Allochthonous Paleogene Carbonates of Paxos Island (Ionian Islands, Greece) Reflect a Complex History of Nearby Platform Evolution and Destruction

Abstract

Paxos Island, one of the smallest of the Ionian Islands that lie off the west coast of Greece, has spectacular, albeit discontinuous or difficult to access, exposures of limestones of the Pre-Apulian zone. Early mapping of the island (Perry et al., 1960) delineated two unnamed units, designated as Up. Cretaceous–mid. Eocene and Up. Eocene–Lo. Miocene. Both units contain mostly reworked material and early mapping did not adequately distinguish true depositional ages from ages of incorporated clasts and grains. The lower unit consists of massive debris flows overlain by turbidite grainstones with only minor interbedded pelagic limestones. Even on outcrop, individual rudists are visible along with coral, sponge, and green algal grains plus solenoporoid and red algal encrusters. Thus, initial impressions are that this is simply synsedimentary detritus shed from a Cretaceous platform margin. Thin section examination of material from four localities, however, shows that the detritus includes a wide range of rock fragments (extraclasts)—reworked material from shelf-margin, shelf interior and upper slope settings. More importantly, all the lower-unit limestones include Middle to Late Eocene benthic and planktic foraminifers. This combination of Cretaceous rock fragments and Eocene fossils is interpreted to result from repeated submarine failures of a Cretaceous-cored platform during the Eocene with simultaneous down-slope transport of both lithified Cretaceous rock fragments and unconsolidated Eocene sediment from marine shelf areas adjacent to the failure scarps. This is similar to Miocene events described from seismic data off the west Florida platform margin (Mullins et al., 1986). Starting in the Late Eocene and continuing through the Miocene, the inferred platform destruction was substantially reduced, although allochthonous deposits of the upper unit continued to be derived from a platform source. Those younger deposits are thinner-bedded and finer-grained than those of the lower unit but still include abundant turbidites, minor debris flows and numerous large, synsedimentary slump structures, indicative of slope deposition. Similar histories of post-Cretaceous platform evolution are recorded in Pre-Apulian deposits on other Ionian islands, especially Zakynthos. The thickness of section and moderate preservation of porosity in the allochthonous carbonate rocks of Paxos indicates some reservoir potential for comparable deposits in the subsurface.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016