Paleomagnetic Scale Research Articles

The Paleogene/Neogene boundary in continental deposits of the West Siberian Plain

This paper presents palynological and paleomagnetic characteristics of three West Siberian horizons: Zhuravka (Upper Oligocene, Chattian), Abrosimovka, and Beshcheul (Lower-Middle Miocene, Aquitanian, Burdigalian, Langhian, and Serravallian). We consider the distribution of dinocysts of the genus Pseudokomewuia in the stratotype section of the Zhuravka Horizon (Zashchitino Village) and in the section of borehole 13 (Chelyuskintsev Village), which exposes the Turtas, Abrosimovka, and Beshcheul Formations. Similar compositions and structures of dinocyst assemblages and similar palynofloras in the Turtas and Abrosimovka Horizons, as well as the sedimentation environment and cyclic structure of lacustrine deposits, suggest that the Paleogene/Neogene boundary should be localized at the base of the Beshcheul Horizon. We propose to include the Abrosimovka Horizon into the Upper Oligocene (upper Chattian). The data are correlated with the regional paleomagnetic scale. These views should be reflected in a new regional stratigraphic chart for the Paleogene-Neogene deposits of the West Siberian Plain.

Mammal faunas in Europe at the end of the Early – Beginning of the Middle Pleistocene

Problems of mammal evolution in the Early and Middle Pleistocene are widely discussed in the literature. The stages of mammal evolution considered in their relation to other paleontological data, geological units and the paleomagnetic scale provide a solid basis for correlation of natural events within this time interval. The analysis of the data on the European mammal fauna makes it possible to compare the evolutionary stages of large and small mammal faunas and the evolutionary changes in indicator phyletic lineages between different regions and to find regional features of similarity or distinction. In this paper the authors made an attempt to analyze data on large and small mammal faunas in Eastern Europe within the interval from the Jaramillo paleomagnetic event to the beginning of the early Middle Pleistocene (1.07–∼0.7 Ma BP) and to compare them with analogous data from Western Europe. Main trends in evolution and distribution of large and small mammals (primarily Arvicolidae) during the studied time interval are revealed. The characteristics of the established principal stages in small mammal faunal sequences are given. The position of these stages with reference to the paleomagnetic and climatic-chronological scales are proposed.

Geological еvents at the Cretaceous – Paleogene boundary in Georgia (Caucasus)

A continuous section at Tetrickaro (South Georgia) of Maastrichtian-Danian shallow-marine paleontologically proved carbonate deposits is being described. Within the section, a boundary clay layer, 15 - 20 cm thick, has been established with anomalously high content of Ir (3.46-5.34 ng/g), with shock-quartz grains and reversed polarity corresponding to R-29 zone of the International Paleomagnetic Scale. Mass extinction of representatives of numerous marine macro- and micro-fossil groups has been established at the Maastrichtian-Danian boundary in Georgia. 18 species of inocerams, 16 species from 9 genera of ammonitids, 5 species of bellemnitids, 25 species from 12 genera of echinoidea, 6 species from 3 genera of orbitoids, 9 species from 3 genera of planktonic foraminifers and 60 species from 29 genera of calcareous nannoplankton have disappeared at the end of Maastrichtian.

Progress in the recognition of neogene diatom datums along the U.S. Atlantic Coast

Twenty-four diatom datums are recognized in the Neogene of the U.S. Atlantic margin. These datums are calibrated with foraminiferal zones of Blow (1969) which in turn are correlated with other bio-zones and the paleomagnetic scale. Calibration of Atlantic margin diatomaceous sequences suggest that hiatuses occur in the Early Miocene, Late Miocene, and Pliocene—Pleistocene. The twenty-four datums allow a more precise correlation of siliceous Atlantic coastal plain units, particularly within the Miocene.

Tertiary and Cretaceous paleoenvironments in the southwest Atlantic Ocean: Preliminary results of Deep Sea Drilling Project Leg 71

DSDP Leg 71 in the South Atlantic confirmed that the early opening (Neocomian-Aptian) of the South Atlantic was marked with restrictive circulation in which shale units high in organic carbon (1.7% to 4.1%) were deposited. Ratios of gaseous hydrocarbons and pyrolysis-fluorescence analyses suggest a fairly high degree of maturity of the black shale. A comparatively complete Cretaceous section provides biostratigraphic reference for the South Atlantic. Major erosion occurred at or near the Tertiary-Cretaceous boundary prior to the opening of the Drake Passage (Oligocene–middle Miocene). The early Tertiary was marked by mild climatic conditions and periods of exceptionally rapid sediment accumulation (as much as 44 m/m.y.) separated by hiatuses or condensed intervals. Paleomagnetic measurements recognize the Brunhes and Matuyama (with Jaramillo and Olduvai events), Gauss (with Kaena and Mammoth events), and Gilbert (with Cochiti event) Epochs. Correlation of this paleomagnetic scale with siliceous microfossil zonations was accomplished. Siliceous and calcareous microfossils reveal pronounced fluctuations of the Polar Front in the Pliocene and Pleistocene. Warm intervals occurred in the late Gilbert and middle Guass Epochs; cooler conditions were prevalent in the late Gilbert-early Gauss. The late Pliocene was marked by climatic deterioration with brief warmings in the uppermost Matuyama and upper Brunhes. Sedimentation rates dropped markedly from 180 m/m.y. in the early Pliocene (Gilbert Epoch) to 2.3 m/m.y. in the Pleistocene (early Brunhes).

A composite paleomognetic section for upper Pliocene-Pleistocene deposits of the Kyzylsu River basin (Southern Tadzhikistan)

On the basis of geologic-geomorphologic, biostratigraphic, and paleomagnetic data, we have correlated upper Pliocene-Pleistocene sections in the Kyzylsu River basin in Southern Tadzhikistan. We have constructed a composite paleomagnetic section and compared it with Cox's paleomagnetic scale. We recognize the principal stratigraphic subdivisions within the range of the upper Pliocene (Kuruksay suite), Eopleistocene (Kayrubak suite), and Pleistocene (including the Vakhsh, Ilyak, and Dushanbe assemblages). We have defined the upper Pliocene - Eopleistocene and Eopleistocene-Pleistocene boundaries on the basis of geologic and paleomagnetic data. —Authors.