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The foraminiferal record in the Holocene evolution of the Mecklenburg Bay (south-western Baltic Sea)

Kostecki Robert, Radziejewska Teresa

Oceanological and Hydrobiological Studies

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2021

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Vol. 50, No. 2

169--183

EN

Foraminiferal assemblages were analyzed in a 620-cm long core retrieved from the central part of the Mecklenburg Bay (MB, south-western Baltic Sea) to aid in the reconstruction of environmental changes occurring in the area during the Holocene and to complement a set of previously investigated palaeoenvironmental proxies. A total of five foraminifera-based stratigraphic units were identified, including an initial 80-cm thick layer devoid of foraminifera. The next two units featured an increasing abundance of the foraminiferal assemblage dominated by the calcareous Ammonia group species. Nearly all the calcareous foraminifera found in the core were decalcified. Following the maximum abundance within the 470–410 cm layer, the foraminiferal abundance declined sharply and the assemblage’s dominance structure changed to domination of the agglutinated foraminiferal species, Eggerelloides scaber, which continued up to the top of the core and marked a pronounced shift in environmental conditions (shallower depth, lower salinity, more dynamic sedimentation conditions). The foraminifera-based stratigraphy of the core proved to be complementary to that emerging from previous analyses of diatoms and sediment geochemistry.

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Luminescence chronology of fluvial and marine records from subsurface core in Kaveri delta, Tamil Nadu: Implications to sea level fluctuations

Goswami Kartika, Krishnan Sivakumar, Kumerasan Anbarasu, Sadasivam Senthil Kumar, Kumar Pankaj, Jaiswal Manoj. K.

Geochronometria

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2019

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Vol. 46, no. 1

125--137

EN

South-Eastern coastal plains of India experience some of the major delta formations of the Indian subcontinent majorly affected by fluctuations of the Indian summer monsoon (ISM) and sea level. Past shoreline signatures in the form of palaeo beach ridges in Kaveri delta (Tamil Nadu, India), suggest a wave-dominated delta and thus past sea-level variations affecting directly the sedimentary dynamics of the Kaveri river forcing the river to either aggrade or prograde. Chronostratigraphic and foraminiferal study of the 25 m deep sediment core taken 2.5 km onshore from Tamil Nadu coast, Kaveri delta shows evidence of changing coastline over the last 150 ka. Various units in the core reflect eight major phases of increased sea level (~3.4 ka, ~5.0 ka, 9–6 ka, 60–57 ka, 89–81 ka, ~102 ka,~121 ka and 143–140 ka) partly coinciding with the global climate cycles MIS 1, MIS 3, MIS 5, MIS 6 respectively during the late Quaternary period. During ~121 ka and 9–6 ka, direct signature of marine transgression is observed by the presence of foraminifera in the core location. The study also shows that the sea transgression during ~121 ka was much longer-lasting and higher than during 9–6 ka, even though not revealed in the Quaternary sea level curve given by previous authors. Depositional breaks are observed in the core during periods of lower sea levels as the river responded by incision. Total organic matter of the deposition between 9–6 ka was observed as high as 2.5–6% suggesting oxygen stressed conditions during the period.

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Foraminifera and Late Cenomanian-Turonian biostratigraphy of the northern palaeobiogeographic district of Western Siberia

Podobina Vera

Geologos

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2013

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Vol. 19, No. 3

201--227

EN

The study of 114 core samples from seven borehole sections of the Van-Eganskaya area in the central part of Western Siberia yielded sufficient data to investigate the Late Cenomanian-Turonian foraminifers, palaeoenvironments, and the Late Cenomanian-Turonian biostratigraphy of this poorly studied area. Two Late Cenomanian foraminifer zones were established, viz. a (lower) Saccammina micra - Ammomarginulina sibirica Zone and an (upper) Trochammina wetteri tumida - Verneuilinoides kansasensis Zone. They reflect changes in the species composition of the foraminifer assemblages and lithology of the host rocks of the Uvatskian Horizon. In the lower part of the upper zone, beds with Gaudryinopsis nanushukensis elongatus are present. The changes in the species composition and lithology of the upper Cenomanian resulted from water-depth variations during the Boreal transgression. Two distinct assemblages and two homonymous zones, viz. the (lower) Gaudryinopsis angustus and the (upper) Pseudoclavulina hastata zones occur in the Turonian clayey cap-rocks of the superimposed Kuznetsovskian Horizon. Comparison of the Late Cenomanian-Turonian assemblages from the West-Siberian and Canadian provinces of the same Arctic palaeobiogeographical realm shows that the West-Siberian species are the same as, and closely related to, Canadian taxa, along with geographical subspecies. This comparison allows a detailed correlation, which results in a precise dating of the foraminifer zones.