INVERTEBRATE TRACE FOSSILS FROM TRIASSIC CONTINENTAL SUCCESSIONS OF SAN JUAN PROVINCE, ARGENTINA

Resumen

This paper is the first report on invertebrate trace fossil assemblages from Marayes-El Carrizal and Ischigualasto-Villa Unión Basins (Triassic), San Juan Province, northwestern Argentina. The four analyzed lithostratigraphic units consist of three different fluvial systems (Carrizal, Ischigualasto, and Los Colorados Formations) and a lacustrine delta (Los Rastros Formation). The ichnofossil content of the Late Triassic Carrizal Formation (fluvial channels and shallow floodplain lakes) includes Taenidium barretti (Bradshaw), and Skolithos isp. The Los Rastros Formation (Middle Triassic) yielded a subaqueous ichnoassemblage that consist of Helminthopsis cf. H. abeli Ksiazkiewicz, Skolithos cf. S. verticalis (Hall), and Palaeophycus isp. Floodplain facies of the Ischigualasto Formation (Late Triassic) contain Taenidium, Skolithos and laterally spreading root systems. Most trace fossils of the Los Colorados Formation (Late Triassic) come from sandy sheetflood facies -with two interbedded paleosols- and consist of Palaeophycus tubularis Hall, cf. Skolithos isp. Taenidium barretti, and Cochlichnus isp. All alluvial successions contain Taenidium and Skolithos, and lack evidence for a fully terrestrial ichnofauna in spite of the presence of abundant paleosols.

KEY WORDS. Argentina. San Juan. Triassic. Continental. Invertebrate ichnofossils, Taenidium. Skolithos.