REVISION OF THE CORAL FAUNA OF AN UPPER JURASSIC PATCH REEF FROM LA MANGA FORMATION, NEUQUÉN BASIN, ARGENTINA -- Preprint doi:10.5710/AMGH.20.03.2019.3236

Martín Hoqui, Graciela S. Bressan, Ricardo M. Palma

Abstract


The coral patch reef of La Manga Formation at Bardas Blancas (Mendoza province) is a good example of this kind of structure for the Upper Jurassic (Oxfordian) of the Neuquén Basin. In previous reports, four different genera of corals were identified: Actinastrea, Australoseris, Garateastrea and Thamnasteria. A new systematic revision on the specimens previously studied and new material lead to the rejection of the assignments to Garateastrea, Actinastrea and Thamnasteria, identified now as Australoseris, Stelidioseris and Etallonasteria respectively, while those identified originally as Australoseris, are maintained. New results are based on a taphonomic analysis carried out to recognise the bias introduced in the systematic assignments by different preservational -taphonomic- grades. Four taphonomic grades were defined as Tg0–Tg3, with an increasing degree of taphonomic distortion. Tg0 is an ideal state with preservation of the microstructure. The loss of microstructural features occurs in Tg1–Tg3, preventing the assignment at suprageneric to specific level. Additionally, those specimens with Tg2 and Tg3 suffered a change in their macrostructural features giving rise to apparent morphological details that may lead to wrong assignments. The Tg3 is the stage of preservation most frequently seen in the field. This is not useful for systematic studies due to the loss of all diagnostic features. Samples with Tg1 are useful for systematic studies because most of the macrostructural characters are preserved almost in their original condition. Taphonomic analysis of the specimens is necessary to carry out reliable systematic studies for later measurements of richness and evenness.

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