Middle Miocene coralgal facies at Maksymivka near Ternopil (Ukraine) : a preliminary account

Abstract

A peculiar coralgal facies is recognized in the Lviv-Ternopil region, Ukraine, from the northern shores of the Middle Miocene (Badenian) Fore-Carpathian Basin. Its complex structure is dominated by algal buildups composed of interfingering red-algal (lithothamnian) colonies and blue-green-algal crusts, associated locally with numerous hermatypic corals ( Tarbellastraea reussiana , Porites vindobonarum prima ), either isolated, or overlapping each other. The holes amidst, and the crevices in, the buildups are filled with coarse bioclastic sediment (shell-grit), burrowed commonly by crustacean decapods (alpheid shrimps). The alpheid burrows, filled with coarser or finer shell-grit, served frequently as taphonomic traps for crustacean decapods (squat lobsters and crabs) and echinoids. Special attention is paid to the activity of rock-boring bivalves ( Jouannetia semicaudata , Lithophaga lithophaga ) in coralgal buildups and/or in particular coral colonies, some of which are redeposited, and riddled densely by bivalve borings. Emphasis is given to the environmental significance of alpheid shrimps, the tiered burrows of which are recorded in the Fore-Carpathian Basin for the first time. Crustacean decapods and echinoids are systematically studied. A comparison of the studied coralgal facies with others of the Lviv-Ternopil region, and those from the territory of Poland, indicates their faunistic and biogeographic identity.