TITHONIAN MARINE REPTILES OF THE WESTERN NEUQUEN BASIN, ARGENTINA. FACIES AND PALAEOENVIRONMENTS

GASPARINI, Z.; SPALLETTI, L.; DE LA FUENTE, M.

GEOBIOS

ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER

Lugar: Paris; Año: 1997 vol. 30 p. 701 - 712

0016-6995

Remains of marine reptiles have been found in the Vaca Muerta Formation, at Trincajuera Creek (Neuquén province, Argentina) in uppermost Tithonian levels, A new specimen of the turtle [Neusticemys neuquina (FERNANDEZ & DE LA FUENTE, 1988)] and a pliosaurid, are described. The Vaca Muerta organic-rich shales and marls represent the basinal sedimentary record of the Tithonian transgression in the Neuqudn Basin. They are associated with nodular limestones rhythmically spaced, isolated coquinas and three sandstone facies. Cycles of two orders are defined through shale/marly-shale alternations. The marine reptiles "assemblage" is composed of pelagic forms. The high content of organic matter, the phosphate concentrations, the absence of benthic organisms and the lack of bioturbation suggest anoxic conditions of the sea floor This euxinic environment was favored by the organic matter productivity and preservation. Productivity is related to upwelling from an oceanic oxygen-minimum zone. Preservation was conditioned by stagnation, controlled by the development of a thermo-pycnocline and very low sedimentation rates. A period of highstand, dry climatic conditions and low surrounding relief may have been favorable for the proposed model. Tithonian ichthyosaurs, plesiosaurs and crocodiles of the Neuquén Basin share several genera with those of the Middle and Late Jurassic European Tethys. The turtles instead, are undoubtedly endemic of western South America.