Huck S.,Ruhr University Bochum |
Heimhofer U.,Ruhr University Bochum |
Rameil N.,Neftex Petroleum Consultants Ltd |
Bodin S.,Ruhr University Bochum |
Immenhauser A.,Ruhr University Bochum
Earth and Planetary Science Letters | Year: 2011
A widely accepted hypothesis proposes that the Early Aptian demise of carbonate platforms in the northern Tethyan realm reflects the impact of environmental changes that eventually led to the deposition of organic-rich basinal sediments during oceanic anoxic event (OAE) 1a. In fact, the temporal correlation of oceanic anoxia and platform drowning has not been rigorously tested and evidence indicating causality is debated. The present paper provides a high-resolution carbon- and strontium-isotope chronostratigraphy combined with detailed sedimentological analysis applied to the Barremian-Aptian Urgonian carbonate platform development at the northern rim of the Tethys (Subalpine Chains, Haute-Savoie, ESE France). A characteristic Barremian-Aptian carbon- and strontium-isotope pattern below the onset of OAE 1a interval permits precise platform-to-basin correlation with the Barremian stratotype locality of Angles (SE France). This chemostratigraphic pattern equally allows for a correlation with well-studied shoal-water and pelagic records of the northern and central Tethys. Strontium-isotope stratigraphy provides a high-resolution numerical age-data set, indicating an earliest Aptian age (<124.5 ± 0.4. Ma) of platform demise in the Subalpine Chains. The detailed platform-to-basin correlation obtained in France clearly illustrates that shoal-water carbonate production in the Urgonian platform ceased about 300. kyr before the most negative values of the characteristic negative carbon-isotope anomaly, which marks the beginning of OAE 1a black-shale deposition. The stratigraphic results confirm (i) the theory of an Early Aptian northern Tethyan platform drowning episode predating OAE 1a and (ii) document the temporal response of shoal-water carbonate platforms to the environmental perturbations prior to the OAE acme. © 2011 Elsevier B.V.
Davies A.,UK National Oceanography Center |
Davies A.,Neftex Petroleum Consultants Ltd |
Kemp A.E.S.,UK National Oceanography Center |
Palike H.,UK National Oceanography Center
Geophysical Research Letters | Year: 2011
The first annually resolved sedimentary record from the Cretaceous is used to develop time series of inter-annual and decadal scale climate variability from the Arctic Ocean. Analysis of records spanning 1000 years reveals strong periodicities in the quasi-biennial oscillation and El Niño - Southern Oscillation (ENSO) band as well as a 14 year period, which all closely match periodicities typical of modern high latitude climate variability. This supports the view that an Arctic Ocean free of permanent sea ice would be driven by similar forcing to the present state, implicating tropical ocean atmosphere interaction and demonstrating that stratosphere-troposphere coupling likely played a prominent role in the transmission of Cretaceous equatorial climate forcing to polar latitudes as has recently been established for the modern earth system. On the other hand, the prominent ENSO periodicities in our records argue against the hypothesized link between past warm climates and "permanent El Niño" states. Copyright © 2011 by the American Geophysical Union.
Ray D.C.,University of Portsmouth |
Ray D.C.,Neftex Petroleum Consultants Ltd |
Collings A.V.J.,Arup |
Worton G.J.,Dudley Museum and Art Gallery |
Jones G.,248 The Broadway
Geological Magazine | Year: 2011
The upper Wenlock Series (Homerian Stage) of the northern Midland Platform, England, contains numerous volcanic bentonite clay layers.AtWren'sNestHill, Dudley, 15 bentonites have been investigated and comparisons with the type-Wenlock have been made by means of two key sections alongWenlock Edge, Shropshire. In total 22 bentonites have been investigated and their clay and sandgrade mineralogies determined. Rare earth element (REE) and yttrium concentrations of apatite grains contained within ten of the bentonites have been established allowing geochemical fingerprinting as an indication of provenance of source magmas and identification of geochemical marker beds. Based on the analysis of REE and yttrium concentrations it seems likely that the majority of these bentonites originated from a granodiorite magmatic source. Comparisons with published Llandovery and lower Wenlock age bentonites indicate generally more enrichment in light REEs relative to heavy REEs. In addition, close geochemical similarities between bentonites along Wenlock Edge and at Wren's Nest Hill strongly argue for their presence as precise stratigraphic equivalents within the upper Much Wenlock Limestone Formation. These correlations are further supported by geophysical data from borehole wire-line logs across the West Midlands. Finally, a chemically distinct mid-Homerian episode of volcanism is identified and represents a potentially important marker interval between the study area and other similarly aged bentonites reported from the Island of Gotland, Sweden. © 2010 Cambridge University Press.
Rameil N.,Ruhr University Bochum |
Rameil N.,Neftex Petroleum Consultants Ltd |
Immenhauser A.,Ruhr University Bochum |
Csoma A.E.,ConocoPhillips |
Warrlich G.,Petroleum Development Oman
Sedimentology | Year: 2012
Discontinuity surfaces in shallow-marine carbonate successions may represent significant time gaps in the geological record of ancient epeiric-neritic seas. Understanding the hidden geological information contained in major discontinuities is thus of key significance in palaeo-environmental analysis, sequence stratigraphy, reconstructions of sea-level change and basin evolution. In the present paper, the Aptian top Lower Shu'aiba Formation discontinuity in the Sultanate of Oman is taken as a prominent example of a regionally extensive (>100000km 2) surface with a long (up to 10Myr) and complex geological history. The top Shu'aiba discontinuity formed on the topographically elevated domain of the Oman platform and represents in essence the Late Aptian time interval. Coeval carbonates in the intrashelf Bab Basin and oceanic rim indicate forced regression and sequence-wise, gradual down-stepping. Available regional, sedimentological, sequence-stratigraphic, petrographic, palaeontological and geochemical evidence from outcrops and cored wells in Oman is summarized, in part complemented by new data, and reviewed in a process-oriented context. In the field, the discontinuity is expressed as a low relief, stained surface with evidence for a marine hardground stage being dominant. Indistinct features that indicate a transient meteoric precursor stage (isotope shifts, meteoric cements, circumgranular cracks, etc.) are present but their interpretation requires careful and detailed work. This feature is remarkable, as a series of relative sea-level falls with amplitudes of up to several tens of metres from the Early to Late Aptian boundary to the end of the Aptian are reported from the Middle East and elsewhere. Despite the palaeogeographic position of the study area in the tropical climate zone, evidence of deep-cutting karst features, characteristic for many long-term exposure surfaces worldwide is scarce. Acknowledging the fact that the modern world offers no genuine analogues for the Lower Aptian carbonate system in Oman, morphological similarities between actualistic, wave-eroded coastal terraces and the top Shu'aiba discontinuity are discussed critically. This discussion may imply that, during an exposure time of several million years, the top Shu'aiba discontinuity experienced repeated stages of shallow flooding and emergence, with each transgression removing portions of the underlying rock record. The data shown here exemplify the complexity of hiatal surfaces in epeiric-neritic carbonates and may serve as a case example for other major discontinuities. © 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists.
Arnaud E.,University of Guelph |
Etienne J.L.,Neftex Petroleum Consultants Ltd
Geological Society Memoir | Year: 2011
This chapter provides an overview and key references of glacial processes and resulting sedimentary products in subglacial, terrestrial proglacial and glaciomarine or glaciolacustrine settings. These settings are characterized by a wide variety of processes ranging from subglacial lodgement and deformation, ice-push and sediment remobilization, which in turn result in a wide range of products such as diamictite, conglomerate, sandstone, siltstone and mudstone. The sedimentary record of proglacial settings exhibits the most lateral and vertical variability due to the dynamic nature of ice margins and the most direct record of climatic fluctuations. Many Neoproterozoic successions, however, preserve glaciomarine deposits that can provide a more continuous and high-resolution (though indirect) record of change. This chapter will enable the reader to identify features that may be used to infer a glacial influence on the formation of ancient deposits. The chapter also outlines some of the important issues that require consideration when evaluating palaeoclimatic models for Neoproterozoic sedimentary successions. These include the equivocal significance of most commonly used proxies such as occurrence of diamictite, outsized clasts in laminated sediments, clast characteristics, lithostratigraphic trends and sequence boundaries. Careful analysis of multiple lines of sedimentary evidence, together with other proxies of climatic changes, can yield meaningful reconstructions and provide a basis for testing palaeoclimate models for this time period. A summary table outlining the characteristics of diamictite with different depositional origins is also included in order to assist with the interpretation of the Neoproterozoic sedimentary record. © The Geological Society of London 2011.