Biostratigraphic Data (biostratigraphic + data)

Distribution by Scientific Domains

Selected Abstracts


Yang Yongtai
Although Mesozoic source and reservoir rocks are known to occur at oilfields in the northern Qaidam Basin (NW China), the precise identification and distribution of Mesozoic rocks in the subsurface are outstanding problems. The Dameigou locality has in the past been considered as the type section for Lower-Middle Jurassic strata in northern Qaidam. Previous studies have concluded that the onset of non-marine sedimentation here took place in the Early Jurassic; and that Mesozoic strata penetrated by wells in the Lenghu structural zone are Middle Jurassic. In this paper, we present new data from the Lengke-1 well, drilled in the Lenghu structural zone in 1997. This data indicates the existence of a more extensive pre-Middle Jurassic stratigraphy than has previously been recognized. Biostratigraphic data together with regional seismic mapping suggest that the pre-Middle Jurassic succession at Lengke-1 includes both Late Triassic and Early Jurassic deposits. The Late Triassic sedimentary rocks appear to have been deposited in local half graben, some of which were later inverted during Jurassic, Cretaceous and Cenozoic tectonism. Lower and Middle Jurassic strata (lacustrine and fluvial deposits) are present in the SW and NE parts of the Lenghu structural zone, respectively. Extensive organic-rich intervals are present in both successions. Lower Jurassic lacustrine mudstones may represent a previously under-appreciated, and potentially large, source rock sequence. [source]

The diversification and extinction of Doushantuo-Pertatataka acritarchs in South China: causes and biostratigraphic significance

Zhou Chuanming
Abstract The Ediacaran Period immediately follows the last Cryogenian glaciation,the ,635,Ma Marinoan or Nantuo glaciation, and it is also punctuated by another brief glaciation,the ,582,Ma Gaskiers glaciation. It is possible that these glaciations may have had significant impact on Ediacaran biological evolution (e.g. the appearance or disappearance of Doushantuo-Pertatataka acritarchs). Alternative hypotheses propose that the diversification of Doushantuo-Pertatataka acritarchs was caused by the Acraman bolide impact or by emerging eumetazoans. To test these hypotheses, high-resolution geochronological and biostratigraphic data are required. The Doushantuo Formation in South China, radiometrically constrained between ,635 and ,551,Ma, has the potential to clarify the global picture of early-middle Ediacaran evolution. Here we present preliminary biostratigraphic data from the Doushantuo Formation in the East Yangtze Gorges area and new ,13C chemostratigraphic data from the Doushantuo Formation at Weng'an. These and previously published palaeontological data, aided by the tool of ,13C chemostratigraphy, indicate that the biostratigraphic record of the Doushantuo Formation is locally sensitive to the availability of specific taphonomic windows. In the East Yangtze Gorges area, Doushantuo-Pertatataka acritarchs first appeared shortly after the termination of the Nantuo glaciation and gradually diversified throughout the Doushantuo Formation. At Weng'an, however, such acritarchs first appear,abruptly and in much greater diversity,in phosphorite of the upper Doushantuo Formation, immediately above a subaerial exposure surface. Thus, the biostratigraphic pattern in the East Yangtze Gorges area permits, whereas that at Weng'an apparently disallows, a causal relationship between the Nantuo glaciation and the diversification of Doushantuo-Pertatataka acritarchs. We conclude that the biostratigraphic record is incomplete at Weng'an, where the early Ediacaran evolutionary history is not preserved. The South China data indicate that special attention has to be paid to taphonomic and palaeoenvironmental analysis before extrapolating local and regional biostratigraphic ranges to make global interpretations. It is less clear when Doushantuo-Pertatataka acritarchs disappeared. Previous investigators have variously suggested that they disappeared before, at, or after, the Gaskiers glaciation. These hypotheses are difficult to test because of the lack of sedimentary evidence for the Gaskiers glaciation in South China and other regions (e.g. South Australia) where Doushantuo-Pertatataka acritarchs are abundant. In Australia, Doushantuo-Pertatataka acritarchs are thought to have experienced a sharp decline after the Egan glaciation, which may well be equivalent to the Gaskiers glaciation. If true, then Doushantuo-Pertatataka acritarchs are largely restricted to the interval between the Nantuo and Gaskiers glaciations. This conclusion allows us to place constraints on the possible causes of the diversification and extinction of Doushantuo-Pertatataka acritarchs and has important implications for the biostratigraphic significance of Doushantuo-Pertatataka acritarchs. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Rock magnetism and paleomagnetic stratigraphy of forearc sediments of the Japan Trench, ODP Sites 1150 and 1151

ISLAND ARC, Issue 1 2004
Toshiya Kanamatsu
Abstract Magnetic measurements were carried out to investigate rock magnetic properties and paleomagnetic directions of late and middle Miocene sediments recovered from the land side of the Japan Trench during the Ocean Drilling Program Leg 186. Because the low coercive component in natural remanent magnetization (NRM) normalized by anhysteretic remanent magnetization shows that the drilling-induced magnetization is severe in the sections obtained by the advanced hydraulic piston coring method, careful analyses of demagnetization of NRM using the ,demagnetization plane' were carried out to decompose the direction and intensity. Magnetostratigraphic correlation down to the upper Miocene, supplemented by biostratigraphic data, revealed that the sedimentation rates are characterized by drastic changes, with the early Pliocene having the highest rate. This high sedimentation rate is related to the subsidence of the southern deep-sea terrace of the Japan Trench. [source]


S.N. Ehrenberg
Eight samples of brachiopod shell material have been analyzed for their strontium isotope composition in order to more accurately date Lower to Upper Permian siliceous biogenic strata of Spitsbergen (Kapp Starostin Formation) and the southern Barents Sea (Røye Formation). The results are interpreted as showing a mid-Artinskian age for the basal Vøringen Member of the Kapp Starostin Formation and a range of late Artinskian to Roadian for the overlying part of this unit. The upper part of the Røye Formation yields ages in the range Roadian to Wuchiapingian. These results are consistent with available biostratigraphic data and confirm the potential of strontium isotope stratigraphy for developing a more accurate chronology of the widespread spiculite deposits that characterize the northern margin of Pangea in late-Early Permian to Late Permian time and which constitute a potential target for petroleum exploration. [source]

The Ediacaran Period: a new addition to the geologic time scale

LETHAIA, Issue 1 2006
The International Union of Geological Sciences has approved a new addition to the geologic time scale: the Ediacaran Period. The Ediacaran is the first Proterozoic period to be recognized on the basis of chronostratigraphic criteria and the first internationally ratified, chronostratigraphically defined period of any age to be introduced in more than a century. In accordance with procedures established by the International Commission on Stratigraphy, the base of the Ediacaran Period is defined by a Global Stratotype Section and Point (GSSP) placed at the base of the Nuccaleena Formation cap carbonate directly above glacial diamictites and associated facies at Enorama Creek in the Flinders Ranges of South Australia. Its top is defined by the initial GSSP of the Cambrian Period. The new Ediacaran Period encompasses a distinctive interval of Earth history that is bounded both above and below by equally distinctive intervals. Both chemostratigraphic and biostratigraphic data indicate that the subdivision of the period into two or more series is feasible, and this should be a primary objective of continuing work by the Ediacaran Subcommission of the ICS. [source]

Stratigraphic evolution of the Triassic,Jurassic succession in the Western Southern Alps (Italy): the record of the two-stage rifting on the distal passive margin of Adria

BASIN RESEARCH, Issue 3 2009
Fabrizio Berra
ABSTRACT The Triassic,Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000 m east of Lago Maggiore to about 500 m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break-up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300 m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre-Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian,Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian,Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian,Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian,Toarcian boundary. This younger rift bridges the gap between the Hettangian,Sinemurian diffuse rifting and the Callovian,Bathonian break-up. The late Pliensbachian,Toarcian rift, which eventually lead to continental break-up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins. [source]