Cyclicity of Cenomanian-Turonian organic-carbon-rich sediments in the Tarfaya Atlantic Coastal Basin (Morocco)

Kuhnt, Wolfgang; Nederbragt, Alexandra J.; Leine, Louis

doi:10.1006/cres.1997.0076

Cited by 127 publications

(117 citation statements)

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“…Average accumulation rates of about 10 cm/kyr for the same Bahloul interval was previously determined by Vonhof et al (1998) suggesting that each 2-m-thick pair of laminated limestone and bioturbated marly limestone represents a precession cycle (20 kyr) rather than an obliquity cycle (40 kyr) as seen in other C/T intervals (e.g. Arthur et al 1987;Kuhnt et al 1997;Sageman et al 1998). Time series analysis performed on Heterohelix spp.…”

Section: Time Series Analysissupporting

confidence: 54%

Time series analysis (orbital cycles) of the uppermost Cenomanian-Lower Turonian sequence on the southern Tethyan margin using foraminifera

Soua¹

2010

Geologica Carpathica

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Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was applied to two foraminiferal genera: the biserial Heterohelix, an oxygen-minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the oceanic anoxic event (OAE2) in each studied section were estimated. The fluctuations in abundance of these two opportunistic species can be related mainly to both precessional (ca. 20 kyr) and eccentricity (100 and 400 kyr) cyclicity suggesting that changes in surface water fertility were linked to climate changes in the Milankovitch frequency band.

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Section: Time Series Analysissupporting

confidence: 54%

Time series analysis (orbital cycles) of the uppermost Cenomanian-Lower Turonian sequence on the southern Tethyan margin using foraminifera

Soua¹

2010

Geologica Carpathica

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“…Fluctuations in TOC may partly be orbitally controlled. The boundary between the finish and start of the 39 ka obliquity cycles from Kuhnt et al (1997) (Fig. 8 Nederbragt et al (2004) modelled the behaviour of P under anoxic conditions, concluding that a change in the oceanic phosphorus cycle was the most realistic way to generate a substantial positive d 13 C excursion.…”

Section: Oceanic Anoxic Eventmentioning

confidence: 98%

“…Given that the oxidation of organic matter is decelerated when the oxygen minimum zone impinges on the shelf sea during sea-level highstands, the gradual relative sea-level (RSL) rise (150 m) could explain the gradual increase in total organic carbon (TOC) contents throughout the Mohammed Plage section (Kolonic et al, 2002;Gebhardt et al, 2004). Kuhnt et al, 1997 noted that maximum organic carbon burial corresponds to benthos-free laminated sediments, which indicates bottom water anoxia.…”

Section: Geochemistry and Cyclostratigraphymentioning

confidence: 99%

“…In the same study, Kuhnt et al (1997) constructed the first cyclostratigraphic framework for the Cenomanian-Turonian sediments in the region, by using density logs from six exploration wells. The attributed cyclic fluctuations in organic carbon and pelagic carbonate content were presumed to have arisen from climate changes driven by Cretaceous obliquity (39 ka) Milankovitch cycles.…”

Section: Geochemistry and Cyclostratigraphymentioning

confidence: 99%

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Organic carbon deposition and phosphorus accumulation during Oceanic Anoxic Event 2 in Tarfaya, Morocco

Mort

Adatte

Keller

et al. 2008

Cretaceous Research

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a b s t r a c tWith a multi-proxy approach, an attempt was made to constrain productivity and bottom-water redox conditions and their effects on the phosphorus accumulation rate at the Mohammed Plage section on the Tarfaya coast, Morocco, during the Cenomanian-Turonian Anoxic Event (OAE 2). A distinct d 13 C org isotope excursion of þ2.5& occurs close to the top of the section. The unusually abrupt shift of the isotope excursion and disappearance of several planktonic foraminiferal species (e.g. Rotalipora cushmani and Rotalipora greenhornensis) in this level suggests a hiatus of between 40-60 kyrs at the excursion onset. Nevertheless, it was possible to determine both the long-term environmental history as well as the processes that took place immediately prior to and during OAE 2. TOC% values increase gradually from the base of the section to the top (from w2.5% to w10%). This is interpreted as the consequence of a longterm eustatic sea-level rise and subsidence causing the encroachment of less oxic waters into the Tarfaya Basin. Similarly a reduction in the mineralogically constructed 'detrital index' can be explained by the decrease in the continental flux of terrigenous material due to a relative sea-level rise. A speciation of phosphorus in the upper part of the section, which spans the start and mid-stages of OAE 2, shows overall higher abundances of P reactive mass accumulation rates before the isotope excursion onset and lower values during the plateau. Due to the probable short hiatus, the onset of the decrease in phosphorus content relative to the isotope excursion is uncertain, although the excursion plateau already contains lower concentrations. The C org /P total and V/Al ratios suggest that this reduction was mostly likely caused by a decrease in the available bottom oxygen content (probably as a result of higher productivity) and a corresponding fall in the phosphorus retention ability of the sediment. Productivity appears to have remained high during the isotope plateau possibly due to a combination of ocean-surface fertilisation via increased aridity (increased K/Al and Ti/Al ratios) and/or higher dissolved inorganic phosphorus content in the water column as a result of the decrease in sediment P retention. The evidence for decreased P-burial has been observed in many other palaeoenvironments during OAE 2. Tarfaya's unique upwelling paleosituation provides strong evidence that the nutrient recycling was a global phenomenon and therefore a critical factor in starting and sustaining OAE 2.

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“…Each of these localities exhibits rhythmic sedimentation indicating orbital scale forcing and permitting millennial-scale time resolution (Gale et al, 2002;Meyers et al, 2001Meyers et al, , 2005Kolonic et al, 2005;Kuhnt et al, 1997Kuhnt et al, , 2004Sageman et al, 2006). Among these three localities, the Tarfaya C-T sequences exposed along the Atlantic coast of southwestern Morocco accumulated exceptionally high rates of black shale (up to 12 cm/ky, Kuhnt et al, 1997Kuhnt et al, , 2004 and burying an estimated w2% of the overall global excess of organic carbon associated with the OAE2 (Kolonic et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Oceanic events and biotic effects of the Cenomanian-Turonian anoxic event, Tarfaya Basin, Morocco

Keller

Adatte

Berner

et al. 2008

Cretaceous Research

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a b s t r a c tProfound biotic changes accompanied the late Cenomanian d 13 C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover , though no mass extinction, beginning with the rapid d 13 C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding d 13 C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in diversity to just two species, the dominant (80-90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.

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Cyclicity of Cenomanian-Turonian organic-carbon-rich sediments in the Tarfaya Atlantic Coastal Basin (Morocco)

Cited by 127 publications

References 0 publications

Time series analysis (orbital cycles) of the uppermost Cenomanian-Lower Turonian sequence on the southern Tethyan margin using foraminifera

Time series analysis (orbital cycles) of the uppermost Cenomanian-Lower Turonian sequence on the southern Tethyan margin using foraminifera

Organic carbon deposition and phosphorus accumulation during Oceanic Anoxic Event 2 in Tarfaya, Morocco

Oceanic events and biotic effects of the Cenomanian-Turonian anoxic event, Tarfaya Basin, Morocco

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