Rock fragments from mud volcanic deposits of the Gulf of Cadiz: An insight into the Eocene-Pliocene sedimentary succession of the basin

Two hundred clasts from the mud breccia extruded by the Yuma mud volcano in the Gulf of Cadiz are used to establish an offshore stratigraphy. The clasts are a very complex mixture of material from the sedimentary successions through which the mud volcano erupted and provide important information about the composition and genesis of deep-seated strata. We deal with fragments of rocks that were deposited millions of years ago, subsequently buried and later erupted on to the seafloor. Rock fragments from the mud breccia, studied in thin section under a polarizing microscope, provide genetic indications suggestive of deep-sea conditions during the accumulation of strata. A reconstruction of the sedimentary succession through which the Yuma mud volcano erupted and the depositional evolution of the Gulf of Cadiz was made on the basis of lithology and age determinations of the rock. Age and depositional environment documented by the clasts indicate that a marine basin existed in the Gulf of Cadiz area at least from the Eocene, and that in the Early and Middle Eocene a deep-sea fan depositional environment prevailed in the region, resulting in the accumulation of thick turbidites. The Late Eocene and Oligocene are not represented among rock fragments from the mud breccia, suggesting regional uplift and non-deposition in the area. Sedimentation was re-established in the Miocene with the accumulation of a clayey Aquitanian-Burdigalian succession. Pelagic carbonate sedimentation became predominant in the Langhian time. The Serravallian-Early Tortonian is characterized by a high supply of terrigenous material, resulting in the deposition of turbiditic clays and sands. Shallow water sedimentation with accumulation of carbonate rocks prevailed in the basin during the Middle Tortonian. © 2003 Elsevier Science B.V. All rights reserved

Middle Coniacian-Santonian foraminiferal bioevents around the Mangyshlak Peninsula and Russian Platform

The distribution of foraminifers and some macrofossils at the Coniacian/Santonian boundary in four selected sections, two on the Mangyshlak Peninsula (West Kazakhstan) and two on the Russian Platform, are compared in this paper. The first occurrence (FO) of Cladoceramus undulatoplicatus (F. Roemer) is the primary marker for the boundary in the Mangyshlak area. Specimens of the Sphenoceramus pachti-cardissoides group occur at the base of the Santonian on the Russian Platform. This is the equivalent to the "Sphenoceramus Teilzone", which characterizes the Coniacian/Santonian boundary interval in Germany. Benthic foraminifers predominate around the boundary in both Mangyshlak and on the Russian Platform and may be used as secondary markers. The following bioevents were recognised close to the boundary in these areas: (1) abundant Stensioeina emscherica (Baryschnikova), the simultaneous FO of Gavelinella vombensis (Brotzen), and the FO of G. thalmanni (Brotzen); (2) the last occurrence (LO) of G. thalmanni (Brotzen); (C) the FOs of Neoflabellina suturalis suturalis (Cushman) and Stensioeina exculpta exculpta (Reuss); and (4) the FO of rare N. gibbera (Wedekind) just below the FO of Cladoceramus undulatoplicatus (F. Roemer). © 2006

Rock fragments from mud volcanic deposits of the Gulf of Cadiz: An insight into the Eocene-Pliocene sedimentary succession of the basin

Two hundred clasts from the mud breccia extruded by the Yuma mud volcano in the Gulf of Cadiz are used to establish an offshore stratigraphy. The clasts are a very complex mixture of material from the sedimentary successions through which the mud volcano erupted and provide important information about the composition and genesis of deep-seated strata. We deal with fragments of rocks that were deposited millions of years ago, subsequently buried and later erupted on to the seafloor. Rock fragments from the mud breccia, studied in thin section under a polarizing microscope, provide genetic indications suggestive of deep-sea conditions during the accumulation of strata. A reconstruction of the sedimentary succession through which the Yuma mud volcano erupted and the depositional evolution of the Gulf of Cadiz was made on the basis of lithology and age determinations of the rock. Age and depositional environment documented by the clasts indicate that a marine basin existed in the Gulf of Cadiz area at least from the Eocene, and that in the Early and Middle Eocene a deep-sea fan depositional environment prevailed in the region, resulting in the accumulation of thick turbidites. The Late Eocene and Oligocene are not represented among rock fragments from the mud breccia, suggesting regional uplift and non-deposition in the area. Sedimentation was re-established in the Miocene with the accumulation of a clayey Aquitanian-Burdigalian succession. Pelagic carbonate sedimentation became predominant in the Langhian time. The Serravallian-Early Tortonian is characterized by a high supply of terrigenous material, resulting in the deposition of turbiditic clays and sands. Shallow water sedimentation with accumulation of carbonate rocks prevailed in the basin during the Middle Tortonian. © 2003 Elsevier Science B.V. All rights reserved

Characterization of Mg/Ca distributions in planktonic foraminifera species by electron microprobe mapping

The distribution of Mg/Ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping. Species include several that are commonly used for estimation of past seawater temperatures (Globigerinoides ruber, G. sacculifer, Neogloboquadrina incompta (synonym of N. pachyderma dex.), N. dutertrei, and G. truncatulinoides). Each of the investigated species displays large variations in Mg/Ca composition within individual tests. However, the pattern of Mg/Ca variation is notably different between symbiont-bearing and symbiont-free species. In symbiotic species, cyclic Mg/Ca compositional banding occurs that is characterized by narrow (<1-3 μm), high-Mg/Ca (typically 8-11 mmol/mol) bands, intercalated between broader low Mg/Ca (typically 1-5 mmol/mol) bands. This factor of 2-3 difference equates to an apparent calcification temperature change of 10°C or more. Such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of Mg/Ca into the tests of symbiont-bearing species. These vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures. Symbiont-free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column. Copyright 2005 by the American Geophysical Union

A sapropelic interlayer in quaternary sediments of the western Balearic Basin (Mediterranean Sea) and depositional environments inferred from planktonic foraminifera

Upper Pleistocene sediments of the western Balearic Basin enclose a sapropelic interlayer 16 cm thick. The quantitative analysis of planktonic foraminiferal assemblages shows that the interlayer deposition was related to an episode of climatic warming and salinity decrease in surface seawater. That episode was complicated by a short-term cooling and associated elevated influx of Atlantic waters. Copyright © 2005 by MAIK "Nauka/Interperiodica" (Russia)