Search results for " Climate"
showing 10 items of 3933 documents
Smithian shoreline migrations and depositional settings in Timpoweap Canyon (Early Triassic, Utah, USA).
2014
AbstractIn Timpoweap Canyon near Hurricane (Utah, USA), spectacular outcrop conditions of Early Triassic rocks document the geometric relationships between a massive Smithian fenestral-microbial unit and underlying, lateral and overlying sedimentary units. This allows us to reconstruct the evolution of depositional environments and high-frequency relative sea-level fluctuations in the studied area. Depositional environments evolved from a coastal plain with continental deposits to peritidal settings with fenestral-microbial limestones, which are overlain by intertidal to shallow subtidal marine bioclastic limestones. This transgressive trend of a large-scale depositional sequence marks a lo…
Climatic fluctuations and seasonality during the Late Jurassic (Oxfordian–Early Kimmeridgian) inferred from delta18O of Paris Basin oyster shells.
2008
10 pages; International audience; Oxygen isotope data from biostratigraphically well-dated oyster shells from the Late Jurassic of the eastern Paris Basin are used to reconstruct the thermal evolution of western Tethyan surface waters during the Early Oxfordian–Early Kimmeridgian interval. Seventy eight oyster shells were carefully screened for potential diagenetic alteration using cathodoluminescence microscopy. Isotope analyses were performed on nonluminescent parts of shells (n=264). Intra-shell δ18O variability was estimated by microsampling along a transect perpendicular to the growth lines of the largest oyster shell. The sinusoidal distribution of the δ18O values along this transect …
Unravelling extrinsic and intrinsic factors of the early Palaeozoic diversification of blastozoan echinoderms
2010
19 pages; International audience; The Subphylum Blastozoa represents more than one third of the early Palaeozoic echinoderm fauna. A comprehensive database including all records of blastozoans was built to provide quantitative analyses of palaeogeography and diversity patterns and processes, for the 10 classes currently included in this subphylum during the early Palaeozoic. The global pattern of taxonomic diversity shows two peaks during the Cambrian Series 3 and the Late Ordovician intervals. In Cambrian times, the high taxonomic diversity seems to be related with a high turnover rate and a high endemicity of blastozoan genera, whereas in Ordovician times, the rise in diversity is associa…
Vegetation dynamics of Kisima Ngeda freshwater spring reflect hydrological changes in northern Tanzania over the past 1200 years: implications for pa…
2021
13 pages; International audience; Kisima Ngeda (KN), a spring on the northern margin of saline Lake Eyasi, Tanzania, sustains an Acacia-Hyphaene palm woodland and Typha swamps, while the surrounding vegetation is semi-desert. To study the vegetation changes associated with this spring, which represents a plausible modern analog for the fossil springs documented in the nearby paleoanthropological and archaeological sites of Olduvai Gorge, we analyzed the pollen content of a 43 cm-long sediment core that documents vegetation changes since the last ~1200 years (from cal yrs. C.E. 841 to 2011). Our results show that (1) Hyphaene palms, which require meso-halophytic soil conditions were most abu…
COMMENT TO LEHRMANN ET AL. NEW SECTIONS AND OBSERVATIONS FROM THE NANPANJIANG BASIN, SOUTH CHINA
2016
In the study of Earth-surface environmental processes during the events associated with the Permian–Triassic boundary, a key issue is the nature of the latest Permian pre-extinction surface in shallow marine limestones in numerous sites, principally within the Tethyan realm. Sediments below this surface pre-date the extinction event, so that the limestones comprising these latest Permian facies contain diverse fossil remains of organisms that lived just before the extinction. At all reported sites, this surface is disconformably overlain by post-extinction sediments, which contain microbialites in many places, particularly in Tethys. The nature of the youngest pre-extinction surface remains…
Using growth and geochemical composition of Clathromorphum compactum to track multiscale North Atlantic hydro-climate variability
2020
International audience; Records of ocean/atmosphere dynamics over the past centuries are essential to understand processes driving climate variability. This is particularly true for the Northwest Atlantic which is a key region with an essential role in global climate regulation. Over the past two decades, coralline red algae have been increasingly used as environmental and climatic archives for the marine realm and hold the potential to extend long-term instrumental measurements. Here, we investigate the possibility to extract climate and environmental information from annual growth patterns and geochemical composition of the coralline red algae, Clathromorphum compactum, from Saint-Pierre …
Detrital-zircon geochronology and provenance of the El Oro Metamorphic Complex, Ecuador: Geodynamic implications for the evolution of the western Gon…
2019
Abstract The El Oro Metamorphic Complex (EOMC) in SW Ecuador has been the subject of debate for several decades. While previous studies have focused on the metamorphic and deformation history of the complex to determine its geodynamic evolution, the pre-metamorphic history and its association to units in the north-central Andes remains poorly understood. Here we present a U-Pb detrital zircon provenance study to provide insights into the depositional history and the geodynamic setting of the EOMC. Our results imply that the southern portion of the EOMC (the Tahuin division) is composed of an older Palaeozoic (pre-Famatinian) sequence in the south (El Tigre unit; c. 525-510 Ma), and younger …
Current Wildland Fire Patterns and Challenges in Europe: A Synthesis of National Perspectives
2021
Changes in climate, land use, and land management impact the occurrence and severity of wildland fires in many parts of the world. This is particularly evident in Europe, where ongoing changes in land use have strongly modified fire patterns over the last decades. Although satellite data by the European Forest Fire Information System provide large-scale wildland fire statistics across European countries, there is still a crucial need to collect and summarize in-depth local analysis and understanding of the wildland fire condition and associated challenges across Europe. This article aims to provide a general overview of the current wildland fire patterns and challenges as perceived by natio…
Ammonite paleobiogeography during the Pliensbachian-Toarcian crisis (Early Jurassic) reflecting paleoclimate, eustasy, and extinctions.
2011
14 pages; International audience; The Pliensbachian-Toarcian crisis (Early Jurassic) is one of the major Mesozoic paleoecological disturbances when ca. 20% of marine and continental families went extinct. Contemporaneously, profound paleobiogeographical changes occurred in most oceanic domains including a disruption of ammonite provincialism during the Early Toarcian. Here, we quantitatively reappraise the structure and evolution of paleobiogeographical patterns displayed by ammonite faunas before, during, and after the biological crisis, over a time-interval including 13 biochronozones. The high-resolution study presented here involves the use of hierarchical Cluster Analyses, non-metric M…
Chronostratigraphy and geochronology: A proposed realignment.
2013
We propose a realignment of the terms geochronology and chronostratigraphy that brings them broadly into line with current use, while simultaneously resolving the debate over whether the Geological Time Scale should have a “single” or “dual” hierarchy of units: Both parallel sets of units are retained, although there remains the option to adopt either a single (i.e., geochronological) or a dual hierarchy in particular studies, as considered appropriate. Thus, geochronology expresses the timing or age of events (depositional, diagenetic, biotic, climatic, tectonic, magmatic) in Earth’s history (e.g., Hirnantian glaciation, Famennian-Frasnian mass extinction). Geochronology can also qualify r…