Bundesanstalt fuer Geowissenschaften und Rohstoffe BGR
Bundesanstalt fuer Geowissenschaften und Rohstoffe BGR
Biari Y.,French Research Institute for Exploitation of the Sea |
Biari Y.,Chouaïb Doukkali University |
Biari Y.,CNRS Oceanic Domains Laboratory |
Klingelhoefer F.,French Research Institute for Exploitation of the Sea |
And 10 more authors.
Tectonophysics | Year: 2015
The structure of the Moroccan and Nova Scotia conjugate rifted margins is of key importance for understanding the Mesozoic break-up and evolution of the northern central Atlantic Ocean basin. Seven combined multichannel reflection (MCS) and wide-angle seismic (OBS) data profiles were acquired along the Atlantic Moroccan margin between the latitudes of 31.5° and 33° N during the MIRROR seismic survey in 2011, in order to image the transition from continental to oceanic crust, to study the variation in crustal structure, and to characterize the crust under the West African Coast Magnetic Anomaly (WACMA).The data were modeled using a forward modeling approach. The final models image crustal thinning from 36. km thickness below the continent to approximately 8. km in the oceanic domain. A 100. km wide zone characterized by rough basement topography and high seismic velocities up to 7.4. km/s in the lower crust is observed westward of the West African Coast Magnetic Anomaly. No basin underlain by continental crust has been imaged in this region, as has been identified north of our study area. Comparison to the conjugate Nova Scotian margin shows a similar continental crustal thickness and layer geometry, and the existence of exhumed and serpentinized upper mantle material on the Canadian side only. The oceanic crustal thickness is lower on the Canadian margin. © 2015 Elsevier B.V.
Redwan M.,Bundesanstalt fuer Geowissenschaften und Rohstoffe BGR |
Redwan M.,Sohag University |
Rammlmair D.,Bundesanstalt fuer Geowissenschaften und Rohstoffe BGR
Soil Science Society of America Journal | Year: 2010
Electrical conductivity can easily be measured, but interpretation is ambiguous since saturation, fluid conductivity, and material properties are interacting parameters. This study aims to indirectly obtain fluid conductivity evolution in time and space in column experiments by repetitively applying two independent non-destructive multi-level methods. Water saturation, is derived from the difference in x-ray attenuation by dry, partially and fully saturated sand filled columns. Also, it is used to calculate fluid conductivity from the electrical conductivity in time intervals for each depth level in the column. The investigated columns show distinct patterns for water saturation, electrical conductivity, and calculated fluid conductivity for individual imbibition and drainage steps at distinct grain-size distributions. During imbibition, the unsaturated capillary fringe head shows a very unusual increase in electrical conductivity gaining with each step of capillary rise. During the drainage cycle, the electrical conductivity peak broadens and moves downward. The calculated fluid conductivities are much higher than expected, but correspond well to conductivity and ion strength of the extracted fluids. The strong increase in electrical conductivity was attributed to the fast rising capillary head fluids, which quickly accumulated all available ions around the particles and moved upward. The slow water was depleted, and showed even a different ion distribution pattern due to slowly reacting minerals. Monitoring of fluid conductivity in time and space by non-destructive methods provides access to enrichment-depletion processes in the critical zone, in the laboratory and in the field. This is essential for understanding the development of hardpans in natural and anthropogenic environments, causing eventually supergene economic enrichment of metals. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved.
Weiss W.,Bundesanstalt fuer Geowissenschaften und Rohstoffe BGR
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen | Year: 2012
A planktonic foraminiferal biostratigraphy is established for the Boreal Lower to Upper Aptian sediments of the Hoheneggelsen KB 9 core (Lower Saxony Basin, northern Germany) and is correlated to planktonic foraminiferal records of coeval Tethyan sections (Switzerland, southeastern France, Italy, Spain, and Tunisia). Planktonic foraminiferal assemblages of the Hoheneggelsen KB 9 core are characterized by well preserved, small Praehedbergella, Blowiella and Leupoldina specimens and species that are known from the Tethyan Realm and indicate northern Tethyan ingressions during the early Aptian. Planktonic foraminiferal assemblages of the Hoheneggelsen KB 9 core reflect the profound palaeoceanographic change of the marine regime in the Lower Saxony Basin, starting in Lower Aptian sediments older than the 2 m thick mid Lower Aptian Fischschiefer Horizon of the Hoheneggelsen KB 9 core, which is correlated particularly with the Blowiella blowi Zone and considered as the Boreal equivalent of the Lower Aptian Oceanic Anoxic Event (OAE) 1a of the Tethyan Realm (Selli Level of Italy, Niveau Goguel of southeastern France). Interregional biostratigraphic correlation of the Hoheneggelsen KB 9 core with Tethyan sections is based on first and last occurrences of planktonic foraminiferal zonal marker species (Blowiella blowi, Leupoldina cabri) and suggests that the OAE 1a interval in the Boreal Hoheneggelsen KB 9 section (northern Germany) and certain Tethyan sections (Roter Sattel, Switzerland; Cassis-La Bédoule, southeastern France; Cau, Spain; Calabianca, Italy) falls within the (upper) Blowiella blowi Zone, whereas the OAE 1a interval in other Tethyan sections (Jebel Messella and Jebel Ressas, Tunisia; Cismon, northern Italy) falls within the upper Blowiella blowi Zone to lower Leupoldina cabri Zone, or only within the lower Leupoldina cabri Zone (Djebel Serdj, Tunisia; Cismon, northern Italy). The comparison shows that the lower boundary of the Leupoldina cabri Zone needs to be recalibrated if the OAE 1a period of time is considered as a synchronous time slice. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.