Sedimentation and paleoecology of Pliocene lagoonal-shallow marine deposits on the island of Rhodes (Greece)

Abstract

A detailed analysis of the depositional and paleontological characteristics of a section of the Pliocene Kritika Formation on the island of Rhodos is presented. The environmental significance of sedimentary structures, the paleoecology of benthonic Foraminifera, and the sequentional arrangement of sediment types are emphasized. Attention is also paid to the textural and compositional properties of the deposits and to the occurrence of other invertebrate fossils: Thecamoebina, planktonic Foraminifera, Ostracoda, Bryozoa, Mollusca, Anthozoa, Annelida and Arthropoda. The vertical distribution in individual strata of horizontal lamination, large scale cross-lamination, small scale cross-lamination of oscillatory origin and burrowing structures is interpreted in terms of an episodical supply of silty-sandy detritus to a normally tranquil or non-depositional environment by wind-driven currents. During phases of sediment supply, mixing of elements of neighbouring faunal communities frequently occurred. The displaced specimens were subject to hydro dynamical selection according to size, nature of hard parts and mode of life. Gradual displacements of environmental boundaries in time and in space produced a superposition of sediments, reflecting a changing energy level and an alteration of autochthonous faunal communities, linked to modifications in the supply of allochthonous faunal components. Coarsening upward- and fining upward sequences are distinguished. The accumulation was controlled by the repeated construction and destruction of barriers in the littoral zone, as a function of subsidence and long-shore sand supply. Several lagoonal environments are distinguished, according to proximity of the barrier-system and exposure to open marine forces. A gradual waning of long-shore supply and a concomittant change in the nature of the lagoonal environments is concluded. The investigated sediments give a condensed picture of a part of the Pliocene history of eastern Rhodos and of the geological and physiographical framework of the Kritika Formation.