Palaeoecology of Late Ladinian (Middle Triassic) benthic faunas from the Schlern/Sciliar and Seiser Alm/Alpe di Siusi area (South Tyrol, Italy)

Abstract

The Schlern and Seiser Alm area (South Tyrol, Italy) is a classical locality for studies of Middle Triassic platform to basin transitions, yet details of the palaeoecology of the rich benthic faunas of this area have been insufficiently known. We present herein a detailed palaeoecological study of the fauna from the Schlernplateau beds (Late Ladinian to Early Carnian) and the more or less time-equivalent Pachycardientuffe (Late Ladinian), which is based on quantitative faunal data. Both the palaeoecology and sedimentary features suggest that the fauna of the Schlernplateau beds represents a lagoonal soft-bottom fauna. The high species richness of the fauna and the locally restricted occurrences of fossils indicate an open-lagoon setting palaeogeographically close to an ocean inlet. The high evenness of the fauna is probably a result of time-averaging. In contrast, the fauna of the Pachycardientuffe shows clear indications of transportation. Ecological features of this fauna and palaeogeographic reconstructions suggest three potential source areas: (1) the lagoon represented by the Schlernplateau beds, (2) the reef fringing this lagoon and (3) a shallow clastic coast of a nearby volcanic island and/or submarine high. A comparison between diversities of selected Early and Middle Triassic lithological units revealed the increasing species richness of all major benthic taxa during the Middle Triassic and a shift from bivalve-dominated Early Triassic faunas to gastropod-dominated faunas.