125 research outputs found
Tertiary geodynamics of Sakhalin (NW Pacific) from anisotropy of magnetic susceptibility fabrics and paleomagnetic data
No full textSakhalin has been affected by several phases of Cretaceous and Tertiary deformation due to the complex interaction of plates in the northwest Pacific region. A detailed understanding of the strain is important because it will provide constraints on plate-scale processes that control the formation and deformation of marginal sedimentary basins. Anisotropy of magnetic susceptibility (AMS) data were obtained from fine-grained mudstones and siltstones from 22 localities in Sakhalin in order to provide information concerning tectonic strain. AMS data reliably record ancient strain tensor orientations before significant deformation of the sediments occurred. Paleomagnetically determined vertical-axis rotations of crustal rocks allow rotation of the fabrics back to their original orientation. Results from southwest Sakhalin indicate a ~N035°E-directed net tectonic transport from the mid-Paleocene to the early Miocene, which is consistent with the present-day relative motion between the Okhotsk Sea and Eurasian plates. Reconstruction of early–late Miocene AMS fabrics in east Sakhalin indicates a tectonic transport direction of ~N040°E. In west Sakhalin, the transport direction appears to have remained relatively consistent from the Oligocene to the late Miocene, but it has a different attitude of ~N080°E. This suggests local deflection of the stress and strain fields, which was probably associated with opening of the northern Tatar Strait. A northward-directed tectonic transport is observed in Miocene sediments in southeast Sakhalin, mid-Eocene sediments in east Sakhalin, and in Late Cretaceous rocks of west and northern Sakhalin, which may be associated with northwestward motion and subduction of the Pacific Plate in the Tertiary period. The boundaries of the separate regions defined by the AMS data are consistent with present-day plate models and, therefore, provide meaningful constraints on the tectonic evolution of Sakhalin
The parameterisation of Mediterranean–Atlantic water exchange in the Hadley Centre model HadCM3, and its effect on modelled North Atlantic climate
No full textMultiple palaeo-proxy and modelling studies suggest that Mediterranean Outflow Water (MOW) is an important driver of Atlantic Meridional Overturning Circulation (AMOC), particularly during periods of weak overturning. Here, we employ the HadCM3 ocean–atmosphere General Circulation Model (GCM) to investigate the effect of using different parameterisations of Mediterranean–Atlantic water exchange on global ocean circulation and climate. In HadCM3, simulating flow through the Gibraltar Straits with an ‘open seaway’ rather than a ‘diffusive pipe’ causes a shoaling and strengthening of the MOW plume. This reorganises shallow Atlantic circulation, producing regional surface air temperature anomalies of up to + 11 °C and ?7.5 °C. We conclude that when investigating the influence of MOW on modelled ocean circulation and climate, an accurate parameterisation of Mediterranean–Atlantic exchange is important and should match observed fresh water and salinity flux constraints. This probably cannot be achieved through a simple ‘diffusive pipe’ with depth invariant mixing coefficient
Precessional drivers of late Miocene Mediterranean sedimentary sequences:African summer monsoon and Atlantic winter storm tracks
No full textCyclic sedimentary patterns in the marine record of the Mediterranean Sea have been consistently correlated with orbitally-driven shifts in climate. Freshwater input driven by the African summer monsoon is thought to be the main control of such hydrological changes, where the runoff signal is transferred from the Eastern to the Western Mediterranean. The geological record from the Atlantic Margin also contains precession-driven dilution cycles that have been correlated with the sedimentary sequences in the Western and Eastern Mediterranean, despite the lack of a direct connection with the basin. In these regions, Atlantic winter storms have also been invoked to explain the wet phases. In the absence of seasonally-resolved proxy data, climate simulations at high temporal resolution can be used to investigate the drivers of Mediterranean hydrologic changes both on precessional and seasonal timescales. Here, we use the results of ocean-atmosphere vegetation simulations through an entire late Miocene precession cycle. These show that the African summer monsoon drives the hydrologic budget in the Eastern Mediterranean during precession minima, while the Western marginal basins are generally dominated by local net evaporative loss. During precession minima, the Western Mediterranean and the Atlantic Margin are also influenced by enhanced winter precipitation from the Atlantic storm tracks. We can, therefore, identify two different moisture sources affectingthe circum-Mediterranean area, characterized by the same phasing with respect to precession, but with opposite seasonality. This supports the inter-regional correlation of geological sections in these areas, as we show for the Messinian and speculate for other time periods
Miocene basin evolution of the Isparta Angle, southern Turkey
No full textThe study of basins developed on top of older suture zones is demonstrably important in the
Tethyan region where rifting and convergence have occurred repeatedly from the Mesozoic
to the present-day. In southern Turkey, three Miocene basins developed in the Isparta
Angle suture zone. Two of these, the Aksu and Köprü basins, are orientated north-south,
parallel to pre-Miocene lineaments in the basement (e. g. Antalya Complex). These basins
are underlain by a mosaic of deformed Mesozoic carbonate platforms, deep-sea sediments
and ophiolitic units. The Manavgat basin, to the east, overlies Permian meta-carbonates
(Alanya Massif) deformed by NW-SE trending basement structures. The northern margin
of the Manavgat basin, in the south-east of the area, is also orientated NW-SE, but it was
open to the Mediterranean Sea to the south.
Prior to Burdigalian-Langhian transgression, a thick (-1.5km) succession of
predominantly continental conglomerates and sandstones accumulated in the south of the
Aksu and Köprü basins (Kizildag Formation). Coeval thrusting of the Lycian Nappes on
the western limb of the Isparta angle is inferred to have induced block faulting of the
foreland, exploiting pre-existing basement weaknesses and generating accommodation
space.
In the Manavgat basin palaeocurrents and south-to-north diachroneity of
transgression demonstrate that the Alanya Massif formed a palaeogeographic high to the
north of the basin. This was colonised by coral and algal fringing reefs, which shed
abundant shallow-water debris, deposited as calcarenites in Langhian times (Oymapinar
Limestone). Elsewhere, to the south and west, Late Burdigalian-Langhian patch reefs
developed within coastal fan-delta conglomeratic sequences. Detailed study of the
interaction between coral growth and clastic influx reveals that relative sea level rise
outstripped sediment influx at this time.
Extensional faulting during the Langhian in the Manavgat basin generated
numerous micro-faults which trend parallel to NW-SE basement lineaments. This faulting
led to the deposition of localised talus (Cakallar Formation) and formation of an
asymmetrical horst-graben structure. Reef deposition was abruptly terminated and 3-500m
of Serravallian planktic foraminiferal marls (Geceleme Formation) then accumulated as
post-rift fill. In the Aksu and Köprü basins, a correlative transition from shallow-water
carbonates to deeper-water turbidite deposition (Karpuzcay Formation) is observed. Palaeocurrents from the Koprii basin suggest that N-S striking lineaments in the basement funnelled sediment southwards in the north of the basin, but had little topographic expression in the south.
In the Early Tortonian, the Geceleme Formation in the Manavgat basin passed
rapidly up into slumped siltstones, sandstones and coarse conglomerates, containing large
(~10m) detached blocks of Alanya Massif metacarbonate. Debris-flow processes
dominated the deposition of this succession (Karpuzçay Formation) and together with
foraminiferal studies, document uplift and infill of the basin during Tortonian-Messinian
times. In the north of the Aksu and Koprii basins, uplift caused a transition from
Karpuzçay turbidites to shallow-marine fan-delta conglomerates with rare patch reefs.
At the end of the Miocene, a compressional event caused the reactivation of the NS
striking lineaments in the Isparta Angle and small-scale inversion of the horst-graben
structure in the Manavgat basin. East- and west-vergent faults and large -scale recumbent
folds deformed Miocene and basement rocks. Compressional forces, oblique or orthogonal
to the N-S fabric of the Isparta Angle, could have been generated both by movement of the
Lycian Nappes to the north-west and westward escape of the Anatolian block. On a more
regional scale, the Isparta Angle basins appear to be part of a transtensional system which
linked the Aegean arc to the west with the Cyprus arc to the east
Trends in Preserving Scholarly Electronic Journals
No full textScholarly electronic journals have become the largest and fastest growing
segment of digital collections for most libraries. Many issues and concerns for
managing electronic journals relate to preserving and providing continued
access to them. The preserving of scholarly electronic journals is a complex
issue with various aspects and is largely different from archiving of print-based
scholarly journals. In this paper the author deals with issues concerning
archiving of scholarly electronic journals. The purpose of this paper is to
identify and discuss different issues related to preserving scholarly electronic
journals. The following issues are discussed: differences between print and
digital media, shift in the responsibility of archiving, copyright and intellectual
property rights, cost of archiving, expertise, selection, redundancy,
organizational issues, etc. Technical issues and challenges related to digital
preservation include a lack of practical implementations of preservation
standards and a lack of technical knowledge, in general, of what information is
required to support the digital preservation process within organizations.
Nevertheless, digital preservation has received considerably more prominence
in recent years, gaining the attention of entities such as national libraries,
national archives and other organizations
Birth, evolution and demise of the Mediterranean Lago-Mare: A biogeochemical perspective on water level and connectivity changes during the final phase of the Messinian Salinity Crisis
No full textThe Mediterranean Sea is a large sea almost completely enclosed by Europe, Africa, and SW Asia. Today, the continuous flow of Atlantic seawater through the Strait of Gibraltar balances the net water loss due to the excess of evaporation over input from rain and rivers and keeps the Mediterranean a marine basin with the water level equal to the global ocean level. In the late Miocene, the input of Atlantic seawater was through shallow gateways in southern Spain and northern Morocco. The exhumation of the Betic and Rif Cordilleras and orbitally-controlled regional climate change contributed to the step-by-step close these marine gateways and transformed the Mediterranean into an inhospitable evaporitic sea, starting at 5.96±0.02 Ma. The environmental and hydrological crisis that followed, known as the Messinian Salinity Crisis, peaked at ~5.55 Ma, when a 1.5-2 km-thick salt layer precipitated on the sea floor, and terminated at ~5.332 Ma, when normal marine conditions were re-established, perhaps as a consequence of catastrophic flooding at Gibraltar. The transitional interval from the giant salina to Mediterranean Sea that resembles what we know today is known as the Lago-Mare phase. Gypsum and brackish water biota from the Central Paratethys (approximately coinciding with the present-day Hungary-Slovenia) are both characteristic of Lago-Mare successions. This sedimentary and paleontological evidence suggest that the Mediterranean, during the Lago-Mare phase, experienced a complex history of inter- and extrabasinal connections, base-level fluctuations and extreme environmental and biological changes. This thesis aims to reconstruct the fiercely debated Mediterranean water level changes and identify the hydrological fluxes responsible for these Lago-Mare environmental and biological turnover events. It focuses on key sections exposed on-land and recovered from deep sea cores along an E-W transect across the Mediterranean with a multi-disciplinary approach that integrates biocyclostratigraphic analyses with high-resolution Sr-isotope ratios. The new data show that the Lago-Mare phase was a far more dynamic period of the Mediterranean history than previously thought. Large areas of the Mediterranean were occupied by an anomalohaline water mass predominantly formed by low-salinity waters from the Eastern Paratethys (i.e. the present-day Black-Caspian seas) and from the larger circum-Mediterranean rivers such as the Nile, the Rhône and currently dried North-African rivers. A small and possibly episodic Atlantic flux was a minor contributor. The regular variability of the Mediterranean’s freshwater budget with the astronomic precession combined with fluctuating Atlantic inflow and negligible outflow resulted in a Mediterranean base level that oscillated dramatically, but consistently below eustatic sea level. These precession-paced fluctuations caused the low-salinity Paratethyan biota to colonize the marginal areas of the Mediterranean at times of high base level and central areas during phases of low base level, gypsum to precipitate only in the deeper basins during the regressive phases and silled regions such as the Adriatic and the North Aegean to exist for long as some of the largest endorheic lakes
Geodynamic implications of paleomagnetic data from Tertiary sediments in Sakhalin, Russia (NW Pacific)
No full textN-S trending right-lateral strike-slip faults, which were active in the Tertiary, transect Sakhalin, Russia, while Mesozoic forearc and accretionary rocks testify to an earlier period of subduction. Several kinematic models have been proposed for the region, but the details required to constrain these models, such as the timing of the transition from subduction to strike-slip tectonics in Sakhalin, are still unknown. Even first-order tectonic features, such as the boundaries of the plates with which Sakhalin evolved during the Tertiary, are poorly known. Paleomagnetic results from around Sakhalin were obtained to constrain the geodynamic evolution of the region. Comparison of paleomagnetic inclination data with the apparent polar wander paths for the Eurasian, Pacific, and North American Plates suggests that Sakhalin probably evolved with the North American Plate, although a history including the Eurasian Plate cannot be ruled out. Paleomagnetic declination data suggest that significant clockwise vertical axis rotation has occurred in Sakhalin since the mid-Paleocene. It is likely that this rotational deformation was accommodated by Tertiary activity on right-lateral strike-slip faults, which may be associated with the opening of the Japan Sea, Tatar Strait, and Kuril Basin. These data contradict a published kinematic model for eastern Sakhalin, where counterclockwise vertical axis rotations were predicted for Neogene basins in the East Sakhalin Mountains. Agreement is better, however, with published paleomagnetic data from southern Sakhalin, where clockwise vertical axis rotations were documented
Flecker c, E. Ducassoud, T. Williams e, and
No full textComunicación oral presentada en: 56th Annual Meeting AASP-The Palynological Society University of Montpellier, 24-28 June, Montpellier (France)
IODP Expedition 401scientists: U. Amarathunga, B. Balestra, M. Berke, C. Blättler, S. Chin, M. Das, K. Egawa, G. Ercilla, F. Estrada, N. Fabregas, S. Feakins, S.C. George, F.J. Hernández Molina, W. Krijgsman, Z. Li, J. Liu, J. Lofi, F. Raad, M. Teixeira, F.J. Rodríguez-Tovar, F.J. Sierro, P. Standring, J. Stine, E. Tanaka, X. Xu, S. Yin, M.Z. YousfiMediterranean-Atlantic oceanic exchange exhibits one of the largest dense saline water outflows of the global ocean. As this plume is thought to be a critical driver of Atlantic Ocean circulation patterns, the transport of water between the Mediterranean Sea and the Atlantic Ocean potentially has great implications for global thermohaline circulation and atmospheric carbon cycling. The evolution of the exchange, from the initiation of the overflow of Mediterranean
Outflow Water (MOW) to the establishment of its modern configuration, can therefore significantly impact these processes. IODP Expedition 401 (December 2023 to February 2024) recovered a nearly complete late Miocene to early Pliocene sedimentary record of the evolution by drilling successions on either side of the Gibraltar Strait. Here, we present the first results from a new palynological research project to be conducted on 145 samples collected from this expedition to evaluate sea-surface conditions (dinoflagellate cysts) and the type of vegetation (pollen and spores) that covered the area adjacent to the drilling paleo-location. The purpose is to provide a detailed chronology of any observed vegetation and environmental changes throughout the late
Miocene to early Pliocene. Preliminary results indicate well preserved organic material with identifiable pollen, spores, and dinoflagellate cysts. Palynology will provide data key to answering expedition-specific questions regarding paleoclimate reconstructions and various environmental parameters including mean annual temperature and mean annual precipitation. Quantification of these environmental parameters has the potential to refine our understanding of the nature of the Mediterranean-Atlantic gateway evolution. Various causes of the gateway changes between the Mediterranean Sea and the Atlantic have been suggested including the local tectonic activity, global climate (e.g., enhanced evaporation), and eustatic changes driven by variations in Antarctic sea ice volume. In addition to serving as a paleoclimate proxy, this work along with calcareous nannofossil analysis will provide a biostratigraphic zonation necessary for the age constraint of the record. Studying regional events such as the evolution of the Mediterranean-Atlantic gateway exchange will help us to understand and characterize their impact on global-scale processes such as ocean circulation patterns, heat transport, and changes in sea ice volume
Birth, evolution and demise of the Mediterranean Lago-Mare: A biogeochemical perspective on water level and connectivity changes during the final phase of the Messinian Salinity Crisis
No full textThe Mediterranean Sea is a large sea almost completely enclosed by Europe, Africa, and SW Asia. Today, the continuous flow of Atlantic seawater through the Strait of Gibraltar balances the net water loss due to the excess of evaporation over input from rain and rivers and keeps the Mediterranean a marine basin with the water level equal to the global ocean level. In the late Miocene, the input of Atlantic seawater was through shallow gateways in southern Spain and northern Morocco. The exhumation of the Betic and Rif Cordilleras and orbitally-controlled regional climate change contributed to the step-by-step close these marine gateways and transformed the Mediterranean into an inhospitable evaporitic sea, starting at 5.96±0.02 Ma. The environmental and hydrological crisis that followed, known as the Messinian Salinity Crisis, peaked at ~5.55 Ma, when a 1.5-2 km-thick salt layer precipitated on the sea floor, and terminated at ~5.332 Ma, when normal marine conditions were re-established, perhaps as a consequence of catastrophic flooding at Gibraltar. The transitional interval from the giant salina to Mediterranean Sea that resembles what we know today is known as the Lago-Mare phase. Gypsum and brackish water biota from the Central Paratethys (approximately coinciding with the present-day Hungary-Slovenia) are both characteristic of Lago-Mare successions. This sedimentary and paleontological evidence suggest that the Mediterranean, during the Lago-Mare phase, experienced a complex history of inter- and extrabasinal connections, base-level fluctuations and extreme environmental and biological changes. This thesis aims to reconstruct the fiercely debated Mediterranean water level changes and identify the hydrological fluxes responsible for these Lago-Mare environmental and biological turnover events. It focuses on key sections exposed on-land and recovered from deep sea cores along an E-W transect across the Mediterranean with a multi-disciplinary approach that integrates biocyclostratigraphic analyses with high-resolution Sr-isotope ratios. The new data show that the Lago-Mare phase was a far more dynamic period of the Mediterranean history than previously thought. Large areas of the Mediterranean were occupied by an anomalohaline water mass predominantly formed by low-salinity waters from the Eastern Paratethys (i.e. the present-day Black-Caspian seas) and from the larger circum-Mediterranean rivers such as the Nile, the Rhône and currently dried North-African rivers. A small and possibly episodic Atlantic flux was a minor contributor. The regular variability of the Mediterranean’s freshwater budget with the astronomic precession combined with fluctuating Atlantic inflow and negligible outflow resulted in a Mediterranean base level that oscillated dramatically, but consistently below eustatic sea level. These precession-paced fluctuations caused the low-salinity Paratethyan biota to colonize the marginal areas of the Mediterranean at times of high base level and central areas during phases of low base level, gypsum to precipitate only in the deeper basins during the regressive phases and silled regions such as the Adriatic and the North Aegean to exist for long as some of the largest endorheic lakes
Miocene to Pleistocene osmium isotopic records of the Mediterranean sediments
No full textIn the late Miocene the Mediterranean Sea experienced a salinity crisis and thick sequences of evaporites precipitated across the deep and marginal basins. In this study we report Os isotopic records from Deep Sea Drilling Project and Ocean Drilling Project cores in the Mediterranean: the Balearic Sea (Site 372), the Tyrrhenian Sea (Site 654), the Ionian Basin (Site 374), and the Florence Rise (Sites 375-376), as well as Integrated Ocean Drilling Project Site U1387 in Gulf of Cadiz, North Atlantic. Pliocene-Pleistocene sediments at all sites show 187Os/188Os values close to that of the coeval ocean water, indicating that the Mediterranean was connected to the North Atlantic. Evaporitic sediments deposited during the latest Miocene, however, have 187Os/188Os values significantly lower than coeval ocean water values. The offset of the Mediterranean evaporite 187Os/188Os is attributed to limited exchange with the North Atlantic during the Messinian salinity crisis. The source of unradiogenic Os is likely to be weathering of ultramafic rocks (ophiolites) cropping out in the Mediterranean's drainage basins. Based on a box model we estimated the amount of unradiogenic Os and the Atlantic-Mediterranean exchange rate to explain this offset. Os isotopic ratios of the pre-evaporite sediments in the western Mediterranean are almost identical to that of the coeval ocean water. In contrast, equivalent sediments from the Florence Rise have significantly lower 187Os/188Os values. The offset in the Os isotopic ratio on the Florence Rise is attributed either to limited water exchange between eastern and western Mediterranean or to local effects associated with exhumation of the Troodos ophiolites (Cyprus)
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