Microbialite-dominated fossil associations in Cipit Boulders from Alpe di Specie and Misurina (St. Cassian Formation, Middle to Upper Triassic, Dolomites, NE Italy)

Abstract

In this paper we describe four new fossil associations of “reef” and “reef”-like environments of the St. Cassian Formation (Ladinian-Carnian, Dolomites, NE Italy), based on thirty thin sections from 10 “Cipit boulders” olistoliths, which slided from the Cassian platform into coeval basin sediments. The fossil associations were determined by means of microfacies analysis using point-counting and visual estimation, as well as with aid of statistical methods, based on all fractions with a biotic significance (biomorpha and microbialites). Cluster Analyses in Q-Mode were performed, coupling three algorithms and two indices. In all samples, the main components of the framework are microbialite (average of 75%), and macrofossils (average of 20%), whereas cements and allochtonous components, such as allomicrite, do not represent a significant fraction. 

Based on both microbialite and fossil content, Chaetetid–microencruster Association, Microbialite–microencruster Association, Dual-type Microbialite Association and Microbialite–Terebella Association, were differentiated. The palaeoenvironmental settings where the associations come from are separately discussed. Microencrusters helped determine energy and luminosity settings. Microencruster abundance and diversity, in addition to the conspicuousness of microbialite, indicate that all associations come either from a deep, or from a cryptic setting.