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1
Bera, M. K., A. Sarkar, P. P. Chakraborty, R. S. Loyal e P. Sanyal. "Marine to continental transition in Himalayan foreland". Geological Society of America Bulletin 120, n. 9-10 (1 settembre 2008): 1214–32. http://dx.doi.org/10.1130/b26265.1.
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Liu, Chao, Hai Tao Xue, Shuang Wang e Yu Jiao Sun. "Study on Law of Structural Evolution and Sedimentary Evolution for North Uskyurt Basin". Advanced Materials Research 671-674 (marzo 2013): 302–5. http://dx.doi.org/10.4028/www.scientific.net/amr.671-674.302.
Testo completoAbstract (sommario):
North Uskyurt Basin, located on Turan Plain, northwestern Central Asian, is continental polycyclic cratonic. The structural evolution of the basin underwent six phases: basement formulation, passive edge, rifting, post-rifting, compression, early Neogene depression. Regional structural evolution takes control of complicated transition of North Uskyurt sedimentary structure. In general, basin sedimentary environment underwent basement (granite, metamorphic rocks) passive edge, late Devonian epoch carboniferous period (marine facies) rifting, late Permian epoch-triassic period (continental facies) post-rifting, Jurassic period-Cretaceous period (Marine-continental Transition Facies, marine facies) compression, late Eocene-Miocene epoch (marine-continental facies coexistence) Neogene depression, Pliocene-Holocene (continental facies). Consequently, sedimentary formation in which various sedimentary environment, such as marine facies, continental facies, are coexisted with various rock types, such as clastic rocks, carbonate rocks, is generated.
3
Singh, B. P. "Marine to continental transition in Himalayan foreland: Discussion". Geological Society of America Bulletin 122, n. 5-6 (6 aprile 2010): 954–55. http://dx.doi.org/10.1130/b26532.1.
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Bera, M. K., A. Sarkar, P. P. Chakraborty, R. S. Loyal e P. Sanyal. "Marine to continental transition in Himalayan foreland: Reply". Geological Society of America Bulletin 122, n. 5-6 (6 aprile 2010): 956–59. http://dx.doi.org/10.1130/b26591.1.
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Wei, Zhifu, Yongli Wang, Gen Wang, Ting Zhang, Wei He, Xueyun Ma e Xiaoli Yu. "Enrichment Mechanism of the Upper Carboniferous-Lower Permian Transitional Shale in the East Margin of the Ordos Basin, China: Evidence from Geochemical Proxies". Geofluids 2020 (6 novembre 2020): 1–14. http://dx.doi.org/10.1155/2020/8867140.
Testo completoAbstract (sommario):
The organic-rich shale of the Upper Carboniferous-Lower Permian transition period in the eastern margin of the Ordos Basin, China, was formed in a marine-continental facies sedimentary environment. With a high content of total organic carbon (TOC) and a large cumulative thickness, it is considered a good source rock for shale gas development. The sedimentary environment of marine-continental transitional shale is obviously different from that of marine shale, which leads to different enrichment characteristics of organic matter. In this paper, shale samples were collected from XX# well of the Taiyuan and Shanxi Formations across the Upper Carboniferous-Lower Permian, which is typical marine-continental transitional shale. The TOC, major elements, and trace elements were measured, and the formation and preservation conditions were investigated using multiple geochemical proxies, including paleoclimate, redox parameters, paleoproductivity, and controls on the accumulation of organic matter. The TOC of Shanxi Formation is higher than that of Taiyuan Formation. In the Taiyuan Formation, TOC is positively related to the redox index (V, U, and V/Cr), indicating that the dysoxic bottom water environment is the key factor controlling organic matter accumulation. For Shanxi Formation, there is a positive correlation between TOC and paleoclimate, which indicates that the enrichment of organic matter is affected by warm and humid paleoclimate and oxic environment. In addition, the paleoproductivity is lower with a positive correlation with TOC for the marine-continental transitional organic-rich shale, suggesting that it was inferior to the gathering of organic matter.
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Mourier, Thomas, Peter Bengtson, Michel Bonhomme, Emile Buge, Henri Cappettta, Jean-Yves Crochet, Monique Feist et al. "The Upper Cretaceous - Lower Tertiary marine to continental transition in the Bagua basin, northern Peru - Paleontology, biostratigraphy, radiometry, correlations". Newsletters on Stratigraphy 19, n. 3 (26 ottobre 1988): 143–77. http://dx.doi.org/10.1127/nos/19/1988/143.
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Cui, Z., S. Davies, K. S. Carslaw e A. M. Blyth. "The response of precipitation to aerosol through riming and melting in deep convective clouds". Atmospheric Chemistry and Physics Discussions 10, n. 11 (25 novembre 2010): 29007–50. http://dx.doi.org/10.5194/acpd-10-29007-2010.
Testo completoAbstract (sommario):
Abstract. We have used a 2-D axisymmetric, non-hydrostatic, bin-resolved cloud model to examine the impact of aerosol changes on the development of mixed-phase convective clouds. We have simulated convective clouds from four different sites (three continental and one tropical marine) with a wide range of realistic aerosol loadings and initial thermodynamic conditions (a total of 93 different clouds). It is found that the accumulated precipitation responds very differently to changing aerosol in the marine and continental environments. For the continental clouds, the scaled total precipitation reaches a maximum for aerosol that produce drop numbers at cloud base between 180–430 cm−3 when other conditions are the same. In contrast, all the tropical marine clouds show an increase in accumulated precipitation and deeper convection with increasing aerosol loading. For continental clouds, drops are rapidly depleted by ice particles shortly after the onset of precipitation. The precipitation is dominantly produced by melting ice particles. The riming rate increases with aerosol when the loading is very low, and decreases when the loading is high. Peak precipitation intensities tend to increase with aerosol up to drop concentrations (at cloud base) of ~500 cm−3 then decrease with further aerosol increases. This behaviour is caused by the initial transition from warm to mixed-phase rain followed by reduced efficiency of mixed-phase rain at very high drop concentrations. The response of tropical marine clouds to increasing aerosol is different to, and larger than, that of continental clouds. In the more humid tropical marine environment with low cloud bases we find that accumulated precipitation increases with increasing aerosol. The increase is driven by the transition from warm to mixed-phase rain. Our study suggests that the response of deep convective clouds to aerosol will be an important contribution to the spatial and temporal variability in cloud microphysics and precipitation.
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Cui, Z., S. Davies, K. S. Carslaw e A. M. Blyth. "The response of precipitation to aerosol through riming and melting in deep convective clouds". Atmospheric Chemistry and Physics 11, n. 7 (15 aprile 2011): 3495–510. http://dx.doi.org/10.5194/acp-11-3495-2011.
Testo completoAbstract (sommario):
Abstract. We have used a 2-D axisymmetric, non-hydrostatic, bin-resolved cloud model to examine the impact of aerosol changes on the development of mixed-phase convective clouds. We have simulated convective clouds from four different sites (three continental and one tropical marine) with a wide range of realistic aerosol loadings and initial thermodynamic conditions (a total of 93 different clouds). It is found that the accumulated precipitation responds very differently to changing aerosol in the marine and continental environments. For the continental clouds, the scaled total precipitation reaches a maximum for aerosol that produce drop numbers at cloud base between 180–430 cm−3 when other conditions are the same. In contrast, all the tropical marine clouds show an increase in accumulated precipitation and deeper convection with increasing aerosol loading. For continental clouds, drops are rapidly depleted by ice particles shortly after the onset of precipitation. The precipitation is dominantly produced by melting ice particles. The riming rate increases with aerosol when the loading is very low, and decreases when the loading is high. Peak precipitation intensities tend to increase with aerosol up to drop concentrations (at cloud base) of ~500 cm−3 then decrease with further aerosol increases. This behaviour is caused by the initial transition from warm to mixed-phase rain followed by reduced efficiency of mixed-phase rain at very high drop concentrations. The response of tropical marine clouds to increasing aerosol is different to, and larger than, that of continental clouds. In the more humid tropical marine environment with low cloud bases we find that accumulated precipitation increases with increasing aerosol. The increase is driven by the transition from warm to mixed-phase rain. Our study suggests that the response of deep convective clouds to aerosol will be an important contribution to the spatial and temporal variability in cloud microphysics and precipitation.
9
Mai, Ana C. G., Lizandra J. Robe, Luis F. Marins e João P. Vieira. "Genetic relationships between landlocked and coastal populations of Lycengraulis grossidens (Engraulidae) in south-eastern South America: evidence for a continental colonisation route with secondary transitions to the coastal region". Marine and Freshwater Research 68, n. 2 (2017): 342. http://dx.doi.org/10.1071/mf15355.
Testo completoAbstract (sommario):
The anchovies of the genus Lycengraulis are the product of an evolutionary transition from a marine to freshwater environment that occurred in South America during the Miocene epoch. Lycengraulis grossidens originated from freshwater lineages and is currently distributed in estuaries and coastal zones. Nevertheless, based on otolith chemistry, there are landlocked individuals in the Uruguay River. The aim of the present study was to investigate the spatiotemporal scenario by which these landlocked individuals reached their current distribution: whether through a north-to-south continental route based on the connection between basins or from the marine environment. To this end, a fragment of the mitochondrial (mt)DNA control region was analysed from individuals collected along freshwater, estuarine and marine environments. We found a significant genetic differentiation between freshwater and coastal (estuarine and marine) populations. Larger haplotype diversities and female effective population size values were found in the coastal population. Nevertheless, the outgroup rooting positioned some Uruguay River haplotypes as hypothetical ancestors in the directed network and as early offshoots in the phylogeny, suggesting the landlocked population as an ancestral lineage. Therefore, the phylogenetic history and biogeography are consistent with a north-to-south continental colonisation route putatively associated with ancient connections between the Amazon and Parana basins followed by new evolutionary transitions to the coastal region associated with Quaternary sea level oscillations.
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Cortés Sánchez, Miguel, Francisco J. Jiménez Espejo, María D. Simón Vallejo, Juan F. Gibaja Bao, António Faustino Carvalho, Francisca Martinez-Ruiz, Marta Rodrigo Gamiz et al. "The Mesolithic–Neolithic transition in southern Iberia". Quaternary Research 77, n. 2 (marzo 2012): 221–34. http://dx.doi.org/10.1016/j.yqres.2011.12.003.
Testo completoAbstract (sommario):
New data and a review of historiographic information from Neolithic sites of the Malaga and Algarve coasts (southern Iberian Peninsula) and from the Maghreb (North Africa) reveal the existence of a Neolithic settlement at least from 7.5 cal ka BP. The agricultural and pastoralist food producing economy of that population rapidly replaced the coastal economies of the Mesolithic populations. The timing of this population and economic turnover coincided with major changes in the continental and marine ecosystems, including upwelling intensity, sea-level changes and increased aridity in the Sahara and along the Iberian coast. These changes likely impacted the subsistence strategies of the Mesolithic populations along the Iberian seascapes and resulted in abandonments manifested as sedimentary hiatuses in some areas during the Mesolithic–Neolithic transition. The rapid expansion and area of dispersal of the early Neolithic traits suggest the use of marine technology. Different evidences for a Maghrebian origin for the first colonists have been summarized. The recognition of an early North-African Neolithic influence in Southern Iberia and the Maghreb is vital for understanding the appearance and development of the Neolithic in Western Europe. Our review suggests links between climate change, resource allocation, and population turnover.
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Ajdanlijsky, George, Annette E. Götz e André Strasser. "The Early to Middle Triassic continental–marine transition of NW Bulgaria: sedimentology, palynology and sequence stratigraphy". Geologica Carpathica 69, n. 2 (1 aprile 2018): 129–48. http://dx.doi.org/10.1515/geoca-2018-0008.
Testo completoAbstract (sommario):
AbstractSedimentary facies and cycles of the Triassic continental–marine transition of NW Bulgaria are documented in detail from reference sections along the Iskar river gorge between the villages of Tserovo and Opletnya. The depositional environments evolved from anastomosing and meandering river systems in the Petrohan Terrigenous Group to mixed fluvial and tidal settings in the Svidol Formation, and to peritidal and shallow-marine conditions in the Opletnya Member of the Mogila Formation. For the first time, the palynostratigraphic data presented here allow for dating the transitional interval and for the precise identification of a major sequence boundary between the Petrohan Terrigenous Group and the Svidol Formation (Iskar Carbonate Group). This boundary most probably corresponds to the major sequence boundary Ol4 occurring in the upper Olenekian of the Tethyan realm and thus enables interregional correlation. The identification of regionally traceable sequence boundaries based on biostratigraphic age control is a first step towards a more accurate stratigraphic correlation and palaeogeographic interpretation of the Early to early Middle Triassic in NW Bulgaria.
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Chi Fru, Ernest, Nathalie P. Rodríguez, Camille A. Partin, Stefan V. Lalonde, Per Andersson, Dominik J. Weiss, Abderrazak El Albani, Ilia Rodushkin e Kurt O. Konhauser. "Cu isotopes in marine black shales record the Great Oxidation Event". Proceedings of the National Academy of Sciences 113, n. 18 (18 aprile 2016): 4941–46. http://dx.doi.org/10.1073/pnas.1523544113.
Testo completoAbstract (sommario):
The oxygenation of the atmosphere ∼2.45–2.32 billion years ago (Ga) is one of the most significant geological events to have affected Earth’s redox history. Our understanding of the timing and processes surrounding this key transition is largely dependent on the development of redox-sensitive proxies, many of which remain unexplored. Here we report a shift from negative to positive copper isotopic compositions (δ65CuERM-AE633) in organic carbon-rich shales spanning the period 2.66–2.08 Ga. We suggest that, before 2.3 Ga, a muted oxidative supply of weathering-derived copper enriched in 65Cu, along with the preferential removal of 65Cu by iron oxides, left seawater and marine biomass depleted in 65Cu but enriched in 63Cu. As banded iron formation deposition waned and continentally sourced Cu became more important, biomass sampled a dissolved Cu reservoir that was progressively less fractionated relative to the continental pool. This evolution toward heavy δ65Cu values coincides with a shift to negative sedimentary δ56Fe values and increased marine sulfate after the Great Oxidation Event (GOE), and is traceable through Phanerozoic shales to modern marine settings, where marine dissolved and sedimentary δ65Cu values are universally positive. Our finding of an important shift in sedimentary Cu isotope compositions across the GOE provides new insights into the Precambrian marine cycling of this critical micronutrient, and demonstrates the proxy potential for sedimentary Cu isotope compositions in the study of biogeochemical cycles and oceanic redox balance in the past.
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Fisher, Erich C., Hayley C. Cawthra, Irene Esteban, Antonieta Jerardino, Frank H. Neumann, Annette Oertle, Justin Pargeter et al. "Coastal occupation and foraging during the last glacial maximum and early Holocene at Waterfall Bluff, eastern Pondoland, South Africa". Quaternary Research 97 (14 maggio 2020): 1–41. http://dx.doi.org/10.1017/qua.2020.26.
Testo completoAbstract (sommario):
AbstractWaterfall Bluff is a rock shelter in eastern Pondoland, South Africa, adjacent to a narrow continental shelf that limited coastline movements across glacial/interglacial cycles. The archaeological deposits are characterized by well-preserved stratigraphy, faunal, and botanical remains alongside abundant stone artifacts and other materials. A comprehensive dating protocol consisting of 5 optically stimulated luminescence ages and 51 accelerator mass spectrometry 14C ages shows that the record of hunter-gatherer occupations at Waterfall Bluff persisted from the late Pleistocene to the Holocene, spanning the last glacial maximum and the transition from the Pleistocene to the Holocene. Here, we provide detailed descriptions about the sedimentary sequence, chronology, and characteristics of the archaeological deposits at Waterfall Bluff. Remains of marine mollusks and marine fish also show, for the first time, that coastal foraging was a component of some hunter-gatherer groups’ subsistence practices during glacial phases in the late Pleistocene. The presence of marine fish and shellfish further demonstrates that hunter-gatherers selectively targeted coastal resources from intertidal and estuarine habitats. Our results therefore underscore the idea that Pondoland's coastline remained a stable and predictable point on the landscape over the last glacial/interglacial transition being well positioned for hunter-gatherers to access resources from the nearby coastline, narrow continental shelf, and inland areas.
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SQUIER, ANGELA H., DOMINIC A. HODGSON e BRENDAN J. KEELY. "Evidence of late Quaternary environmental change in a continental east Antarctic lake from lacustrine sedimentary pigment distributions". Antarctic Science 17, n. 3 (17 agosto 2005): 361–76. http://dx.doi.org/10.1017/s0954102005002804.
Testo completoAbstract (sommario):
A sediment core from Progress Lake, one of the oldest lacustrine sequences in East Antarctica, contains distinct zones dating from a previous interglacial (most likely Marine Isotope Stage 5e, c. 125–115 kyr BP) and the present interglacial (Marine Isotope Stage 1), separated by a transition zone representing when the lake became sub-glacial. Profiles of fossil pigments, determined using high performance liquid chromatography and liquid chromatography-tandem mass spectrometry, show distinct differences in the photoautotrophic community during these two interglacial periods. The first was dominated by algae and purple phototrophic bacteria, with periods of photic zone euxinia indicated by pigments from anoxygenic phototrophic bacteria. Specific chlorophyll a derivatives reveal periods when grazing pressure impacted significantly on the phytoplankton community. The virtual absence of pigments in the transition zone reflects severe restriction of photoautotrophic activity, consistent with the lake having become sub-glacial. Retreat of snow and ice in the late Holocene (3345 14C yr BP) allowed establishment of a less diverse primary producer community, restricted to algae and cyanobacteria. Grazers were severely restricted and oxidative transformation was more important than during the previous interglacial. The pigment data provide a unique and detailed insight in to the evolution of the lake ecology over an interglacial-glacial-interglacial transition and strong evidence that the Marine Isotope Stage 5e interglacial in this region of coastal East Antarctica was several degrees warmer than at present.
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Sheldon, Nathan D., Stephen T. Grimes, Jerry J. Hooker, Margaret E. Collinson, Melanie J. Bugler, Michael T. Hren, Gregory D. Price e Paul A. Sutton. "Coupling of marine and continental oxygen isotope records during the Eocene-Oligocene transition". Geological Society of America Bulletin 128, n. 3-4 (14 settembre 2015): 502–10. http://dx.doi.org/10.1130/b31315.1.
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Monesi, Edoardo, Giovanni Muttoni, Giancarlo Scardia, Fabrizio Felletti, Fabio Bona, Benedetto Sala, Fabrizio Tremolada, Carlo Francou e Gianluca Raineri. "Insights on the opening of the Galerian mammal migration pathway from magnetostratigraphy of the Pleistocene marine-continental transition in the Arda River section (northern Italy)". Quaternary Research 86, n. 2 (settembre 2016): 220–31. http://dx.doi.org/10.1016/j.yqres.2016.07.006.
Testo completoAbstract (sommario):
AbstractWe investigated the magnetostratigraphy of the Arda River section (northern Italy) where the transition from marine to continental sedimentation occurring in the Po River basin during the Pleistocene is registered. Four magnetic polarity reversals were used to construct an age model of sedimentation aided by marine biostratigraphy and tied to a standard δ18O curve from the literature. The section spans from the Olduvai subchron (1.94-1.78 Ma) across the Jaramillo subchron (1.07-0.99 Ma) up to the Brunhes—Matuyama boundary (0.78 Ma). The onset of continental deposition occurred during marine isotope stage (MIS) 30 at ∼1.04 Ma. An association of Villafranchian and Early Galerian mammals, including Sus strozzii and Ursus dolinensis, has been found in the continental sediments dated to MIS 29-27 (∼0.99 Ma). Above follows a prominent fluvial conglomerate attributed to the first major low stand of the Pleistocene culminating with MIS 22 at ∼0.9 Ma during the late Early Pleistocene climate turnover (EPT). These and other data from the literature are used to reconstruct the onset of continental deposition in the greater Po basin and shed light on the opening of the migration pathway that brought far-traveled Galerian mammal immigrants to enter Europe for the first time during the EPT.
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Vilas-Boas, Margarida, Zélia Pereira, Simonetta Cirilli, Luís Vítor Duarte, Sérgio Luis Rodrigues Sêco e Paulo Fernandes. "Palynology and palynofacies studies in the lowermost Jurassic of the Lusitanian Basin (Pereiros Formation of the Silves Group), Portugal: evidence of the first transgressive episode". Acta Palaeobotanica 63, n. 2 (31 dicembre 2023): 129–50. http://dx.doi.org/10.35535/acpa-2023-0008.
Testo completoAbstract (sommario):
The Silves Group of the Lusitanian Basin in Portugal represents the initial infill of the continental rifting basins that formed during the breakup of northern Pangaea regions. Evaporites, especially halite, mark the transition from continental to marine settings and the beginning of the deposition in passive margin basins. This work presents the results of the palynostratigraphic and palynofacies analysis of two partial sections from the Pereiros Formation at the top of the Silves Group. The two sections are composed of sandstones, mudstones and dolostones interpreted as deposited in fluvial and lacustrine settings without apparent marine influence. The palynological content is diverse and wellpreserved, dating both sections to the early Hettangian (Lower Jurassic), indicated by the presence of spores Ischyosporites variegatus, Kraeuselisporites reissingeri, Porcellispora longdonensis and the pollen grains Perinopollenites elatoides and Pinuspollenites minimus. The palynological content of one of the sections (Lamas I) is noticeable by microforaminifera linings, suggesting evidence for a hitherto marine incursion at this age in the Silves Group stratigraphy. The beds that yielded the microforaminifera linings are interpreted as having been deposited in an estuarine-type setting, created by the first and short-lived marine transgressive event in the Lusitanian Basin during the early Hettangian.
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Domack, Eugene W., e P. T. Harris. "A new depositional model for ice shelves, based upon sediment cores from the Ross Sea and the MaC. Robertson shelf, Antarctica". Annals of Glaciology 27 (1998): 281–84. http://dx.doi.org/10.3189/1998aog27-1-281-284.
Testo completoAbstract (sommario):
We document the similarity of depositional facies occurring in gravity cores recovered from two disjunct regions of the Antarctic continental shelf: the Ross Sea and the MaC. Robertson shelf. The facies sequence model is represented in two cores, one collected during the 1995-1 cruise of the R/VNathaniel R. Palmer(core NBP95 TC-18) and the other collected by the RSVAurora Australisduring cruise 149 in 1995 (core 149 39GC38). Both cores show a succession of facies indicative of ice-shelf retreat during the late-Pleistocene to Holocene transition. Distinct lithofacies range in thickness from a few tens of cm to 1 m and consist of (from bottom to top) a coarse, granulated sandy mud; laminated silt and clay; structureless silly clay; poorly sorted sandy siliceous mud; and siliceous mud and ooze. These facies represent the passage of distinct depositional regimes across the core sites, including sub-ice shelf beneath a basal debris zone; sub-ice shell distal to a debris zone; calving-line transition; and open marine. This facies model represents an advance in our understanding of Glacial marine stratigraphy for the Antarctic continental shelf and will provide the basis for more realistic palaeoglacial reconstructions.
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DELMER, André, Michiel DUSAR e Bernard DELCAMBRE. "Upper Carboniferous lithostratigraphic units (Belgium)". Geologica Belgica 4, n. 1-2 (15 aprile 2002): 95–103. http://dx.doi.org/10.20341/gb.2014.045.
Testo completoAbstract (sommario):
Upper Carboniferous, Namurian to Westphalian coal measures in Belgium form part of the Variscan Foredeep in northwestern Europe, with maximum preserved thickness over 3500 m. Despite post-depositional separation of the Wallonian and Campine coal basins by the Brabant Massif and different tectonic styles, a common lithostratigraphic nomenclature can be applied. The stratigraphic subdivision is based on the distinction between a carbonate-dominated marine "Dinantian" and siliciclastic continental, coal-bearing "Silesian". Basal units testify of a marine transgression, locally continuous with Dinantian carbonate sedimentation, elsewhere drowning an emergent karst landscape. Progressive advance and uplift of the Variscan orogenic belt caused rapid subsidence in the foreland and transition from prodelta mudstones to upper alluvial plain conglomerates, with fewer marine incursions. The Belgian Coal Measures Group encompasses this complete tectonically-driven sedimentary succession.
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Deconinck, J. F., A. Strasser e P. Debrabant. "Formation of illitic minerals at surface temperatures in Purbeckian sediments (Lower Berriasian, Swiss and French Jura)". Clay Minerals 23, n. 1 (marzo 1988): 91–103. http://dx.doi.org/10.1180/claymin.1988.023.1.09.
Testo completoAbstract (sommario):
AbstractThe clay-mineralogical assemblages of Purbeckian carbonate sediments of the Swiss and French Jura Mountains are often composed of illite and interstratified illite-smectite. These illitic minerals occur mainly in thin layers of green marls which show evidence of subaerial exposure and mark the top of shallowing-upward sequences. X-ray diffraction, chemical and thermal analyses coupled with transmission electron microscopy suggest that the Purbeckian illitic minerals replaced smectite in intermediate continental-marine environments. The transition from smectite to illite and interstratified illite-smectite probably resulted from repeated cycles of wetting by marine waters and subsequent drying in hypersaline environments, under a hot Purbeckian climate.
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Olsen, Paul E., Dennis V. Kent e Jessica H. Whiteside. "Implications of the Newark Supergroup-based astrochronology and geomagnetic polarity time scale (Newark-APTS) for the tempo and mode of the early diversification of the Dinosauria". Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101, n. 3-4 (settembre 2010): 201–29. http://dx.doi.org/10.1017/s1755691011020032.
Testo completoAbstract (sommario):
ABSTRACTThe Newark-APTS established a high-resolution framework for the Late Triassic and Early Jurassic. Palaeomagnetic polarity correlations to marine sections show that stage-level correlations of continental sequences were off by as much as 10 million years. New U–Pb ages show the new correlations and the Newark basin astrochronology to be accurate. Correlation of Newark-APTS to the Chinle Formation/Dockum Group, Glen Canyon Group, Fleming Fjord Formation and Ischigualasto Formation led to the following conclusions: (1) there are no unequivocal Carnian-age dinosaurs; (2) the Norian Age was characterised by a slowly increasing saurischian diversity but no unequivocal ornithischians; (3) there was profound Norian and Rhaetian continental provinciality; (4) the classic Chinle-, Germanic- and Los Colorados-type assemblages may have persisted to the close of the Rhaetian; (5) the distinct genus-level biotic transition traditionally correlated with the marine Carnian–Norian is in fact mid-Norian in age and within published error of the Manicouagan impact; (6) the end-Triassic marine and continental extinctions as seen in eastern North America were contemporaneous; and (7) compared to Triassic communities, Hettangian and Sinemurian age terrestrial communities were nearly globally homogenous and of low diversity. Consequently, the complex emerging picture of dinosaur diversification demands biostratigraphically-independent geochronologies in each of the faunally-important regions.
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Nieto, Luis M., José Miguel Molina, Pedro Alejandro Ruiz-Ortiz, José Manuel Castro, Matías Reolid e Ginés A. de Gea. "Palustrine Sediments between Two Isolated Shallow Carbonate Platforms (Aptian–Albian Transition, Prebetic of Jaén, South Spain)". Minerals 12, n. 2 (20 gennaio 2022): 116. http://dx.doi.org/10.3390/min12020116.
Testo completoAbstract (sommario):
During the Aptian-Albian transition, an extensional phase of the Central Atlantic which affected the Prebetic carbonate platform (South Iberian Continental Margin, northwestern margin of the Tethys) occurred. A graben morphology was developed in the platform coeval to a relative sea level fall. As a consequence, palustrine facies characterized by rhizoliths and some pond deposits of black lutites were established. Over these palustrine sediments, a second shallow carbonate platform was built during the early Albian. However, this process was not abrupt, as several levels with orbitolines and rudists were deposited intercalated between the continental facies, recording the transition to a new shallow marine carbonate platform developped during the Early Albian. The presence of these continental palustrine sediments between two episodes of shallow carbonate platform is described for the first time in the Prebetic. The demise of an upper Aptian isolated shallow carbonate platform drove to the deposition of these palustrine sediments in an extensional tectonic regime.
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Szameitat, Luizemara Soares Alves, Francisco José Fonseca Ferreira, Gianreto Manatschal e Monica da Costa Pereira Lavalle Helbron. "EVIDENCE OF MANTLE INHERITANCE ON THE ULTRA-DISTAL WESTERN IBERIAN MARGIN FROM TRANSFORMED TOTAL MAGNETIC ANOMALY". Revista Brasileira de Geofísica 36, n. 3 (6 settembre 2018): 1. http://dx.doi.org/10.22564/rbgf.v36i3.1957.
Testo completoAbstract (sommario):
ABSTRACT. Inheritance on continental lithosphere is considered as an important aspect on passive margins, since they may control magmatic budget and strain evolution during rifting and lithospheric breakup. On the distal Western Iberian margin, the transition to a steady state oceanic crust was little sampled and less investigated, in comparison to the more proximal parts near to the continental edge. In this work, we use marine magnetic data to analyze some aspects of the transition between the zone of exhumed continental mantle (ZECM) and the unequivocal oceanic crust, using transformed magnetic data. We observe that the end of the ZECM presents some straight magnetic features, especially at the eastern limit of the J anomaly. These magnetic lineaments are consistent with Early Cretaceous flow lines of the Iberian Plate. Straight structures are not expected in a newly formed oceanic lithosphere. Instead, it seems to be controlled by mantle inheritance. These straight magnetic features may indicate basement inheritance controlling magmatic insertions at the beginning of the oceanic crust formation.Keywords: Iberia, Magnetometry, Ocean-Continent Transition, Inherited Structures, Magma-Poor Margin. RESUMO. Estruturas herdadas na litosfera continental são um aspecto importante em margens passivas, pois poderão condicionar a entrada de magma e a evolução da deformação durante o rifteamento e quebra litosférica. Na porção distal da Margem Ibérica Ocidental, a transição da crosta continental até a crosta oceânica bem estabelecida possui menos dados e é menos investigada em comparação com a porção junto do limite de crosta continental. Neste trabalho, usamos dados magnéticos marinhos para analisar alguns aspectos entre a zona de exumação mantélica e a crosta oceânica inequívoca, através de dados magnéticos transformados. Observa-se que o final da zona de exumação mantélica apresenta algumas feições retilíneas, especialmente no limite leste da Anomalia J. Estes lineamentos magnéticos estão em conformidade com linhas de fluxo mesozoicas da Placa Ibérica. Feições retilíneas não são esperadas em uma litosfera oceânica neoformada. Ao contrário, estas aparentam ser um controle dado por estruturas pretéritas do manto. Portanto, estas feições magnéticas retilíneas sugerem uma herança do embasamento continental controlando as intrusões magmáticas no início da formação da crosta oceânica.Palavras-chave: Ibéria, Magnetometria, Transição Continente-Oceano, Estruturas Herdadas, Margem Pobre em Magma.
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Occhietti, Serge, Sanda Balescu, Michel Lamothe, Martine Clet, Thomas Cronin, Pierre Ferland e Pierre Pichet. "Late Stage 5 Glacio-isostatic Sea in the St. Lawrence Valley, Canada and United States". Quaternary Research 45, n. 2 (marzo 1996): 128–37. http://dx.doi.org/10.1006/qres.1996.0015.
Testo completoAbstract (sommario):
AbstractAlthough post-glacial marine sediments of late Wisconsinan and early Holocene age are common in eastern Canada and the northeastern United States, remnants of older Pleistocene marine sediments are scarce. A fossiliferous marine clay that predates the classical Wisconsinan was recently discovered in the St. Lawrence Valley. A dominantly estuarine environment is inferred from the geochemistry of the shells (δ18O = −7.1) and from benthic foraminifer and ostracode assemblages. The clay indicates a marine invasion (Cartier Sea) shallower and probably shorter than that during the upper late Wisconsinan Champlain Sea episode (12,000–9,500 yr B.P.). The pollen content shows that regional vegetation during the marine episode began as open tundra, then became a Betula and Alnus crispa forest, reached a climatic optimum with Quercus, Corylus, and Abies, and concluded as a Pinus/Picea boreal forest. A corrected infrared stimulated luminescence age of 98,000 ± 9000 yr is compatible with the epimerization ratio of shells. The Cartier Sea resulted from a post-glacial glacio-isostatic marine invasion in the St. Lawrence lowlands. It probably occurred during late stage 5 and is tentatively assigned to the transition of oxygen isotope substages 5b/5a. This marine episode dates to stage 5 of the preceding continental glacier which extended to middle latitudes in NE America.
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Nittrouer, Charles A., David J. DeMaster, Steven A. Kuehl, Alberto G. Figueiredo, Richard W. Sternberg, L. Ercilio C. Faria, Odete M. Silveira et al. "Amazon Sediment Transport and Accumulation Along the Continuum of Mixed Fluvial and Marine Processes". Annual Review of Marine Science 13, n. 1 (3 gennaio 2021): 501–36. http://dx.doi.org/10.1146/annurev-marine-010816-060457.
Testo completoAbstract (sommario):
Sediment transfer from land to ocean begins in coastal settings and, for large rivers such as the Amazon, has dramatic impacts over thousands of kilometers covering diverse environmental conditions. In the relatively natural Amazon tidal river, combinations of fluvial and marine processes transition toward the ocean, affecting the transport and accumulation of sediment in floodplains and tributary mouths. The enormous discharge of Amazon fresh water causes estuarine processes to occur on the continental shelf, where much sediment accumulation creates a large clinoform structure and where additional sediment accumulates along its shoreward boundary in tidal flats and mangrove forests. Some remaining Amazon sediment is transported beyond the region near the river mouth, and fluvial forces on it diminish. Numerous perturbations to Amazon sediment transport and accumulation occur naturally, but human actions will likely dominate future change, and now is the time to document, understand, and mitigate their impacts.
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Ramos, Amparo. "Transition from alluvial to coastal deposits (Permian–Triassic) on the Island of Mallorca, western Mediterranean". Geological Magazine 132, n. 4 (luglio 1995): 435–47. http://dx.doi.org/10.1017/s001675680002149x.
Testo completoAbstract (sommario):
AbstractNon-marine redbeds (Permian and Triassic) in the island of Mallorca consist of a 0.4 km-thick alluvial succession that passes upwards into siliciclastic–carbonate coastal deposits. Tectonics and sealevel changes have been the main influences in their evolution. Low in this succession (the ‘Areniscas y lutitas de Port des Canonge’ unit) sandstone sheets with lateral accretion surfaces (macroscale inclined strata) and mudstones with frequent exposure structures are interpreted as the products of a sinuous alluvial system and floodplain. Climatic fluctuations are considered to be responsible for some significant up-section changes in the evolution of the alluvial deposits. Low-angle or horizontally stratified sandy units, interpreted as the result of flash floods, alternate upwards with point-bar deposits in the ‘Areniscas de Asá’. The hydrological response to minor climatic changes was evidently nearly instantaneous due to the lack of significant vegetation cover.During accumulation of mudstones and sandstones of the overlying ‘Lutitas y Areniscas de Son Serralta’ unit, the interpreted environment of deposition changed from a distal braidplain, mainly constructed by superposition of sandy bedforms with straight or linguoid crestlines in low sinuosity river channels, into a coastal plain with evidence of both continental and marine influences. The overlying carbonate platform (Muschelkalk) marks the development of a more homogeneous marine environment resulting from the Tethyan transgressive event that affected the whole peri-Mediterranean realm during the Anisian (middle Triassic).
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van der Ploeg, Robin, Bernard P. Boudreau, Jack J. Middelburg e Appy Sluijs. "Cenozoic carbonate burial along continental margins". Geology 47, n. 11 (6 settembre 2019): 1025–28. http://dx.doi.org/10.1130/g46418.1.
Testo completoAbstract (sommario):
Abstract Marine carbonate burial represents the largest long-term carbon sink at Earth’s surface, occurring in both deep-sea (pelagic) environments and shallower waters along continental margins. The distribution of carbonate accumulation has varied over geological history and impacts the carbon cycle and ocean chemistry, but it remains difficult to quantitatively constrain. Here, we reconstruct Cenozoic carbonate burial along continental margins using a mass balance for global carbonate alkalinity, which integrates independent estimates for continental weathering and pelagic carbonate burial. Our results indicate that major changes in marginal carbonate burial were associated with important climate and sea-level change events, including the Eocene-Oligocene transition (ca. 34 Ma), the Oligocene-Miocene boundary Mi-1 glaciation (ca. 23 Ma), and the middle Miocene climate transition (ca. 14 Ma). In addition, we find that a major increase in continental weathering from ca. 10 Ma to the present may have driven a concomitant increase in pelagic carbonate burial. Together, our results show that changes in global climate, sea level, and continental weathering have all impacted carbonate burial over the Cenozoic, but the relative importance of these processes may have varied through time.
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Wu, Yuyang, Jinnan Tong, Thomas J. Algeo, Daoliang Chu, Ying Cui, Huyue Song, Wenchao Shu e Yong Du. "Organic carbon isotopes in terrestrial Permian-Triassic boundary sections of North China: Implications for global carbon cycle perturbations". GSA Bulletin 132, n. 5-6 (16 ottobre 2019): 1106–18. http://dx.doi.org/10.1130/b35228.1.
Testo completoAbstract (sommario):
Abstract The end-Permian mass extinction (ca. 252 Ma) represents the most severe biotic crisis of the Phanerozoic, and it was accompanied by profound environmental perturbations, especially to the global carbon cycle, as indicated by sharp negative carbon isotope excursions (CIE) in both carbonates (δ13Ccarb) and organic matter (δ13Corg). To date, carbon isotope records are mostly from marine Permian-Triassic transitional sequences with relatively few high-resolution carbon isotope profiles having been generated for terrestrial facies. Terrestrial Permian-Triassic sequences suitable for high-resolution carbon isotope study are rare globally and are difficult to correlate with better-studied marine sequences. However, carbon isotope records from continental facies are essential to a full understanding of global carbon cycle changes during the Permian-Triassic transition. Here, we present bulk δ13Corg profiles for three terrestrial sections in North China representing Permian-Triassic transitional beds. These profiles exhibit similar patterns of secular variation defining three stages: (1) a pre-CIE interval, (2) a CIE interval, characterized by a rapid negative shift of 1.7‰–2.2‰ within the middle part of the Sunjiagou Formation, and (3) a post-CIE interval. The similarity of the CIE in all three study sections facilitates correlations among them, and its presence in the Permian-Triassic transitional beds suggests that it is equivalent to the negative CIE at the Permian-Triassic boundary in the Meishan global stratotype section and point (GSSP) and in coeval marine and terrestrial sections globally. The end-Permian CIE was probably triggered by a massive release of 13C-depleted carbon from volcanogenic sources leading to elevated atmospheric pCO2, although oceanic sources of CO2 cannot be ruled out at present.
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Ng, Christiano, Cristina Silveira Vega e Maria da Saudade Araujo Santos Maranhão. "Mixed carbonate-siliciclastic microfacies from Permian deposits of Western Gondwana: Evidence of gradual marine to continental transition or episodes of marine transgression?" Sedimentary Geology 390 (luglio 2019): 62–82. http://dx.doi.org/10.1016/j.sedgeo.2019.07.006.
Testo completo
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Bender, Adrian M., Richard O. Lease, Lee B. Corbett, Paul R. Bierman, Marc W. Caffee, James V. Jones e Doug Kreiner. "Yukon River incision drove organic carbon burial in the Bering Sea during global climate changes at 2.6 and 1 Ma". Earth Surface Dynamics 10, n. 5 (28 ottobre 2022): 1041–53. http://dx.doi.org/10.5194/esurf-10-1041-2022.
Testo completoAbstract (sommario):
Abstract. River erosion affects the carbon cycle and thus climate by exporting terrigenous carbon to seafloor sediment and by nourishing CO2-consuming marine life. The Yukon River–Bering Sea system preserves rare source-to-sink records of these processes across profound changes in global climate during the past 5 million years (Ma). Here, we expand the terrestrial erosion record by dating terraces along the Charley River, Alaska, and explore linkages among previously published Yukon River tributary incision chronologies and Bering Sea sedimentation. Cosmogenic 26Al/10Be isochron burial ages of Charley River terraces match previously documented central Yukon River tributary incision from 2.6 to 1.6 Ma during Pliocene–Pleistocene glacial expansion, and at 1.1 Ma during the 1.2–0.7 Ma Middle Pleistocene climate transition. Bering Sea sediments preserve 2–4-fold rate increases of Yukon River-derived continental detritus, terrestrial and marine organic carbon, and silicate microfossil deposition at 2.6–2.1 and 1.1–0.8 Ma. These tightly coupled records demonstrate elevated terrigenous nutrient and carbon export and concomitant Bering Sea productivity in response to climate-forced Yukon River incision. Carbon burial related to accelerated terrestrial erosion may contribute to CO2 drawdown across the Pliocene–Pleistocene and Middle Pleistocene climate transitions observed in many proxy records worldwide.
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Herrero-Hernández, Antonio, Fernando Gómez-Fernández e Francisco Javier López-Moro. "Upper Cretaceous marine-continental transition (Leonese Area, NW Spain) defined from integrated outcrop and seismic stratigraphy". Geological Journal 50, n. 1 (8 agosto 2013): 39–55. http://dx.doi.org/10.1002/gj.2525.
Testo completo
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Morales, Ethel, Hung Kiang Chang, Matías Soto, Gerardo Veroslavsky, Bruno Conti, Héctor de Santa Ana e Fernando Santos Corrêa. "Speculative petroleum systems of the Punta del Este Basin (offshore Uruguay)". Brazilian Journal of Geology 47, n. 4 (dicembre 2017): 645–56. http://dx.doi.org/10.1590/2317-4889201720170078.
Testo completoAbstract (sommario):
ABSTRACT: The Uruguayan continental margin was generated as the result of the breakup of Gondwana and, later, the opening of the South Atlantic Ocean, which began in the Jurassic. Three major areas of Meso-Cenozoic sedimentation are located in the Uruguayan offshore: the Punta del Este Basin, the southernmost sector of the Pelotas Basin and the Oriental del Plata Basin. These basins share the classical stages of tectono-sedimentary evolution of the other Atlantic basins, including the prerift (Paleozoic), rift (Jurassic-Early Cretaceous), transition (Barremian-Aptian) and postrift (Aptian-present) phases. Based on the analysis of basin evolution through seismic sections and well data as well as on the establishment of analogies with productive Atlantic basins, four speculative petroleum systems are proposed for the Punta del Este Basin: 1) Marine petroleum system of the prerift stage: Devonian/Permian-Devonian/Permian(?), 2) Lacustrine petroleum system of the synrift stage: Neocomian-Neocomian(?), 3) Marine petroleum system of the Cretaceous postrift: Aptian-Late Cretaceous(?), 4) Marine petroleum system of the Cenozoic postrift: Paleocene-Paleogene/Neogene(?).
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Amine, H., J. Halwani, E. Gomez e F. Merhabi. "Study of polycyclic aromatic hydrocarbon contamination in sediments and northern waters Lebanon: Rivers, transition zones and port sites." Lebanese Science Journal 19, n. 3 (27 dicembre 2018): 343–72. http://dx.doi.org/10.22453/lsj-019.3.343372.
Testo completoAbstract (sommario):
Contamination of the marine environment is associated with continental activities, marine activities and accidental spills. Providing answers to the origin of the contamination ofthe aquatic environment by PAHsis an objective of the present work. The originality of this work is to study pollutants in two types of matrix (water and sediments) during2 seasons (dry and wet) for an environmental monitoringof 6 years. This study provides a more complete overview of the state of contaminationin three coastal rivers, their transition zones and harborsin the Eastern Mediterranean following the Jiyyeh oil spill in 2006.Contaminantsconcentrations wereexpressed asthe sum of the 16 PAHs classified as prority substances by the United StatesEnvironmental Protection Agency(US-EPA). Overall,contamination was noted for all the analyzedsites. Oil spill seem to be one of the main sources of pollution in the area, as the highest levels of PAH(> 9000 ng.g-1s.w&> 8000 ng.L-1) were reported in the coastal environment of the three rivers and harbors.High levels of PAHswere also observed in rivers transitional zones, revealing the importance of terrestrial inputs (untreated wastewater discharge, leachate, solid wastes, etc.).Comparing the PAHsconcentrations measured in the sediments of the sitesanalyzed with the empirical sediment quality criteria "SQG" for the support of the general assessment of sediment toxicity, we can notice that some individual PAHand their sum can present a significant ecotoxicological risk to aquatic organisms. Further research through monitoring campaigns and toxicity tests is encouraged, as the exposure of the resident aquatic organisms and human population to these chemicals might be expected to increase over the years.
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Zanchetta, Giovanni, Eleonora Regattieri, Biagio Giaccio, Bernd Wagner, Roberto Sulpizio, Alex Francke, Hendrik Vogel et al. "Aligning and synchronization of MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: implications for DEEP core chronology". Biogeosciences 13, n. 9 (11 maggio 2016): 2757–68. http://dx.doi.org/10.5194/bg-13-2757-2016.
Testo completoAbstract (sommario):
Abstract. The DEEP site sediment sequence obtained during the ICDP SCOPSCO project at Lake Ohrid was dated using tephrostratigraphic information, cyclostratigraphy, and orbital tuning through the marine isotope stages (MIS) 15-1. Although this approach is suitable for the generation of a general chronological framework of the long succession, it is insufficient to resolve more detailed palaeoclimatological questions, such as leads and lags of climate events between marine and terrestrial records or between different regions. Here, we demonstrate how the use of different tie points can affect cyclostratigraphy and orbital tuning for the period between ca. 140 and 70 ka and how the results can be correlated with directly/indirectly radiometrically dated Mediterranean marine and continental proxy records. The alternative age model presented here shows consistent differences with that initially proposed by Francke et al. (2015) for the same interval, in particular at the level of the MIS6-5e transition. According to this new age model, different proxies from the DEEP site sediment record support an increase of temperatures between glacial to interglacial conditions, which is almost synchronous with a rapid increase in sea surface temperature observed in the western Mediterranean. The results show how a detailed study of independent chronological tie points is important to align different records and to highlight asynchronisms of climate events. Moreover, Francke et al. (2016) have incorporated the new chronology proposed for tephra OH-DP-0499 in the final DEEP age model. This has reduced substantially the chronological discrepancies between the DEEP site age model and the model proposed here for the last glacial-interglacial transition.
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Schulz, Hartmut, Kay-Christian Emeis, Helmut Erlenkeuser, Ulrich von Rad e Christian Rolf. "The Toba Volcanic Event and Interstadial/Stadial Climates at the Marine Isotopic Stage 5 to 4 Transition in the Northern Indian Ocean". Quaternary Research 57, n. 1 (gennaio 2002): 22–31. http://dx.doi.org/10.1006/qres.2001.2291.
Testo completoAbstract (sommario):
AbstractThe Toba volcanic event, one of the largest eruptions during the Quaternary, is documented in marine sediment cores from the northeastern Arabian Sea. On the crest of the Murray Ridge and along the western Indian continental margin, we detected distinct concentration spikes and ash layers of rhyolithic volcanic shards near the marine isotope stage 5–4 boundary with the chemical composition of the “Youngest Toba Tuff.” Time series of the Uk′37-alkenone index, planktic foraminiferal species, magnetic susceptibility, and sediment accumulation rates from this interval show that the Toba event occurred between two warm periods lasting a few millennia. Using Toba as an instantaneous stratigraphic marker for correlation between the marine- and ice-core chronostratigraphies, these two Arabian Sea climatic events correspond to Greenland interstadials 20 and 19, respectively. Our data sets thus depict substantial interstadial/stadial fluctuations in sea-surface temperature and surface-water productivity. We show that variable terrigenous (eolian) sediment supply played a crucial role in transferring and preserving the productivity signal in the sediment record. Within the provided stratigraphic resolution of several decades to centennials, none of these proxies shows a particular impact of the Toba eruption. However, our results are additional support that Toba, despite its exceptional magnitude, had only a minor impact on the evolution of low-latitude monsoonal climate on centennial to millennial time scales.
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Ma, Yuanzhen, Meng Wang, Ruying Ma, Jiamin Li, Asiya Bake e Yadi Shan. "Micropore Characteristics and Gas-Bearing Characteristics of Marine-Continental Transitional Shale Reservoirs in the East Margin of Ordos Basin". Adsorption Science & Technology 2021 (22 maggio 2021): 1–15. http://dx.doi.org/10.1155/2021/5593245.
Testo completoAbstract (sommario):
In order to deeply study the exploration potential of Carboniferous-Permian marine-continental transitional shale reservoirs in the Ordos Basin, the shale samples from well Y1 in the central-southern part of the Hedong Coalfield were used as the research object. The organic geochemical test, scanning electron microscope, X-ray diffraction, and high pressure mercury injection and low-temperature nitrogen adsorption experiments have studied the microscopic characteristics and gas content characteristics of shale reservoirs. The results show that the organic matter type of the sample is type III; the TOC content ranges from 0.28% to 16.87%, with an average of 2.15%; R o is from 2.45% to 3.36%, with an average value of 2.86%; the shale pores in the study area are well developed, containing more organic pores and intergranular pores of clay minerals. Based on the two-dimensional SEM image fractal theory to study different types of pores, the fractal dimension of shale pore fracture morphology is between 2.34 and 2.50, and the heterogeneity is moderate. The high-pressure mercury intrusion experiment characterizes the pore size distribution of shale macropores and transition pores. The pore diameters are mostly nm-scale. Transition pores are the main pores of the shale in the study area. Based on the characteristics of the pore structure, the adsorption capacity and gas content of CH4 in shale reservoir were analyzed by methane isothermal adsorption and gas content experiments. The results showed that the pore volume and specific surface area were positively correlated with clay mineral content, TOC, and RO, but negatively correlated with the quartz content. In clay minerals and brittle minerals, pore volume and specific surface area are positively correlated with illite content and negatively correlated with the quartz and kaolinite content. The measured total gas content and desorbed gas content are significantly positively correlated with TOC, but are weakly positively correlated with the quartz and illite content. This study finely characterizes the physical properties, micropore characteristics, gas-bearing characteristics, and influencing factors of shale reservoirs, which has certain theoretical guiding significance for the research and development of coal-measure shale in the Ordos Basin.
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Shczepetov, S. V., A. B. Herman e Е. В. Бугдаева. "Phytostratigraphic Scale of the Non-Marine Cretaceous of North-Eastern Russia: An Attempt to Create and Results". Стратиграфия 31, n. 4 (1 luglio 2023): 87–102. http://dx.doi.org/10.31857/s0869592x2304004x.
Testo completoAbstract (sommario):
In the early 1970s, palaeobotanist V.A. Samylina published her concept of stratofloras – a stratigraphic scale of the Cretaceous non-marine deposits of North-Eastern Asia based on plant megafossils. It was based on data on the evolution of the systematic composition of plant communities during the transition from the Mesophyte to Cenophyte. Since the detail of this scale was not inferior to that of marine deposits, it almost immediately began to be used to determine the age and correlation of continental deposits in the region. The paper considers changes in ideas on the development of the regional flora in the process of receiving new data. It is shown that it is impossible to create a single regional scale, since the palaeolandscape environments in this territory were different. The precision of the scales for parts of the region with the same palaeolandscape setting appeares to be lower than the stages of the General Stratigraphic Scale.
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Chaaou, Ismail, Lahcen Kabiri e Badre Essafraoui. "Lithostratigraphic and Paleoenvironmental Characterization of the Senonian Series of the Errachidia-Boudenib-Erfoud Basin, South-East Morocco". Iraqi Geological Journal 56, n. 2D (31 ottobre 2023): 76–93. http://dx.doi.org/10.46717/igj.56.2d.6ms-2023-10-12.
Testo completoAbstract (sommario):
Six lithostratigraphic sections distributed in different parts of the Errachidia-Boudenib-Erfoud basin (SE Morocco) were surveyed bed by bed and sampled in order to study stratigraphy, analyzed the facies, and characterized the depositional environment of the Senonian series. This study shows that this series is mainly constituted of three lithostratigraphic units: the first one is mixed, attesting to an alluvial plain environment disturbed by marine incursions at the base. The second is dominated by "kerkoub" sandstone bars intercalated by silt-clay intervals, reflecting a floodplain environment. The third is dominated by gypsum versicolored facies, marking an evaporitic playa environment. The correlation of the studied sections shows that the Senonian sedimentary prism opens progressively to the East. The series ends with Tertiary deposition: western marine carbonates and eastern continental conglomerates. The non-deposition of these faces in the center of the basin could be the result of the presence of a paleorelief at the Tinejdad-Goulmima transition.
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Stori, L., J. B. Diez, M. Juncal, R. De la Horra, V. Borruel-Abadía, J. Martín-Chivelet, J. F. Barrenechea, J. López-Gómez e A. Ronchi. "The Anisian continental-marine transition in Sardinia (Italy): state of the art, new palynological data and regional chronostratigraphic correlation". Journal of Iberian Geology 48, n. 1 (16 febbraio 2022): 79–106. http://dx.doi.org/10.1007/s41513-021-00184-x.
Testo completoAbstract (sommario):
AbstractThe scarce evidence of paleontological records between the upper Permian and the Anisian (Middle Triassic) of Western Europe could reflect (1) large stratigraphic gaps in the continental successions and/or (2) the persistence of disturbed conditions after the Permian–Triassic Boundary extinction event and the succession of ecological crises that occurred during the Early Triassic. In this context, the study of palynological associations, integrated with the stratigraphical and sedimentological data, plays a key role in dating and correlating the successions of the Western European domain and improves our understanding of environmental and paleoclimatic conditions. In some cases, pre-Anisian paleontological evidence is lacking, as in Sardinia (Italy), where a long gap encompasses the middle Permian (pars) to late Lower Triassic successions. Although fragmented and disseminated, the continental Lower-Middle Triassic sedimentary successions (Buntsandstein) of Sardinia have proved crucial to our understanding of the evolution of the southern edge of the Paleo-Europe and the different timings of the Tethys transgression (Muschelkalk facies) in some of these areas. Various paleogeographic reconstructions were attempted in previous works, without providing any consensus on the precise position of Sardinia and its surrounding seaways in the Western Tethys domain during this time interval. At present, the configuration and distribution of the subsiding and emerging landmasses and the temporal development of the transgressions of the Western Tethys during the Middle Triassic remain unclear. This work focuses on the stratigraphical, sedimentological and palynological aspects of three Middle Triassic continental-marine sedimentary successions in Sardinia, with particular attention to the analysis of the palynological associations sampled there, and it also provides a detailed review of all previous palynological publications on the Sardinian Anisian. The studied successions are: Su Passu Malu section (Campumari, SW Sardinia), Arcu is Fronestas section and Escalaplano section (Escalaplano, Central Sardinia). These sections were also correlated to other significant sections in the SW (Scivu Is Arenas) and NW (Nurra) parts of the island.
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OLIVIER, NICOLAS, ARNAUD BRAYARD, EMMANUEL FARA, KEVIN G. BYLUND, JAMES F. JENKS, EMMANUELLE VENNIN, DANIEL A. STEPHEN e GILLES ESCARGUEL. "Smithian shoreline migrations and depositional settings in Timpoweap Canyon (Early Triassic, Utah, USA)". Geological Magazine 151, n. 5 (17 gennaio 2014): 938–55. http://dx.doi.org/10.1017/s0016756813000988.
Testo completoAbstract (sommario):
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 long-term sea-level rise that is identified worldwide after the Permian–Triassic boundary. The fenestral-microbial sediments were deposited at the transition between continental settings (with terrigenous deposits) and shallow subtidal marine environments (with bioturbated and bioclastic limestones). Such a lateral zonation questions the interpretation of microbial deposits as anachronistic and disaster facies in the western USA basin. The depositional setting may have triggered the distribution of microbial deposits and contemporaneous marine biota. The fenestral-microbial unit is truncated by an erosional surface reflecting a drop in relative sea level at the scale of a medium depositional sequence. The local inherited topography allowed the recording of small-scale sequences characterized by clinoforms and short-distance lateral facies changes. Stratal stacking pattern and surface geometries allow the reconstruction of relative sea-level fluctuations and tracking of shoreline migrations. The stacking pattern of these small-scale sequences and the amplitude of corresponding high-frequency sea-level fluctuations are consistent with climatic control. Large- and medium-scale sequences suggest a regional tectonic control.
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Barroso, Tarcyana Câmara, Paulo Roberto Silva Pessoa, Antônio Rodrigues Ximenes Neto e Jáder Onofre de Morais. "CARACTERIZAÇÃO DOS ASPECTOS SEDIMENTOLÓGICOS E GRANULOMÉTRICOS ASSOCIADOS À FOZ DO RIO COREAÚ – CE, BRASIL". Revista da Casa da Geografia de Sobral (RCGS) 21, n. 2 (30 settembre 2019): 265–78. http://dx.doi.org/10.35701/rcgs.v21n2.499.
Testo completoAbstract (sommario):
A zona costeira é um ambiente dinâmico de transição que apresenta uma interface entre os sistemas continentais, marinhos e atmosféricos. A área de estudo se localiza no município de Camocim-CE na região da foz do rio Coreaú, compreendendo também áreas adjacentes em ambas às margens. O objetivo deste trabalho foi analisar os aspectos deposicionais a partir da granulometria dos sistemas ambientais costeiros, para caracterização sedimentológica das principais unidades geomorfológicas da foz do rio Coreaú. Em campo foram coletadas amostras superficiais de três sistemas litorâneos – Duna; Estirâncio e Estuário. A sedimentação da área estudada é controlada pela influência marinha, com a predominância de areias quartzosas muito fina no subsistema duna e estuário. No estirâncio defronte a falésia costeira na margem esquerda houve predominância de cascalho fino. Já o estirâncio da Ilha do amor apresentou areia grossa e muito fina no estirâncio superior e inferior, respectivamente.Palavras-chave: Rio Coreaú; Sedimentologia; Granulometria. ABSTRACTThe coastal zone is a dynamic transition between the continental, marine, and atmospheric systems. The study area is located in the Coreaú river mouth, Camocim-CE. The aim was to characterize the depositional aspects from the grain size and sedimentology of coastal environmental systems to characterize the main geomorphological units. It was collected superficial samples of three coastal systems - Dune; Foreshore and Estuary. The sedimentation is controlled by the marine influence, with the predominance of very fine-grained quartz sands in the dune and estuary. In the foreshore of the coastal cliff at the left margin there was a predominance of fine gravel, as well as coarse and very fine sand in the upper and lower foreshore, respectively (Ilha do Amor).Keywords: Coreaú River; Sedimentology; Grain Size. RESUMEN La zona costera es un entorno dinámico de transición que presenta una interfaz entre los sistemas continentales, marinos y atmosféricos. La zona de investigación está ubicada en la ciudad de Camocim-CE, en la desembocadura del río Coreaú, y además comprende zonas adyacentes en ambas márgenes. El objetivo de la investigación fue caracterizar los aspectos deposicionales desde la granulometría de los sistemas ambientales costeros presentes en la zona, para caracterización sedimentario de las principales unidades geomorfológicas de la desembocadura del río Coreaú. La continuación se recogieron muestras superficiales de tres sistemas litorales – Duna; estrán y estuario. La sedimentación del área está controlada por la influencia marina, con la predominancia de arenas cuarzo muy fina en el subsistema duna y estuario. En la zona intermareale frente al acantilado costero en la margen izquierda hubo predominancia de arena fina. Ya en la zona intermareale de la Ilha do Amor presentó arena gruesa y muy fina en la estrán superior e inferior, respectivamente.Palabras clave: Río Coreaú; sedimentología; granulometría.
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Smith, D. B., J. C. M. Taylor, R. S. Arthurton, M. E. Brookfield e K. W. Glennie. "Permian". Geological Society, London, Memoirs 13, n. 1 (1992): 87–96. http://dx.doi.org/10.1144/gsl.mem.1992.013.01.10.
Testo completoAbstract (sommario):
AbstractPermian strata in the British Isles crop out mainly in northern and central England but are extensive in the subsurface both on land and in several adjoining offshore areas. Their base is defined as in Smith et al. (1974) and their top is within red beds, overlying the Zechstein evaporites.We emphasize that both the base and the top of the nominally Permian rocks lie in continental strata almost devoid of stratigraphically useful fossils and that, accordingly, these boundaries are only doubtfully correlated with internationally acceptable biostratigraphic standards.Subdivision of British Permian strata into Lower and Upper series follows the traditional view summarized by Smith et al. (1974). The junction between the series is taken at the incoming of marine strata in northern England and adjoining offshore areas, and at approximately equivalent levels in continuous continental sequences elsewhere; recent limited palynological studies suggest that the early Permian-late Permian transition adopted here and in most of northwest Europe may be mid or late Kazanian or even Tatarian in age which is somewhat younger than the base-Kazanian/Ufimian position taken in more continuous marine sequences.There has been no comprehensive revision of the stratigraphy and nomenclature of early Permian strata in and around the British Isles since the work of Smith et al. (1974) and Rhys (1974), but these aspects of the early Permian continental deposits of several cuvettes and inland drainage basins in southwest Scotland were reviewed by Brookfield (1978) and the age of continental deposits in the Elgin area was reconsidered
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Zanchetta, G., E. Regattieri, B. Giaccio, B. Wagner, R. Sulpizio, A. Francke, L. H. Vogel et al. "Aligning MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: implications for core chronology". Biogeosciences Discussions 12, n. 20 (21 ottobre 2015): 16979–7007. http://dx.doi.org/10.5194/bgd-12-16979-2015.
Testo completoAbstract (sommario):
Abstract. The DEEP site sediment sequence obtained during the ICDP SCOPSCO project at Lake Ohrid was dated using tephrostratigraphic information, cyclostratigraphy, and orbital tuning through marine isotope record. Although this approach is suitable for the generation of a general chronological framework of the long succession, it is insufficient to resolve more detailed paleoclimatological questions, such as leads and lags of climate events between marine and terrestrial records or between different regions. In this paper, we demonstrate how the use of different tie points can affect cyclostratigraphy and orbital tuning for the period between ca. 140 and 70 ka and how the results can be correlated with directly/indirectly radiometrically-dated Mediterranean marine and continental proxy records. The alternative age model obtained shows consistent differences with that proposed by Francke et al. (2015) for the same interval, in particular at the level of the MIS6-5e transition. According to this age model, different proxies from the DEEP site sediment record support an increase of temperatures between glacial to interglacial conditions, which is almost synchronous with a rapid increase in sea surface temperature observed in the western Mediterranean. The results show how important a detailed study of independent chronological tie points is for synchronizing different records and to highlight asynchronisms of climate events.
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Perdahl, Jan‐Anders, e Örjan Einarsson. "The marine‐continental transition of the early proterozoic Skellefte‐Arvidsjaur volcanic arc in the Bure area, Northern Sweden". GFF 116, n. 3 (settembre 1994): 133–38. http://dx.doi.org/10.1080/11035899409546175.
Testo completo
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Sutter, Johannes, Hubertus Fischer, Klaus Grosfeld, Nanna B. Karlsson, Thomas Kleiner, Brice Van Liefferinge e Olaf Eisen. "Modelling the Antarctic Ice Sheet across the mid-Pleistocene transition – implications for Oldest Ice". Cryosphere 13, n. 7 (19 luglio 2019): 2023–41. http://dx.doi.org/10.5194/tc-13-2023-2019.
Testo completoAbstract (sommario):
Abstract. The international endeavour to retrieve a continuous ice core, which spans the middle Pleistocene climate transition ca. 1.2–0.9 Myr ago, encompasses a multitude of field and model-based pre-site surveys. We expand on the current efforts to locate a suitable drilling site for the oldest Antarctic ice core by means of 3-D continental ice-sheet modelling. To this end, we present an ensemble of ice-sheet simulations spanning the last 2 Myr, employing transient boundary conditions derived from climate modelling and climate proxy records. We discuss the imprint of changing climate conditions, sea level and geothermal heat flux on the ice thickness, and basal conditions around previously identified sites with continuous records of old ice. Our modelling results show a range of configurational ice-sheet changes across the middle Pleistocene transition, suggesting a potential shift of the West Antarctic Ice Sheet to a marine-based configuration. Despite the middle Pleistocene climate reorganisation and associated ice-dynamic changes, we identify several regions conducive to conditions maintaining 1.5 Myr (million years) old ice, particularly around Dome Fuji, Dome C and Ridge B, which is in agreement with previous studies. This finding strengthens the notion that continuous records with such old ice do exist in previously identified regions, while we are also providing a dynamic continental ice-sheet context.
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Tubbs, Robert E., Hussein G. Aly Fouda, Abdulkader M. Afifi, Nickolas S. Raterman, Geraint W. Hughes e Yousuf K. Fadolalkarem. "Midyan Peninsula, northern Red Sea, Saudi Arabia: Seismic imaging and regional interpretation". GeoArabia 19, n. 3 (1 luglio 2014): 165–84. http://dx.doi.org/10.2113/geoarabia1903165.
Testo completoAbstract (sommario):
ABSTRACT The Midyan Peninsula of northwest Saudi Arabia offers an exceptional opportunity to observe a complex interplay of rifting, salt tectonics, and strike-slip faulting. Recently onshore 3-D, transition zone 2-D, and offshore 2-D seismic data have been acquired in the area. In addition, ongoing fieldwork and an active drilling program have provided new insights into the geologic history of the region. The initial stages of continental rifting began during the Early Oligocene (ca. 33 Ma) and often utilized pre-existing basement fault trends. The early syn-rift sedimentary record is typified by formation of deep half-grabens filled with thick wedges of primarily continental sediments, with lesser amounts of evaporitic and marine deposits. Seismic data show a distinct break in deposition occurred ca. 21 Ma characterized by a persistent angular unconformity near the basin-bounding fault, before a shift to marine and offshore deposits of the Lower Miocene Burqan Formation. Post-Burqan a second angular unconformity termed the mid-clysmic event is evident away from the basin edge. This surface exhibits significant relief created by re-activation of older EW-trending faults and lower Maqna Group sediments display substantial thickening across these faults. Overall, the Maqna section transitions from normal marine sedimentation to more restricted basin conditions before being succeeded by the thick-layered evaporite sequence of the Mansiyah Formation. Approximately 15–12 Ma active strike-slip faults appeared in the Red Sea and shifted the extension from rift normal to highly oblique directed at N15°–20°E, parallel to the Gulf of Aqaba. During this transition the composition of the rift-fill changed as well from basin-wide precipitates to thick siliciclastic wedges of the Ghawwas Formation. Seismic images of the Ghawwas show abrupt thickness changes and stratal geometries that date deposition as coincident with both the growth of Mansiyah Formation diapirs and the movement of a large detachment at the base of the Mansiyah. Roughly five million years ago, organized seafloor spreading began in the southern Red Sea and strike-slip motion intensified as deformation began to focus along the Dead Sea/Aqaba strike-slip fault system. Adjacent to Midyan, a pull-apart basin in the Gulf of Aqaba has opened over 26 km perpendicular to the strike-slip system resulting in significant footwall uplift. The positive interference of the Aqaba/Dead Sea and Red Sea footwall uplifts has uniquely exposed the full syn-rift stratigraphic section from basement to Upper Miocene at Midyan, making the area an ideal locality for field studies. Presence of the complete Miocene section on the Aqaba shoulder uplift clearly indicates the uplift occurred after the Miocene. Salt-filled pull-apart basins in the same orientation as the Gulf of Aqaba are also observed on 3-D seismic data in the Ifal Basin.
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Hoem, Frida S., Isabel Sauermilch, Suning Hou, Henk Brinkhuis, Francesca Sangiorgi e Peter K. Bijl. "Late Eocene–early Miocene evolution of the southern Australian subtropical front: a marine palynological approach". Journal of Micropalaeontology 40, n. 2 (29 ottobre 2021): 175–93. http://dx.doi.org/10.5194/jm-40-175-2021.
Testo completoAbstract (sommario):
Abstract. Improvements in our capability to reconstruct ancient surface-ocean conditions based on organic-walled dinoflagellate cyst (dinocyst) assemblages from the Southern Ocean provide an opportunity to better establish past position, strength and oceanography of the subtropical front (STF). Here, we aim to reconstruct the late Eocene to early Miocene (37–20 Ma) depositional and palaeoceanographic history of the STF in the context of the evolving Tasmanian Gateway as well as the potential influence of Antarctic circumpolar flow and intense waxing and waning of ice. We approach this by combining information from seismic lines (revisiting existing data and generating new marine palynological data from Ocean Drilling Program (ODP) Hole 1168A) in the western Tasmanian continental slope. We apply improved taxonomic insights and palaeoecological models to reconstruct the sea surface palaeoenvironmental evolution. Late Eocene–early Oligocene (37–30.5 Ma) assemblages show a progressive transition from dominant terrestrial palynomorphs and inner-neritic dinocyst taxa as well as cysts produced by heterotrophic dinoflagellates to predominantly outer-neritic/oceanic autotrophic taxa. This transition reflects the progressive deepening of the western Tasmanian continental margin, an interpretation supported by our new seismic investigations. The dominance of autotrophic species like Spiniferites spp. and Operculodinium spp. reflects relatively oligotrophic conditions, like those of regions north of the modern-day STF. The increased abundance in the earliest Miocene of Nematosphaeropsis labyrinthus, typical for modern subantarctic zone (frontal) conditions, indicates a cooling and/or closer proximity of the STF to the site . The absence of major shifts in dinocyst assemblages contrasts with other records in the region and suggests that small changes in surface oceanographic conditions occurred during the Oligocene. Despite the relatively southerly (63–55∘ S) location of Site 1168, the rather stable oceanographic conditions reflect the continued influence of the proto-Leeuwin Current along the southern Australian coast as Australia continued to drift northward. The relatively “warm” dinocyst assemblages at ODP Site 1168, compared with the cold assemblages at Antarctic Integrated Ocean Drilling Program (IODP) Site U1356, testify to the establishment of a pronounced latitudinal temperature gradient in the Oligocene Southern Ocean.
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Young, N. W., M. De Angelis e D. Davies. "Evidence Of Environmental Change Since The Last Glacial Maximum Inferred From Chemical Analysis Of An Ice Core From Law Dome, Antarctica". Annals of Glaciology 14 (1990): 365. http://dx.doi.org/10.3189/s0260305500009459.
Testo completoAbstract (sommario):
An ice core, drilled near the margin of the Law Dome ice cap at Cape Folger, has been analysed for trace chemical content. The concentration of the major anions and cations has been measured on samples selected from the ice core to give information on the major environmental changes which have occurred in the period 6–26 ka B.P. The chemical species can be divided into two fractions representing the two major sources of trace chemicals; marine and continental sources. Four species are chosen to illustrate the main features in the record; aluminium as an indicator of the continental fraction, sodium and magnesium as indicators of the marine fraction and methane sulphonic acid (MSA). Sodium and magnesium concentrations in the Law Dome core are predominantly derived from marine sources, although they usually include also small contributions from the continental sources. MSA has a marine biogenic source and exhibits a pattern which is generally unrelated to the variations in the two main fractions. Measured oxygen isotope ratios provide an additional data source. Concentrations of the same species in the Dome C core (De Angelis and others, 1982; Saigne and Legrand, 1987) are used as indicators of the global background atmospheric chemical content, and by inter-comparison of the records from the two cores are used to derive a proxy chronology for the Law Dome core.The interval in each core corresponding to the final stages of the Last Glacial Maximum (LGM) can be identified from the oxygen isotope records (Budd and Morgan, 1977; Lorius and others, 1984). Both cores have high aluminium concentrations in this interval reducing to very low concentrations towards the end of the transition to the Holocene. A similar sharp change from high to very low concentration is also observed for MSA. Very low concentrations of other species are also observed in this interval in the transition period. By assuming that these changes in the two cores are contemporaneous, the age scale from the Dome C core (Lorius and others, 1984) can be applied to the Law Dome core. An age of 13 ka B.p. is assigned to the very clean interval near the end of the transition. Other, less obvious, events in the chemical and isotope records distinguish intervals corresponding to ages of approximately 7.5, 15.5, and 26 ka B.P. Ages for intermediate intervals are derived by interpolation and reference to a modelled age-depth relation.The records from each of the cores for MSA and the continental fraction, represented by aluminium, show similar features at the Law Dome site as at Dome C. But the records for the marine fraction show distinct differences. On Law Dome there is a clear trend of decreasing concentration with depth, consistent with the ice at greater depth having an origin at higher elevation further inland on the ice cap. Very low concentrations occur in the lower part of the core, which includes the interval corresponding to the LGM. By way of contrast, at Dome C the concentration of sodium in the interval corresponding to the Holocene is low, but relatively higher in the LGM interval. The concentrations during the LGM, of both the marine and continental fractions, are lower in Law Dome by a factor generally between 1 and 2 than those at Dome C as a result of dilution caused by the higher precipitation and snow accumulation rates near the coast.For interpretation of the records, the concentrations in the Dome C core are assumed to indicate changes in the global background atmospheric loading and atmospheric circulation. On Law Dome, the general trend of decreasing concentra- tion with depth for the marine fraction is modulated by variations in the background atmospheric loading, and the effect of variations in past ice sheet and sea ice extent and thus distance to the source. At about 11 ka B.P., sodium and magnesium concentrations increase sharply to about three times the background level, and are maintained till about 9.5 ka B.P. This event is not apparent in the Dome C record. During the period 6–8 ka B P., sodium and magnesium concentrations are higher by a factor between 1.5 and 2 in conjunction with colder (more negative) values of the oxygen isotope ratio. There is some evidence of similar variations in the Dome C record.This suggests two separate scenarios. For the period 9.5–11 ka B P., one or more of the following events probably occurred: a change in the seasonal pattern of variation in sea ice extent and distribution; lesser sea ice extent; more open water closer to the coast; increased storminess in the coastal region, each of which could lead to an increased supply of material with marine source (sodium and magnesium) by either more vigorous atmospheric circulation or less distance to the source. Coincidentally, increased storminess is consistent with an increased fraction of open water in the sea ice zone. But there is apparently no change in the concnetration of MSA above background levels during this period. This could provide a constraint on the possible mechanisms causing the observed event. For the more recent period, 6–8 ka B.P., the changes found in both cores probably reflect climatic variation on a broader hemispheric or global scale, involving lower temperatures in at least the high latitudes, probably increased zonal atmospheric circulation, and perhaps changes in the seasonal sea ice distribution and total extent.
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Young, N. W., M. De Angelis e D. Davies. "Evidence Of Environmental Change Since The Last Glacial Maximum Inferred From Chemical Analysis Of An Ice Core From Law Dome, Antarctica". Annals of Glaciology 14 (1990): 365. http://dx.doi.org/10.1017/s0260305500009459.
Testo completoAbstract (sommario):
An ice core, drilled near the margin of the Law Dome ice cap at Cape Folger, has been analysed for trace chemical content. The concentration of the major anions and cations has been measured on samples selected from the ice core to give information on the major environmental changes which have occurred in the period 6–26 ka B.P. The chemical species can be divided into two fractions representing the two major sources of trace chemicals; marine and continental sources. Four species are chosen to illustrate the main features in the record; aluminium as an indicator of the continental fraction, sodium and magnesium as indicators of the marine fraction and methane sulphonic acid (MSA). Sodium and magnesium concentrations in the Law Dome core are predominantly derived from marine sources, although they usually include also small contributions from the continental sources. MSA has a marine biogenic source and exhibits a pattern which is generally unrelated to the variations in the two main fractions. Measured oxygen isotope ratios provide an additional data source. Concentrations of the same species in the Dome C core (De Angelis and others, 1982; Saigne and Legrand, 1987) are used as indicators of the global background atmospheric chemical content, and by inter-comparison of the records from the two cores are used to derive a proxy chronology for the Law Dome core. The interval in each core corresponding to the final stages of the Last Glacial Maximum (LGM) can be identified from the oxygen isotope records (Budd and Morgan, 1977; Lorius and others, 1984). Both cores have high aluminium concentrations in this interval reducing to very low concentrations towards the end of the transition to the Holocene. A similar sharp change from high to very low concentration is also observed for MSA. Very low concentrations of other species are also observed in this interval in the transition period. By assuming that these changes in the two cores are contemporaneous, the age scale from the Dome C core (Lorius and others, 1984) can be applied to the Law Dome core. An age of 13 ka B.p. is assigned to the very clean interval near the end of the transition. Other, less obvious, events in the chemical and isotope records distinguish intervals corresponding to ages of approximately 7.5, 15.5, and 26 ka B.P. Ages for intermediate intervals are derived by interpolation and reference to a modelled age-depth relation. The records from each of the cores for MSA and the continental fraction, represented by aluminium, show similar features at the Law Dome site as at Dome C. But the records for the marine fraction show distinct differences. On Law Dome there is a clear trend of decreasing concentration with depth, consistent with the ice at greater depth having an origin at higher elevation further inland on the ice cap. Very low concentrations occur in the lower part of the core, which includes the interval corresponding to the LGM. By way of contrast, at Dome C the concentration of sodium in the interval corresponding to the Holocene is low, but relatively higher in the LGM interval. The concentrations during the LGM, of both the marine and continental fractions, are lower in Law Dome by a factor generally between 1 and 2 than those at Dome C as a result of dilution caused by the higher precipitation and snow accumulation rates near the coast. For interpretation of the records, the concentrations in the Dome C core are assumed to indicate changes in the global background atmospheric loading and atmospheric circulation. On Law Dome, the general trend of decreasing concentra- tion with depth for the marine fraction is modulated by variations in the background atmospheric loading, and the effect of variations in past ice sheet and sea ice extent and thus distance to the source. At about 11 ka B.P., sodium and magnesium concentrations increase sharply to about three times the background level, and are maintained till about 9.5 ka B.P. This event is not apparent in the Dome C record. During the period 6–8 ka B P., sodium and magnesium concentrations are higher by a factor between 1.5 and 2 in conjunction with colder (more negative) values of the oxygen isotope ratio. There is some evidence of similar variations in the Dome C record. This suggests two separate scenarios. For the period 9.5–11 ka B P., one or more of the following events probably occurred: a change in the seasonal pattern of variation in sea ice extent and distribution; lesser sea ice extent; more open water closer to the coast; increased storminess in the coastal region, each of which could lead to an increased supply of material with marine source (sodium and magnesium) by either more vigorous atmospheric circulation or less distance to the source. Coincidentally, increased storminess is consistent with an increased fraction of open water in the sea ice zone. But there is apparently no change in the concnetration of MSA above background levels during this period. This could provide a constraint on the possible mechanisms causing the observed event. For the more recent period, 6–8 ka B.P., the changes found in both cores probably reflect climatic variation on a broader hemispheric or global scale, involving lower temperatures in at least the high latitudes, probably increased zonal atmospheric circulation, and perhaps changes in the seasonal sea ice distribution and total extent.
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WELCOMME, JEAN-LOUP, MOULOUD BENAMMI, JEAN-YVES CROCHET, LAURENT MARIVAUX, GRÉGOIRE MÉTAIS, PIERRE-OLIVIER ANTOINE e IBRAHIM BALOCH. "Himalayan Forelands: palaeontological evidence for Oligocene detrital deposits in the Bugti Hills (Balochistan, Pakistan)". Geological Magazine 138, n. 4 (luglio 2001): 397–405. http://dx.doi.org/10.1017/s0016756801005428.
Testo completoAbstract (sommario):
In the southwestern Sulaiman geological province (Balochistan, Pakistan), terrestrial detrital facies from the Bugti Hills region have yielded the richest Tertiary vertebrate faunas to be found in Asia thus far. New fossils from five successive and distinct ‘bone beds’ bridge the supposed Oligocene sedimentary hiatus within the Sulaiman geological province; the lowermost continental levels of the previously described Miocene Chitarwata Formation, known as the Bugti Member, are Oligocene in age in the Bugti area. Neither a mixture of heterochronic faunal elements nor endemism of any fauna is evident in this area. Additional microfaunal material from the Bugti Member constrains an Oligocene age for the lower Chitarwata Formation in Zinda Pir (northeast of the Bugti Hills). This Oligocene transition between the marine Kirthar (Eocene) and continental Siwalik (Miocene) deposits consists of a regressive fluvio-deltaic system occupying a vast floodplain. It represents an early-stage molasse in the palaeo-Indus Basin which drained western orogenic highlands resulting from the collision between the Indian and Eurasian plates.