Integrated microfossil biostratigraphy,Mid-Cretaceous (Albian to Saronian)

An attempt is made to integrate biozones based on planktic Foraminifera with those on calcareous nannofossils, mainly on first order correlation. An approximate correlation with ammonite zones, magnetic events and radiometric age values, partly on first-order data, partly from the literature, is added.     

Geochemistry of the late Cenomanian-early Turonian chalks of the Paris Basin: Manganese and carbon isotopes in carbonates as paleooceanographic indicators

In the North Atlantic DSDP/IPOD cores, carbon isotope data on the bulk carbonates show significant fluctuations. In sediments now exposed on land coeval fluctuations in the carbon isotope concentrations are also recorded in pelagic and epeiric facies. For instance, in the Upper Cretaceous chalks of the Paris Basin, there is a major break at the Cenomanian-Turonian boundary. At this time, the manganese content of the chalks was also at a maximum and consequently a positive relation can be demonstrated between δ¹³C and manganese concentrations. The same positive correlation is also recorded in many pelagic limestones.In the North Atlantic cores, carbon isotope events are related to the black shale facies and to global oceanic anoxic events and one can suppose that in sediments deposited on the continental margins they are also related to mildly anoxic conditions. Considering the manganese geochemistry in carbonate rocks, a high manganese content in such a reducing environment can be found in the sediments only if the Mn concentration of the interstitial solutions are abnormally high. As a high Mn content in marine pore waters is believed to originate from hydrothermal process, Mn and δ¹³C positive excursions are ultimately related to mid-oceanic ridge activity and to a closely connected phenomenon, the great transgressive pulses during which mid-depth waters may have been anoxic. Consequently, major Mn and carbon isotope events would seem to be useful tools in paleooceanographic reconstructions.     

Radiolarians of the upper Cenomanian and lower Turonian from deposits of the Ananuri Formation, the western Caucasus (Lazarevskoe area)

Diverse radiolarians (over 70 species) are detected in cherty rocks above the bituminous shale horizon, the marker of anoxic event OAE-2 recorded across the Cenomanian-Turonian boundary in the upper part of the Ananuri Formation of flyschoid deposits, the Lazarevskoe area of the western Caucasus. The radiolarian assemblages studied are comparable in composition with radiolarians from concurrent Cenomanian-Turonian boundary strata in other Mediterranean regions (e.g., in the Crimea and Turkey). The lower radiolarian assemblage includes index species Dactyliosphaera silviae of synonymous Cenomanian zone. Alievium superbum present in the upper assemblage is index species of the relevant Turonian zone. Within the studied flyschoid sequence, sediments indicative of the above event (bituminous shales and cherts) are confined to upper elements of flysch rhythms.     

Quantitative Method of Classification and Discrimination of a Porous Carbonate Reservoir Integrating K-means Clustering and Bayesian Theory

Reservoir classification is a key link in reservoir evaluation. However, traditional manual means are inefficient,subjective, and classification standards are not uniform. Therefore, taking the Mishrif Formation of the Western Iraq as an example, a new reservoir classification and discrimination method is established by using the K-means clustering method and the Bayesian discrimination method. These methods are applied to non-cored wells to calculate the discrimination accuracy of the reservoir...     

Orbitally forced sea-level changes in the upper Turonian–lower Coniacian of the Tethyan Himalaya,southern Tibet

Although the mid-Cretaceous is considered to be a typical interval of greenhouse climate and high sea level, cooling events associated with regressions were inferred in recent years. We conducted a biostratigraphic, chemostratigraphic, sequence stratigraphic and cyclostratigraphic investigation of upper Turonian–lower Coniacian marine strata in the Tethyan Himalaya zone, to retrace the sea-level variations and to clarify their global correlations. According to the planktonic foraminiferal zonation, the studied interval is part of the late Turonian–early Coniacian Marginoruncana sigali and D. concavata Zones. The carbon isotope curve shows a good correlation to reference curves in the Boreal and western Tethys realms with all major and minor late Turonian δ¹³C events identified, indicating that the C-isotope curve provides an excellent tool for global stratigraphic correlation in the Turonian. Based on the lithological variations of clastic input and physical and chemical proxies, the succession is divided into two third order and eight fourth order sequences. Spectral analysis indicates that fourth order sea-level changes were linked to the astronomically stable 405-kyr eccentricity cycle. Comparison with classic global sea-level curves, we suggest that late Turonian–early Coniacian sea-level changes along the southeastern Tethyan margin were controlled by eustasy. The significant regressions during ∼90–89.8 Ma and ∼92–91.4 Ma, which are recorded in different continents, may be interpreted as the result of continental ice expansion, giving some support to the notion that ephemeral polar ice sheets existed even in the super-greenhouse world.     

A new fossil species of snakeflies (Raphidioptera: Mesoraphidiidae) from the Late Cretaceous of Kazakhstan,with notes on Turonian Neuropterida

Alloraphidia kyzylzharica sp. nov. is described from the Late Cretaceous (early Turonian) locality at Kyzylzhar, southern Kazakhstan. It is very similar to A. dorfi, but easily distinguished from it by wing shape and venation. We restrict the genus Alloraphidia to these two species. Ascalapharia raphidiformis is considered a member of Baissopteridae, sit. nov. Turonian Neuropterida are mainly characterized by a mixture of specialized genera of extinct families, and genera (sometimes modern) of highly advanced taxa, reflecting a sequence of global mid-Cretaceous crisis of non-marine biocoenoses.     

Application of sequence stratigraphic concepts to the Upper Cretaceous Tununk Shale Member of the Mancos Shale Formation,south-central Utah: Parasequence styles in shelfal mudstone strata

Although sequence stratigraphic concepts have been applied extensively to coarse-grained siliciclastic deposits in nearshore environments, high-resolution sequence stratigraphic analysis has not been widely applied to mudstone-dominated sedimentary successions deposited in more distal hemipelagic to pelagic settings. To examine how sequence stratigraphic frameworks can be derived from the facies variability of mudstone-dominated successions, the Tununk Shale Member of the Mancos Shale Formation in south-central Utah (USA) was examined in detail through a combination of sedimentological, stratigraphic and petrographic methods. The Tununk Shale accumulated on a storm-dominated shelf during the second-order Greenhorn sea-level cycle. During this eustatic event, the depositional environment of the Tununk Shale shifted laterally from distal middle shelf to outer shelf, then from an outer shelf to an inner shelf environment. At least 49 parasequences can be identified within the Tununk Shale. Each parasequence shows a coarsening-upward trend via upward increases in silt and sand content, thickness and lateral continuity of laminae/beds, and abundance of storm-generated sedimentary structures. Variations in bioturbation styles within parasequences are complex, although abrupt changes in bioturbation intensity or diversity commonly occur across parasequence boundaries (i.e. flooding surfaces). Due to changes in depositional environments, dominant sediment supply and bioturbation characteristics, parasequence styles in the Tununk Shale show considerable variability. Based on parasequence stacking patterns, eleven system tracts, four depositional sequences and key sequence stratigraphic surfaces can be identified. The high-resolution sequence stratigraphic framework of the Tununk Shale reveals a hierarchy of stratal cyclicity. Application of sequence stratigraphic concepts to this thick mudstone-dominated succession provides important insights into the underlying causes of heterogeneity in these rocks over multiple thickness scales (millimetre-scale to metre-scale). The detailed sedimentological characterization of parasequences, system tracts and depositional sequences in the Tununk Shale provides conceptual approaches that can aid the development of high-resolution sequence stratigraphic frameworks in other ancient shelf mudstone successions.     

土耳其Sinop盆地晚白垩世大洋红层中的放射虫

在土耳其北部Sinop盆地Kayadibi剖面上发育了一套以红色灰岩及红色硅质岩为特征的,被称之为Kapanboˇgazi组的远洋或半远洋环境下的海相红色沉积。其中的硅质岩里产丰富且保存完好的放射虫化石。其放射虫组合以Crucella cachensis, Alievum superbum?, Patellula verteoensis, Patellula ecliptica, Dictyo mitra multicostata, Pseudodictyomitra pseudomacrocephala, Halesium triacanthum, Pessagnobrachia fabia nii, Pseudoaulophacus putahensis 和Paronaella communis 等属种同时出现为特征,可以与北美、西特提斯及俄罗斯等地建立的Alievum superbum 放射虫带对比,时代为土仑期。     

松科1井南孔白垩系青山口组一段沉积序列精细描述:岩石地层、沉积相与旋回地层

中国白垩纪大陆科学钻探松科1井南孔连续取青山口组一段岩心81.41m,收获率为100%。青一段沉积时期应与土仑阶对应。通过对松科1井南孔青一段岩心的精细描述,揭示其岩性-岩相-旋回的沉积序列及其过程。青一段识别出6种岩石类型(泥岩、白云岩、泥灰岩、重结晶灰岩、介形虫灰岩和火山灰)。相类型为深湖亚相以及白云岩沉积、泥灰岩沉积、灰岩沉积、深湖浊流沉积、火山灰沉积和深湖静水泥沉积共6种沉积微相。青一段中可识别的米级旋回(六级旋回)有4种类型,可划分出81个米级旋回。这些米级旋回叠加成25个五级旋回、6个四级旋回,识别出1个三级旋回界面。对青山口组一段暗色泥岩、白云岩、火山灰等特殊事件层的精细刻画对于松辽盆地的缺氧事件、烃源岩、湖海沟通事件研究具有重要意义。