Search results for "Cretaceous"
showing 10 items of 182 documents
A new giant ground bird from the Upper Cretaceous of southern France
1998
New discoveries afford a much better knowledge of the large birds previously reported from the Upper Cretaceous of southern France on the basis of a single synsacrum fragment. An incomplete pelvis consisting of the synsacrum with part of the ilia is used to define a new taxon of bird, Gargantuavis philoinos , to which a femur is also referred. This bird is characterized by its very large size (comparable to that of an ostrich), a broad pelvis with an anteriorly placed acetabulum, and a short robust femur. The occurrence of this very large, flightless, bird in the Late Cretaceous shows that, contrary to widespread opinion, the evolution of large terrestrial birds was not simply the result of…
Weathering Products of a Dismantled Variscan Basement. Minero-Chemical Proxies to Insight on Cretaceous Palaeogeography and Late Neogene Palaeoclimat…
2020
This study compares, for the first time, the mineralogy and geochemistry of two residual-clay deposits in NW Sardinia (Nurra district) that formed at different times in tropical and sub-tropical climates. Both deposits represent palaeosols with deep-weathered residual profiles and overlie Mesozoic carbonate rocks that were deposited on the south European palaeomargin. The older alterite is Cenomanian–Turonian in age and grades upward into a horizon of karstic bauxite, whereas the younger unit occurs within alluvial deposits of Late Neogene age. The Cretaceous palaeosol represents the precursor of the overlying bauxite and formed from unknown sedimentary parent rocks. In contrast, the Messin…
Ammonite extinction and nautilid survival at the end of the Cretaceous
2014
One of the puzzles about the end-Cretaceous extinctions is why some organisms disappeared and others survived. A notable example is the differential extinction of ammonites and survival of nautilids, the two groups of co-occurring, externally shelled cephalopods at the end of the Cretaceous. To investigate the role of geographic distribution in explaining this outcome, we compiled a database of all the occurrences of ammonites and the nautilid genus Eutrephoceras in the last 0.5 m.y. of the Maastrichtian. We also included recently published data on ammonite genera that appear to have briefly survived into the Paleocene. Using two metrics to evaluate the geographic range of each genus (first…
Astérides du Cénomanien de Charente-Maritime (SW France)
1993
Resume Des restes d'Asterides (plaques infero- et superomarginales) ont ete trouves dans les sediments du Cenomanien deCharente-Maritime (Sud-Ouest de la France). Ils appartiennent a 17 taxons, dont la nouvelle espece Calliderma moreaui nov. sp., et correspondent a 5 familles differentes: Goniasteridae, Pycinasteridae, Stauranderasteridae, Sphaerasteridae et Astropectinidae. Leur description est suivie d'une breve analyse de leurs repartitions stratigraphique et paleobiogeographique.
Characterization of a fractured basement reservoir using high-resolution 3D seismic and logging datasets: A case study of the Sab'atayn Basin, Yemen.
2018
The Sab'atayn Basin is one of the most prolific Mesozoic hydrocarbon basins located in central Yemen. It has many oil producing fields including the Habban Field with oil occurrences in fractured basement rocks. A comprehensive seismic analysis of fractured basement reservoirs was performed to identify the structural pattern and mechanism of hydrocarbon entrapment and reservoir characteristics. A 3D post-stack time migration seismic cube and logging data of 20 wells were used and several 2D seismic sections were constructed and interpreted. Depth structure maps were generated for the basement reservoir and overlying formations. The top of the basement reservoir is dissected by a set of NW-S…
An orbital floating time scale of the Hauterivian/Barremian GSSP from a magnetic susceptibility signal (Río Argos, Spain).
2012
10 pages; International audience; An orbital floating time scale of the HauterivianeBarremian transition (Early Cretaceous) is proposed using high-resolution magnetic susceptibility measurements. Orbital tuning was performed on the Río Argos section (southeast Spain), the candidate for a Global boundary Stratotype Section and Point (GSSP) for the HauterivianeBarremian transition. Spectral analyses of MS variations, coupled with the frequency ratio method, allow the recognition of precession, obliquity and eccentricity frequency bands. Orbitallytuned magnetic susceptibility provides minimum durations for ammonite biozones. The durations of well-constrained ammonite zones are assessed at 0.78…
Geoconservation in Sicily (Italy): the Example of the Isola delle Femmine (Palermo)
2022
Abstract The Regional Administration of Sicily recently erected Isola delle Femmine—a small island of the Tyrrhenian Sea, close to Palermo—as a geosite. A detailed geological survey has been carried out in order to define the most important geological features of the island together with the development of a new geological map based on topographic data and a digital model at 1:2.000 scale specially processed. Finally, a geological pathway through the island has been traced and illustrated. The geological substrate of Isola delle Femmine consists of a Mesozoic carbonate succession belonging to the Panormide Carbonate Platform. Two lithostratigraphic units have been differentiated. The lowest…
Constraints on the Cretaceous thermal event in the Transantarctic Mountains from alteration processes in Ferrar flood basalts
1999
Abstract K–Ar and 40 Ar/ 39 Ar incremental-heating analyses on apophyllite formed during hydrothermal alteration of volcanic rocks from the Ferrar Supergroup in North Victoria Land, Antarctica, provide strong evidence for hydrothermal events during mid-Cretaceous time. A last event has been dated at 96.7±0.6 Ma. Variable older ages between 112 and 125 Ma are interpreted as mixed ages of hydrothermal events or may be caused by disturbances of the Ar–Ar system. The Rb–Sr isotope system of the apophyllites is not applicable to dating because a large portion of the Sr is radiogenic and because of Rb-mobility in the crystal structure. Secondary mineralogy suggests a temperature for alteration be…
Tectonic denudation of a Late Cretaceous-Tertiary collisional belt: Regionally symmetric cooling patterns and their relation to extensional faults in…
2003
Thermochronological data reveal that the Late Cretaceous–Tertiary nappe pile of the Anatolide belt of western Turkey displays a two-stage cooling history. Three crustal segments differing in structure and cooling history have been identified. The Central Menderes metamorphic core complex represents an ‘inner’ axial segment of the Anatolide belt and exposes the lowest structural levels of the nappe pile, whereas the two ‘outer’ submassifs, the Gördes submassif to the north and the Çine submassif to the south, represent higher levels of the nappe pile. A regionally significant phase of cooling in the Late Oligocene and Early Miocene affected the outer two submassifs and the upper structural l…
Influencia de la litología en los procesos de erosión en <i>badlands</i>. Los casos de Anna (Valencia) y Petrer (Alicante)
1997
By means of experiments with simulated rainfall the hydrological and erosional behaviour of degraded surfaces (badlands) developed on two different parent materials (marls and clays) is studied. On the Keuper clays, the ponding (4'07") and runoff (6' 36") initiation is delayed, the infiltration rates (38.63 mm h<sup>-1</sup>) are high, and the runoff coefficient (11.2 % after 30 minutes and 19.4 % after 60 minutes) and the erosion rates (13 g m<sup>2</sup> h<sup>-1</sup>) are low. On the contrary, over Cretaceous marls, the ponding (1’ 37") and the surface runoff (2' 52") initiation is very rapid, the infiltration rates are low (11.2 mm h<sup>-1<…