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Sedimentary Sequence (sedimentary + sequence)

Distribution by Scientific Domains

Earth and Environmental Science	72%
Life Sciences	12%

Selected Abstracts

The sedimentary records in Mediterranean rockshelters and caves: Archives of environmental change

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2001
Jamie C. Woodward
It is important to develop rigorous methods and robust conceptual models for the interpretation of rockshelter and cave sediment records so that the cultural sequences they contain can be considered in their proper environmental context. Much of what we know about the prehistory of the Mediterranean region and adjacent areas has largely been pieced together from materials excavated from sedimentary sequences in these environments. The rockshelters and caves of the region form important environmental and sedimentary archives. Recent work has begun to consider if the remarkable climatic variability evident in the high resolution lacustrine and ice core records is manifest in the rockshelter and cave sediment records of the area. In this context, the two main characteristics of a rockshelter or cave site which control its usefulness as an archive of environmental change are the temporal resolution of the sedimentary record and the environmental sensitivity of the site. Many rockshelters and caves can be described as either Active Karst Settings (AKS) or Passive Karst Settings (PKS) and site type is an important influence on climatic sensitivity with a direct influence upon the usefulness of the sedimentary sequence as a proxy record of climate change. It is now clear that some sites may preserve detailed paleoclimatic records and the climatic signal may be represented by distinctive suites of micromorphological features, by variations in the input of allogenic sediment, or by fluctuations in the mineral magnetic properties of the fine sediment fraction. It can be argued that data derived from the analysis of bulk coarse-grained samples often lacks the stratigraphic resolution and environmental sensitivity that can be obtained from other approaches. The most favorable sites for detailed paleoclimatic reconstruction appear to be in active karst settings such as Theopetra Cave (Greece) and Pigeon Cave (Morocco) where micromorphological analyses offer insights into the stratigraphic record that are not otherwise obtainable. The temporal resolution of a site can only be established through a rigorous stratigraphic analysis and a comprehensive dating program. These are fundamental considerations in the study of rockshelter sediment records, especially when attempting to correlate between sites and draw comparisons with other proxy records of environmental change derived from sedimentary environments with rather different characteristics. Rockshelters and caves are part of a wider sediment system, and their investigation must be accompanied by detailed geomorphological, sedimentological, paleoecological, and geochronological studies of the off-site Quaternary record. © 2001 John Wiley & Sons, Inc. [source]

Late-glacial remains of woolly mammoth (Mammuthus primigenius) from Shropshire, UK: stratigraphy, sedimentology and geochronology of the Condover site

GEOLOGICAL JOURNAL, Issue 4 2009
J. D. Scourse
Abstract In 1986 remains of an adult woolly mammoth, Mammuthus primigenius (Blumenbach), were discovered at Norton Farm Pit, Condover, south of Shrewsbury, UK. Preliminary stratigraphical investigations indicated that this individual dated to the Devensian Late-glacial Interstadial, then the first evidence for survival of mammoth in Britain following the Last Glacial Maximum. Initial radiocarbon analysis confirmed this interpretation. Subsequent excavations in 1987/1988 recovered the remains of a further three juvenile mammoth individuals. All of these remains were found in the spoil heaps of overburden (ex situ) and their true stratigraphical context had to be reconstructed from the remnants surviving in the Pit. The 1987/1988 excavations enabled stratigraphical investigation of the site and submission of samples for radiocarbon (14C) dating, including the use of ultrafiltration pretreatment for bone samples, with the aims of reconstructing the geological and palaeoenvironmental evolution of the site and the sedimentary context of the unstratified mammoth remains. These results are presented here. This investigation indicates that the woolly mammoth remains at Condover derive from a dead-ice landscape dominated by eskers, kames and kettle-hole basins, and that the sedimentary sequence in which the mammoth remains were found forms the infilling of a kettle-hole basin. The sedimentary infilling and formation of the kettle-hole basin through ice block melt-induced subsidence were syngenetic. 14C determinations indicate that basin infill was initiated prior to Greenland Interstadial 1, and probably in Greenland Stadial 2 i.e. before 14.7,ka BP and that it continued until the early Holocene, around 8,ka BP. The sedimentological and 14C data indicate that the unstratified mammoth remains can be attributed to a dark grey clayey sandy silt (Unit C1), which accumulated during the earlier part of Greenland Interstadial 1 (14 to 14.5,ka BP) within an actively subsiding slow-flowing, beaded, fluvial network characterized by channels and pools/lakes, and with relatively shallow marginal slopes. The sedimentary architecture indicates survival of the buried ice block into Greenland Interstadial 1 and final melting only towards the end of the Interstadial at ca. 12.65,ka BP. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Geological evolution and structural style of the Palaeozoic Tafilalt sub-basin, eastern Anti-Atlas (Morocco, North Africa)

GEOLOGICAL JOURNAL, Issue 1 2008
E. A. Toto
Abstract The Tafilalt is one of a number of generally unexplored sub-basins in the eastern Anti-Atlas of Morocco, all of which probably underwent a similar tectono-stratigraphic evolution during the Palaeozoic Era. Analysis of over 1000,km of 2-D seismic reflection profiles, with the interpretation of ten regional seismic sections and five isopach and isobath maps, suggests a multi-phase deformation history for the Palaeozoic-aged Tafilalt sub-basins. Extensional phases were probably initiated in the Cambrian, followed by uniform thermal subsidence up to at least the end of the Silurian. Major extension and subsidence did not begin prior to Middle/Upper Devonian times. Extensional movements on the major faults bounding the basin to the north and to the south took place in synchronisation with Upper Devonian sedimentation, which provides the thickest part of the sedimentary sequence in the basin. The onset of the compressional phase in Carboniferous times is indicated by reflectors in the Carboniferous sequence progressively onlapping onto the Upper Devonian sequence. This period of compression developed folds and faults in the Upper Palaeozoic-aged strata, producing a structural style characteristic of thin-skinned fold and thrust belts. The Late Palaeozoic units are detached over a regional décollement with a northward tectonic vergence. The folds have been formed by the process of fault-propagation folding related to the thrust imbricates that ramp up-section from the décollement. Copyright © 2007 John Wiley & Sons, Ltd. [source]

The Cretaceous volcanic succession around the Songliao Basin, NE China: relationship between volcanism and sedimentation

GEOLOGICAL JOURNAL, Issue 2 2002
Pujun Wang
Abstract With volume ratio of 8:1:1.5 amongst acidic, intermediate and basaltic rocks, the Cretaceous volcanics around the Songliao Basin are a series of high-K or medium-K, peraluminous or metaluminous, calc-alkaline rocks, lacking typical basalts and peralkaline members of typical rift-related types. Their eruption ages range between 133 and 127,Ma, 124 and 122,Ma and 117 and 113,Ma respectively. They are high in total (Rare earth element) REE contents (96.1,326,ppm), enriched in LREE and depleted in HREE (LREE/HREE,=,4.6,13.8), with negative Eu and Ce anomalies (Eu/Eu*,=,0.04,0.88; Ce/Ce*,=,0.60,0.97). They have enriched large-ion lithophile elements (e.g. K, Ba, Th) and depleted high field strength elements (e.g. Nb, Ti and Y), suggesting a subduction-related tectonic setting. The volcanic activities migrated from south to north, forming a successively northward-stepping volcanic series and showing a feature significantly different from the overlying sedimentary sequence striking northeast. Thus, an overlap basin model was proposed. Accompanied by opening of the basin, the volcanogenic succession was formed at the block-faulting stage (131,113,Ma) owing to the closure of the Mongolia,Okhotsk ocean in the Jurassic and early Cretaceous, while the overlying sedimentary sequence was unconformably deposited at the spreading stage (Albian,Maastrichtian) owing to the oblique subduction of the Pacific plate under the Eurasian plate. The volcanic succession constitutes the lower unit of basin filling and is the forerunner of further basin spreading. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Evolution of an accretionary complex along the north arm of the Island of Sulawesi, Indonesia

ISLAND ARC, Issue 1 2004
Yusuf Surachman Djajadihardja
Abstract Seismic reflections across the accretionary prism of the North Sulawesi provide excellent images of the various structural domains landward of the frontal thrust. The structural domain in the accretionary prism area of the North Sulawesi Trench can be divided into four zones: (i) trench area; (ii) Zone A; (iii) Zone B; and (iv) Zone C. Zone A is an active imbrication zone where a decollement is well imaged. Zone B is dominated by out-of-sequence thrusts and small slope basins. Zone C is structurally high in the forearc basin, overlain by a thick sedimentary sequence. The subducted and accreted sedimentary packages are separated by the decollement. Topography of the oceanic basement is rough, both in the basin and beneath the wedge. The accretionary prism along the North Sulawesi Trench grew because of the collision between eastern Sulawesi and the Bangai,Sula microcontinent along the Sorong Fault in the middle Miocene. This collision produced a large rotation of the north arm of Sulawesi Island. Rotation and northward movement of the north arm of Sulawesi may have resulted in southward subduction and development of the accretionary wedge along North Sulawesi. Lateral variations are wider in the western areas relative to the eastern areas. This is due to greater convergence rates in the western area: 5 km/My for the west and 1.5 km/My for the east. An accretionary prism model indicates that the initiation of growth of the accretionary prism in the North Sulawesi Trench occurred approximately 5 Ma. A comparison between the North Sulawesi accretionary prism and the Nankai accretionary prism of Japan reveals similar internal structures, suggesting similar mechanical processes and structural evolution. [source]

Neoproterozoic high-pressure/low-temperature metamorphic rocks in the Avalon terrane, southern New Brunswick, Canada

JOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2001
C. E. White
Abstract High -P/low -T metamorphic rocks of the Hammondvale metamorphic suite (HMS) are exposed in an area of 10 km2 on the NW margin of the Caledonian (Avalon) terrane in southern New Brunswick, Canada. The HMS is in faulted contact on the SE with c. 560,550 Ma volcanic and sedimentary rocks and co-magmatic plutonic units of the Caledonian terrane. The HMS consists of albite- and garnet-porphyroblastic mica schist, with minor marble, calc-silicate rocks and quartzite. Pressure and temperature estimates from metamorphic assemblages in the mica schist and calc-silicate rocks using TWQ indicate that peak pressure conditions were 12.4 kbar at 430 °C. Peak temperature conditions were 580 °C at 9.0 kbar. 40Ar/39Ar muscovite ages from three samples range up to 618,615 Ma, a minimum age for high -P/low- T metamorphism in this unit. These ages indicate that the HMS is related to the c. 625,600 Ma subduction-generated volcanic and plutonic units exposed to the SE in the Caledonian terrane. The ages are also similar to those obtained from detrital muscovite in a Neoproterozoic-Cambrian sedimentary sequence in the Caledonian terrane, suggesting that the HMS was exposed by latest Neoproterozoic time and supplied detritus to the sedimentary units. The HMS is interpreted to represent a fragment of an accretionary complex, similar to the Sanbagawa Belt in Japan. It confirms the presence of a major cryptic suture between the Avalon terrane sensu stricto and the now-adjacent Brookville terrane. [source]

Geological overview and cratering model for the Haughton impact structure, Devon Island, Canadian High Arctic

METEORITICS & PLANETARY SCIENCE, Issue 12 2005
Gordon R. Osinski
Regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to ,1880 m. New 40Ar,39Ar dates place the impact event at ,39 Ma, in the late Eocene. Haughton has an apparent crater diameter of ,23 km, with an estimated rim (final crater) diameter of ,16 km. The structure lacks a central topographic peak or peak ring, which is unusual for craters of this size. Geological mapping and sampling reveals that a series of different impactites are present at Haughton. The volumetrically dominant crater-fill impact melt breccias contain a calcite-anhydrite-silicate glass groundmass, all of which have been shown to represent impact-generated melt phases. These impactites are, therefore, stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets. The crater-fill impactites provided a heat source that drove a post-impact hydrothermal system. During this time, Haughton would have represented a transient, warm, wet microbial oasis. A subsequent episode of erosion, during which time substantial amounts of impactites were removed, was followed by the deposition of intra-crater lacustrine sediments of the Haughton Formation during the Miocene. Present-day intra-crater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the High Arctic. Modern modification of the landscape is dominated by seasonal regional glacial and niveal melting, and local periglacial processes. The impact processing of target materials improved the opportunities for colonization and has provided several present-day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain. [source]

Structure and impact indicators of the Cretaceous sequence of the ICDP drill core Yaxcopoil-1, Chicxulub impact crater, Mexico

METEORITICS & PLANETARY SCIENCE, Issue 7 2004
T. KENKMANN
The Cretaceous rocks are investigated with respect to deformation features and shock metamorphism to better constrain the deformational overprint and the kinematics of the cratering process. The sequence displays variable degrees of impact-induced brittle damage and post-impact brittle deformation. The degree of tilting and faulting of the Cretaceous sequence was analyzed using 360°-core scans and dip-meter log data. In accordance with lithological information, these data suggest that the sedimentary sequence represents a number of structural units that are tilted and moved with respect to each other. Three main units and nine sub-units were discriminated. Brittle deformation is most intense at the top of the sequence and at 1300,1400 m. Within these zones, suevitic dikes, polymict clastic dikes, and impact melt rock dikes occur and may locally act as decoupling horizons. The degree of brittle deformation depends on lithology; massive dolomites are affected by penetrative faulting, while stratified calcarenites and bituminous limestones display localized faulting. The deformation pattern is consistent with a collapse scenario of the Chicxulub transient crater cavity. It is believed that the Cretaceous sequence was originally located outside the transient crater cavity and eventually moved downward and toward the center to its present position between the peak ring and the crater rim, thereby separating into blocks. Whether or not the stack of deformed Cretaceous blocks was already displaced during the excavation process remains an open question. The analysis of the deformation microstructure indicates that a shock metamorphic overprint is restricted to dike injections with an exception of the so called "paraconglomerate." Abundant organic matter in the Yax-1 core was present before the impact and was mobilized by impact-induced heating and suggests that >12 km3 of organic material was excavated during the cratering process. [source]

Short-term environmental changes in Lake Morenito (41°S, 71°W, Patagonia, Argentina) from the analysis of sub-fossil chironomids

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2005
Julieta Massaferro
Abstract 1.A short sediment core from Lake Morenito was studied to assess the impact of environmental changes on chironomid communities occurring during the last ca 100 yr. 2.Lake Morenito (41°S, 71°W) is located 20 km west of the city of Bariloche, in northern Patagonia, Argentina. Before 1960, this lake was a branch of Lake Moreno; by that time, an artificial dam closed the system, establishing the new lake. Another human disturbance that took place during the time span of the core was the introduction of salmonids to the area ca 1910. 3.The most important natural events that occurred in the area during the last 100 yr were related to volcanic episodes. One of them, occured in Chile in 1960 affecting the Argentinian side, coincided with the dam's construction. 4.Changes in the chironomid community were recorded by studying the sub-fossil remains (the chitinized head capsule of the larvae) present in the sedimentary sequence. The results show that volcanic tephra layers deposited along the core led to a sharp instantaneous drop in the diversity and abundance of chironomid assemblages. Human activities are also associated with a change in chironomid community composition. 5.Chironomus reached its maximum abundance values in 1910 and 1960. The organic matter content also increased at the same time. The increase of Chironomus after 1910 is clearly related to an increase in the trophic status of the lake. However, owing to the synchronicity of events in 1960, i.e. the volcanic event and the dam's construction, it is difficult to establish whether the change in the chironomid assemblage was in response to an increase in trophic enrichment, to natural disturbance, or both. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Towards ground truthing exploration in the central Arctic Ocean: a Cenozoic compaction history from the Lomonosov Ridge

BASIN RESEARCH, Issue 2 2010
M. O'Regan
ABSTRACT The Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high-resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10,30 m Myr,1) and high permeability values (10,15,10,18 m2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One-dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifies the Opal A,C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source. However, the combined rate of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A,C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean. [source]

The physical scale modelling of braided alluvial architecture and estimation of subsurface permeability

BASIN RESEARCH, Issue 3 2002
D. J. Moreton
ABSTRACT The quantitative modelling of fluvial reservoirs, especially in the stages of enhanced oil recovery, requires detailed three-dimensional data at both the scale of the channel belt and within-channel. Although studies from core, analogue outcrop and modern environments may partially meet these needs, they often cannot provide detail on the smaller-scale (i.e. channel-scale) heterogeneity, frequently suffer from limited three-dimensional exposure and cannot be used to examine the influence of different variables on the process,deposit relationship. Physical modelling offers a complementary technique that can address many of these quantitative requirements and holds great future potential for integration with reservoir modelling. Physical modelling provides the potential to upscale results and derive reservoir information on three-dimensional facies geometry, connectivity and permeability. This paper describes the development and use of physical modelling, which employs generic Froude-scaling principles, in an experimental basin that permits aggradation in order to model the morphology and subsurface depositional stratigraphy of coarse-grained braided rivers. An example is presented of a 1:50 scale model based on the braided Ashburton River, Canterbury Plains, New Zealand and the adjacent late Quaternary braided alluvium exposed in the coastal cliffs. Critically, a full, bimodal grain size distribution (20% sand and 80% gravel) was used to replicate the prototype, which allows the realistic reproduction of the surface morphology and importantly permits grain size sorting during deposition. Uncertainties associated with the compression of time, sediment mass balance and the hydrodynamics of the finest particle sizes do not appear to affect the reproducibility of stratigraphy between experimental and natural environments. Sectioning of the preserved sedimentary sequence in the physical model allows quantification of the geometry, shape, spatial distribution and internal sedimentary structure of the coarse- and fine-grained facies. A six-fold facies scheme is proposed for the model braided alluvium and a direct link is established between the grain size distribution and facies type: this allows permeability to be estimated for each facies, which can be mapped onto two-dimensional vertical cross-sections of the preserved stratigraphy. Results demonstrate the dominance of four facies based on permeability that range over three orders of magnitude in hydraulic conductivity. Quantification of such variability, and linkage to both vertical proportion curves for facies distribution and connectivity presents significant advantages over other methodologies and offers great potential for the modelling of heterogeneous braided river sediments at the within channel-belt scale. This paper outlines how physical models may be used to develop high-resolution, geologically-accurate, object-based reservoir simulation models. [source]

Middle Weichselian glacial event in the central part of the Scandinavian Ice Sheet recorded in the Hitura pit, Ostrobothnia, Finland

BOREAS, Issue 1 2008
VELI-PEKKA SALONEN
The Hitura open pit exposes a sedimentary sequence up to 50 m thick representing Late Saalian to Holocene glacial and non-glacial sediments. The sequence was investigated using sedimentological methods, OSL-dating and pollen and diatom analyses to reconstruct the Middle Weichselian (MWG) glacial event in the central part of the Scandinavian Ice Sheet (SIS). The results indicate that the sediment succession represents two entire glacial advance and retreat cycles. The lowermost deposits are Late Saalian esker and delta sediments overlain by sediments that correlate with the early Eemian lacustrine phase. Remnants of the Eemian soil post-dating the lacustrine phase were also observed. The area was ice-free during the entire Early Weichselian (EWG). The first glacial advance recorded in the sediments is related to the MWG. It started 79 kyr ago, deformed underlying sediments and deposited an immature till, including large detached sediment pods containing remains of organic material, soils and fluvial sediments representing allochthonous material from EWG ice-free stadials and interstadials. The glacial deposits are conformably overlain by glaciolacustrine and littoral accumulations, indicating MWG deglaciation between 62 and 55 kyr ago. Based on the fabric measurements from the till unit overlying the MWG sediments, ice advance during the Late Weichselian (LWG) was initially from the west and later from a north-northwesterly direction. The Hitura strata provide the first dating of the MWG deglaciation (55 to 62 kyr ago) from central parts of the SIS. It can be considered as a key site for studying the growth and decay of SIS during the poorly known early parts of the glaciation. [source]

Detection of Lateglacial distal tephra layers in the Netherlands

BOREAS, Issue 2 2005
SIWAN M. DAVIES
Davies, S. M., Hoek, W. Z., Bohncke, S. J. P., Lowe, J. J., Pyne O'Donnell, S. & Turney, C. S. M. 2005 (May): Detection of Lateglacial distal tephra layers in the Netherlands. Boreas, Vol. 34, pp. 123,135. Oslo. ISSN 0300,9483. Three distal tephra layers or cryptotephras have been detected within a sedimentary sequence from the Netherlands that spans the last glacial-interglacial transition. Geochemical analyses identify one as the Vedde Ash, which represents the southernmost discovery of this mid-Younger Dryas tephra so far. This tephra was found as a distinct horizon in three different cores sampled within the basin. The remaining two tephras have not been geochemically ,fingerprinted', partly due to low concentrations and uneven distributions of shards within the sequences sampled. Nevertheless, there is the potential for tracing these tephra layers throughout the Netherlands and into other parts of continental Europe. Accordingly, the possibilities for precise correlation of Dutch palaeoenvironmental records with other continental, marine and ice-core records from the North Atlantic region are highlighted. [source]

Holocene paleogeographies of the Palairos coastal plain (Akarnania, northwest Greece) and their geoarchaeological implications

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2006
Andreas Vött
Sediments from the Palairos coastal plain (Akarnania, northwest Greece) were studied to establish paleogeographical scenarios of Holocene landscape evolution. Near coast vibracore profiles revealed regressive sedimentary sequences, the base of which is dominated by marine sand and/or lagoonal mud. The middle and upper parts of the sequences are made up of lacustrine mud and fine- to coarse-grained alluvial deposits reflecting the increased activity of torrential river systems. In the southern plain, marine sediments of the maximum incursion of the Ionian Sea were found 1 km inland and date from the seventh millennium B.C. This proves that the Lake Voulkaria in the northern plain does not represent the remains of a former marine embayment. Subsequently, a large lagoon developed and existed until the fourth millennium B.C. The central plain was mainly exposed to subaerial conditions when man started to colonize the area in the seventh millennium B.C. In the fifth millennium B.C., the Palairos lagoon turned into a freshwater lake. When ancient Palairos was founded in the 6th century B.C., shallow lakes and swamps dominated the southern and central parts of the plain. At that time, a narrow canal-like connection between the Bay of Palairos-Pogonia and the Lake Voulkaria existed and was possibly used as a slipway for ships. During the last 4000 years, the Palairos plain experienced strong input of fluvial sediments which finally filled up the coastal lake as well as the swampy grounds. © 2006 Wiley Periodicals, Inc. [source]

The microstratigraphic record of abrupt climate changes in cave sediments of the Western Mediterranean

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2001
Marie-Agnès Courty
The purpose of this paper is to illustrate how calcareous sediments from Pleistocene and Holocene rockshelters and open caves of the Western Mediterranean can provide a stratigraphic record of abrupt climate change. The method proposed here is based on microstratigraphic examination of sedimentary sequences using microscopic techniques. The most important processes for characterizing the sensitivity of each cave to climate variables are: (1) the modes and rate of carbonate sediment production, (2) the nature and intensity of the pedogenic processes responsible for the synchronous alteration of carbonate materials (either those derived from the cave walls or those deposited on the ground surface), and (3) the supply of allogenic sediments, particularly by eolian activity. The cave sediment sequences presented record the marked coolings known as Dansgaard-Oeschger stadials and Heinrich events that occurred during the Pleistocene and the Holocene, as demonstrated by the high resolution records from ice and deep sea cores. At Abric Romanì in northeastern Spain, a series of sharp climatic deteriorations of increasing severity is shown to have occurred synchronously with the transition from the Middle to the Upper Paleolithic, with a period of seasonal frost and strong winds at ca. 37,000 yr B.P., tentatively correlated with Heinrich event 4. At Pigeon Cave, Taforalt (northern Morocco), the transition from the Aterian to Ibero-Maurusian/Epipalaeolithic cultures is dated to around 24,000,20,000 yr B.P. and is punctuated by a series of short cold pulses with evidence for seasonal freezing, soil erosion, and minimal evapotranspiration. In El Miron cave in north-central Spain, the exceptional nature of the Younger Dryas cooling produced a marked destabilization of the cave walls and roof. At El Miron, the stratigraphic evidence for sediment removal due to the rapid percolation of snow melt under a degraded soil cover allows us to reconstruct the nature of the negative excursion at ca. 8200 yr B.P. This example also illustrates how climate-controlled pedogenic processes can create a stratigraphic signature which has often been confused with a sedimentary hiatus. We conclude that cave sediments provide a valuable record of Pleistocene and Holocene climate changes. In appropriate contexts, these sequences allow us to examine the ecological stress generated by these unique global events at a local and regional level and improve our understanding of the complex anthropological processes that occurred at the same time. © 2001 John Wiley & Sons, Inc. [source]

The sedimentary records in Mediterranean rockshelters and caves: Archives of environmental change

Mud volcanoes of Italy

GEOLOGICAL JOURNAL, Issue 1 2004
Giovanni Martinelli
Abstract The locations and information about the sizes of 61 mud volcanoes on the Italian mainland and Sicily, plus an area of mud diapirism in the Italian Adriatic Sea, are presented. Data about the emission products are also provided. The majority of these mud volcanoes are found where thick sedimentary sequences occur within a zone of tectonic compression associated with local plate tectonic activity: the movement of the Adriatic microplate between the converging African and Eurasian plates. The principal gas emitted by these mud volcanoes is methane, which probably originates from deep within the sediments. Other mud volcanoes, associated with igneous volcanism, produce mainly carbon dioxide. The mud diapirs in the Adriatic Sea are thought to form as a result of the mobilization of shallow gassy sediments. It has been shown that radon emissions from mud volcanoes are indicators of forthcoming earthquake events. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Threshold response of Madagascar's littoral forest to sea-level rise

GLOBAL ECOLOGY, Issue 1 2009
Malika Virah-Sawmy
ABSTRACT Aim, Coastal biodiversity hotspots are globally threatened by sea-level rise. As such it is important to understand how ecosystems resist, respond and adapt to sea-level rise. Using pollen, geochemistry, charcoal and diatom records in conjunction with previously published palaeoclimatic records, we investigated the mechanism, interactions and ecosystem response and resilience of Madagascar's littoral forest to late Holocene sea-level rise. Location, Sediment sequences were collected along the south-east coast of Madagascar in two adjacent habitats in Mandena; the highly diverse littoral forest fragment and species-poor Erica -matrix. Methods, We used a multi-proxy approach to investigate the relative influence of environmental changes on the littoral ecosystem. We reconstructed past vegetation and fire dynamics over the past 6500 years at two sites in the littoral forest using fossil pollen and macrofossil charcoal contained in sedimentary sequences. Alongside these records we reconstructed past marine transgressions from the same sedimentary sequences using geochemical analyses, and a salinity and drought index through the analysis of fossil diatoms. Results, Our findings indicated that it was the synergistic effect of sea-level rise coupled with rainfall deficits that triggered a threshold event with a switch from two types of littoral forest (an open Uapaca forest and a closed littoral forest fragment) to an Erica,Myrica heath/grassland occurring in approximately less than 100 years. Resilience to sea-level rise differed in the two adjacent habitats, suggesting that the littoral forest fragment was more resilient to the impacts of sea-level change and aridity than the open Uapaca woodland. Conclusions, We demonstrated that the littoral ecosystem was influenced by late Holocene sea-level rise and climatic desiccation. While climate change-integrated conservation strategies address the effects of climate change on species distribution and dispersal, our work suggests that more attention should be paid to the impacts of interactive climatic variables that affect ecosystem thresholds. [source]

Lithostratigraphy of Permian marine sequences, Khao Pun Area, central Thailand: Paleoenvironments and tectonic history

ISLAND ARC, Issue 2 2000
Vichai Chutakositkanon
Abstract Geologic mapping and subsurface lithostratigraphic investigations were carried out in the Khao Pun area (4 km2), central Thailand. More than 250 hand specimens, 70 rock slabs, and 70 thin sections were studied in conjunction with geochemical data in order to elucidate paleoenvironments and tectonic setting of the Permian marine sedimentary sequences. This sedimentary succession (2485 m thick) was re-accessed and re-grouped into three lithostratigraphic units, namely, in ascending order, the Phu Phe, Khao Sung and Khao Pun Formations. The Lower to lower Upper Permian sedimentary facies indicated the transgressive/regressive succession of shelf sea/platform environment to pelagic or abyssal environment below the carbonate compensation depth. The sedimentological and paleontological aspects, together with petrochemical and lithological points of view, reveal that the oldest unit might indicate an Early Permian sheltered shallow or lagoonal environment. Then the depositional basin became deeper, as suggested by the prolonged occurrence of bedded chert-limestone intercalation with the local exposure of shallower carbonate build-up. Following this, the depositional environment changed to pelagic deposition, as indicated by laminated radiolarian (e.g. Follicucullus sp.) cherts. This cryptic evidence might indicate the abyssal environment during middle Middle to early Late Permian; whereas, previous studies advocated shelf-facies environments. Following this, the depositional condition might be a major regression on the microcontinent close to Indochina, from the minor transgressive/regressive cycles that developed within a skeletal barrier, and through the lagoon with limited circulational and anaerobic conditions, on to the tidal flat to the sheltered lagoon without effective land-derived sediments. [source]

Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods,

JOURNAL OF QUATERNARY SCIENCE, Issue 4 2006
B. Wohlfarth
Abstract The sediment sequence from Hässeldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hässeldalen Tephra and the 10-ka Askja Tephra. Twenty-eight high-resolution 14C measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono- and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hässeldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and ,realistic' age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hässeldala port are large and calendar year estimates differ according to the assumptions of the age-model. Not only do these results provide a cautionary note for over-dependence on one age-model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age,depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Palaeoenvironmental evolution and sea-level fluctuations along the southeastern Pampa grasslands coast of Argentina during the Holocene,

JOURNAL OF QUATERNARY SCIENCE, Issue 3 2006
Isabel Vilanova
Abstract Holocene pollen and diatom analyses and complementary data from ,18O and ,13C, malacology and sedimentology have provided a detailed record of vegetation history and palaeoenvironmental change at arroyo Las Brusquitas, on the southeastern coast of the pampas of Argentina especially in relation to past sea levels. Holocene palaeosalinity trends were estimated by Detrended Correspondence Analysis and by salinity indexes based on pollen and diatom data. As a consequence of sea-level rise from the postglacial an extensive wave-cut platform formed over which Holocene infilling sequences were deposited unconformably. In these sequences, variation in pollen and diatom assemblages occurred in agreement with changes in mollusc diversity and abundance, isotope values, and sediment deposits. Between ca. 6700 and 6190 14C yr BP (6279,6998,cal. yr BP) saline conditions predominated in an environment highly influenced by tides and salt water during the Holocene sea-level highstand. Between ca. 6200 and 3900 14C yr BP (4235,4608,cal. yr BP) shallow brackish water bodies formed surrounded by saltmarsh vegetation that became more widespread from 5180 14C yr BP (5830,6173,cal. yr BP) to 3900 14C yr BP in relation to a sea-level stabilisation period within the regression phase. Less saline conditions marked by frequent variations in salinity predominated between ca. 3900 and 2040,yr 14C BP (1830,2160,cal. yr BP). The intertidal saltmarsh environment changed into a brackish marsh dominated by freshwater conditions and sporadic tidal influence. Halophytic vegetation increased towards ca. 200014C yr BP indicating that saline conditions may be due to either desiccation or an unusually high tide range with rare frequency. After ca. 2000 14C yr BP the sedimentary sequences were buried by aeolian sand dunes. Changes in Holocene vegetation and environments in Las Brusquitas area are in agreement with data obtained from various southeastern coastal sites of the Pampa grasslands. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Geoarchaeology of the Milfield Basin, northern England; towards an integrated archaeological prospection, research and management framework

ARCHAEOLOGICAL PROSPECTION, Issue 2 2002
David G. Passmore
Abstract This paper presents the results of geoarchaeological investigations undertaken on the valley floor of the Milfield Basin in Northumberland, northern England. The area has a regionally and nationally important archaeological record, including a series of major neolithic and Anglian settlements, but has hitherto lacked archaeological assessment and management guidelines appropriate to the wide range of late-glacial and post-glacial environmental settings in the basin. This project has used geomorphological techniques to delimit and classify a total of nine valley floor landform elements in terms of their geomorphology and their known and potential archaeological and palaeoenvironmental associations. Terraced glaciodeltaic and glaciofluvial sand and gravel landforms comprise the oldest landform elements described here and have formed the primary regional focus for prehistoric and early historic settlement and associated subsistence and ritual activity. These landforms have experienced little post-glacial geomorphological activity, but their multiperiod archaeological landscapes lie beneath a shallow soil cover and are vulnerable to land-use activities that disturb terrace soils and underlying sediments. A second group of landform elements are of Holocene age and include localized surface peats, alluvial fans, colluvial deposits and extensive deposits of terraced alluvium. Archaeological landscapes in these environments may lie buried intact and unrecorded beneath protective covers of sediment although locally they may have been subject to erosion and reworking by fluvial and slope processes. Holocene alluviation may account, at least in part, for the paucity of recorded archaeology in these parts of the basin. However, peat and organic-rich sedimentary sequences identified here (including four 14C dated peat sequences) offer an opportunity to elucidate the environmental context and land-use histories of local prehistoric and early historic communities in the basin, and hence also should be regarded as an archaeological resource. Discussion of landform elements and their archaeological associations is followed by a brief outline of evaluation criteria developed with the aim of ensuring effective long-term management of archaeological and palaeoenvironmental resources. It is concluded that geoarchaeological analysis of landform elements may be considered central to development of frameworks intended to underpin future programmes of archaeological research and the development of cultural resource management and evaluation strategies. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Mudstone compaction curves in basin modelling: a study of Mesozoic and Cenozoic Sediments in the northern North Sea

BASIN RESEARCH, Issue 3 2010
Ø. Marcussen
ABSTRACT Basin modelling studies are carried out in order to understand the basin evolution and palaeotemperature history of sedimentary basins. The results of basin modelling are sensitive to changes in the physical properties of the rocks in the sedimentary sequences. The rate of basin subsidence depends, to a large extent, on the density of the sedimentary column, which is largely dependent on the porosity and therefore on the rate of compaction. This study has tested the sensitivity of varying porosity/depth curves and related thermal conductivities for the Cenozoic succession along a cross-section in the northern North Sea basin, offshore Norway. End-member porosity/depth curves, assuming clay with smectite and kaolinite properties, are compared with a standard compaction curve for shale normally applied to the North Sea. Using these alternate relationships, basin geometries of the Cenozoic succession may vary up to 15% from those predicted using the standard compaction curve. Isostatic subsidence along the cross-section varies 2.3,4.6% between the two end-member cases. This leads to a 3,8% difference in tectonic subsidence, with maximum values in the basin centre. Owing to this, the estimated stretching factors vary up to 7.8%, which further gives rise to a maximum difference in heat flow of more than 8.5% in the basin centre. The modelled temperatures for an Upper Jurassic source rock show a deviation of more than 20 °C at present dependent on the thermal conductivity properties in the post-rift succession. This will influence the modelled hydrocarbon generation history of the basin, which is an essential output from basin modelling analysis. Results from the northern North Sea have shown that varying compaction trends in sediments with varying thermal properties are important parameters to constrain when analysing sedimentary basins. [source]

Late Weichselian glacial history and postglacial emergence of Phippsøya, Sjuøyane, northern Svalbard: a comparison of modelled and empirical estimates of a glacial-rebound hinge line

BOREAS, Issue 1 2000
STEVEN L. FORMAN
Field research on Phippsøya, the largest island in the Sjuøyane archipelago, defines the course and timing of postglacial emergence, documents past-glacier movements, and reinterprets deglacial sedimentary sequences. Previously described tills were not identified in sections exposed along the northeast shore of Phippsøya, but instead sublittoral sediments with rock-fall concentrations derived from the adjacent slope. A glacio-isostatically higher sea level >40 ka deposited sublittoral sediment and is possibly correlative to a deglacial event in oxygen isotope stage 4 or 5 identified at other sites on Svalbard. The postglacial marine limit is 22 ± 1 m aht and occurs as an escarpment or washing limit into a stony drift. This drift contains granite and quartzite erratics from Nordaustlandet that indicate coverage by a northward flowing ice sheet during the Late Weichselian. Datable material on the raised-beach sequence was rare and a 14C age of c. 9.2 ka on an articulated Balanus balanus from 10 m aht provides a minimum constraining age on the marine limit. A mild transgression occurred by 6.2 ka, with sea level falling close to present levels by c. 5.0 ka. The zone of zero emergence (hinge line) lies 10 to 20 km north of Sjuøyane and is approximately coincident with the last glacial maximum limit on the continental shelf. There is an approximately 75 to 100 km offset between observed and modelled zone of zero emergence, indicating a need to refine earth rheology-based ice-sheet models. [source]