Paleoceanographic Implications of StableIsotope Data from Upper MioceneLower Pliocene Sediments from the Southeast Atlantic (Deep Sea Drilling Project Site 519)
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A stable-isotope stratigraphy was established for planktonic and benthic foraminifers from upper Miocene-lower Pliocene pelagic sediments from the Mid-Atlantic Ridge.A correlation of stable-isotope and biostratigraphic data with magnetostratigraphic age revealed the following: (1) the late Miocene carbon-isotope shift in the South Atlantic bottom waters was minute compared with the shift reported for other deep-sea locations (Haq et al., 1980), (2) a significant cooling or continental ice-volume increase occurred between 5.7 and 5.2 Ma, and (3) a period of warming or ice-volume decrease followed, with the rate of warming increasing beginning at 4.5 Ma and reaching a climax at 4.3 Ma.The timing of these paleoceanographic events is correlated with the onset and termination of the Messinian salinity crisis in the Mediterranean Sea.Keywords:
Magnetostratigraphy
Holocene climatic optimum
Reversals of the geomagnetic field In the geological past are recorded globally in the natural remanent magnetization (NRM) of igneous and sedimentary rock sequences. The accurate and rei iable reconstruction of this record is the basis of magnetostratigraphy. The magnetostratigraphy of Late Miocene sediments at several locations in the Mediterranean area Is the main subject of this study.
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Natural remanent magnetization
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Hypoxia
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A detailed magnetostratigraphic study has been carried out in the early to middle Miocene distal alluvial and lacustrine sediments of the Montes de Castejon (central Ebro Basin). The study was based on the analysis of 196 magnetostratigraphic sites sampled along a stratigraphic interval of about 240 meters. Local magnetostratigraphy yielded a sequence of 12 magnetozones (6 normal and 6 reverse) which could be correlated with the Geomagnetic Polarity Time Scale (GPTS) interval C5Cr to C5AD (between 17 and 14.3 Ma.). The sampled sedimentary sequences include the boundary between two tectosedimentary units (TSU, T5 and T6) already defined in the Ebro Basin. The magnetostratigraphy of the Montes de Castejon allows to date the T5/T6 TSU boundary at 16.14 Ma, within chron C5Cn.1n. This magnetostratigraphy also allows us to analyse in detail as well as to discuss the variations in sedimentation rates through space and time between different lacustrine environments: Outer carbonate lacustrine fringes and distal alluvial plains (Montes de Castejon sections) show higher sedimentation rates than offshore lacustrine areas (San Caprasio section, 50 km east of Montes de Castejon).
Magnetostratigraphy
Neogene
Alluvial fan
Alluvial plain
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Magnetostratigraphy
Geomagnetic reversal
Polarity (international relations)
Paleogene
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Reversals of the geomagnetic field In the geological past are
recorded globally in the natural remanent magnetization (NRM) of
igneous and sedimentary rock sequences. The accurate and rei iable
reconstruction of this record is the basis of magnetostratigraphy.
The magnetostratigraphy of Late Miocene sediments at several locations
in the Mediterranean area Is the main subject of this study
Magnetostratigraphy
Natural remanent magnetization
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Magnetostratigraphy, calpionellid and calcareous nannofossil biostratigraphy of the upper Tithonian and lower Berriasian of section Barlya in the West Balkan Mts are herein presented. The studied interval comprises the magnetozones from M21r to M17r, with a large interval of partial remagnetization. It has been directly correlated with a continuous succession of the calpionellid Chitinoidella, Praetintinnopsella, Crassicollaria and Calpionella zones, and with the nannofossil zones from NJT 15b to NK-1. The accumulated evidence in the last twenty years on the magnetostratigraphy, calpionellid and calcareous nannofossil biostratigraphy and events across the J/K boundary in the European Tethys has provoked the authors to plot the main micropalaeontological events against magnetostratigraphic column in order to assess the extent of diachronism of these events. Data from Slovakia, Poland, Italy, Austria, Hungary, France, Spain and Bulgaria has shown specific behaviour of different calpionellid and nannofossil events with respect to the column of the magnetic polarity chrons, which have been considered as ‘isochronous’ or at least less diachronous than the microfossil events. Thus, some rather consistent events have appeared, such as the first occurrences (FOs) of calpionellids Calpionella grandalpina, Crassicollaria brevis, Calpionella minuta and Remaniella ferasini, and the FOs of calcareous nannofossils Nannoconus globulus minor, Hexalithus geometricus, Nannoconus wintereri, Nannoconus steinmannii minor and Nannoconus kamptneri minor. The J/K boundary, as widely accepted, has been traced in section Barlya at the base of the Calpionella alpina Subzone.Financial support from the Synthesys Program at the National History Museum, Stockholm, is gratefully acknowledged.
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Diachronous
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Magnetostratigraphy
Lithostratigraphy
Geochronology
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