22 Fossils as Paleobathymetric and Paleocurrent Indicators

Tuesday, 25 March 2003
2:00 PM - 4:00 PM

DEEPWATER TANAIDACEA (CRUSTACEA: NEOTANAIDAE) FROM THE LADINIAN (MIDDLE TRIASSIC) OF HUNGARY

Paper number: 22-3
Program: SYMPOSIA SESSIONS
Time: 2:20 PM – 2:40 PM

Authors

Abstract

Tanaidaceans are a diverse group of small, specialized, epifaunal malacostracan crustaceans typically associated with the floor of the deep sea. Their fossil record is scanty. We have identified crustacean material, including tanaidaceans, from Ladinian (Middle Triassic) carbonate rocks at a quarry near Litér, Hungary. The Litér region is located within the Transdanubian Range. The quarry is located northeast of Lake Balaton in an area characterized by complex tectonics and extensive Triassic deposits. The silicified crustacean material was found by processing samples with hydrochloric acid. The crustacean material from the site consists of carapace, abdominal, and appendage parts. Several abdominal somites (pleonites) in the assemblage are referable to the deep-sea family Neotanaidae. Some other material (carapace, mandible, pleurite, and telson) is less certainly assigned to the family. Several species may be represented; single modern deep-sea samples may contain several species of neotanaids. This is the first record of neotanaids in the fossil record. The only previous tanaidaceans described from the Triassic are nondiagnostic chela from the Rhaetian (Late Triassic) of Hungary that were originally placed in the genus Ophthalmapseudes but subsequently referred to the apseudomorph genus Jurapseudes. The material described here supports the view of Schram and others that the radiation of the modern Tanaidacea occurred by the end of the Mesozoic.

Neotanaids are epifaunal forms found in bathyal to hadal oceanic environments. The mean depth of stations from which extant neotanaids have been collected has been reported to be about 3000 meters. Therefore, the presence of neotanaids suggests that the rock layers containing them at the Litér locality are deep water deposits. This depth determination is in agreement with psychrospheric ostracods (including Polycope species) found in the same layers.

The presence of neotanaids provides an indication of water depth independent of, and probably more accurate than, that provided by ammonoids and some other taxa typically used as bathymetric indicators.