Distribution by Scientific Domains
Distribution within Earth and Environmental Science

Kinds of Stratigraphy

  • jurassic stratigraphy
  • pollen stratigraphy
  • sequence stratigraphy
  • site stratigraphy

  • Selected Abstracts


    M. Nadjafi
    The Oligo-Miocene Asmari Formation is one of the most important petroleum reservoir units in the Zagros Basin of south and SW Iran. It mainly consists of limestones and dolomitic limestones with interbedded shales, together with a few intervals of sandstone and gypsum assigned to the Ahwaz and Kalhur Members, respectively. The Asmari Formation rests on the thin-bedded limestones of the Jahrum Formation (Paleocene-Eocene). In this paper, we report on the lithofacies characteristics of these two formations using data from three measured outcrop sections near Shiraz in SW Iran. From field and petrographic data, we have identified four major lithofacies and twelve subfacies which are interpreted to have been deposited in open-marine, shoal, lagoon and tidal flat settings. We show that the Asmari and Jahrum Formations constitute two separate depositional sequences which are separated by a thin palaeosol, representing a type-one sequence boundary which can be correlated with global curves of relative sea-level. Each depositional sequence is composed of many metre-scale shallowing-upward parasequences. This is the first time that the Asmari and Jahrum Formations have been differentiated in the study area. We hope that this study will lead to a better understanding of the Asmari Formation in the subsurface in other parts of the Zagros Basin. [source]


    Yang Yongtai
    Although Mesozoic source and reservoir rocks are known to occur at oilfields in the northern Qaidam Basin (NW China), the precise identification and distribution of Mesozoic rocks in the subsurface are outstanding problems. The Dameigou locality has in the past been considered as the type section for Lower-Middle Jurassic strata in northern Qaidam. Previous studies have concluded that the onset of non-marine sedimentation here took place in the Early Jurassic; and that Mesozoic strata penetrated by wells in the Lenghu structural zone are Middle Jurassic. In this paper, we present new data from the Lengke-1 well, drilled in the Lenghu structural zone in 1997. This data indicates the existence of a more extensive pre-Middle Jurassic stratigraphy than has previously been recognized. Biostratigraphic data together with regional seismic mapping suggest that the pre-Middle Jurassic succession at Lengke-1 includes both Late Triassic and Early Jurassic deposits. The Late Triassic sedimentary rocks appear to have been deposited in local half graben, some of which were later inverted during Jurassic, Cretaceous and Cenozoic tectonism. Lower and Middle Jurassic strata (lacustrine and fluvial deposits) are present in the SW and NE parts of the Lenghu structural zone, respectively. Extensive organic-rich intervals are present in both successions. Lower Jurassic lacustrine mudstones may represent a previously under-appreciated, and potentially large, source rock sequence. [source]


    PALAEONTOLOGY, Issue 1 2007
    Abstract:, The Much Wenlock Limestone Formation of the Dudley inliers, West Midlands, contains one of the world's richest and most exquisitely preserved Silurian marine biotas. However, for most museum specimens, little is known of their exact provenance and mode of preservation. Detailed comparisons between outcrops and museum collections allow the identification of five faunal-lithological associations and numerous horizons of exceptional skeletal preservation. The associations are interpreted as a series of transient carbonate mid-platform environments extending from below storm wave-base to above fair-weather wave-base. Erosive surfaces, condensed sections, flooding surfaces and the stacking patterns of genetically related bed-sets (parasequences) have allowed the formation to be interpreted as a single third-order sequence stratigraphic cycle of sea-level change. The articulated preservation of taxa such as pelmatozoan echinoderms and trilobites can be attributed to either rapid burial by obrution deposits close to fair-weather wave-base or smothering by storm sequestered muds in slightly deeper-water settings. Such intervals of exceptional preservation are commonly associated with flooding surfaces, presumably reflecting reduced likelihood of reworking once rapid burial had taken place. [source]

    Stratigraphy and formation processes of the Upper Pleistocene deposit at Gruta da Oliveira, Almonda karstic system, Torres Novas, Portugal

    Diego E. Angelucci
    Gruta da Oliveira is a cave located in the Almonda karstic system in central Portugal. Its Upper Pleistocene fill is made up of gravitational sediments with varied biogenic and anthropogenic inputs. The archaeological sequence (35,70 ka) is fairly homogeneous, reflecting a predominantly moist climatic context modulated by millennial-scale variations. Human occupation was almost continuous throughout. In the richer archaeological layers (8,14), the anthropogenic components are in primary position, and post-depositional processes are restricted, although penecontemporaneous biological activity,such as hyena scavenging,overprinted the record. In layers 15,19, the excavated area corresponds to the footslope of a talus, where accumulation proceeded mainly through runoff and where the lithics and bones derive from occupations situated ca. 5m outward. The base of the deposit is >2m from the current base of the excavation, suggesting that Oxygen Isotope Stage (OIS)-4 and OIS-5 sediments underlay the deposit already exposed. This study confirms the archaeological integrity of the Mousterian assemblages found in the different layers, and, given the dates for layer 8, supports the hypothesis that Neanderthals survived in western Iberia until at least 35,000,38,000 calendar years ago. © 2009 Wiley Periodicals, Inc. [source]

    Distribution of Chemical Constituents in Superimposed Ice from Austre Brøggerbreen, Spitsbergen

    H. Motoyama
    10 m and 2.3 m ice cores were obtained on Austre Brøggerbreen, Spitsbergen in Svalbard (78°53,N, 11°56,E, 450 m a.s.l.) in September 1994 and in March 1995, respectively. Stratigraphy, bulk density, pH, electrical conductivity, and major ions were obtained from the core samples. The chemical effect of meltwater percolation through snow/ice is examined. Good correlation between Cl, and Na+ was obtained. The ratio of Cl, to Na+ was 1.14 which was nearly the same value as in bulk sea water. However, the variation of Cl,/Na+ shows that higher ratio occured in the bubble-free ice. Furthermore the Cl, ions remain in higher concentration than SO 4 2, or Na+ ions. [source]

    Stratigraphy and volcanology of the Türkbükü volcanics: products of a stratovolcano in the Bodrum Peninsula, SW Anatolia

    GEOLOGICAL JOURNAL, Issue 2 2006
    Zekiye Karacik
    Abstract The Middle-Upper Miocene Bodrum magmatic complex of the Aegean region, southwestern Turkey, is mainly represented by intermediate stocks, lavas, pyroclastic and volcaniclastic deposits. Monzonitic stocks and connected porphyry intrusions and extrusions are the first products of the magmatism. These are followed by a volcanic succession consisting of andesitic-latitic lavas, autobrecciated lavas, pyroclastic and volcaniclastic deposits. The final stage is represented by basaltic and basaltic andesitic flows and dykes intruded into previous units. The volcanic succession crops out in the northern part of the Bodrum peninsula. In the lower part of this succession are widespread pyroclastic deposits, composed of pyroclastic fall and flow units, alternating with epiclastic deposits. Grain size, volume and thickness of the pyroclastic deposits were mainly controlled by the type, magnitude and intensity of the eruption. Further up the section, there are two horizons of debris avalanche deposits forming the coarsest and thickest deposits of the volcaniclastic succession. The debris avalanche deposits indicate at least two different flank collapses coeval with the volcanism. The stratigraphy and map pattern of these volcanic units imply that the northern part of the Bodrum peninsula was the north-facing flank of a stratovolcano during the mid-Late Miocene. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Stratigraphy of upper Viséan carbonate platform rocks in the Carlow area, southeast Ireland

    GEOLOGICAL JOURNAL, Issue 1 2005
    P. Cózar
    Abstract The stratigraphy of the upper Viséan (Asbian to Brigantian) carbonate succession in southeast Ireland is revised on the basis of seven quarry and two borehole sections. Six lithological units have been distinguished, two units (units 1 and 2) in the upper Asbian Ballyadams Formation, and four units (units 4 to 6) in the Brigantian Clogrenan Formation (both formations are dated precisely using foraminiferans, calcareous algae and rugose corals). The boundary between the Ballyadams and Clogrenan formations is redefined 19,m below the horizon proposed by the Geological Survey of Ireland, and thus, lithological characteristics of both formations are redescribed. The upper part of the Ballyadams Formation is characterized by well-developed large-scale cyclicity, with common subaerial exposure surfaces. Fine- to medium-grained thin-bedded limestones with thin shales occur in the lower part of cycles, passing up into medium-grained pale grey massive limestones in the upper part. The Clogrenan Formation is composed mainly of medium- to coarse-grained thick limestone beds with variable presence of shales; but no large-scale cyclicity. There is a decrease in the number of subaerial exposure surfaces towards the top of the formation and common chert nodules; macrofauna occurs mostly concentrated in bands. The six units recognized in the Carlow area are comparable with other units described for the same time interval (Asbian,Brigantian) from south and southwest Ireland, demonstrating the existence of a stable platform for most parts of southern Ireland, controlled principally by glacioeustatics. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Deterministic and Stochastic Modeling of Aquifer Stratigraphy, South Carolina

    GROUND WATER, Issue 2 2000
    Russell B. Miller
    Deterministic and stochastic methods of three-dimensional hydrogeologic modeling are applied to characterization of contaminated Eocene aquifers at the Savannah River Site, South Carolina. The results address several important issues, including the use of multiple types of data in creating high-resolution aquifer models and the application of sequence-stratigraphic constraints. Specific procedures used include defining grid architecture stratigraphically, upscaling, modeling lithologic properties, and creating multiple equiprobable realizations of aquifer stratigraphy. An important question answered by the study is how to incorporate gamma-ray borehole-geophysical data in areas of anomalous log response, which occurs commonly in aquifers and confining units of the Atlantic Coastal Plain and other areas. To overcome this problem, gamma-ray models were conditioned to grain-size and lithofacies realizations. The investigation contributes to identifying potential pathways for downward migration of contaminants, which have been detected in confined aquifers at the modeling site. The approach followed in this investigation produces quantitative, stratigraphically constrained, geocellular models that incorporate multiple types of data from borehole-geophysical logs and continuous cores. The use of core-based stochastic realizations in conditioning deterministic models provides the advantage of incorporating lithologic information based on direct observations of cores rather than using only indirect measurements from geophysical logs. The high resolution of the models is demonstrated by the representation of thin, discontinuous clay beds that act as local barriers to flow. The models are effective in depicting the contrasts in geometry and heterogeneity between sheet-like nearshore-transgressive sands and laterally discontinuous sands of complex shoreline environments. [source]

    Stratigraphy of the mid- to upper-Cretaceous System in the Aridagawa area, Wakayama, Southwest Japan

    ISLAND ARC, Issue 3 2010
    Akihiro Misaki
    Abstract The litho- and biostratigraphy of the mid- to upper-Cretaceous System around the Yagumaike Pond in the Aridagawa area, Wakayama, Southwest Japan, were investigated. Many Middle to Late Albian megafossils were found in the strata of a block bounded by faults. It was also revealed that the Upper Cretaceous System of other blocks ranges from the Middle Turonian to Santonian. The Albian megafossil assemblage contains few benthic organisms, in contrast with the abundance of nektons found (e.g. cephalopods). Sedimentological observations of the mudstone profiles also indicate that scarcely or weakly bioturbated, well-laminated mudstone is dominant among the Albian deposits. These results suggest deposition of the Albian mudstone under a dysaerobic to anoxic environment. It is comparable to the extended oceanic anoxia (OAEs) in mid-Cretaceous time. Albian deposits with similar characteristics are also known to exist in Shikoku, Southwest Japan. A wide sedimentary basin that was directly affected by global environmental events, such as OAEs, seemed to be formed on the Chichibu Belt in the Albian. The Upper Cretaceous strata in the study area are extremely thin, similar to the coeval deposits on the Chichibu Belt in Shikoku. It is suggested that the sedimentation rate in the sedimentary basin on the Chichibu Belt was extremely low during early Late Cretaceous time. [source]

    Formal ratification of the Quaternary System/Period and the Pleistocene Series/Epoch with a base at 2.58 Ma,

    Philip L. Gibbard
    Abstract In June 2009, the Executive Committee of the International Union of Geological Sciences (IUGS) formally ratified a proposal by the International Commission on Stratigraphy to lower the base of the Quaternary System/Period to the Global Stratotype Section and Point (GSSP) of the Gelasian Stage/Age at Monte San Nicola, Sicily, Italy. The Gelasian until then had been the uppermost stage of the Pliocene Series/Epoch. The base of the Gelasian corresponds to Marine Isotope Stage 103, and has an astronomically tuned age of 2.58 Ma. A proposal that the base of the Pleistocene Series/Epoch be lowered to coincide with that of the Quaternary (the Gelasian GSSP) was also accepted by the IUGS Executive Committee. The GSSP at Vrica, Calabria, Italy, which had hitherto defined the basal boundary of both the Quaternary and the Pleistocene, remains available as the base of the Calabrian Stage/Age (now the second stage of the revised Pleistocene). In ratifying these proposals, the IUGS has acknowledged the distinctive qualities of the Quaternary by reaffirming it as a full system/period, correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the Pleistocene to that of the Quaternary, and fully respected the historical and widespread current usage of both the terms ,Quaternary' and ,Pleistocene'. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    The Ediacaran Period: a new addition to the geologic time scale

    LETHAIA, Issue 1 2006
    The International Union of Geological Sciences has approved a new addition to the geologic time scale: the Ediacaran Period. The Ediacaran is the first Proterozoic period to be recognized on the basis of chronostratigraphic criteria and the first internationally ratified, chronostratigraphically defined period of any age to be introduced in more than a century. In accordance with procedures established by the International Commission on Stratigraphy, the base of the Ediacaran Period is defined by a Global Stratotype Section and Point (GSSP) placed at the base of the Nuccaleena Formation cap carbonate directly above glacial diamictites and associated facies at Enorama Creek in the Flinders Ranges of South Australia. Its top is defined by the initial GSSP of the Cambrian Period. The new Ediacaran Period encompasses a distinctive interval of Earth history that is bounded both above and below by equally distinctive intervals. Both chemostratigraphic and biostratigraphic data indicate that the subdivision of the period into two or more series is feasible, and this should be a primary objective of continuing work by the Ediacaran Subcommission of the ICS. [source]

    Geologic Time Scale 2004 , why, how, and where next!

    LETHAIA, Issue 2 2004
    A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. The construction of Geologic Time Scale 2004 (GTS2004) incorporated different techniques depending on the data available within each interval. Construction involved a large number of specialists, including contributions by past and present subcommissions officers of the International Commission on Stratigraphy (ICS), geochemists working with radiogenic and stable isotopes, stratigraphers using diverse tools from traditional fossils to astronomical cycles to database programming, and geomathematicians. Anticipated advances during the next four years include formalization of all Phanerozoic stage boundaries, orbital tuning extended into the Cretaceous, standardization of radiometric dating methods and resolving poorly dated intervals, detailed integrated stratigraphy for all periods, and on-line stratigraphic databases and tools. The geochronological science community and the International Commission on Stratigraphy are focusing on these issues. The next version of the Geologic Time Scale is planned for 2008, concurrent with the planned completion of boundary-stratotype (GSSP) definitions for all international stages. [source]


    ARCHAEOMETRY, Issue 1 2007
    Many authors have considered pottery manufacturing constraints and sociocultural elements as factors in change in past civilizations over time. The main issue of this research is to better understand the reasons for changes, or choices, in pottery raw materials. The very precise and detailed stratigraphy and cultural succession of occupations is based on dendrochronological data from the lake-dwelling sites of Chalain (Jura, France). Petrographic, palaeontological and chemical analyses were used to determine the nature and origins of the raw materials used by the Neolithic potters. Stratigraphy and dendrochronological data were used to reconstruct in detail the evolution dynamics of fabric changes. Several raw material sources were identified for many of the pottery groups. Each of them was sampled for qualitative experimental tests of pottery forming. The experimental results show a high variability between the sediments tested. This variability was quantitatively estimated by XRF, XRD, the Rietveld method, calcium carbonate quantification and laser grain-size analyses of matrices, indirect measures of plasticity. These analytical results allow a better understanding of the differences observed in the experimental tests. On the basis of these experimental and analytical results, changing parameters such as pottery manufacturing constraints, mineralogical characteristics of raw materials and sociocultural factors are considered. In conclusion, all the social and technical parameters, in each archaeological context, must be taken into account for a better understanding of the changes occurring throughout the chronological sequence. [source]

    Late Carboniferous-Early Permian Sequence Stratigraphy and Depositional Evolution in the Northeast Ordos Basin, North China

    YANG Minghui
    Abstract: Sequence stratigraphical analysis was applied to the Upper Carboniferous-Lower Permian sedimentary succession of the northeastern Ordos Basin, north China based on data acquired from ten entire logging curves and eight outcrops. The facies framework of the lithostratigraphical unit, the Taiyuan Formation comprises seven facies in two facies associations, varying from fluvio-delta to shelf-barrier islands. The facies are presented within a chronostratigraphical framework, linked by systems tract, which in turn are limited by flooding surfaces and sequence boundaries. Six third-order depositional sequences are recognised, bounded by six type 2 unconformities. An upwards-shallowing epicontinental sea sedimentary model is created, which consists of a sandstone, coal seam and carbonate succession. [source]

    Stratigraphy, sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end-moraine zone

    BOREAS, Issue 2 2010
    Johnson, M. D. & Ståhl, Y. 2009: Stratigraphy, sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end-moraine zone. Boreas, 10.1111/j.1502-3885.2009.00124.x. ISSN 0300-9483 Deglaciation of the Middle Swedish end-moraine zone and age of the sediment in and between the moraines have been discussed for about a hundred years. The goal of this project was to determine the stratigraphy and age of the sediment in and between the moraines. Inter-moraine flats are underlain by clay, 10,25 m thick, overlying thin sand and gravel or till on bedrock. The clay is overlain by a few metres of sand and gravel. Much of the clay beneath the flats consists of rhythmites that grade from grey to red and are 2,74 cm thick. Our interpretation of these rhythmites as being varves is supported by grain size and mineralogical and elemental variations. Foraminifera and ostracods show that the clay was deposited in an arctic marine environment, while radiocarbon dating of the microfossils indicates that the clay was deposited 12 150 cal. 14C years ago, during the Younger Dryas chronozone (YD). Most of the optical stimulated luminescence dates on the clay are much older, containing quartz sand that was insufficiently bleached. The stratigraphy indicates that the moraines are composed of YD clay pushed into ridge forms during ice-front oscillations. It is not possible to determine how far north the Scandinavian Ice Sheet retreated prior to the YD advance. We neither support nor reject the suggestion that the ice margin retreated to the northern edge of Mt. Billingen during the Allerød, causing the Baltic Ice Lake to drain. [source]

    Stratigraphy and sedimentation of the stratotype sections of the Catfish Creek Drift Formation between Bradtville and Plum Point, north shore, Lake Erie, southwestern Ontario, Canada

    BOREAS, Issue 2 2005
    Dreimanis, A. & Gibbard, P. 2005 (May): Stratigraphy and sedimentation of the stratotype sections of the Catfish Creek Drift Formation between Bradtville and Plum Point, north shore, Lake Erie, southwestern Ontario, Canada. Boreas, Vol. 34, pp. 101,122. Oslo. ISSN 0300,9483. The Catfish Creek Drift Formation is a significant and extensive lithostratigraphical marker unit in SW Ontario. Here the stratotype, exposed in the Lake Erie bluffs of the Plum Point-Bradtville (Grandview) area south of London, Ontario, Canada, is proposed. It consists of subglacial and proglacial sediments deposited at the beginning of the Nissouri Phase of the Wisconsinan glaciation. In the 2.5-km-long stratotype section, the Catfish Creek Drift consists of 9 members. Five of them, the Dunwich and Grandview I-IV members, mainly consist of till, with minor components of stratified drift. The Dunwich till was deposited by the Huron-Georgian Bay lobe, but the Grandview I-IV tills by the Erie lobe. The Zettler Farm Member consists of co-lobal till in the central part of the section and of a proglacial waterlain flow diamicton and a subglacial undermelt diamicton in the SW part. Three members consist entirely of stratified drift; the glaciolacustrine silty and clayey Waite Farm Member, the ice-marginal deltaic Oosprink Farm Member and the Boy Scout Camp Member , deposited by meltwater streams in subglacial channels. The sequence of interbedded till and stratified drift represents the oscillating advance of the Laurentide Ice Sheet in the Lake Erie basin. [source]

    Stratigraphic investigations at Los Buchillones, a coastal Taino site in north-central Cuba

    Matthew C. Peros
    The authors present stratigraphic data from Los Buchillones, a now submerged Taino village on the north coast of central Cuba that was occupied from some time prior to A.D. 1220 until 1640 or later. Los Buchillones is one of the best-preserved sites in the Caribbean, with material culture remains that include palm thatch and wooden structural elements from some of the more than 40 collapsed structures. The purpose of this study was to investigate the environment and site-formation processes of the Taino settlement. Sediment cores were sampled from the site and its vicinity to permit integration of the geological and archaeological stratigraphies. The cores were analyzed for color, texture, mollusk content, elemental geochemistry, and mineralogy. The results of the stratigraphic work are consistent with regional sealevel data that shows relative sea level has risen gradually during the late Holocene, but has remained relatively stable since the time the Taino first occupied Los Buchillones. Of the two structures partially cleared, at least one appears to have been built over the water, supported on pilings. Site selection is likely to have resulted from a consideration of environmental factors, such as access to marine, terrestrial, and lagoonal resources, and proximity to freshwater springs. © 2006 Wiley Periodicals, Inc. [source]

    Persistence of coastal spruce refugia during the Holocene in northern New England, USA, detected by stand-scale pollen stratigraphies

    JOURNAL OF ECOLOGY, Issue 2 2002
    Molly Schauffler
    Summary 1 Pollen data from wet, forested hollows in five spruce (Picea) stands on the eastern coast of Maine, USA, reveal that spruce has been well-established (spruce pollen > 6%) for at least 5000 years at four of the sites (Isle au Haut, Schoodic Peninsula, and Roque Island). Spruce became dominant in the fifth stand (Blackwoods, Mount Desert Island) only in the last 2000 years. This is in contrast to pollen stratigraphies from two inland forest hollows and from inland lakes that indicate a significant region-wide increase in the abundance of spruce only 1000 years ago. 2 All five coastal pollen stratigraphies suggest that conditions along the east coast of Maine became cooler and moister sometime between 6000 and 5000 years ago. Mid-Holocene changes in vegetation and sediment accumulation correspond with the timing of rapid increases in tidal amplitude and diurnal mixing of cold water in the Gulf of Maine, suggestive that these resulted in increased marine effects on the local climate at a time that was generally warmer than present. 3 Two inland forest-hollow stratigraphies do not show evidence of mid-Holocene cooling. Coastal effects therefore persisted for several thousand years despite regional climate changes. 4 The pollen data suggest that refugia along the coast (and probably in isolated sites inland), may have played a critical role in allowing the rapid regional expansion of spruce around 1000 years ago. The steep increases in the abundance of spruce pollen in all forest-hollow and lake pollen stratigraphies in northern New England at that time corroborate other evidence of a region-wide shift to cooler and moister conditions. 5 Pollen stratigraphies from small forested hollows provide a means to examine local vegetation dynamics and interpret those dynamics in the context of regional signals. [source]

    Quantitative palaeotemperature records inferred from fossil pollen and chironomid assemblages from Lake Gilltjärnen, northern central Sweden,

    Karin Antonsson
    Abstract Palaeotemperature reconstructions based on radiocarbon-dated fossil pollen and chironomid stratigraphies obtained from Lake Gilltjärnen provide evidence of climate changes during the last 11,000 years in the boreal zone of northern central Sweden. The records show consistent trends during the early and mid-Holocene, indicating low temperatures at 11,000,10,000,cal.,yr,BP, followed by a rising trend and a period of maximum values from about 7000 to 4000,cal.,yr,BP. At 3000,cal.,yr,BP the chironomid-inferred temperature values rise abruptly, deviating from the late-Holocene cooling trend indicated by the pollen-based reconstruction and most of the other palaeotemperature records from central Scandinavia, probably as a result of local limnological changes in Lake Gilltjärnen and its catchment. Comparison of the present results with a lake-level reconstruction from Lake Ljustjärnen, ca. 100,km southwest of Lake Gilltjärnen, shows that the low early-Holocene temperatures were associated with high lake-levels at 10,500,8500,cal.,yr,BP, whereas low lake-levels and dry conditions prevailed during the period of high temperatures at between 7500 and 5000,cal.,yr,BP, probably due to high summer evapotranspiration and lower precipitation. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview

    BASIN RESEARCH, Issue 4 2010
    Mads Huuse
    ABSTRACT Subsurface sediment remobilization and fluid flow processes and their products are increasingly being recognized as significant dynamic components of sedimentary basins. The geological structures formed by these processes have traditionally been grouped into mud volcano systems, fluid flow pipes and sandstone intrusion complexes. But the boundaries between these groups are not always distinct because there can be similarities in their geometries and the causal geological processes. For instance, the process model for both mud and sand remobilization and injection involves a source of fluid that can be separate from the source of sediment, and diapirism is now largely discarded as a deformation mechanism for both lithologies. Both mud and sand form dykes and sills in the subsurface and extrusive edifices when intersecting the sediment surface, although the relative proportions of intrusive and extrusive components are very different, with mud volcano systems being largely extrusive and sand injectite systems being mainly intrusive. Focused fluid flow pipes may transfer fluids over hundreds of metres of vertical section for millions of years and may develop into mud volcano feeder systems under conditions of sufficiently voluminous and rapid fluid ascent associated with deeper focus points and overpressured aquifers. Both mud and sand remobilization is facilitated by overpressure and generally will be activated by an external trigger such as an earthquake, although some mud volcano systems may be driven by the re-charge dynamics of their fluid source. Future research should aim to provide spatio-temporal ,injectite' stratigraphies to help constrain sediment remobilization processes in their basinal context and identify and study outcrop analogues of mud volcano feeders and pipes, which are virtually unknown at present. Further data-driven research would be significantly boosted by numerical and analogue process modelling to constrain the mechanics of deep subsurface sediment remobilization as these processes can not be readily observed, unlike many conventional sediment transport phenomena. [source]

    Sediment compaction rates and subsidence in deltaic plains: numerical constraints and stratigraphic influences

    BASIN RESEARCH, Issue 1 2007
    T. A. Meckel
    ABSTRACT Natural sediment compaction in deltaic plains influences subsidence rates and the evolution of deltaic morphology. Determining compaction rates requires detailed knowledge of subsurface geotechnical properties and depositional history, neither of which is often readily available. To overcome this lack of knowledge, we numerically forward model the incremental sedimentation and compaction of stochastically generated stratigraphies with geotechnical properties typical of modern depositional environments in the Mississippi River delta plain. Using a Monte Carlo approach, the range of probable compaction rates for stratigraphies with compacted thicknesses <150 m and accumulation times <20 kyr. varies, but maximum values rarely exceed a few mm yr,1. The fastest compacting stratigraphies are composed primarily of peat and bar sand, whereas the slowest compacting stratigraphies are composed of prodelta mud and natural levee deposits. These results suggest that compaction rates can significantly influence vertical and lateral stratigraphic trends during deltaic evolution. [source]

    Late Weichselian pollen stratigraphy, clay varve chronology and palaeomagnetic secular variations in Lake Bolmen, Småland, south Sweden

    BOREAS, Issue 3 2001
    Pollen analysis, glacial varve chronology and palaeomagnetic measurements were carried out on Late Weichselian lake sediments from southwestern Smaland, south Sweden. The sequence is correlated to the GRIP event stratigraphy, expressed in calendar years BP, and covers the period from the deglaciation at c. 14 400 to 11 300 calendar years BP. The series encompasses c. 930 varves and has been connected to the local varve chronology. Varve thickness increases markedly after the Older Dryas stadial, which indicates an accelerated deglaciation and melting of dead ice. The pollen diagram displays the vegetation development from the deglaciation at c. 14 400 calendar years BP to the transition to the Holocene. The vegetation succession starts with an arctic pioneer vegetation at the deglaciation, changes to a more stable tundra environment and displays a development which concurs with the traditional lateglacial pollen stratigraphy for southern Sweden. A palaeo-magnetic secular variation curve is presented displaying two westerly declination swings at 14200-13800 and 12 800-11 600 calendar years BP, respectively. The upper one can be recognized from other palaeomagnetic stratigraphies from southern Sweden and Estonia. [source]

    The use of multivariate statistics to elucidate patterns of floodplain sedimentation at different spatial scales

    Martin C. Thoms
    Abstract Floodplains are depositional features of riverine landscapes that display complex sedimentation patterns that are amenable to multi-scale approaches. We examined sedimentation in the Lower Balonne floodplain, Queensland, Australia, at three different spatial scales: the channel (103 km), floodplain process zone (10 km) and geomorphic unit (102 m) scales, and compared scale-related patterns evident from stratigraphy with those evident from quantitative multivariate analysis. Three stratigraphic sequences were found in the Lower Balonne floodplain: generally fining upward, episodic fining upward, and mud-dominated. Stratigraphical analysis revealed the detailed character of sedimentary sequences embedded within the scale patterns derived from multivariate analysis. Multivariate statistical analyses of a range of textural and geochemical data revealed different patterns of floodplain sedimentation at each scale. At the channel scale, sediment texture and geochemistry were more heterogeneous in the Culgoa River than in Briarie Creek. At the floodplain process zone scale clear patterns of sediment texture and geochemistry were observed along the upper, mid and lower floodplain process zones of Briarie Creek, but not along the Culgoa River. At the geomorphic unit scale, clear patterns of sediment texture and geochemistry were observed among the bank, buried channel and flat floodplain units of the Culgoa River, but were not as clear in Briarie Creek. Recognition of rivers as hierarchically organized systems is an emerging paradigm in river science. Our study supports this paradigm by demonstrating that different sedimentation patterns occur at different scales to reveal a hierarchically organized floodplain environment. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Investigations regarding Alpine talus slopes using ground-penetrating radar (GPR) in the Bavarian Alps, Germany

    Oliver Sass
    Abstract The applicability of ground-penetrating radar (GPR) for the investigation of loose debris was tested at two sites (Viererkar and Zugspitzplatt). A pulseEKKO 100 GPR system equipped with 25 MHz antennae was utilized. The aim of the investigation was to record the base of the debris layer, and thereby acquire an estimation of the backweathering rates of the adjacent rockwalls. The study areas are situated in the Northern Alps near the German,Austrian border. The sites are characterized by steep limestone rockwalls and extensive talus accumulations. A total of six profiles was surveyed. The method is suitable and effective for a quick survey in this dry, high-ohmic substrate. The GPR system was able to deliver information about the subsurface stratigraphy to c. 70 m depth. The boundary line to the bedrock was discovered , depending upon the profile surveyed ,5 to 25 m below the surface. The base of the debris material sometimes shows no distinct reflection. Buried features (V-shaped furrows, zones overdeepened by ice action, geological structures) could be detected. Arched structures well below the talus,bedrock interface can be interpreted as drainage systems in the karstic bedrock. A thick scree layer of Late Glacial age was separated from a thinner layer on the talus surface, which was related to the Holocene. The backweathering rates were fixed by a calculation of talus volume to c. 100 mm/103 a during the Holocene (Viererkar) and 150,300 mm/103 a (Zugspitzplatt). The detrital formation in north-exposed sites is twice as intense as in south-exposed sites. These results match the rates of recent rockfall in the same area of investigation. The calculated backweathering for the late glacial period is 150,730 mm/103 a. The magnitude of the calculated rockwall retreat lies well within the range of previous measurements. The discrepancy between some weathering rates highlights the fact that recent and past relief formation must be differentiated. Otherwise recent removal rates may be overestimated. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Sources for sedimentary bacteriohopanepolyols as revealed by 16S rDNA stratigraphy

    Marco J. L. Coolen
    Summary Bacteriohopanoids are widespread lipid biomarkers in the sedimentary record. Many aerobic and anaerobic bacteria are potential sources of these lipids which sometimes complicates the use of these biomarkers as proxies for ecological and environmental changes. Therefore, we applied preserved 16S ribosomal RNA genes to identify likely Holocene biological sources of bacteriohopanepolyols (BHPs) in the sulfidic sediments of the permanently stratified postglacial Ace Lake, Antarctica. A suite of intact BHPs were identified, which revealed a variety of structural forms whose composition differed through the sediment core reflecting changes in bacterial populations induced by large changes in lake salinity. Stable isotopic compositions of the hopanols formed from periodic acid-cleaved BHPs, showed that some were substantially depleted in 13C, indicative of their methanotrophic origin. Using sensitive molecular tools, we found that Type I and II methanotrophic bacteria (respectively Methylomonas and Methylocystis) were unique to the oldest lacustrine sediments (> 9400 years BP), but quantification of fossil DNA revealed that the Type I methanotrophs, including methanotrophs related to methanotrophic gill symbionts of deep-sea cold-seep mussels, were the main precursors of the 35-amino BHPs (i.e. aminopentol, -tetrol and -triols). After isolation of the lake ,3000 years ago, one Type I methanotroph of the ,methanotrophic gill symbionts cluster' remained the most obvious source of aminotetrol and -triol. We, furthermore, identified a Synechococcus phylotype related to pelagic freshwater strains in the oldest lacustrine sediments as a putative source of 2-methylbacteriohopanetetrol (2-Me BHT). This combined application of advanced geochemical and paleogenomical tools further refined our knowledge about Holocene biogeochemical processes in Ace Lake. [source]

    The Tendaguru Formation (Late Jurassic to Early Cretaceous, southern Tanzania): definition, palaeoenvironments, and sequence stratigraphy

    Robert Bussert
    Abstract The well-known Late Jurassic to Early Cretaceous Tendaguru Beds of southern Tanzania have yielded fossil plant remains, invertebrates and vertebrates, notably dinosaurs, of exceptional scientific importance. Based on data of the German-Tanzanian Tendaguru Expedition 2000 and previous studies, and in accordance with the international stratigraphic guide, we raise the Tendaguru Beds to formational rank and recognise six members (from bottom to top): Lower Dinosaur Member, Nerinella Member, Middle Dinosaur Member, Indotrigonia africana Member, Upper Dinosaur Member, and Rutitrigonia bornhardti-schwarzi Member. We characterise and discuss each member in detail in terms of derivation of name, definition of a type section, distribution, thickness, lithofacies, boundaries, palaeontology, and age. The age of the whole formation apparently ranges at least from the middle Oxfordian to the Valanginian through Hauterivian or possibly Aptian. The Tendaguru Formation constitutes a cyclic sedimentary succession, consisting of three marginal marine, sandstone-dominated depositional units and three predominantly coastal to tidal plain, fine-grained depositional units with dinosaur remains. It represents four third-order sequences, which are composed of transgressive and highstand systems tracts. Sequence boundaries are represented by transgressive ravinement surfaces and maximum flooding surfaces. In a more simple way, the depositional sequences can be subdivided into transgressive and regressive sequences/systems tracts. Whereas the transgressive systems tracts are mainly represented by shallow marine shoreface, tidal channel and sand bar sandstones, the regressive systems tracts predominantly consist of shallow tidal channel, tidal flat, and marginal lagoonal to supratidal deposits. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Do phytoplankton communities correctly track trophic changes?

    FRESHWATER BIOLOGY, Issue 10 2005
    An assessment using directly measured, palaeolimnological data
    Summary 1. Measurements of total phosphorus (TP) concentrations since 1975 and a 50-year time series of phytoplankton biovolume and species composition from Lake Mondsee (Austria) were combined with palaeolimnological information on diatom composition and reconstructed TP-levels to describe the response of phytoplankton communities to changing nutrient conditions. 2. Four phases were identified in the long-term record. Phase I was the pre-eutrophication period characterised by TP-levels of about 6 ,g L,1 and diatom dominance. Phase II began in 1966 with an increase in TP concentration followed by the invasion of Planktothrix rubescens in 1968, characterising mesotrophic conditions. Phase III, from 1976 to 1979, had the highest annual mean TP concentrations (up to 36 ,g L,1) and phytoplankton biovolumes (3.57 mm3 L,1), although reductions in external nutrient loading started in 1974. Phases II and III saw an expansion of species characteristic of higher nutrient levels as reflected in the diatom stratigraphy. Oligotrophication (phase IV) began in 1980 when annual average TP concentration, Secchi depth and algal biovolume began to decline, accompanied by increasing concentrations of soluble reactive silica. 3. The period from 1981 to 1986 was characterised by asynchronous trends. Annual mean and maximum total phytoplankton biovolume initially continued to increase after TP concentration began to decline. Reductions in phytoplankton biovolume were delayed by about 5 years. Several phytoplankton species differed in the timing of their responses to changing nutrient conditions. For example, while P. rubescens declined concomitantly with the decline in TP concentration, other species indicative of higher phosphorus concentrations, such as Tabellaria flocculosa var. asterionelloides, tended to increase further. 4. These data therefore do not support the hypotheses that a reduction in TP concentration is accompanied by (i) an immediate decline in total phytoplankton biovolume and (ii) persistence of the species composition characterising the phytoplankton community before nutrient reduction. [source]

    Bronze Age paleohydrography of the southern Venetian Plain

    Silvia Piovan
    The Bronze Age paleohydrography of the distal Adige and Po alluvial plain (northeastern Italy) is notable for its relations with protohistoric human activities in this area. This paper regards the stratigraphy and petrography of the Saline,Cona alluvial ridge, upon which the Saline, Sarzano, and Cantarana Bronze Age sites lie, and the petrography of Fratta alluvial ridge, upon which the Frattesina complex (Bronze,Iron Age) lies. Sand analyses indicate the Po River as the source for sediments underlying the alluvial ridge that runs through Fratta Polesine, Rovigo, Sarzano, and Cona. Radiometric ages indicate that the branch of the Saline,Cona ridge was formed by the Po River between the second half of the 3rd millennium B.C. and the end of 2nd millennium B.C. This ridge represents the maximum northward expansion of the Po alluvial system, through the same area of coastal plain crossed by the Adige and Brenta paleochannels. This paleohydrographic setting implies that fluvial connections between the Central Po Plain settlements, the Venetian Plain and Alps were relatively less complex in the Early and Middle Bronze Age than in the Late Bronze Age, when the terminal reach of the Po River was separated by the Adige River by hundreds of km2 of swampy terrain. © 2009 Wiley Periodicals, Inc. [source]

    A Reassessment of the holocene stratigraphy of the Wadi Hasa Terrace and Hasa formation, Jordan

    Joseph Schuldenrein
    Vita-Finzi's 1960s model for Mediterranean terrace evolution was once the basis for regional valley histories across much of the Levant. A revisit to the Hasa terrace, formerly considered Early to Middle Holocene in age, resulted in a revised chronostratigraphy. Sedimentological and geochemical analyses bolstered by radiocarbon dating indicate that valley floor construction began shortly after the end of the Middle Holocene, at least 2000 years later than initially proposed. An updated model for floodplain evolution proposes three discrete phases of accretion and alluvial plain formation. A weak cambic soil overprints the alluvium and suggests slightly moister climates than at present for much of the Late Holocene. This model is in accord with settlement data. Intensified uplands agropastoralism accelerated the erosion of slope soils that were recycled and deposited as alluvium across the valley floor. The valley floor sequences of the Hasa are analogous to alluvial chronologies for neighboring wadis of the eastern Jordan Rift and can be tied to key Middle and Late Holocene geomorphic events in the Dead Sea and the southwestern Levant. The data strongly indicate that alluvial fill histories after 1800 cal B.C. were anthropogenically driven, whereas Middle Holocene landscape changes were climatically and structurally triggered. © 2007 Wiley Periodicals, Inc. [source]

    Geoarchaeology of the Boca Negra Wash Area, Albuquerque Basin, New Mexico, USA

    Vance T. Holliday
    Dozens of Paleoindian sites, including the Boca Negra Wash (BNW) Folsom site (LA 124474), are scattered across a basalt plateau (the West Mesa) on the western side of the Albuquerque Basin, and adjacent uplands. The BNW site, like many others in the area, is located near a small (,60 × 90 m) playa basin that formed in a depression on the basalt surface and was subsequently covered by an eolian sand sheet (Unit 1) dated by OSL to ,23,000 yr B.P. Most of the basin fill is ,2 m of playa mud (Units 2 and 3) dating ,13,970 14C yr B.P. (17,160,16,140 cal yr B.P.) at the sand,mud interface to ,2810 14C yr B.P. (,2960,2860 cal yr B.P.) at the top. C/N ratios suggest that the BNW playa basin probably held water more often during the Folsom occupation; stable carbon isotope values indicate C3 vegetation was more common as well, but C4 grasses became dominant in the Holocene. Cores extracted from four playa basins nearby revealed a similar stratigraphy and geochronology, documenting presence of wetlands on playa floors during the Paleoindian occupation of the area. © 2006 Wiley Periodicals, Inc. [source]