New insight into the Cretaceous OAE’s from the south-eastern Tethyan Oman Mountains – A bridge between the Pacific and the Tethys/Atlantic
Monday, 15 December 2014
The Oman Mountains provide the opportunity to trace evolution of deep south-eastern Tethys in successions from the Hawasina Basin, which is located adjacent to the Arabian carbonate shelf. White pelagic nannofossil limestones alternating with radiolarian chert of latest Jurassic to earliest Cretaceous age were deposited in water depth of probably more than 1000m. Carbonate turbididtes and breccias derived from the nearby Arabian shelf are intercalated with cherts and micritic limestones. Successions near the margin of the Arabian shelf were chosen for reconstruction of an Early Cretaceous carbon-isotope stratigraphy. New carbon isotope data suggest that major changes in pelagic sedimentation occurred in the Late Valanginian and in the Early Aptian. Shallowing of the CCD was caused by changes in oceanography at times of global carbon perturbations and/or by changing sea-level. In the Aptian the appearance of chert and/or highly silicified limestone coincides with a negative shift in the C-isotope values, which is interpreted as the C3-negative shift marking the base of OAE1a. Intensification of upwelling of nutrient rich water masses may explain these chert pulses during the onset of the OAE1a. Remarkable seems the observation that the Hawasina successions contain no evidence of black shale formation. The open ocean character of the easternmost Tethys (Hawasina Basin) resulted in a well-ventilated ocean circulation and therefore bottom-ocean anoxia never appeared during the Cretaceous OAE’s. Observations are in agreement with ocean circulation models (Hotinski and Toggweiler, Paleoceanography, 2003) suggesting wind driven east-west directed equatorial current combined with equatorial upwelling. These conditions were most active during extreme greenhouse conditions. Well ventilated deep-water masses of the Pacific, Indic and easternmost Tethys (Hawasina Basin) stay in contrast to the Central Tethys and also the Northern Atlantic were the global Cretaceous OAE’s commonly appear in combination with black shales.