Dimerelloid rhynchonellide brachiopods in the Lower Jurassic of the Engadine (Canton Graubünden, National Park, Switzerland)

Abstract

New brachiopods (Dimerelloidea, Rhynchonellida) from Lower Jurassic (?lower Hettangian) hemipelagic sediments of the Swiss National Park in south-eastern Engadine are described: Sulcirostra doesseggeri sp. nov. and Carapezzia engadinensis sp. nov. Sulcirostra doesseggeri is externally similar to S. fuggeri (FRAUSCHER 1883), a dubious species, that could not be included in a comparative study, because relevant samples no longer exist. A single specimen was tentatively assigned to Sulcirostra ?zitteli (BÖSE 1894) by comparison of its external morphology with S. zitteli from the type locality. The partly silicified brachiopods are associated with sponge spicules, radiolarians and crinoid ossicles. Macrofossils are rare: dictyid sponges, gastropods, bivalves, crustaceans, shark teeth and scales of an actinopterygian fish. The Lower Jurassic sediments (Alpisella beds, a basal member of the Allgäu Formation) preserving the brachiopods belong to the Ortler nappe (Upper Austroalpine nappes). The exact age of the Alpisella beds is not known, as index fossils are lacking. Their stratigraphic position above the Rhaetian Kössen Formation and below the ammonite-dated Trupchun beds suggests a very Early Jurassic, probably early Hettangian age for the new brachiopod fauna. The new species of Sulcirostra and Carapezzia are confined to a very small geographic area, a peculiarity also observed in other Early Jurassic dimerelloid brachiopods. These brachiopods presumably adapted to current-dominated submarine highs, where their shells could not accumulate, except when trapped in submarine cavities or re-deposited in submarine fans. Transport by turbidity currents is suggested for the Early Jurassic dimerelloids from the Engadine. Problems with the generic definition of Sulcirostra and the higher rank classification of Carapezzia are discussed. ZUSAMMENFASSUNG

A new polychelidan lobster from the Alpine Lower Jurassic of southeastern Switzerland

“…Shells and other skeletal elements of dead organisms were transported into the neighbouring basin together with loose sediment. The submarine high was approximately 100 metres below sea level or even deeper, given the total absence of phototrophic organisms such as corals or algae, and the surrounding basin was probably several hundred metres deep (SULSER & FURRER 2008).…”

“…However, the Alpisella beds, deposited just above the megabreccias are tilted, but not folded blocks of Upper Triassic carbonates and do not show tectonic deformation. The effects of deformation are also absent from brachiopods found in the same beds as the crustaceans (SULSER & FURRER 2008) and in the crustaceans themselves the appendages of the cephalothorax do not appear to have been deformed significantly in any particular direction. Therefore, it is likely that the original shape of the new form is preservedand that it was undoubtedly narrow.Although the margins of the cephalothoracic shield are poorly preserved, several small antrorse spines are observed that often occur on the lateral margin in other polychelidan lobsters, suggesting the margins in this specimen to be complete and not damaged during either the fossilisation process or subsequent preparation.…”

“…Angusteryon oberlii nov. gen., nov. sp. was initially identified by one of us (HF) (see SULSER & FURRER 2008) as Coleia viallii (see Fig. 4C-E).…”

Trace-fossil assemblages with a new ichnogenus in “spotted”

“…bivalves, echinoderms, or brachiopods) is mostly very low (operationally, no or very few skeletal remains encountered along 5 m-long bed transects), implying the presence of conditions that were limiting calcimass production by macroinvertebrates. Beds with relatively frequent bivalves, echinoderms, or brachiopods occur but are rather scarce at outcrop and formation scales (Gaździcki et al 1979;Sulser & Furrer 2008) and skeletal-rich deposits are absent in the spotted deposits. However, this paradox and the causes of the paleocommunity structure that characterizes spotted deposits are poorly explored (Wieczorek 1995;Uchman & Myczyński 2006), even when this type of habitat was highly widespread GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA GEOLOGICA CARPATHICA, 2013, 64, 5, 355-374 and recurrent in environments of the Tethys during the Early Jurassic.…”