pelagic facies was achieved mainly through compaction and the precipitation of equant/blocky and syntaxial overgrowth cements. These cements, in association with recrystallization, occluded primary porosity almost completely. Nevertheless, some intergranular porosity was gained through later dissolution specifically in the coarser-grained high-density turbidites. Petrophysical data show that these Eocene limestones generally have low porosity values (total mean porosity = 10.87%), as well as very low permeabilities (generally <1mD). The high-density turbidites are exceptions to this pattern and locally have 27% porosity and mean permeability of 22.79mD. The latter clearly indicates substantial "effective porosity" and good reservoir characteristics, especially where it is combined with the fine-grained low-density turbidites and/or pelagic sediments that surround and act as seals for this facies.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece