Earth and Environmental Science Transactions of the Royal Society of Edinburgh

Research Article

Lower Permian brachiopods from Oman: their potential as climatic proxies

L. Angiolinia1, D. P. F. Darbyshirea2, M. H. Stephensona3, M. J. Lenga2a4, T. S. Brewera5, F. Berraa1 and F. Jadoula1

a1 Dipartimento di Scienze della Terra ‘A. Desio’, Università degli Studi di Milano, Via Mangiagalli 34, Milano, 20133, Italy. E-mail: lucia.angiolini@unimi.it

a2 NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

a3 British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

a4 School of Geography, University of Nottingham, Nottingham NG7 2RD, UK

a5 Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK

ABSTRACT

The Lower Permian of the Haushi basin, Interior Oman (Al Khlata Formation to Saiwan Formation/lower Gharif member) records climate change from glaciation, through marine sedimentation in the Haushi sea, to subtropical desert. To investigate the palaeoclimatic evolution of the Haushi Sea we used O, C, and Sr isotopes from 31 brachiopod shells of eight species collected bed by bed within the type-section of the Saiwan Formation. We assessed diagenesis by scanning electron microscopy of ultrastructure, cathodoluminescence, and geochemistry, and rejected fifteen shells not meeting specific preservation criteria. Spiriferids and spiriferinids show better preservation of the fibrous secondary layer than do orthotetids and productids and are therefore more suitable for isotopic analysis. δ18O of −3·7 to −3·1℅ from brachiopods at the base of the Saiwan Formation are probably related to glacial meltwater. Above this, an increase in δ18O may indicate ice accumulation elsewhere in Gondwana or more probably that the Haushi sea was an evaporating embayment of the Neotethys Ocean. δ13C varies little and is within the range of published data: its trend towards heavier values is consistent with increasing aridity and oligotrophy. Saiwan Sr isotope signatures are less radiogenic than those of the Sakmarian LOWESS seawater curve, which is based on extrapolation between few data points. In the scenario of evaporation in a restricted Haushi basin, the variation in Sr isotope composition may reflect a fluvial component.

Key Words:

  • cathodoluminescence;
  • geochemistry;
  • Gondwana deglaciation;
  • late Sakmarian;
  • oxygen;
  • strontium isotopes;
  • ultrastructure