Palaeoecology of new fossil associations from the Cipit boulders, St. Cassian Formation (Ladinian-Carnian, Middle-Upper Triassic; Dolomites, NE Italy)

Abstract

Six fossil associations from 59 thin sections obtained out of 23 Cipit boulders of the Middle-Late Triassic St. Cassian Formation are described. Grouping and obtainment of these associations were performed considering all biomorpha and microbialites contained in the thin sections by means of cluster analysis in Q-mode using three algorithms and two indices. Further microfacial categories observed in the thin sections were allochthonous components, cements and microsparite, although they do not represent a significant fraction in any case. The associations include the following: Dendronella-Hexactinellida Association, Cassianothalamia Association I, Cassianothalamia Association II, Patch Reef Association I (Balatonia-microencruster Association), Patch Reef Association II (Solenopora-Dendronella Association) and Patch Reef Association III (Spongiomorpha ramosa Association). The possible palaeoenvironmental settings, from which each association is derived, are discussed individually. These settings were elucidated based on each fossil contained in the associations, since many of them are diagnostic for establishing specific environmental criteria. Although most associations are described here for the first time, some of them may be related to the "Cassian Patch Reefs', while one of them ("Cassianothalamia-Gemeinschaft') is reviewed.