Wyniki wyszukiwania - Biblioteka Nauki

1

Dubki (Saratov region, Russia), the reference section for the Callovian/Oxfordian boundary

100%

Kiselev D. , Rogov M. , Guzhikov A. , Pimenov M. , Tesakova E. , Dzyuba O.

|

tom Vol. 4, no. 1

177-179

EN

Efforts in the choosing of GSSP for the Cl/Ox boundary have led to distinction of some available sections with good succession of the ammonite faunal horizons in the vicinities of Saratov. One of the primary criteria for GSSP proposal is the good traceability across the world, and hence, the study of reference section (especially in the region with mixed faunas) in the terms of integral stratigraphy. Additional importance of the investigation of the reference sections for the Cl/Ox boundary is connected with wide distribution of the condensed facies and gaps perhaps due to the suggested sharp changes in climate of the Northern Hemisphere. Few variants of the infrasubzonal units for the Cl/Ox transitional beds of the Russian Platform were suggested recently. Here we are using the scheme of Kiselev and Rogov (2005). The Dubki section is located few kilometers north from Saratov and originally was a temporary quarry for the nearby road-building. Recently this section and/or ammonites from this section were briefly described by Mitta (Keupp & Mitta 2004) and by the present authors (Rogov & Egorov 2003). In addition, this section has recently been proposed as possible candidate for the Cl/Ox GSSP (Kiselev & Rogov 2004). Precise ammonite sampling permits establishing a succession of faunal horizons close to that of Northwest Europe (Fig. 1). Inclined boundaries between some horizons in the figure mean short transitional span, where index species (or both morphologies in lineage) co-occur. Only ranges of the few, most important taxa are shown. Strong Tethyan influence is fixed in the mojarowskii and baccatum horizons, while Boreal cardioceratids dominate in the other intervals. Among the Belemnitida two main groups are recorded. Belemnotheutids are generally scarce; they range from Henrici to Praecordatum subzones. Belemnitids are typically of Tethyan origin (Hibolithes). Boreal forms are common only in two restricted levels. Ostracods are numerous and diverse. However, they show wide oscillations in these two characters through the section, possibly reflecting sea-level changes. Remarkably, Infacythere dulcis is replaced by Nophrecythere oxfordiana at the Cl/Ox boundary as determined by ammonite biostratigraphy. Quite exceptionally, some levels in the studied section provided good samples for magnetostratigraphic studies across the Cl/Ox boundary. Lamberti Zone is chiefly characterized by normal polarity, whereas Mariae and Cordatum zones show dominant reverse polarity, corresponding to polarity structure of the M-35-M37 Chrons (Ogg 2004).

2

Eco-biostratigraphic advances in late Quaternary geochronology and palaeoclimate : the marginal Gulf of Mexico analogue

75%

Antonarakou A. , Kontakiotis G. , Karageorgis A. P. , Besiou E. , Zarkogiannis S. , Drinia H. , Mortyn G. P. , Tripsanas E.

|

tom Vol. 63, No. 1

178--191

EN

This study combines high-resolution planktonic foraminiferal eco-biostratigraphy and palaeoclimatic data from the high-sedimentation-rate core J PC-26 from the northwestern margin of the Gulf of Mexico (GoM). The eco-biozones recognized (GOMPFE1-12) being correlated with published Mg/Ca-based sea surface temperatures. This updated palaeoclimatic and stratigraphic reference record facilitates correlations with the Greenland ice core events and their climatic relationships, and also provides a solid stratigraphic framework for correlations with other palaeoclimatic and palaeoceanographic records in the circum-GOM/Caribbean region. This multidisciplinary approach underlines the utility of supporting conventional dating methodologies with different constraints, and further reveals a powerful tool for reliably correlating marine records between comparable deep-sea marginal settings and coeval sequences of this region.

3

Jurassic Chronostratigraphic Database and the TimeScale Creator Visualization System

63%

Ogg J. , Przybylski P.

|

tom Vol. 7, no. 1

175-179

EN

A joint project of the International Commission on Stratigraphy (ICS) and CHRONOS database program is to provide detailed global and regional “reference” scales of Earth history. Such scales integrate biostratigraphy (zones, datums for marine and terrestrial realms), sea-level (curves, sequences), geochemistry (trends, events), magnetic polarity chrons and astronomical cycles. The current Jurassic scale contains over 1000 events and zones correlated to Tethyan and Boreal ammonite zones with approximate numerical ages from Geologic Time Scale 2004 (Gradstein et al. 2004). This public database will be progressively enhanced through the efforts of the Jurassic Subcommission of the ICS and by other stratigraphic and regional experts. On-screen display and production of usertailored time-scale charts is provided by the TimeScale Creator, a Java package freely available from the ICS Subcommission for Stratigraphic Information or the TS-Creator websites (http://stratigraphy.science.purdue.edu or www.tscreator.org). After specifying the time interval and vertical scale, a user selects a subset of stratigraphic columns and trends. In addition to screen views and a scalable-vector graphics (SVG) file for importation into popular graphics programs, the on-screen display also has “hot-curser-points” to open windows providing additional information on events, zones and boundaries. The database and visualization package are envisioned as a convenient reference tool, chart-production assistant, and a window into the geologic history of our planet.

4

Occurrence and significance of Cenomanian belemnites in the lower Danubian Cretaceous Group (Bavaria, southern Germany)

63%

Wilmsen M. , Niebuhr B. , Chellouche P.

|

tom Vol. 60, no. 2

231-241

EN

The belemnite records of the lower Danubian Cretaceous Group (DCG, northeastern Bavaria, southern Germany) are compiled, taxonomically described and placed within the new integrated stratigraphic framework of the group. Three specimens from the lower Regensburg Formation (Saal Member) south of Regensburg can be assigned to Neohibolites cf. ultimus (d'Orbigny) and are dated as late Early Cenomanian (Mantelliceras dixoni Zone). Eight specimens represent Praeactinocamax plenus (Blainville) and occur in an event (plenus Event) in the lower Eibrunn Formation (Regensburg area) or basal Regensburg Formation (Roding area in the Bodenwohrer Senke). Biostratigraphy and carbon stable isotopes suggest that the belemnite horizon with P. plenus in the DCG has strictly the same chronostratigraphic position (mid-Late Cenomanian, middle Metoicoceras geslinianum Zone) as elsewhere in Central and NW Europe. The lithostratigraphic units of the lower Danubian Cretaceous Group (i.e., the Regensburg and Ebirunn formations), however, are characterized by a pronounced diachronism based on their time-transgressive (i.e., onlapping) deposition during the Cenomanian.Early Turonian transgression. The distribution of P. plenus around the Mid-European Island can be easily explained by migration around the positive area without the necessity of a marine strait across the Bohemian Massif.

5

Facies and integrated stratigraphy of the Upper Turonian (Upper Cretaceous) Grossberg Formation south of Regensburg (Bavaria, southern Germany)

63%

Niebuhr B. , Richardt N. , Wilmsen M.

Acta Geologica Polonica

|

2012

|

tom Vol. 62, no. 4

595-615

EN

The Upper Turonian Grossberg Formation of the Regensburg area (Danubian Cretaceous Group, Bavaria, southern Germany) has a mean thickness of 20-25 m and consists of sandy bioclastic calcarenites and calcareous sandstones which are rich in bryozoans, serpulids and bivalves (oysters, rudists, inoceramids). Eight facies types have been recognized that characterize deposition on a southward dipping homoclinal ramp: the inner ramp sub-environment was characterized by high-energy sandwave deposits (sandy bioclastic rud- and grainstones, bioclastic sandstones) with sheltered inter-shoal areas. In mid-ramp settings, bioturbated, glauconitic, calcareous sand- and siltstones as well as bioturbated, bioclastic wacke- and packstones predominate. The carbonate grain association of the Grossberg Formation describes a temperate bryomol facies with indicators of warm-water influences. An inferred surplus of land-derived nutrients resulted in eutrophic conditions and favoured the heterozoan communities of the Grossberg Ramp. Carbon stable isotope geochemistry cannot significantly contribute to the stratigraphic calibration of the Grossberg Formation due to the depleted and trendless bulk-rock [delta^13]C values, probably resulting from a shallow-water aquafacies with depleted [delta^13]C DIC values and low [delta^13]C values of syndepositional and early diagenetic carbonate phases. However, strongly enriched skeletal calcite [delta^13]C values support a correlation of the Grossberg Formation with the mid-Late Turonian positive Hitch Wood isotope event (Hyphantoceras Event of northern Germany). This interpretation is supported by biostratigraphic data and a range from the Mytiloides striatoconcentricus Zone into the lower My. scupini Zone is indicated by inoceramid bivalves. Both the base and top of the Grossberg Formation are characterized by unconformities. Sequence boundary SB Tu 4 at the base is a major regional erosion surface (erosional truncation of the underlying Kagerhoh Formation in the Regensburg area, fluvial incision at the base of the Seugast Member of the Roding Formation in the Bodenwohr area towards the north and northeast). It is suggested that this unconformity corresponds to a major sea-level drop recognized in many other Cretaceous basins below the Hitch Wood or Hyphantoceras Event. The transgression and highstand of the Grossberg Formation is concomitant to the deposition of the fluvial Seugast Member and the onlap of the marginal-marine. Veldensteiner Sandstein. onto the Frankische Alb. The unconformity at the top of the Grossberg Formation (late Late Turonian SB Tu 5) is indicated by a ferruginous firm-/ hardground and an underlying zone of strongly depleted [delta^13]C values. The abrupt superposition by deeper marine marls of the lower Hellkofen Formation (uppermost Turonian.Lower Coniacian) may be connected with inversion tectonics at the southwestern margin of the Bohemian Massif.

6

Integrated stratigraphy of the reference sections for the Callovian-Oxfordian boundary in European Russia

51%

Kiselev D. , Rogov M. , Glinskikh L. , Guzhikov A. , Pimenov M. , Mikhailov A. , Dzyuba O. , Matveev A. , Tesakova E.

|

tom Vol. 11, no. 1

59–-96

EN

The most complete succession of the Callovian-Oxfordian boundary recorded in European Russia is the Dubki section, where the authors have carried out integrated paleontological and magnetostratigraphical studies. A continuous sequence of the West-European biostratigraphic units in the interval from the Lamberti to the Cordatum Zones is present in this section, and 10 ammonite biohorizons have been recognized. Additional data concerning nannofossil assemblages, foraminifers, ostracods, belemnoids and the paleomagnetic polarity for the Dubki section are also presented. The Callovian-Oxfordian boundary, marked by FAD of the genus Cardioceras, is placed at the base of the scarburgense biohorizon. The paleontological richness and continuity of the succession make the Dubki section a possible GSSP candidate for the Callovian/Oxfordian boundary. Correlation of the Dubki ammonite succession with those of the other GSSP candidates, Redcliff Point and Thuoux, is proposed. Other sections studied in Russia have yielded some additional observations on the Callovian-Oxfordian boundary beds. Although in the Dubki section the praemartini biohorizon is not found, its existence is proved, however, in Orenburg region (Khanskaya Gora). In the Datchovskaya section (Northern Caucasus) the paucicostatum biohorizon is characterized by an unusual combination of Subtethyan and Boreal ammonites, including Kosmoceras, which is not typical of the paucicostatum biohorizon outside the Northern Caucasus.