The Albian to Turonian carbon isotope record from the Shilaif Basin (United Arab Emirates) and its regional and intercontinental correlation     

Dominik Hennhoefer  Aisha Al Suwaidi  Cinzia Bottini  Emina Helja  Thomas Steuber 《Sedimentology》2019,66(2):536-555

The sedimentary record of the Arabian Shelf offers a unique opportunity to study the Cretaceous (Albian–Turonian) greenhouse climate from a palaeoequatorial perspective. In particular, hemipelagic to pelagic carbonate successions from the extensive Shilaif intra‐shelf basin have the potential to produce an excellent record of carbon cycle perturbations during this interval. This study presents a 269 m thick chemostratigraphic (carbonate δ¹³C and δ¹⁸O) record from the Middle Albian to Early Turonian of central Abu Dhabi (United Arab Emirates), representing over 14 Myr of uninterrupted carbonate sedimentation. The Mauddud to Shilaif formations represent outer ramp to basinal intra‐shelf carbonates with variations from laminated organic‐rich to clean bioturbated intervals. Isotopic evidence of the latest Albian Anoxic Event (Oceanic Anoxic Event 1d), Middle Cenomanian Event I and the Cenomanian–Turonian Anoxic Event (Oceanic Anoxic Event 2) are confirmed and biostratigraphically calibrated by means of calcareous nannofossils. The carbon isotope record allows correlation with other regional records and well‐calibrated records across the Tethyan Ocean and represents a significant improvement of the chronostratigraphic framework of the United Arab Emirates (Shilaif) and Oman (Natih) intra‐shelf basins. The study further confirms that low carbon isotope values corresponding to the two source rock intervals in the Shilaif Formation clearly precede the isotopic expressions of Oceanic Anoxic Event 1d and Oceanic Anoxic Event 2.  相似文献   

Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk          下载免费PDF全文

Toms Buls  Kresten Anderskouv  Patrick L. Friend  Charlotte E. L. Thompson  Lars Stemmerik 《Sedimentology》2017,64(2):478-507

Geomorphic features such as drifts, sediment waves and channels have been documented in the Upper Cretaceous of north‐west Europe. These features are interpreted to result from bottom currents and have been used to refine chalk depositional models and quantify palaeocirculation patterns. Chalk was first deposited as calcareous nannofossil ooze and geomorphic features are the result of sediment reworking after deposition. There is limited knowledge on the processes that govern nannofossil ooze mobility, thus forcing uncertainty onto numerical models based on sedimentological observations. This article provides an extensive view of the erosional and depositional behaviour of calcareous nannofossil ooze based on experimental work using annular flumes. A fundamental observation of this study is the significant decrease of nannofossil ooze mobility with decreasing bed porosity. Erosion characteristics, labelled as erosion types, vary with total bed porosity (φ) and applied shear stress (τ₀). High‐porosity ooze (φ >80%) is characterized by constant erosion rates (E_m). At φ <77%, however, erosion characteristics showed greater variance. Surface erosion was typically followed by transitional erosion (with asymptotically decreasing E_m), and stages of erosion with constant, and exponential erosion rates. The estimated erosion thresholds (τ_c) vary from ca 0·05 to 0·08 Pa for the onset of surface erosion and up to ca 0·19 Pa for the onset of constant erosion (φ of 60 to 85%). Variability of deposition thresholds (τ_cd) from ca 0·04 to 0·13 Pa reflects the influence of variable suspended sediment concentration and τ₀ on settling particle size due to the identified potential for chalk ooze aggregation and flocculation. Additionally, deposition thresholds seem to be affected by the size of eroded aggregates whose size correlates with bed porosity. Lastly, slow sediment transport without resuspension occurred in high‐porosity ooze as surface creep, forming low‐relief sedimentary features resembling ripples. This process represents a previously undescribed mode of fine‐grained nannofossil ooze transport.  相似文献   

Calcareous nannofossil biostratigraphy of Campanian strata (Abtalkh Formation) from the eastern Koppeh-Dagh Basin,NE Iran     

《Cretaceous Research》2017

The Campanian of the eastern Koppeh-Dagh Basin (NE Iran) is generally considered to be represented by the upper part of the Abderaz and the Abtalkh formations. The Abtalkh Formation, which is studied here, reaches thicknesses of up to 1750 m in the area. The formation is characterized by abundant, diverse, and poor to moderately well preserved calcareous nannofossil assemblages of Tethyan affinity. The assemblages were studied in detail in two sections in eastern Koppeh-Dagh, allowing construction of a precise biozonation for this stage. The Abtalkh Formation at sections in Abtalkh village and Padeha spans biozones CC20 to CC23a (UC15b^TP to UC16). The results of this study indicate a late early to late Campanian age for the formation in the area. The most complete Campanian sequence is in the southeast, where the Padeha section is located. Nannofossil abundance and diversity decreases upwards, showing a trend from the base to top of the formation. Dominance of warm water taxa, and low abundance of high latitude taxa, confirm placement of the basin in low to mid palaeolatitudes during deposition of the formation.  相似文献   

Paleogene-Neogene calcareous nannofossil biostratigraphy and paleoecological inferences from northern Campos Basin,Brazil (well Campos-01)     

《Journal of South American Earth Sciences》2016

Quantitative analyses of calcareous nannofossils were performed on 50 ditch-cuttings samples from a well drilled in the northern Campos Basin, Brazil. Nine zones and two subzones were recognised in the Paleogene-Neogene section. The absence of zones NN9-NN7 (earliest late-latest middle Miocene), NP25-NP21 (Oligocene) and NP18-NP1 (earliest late Eocene-Paleocene) implies the occurrence of three stratigraphic breaks/unconformities within the studied interval. Nannofossil assemblages present suggest an open-ocean depositional environment under oligotrophic-surface water conditions for the Miocene section of the well. Hughesius spp. and Umbilicosphaera spp., here named the “small dark” group, were recognised as an index of high nutrient concentration. We suggest that small coccolith/nannolith size is a better indicator of eutrophic condition than taxonomic affinity. Morphometric analysis of specimens of Sphenolithus belemnos and Sphenolithus disbelemnos showed that size tends to decrease within the highstand system tract. The influx of nutrients associated with the highstand could explain this size reduction and may also support our hypothesis that small specimens are indicative of high nutrient concentrations in the surface water.  相似文献   

Role of cyanobacteria in C_org-rich deposits: an example from the Indidura Formation (Cenomanian-Turonian), northeastern Mexico     

Fabian Duque-Botero  Florentin J.-M.R. Maurrasse 《Cretaceous Research》2008,29(5-6):957

We present evidence of accumulation of calcareous cyanobacterial “microspheroids” as predominant components of the Cenomanian-Turonian Indidura Formation of northeastern Mexico. The unit at Parras de la Fuente includes a sequence of limestones and marls with well-defined light-dark rhythms at the decimetric to millimetric scale, in which CaCO₃ and total organic carbon vary between 43–78% and 0.3–3.6%, respectively.A distinctive feature of the section is the presence of abundant millimeter-scale microlaminae arranged in nearly even-parallel white and dark gray “varve like” dual lamination less than 3 mm thick, in which the darker units contain scattered planktonic foraminifera and radiolaria, whereas the lighter microlaminae are dominated by calcitic microspheroids (20–40 μm). The white laminae are evidently the result of recurring cycles of calcareous cyanobacterial blooms, possibly associated with fluvial dilution of surface waters.The organic carbon-rich laminated marlstones and laminated biocalcilutites of the Indidura Formation document paleoceanographic conditions favorable to unusual cyanobacterial productivity cycles that were also characterized by strong dysoxic/anoxic bottom conditions.  相似文献   

Calcareous nannofossil biostratigraphy and paleoecology of the Cenomanian – Turonian transition in the Tarfaya Basin, southern Morocco     

Abdel Aziz Tantawy   《Cretaceous Research》2008,29(5-6):995

An abundant and diverse nannoflora occurs across the Cenomanian/Turonian (C/T) boundary at Tazra in the Tarfaya Basin of southern Morocco. The nannoflora of this sequence permits recognition of three biozones (CC10-CC12), three subzones (CC10a, CC10b and CC10c), and thirteen important nannolith bioevents previously reported from this interval elsewhere. The floral record shows erratic species abundance fluctuations that clearly vary with lithology and reflect at least in part preservational bias and diagenetic processes. In general, four dissolution resistant taxa are dominant: Watznaueria barnesae, Eiffellithus turriseiffelii, Eprolithus floralis, and Zeugrhabdotus spp. The late Cenomanian Zone CC10 marks a rapid excursion in ∂¹³C and is characterized by the successive extinction of four taxa, which are widely recognized as reliable biomarkers: Corollithion kennedyi, Axopodorhabdus albianus, Lithraphidites acutus, and Helenea chiastia. This interval is also marked by high species richness and high abundance of the tropical species Watznaueria barnesae, suggesting warm tropical waters. The subsequent ∂¹³C plateau and organic carbon-rich black shale deposition of the oceanic anoxic event (OAE2) is characterized by low species richness, but high nannofossil abundance, and peak abundance of the cool water and high productivity indicator Zeugrhabdotus spp., followed by the first peak abundance of cool water Eprolithus floralis. This interval correlates with the planktic foraminiferal diversity minimum and the Heterohelix shift, which marks the expansion of the oxygen minimum zone (OMZ). The C/T boundary is identified based on the FO of Quadrum gartneri, which is <1 m below the FO of the planktic foraminifer C/T marker Helvetoglobotruncana helvetica. In the early and middle Turonian, the two dominant species, tropical W. barnesae and cool water E. floralis, alternate in abundance and suggest fluctuating climatic conditions.  相似文献   

Dating the Penninic Ocean subduction: new data from planktonic foraminifera     

O. Mandic  A. Lukeneder 《Cretaceous Research》2008,29(5-6):901

The Penninic Ocean was a side tract of the Central Atlantic Oceanic System intercalated between the European and the Austroalpine plates. Its closure started in the Early Cretaceous, as subduction of the oceanic crust beyond the Austroalpine plate. The sedimentary change on the Austroalpine shelf from pelagic carbonates into deep-water siliciclastics correlated with the denudation of the accretionary wedge resulting from that subduction. Within the Bajuvaric Unit of the Upper Austroalpine, this transition is reflected by the lithostratigraphic boundary between the older Schrambach and the younger Tannheim Formation. This boundary is well exposed in a newly discovered site at Sittendorf, southwest of Vienna. This new outcrop yields an extraordinarily rich planktonic foraminifera assemblage characterized by typical Aptian species belonging to Blowiella, Globigerinelloides, Hedbergella, Leupoldina, and Praehedbergella. A detailed biostratigraphic analysis based on thin-section investigations precisely dated the lithostratigraphic boundary within the lower part of the early Aptian Leupoldina cabri Acme Zone, having an approximate age of 123 Ma. Along with the biostratigraphic analyses, the gamma-log outcrop measurement was a powerful tool in interpreting the stratigraphy and the tectonic setting in the outcrop, which intersects one smaller-scale isoclinal fold.  相似文献   

Morelletpora turgida (Radoičić, 1975 non 1965) a Tethyan calcareous green alga (Dasycladales): Taxonomy,stratigraphy and paleogeography     

《Cretaceous Research》2016

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Upper Campanian-Maastrichtian nannofossil biostratigraphy and high-resolution carbon-isotope stratigraphy of the Danish Basin: Towards a standard δC curve for the Boreal Realm     

Nicolas Thibault  Rikke HarlouNiels Schovsbo  Poul SchiølerFabrice Minoletti  Bruno GalbrunBodil W. Lauridsen  Emma SheldonLars Stemmerik  Finn Surlyk 《Cretaceous Research》2012,33(1):72-90

High-resolution carbon isotope stratigraphy of the upper Campanian-Maastrichtian is recorded in the Boreal Realm from a total of 1968 bulk chalk samples of the Stevns-1 core, eastern Denmark. Isotopic trends are calibrated by calcareous nannofossil bio-events and are correlated with a lower-resolution δ¹³C profile from Rørdal, northwestern Denmark. A quantitative approach is used to test the reliability of Upper Cretaceous nannofossil bio-events and provides accurate biohorizons for the correlation of δ¹³C profiles. The Campanian-Maastrichtian boundary (CMB) is identified through the correlation of dinoflagellate biostratigraphy and δ¹³C stratigraphy between Stevns-1 and the Global boundary Standard Stratotype-section and Point at Tercis les Bains (SW France), allowing the identification of new chemical and biostratigraphic markers that provide a precise placement of the stage boundary on a regional scale. The boundary interval corresponds to the third phase of a stepwise 0.8‰ negative δ¹³C excursion, lies in calcareous nannofossil subzone UC16d^BP, and encompasses the last occurrence of nannofossil Tranolithus stemmerikii and first occurrence of nannofossil Prediscosphaera mgayae. Fifteen δ¹³C events are defined and correlated to sixteen reliable nannofossil biohorizons, thus providing a well-calibrated standard high-resolution δ¹³C curve for the Boreal Realm.  相似文献   

基于随机模型溶蚀岩体强度参数研究     

朱雷  王小群  聂德新  郑百录  姚男 《工程地质学报》2014,22(6):1034-1038

由于溶蚀岩体独特的细观结构及其溶蚀发育的差异性,导致了现场原位实验和室内实验获得的单点强度值很难应用于工程中。以溶蚀砾岩为例,在现场调查的基础上,获得了砾岩的溶蚀发育规律,并建立起其概率统计模型,在此基础上利用FLAC3D 建立起数值模型,并对其进行数值三轴试验,获得了其应力-应变曲线; 同时,对不同溶蚀程度的砾岩进行数值三轴试验,获得了大量的强度参数,建立起溶蚀程度与强度之间的关系。另外,对溶蚀砾岩进行室内三轴实验,获得了其强度参数,并和数值试验取得了较为一致的结果。  相似文献