THE RUSSIAN PLATFORM AS A KEY REGION FOR VOLGIAN/TITHONIAN CORRELATION: A REVIEW OF THE MEDITERRANEAN FAUNAL ELEMENTS AND AMMONITE BIOSTRATIGRAPHY OF THE VOLGIAN STAGE

A review of the ammonite faunas and biostratigraphy of the uppermost Kimmeridgian - lowermost Middle Volgian of Central Russia is presented. The major role of the Sub-mediterranean ammonites in the Volgian assemblages is described, providing additional detail to the existing scheme of Tithonian-Volgian correlations. The base of the Tithonian and the base of the Volgian are coincident, based on the association of Neochetoceras steraspis-Lingulaticeras solenoides. The Klimovi Zone corresponds to most of the Hybonotum Zone. However, the top of the Hybonotum Zone, based on the distribution of Paralingulaticeras, falls within the Sokolovi Zone. The allocation of a Tenuicostata Subzone (with two horizons: neoburgense and puschi) in the Pseudoscythica Zone is proven. The neoburgense horizon may be correlated with the ciliata and penicillatum horizons of Neuburg and, probably, with the Semiforme Zone. The findings of Lingulaticeras blaschkei, Pseudolissoceras, and Sutneria in the Panderi Zone of the Middle Tithonian suggest that the base of the Middle Volgian may not be younger than the Middle Tithonian Fallauxi Zone

THE BOREAL-TETHYAN BIOGEOGRAPHICAL MOLLUSC ECOTONE IN EUROPE DURING THE JURASSIC-CRETACEOUS TRANSITION

Late Jurassic and earliest Cretaceous molluscs of the northern hemisphere were distinctly differentiated geographically into Boreal taxa, usually north of 50° N, and Tethyan taxa, usually south of 45° N. Between these latitudes certain areas were displaced from time to time, although the biogeographical ecotone was stable. The magnitude of the ecotone and the migration of molluscs inside the ecotone varied in time and space, in direction (unidirectional and bidirectional) and intensity (expansion and "isolate straying"). The frequency of the Boreal-Tethyan migrations of molluscs is explained by eustacy and by geographical barriers existing between the Northern Caucasus and Middle-Russian basins

Global risk factors

The paper deals with a problem of solar and geomagnetic activity as global risk factors in financial risk management. The history of the idea of solar – earth relations is rather long (Hershel, 1804; Jevans, 1870 – Theory of Solar cycles, Chizhevsky, 1920 ‐ Theory of Heliotaraxy; Collins, 1965 etc.), but financial risk management does not use these facts really and this paper may help to demonstrate some new risk management tools based on new results of the author's studies (Rogov 2003). Firstd Published Online: 14 Oct 201

Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia)

The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite d18O data show an irregular decrease from values reaching up to 1.6 in the Middle Oxfordian and from 0.8 to 1.7 in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon d13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem.Web of Science33art. no. 1971

Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia)

The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite d18O data show an irregular decrease from values reaching up to 1.6 in the Middle Oxfordian and from 0.8 to 1.7 in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon d13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem.Web of Science33art. no. 1971

Palaeoenvironments and palaeoceanography changes across the Jurassic/Cretaceous boundary in the Arctic realm: case study of the Nordvik section (north Siberia, Russia)

The Jurassic/Cretaceous transition was accompanied by significant changes in palaeoceanography and palaeoenvironments in the Tethyan Realm, but outside the Tethys such data are very scarce. Here we present results of a study of the most complete section in the Panboreal Superrealm, the Nordvik section. Belemnite d18O data show an irregular decrease from values reaching up to 1.6 in the Middle Oxfordian and from 0.8 to 1.7 in the basal Ryazanian, indicating a prolonged warming. The biodiversity changes were strongly related to sea-level oscillations, showing a relatively low belemnite and high ammonite diversity during sea-level rise, accompanied by a decrease of the macrobenthos taxonomical richness. The most prominent sea-level rise is marked by the occurrence of open sea ammonites with Pacific affinities. Peak abundances of spores and prasinophytes correlate with a negative excursion in organic carbon d13C near the J/K boundary and could reflect blooms of green algae caused by disturbance of the marine ecosystem.Web of Science33art. no. 1971

Clumped isotope record of salinity variations in the Subboreal Province at the Middle–Late Jurassic transition

Results of clumped isotope, oxygen isotope and elemental (Mg/Ca, Sr/Ca) analyses of exceptionally well-preserved belemnite rostra and ammonite shells from the uppermost Callovian–Upper Kimmeridgian (Lamberti–Mutabilis zones) of the Russian Platform are presented. Despite a significant decrease in belemnite δ18O values across the Upper Oxfordian–Lower Kimmeridgian, the clumped isotope data show a constant seawater temperature (ca. 16 °C) in the studied interval. The decrease in belemnite δ18O values and lower δ18O values measured from ammonite shells are interpreted as a result of the salinity decline of the Middle Russian Sea of ca. 12‰, and salinity stratification of the water column, respectively. The postulated secular palaeoenvironmental changes are linked to the inflow of subtropical, saline waters from the Tethys Ocean during a sea-level highstand at the Middle–Late Jurassic transition, and progressive isolation and freshening of the Middle Russian Sea during the Late Oxfordian–Kimmeridgian. The obtained clumped isotope data demonstrate relative stability of the Late Jurassic climate and a paramount effect of local palaeoceanographic conditions on carbonate δ18O record of shallow epeiric seas belonging to the Subboreal Province. Variations in Mg/Ca and Sr/Ca ratios of cylindroteuthid belemnite rostra, which are regarded by some authors as temperature proxies, are, in turn, interpreted to be primarily dependent on global changes in seawater chemistry. The paleoenvironmental variations deduced from clumped and oxygen isotope records of the Russian Platform correspond well with changes in local cephalopod and microfossil faunas, which show increasing provincialism during the Late Oxfordian and the Early Kimmeridgian. Based on the review of literature data it is suggested that the observed salinity decrease and restriction of Subboreal basins during the Late Jurassic played a major role in the formation of periodic bottom water anoxia and sedimentation of organic rich facies