Search results for "Sediment"

Milankovitch and sub-Milankovitch forcing of the Oxfordian (Late Jurassic) Terres Noires Formation (SE France) and global implications

2010

ABSTRACT High‐resolution analysis (2277 samples) of magnetic susceptibility (MS) was performed on ∼700‐m‐thick Early–Middle Oxfordian marine marls of the Terres Noires Formation, SE France. MS variations within these sediments record sub‐Milankovitch to Milankovitch frequencies with long‐term eccentricity (405 kyr and ∼2 Myr) being the most prominent. The 405 kyr cycle was used as a high‐resolution geochronometer for astronomical calibration of this poorly constrained interval of Late Jurassic time. The estimated duration of this Early–Middle Oxfordian interval concurs with the current International Geologic Time Scale GTS2004 (∼4 Myr), but the estimated durations of the corresponding ammon…

Spatial and temporal distribution of ooids along a Jurassic carbonate ramp: Amellago outcrop transect, High-Atlas, Morocco

2010

Carbonate ramp systems are widespread throughout the geological record, but very few areas have seismic-scale, continuous and structurally undeformed outcrops that allow reliable interpretation of facies distributions and stacking patterns. The Amellago outcrop shows the detailed depositional and stratigraphic relationships of an ooid-dominated ramp system that is almost completely exposed along a dip profile (37 km long and 1000 m thick) in the Lower to Middle Jurassic of the southern High Atlas, Morocco. Ammonite and brachiopod fauna provide excellent biostratigraphic control on small scale stacking patterns. At Amellago, the evolution of depositional environments is evident at different …

A record of the Jurassic/Cretaceous boundary climatic variation on the southern margin of the Tethys : clay minerals and palynofacies of the early Cr…

2005

Abstract In order to precise the paleogeographic extension of the climatic variation known at the Jurassic/Cretaceous boundary, the sedimentary organic matter (palynofacies and Rock-Eval) and the clay minerals content of Berriasian sediments of the Sidi Kralif Formation are studied on the Jebel Meloussi section, central Tunisia. Standard sedimentological and palynofacies analysis allow to reconstruct the bathymetric curve and the sequence stratigraphic scheme. Using existing biostratigraphy based on calpionellids and ammonite zonation, the sequence stratigraphic interpretation can be correlated with the established eustatic chart. Clay mineral assemblages are characterized by a shift in the…

Episodic deposition of the Lias in the Medianes nappe (western Switzerland): a record from mineralized ammonite-bearing beds

1992

Abstract Sinemurian and Pliensbachian depositional sequences from the starved distal northern continental margin of the Tethys are preserved in the Medianes Nappe (Western Swiss Prealps). They contain mineralized beds which include a variety of facies. The northern continental margin of the Tethys was broken into blocks, less than 50 km wide, during an extensional phase. The Sinemurian and Pliensbachian sediments in the study are vary in thickness from less than 50 m in the north to more than 200 m in the south. Although the upper Sinemurian to Pliensbachian mineralized beds are thin, between 0.10 and 0.50 m thick, they commonly contain several distinct faunal horizons stacked one upon anot…

Albian ammonites of the Benguela Basin (Angola): a biostratigraphic framework.

2007

20 pages; The study of the Albian ammonite fauna of the sedimentary series in the Benguela Basin (Angola) allows a major revision of the biostratigraphy of the south Atlantic area. The new biostratigraphic approach allows the recognition of 17 horizons distributed in 8 subzones correlated with the ammonite zonation of the Tethyan Province. The Lower Albian is characterized by the Douvilleiceras inaequinodum Subzone (including the D. mammillatum aequinodum Horizon). The Middle Albian is represented by the Oxytropidoceras (Mirapelia) buarquianum Subzone (subdivided into O. (M.) buarquianum and O. (M.) sergipense horizons). The Upper Albian is characterized by the Dipoloceras sp. Subzone (defi…

Settlement down again patterns of a carbonated platform following up a sedimentary crisis : example of the middle-late Jurassic boundary in the south…

2004

Abstract Following a sedimentary crisis which begins in the late Lower Callovian and spans all the early Oxfordian, the settlement down patterns of a platform with carbonated sedimentation are analysed in a southeastern area of the Paris Basin (fig. 1). Ten lithostratigraphic units (reefal formations, associated bioclastic facies and marly distal lateral facies ; fig. 2) are defined (fig. 3). New ammonite and brachiopod faunas, collected in situ, allow to date accurately the sedimentary units with a precision matching an ammonite subzone of the standard bio-chronostratigraphic scale (fig. 4) of the middle-late Oxfordian (from the Parandieri Subzone, at the base of the Transversarium Zone, t…

Studio delle associazioni ad ammoniti dell'Oxfordiano della Sicilia occidentale

2004

Sistematica, tafonomia e paleobiogeografia delle associazioni ad ammoniti del Giurassico Medio e Superiore della Sicilia Occidentale con particolare …

2012

Sediment quality assessment using Gmelinoides fasciatus and Monoporeia affinis (Amphipoda, Gammaridea) in the northeastern Baltic Sea

2013

Crustaceans in the order Amphipoda are sensitive organisms for the assessment of sediment quality. In this work we performed 10-day toxicity tests on muddy sediments collected from a total of 29 sites in the Gulf of Finland, the Gulf of Riga and the Gulf of Bothnia (northeastern Baltic Sea) using Baltic Sea species such as the native amphipod Monoporeia affinis (Bousfield, 1989) and the invasive amphipod Gmelinoides fasciatus (Stebbing, 1899), and also compared these results with those of bioassays carried out using the standard test species, laboratory-cultivated amphipod Hyalella azteca (Saussure, 1858). The sediment samples (three cm of the upper layer) were collected by a GEMAX Dual Cor…

Holocene treeline in the northern Andes (Ecuador): new evidence from soil charcoals

2006

Soil charcoals represent a record for palaeoecological studies. For the first time pedoanthracology is applied to northern Andes of Ecuador to study the Holocene treeline. The first results show that the upper treeline was lower than today in the late Pleistocene and in the Middle Holocene. A wide amount of charcoals dated ca. 13000 cal. yr. BP could be caused by fires linked to the first presence of man at these altitudes.