Patterns of reef sedimentation and diagenesis in the Miocene of Cyprus

Abstract

An Early Tertiary regressive sedimentary succession developed along an active plate margin in Cyprus. A varied clastic and carbonate succession of the Miocene Pakhna Formation and then Messinian evaporites culminate the regression. Within the Pakhna Formation, two phases of reef growth were developed: the Aquitanian—Burdigalian, Terra Member, and the Tortonian, Koronia Member. The Terra Member is exposed only in west and southeast Cyprus, mainly between pelagic carbonates. The Koronia Member is exposed around the margins of the Troodos Massif in north, south and west Cyprus and on the Akamas Peninsula in northwest Cyprus. There was little tectonic influence on the growth pattern of the Terra Member reefs. The Koronia Member reefs, however, are developed on up-faulted blocks. Most of the Koronia Member fore-reef facies and associated clastic input was shed into downfaulted basinal depocentres. There are differences between the first and second Miocene reef phases in Cyprus in primary reef construction and in the level of background carbonate pelagic sedimentation. The Terra Member reefs are dominantly framestones, comprising faviids and domal poritids with several types of secondary reef-dwelling corals. There is no indication of a connection with the Indo-Pacific coral faunal province. Benthonic foraminifera and fragments of crustose coralline algae are abundant in the off-reef. By contrast, the Koronia Member is a bindstone comprising virtually monospecific, laminar poritid corals but with coralline algae also playing a role in encrustation. The Koronia Member off-reef facies comprises decimetre-thick beds of bioclastic reef detritus. In north Cyprus however, beds of similar detritus (centimetres in thickness), are overlain by progressively thicker (up to several metres) debris-flow sheets. The Terra Member reefs have limited acicular fringe cement (probably aragonitic). This is overlain by an abundant, marine, bladed, formerly high-Mg calcite cement. Later cements present in the reef facies include micritised calcite spars, perhaps indicating microboring in cements during their precipitation. Neomorphism was extensive, converting most cements to low-Mg calcite. Stable isotopic data for all the Cyprus calcites exhibit depletion in the heavier isotopes, 18O and 13C, indicative of meteoric alteration. The Koronia Member limestones show abundant indication of early lithification with fringing acicular aragonite and micrite cements. Stable isotopic data of the botryoidal aragonite cements indicate a marine origin. The dolomite is thought to result from marine—freshwater mixing and to be of Pliocene age, on the basis of stratigraphical, solution-replacement fabric and stable isotopic data. Sr isotopic data do not contradict a Pliocene age. Dolomite characteristically replaces the Pliocene fissure fill contents in southeast Cyprus and off-reef horizons in the Terra Member of west Cyprus and Koronia Member of north Cyprus. The growth and burial history of Miocene reefs contribute to the understanding of the tectonic history and palaeogeographical evolution of Cyprus.