Plio-Pleistocene cliff-bound, wedge-shaped, warm-temperate carbonate deposits from Rhodes (Greece): Sedimentology and facies

Abstract

The Pliocene to Pleistocene temperate carbonates of Rhodes were deposited in a tectonically active region, strongly influenced by a complicated and rapidly changing topography, provided by the highly tectonised late Cretaceous Lindos Limestone as basement rock. Deposition on this basement took place in accommodation loci restricted to micrograbens and their downslope extension, to the foot of steep submarine cliffs, to basement neptunian dykes and depressions in the basement rock. Consequently the sediments comprise a high degree of facies variability, and are typically thin and laterally discontinuous. The integration of several outcrops is necessary for the reconstruction of the stratigraphy and the relative sea-level changes. The sediments were deposited during a large-scale, tectonically driven transgressive–regressive cycle in water depths changing from zero to several hundreds of metres. At the studied Lindos–Pefkos Road cutting the Kolymbia Limestone, bound to the foot of Lindos Limestone cliffs, marks the onset of the marine deposition in the late Pliocene. Its fabric is a rudstone consisting of unsorted angular Lindos Limestone clasts (up to boulder-size) with a matrix dominated by molluscs and coralline algae. The overlying Plio-Pleistocene St. Paul's Bay Limestone consists of deep-water float- and rudstones containing the ‘white coral community’ dominated by the coral Lophelia pertusa. Its matrix shows a complex fabric of up to five sediment zones separated by differing states of lithification. In this maximum flooding phase, mineralised hardgrounds indicate depositional hiati. The subsequent shallowing phase is represented by the Cape Arkhangelos Calcarenite, a series of distinctive facies of very patchy distribution. They are characterised by the Bryozoan–Brachiopod Facies, overlain by a facies heavily dominated by the bivalve Mytilaster sp. ( Mytilaster Facies). Conspicuous for the Mytilaster Facies is the inverse, concave-up, stacking pattern of shelly material. This facies is followed by a serpulid framestone and associated serpulid rudstone. Neptunian dykes cut through the first two facies and are filled with an intraformational breccia grading into a breccia with abundant Mytilaster Facies clasts (Neptunian Dyke Facies). The sedimentology and interpretation of each facies include a description of the ichnology, in particular the bioerosion peculiar to each facies. The separation of different gravity transport processes in steep submarine environments is rarely described and most of the literature concentrates on siliciclastic-dominated coarse-grained, sandy or gravely sand delta environments. For a classification of the transport processes of the examined deposits, the following criteria were evaluated: sediment body symmetry, inclination of the palaeorelief, sediment constituents, fabric complexity, sedimentary structures and availability of fine matrix. Sedimentary structures and grading can be camouflaged in carbonates due to density differences of bioclasts; however bioclast-orientations such as bivalve stacking patterns can give information about the sedimentary process. We suggest the inverse, concave-up, stacking pattern of bivalve shells to be a texture potentially indicative for debris falls. Because of the above-mentioned criteria we classified the Kolymbia Limestone as rock-fall deposits and the St. Paul's Bay Limestone as well as the Mytilaster Facies of the Cape Arkhangelos Calcarenite as debris-fall deposits. The Bryozoan–Brachiopod Facies could not be classified with certainty because of the lack of sedimentary structures and bioclast-orientation. However, a grain-flow or most likely a debris-fall transport process seems probable.