EPIBIONTS, THEIR HARD-ROCK SUBSTRATES, AND PHOSPHOGENESIS DURING THE CENOMANIAN-TURONIAN BOUNDARY INTERVAL (BOHEMIAN CRETACEOUS BASIN, CZECH-REPUBLIC)

Hard inorganic substrates (rock clasts and rocky bottom) belonging to the Kank Member of the Korycany Formation (upper Cenomanian-Power Turo nian) and to the Bila Hora Formation (lower Turonian) have offered a g ood opportunity for the study of encrusting faunas of the Cenomanian-T uronian boundary interval. Distributional features of cemented epibion ts and the recorded period of phosphogenesis enabled the differentiati on of two-phases in the Kank Member conglomerate formation. During the first phase, the rock substrates were occupied by a so-called A-assoc iation of encrusters (29 species, with dominance of oysters and bryozo ans). This fauna partly changed during the subsequent phosphogenic per iod and not only survived the following period of reworking and the se cond phase of conglomerate formation, but also persisted until the ons et of calmer sedimentation in the early Turonian. This changed communi ty is named the Atreta-Bdelloidina community (23 species). The opportu nistic agglutinated foraminifers Bdelloidina cribrosa and/or Acruliamm ina longa locally dominated the respective communities during several physico-chemically stressed episodes. On sloping substrates, the bival ves Atreta and Spondylus attached themselves in a preferred orientatio n (so-called slope orientation). This feature indicates the original p osition in which some mobile substrates were colonized. Other question s, such as the taphonomy of encrusters and the character of their subs trates are also briefly discussed. (C) 1996 Academic Press Limited