Hettangian Isle of Skye Corals Give Insight to Post Triassic-Jurassic Mass Extinction Paleoenvironment

The Hettangian corals of the Isle of Skye (Scotland): An opportunity to better understand the palaeoenvironmental conditions during the aftermath of the Triassic – Jurassic boundary crisis

Authors:

1. M. Gretz (a)
2. B. Lathuilière (b, c)
3. R. Martini (a)
4. A. Bartolini (d)

Affiliations:

a. Department of Geology and Paleontology, University of Geneva, 13 rue des Maraîchers, 1205 Geneva, Switzerland

b. Université de Lorraine G2R, UMR 7566, Vandoeuvre-lès-Nancy, BP 239, F-54506, France

c. CNRS G2R, UMR 7566, Vandoeuvre-lès-Nancy, BP 239, F-54506, France

d. Muséum National D’Histoire Naturelle, CR2P « centre de Recherche sur la Paléodiversité et les paléoenvironnements » CNRS UMR 7207, 8 rue Buffon, 75231 Paris Cedex 05, France

Abstract:

At Ob Lusa (Isle of Skye, Scotland), six distinct coral beds were observed in a modern outcrop where a Hettangian succession is exposed. The coral associations are monogenic, belonging to Lepidophyllia, a massive cerioid genus. The lowest bed has relatively well-developed colonies that form small bioconstructions, whereas the other beds have small and dispersed colonies that are completely drowned in the matrix. Their morphology and size can vary, but the general growth fabric is dominated by platy colonies. This type of growth fabric is defined as a platestone. The most surprising characteristic of these specimens, especially for the platy corals, is their growth pattern; many samples do not exhibit the classical growth polarity because they are bifacial. Geochemical analyses (δ180, δ13C) were conducted on oyster shells that were associated with the corals. The results indicate that the mean palaeotemperature was approximately 22 °C. Sedimentological analysis revealed shallow settings where the hydrodynamic energy and siliciclastic inputs fluctuated. The general faunal assemblage of the outcrop had low diversity and was mainly composed of allochthonous bioclasts. The corals at Ob Lusa clearly did not live under ideal environmental conditions for the development of corals.