Late Jurassic to Cretaceous evolution of the eastern Tethyan Hawasina Basin (Oman Mountains)

Abstract

Remnants of a Mesozoic continental margin can be studied today in the nappe pile of the Oman Mountains. Successions of the Arabian carbonate platform and the adjacent deep Hawasina Basin are preserved in the nappe pile and in the foothills of this Mountain range. The Jurassic-Cretaceous sediment successions of the Hawasina Basin (Sumeini and Hamrat Duru Group) are focus of this study. These basinal archives contain information on the response of an eastern Tethyan equatorial ocean system to multiple perturbations of the carbon cycle and of climate during the Cretaceous. Turbiditic continental slope and basinal successions formed near the Calcite Compensation Depth are difficult to date with biostratigraphy and sequence stratigraphy. The available stratigraphic framework for the Hawasina successions was not sufficient for tracing palaeoceanography through the time window of interest in this study. Therefore, existing sequence stratigraphy and biostratigraphy are complemented by additional biostratigraphic data and with a newly established carbon and strontium isotope chemostratigraphy. The Hawasina Basin was affected by sea-level variations, by changes in oceanography and also by regional tectonics. A first major modification of oceanography occurred at the end of the Jurassic when pelagic Maiolica-type sediments were accumulated in the deep basin and on adjacent submarine highs (Lower Member of Huwar and Sid'r formations). Pelagic to hemipelagic conditions existed until the Valanginian, marked by a major carbon isotope excursion. Pelagic sediments were replaced afterwards by a succession of fine to coarse-grained turbidites of Hauterivian to Aptian age. The transition into the mid-Cretaceous is marked by a sudden shift to fine-grained siliceous or chert deposits, at a time when sediments enriched in organic carbon were accumulated in the western Tethys and Atlantic Oceans. The continental slope as well as the Hawasina Basin seemed to have been well-ventilated during Early and mid-Cretaceous time. Siliceous limestones and chert are indicators of wellmixed and nutrient-rich surface water, while the absence of black shales suggests young and oxygenated deep water with a possible source on the vast Arabian platform. These peculiar oceanographic conditions were most pronounced during the onset of the extreme greenhouse episodes of the Oceanic Anoxic Event 1a. 87

Disentangling shallow‐water bulk carbonate carbon isotope archives with evidence for multi‐stage diagenesis: An in‐depth component‐specific petrographic and geochemical study from Oman (mid‐Cretaceous)

“…Note an isotopic cluster representing the mixing of spA and spB signatures and a small cluster of micrite samples plotting along the meteoric calcite line of Lohmann (). The white rectangle marks the range of δ 13 C and δ 18 O values for Barremian open marine sea water (Jenkyns, ; Weissert & Erba, ; Godet et al ., ; Sprovieri et al ., ; Prokoph et al ., ; Bodin et al ., ; Wohlwend et al ., ). Here, established threshold values both for δ 13 C and δ 18 O are indicated by red triangles.…”

“…Unfortunately, the petrographic inspection of bivalve shell fragments derived from the Jabal Madar section provides clear evidence for a moderate recrystallization and partial silicification of the fibrous low‐Mg calcite ultrastructure. The majority of bivalve and matrix micrite carbon isotope values, in contrast to the highly variable bulk carbonate values, are close to the expected Barremian mean open marine δ 13 C value of about 1 to 3‰ as recorded in Tethyan and Pacific pelagic sections (Weissert et al ., ; Jenkyns, ; Weissert & Erba, ; Godet et al ., ; Sprovieri et al ., ; Prokoph et al ., ; Bodin et al ., ; Wohlwend et al ., ). At first glance, this would imply that the most fine‐grained portions of the Jabal Madar section escaped considerable overprint of their δ 13 C signal by diagenetic fluids and thus, might be regarded as a suitable archive for secular carbon isotope trends of dissolved inorganic carbon (DIC).…”

“…The least 13 C‐depleted set of samples (spA‐2) is characterized by a well‐expressed zoned luminescence and low strontium contents (mean: 185 p.p.m. ), and thus corresponds to shallow burial conditions, while the major departure from the expected marine δ 18 O signal (Weissert et al ., ; Jenkyns, ; Weissert & Erba, ; Godet et al ., ; Sprovieri et al ., ; Prokoph et al ., ; Bodin et al ., ; Wohlwend et al ., ) recorded by spA‐1 cements is at first glance consistent with deep burial fluids, as previously discussed.…”

“…Mudstone ( (Jenkyns, 1995;Weissert & Erba, 2004;Godet et al, 2006;Sprovieri et al, 2006;Prokoph et al, 2008;Bodin et al, 2009;Wohlwend et al, 2017). Here, established threshold values both for d 13 C and d 18 O are indicated by red triangles.…”

Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert

“…Although sediments in these terranes are often diagenetically altered and, in some cases, weakly metamorphosed, they can still provide valuable evidence for variations in the record of palaeoceanographic events, including carbon‐isotope stratigraphy that provides correlations to other regions (e.g. Robinson et al ., ; Ikeda & Hori, ; Wohlwend et al ., ). In addition to searching for new records of OAEs, it is also informative to consider periods of more localized organic‐carbon accumulation that did not occur during OAEs in order to assess the controls on this process under ‘normal’ conditions during the Mesozoic and the role of orbital forcing (e.g.…”