Sedimentology and environmental change at the Triassic-Jurassic boundary in Ras Al Khaimah (UAE)

  • Ge Yuzhu

Student thesis: Master's Thesis

Abstract

The Triassic–Jurassic (Tr–J) boundary interval has been studied in sections exposed in Wadi Ghalilah, Wadi Milaha and Wadi Naqab, northeast UAE, based on sedimentological and stable isotope analysis (carbon and oxygen). The study offers potentially continuous shallow-marine carbonate sections across the Tr–J boundary. The Triassic sedimentary rocks consist of bedded bioclastic limestone, in which corals are abundant but do not serve as reef-builders. The Jurassic deposits are characterized by ooid-shoal sediments and microbialites in the lower part and peritidal sediments in the upper part. The Tr–J boundary is defined based on the disappearance of skeletal biota and correlation of carbon isotope excursions. The carbon isotope signal shows the most negative excursion (referred to as the initial carbon-isotope excursion, CIE) in the bioclastic limestone and a subsequent positive excursion (positive CIE) in the oolitic limestone. The initial CIE occurs with a dramatic decrease in bioclastic size, nodular limestone and just before the disappearance of bioclasts. Sea-level fluctuation and changes in seawater chemistry induced by volcanism of the Central Atlantic Magmatic Province (CAMP) and gas hydrate release possibly combined to cause the initial CIE and subsequent mass-extinction event. The equatorial location in paleogeography of our sections seems to be less effected by environmental change compared with other locations in higher latitude and weakened the biocrisis in the studied sections. The formation of ooids and microbialites at the base of the positive CIE indicates stressed environment, ocean carbonate supersaturation and a change from skeletal to inorganic and microbial carbonate production after the mass extinction. The carbonate supersaturation of the positive CIE may be related to intensive terrestrial weathering process as a response for massive CO2 influx into the atmosphere. Facilitated by the weathering products and high CO 2 concentration, increasing primary production and organic carbon burial are considered as the reasons for the positive CIE.
Date of AwardDec 2016
Original languageAmerican English
SupervisorThomas Steuber (Supervisor)

Keywords

  • Applied sciences
  • Ras al khaimah
  • Sedimentology
  • Triassic-jurassic
  • Petroleum engineering
  • 0765:Petroleum engineering

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