From fossil associations to ecological communities: a case study from the ‘Cipit boulders’ of the upper Ladinian–lower Carnian St Cassian Formation, Dolomites, NE Italy

Abstract

The definition of a fossil ecological community from fossil associations has always been problematic. Determining coevality of the members of a fossil association has posed one of the most ravelling problems in this matter. However, in case of relicts of fossil reefs, this problem seems, to some extent, solvable due to the frequency of fossil findings in life position. In addition, the interaction between these fossils poses the possibility of performing statistical analyses in order to effectively quantify the relation that existed among the members of a fossil association as well as between fossil associations. In this paper, we present a method to obtain fossil communities by means of a combined algorithm (WPGMA-Jaccard Index) performed onto 14 fossil associations from the Cipit boulders from the Middle-to-Late Triassic St Cassian Formation (Dolomites, Northeastern Italy), which have been previously reported in the literature. Presence/absence data of environmentally diagnostic micro-encrusters and hexactinellid sponges were input into a matrix, which underwent cluster analysis. This analysis rendered a phenogram, where five different communities (phena) could be recognized. Each community has its particular palaeoenvironmental constraints, defined in turn by the particular array of micro-encrusters/hexactinellid sponges. The method used in this work could be successfully applied in other Triassic reef deposits, taking into account the extensive amount of reports performed in the last decade.