Marine Circulation Research Articles

Tidal shelf sedimentation in the Neoproterozoic Chattisgarh succession of central India

The Neoproterozoic Kansapathar Sandstone of the Chattisgarh basin, a shallow marine shelf bar sequence, consists of mineralogically and texturally mature sandstones with subordinate siltstones, mudstones and conglomerates. The sediments were transported, reworked and deposited in subtidal environments by strong tidal currents of macrotidal regime as well as storms, and accumulated as discrete shoaling-upward features, separated from each other by muddy to low-energy sandy deposits. The sandbodies developed into shoaling up linear bars, often more than a kilometre in length, through accretion of thick cross-stratified units in transverse directions under the influence of ebb and flood tidal currents, as well as in longitudinal direction affected by southeasterly flowing along-shore currents. The aggrading upper surfaces of the bars experienced protracted reworking by strong oscillatory wave currents leading to extensive development of subaqueous 2D or 3D dunes mantled with lag pebble deposits at different points. With continued shoaling and progradation, the bars amalgamated into large sandstone sheets with the development of high energy beach deposits and coastal sand flats in the uppermost part of the sequence. The presence of rill marks, flat-topped ripples, wrinkle marks, desiccation cracks and adhesion warts point to intertidal conditions with intermittent exposure. The high energy sandstone bars overlie a thick mudstone-dominated shelf sequence across a sharp interface indicating rapid change in the sea-level, provenance, rate of sediment generation and sediment input, and circulation condition in the shelf. A quiet muddy shelf was replaced by a major sand-depositing environment with strong, open marine circulation. An interplay of tidal currents, oscillatory wave currents and storm currents generated a complex flow pattern that varied in time and space from bimodal-bipolar to strongly unimodal flows.Close parallelism of wave ripple crests, trend of linear bars and unidirectional flows suggest that the elongate bars were parallel to sub-parallel to the coastline, and were strongly influenced by along shore drift. The inferred coastline was broadly N-S. The large-scale structures in the bar sandstones, emplacement of vast amount of sand and migration of large bedforms under strong macrotidal currents collectively indicate that the Kansapathar shelf was intimately connected with an open ocean basin towards north-northwest.

Surface winds in the Euro-Mediterranean area: the real resolution of numerical grids

Abstract. Surface wind is a variable of great importance in forcing marine waves and circulations, modulating surface fluxes, etc. Surface wind defined on numerical grids is currently used in forecast-analysis, as well as in climatology. Gridded fields, however, suffer for systematic errors associated with the numerical procedures adopted in computing them. In this paper the climatology of surface wind produced by three different numerical models in the European-Mediterranean area is analyzed. The systematic loss of power at the smallest grid-scales appears in the power spectrum of all the different models. Some prototype numerical integrations show that this systematic over-smoothing is due to numerical stabilization operators that represent the main source of the diagnosed error; the error progression in space and time is also analyzed. Key words. Meteorology and atmospheric dynamics (Mesoscale meteorology; Ocean-atmosphere interaction; Climatology)

Evolution diagénétique dans la craie pélagique dolomitisée du crétacé supérieur du bassin de Paris (région de Provins, France)

Two deep scientific boreholes, named Poigny 701 and Sainte-Colombe 702, located in the Paris Basin near Provins (Seine-et-Marne, France), recovered a complete Upper Cretaceous chalk succession. A correlation between the boreholes lithostratigraphy, reflexion seismic profiles and diagenetic patterns shows that major velocity variations measured in the seismic reflection profiles correspond to dolomitized chalk intervals. Dolomitisations occurred during early and burial diagenesis. The understanding of these complex diagenetic events has an important economic consequence on the static correction of the chalk formation in the Paris Basin. Optimisation of petroleum prospecting below chalk cover is thus possible. The chalk series of the 701 and 702 boreholes range from the Cenomanian to the upper Campanian. In this succession, micrite has a primarily biogenic origin; it consists of pelagic organisms, indicative of warm seawater with values around 25°C. Several hiatuses occur in the 701 borehole. These hiatuses indicate the existence of particular hydrodynamic conditions. Deep-water channels were locally recognised in the Paris Basin as in Normandy and Picardy. In the 702 borehole, massive dolomitisation affected the upper meters of sediment below the sea floor. This early phase of massive dolomitisation was induced by slow circulation of a magnesium-rich seawater mass, along the seawater/sediment interface. Thus, this area was a zone of intense marine circulation between the North-West infralittoral and the South-West bathyal domains, across the London-Paris Basin. Magnesium-rich seawater had as origin the recrystallisation of the biogenic peri-plateform carbonates. During both dolomitisation and dissolution of the calcite matrix of the massive dolomite, the calcite had cemented chalk around the massive dolomite body. After deposition, the chalk series was progressively compacted and lithified by burial calcite cement. During the late Campanian-Maastrichtian, the burial compaction of the chalk and thermal gradient reached their maximum, as compressive stresses from the Pyrenean orogenesis affected the Paris Basin. At this time, compaction of the massive dolomite induced the expulsion of magnesian-rich fluids into the underlying already compacted chalk series. In 702 borehole, a diffuse dolomitisation then affected strongly underlying the chalk series. In 701 borehole, this diffuse dolomitisation affected slightly the lower half of the chalk series. Laterally, dolomitisation decreases gradually and affected a only smaller thickness of the chalk series, disappearing laterally. During the progressive emergence of the Paris Basin, from the Paleogene to the Quaternary, the chalk series were partially invaded by continental fresh water. Thus partial dedolomitisation affected the massive dolomite, whereas total dedolomitisation affected only the upper first meters of it.

Lithostratigraphy of the Neoproterozoic Chattisgarh Sequence, its Bearing on the Tectonics and Palaeogeography

The Neoproterozoic Purana succession in the eastern part of Chattisgarh basin around Sarangarh has been classified into a conglomerate-sandstone-shale dominated proximal assemblage, and a lithographic limestone-shale dominated distal assemblage. The proximal assemblage constitutes the Chandarpur Group, and unconformably overlies the Archean crystalline basement complex. The Chandarpur succession has been classified into three formations that were deposited in fan-fan delta, deep water prodelta and storm- tide dominated prograding shelf environments. The distal assemblage, the Raipur Group, conformably overlies the Chandarpur Group, and may be subdivided into two shale-dominated formations separated by a limestone-dominated formation. The limestone sequence, the Sarangarh Limestone, comprises a lower member of mixed carbonate-siliciclastic succession deposited in a storm dominated shallow water platform, and an upper member of pelagic limestone that grades upward into a deep water shale, the Gunderdehi Shale. The rapid transition from shallow water platformal succession to deep-water pelagic limestone and shale points to abrupt deepening of the basin and drowning of the craton. The peak of transgression is represented by a persistent horizon of black limestone, a product of basin wide anoxia. Disposition of facies belts in proximal and distal assemblages and palaeocurrent directions measured from different facies belts point to a north-northwesterly palaeoslope of the basin. Signatures of intense storm and tidal currents in different litho-units collectively point to an open marine circulation condition. It has been inferred that the basin was connected to a major seaway that skirted the northern and north-western margin of the craton. Development of thick fan-delta sequence at the base of the succession, occurrence of felsic welded tuff within the Gunderdehi Shale, thick sandstone-mudstone cyclothems in the Chandarpur Group, and abrupt drowning of the carbonate platform leading to pelagic sedimentation collectively point to major tectonic control on basin evolution. The basin developed as a cratonic rift and evolved into a deeply subsiding one, without any major stratigraphic hiatus, through episodic tectonic pulses.

Spatiotemporal variation of phosphorus and the effect of local currents on its distribution in Petacalco Bay, Guerrero, Mexico

The contribution of continental water to the coastal zone has a significant impact on ecosystems worldwide. Continental waters provide nutrients in different concentrations and their distribution is conditioned by local marine circulation dynamics and seasonality of river inputs. The Balsas River, one of the most important in Mexico, discharges its water into Petacalco Bay, with a considerable nutrient content. This work studied the spatiotemporal variability of the orthophosphate and total phosphorus contents and their relation with salinity, turbidity and coastal circulation. Maximum orthophosphate concentrations in the bay were 19.56 ∞M in April/May, 10.50 ∞M in February and 9.31 ∞M in August. The high total phosphorus contents were 40.98 ∞M in April/May and 20.54 ∞M in August, indicating an eutrophied coastal environment, result of the wastewaters discharged by the industries established along the river's estuary and dispersed throughout the bay by the local currents. An accumulation of water originating from the Balsas River was recorded in the central-eastern portion of the bay. There were small cyclonic and anticyclonic superficial gyres off the Petacalco Estuary during most of the months studied (February, June, August, October and December) that had the same direction at 10 m depth or were inverted in April and December, with a displacement toward the E–NE, allowing us to verify the diffusion of the phosphorus.

A Numerical Approach to Marine Circulation Using Free Surface or Rigid-lid Modeling: Application in the Bay of Calvi

When establishing a model of fluid flow in marine modeling, a key issue is the choice between a rigid-lid approach or a free surface level model. This is not a trivial issue as it plays an important role, not only in the choice of the numerical techniques, but also in the qualitative and quantitative aspects of the numerical results. Most software use either free surface or rigid-lid hypotheses, but comparing their results is difficult, since the numerical tools used are in general, extremely different. In this work, some numerical investigations comparing rigid-lid and free surface models are presented. A numerical method using Galerkin's method, but with a new basis, is applied to solve the rigid-lid equations in a realistic domain with varying bottom. A numerical method, similar to the one already used for free surface equations (the same truncating method and precision level) is applied, where the main differences between the simulation results depend only on the model employed. In addition, a comparative simulation between rigid-lid and free surface models to study marine circulation in the bay of Calvi (Corsica) is presented, and numerical results in the non-stratified case only (fluid with constant density) are described, as no further difficulties appear in the stratified case.

Numerical paleoceanographic study of the Early Jurassic Transcontinental Laurasian Seaway

The forces governing marine circulation of a meridional transcontinental seaway is explored with the Princeton Ocean Model. The Jurassic Laurasian Seaway, which connected the low‐latitude Tethys Ocean with the Arctic Sea is modeled quantitatively. The global ocean is found to have a profound influence on seaway dynamics. A north‐south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow. When the Tethys waters were the denser water, the net seaway flow was southward, and conversely, it was northward for denser Arctic waters. Marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by Boreal faunal groups and reduced salinities several times in the Jurassic. The model results suggest that this can be explained by southward flowing seaway currents, which may have been related to an oceanic thermohaline circulation where no northern high‐latitude deep convection occurred.

Identification of sources of PM 10 aerosols in Hong Kong by wind trajectory analysis

Light scattering and absorption coefficients were measured from September 1997 to April 1999 at a station at Cape D'Aguilar, a remote area at the southeastern tip of Hong Kong. The sum of the coefficients was converted to particulate mass concentration of aerosols and compared with those measured at other urban stations. Using back trajectories, the air masses arriving Hong Kong can be classified into seven types. Air masses originating in the Asian continent generally brought in higher aerosol concentrations than those from the ocean. The South Marine Circulation type trajectories (SMC) brought in the lowest aerosol mass concentration of about 10 μg m −3 measured at the Cape D'Aguilar station. This can be used as the value for background mass concentration in the Hong Kong region. Based on measurements at stations located at different parts in the territory the sources of aerosols in Hong Kong were speculated to be mainly due to emissions from the Asian continent and local sources in winter. Local emissions were thought to be mainly responsible for the aerosol concentrations in summer.

Late Cretaceous (Cenomanian to Campanian) paleoenvironmental history of the Eastern Canadian margin of the Western Interior Seaway: bonebeds and anoxic events

Upper Cretaceous strata in the Pasquia Hills of the northern Manitoba Escarpment, eastern Saskatchewan, Canada provide a detailed paleoenvironmental and sea-level record of the eastern margin of the Western Interior Seaway. Sediments deposited during the Cenomanian/Turonian Greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column, with bottom-water anoxia recurrently reaching into the photic zone. A middle Cenomanian sea-level lowstand event followed by transgression left a series of bonebeds within the Belle Fourche Member of the Ashville Formation, indicating a sedimentary environment starved of coarse siliciclastics. Maximum sea level resulted in the formation of limestone beds within the Favel Formation, further favoured by reduced terrigenous sediment input compared to the western margin. Limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions, and reducing zoo- and phytoplankton diversities. During final Greenhorn regression, eastern Saskatchewan probably turned into a restricted basin severely limiting marine circulation. Poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the Cenomanian/Turonian transgressive/regressive cycle. This was caused either by a freshwater lid, stratification of Boreal and Tethyan-derived watermasses, or both, to various intensities affected by changing sea level. Basin oxygenation during Niobrara time varies between localities along the eastern margin as documented by presence/absence of benthic and planktic foraminifera.

Integrated paleontologic and paleomagnetic stratigraphy of the upper Neogene deposits around Limon, Costa Rica: A coastal emergence record of the Central American Isthmus

A chronostratigraphic study of mixed carbonate and siliciclastic sediments (Limon Group) along the Caribbean side of the Central American Isthmus was conducted to provide refined depositional ages on the uplifted, nearshore marine sequence exposed near Limon, Costa Rica. These upper Neogene sediments provide a rich faunal history that spanned the closure of the isthmus and cessation of marine circulation between the Pacific Ocean and Caribbean Sea. This faunal archive provides a critical link in regional assessment of evolutionary changes that resulted from the development of the Central American Isthmus. Results from this study have shown that integrated biostratigraphic and magnetostratigraphic techniques can be successfully combined to provide refined age dating in shallow-marine sediments, even where some microfossil reworking has occurred. We propose the new Quebrada Chocolate Formation to represent latest early–early late Pliocene mixed reefal and siliciclastic deposits that overlie the early Pliocene Rio Banano Formation. The superjacent Moin Formation is expanded to include a second reefal interval deposited near the late Pliocene-Pleistocene boundary as well as fine-grained, mollusk-rich deposits in the forereef and lagoon. The style of mixed-system reef geometry between the two units is distinct. The Quebrada Chocolate Formation reefs consist of a lower interval of alternating reefal units buried by siliciclastic sediment and an upper unit comprised of stacked, reefal buildups with relatively minor siliciclastic matrix. These stacked reefs formed on a rising sea level. In contrast, the Moin Formation reefs are isolated corals and patch reefs within a siliciclastic matrix that were deposited during the peak (maximum flooding) of the sea-level highstand. Our refined age model for the Limon Group sediments allows reassessment of Pleistocene uplift rates. We calculate a rate of about 50 m/m.y., slightly less than previous rate estimates, attributed to the shallow subduction in the Pacific of the Cocos Ridge beneath the Central American island-arc system. Development of similar high-resolution age models from other marine basins should provide the chronostratigraphic control necessary to assess environmental events and evolutionary trends in shallow-marine faunas separated and isolated by the Central American Isthmus.

A Coupled Air–Sea Mesoscale Model: Experiments in Atmospheric Sensitivity to Marine Roughness

A coupled air‐sea numerical model comprising a mesoscale atmospheric model, a marine circulation model, and a surface wave model is presented. The coupled model is tested through simulations of an event of frontal passage through the Lake Erie region. Experiments investigate the effects of different sea surface roughness parameterizations on the atmospheric simulations. The coupled system’s components are the fifth-generation Pennsylvania State University‐National Center for Atmospheric Research Mesoscale Model (MM5), the Princeton Numerical Ocean Model (POM), and the GLERL‐ Donelan Wave Model (GDM). The finest of the MM5’s three nested grids covers Lake Erie, on which the POM and GDM operate. The MM5 provides surface heat and momentum fluxes to the POM, and the POM returns lake surface temperatures to the MM5. The MM5 provides 10-m winds to the GDM, and the GDM returns sea state information to the MM5. The MM5 uses this sea state information in calculating overwater roughness lengths (z 0’s). Experiments varying the MM5’s roughness parameterization over Lake Erie are performed, resulting in a broad range of z 0’s. It is found that wave model coupling can significantly increase overwater roughnesses in the MM5, leading to increased surface heat and moisture fluxes and to changes in PBL characteristics. The impacts on the atmosphere from marine model coupling can appear far downstream of the coupled zones. The accuracy of the mesoscale atmospheric simulation appears sensitive to the assumptions behind the marine roughness parameterizations used. The results suggest that, for consistent forecast improvement, marine roughness parameterizations should account for wave age. In addition, it is found that accounting for wave movement in an air‐sea coupling scheme can be a significant factor in the calculation of surface stresses and, with them, surface heat fluxes over marine areas. Thus, the approach with which a coupling scheme implements sea-statedependent roughness parameterizations can be as influential as the parameterizations themselves.

The Cadiz margin study off Spain: an introduction

The Cadiz continental margin of the northeastern Gulf of Cadiz off Spain was selected for a multidisciplinary project because of the interplay of complex tectonic history between the Iberian and African plates, sediment supply from multiple sources, and unique Mediterranean Gateway inflow and outflow currents. The nature of this complex margin, particularly during the last 5 million years, was investigated with emphasis on tectonic history, stratigraphic sequences, marine circulation, contourite depositional facies, geotechnical properties, geologic hazards, and human influences such as dispersal of river contaminants. This study provides an integrated view of the tectonic, sediment supply and oceanographic factors that control depositional processes and growth patterns of the Cadiz and similar modern and ancient continental margins.

Conditions de depôt des diatomites messiniennes en contexte de plateforme carbonatée d'après l'etude des assemblages de diatomées: Exemple du Djebel Murdjadjo (Algérie)

Diatomitic accumulations occur in the outer part of the Messinian carbonate platform of Oran vicinity.The diatom assemblages reveal the environmental evolution during the platform edification with two different diatomitic episodes. The first one contains diatom assemblage of tropical open sea and marks the distal talus of prograding bioclastic and reefal units. The second diatomitic episode, following the prograding coral reef complex, represents for numerous authors the equivalent of the base of the so-called salinity crisis. The diatom assemblage reveals a littoral marine environment, with variable salinity, in relatively stagnant warm water. This evolution is consequent with the hypotesis of a general infilling of accomodation during the carbonate platform development which lead to a restrictive marine circulation conditions.

Production and preservation of organic matter during deposition of the Bakken Formation (Late Devonian and Early Mississippian), Williston Basin

The organic-rich (up to 35% TOC) lower and upper black mudstone members of the Bakken Formation (Late Devonian and Early Mississippian) accumulated in response to both increased productivity and enhanced preservation that resulted from unique palaeogeographic, palaeoceanographic and palaeoclimatic conditions. During Bakken deposition the semi-isolated Williston Basin was located close to the Equator (5° to 10°N) in a zone of prevailing east to west winds. A pattern of estuarine-like marine circulation between the Williston Basin and open-ocean conditions at the western craton edge of North America is proposed. Surface water discharged from the basin was replaced by nutrient-rich deeper water sourced from the equatorial undercurrent in the Pacific Basin. Undercurrent flow into the Williston Basin upwelled providing a potentially sustainable source of nutrients to enhance productivity in the surface photic zone during black mudstone deposition. In response to increased productivity, that led to a high rate of organic sedimentation, and quiescent, deep-water conditions, due primarily to the geographic isolation of the basin and the restriction of estuarine-like circulation to the upper water column, anoxic bottom water developed on the basin floor. As sea-level rose during lower and upper black mudstone deposition, anoxic bottom water expanded across the basin enhancing organic matter preservation. Conditions in the Williston Basin demonstrate that both increased productivity and improved preservation can be essential and complementary factors affecting organic-rich mud deposition. These results have potentially important implications for the accumulation of similarly organic-rich deposits across the North American interior during Late Devonian and Early Mississippian time.

Deciphering the sedimentological expression of tectonics, eustasy, and climate: a basinwide study of the Corallian Formation, southern England

ABSTRACT Jurassic Corallian Formation outcrops along the Dorset coast, composed of carbonate and siliciclastic shallow-marine facies, are classic sites for British geologists. They have been regarded as typical of cyclically deposited strata, characterized by repeated sandstone, mudstone, and carbonate lithologies. The stratigraphy has been interpreted as evidence for rapid eustatic sea-level change throughout the Oxfordian. This study's basinwide database, however, shows that study of the outcrops alone has led to oversimplified conclusions. The stratigraphy records the migration of siliciclastic source areas through time. Pulses of terrigenous sand reflect local uplift and increased weathering, rather than rapid eustatic sea-level falls. The recognition of mixed siliciclastic-carbonate beds makes an argument for rapid changes in water depth less convincing, and reveals that lateral migration of shallow-water facies is a more plausible explanation for the observed stratigraphy. Coeval carbonate and siliciclastic deposition around the basin shows that neither eustasy nor climatic change can be solely responsible for the stratigraphy. The strata reflect, instead, a complex interplay of episodic local tectonism, siliciclastic source area migration, and marine circulation patterns.

The Northeast Shelf Ecosystem: Assessment, Sustainability, and Management

Part 1 Ecosystem sustainability: marine ecosystem sustainability the Northeast Shelf ecosystem - stress, migration and sustainability ecological research for biosphere. Part 2 Physical and biological characteristics: physical oceanography of the Shelf and slope seas from Cape Hatteras to Georges Bank - a brief overview meteorology of the Northeast Shelf climate change and winter coastal marine circulation in the mid-Atlantic I region of the United States the Continental Shelf ecosystem off the Northeast Coast of the United States. Part 3 Population assessments: zooplankton dynamics in the Northeast Shelf ecosystems the state of groundfish resources of the Northeastern United States shifts in Northeast Shelf cetacean distributions relative to trends on Gulf of Maine/Georges Bank finfish abundance the state of marine bird populations from Cape Hatteras to the Gulf of Maine zooplankton prey field variability during collapse and recovery of pelagic fish in the Northeast Shelf ecosystem. Part 4 Environmental stresses on the ecosystem: coastal contamination in the Northeast Shelf large marine ecosystem metal concentrations in winter flounder American lobster and bivalve mollusks from Boston Harbour, Salem Harbour and Coastal Massachusetts riverine contributions to heavy metal inputs to the Northeast Shelf ecosystem trends in nutrient loading and eutrophication a comparison of the Chesapeake Bay and the Hudson River estuarine systems preliminary estimates of the pollutant loads and fluxes into the Northeast shelf ecosystem. Part 5 Habitat degradation. Part 6 Stress migration - environmental and biological considerations. (Part contents)

The Mediterranean Sea, coastal and deep-sea signatures of climatic and environmental changes

At great scales of time and space, the dynamics of the Mediterranean Sea, a concentration basin, are mainly linked to its freshwater budget. This budget is subject to evolutions due to man's use of freshwater and to climatic changes affecting precipitation and/or evaporation. Marine dynamics and Atlantic, atmospheric and terrestrial inputs are strong constraints for the geochemical behaviour of the Mediterranean Sea. From measurements made during the last decades in the deep western water, it appeared that temperature, salinity, nutrients and trace metal concentrations were changing with time. In spite of its depth, the Mediterranean Sea looks like a coastal ocean, according to its coast length, watershed and number of inhabitants and to its fast response to climatic and environmental changes. The changes discovered in deep homogeneous waters are signatures of evolutions occurred in the surface layer. But in this layer and particularly in coastal waters, climatic and/or environmental trends may be masked by seasonal and interannual variabilities of not only physical and chemical characteristics but also climatic forcing or anthropic inputs. Analyses of river runoff, atmospheric inputs or climatic trends together with marine evolutions indicate constraints concerning probable changes in the coastal sea and/or in the surface water and processes involved at the interfaces. Moreover, changes observed in coastal or deep-water constitute new constraints for the modelling of the marine circulation and the transfer of matter.

Stable isotope stratigraphy and paleoclimatology of the Paleogene Bighorn Basin (Wyoming, USA)

Abstract Climatic warming from the late Paleocene into the early Eocene had profound effects on atmospheric and marine circulation, marine thermal gradients, and benthic biota. In addition, marine carbon isotope values decreased substantially in both surface and deep waters. Because carbon is rapidly exchanged between reservoirs at the earth's surface, such as marine surface water, the atmosphere, land plants, and materials that obtain carbon from plants (e.g., soil minerals and herbivores), carbon isotope fluctuations provide time lines linking the marine and continental records. We analyzed the carbon isotope composition of paleosol carbonates and mammalian tooth enamel from stratigraphic sections in northwestern Wyoming. Carbon isotope correlation demonstrates that a short interval of extreme high-latitude warming coincided precisely with the first appearance of several important modern mammalian orders. In addition, oxygen isotope analyses of fossils and paleosol carbonates provide information about climatic conditions on land in the Paleogene. We reconstructed the oxygen isotope composition of local meteoric water using biogenic minerals. Paleocene-Eocene meteoric water was significantly 18 O-depleted, indicating substantial loss of water vapor during its transport to the region. Soil temperature was calculated as a proxy for mean annual temperature, assuming oxygen isotope equilibrium between soil carbonate and meteoric water. Calculated temperatures were plausible (≈10–25°C), but highly variable, prohibiting high-resolution analysis of local temperature variations in response to global climatic warming.

Tectonics and sequence stratigraphy in Messinian basins, Sicily: Constraints on the initiation and termination of the Mediterranean salinity crisis

Research Article| April 01, 1995 Tectonics and sequence stratigraphy in Messinian basins, Sicily: Constraints on the initiation and termination of the Mediterranean salinity crisis Robert W. H. Butler; Robert W. H. Butler 1Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom Search for other works by this author on: GSW Google Scholar W. Henry Lickorish; W. Henry Lickorish 1Department of Earth Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom Search for other works by this author on: GSW Google Scholar Mario Grasso; Mario Grasso 2Istituto di Geologia e Geofisica, Università di Catania, Corso Italia, Catania, Italy Search for other works by this author on: GSW Google Scholar H. Martyn Pedley; H. Martyn Pedley 3School of Geography and Earth Resources, University of Hull, Hull HU6 7RX, and Department of Geology, University of Leicester, Leicester, United Kingdom Search for other works by this author on: GSW Google Scholar Lamberto Ramberti Lamberto Ramberti 4Italkali, Palermo, Italy Search for other works by this author on: GSW Google Scholar GSA Bulletin (1995) 107 (4): 425–439. https://doi.org/10.1130/0016-7606(1995)107<0425:TASSIM>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Robert W. H. Butler, W. Henry Lickorish, Mario Grasso, H. Martyn Pedley, Lamberto Ramberti; Tectonics and sequence stratigraphy in Messinian basins, Sicily: Constraints on the initiation and termination of the Mediterranean salinity crisis. GSA Bulletin 1995;; 107 (4): 425–439. doi: https://doi.org/10.1130/0016-7606(1995)107<0425:TASSIM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Deposits within the Caltanissetta basin of central Sicily have been important for developing the desiccating deep basin model for the Messinian salinity crisis in the Mediterranean. Linked structural and stratigraphic studies show that the Sicilian depocenters are synclines related to underlying thrust structures of the frontal part of the Maghrebian chain. Prior to the salinity crisis these basins were hydrodynamically linked through the foredeep to the Mediterranean. The precursor sediments (Terravecchia Formation) formed a delta, sourced from the north. Early Messinian regression acted on a range of paleobathymetries, shallow in the north and progressively deeper in the south, locally complicated by active thrust structures. Initial draw-down of Mediterranean base level is marked across the thrust belt by first cycle carbonates and evaporites on the structural highs and lows, respectively. Vast accumulations of halite and potassium salts (up to 1200 m) are restricted to growing thrust synclines. The different evaporite signatures may be related to different water conditions reflecting various meteoric and marine circulations across various subbasins, with cyclicity reflecting high-frequency variations in sea level. A sequence stratigraphic model is developed to explain fractionation of evaporite facies between different paleobathymetric settings and to predict the temporal evolution of the successions in different subbasins. Thrusting provides accommodation space for evaporites and also controls the water pathways into the desiccating basins. The intra-Messinian unconformity separating first and second cycle evaporites is a “type 1 sequence boundary” related to the forced regression associated with the acme of Mediterranean desiccation, an interpretation supported by local ravinement and incised valley fills. The overlying second cycle evaporites are a combination of detrital, reworked first cycle material and primary gypsum formed under brackish water. Regional onlap relationships and bed continuity suggest that this water body was of regional extent with a systematically rising base level. These interpretations have several implications for Messinian correlations in the Mediterranean: The deep basin evaporites correlate with an intra-Messinian unconformity that separates the two cycles on Sicily and postdate the first cycle deposits; regional base level was largely restored before the end of the salinity crisis. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geochemistry of precambrian carbonates: VI. Aphebian albanel formations, Quebec, Canada

Abstract The ~1.85 + 0.15 Ga old Albanel Formations of northern Quebec, Canada, an example of Paleoproterozoic carbonate buildups, are lithologically composed of cherty dolostones. Subordinate limestones are encountered only near the base of the sequence, coincident with maximal transgression. The chemistry of the bulk rocks is almost entirely controlled by noncarbonate phases, such as chert, quartz, plagioclase, illite (±K-spar), pyrite and Fe-Mn oxides, all abundant particularly in the basal part of the section. The chemistry of the carbonate portion of limestones is strongly reset by post-depositional phenomena, but the relict high Sr contents suggest that aragonite may have been an original precursor phase. Geochemically, the carbonate portion of dolostones can be subdivided into two populations, reflecting the stratigraphie bottom and top of the sequence. Trace element and oxygen isotope criteria suggest that the entire sequence was subjected to meteoric and subsequent burial diagenesis, with the less deeply buried top portion of the sequence having recrystallized and stabilized at lower temperatures, but in a more open system. The latter reflects the greater lithological variability and permeability of the younger strata. The δ13C varies up-section from about +3 to + 1‰, perhaps a reflection of progressively more open marine circulation. The associated four generations of post-depositional pyrites have overlapping δ34S, from -7.1 to +54‰, with a mean of +24‰; a reflection of dissimilatory bacterial sulfate reduction in a relatively closed diagenetic system with perhaps a limited sulfate availability and/or replenishment. The best measured 87 Sr 86 Sr of 0.70600, although possibly not a direct reflection of the coeval seawater, may still be a near-original value, as indicated by its coherency with the roughly co-stratigraphic Paleo-proterozoic sequences. Evaluation of the existing data indicates that strontium isotopic composition of the Precambrian seawater was characterized by oscillations similar to those of the Phanerozoic, the interval of ~0.8–1.5 Ga ago being dominated by relatively nonradiogenic values, followed by a radiogenic period at ~ 1.6–2.2 Ga ago, near-mantle values during the late Archean, and possibly another radiogenic peak at ~3.5 Ga ago.