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  • 1
    Publication Date: 2016-05-06
    Description: The Oman Mountains preserve a Cretaceous continental margin transect with the proximal Arabian carbonate shelf and the adjacent deep Hawasina Basin. Today, the sediments from the Arabian Platform outcrop in the Oman Mountains (Jabal Akdhar and Saih Hatat) and in the Adam Foothills. The western part of the Adam Foothills provides insight into the evolution of a Late Cretaceous intra-platform basin with organic-rich sediments in the central part of this basin. The aims of this study are (a) to establish a bio- and chemostratigraphy of the Natih Formation and (b) to reconstruct depositional conditions of organic-rich sediments in an intra-platform basin during Cenomanian-Turonian times. The hypothesis that local black shale formation is an expression of global perturbations of the global carbon cycle will be tested. Reconstruction of the depositional history of the Arabian Platform and its intra-platform basin within a global palaeoclimatic framework requires an accurate time frame. The Upper Albian to mid-Turonian biostratigraphy of the Natih Formation has resulted in controversial age models that will be integrated into a solid chemostratigraphic framework with additional biostratigraphic data. A major positive δ 13 C excursion (+4.6‰) has been identified as of Middle Cenomanian age, which is confirmed by an ammonite datum. A second positive δ 13 C excursion (+4.5‰) following a major negative excursion (-1.0‰) confirms the existence of the Cenomanian/Turonian Boundary Event. The accurate chemo- and biostratigraphy confirms that major source rocks in the Mishrif-Natih Basin precede OAE2. Low δ 13 C values measured in the sediments of the Natih B member are considered a consequence of diagenetic alteration. Elevated organic carbon contents and argillaceous sediments alternating with limestones resulted in diagenetic conditions favouring formation of authigenic calcite depleted in C-13. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 2055-4877
    Topics: Geosciences
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  • 2
    Publication Date: 2016-04-09
    Description: The pelagic Marne a Fucoidi Formation from the Umbria–Marche Basin (Central Italy) is one of the best-preserved deep-marine archives of the Aptian–Albian. Frequent changes in lithology, from black to green and red marlstones and limestones, record fluctuating oceanographic and climatic conditions during the deposition of these sediments. Here the lithological changes in the Albian of the Marne a Fucoidi Formation are studied with unprecedented resolution using X-ray flourescence core scanning measurements of major and minor element abundances, as well as statistical analyses of calcareous nannofossil indices. The results obtained with these two independent methodologies are in good agreement and allow for improving the understanding of the peculiar palaeoceanographic conditions of the western Tethys during the Albian. Black shale-marlstone couplets were driven by orbitally forced changes in physical oceanography, resulting in oxygen depleted bottom water at times of decreased mixing of shallow water masses. On the other hand, red marlstones represent episodes of enhanced oxygenation at the bottom, probably due to the influence of deep waters from the eastern Tethys. Overall, the Marne a Fucoidi Formation is the expression of highly variable oceanographic conditions related to an unstable Albian circulation mode. This article is protected by copyright. All rights reserved.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
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  • 3
    Publication Date: 2016-09-17
    Description: 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 afterwards replaced by a succession of fine to coarse grained turbidites of Hauterivian to Aptian in 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 indicator of well-mixed and nutrient-rich surface water, while 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. This article is protected by copyright. All rights reserved.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
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  • 4
    Publication Date: 2012-01-21
    Description: We established a new high-resolution carbonate carbon isotope record of the Albian interval of the Marne a Fucoidi Formation (Central Apennines, Italy), which was deposited on the southern margin of the western Tethys Ocean. Bulk carbonate sampled with 10–15 cm spacing was used for the construction of a continuous carbon isotope curve through the Albian stage. Spectral analyses reveal prominent 400 kyr cyclicity in the δ13C curve, which correlates with Milankovitch long eccentricity changes. Cycles occurring in our record resemble those observed in several Cenozoic δ13C records, suggesting that a link between orbital forcing and carbon cycling existed also under mid-Cretaceous greenhouse conditions. Based on comparisons with Cenozoic eccentricity-carbon cycle links we hypothesize that 400 kyr cycles in the mid-Cretaceous were related to a fluctuating monsoonal regime, coupled with an unstable oceanic structure, which made the oceanic carbon reservoir sensitive to orbital variations. In the Tethys these oceanographic conditions lasted until the Late Albian, and then were replaced by a more stable circulation mode, less sensitive to orbital forcing.
    Print ISSN: 0883-8305
    Electronic ISSN: 1944-9186
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2013-01-24
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
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  • 6
    Publication Date: 2012-11-05
    Description: The Middle Jurassic Burgundy carbonate platform occupied a central part of the Central European Epeiric Sea during the Middle Jurassic. The facies architecture of the oolitic calcarenite bodies was affected by tidal currents on the platform and relative sea-level changes. The δ 13 C-values of inorganic carbonates, sampled in biostratigraphic-defined intervals, do not match very well between closely spaced sections and hence, are of restricted use for stratigraphic purposes. It appears that the platform interior might have been decoupled from the global carbon pool. Although deposited in a rapidly accumulating setting, the recorded isotope signatures might be affected by some local stratigraphic gaps. Nonetheless, the carbon isotope data imply lateral changes of the platform waters; these appear to be related to the position on the platform and to the sediment dispersal pattern as evidenced by clay minerals. Adjacent to the eastern margin of the platform detrital chlorite and illite occur in considerable proportions, both ascribed to a boreal source to the east and north-east. In contrast, smectite-rich mixed-layer clay mineral content increases significantly towards the platform interior, pointing to a delivery from the north-west. All these data are suggestive of an overall clockwise current pattern in the Central European Epeiric Sea during the Middle Jurassic.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
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  • 7
    Publication Date: 2015-02-06
    Description: Mesozoic Oceanic Anoxic Events (OAEs) are an expression of major physical oceanographic changes at times of perturbation of the global carbon cycle. A northern Tethyan record of OAE2 is preserved in expanded Cenomanian–Turonian pelagic limestone sections (Seewen Formation) in eastern Switzerland. The new carbonate carbon-isotope stratigraphy extracted from these limestones demonstrates that the OAE2 is condensed in all the studied successions and only the onset of the δ 13 C excursion (5.0‰) is present. The condensed interval is characterized by dissolution features, which are filled by a glauconite quartz sandstone. This bed is overlain by a well-sorted sandstone with intercalated limestone pebbles (Götzis Member), which can be compared with palimpsest sands forming today along current-swept shelves. The wide distribution of this thin sandstone layer within OAE2 indicates that an intense, erosive, east-west trending shelf current was active during the highest sea-level and most extreme carbon-cycle perturbation of the OAE2. This article is protected by copyright. All rights reserved.
    Print ISSN: 0954-4879
    Electronic ISSN: 1365-3121
    Topics: Geosciences
    Published by Wiley
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  • 8
    Publication Date: 1995-01-01
    Print ISSN: 1527-1404
    Electronic ISSN: 1938-3681
    Topics: Geosciences
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  • 9
    Publication Date: 1994-01-01
    Print ISSN: 0149-1423
    Electronic ISSN: 1943-2674
    Topics: Geosciences
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