Search results for "Surface Processes"
showing 10 items of 1294 documents
Biogeography and diversity of South Atlantic Cretaceous echinoids: implications for circulation patterns
2000
Abstract This survey of echinoid species living on the African and South American margins of the South Atlantic Ocean in Cretaceous times is based on a review of published species and abundant unpublished material. The synthetic approach is used to ascertain how the South Atlantic was colonised by echinoids from the time it first opened in the Early Cretaceous until communications were established with the North Atlantic and Mediterranean–Tethys in the Late Cretaceous. The survey focuses on the biogeographical origin of immigrant species and their relations with Indo-Madagascan, North Atlantic and Mediterranean–Tethyan faunas. Qualitative variations in species diversity are also studied whe…
Palaeoceanographic significance of the Tethyan ‘Livello Selli’ (Early Aptian) from the Hybla Formation, northwestern Sicily: biostratigraphy and high…
2002
High-resolution micropalaeontological and chemostratigraphic records for the Hauterivian–Aptian succession outcropping at Calabianca (NW Sicily) provide new insight into the palaeoclimatic and palaeoceanographic evolution of the Tethys Ocean. Calcareous nannofossil and planktonic foraminiferal biostratigraphy together with δ13C chemostratigraphy allowed the identification of a hiatus in the Barremian and a major one including most of the Upper Aptian, the entire Lower Albian and part of the Middle Albian. The Livello Selli equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy as well as by the δ13C curve. The multi-proxy record from …
Isothermal decompression history in the “Western Granulite” terrain, central Tanzania: Evidence from reaction textures and trapped fluids in metapeli…
2008
Abstract The Mozambique Belt (MB) of the East Africa Orogen contains large areas of granulite-facies migmatitic gneisses with Archaean and Palaeoproterozoic protolith ages and that were recycled during the Neoproterozoic Pan-African orogeny. The study area is situated along the Great Ruaha River and within the Mikumi National Park in central Tanzania where migmatitic gneisses and mafic to intermediate granulites are interlayered with Neoproterozoic granulite-facies migmatitic metapelites. Mineral textures suggest isothermal decompression, with the peak mineral assemblage comprising Grt–Bt–Ky–Kfs–Pl–Qtz ± Phn ± Ti-Oxide ± melt and amphibolite-facies retrograde assemblage Grt–Bt–Sil–Ms–Kfs–Pl…
The petrology of two distinct granulite types in the Hengshan Mts, China, and tectonic implications
2005
Abstract The Archean to Proterozoic Hengshan Complex (North China Craton), comprises tonalitic and granodioritic gneisses with subordinate mafic lenses, pegmatites and granites. Amphibolite facies assemblages predominate, although granulite-facies relics are widespread, and greenschist-facies retrogression occurs in km-wide shear zones. Mafic lenses, locally abundant, occur as strongly deformed amphibolite (hornblende+plagioclase) boudins or sheets. In contrast to previously published models we find two series of mafic rocks with distinctly different granulite-facies evolutions. In the north of the Complex, relict high-pressure mafic granulites are garnet+clinopyroxene-bearing rocks with a …
A 45-year sub-annual reconstruction of seawater temperature in the Bay of Brest, France, using the shell oxygen isotope composition of the bivalve Gl…
2020
A reconstruction of sea surface temperature (SST) spanning 45 years (1966–2011) was developed from δ18O obtained from the aragonitic shells of Glycymeris glycymeris, collected from the Bay of Brest, France. Bivalve sampling was undertaken monthly between 2014 and 2015 using a dredge. In total, 401 live specimens and 243 articulated paired valves from dead specimens were collected, of which 24 individuals were used to reconstruct SST. Temperatures determined using the palaeotemperature equation of Royer et al. compared well with observed SST during the growing season between 1998 and 2010 (Pearson’s correlation: p = 0.002, r = 0.760). Furthermore, a significant negative correlation was foun…
The relationship between water and air temperature in chironomid-based paleoclimate reconstructions: Records from boreal and subarctic Finland
2014
Fossil remains of larval chironomids are one of the most useful paleolimnological proxies to reconstruct Holocene paleoclimate. We investigate the within-lake distribution of chironomids in relation to water temperature and test the usability of intralake calibration in chironomid-based temperature reconstructions. We compare our findings against the traditional multilake calibration technique in Holocene sediment cores from Finland. The results show that intralake water temperature optima of common taxa correspond closely with mean July air temperature optima in a regional multilake dataset, with exception of a few vegetation-associated taxa. A calibration model based on intralake water t…
Human adaptation strategies to abrupt climate change in Puerto Rico ca. 3.5 ka
2015
The connection between climatic change and social response is complex because change articulates a number of inter-related factors. Human decisions are filtered by social buffers – including social memory, risk perception, and cultural priorities – and the rate and scale of climate change is usually much larger than the scale of human decision-making. In this article, we provide information on climate change based on precisely dated speleothems with the response evident in archaeological sites that have radiocarbon date ranges within the same time frame. A stalagmite recovered from within the catchment area for aquifer recharge of the Pre-Arawak site of Angostura in Barceloneta, Puerto Ric…
Anthropogenic soils are the golden spikes for the Anthropocene
2011
We propose that the Anthropocene be defined as the last c. 2000 years of the late Holocene and characterized on the basis of anthropogenic soils. This contrasts with the original definition of the Anthropocene as the last c. 250 years (since the Industrial Revolution) and more recent proposals that the Anthropocene began some 5000 to 8000 years ago in the early to mid Holocene (the early-Anthropocene hypothesis). Anthropogenic soil horizons, of which several types are recognized, provide extensive terrestrial stratigraphic markers for defining the start of the Anthropocene. The pedosphere is regarded as the best indicator of the rise to dominance of human impacts on the total environment b…
Decadal climate variability of the North Sea during the last millennium reconstructed from bivalve shells (Arctica islandica)
2014
Uninterrupted, annually resolved paleoclimate records are crucial to contextualize the current global change. Such information is particularly relevant for the Europe realm for which weather and climate projections are still very challenging if not virtually impossible. This study presents the first precisely dated, annually resolved, multiregional Arctica islandica chronologies from the North Sea which cover the time interval ad 1040–2010 and contain important information on supra-regional climatic conditions (sea surface temperature (SST), ocean productivity, wind stress). Shell growth varied periodically on timescales of 3–8, 12–16, 28–36, 50–80, and 120–240 years, possibly indicating a…
The seasonal water temperature cycle in the Arctic Dicksonfjord (Svalbard) during the Holocene Climate Optimum derived from subfossil Arctica islandi…
2015
Future climate change will have significant effects on ecosystems worldwide and on polar regions in particular. Hence, palaeo-environmental studies focussing on the last warmer-than-today phase (i.e. the early Holocene) in higher latitudes are of particular importance to understand climate development and its potential impact in polar systems. Molluscan bivalve shells constitute suitable bio-archives for high-resolution palaeo-environmental reconstructions. Here, we present a first reconstruction of early Holocene seasonal water temperature cycle in an Arctic fjord based on stable oxygen isotope (δ18Oshell) profiles in shells of Arctica islandica (Bivalvia) from raised beach deposits in Di…