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 softbottom 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 andpalaeogeographic 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.

Fossil liberation: a model to explain high biodiversity in the Triassic Cassian Formation

“…Only two old monographs (Böhm ; Salomon ) provide detailed taxonomic accounts of the Marmolata, listing 290 benthic species (Friesenbichler et al . ) The number of benthic Cassian species is again approximately 4.5 times greater, although here the factors for benthic molluscs and especially gastropods are smaller (3.5 and 2.7, respectively). A problem with this comparison is the much poorer research effort and lack of taxonomic revision in the Marmolata.…”

“…This is surprising because we attribute the Cassian gastropod richness to the liberation effect, whereas most of the other faunas listed by Friesenbichler et al . () are not of liberation type. Monographic bias is the most likely explanation.…”

“…Several Middle to Late Triassic tropical settings show a similar contribution of gastropods to total diversity as we find in the Cassian (Friesenbichler et al . ). This is surprising because we attribute the Cassian gastropod richness to the liberation effect, whereas most of the other faunas listed by Friesenbichler et al .…”

A highly diverse bivalve fauna from a Bithynian (Anisian, Middle Triassic) Tubiphytes‐microbial buildup in North Dobrogea (Romania)

“…Factors such as oversplitting (see also Friesenbichler et al . 2019), a long history of research and a large outcrop area (concerning e.g. the Germanic Triassic) or a Lagerstätten effect (e.g.…”

“…The comparison of diversities of Early and Middle Triassic bivalve faunas is based on a previous analysis (Friesenbichler et al . 2019) and additional literature. The occurrences of identified bivalve species and genera during the Early and Middle Triassic were analysed based on the literature including the compendium of Ros‐Franch et al .…”