Changes In Sedimentation Patterns Research Articles

First insights into mineralogy, geochemistry, and isotopic signatures of the Upper Triassic high‑sulfur coals from the Thai Nguyen Coal field, NE Vietnam

This paper represents the first integrated research on the mineralogical, geochemical and stable isotope characteristics of the Upper Triassic high‑sulfur coals from the Khanh Hoa open-pit mine, Thai Nguyen Coalfield, NE Vietnam. Formed in a marine-influenced carbonate succession, the Khanh Hoa coal is characterized by medium ash yield, low volatile matter yield, and high sulfur content. Minerals in the Khanh Hoa coal are predominantly composed of authigenic calcite in the upper portion; and pyrite, quartz, with minor amounts of tobelite ([(NH4), K] (Si, Al)4Al2O10(OH)2), gypsum in the middle and lower portions. The high‑sulfur Khanh Hoa coal is enriched in an As-Mo-Sb-U-Cs-P assemblage, which presents both an organic and inorganic mode of occurrence, and is largely ascribed to hydrothermal fluids. The δ13C values of the Khanh Hoa coal range from −24.77‰ to −22.80‰ (avg. −23.33‰), reflecting a change in sedimentation pattern (from transgressive to high stand system upwards). The δ15N values of the Khanh Hoa coal range from 2.41‰ to 3.73‰ (avg. 3.30‰), possibly resulted from influenced by seawater influence and a redox environment. The mineralogical, geochemical and isotopic characteristics reflected that the high‑sulfur Khanh Hoa coal was formed/preserved in marine-influenced anoxic environment, with low detrital input, and strong activities of multi-stage hydrothermal solutions.

Investigation of Changes in Beach Morphology due to Coastal Armoring

The Tsunami, which struck the east coast of India on 26th December 2004, caused huge damage to life, property and environment. Beyond the heavy toll on human lives, it had caused an enormous environmental impact. Kalpakkam located in the south east coast of India is one of the areas affected by the tsunami. At some locations along the coast around Kalpakkam, morphological changes, vegetation loss and fatality were reported. Later, a slew of remedial measures were initiated at Kalpakkam in 2006 and construction of coastal armoring in the form of Tsunami Protection Wall (TPW) of 3.2 km length was one of them. A study was undertaken to assess the impact of this TPW on the surroundings based on periodic measurements of High Water Line (HWL) before and after construction of the wall. Also beach profiles were made at selected locations to observe seasonal changes in sedimentation pattern (i.e. accretion and erosion). As the residential area at Kalpakkam is located between fishing hamlets at northern and southern side, it is necessary to understand the impact of TPW, if any, in the surrounding area and on the fishing hamlets. Towards this assessment, high resolution satellite data such as Quickbird and IKONOS were employed (for the years 2002, 2003, 2009 and 2011) to measure the HWL. In addition, monthly beach profiles were carried out to measure the sedimentation pattern at selected transects with the help of N3 Precision Level survey instrument for the year 2009. The detailed investigations and analysis revealed no significant impact on the beach morphology and sedimentation patterns due to the construction of TPW, within the residential areas as well as at fishing hamlets. The average variations in the position of HWL along the coast was 4.6m and sedimentation changes were in the range of ≈ 0.5m in the berm of backshore region and ≈ 1.7m in the swash zone of the foreshore region all along the study area. No adverse effect is observed and the variations observed are similar to that in an unarmored control beach. The study provides the confidence that multi-dated satellite monitoring together with the profiling of beach would suffice the need for understanding the changes in the beach morphology due to the construction of beach armoring.

Quantifying sedimentation patterns of small landslide‐dammed lakes in the central Oregon Coast Range

AbstractUnderstanding sedimentation patterns in small coastal watersheds due to landscape perturbations is critical for connecting hillslope and fluvial processes, in addition to managing aquatic habitats for anadromous fish and other aquatic species in the Oregon Coast Range (OCR). Changes in sedimentation patterns spanning the last 250 years are preserved in two landslide‐dammed lakes in small watersheds (< 10 km2) underlain by the Tyee Formation in the central OCR. Dendrochronology of drowned Douglas‐fir stumps in both lakes provided precise timing of the damming and formation of the lakes, with Klickitat Lake forming in winter ad 1751/52 and Wasson Lake in winter ad 1819/20. Perturbations from wildfires, logging and road development, and previously underappreciated snow events affect sedimentation rates in the lakes to different degrees, and are identified in the sediment record using cesium‐137 (137Cs), high‐resolution charcoal stratigraphy, local fire records, and aerial photography. Each lake has variable sedimentation accumulation rates (0.05–4.4 cm yr−1) and mass accumulation rates (0.02–1.42 g cm−2 yr−1). Sedimentation rates remained low from the landslide‐damming events until the mid‐19th century, when they increased following stand‐replacing wildfires. Aside from a sediment remobilization triggered by human modification of the landslide dam at Klickitat Lake around 1960, the largest peaks in mass accumulation rates in the mid‐20th century at both lakes in the early 1950s precede major road construction and logging activity in the watersheds. Subsequent sedimentation rates are lower, but variable, and possible effects of logging and road development might be exacerbated by abnormal precipitation and heavy snow events. A comparison of previous studies of landslide‐dammed lakes in larger watershed of the OCR are consistent with our findings of increased sedimentation in the mid‐20th century, as well as higher sedimentation rates in the debris‐flow dominated southern Tyee Formation than in the lower‐relief northern Tyee Formation.

Marine or freshwater? Accessing the paleoenvironmental parameters of the Caldas Bed, a key marker bed in the Crato Formation (Araripe Basin, NE Brazil)

The Aptian Crato Formation is world renowned for its well-preserved fossils in microbially-induced laminated limestones, which are regarded as one of the main Cretaceous Konservat-Lagerstätte of the geological record. Detailed stratigraphic investigation and mapping of the up to 90-m-thick Crato Formation at the eastern border of the Araripe Plateau allowed recognition of a regionally persistent fossil-bearing muddy interval, herein defined as the Caldas Bed. At its type locality, it is defined as an up to 2-m-thick coarsening-upward succession of grey/green mudstone and interbedded sandy siltstone and claystone. The 0.85- to 2-m-thick interval was recognized in several localities along the outcrop belt, and it is bounded by sharp, lower (Konservat-Lagerstätte limestone) and upper (sandstone and heterolithic facies) contacts. Despite previous literature data suggesting the presence of marine mollusks, the bed contains freshwater bivalves, small gastropods, spinicaudatans, plant remains, trace fossils, and rare ostracods. The Caldas Bed records benthic paleocommunities representing a short-term isochronous regional freshening event, marked by abrupt changes in sedimentation pattern, bathymetry, salinity, oxygenation and water chemistry.

Historical sedimentation at an artificial lake margin, Bangudae Petroglyphs site, SE Korea

The Bangudae Petroglyphs is Korea’s National Treasure No. 285, carved on a vertical rock face on the riverside of a mountain stream (Daegokcheon) near Ulsan. Since the construction of the Sayeon Dam in the downstream area in 1965, the petroglyphs was repeatedly flooded and submerged, raising concerns of erosion and water damage of the prehistoric rock-art motifs. Recent excavation of the fluvial sediments in front of the petroglyphs provided an opportunity to investigate the changes in sedimentation pattern before and after the construction of the dam and the consequences of human activity on natural environments. Sedimentological observations of trench sections and radiocarbon, OSL, and garbage dating of sediments reveal that the sediments comprises gravelly to sandy fluvial sediments in the lower part that accumulated since the early to middle Holocene or early to middle Neolithic Era until 1965. Above this, 25 units of alternating horizontally laminated sand and massive, mottled mud with abundant rootlets occur. This sand/mud sequence is interpreted to have accumulated after the construction of the Sayeon Dam in 1965, which caused repetitive flooding and submergence of the study area every year or two. The alternations of horizontally laminated sand and massive mud are interpreted to have resulted from rainfall-induced floods and subsequent suspension settling of fines in stagnant water after the area was inundated and temporarily transformed into a lacustrine margin setting. Afterwards, the depositional site was exposed and vegetated until the next flood event. Comparison of the deposit features with the precipitation data in Ulsan area, the water level data of the Sayeon Dam, and age data suggests that this flood-related sedimentation occurred almost every year until 2005 when the water level of the Sayeon Dam was lowered permanently because of the construction of another dam in the upstream section of the stream. This study thus provides a good example of a dramatic environmental change of a mountain stream caused by artificial disturbance of a river system due to construction of dams and an example of high-resolution sedimentary records of meteorologically induced floods in an artificial lake margin.

Effects of river infrastructures on the floodplain sedimentary environment in the Rhône River

River infrastructures such as dikes, groynes, and dams are ubiquitous on most large rivers, and although their consequences on the riverbed morphology have often been studied, the effect they might have on the river floodplain and margins remains largely unknown. By investigating the structure and composition of floodplain sediments in three areas along the Rhone River that were extensively engineered during the last 150 years, this paper aims to understand whether river infrastructures might systematically induce a change in sedimentation patterns in the river margins. A total of fifteen sediment cores were sampled in three distinct reaches of the Rhone valley downstream of Lyon. They were thoroughly analyzed in terms of grain size, using heatmap representations and end-member analysis. Six metallic elements (Zn, Cr, Pb, Cu, Ni, Cd) were systematically quantified. In six out of the fifteen cores, total organic carbon (TOC), organic contaminants (PCBs) concentrations, and 137Cs activity were also assessed. A sharp change in grain size distribution is consistently identified in the sediment cores of all three study reaches. The sediments above this change are fine (D50 < 100 μm), poorly classified and homogenous. They also show a relative increase in contamination when compared with deeper sediments. We interpret this change in sediment characteristics as the consequence of an abrupt decrease in connectivity between the floodplain and the river channel, likely due to the implementation of navigation infrastructures in the channel in the second half of the nineteenth century. In one case, the dating of the sediment cores allows linking the grain size change to the implementation of navigation infrastructures in the channel. In the other study areas, the effect of engineering seems delayed in time due to local variability. The implementation of river infrastructures resulted in a loss of connectivity between the floodplain and the channel. This was reflected as the homogenization of the floodplain sedimentary environment of the Rhone River all along its course from Lyon to the sea. A similar phenomenon might be present in most engineered rivers across Europe.

Refinement of Miocene sea level and monsoon events from the sedimentary archive of the Maldives (Indian Ocean)

International Ocean Discovery Program (IODP) Expedition 359 cored sediments from eight borehole locations in the carbonate platform of the Maldives in the Indian Ocean. The expedition set out to unravel the timing of Neogene climate changes, in particular the evolution of the South Asian monsoon and fluctuations of the sea level. The timing of these changes are assessed by dating resultant sedimentary alterations that mark stratigraphic turning points in the Neogene Maldives platform system. The first four turning points during the early and middle Miocene are related to sea-level changes. These are reliably recorded in the stratigraphy of the carbonate sequences in which sequence boundaries provide the ages of the sea-level lowstand. Phases of aggradational platform growth give precise age brackets of long-term sea-level high stands during the early Miocene and the early to middle Miocene Climate Optimum that is dated here between 17 to 15.1 Ma. The subsequent middle Miocene cooling coincident with the eastern Antarctic ice sheet expansion resulted in a long-term lowering of sea level that is reflected by a progradational platform growth. The change in platform architecture from aggradation to progradation marks this turning point at 15.1 Ma.An abrupt change in sedimentation pattern is recognized across the entire archipelago at a sequence boundary dated as 12.9–13 Ma. At this turning point, the platform sedimentation switched to a current-controlled mode when the monsoon-wind-driven circulation started in the Indian Ocean. The similar age of the onset of drift deposition from monsoon-wind-driven circulation across the entire archipelago indicates an abrupt onset of monsoon winds in the Indian Ocean. Ten unconformities dissect the drift sequences, attesting changes in current strength or direction that are likely caused by the combined product of changes in the monsoon-wind intensity and sea level fluctuations in the last 13 Ma. A major shift in the drift packages is dated with 3.8 Ma that coincides with the end of stepwise platform drowning and a reduction of the oxygen minimum zone in the Inner Sea.The strata of the Maldives platform provides a detailed record of the extrinsic controlling factors on carbonate platform growth through time. This potential of carbonate platforms for dating the Neogene climate and current changes has been exploited in other platforms drilled by the Ocean Drilling Program. For example, Great Bahama Bank, the Queensland Plateau, and the platforms on the Marion Plateau show similar histories with sediment architectures driven by sea level in their early history (early to middle Miocene) replaced by current-driven drowning or partial drowning during their later history (Late Miocene). In all three platform systems, the influence of currents on sedimentations is reported between 11 and 13 Ma.

The Lower Siwalik foreland basin sedimentation in the Kumaun Himalaya (India): A transition from megafan setting to incised valley fills

About 300–900 m thick the Lower Siwalik Subgroup exposed in the Kumaun Himalaya has been studied along three far spaced sections, which show variable stratigraphic changes in sedimentation pattern. Available magnetostratigraphic dates in the Kathgodam–Ranibagh section indicate Late Miocene age (12–10Ma) of the Lower Siwalik Subgroup. Detailed lithofacies analysis reveals four depositional settings namely, the Sandstone Lithofacies Association (Channel deposits), the Mudstone Lithofacies Association (Floodplain deposits), the Mottled Mudstone Lithofacies Association (Distal floodplain palaeosols), and the Mottled Siltstone Lithofacies Association (Interfluve deposits). Based on available data on channel pattern, lithofacies association, palaeocurrent pattern, and petrography, stratigraphic cyclicity is analyzed. The complete group is interpreted to be deposited in two Megacycles A and B. About 500 m thick, coarsening upward Megacycle A is internally made up of two Lithofacies sucessions I and II. The cycle is made up of meandering and anastomosing rivers towards the base (Lithofacies Succession I) that gradually evolves into braided rivers towards top (Lithofacies Succession II). This megacycle is inferred as prograding megafan deposit.In contrast, about 400 m thick Megacycle B, made up of two Lithofacies successions III and IV, is fining upward. This cycle is made up of thickly developed meandering – braided river systems at base interbedded with thick interfluve and distal flood plain deposits (Lithofacies Succession III) that gradually becomes thinner towards top, and river system changes to predominantly meandering type (Lithofacies Succession IV). The Megacycle B is inferred to be deposited in tectonically active basin, characterized by incision of rivers.

Volcanic influence of Mt. Fuji on the watershed of Lake Motosu and its impact on the lacustrine sedimentary record

Lacustrine sediments are particularly sensitive to modifications within the lake catchment. In a volcanic area, sedimentation rates are directly affected by the history of the volcano and its eruptions. Here, we investigate the impact of Mt. Fuji Volcano (Japan) on Lake Motosu and its watershed. The lacustrine infill is studied by combining seismic reflection profiles and sediment cores. We show evidence of changes in sedimentation patterns during the depositional history of Lake Motosu. The frequency of large mass-transport deposits recorded within the lake decreases over the Holocene. Before ~8000cal yr BP, large sublacustrine landslides and turbidites were filling the lacustrine depression. After 8000cal yr BP, only one large sublacustrine landslide was recorded. The change in sedimentation pattern coincides with a change in sediment accumulation rate. Over the last 8000cal yr BP, the sediment accumulation rate was not sufficient enough to produce large sublacustrine slope failures. Consequently, the frequency of large mass-transport deposits decreased and only turbidites resulting from surficial slope reworking occurred. These constitute the main sedimentary infill of the deep basin. We link the change in sediment accumulation rate with (i) climate and vegetation changes; and (ii) the Mt. Fuji eruptions which affected the Lake Motosu watershed by reducing its size and strongly modified its topography. Moreover, this study highlights that the deposition of turbidites in the deep basin of Lake Motosu is mainly controlled by the paleobathymetry of the lakefloor. Two large mass-transport deposits, occurring around ~8000cal yr BP and ~2000cal yr BP respectively, modified the paleobathymetry of the lakefloor and therefore changed the turbidite depositional pattern of Lake Motosu.

NUMERICAL SIMULATION OF TIDAL CIRCULATION IN THE PICHAVARAM MANGROVE ESTUARY

A vertically averaged numerical model is developed using the Surface water Modeling System (SMS) for t he Pichavaram Mangrove Estuary to study the tidal characteristics which en ables the simulation of the whole water circulation within the water body. The Pichavaram mangrove ecosystem is a complex network of creeks, mangroves and mud flats housed between t he Vellar and Coleroon rivers, 15 km north of Chidambaram, Tamil Nadu, Ind ia. A portion of the Coleroon river drains into the mangroves, and tidal flow is through the Coleroon mouth and a small inflow from an inlet in the north. The reduction of freshwater flow over the years has led to a degradation of the mangroves and changes in sedimen tation patterns. The results are calibrated against data collected previously. From the simulated results it is noticed that the tflow from the Coleroon mouth dominates the ent ire system. The maximum flood and ebb tide speed reached 0.777 ms -1 and 0.468 ms -1 during monsoon and post monsoon periods, respectiv ely. The tide showed a pronounced asymmetry in mangroves and a 12% increas e in total depth of water with a maximum increase i n water level of about 5 cm is noticed between monsoon and post monsoon cond itions. The dominance of ebb tide is noticed due to friction in the mangrove forest, which has resulted in slower flood current and greater tidal asymmetry in the waterway.

Influence of varying tidal prism on hydrodynamics and sedimentary processes in a hypertidal salt marsh creek

ABSTRACTRecent initiatives directing tidal power development in the Bay of Fundy have raised questions about far‐field environmental impacts related to energy extraction. It is understood that commercial scale tidal power installations in the Minas Passage will result in an overall decrease in tidal amplitude in the Minas Basin. Corresponding changes in sedimentation patterns may or may not be within the natural range of variability, and it is hypothesized that intertidal sedimentation rates will demonstrate a non‐linear response to modification of the tidal energy regime. This research considers acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) data from a sheltered tidal creek in the Minas Basin, for analysis of tidal characteristics in a hypertidal creek environment over spring and neap tidal cycles. Sediment deposition in the creek was also measured. Results show a first‐order control of topography on flow magnitude in the tidal creek, which impacts net sediment deposition through resuspension and removal of newly introduced material. This study demonstrates that tides which peak around the bankfull level show reduced early ebb stage turbulence and flow velocity and encourage an extended depositional period. The dynamics of marshfull tides may be responsible for the maximum sediment deposition in tidal creeks, providing large amounts of material that is eventually distributed to and deposited on marsh surfaces. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Lithology, radiocarbon chronology and sedimentological interpretation of the lacustrine record from Laguna Potrok Aike, southern Patagonia

The 106 m long composite profile from site 2 of ICDP expedition 5022 (PASADO) at Laguna Potrok Aike documents a distinct change in sedimentation patterns from pelagic sediments at the top to dominating mass movement deposits at its base. The main lithological units correspond to the Holocene, to the Lateglacial and to the last glacial period and can be interpreted as the result of distinct environmental variations. Overflow conditions might have been achieved during the last glacial period, while signs of desiccation are absent in the studied sediment record. Altogether, 58 radiocarbon dates were used to establish a consistent age-depth model by applying the mixed-effect regression procedure which results in a basal age of 51.2 cal. ka BP. Radiocarbon dates show a considerable increase in scatter with depth which is related to the high amount of reworking. Validation of the obtained chronology was achieved with geomagnetic relative paleointensity data and tephra correlation.

Surprisingly complex community discovered in the mid-Devonian fossil forest at Gilboa

The origin of trees by the mid-Devonian epoch (398-385 million years ago) signals a major change in terrestrial ecosystems with potential long-term consequences including increased weathering, drop in atmospheric CO(2), modified climate, changes in sedimentation patterns and mass extinction. However, little is known about the ecology of early forests or how changes in early terrestrial ecosystems influenced global processes. One of the most famous palaeontological records for this time is the 'oldest fossil forest' at Riverside Quarry, Gilboa, New York, USA, discovered in the 1920s. Hundreds of large Eospermatopteris sandstone casts, now thought to represent the bases of standing cladoxylopsid trees, were recovered from a horizon that was originally interpreted as a muddy swamp. After quarry operations ceased, relatively minor outcrops of similar fossils at nearby localities have provided limited opportunities to evaluate this pervasive view using modern methods. In 2010, removal of the quarry backfill enabled reappraisal of the palaeoecology of this important site. Here we describe a 1,200 m(2) map showing numerous Eospermatopteris root systems in life position within a mixed-age stand of trees. Unexpectedly, large woody rhizomes with adventitious roots and aerial branch systems identified as aneurophytalean progymnosperms run between, and probably climb into, Eospermatopteris trees. We describe the overall habit for these surprisingly large aneurophytaleans, the earliest fossil group having wood produced by a bifacial vascular cambium. The site also provides evidence for arborescence within lycopsids, extending the North American range for trees in this ecologically critical group. The rooting horizon is a dark grey sandy mudstone showing limited root penetration. Although clearly belonging to a wetland coastal plain environment, the forest was probably limited in duration and subject to periodic disturbance. These observations provide fundamental clarification of the palaeoecology of this mixed-group early forest, with important implications for interpreting coeval assemblage data worldwide.

A Study of Decadal Sedimentation Trend Changes by Waterline Comparisons within the Ganghwa Tidal Flats Initiated by Human Activities

Abstract This study presents results of a human impact investigation of large-scale construction projects on sedimentation trend and morphologic changes in the Ganghwa tidal flats over 10 years using time-series waterlines from Landsat thematic mapper/enhanced thematic mapper. Waterlines were extracted from remotely sensed images. These images are useful for studying changes in coastlines and tidal flat topography. A reference digital elevation model (DEM) was constructed; then actual waterlines from satellite images were compared with modeled waterlines from the reference DEM. Systematic comparison with respect to horizontal differences between the two waterlines provided information on local conditions of sediment trends within the study area. Seaward or landward migration of waterlines was a clear indication of the change in sedimentation pattern. Deposition has been dominant at the main channel between the southern Ganghwa and the Yeongjong tidal flats, whereas erosion has been dominant at the eastern...

Continental-scale detrital zircon provenance signatures in Lower Cretaceous strata, western North America

Lower Cretaceous strata and the underlying sub-Cretaceous unconformity in western North America record a profound, but poorly understood change in sedimentation patterns and basin dynamics in the Cordilleran foreland basin. To better understand the regional sedimentary systems and provenance during Early Cretaceous time, we sampled 10 Lower Cretaceous sandstone and conglomerate units that overlie the sub-Cretaceous unconformity in Canada and the United States for detrital zircon uranium-lead (U-Pb) geochronology. These Lower Cretaceous strata contain two distinct detrital zircon U-Pb age signatures. A “northern” signature, present in strata in Alberta and British Columbia, contains zircons with ages of ca. 120 Ma and 1850 Ma, and is composed of zircons from the Cordilleran arc and grains recycled from strata of the Canadian miogeocline. A “southern” signature, present in strata from southwestern United States to central Montana, contains zircons with ages of ca. 160 Ma, ca. 250–650 Ma, and ca. 1040 Ma, and consists of zircons from the Cordilleran arc and grains recycled from late Paleozoic strata and Mesozoic eolianite units in the western United States. We propose that the differences in detrital zircon U-Pb age populations between northern and southern areas of western North America are due to differences in zircon populations in the sediment source strata exposed in the contemporaneous thrust belt, and possibly a subtle paleohydraulic divide in Montana. These distinct provenance signatures along the Cordillera suggest that the mechanisms responsible for Early Cretaceous changes in foreland basin dynamics occurred along the length of the Cordillera in both the U.S. and Canada.

Geologist at Sea: Aspects of Ocean History

Ocean history is largely read from deep-sea sediments, using microscopic fossils, notably foraminifers. Ice age fluctuations in the ocean's sediments provided for a new geologic understanding of climate change. The discovery of rapid decay of ice masses at the end of glacial periods was especially important, yielding rates of sea level rise reaching values of 1 to 2 m per century for millennia. Thanks to deep-ocean drilling, the overall planetary cooling trend in the Cenozoic was recognized as occurring in three large steps. The first step is at the Eocene-Oligocene boundary and is marked by a great change in sedimentation patterns; the second is in the middle Miocene, associated with a major pulse in the buildup of Antarctic ice masses and the intensification of upwelling regimes; and the third is within the late Pliocene and led into the northern ice ages. Evolution in the sea is linked to these various steps.

Volcanic ash in sediments of the Sea of Okhotsk: Identification based on minor and rare earth elements

The study of deepwater sediments in two bottom cores from the Sea of Okhotsk revealed substantial changes in sedimentation patterns during the Pleis� tocene and Holocene depending on climate variations related to alternating cooling and warming periods, which were determined by different factors, explosive volcanism included. It is established that catastrophic eruptions such as Tambora in 1815 and Krakatau in 1883, which yielded tremendous volumes of fine� grained pyroclastic material, resulted in a global tem� perature fall [1, 2]. A similarly strong impact is also !" !" # $%! & " # $%! & " # $%! & " %’$ #$’( ()( %* !*+’%$%%$ ,*’)$ -. +( -%’ %!&" -%’ %!&" -%’ %!&" !(+)*!/% ’!/% !(+)*!/% -%’ %!&" -%’ %!&" -%’ %!&"

Coastal sediments from the Algarve: low-latitude climate archive for the Aptian-Albian

The Late Aptian to Early Albian transition has previously been identified as a possible example of substantial climate cooling within the mid-Cretaceous greenhouse period. To study the response of continental weathering and terrestrial vegetation to this cooling episode at low- to mid-latitudes, marine nearshore deposits from the Algarve Basin (SW Portugal) have been investigated with a combined approach including palynology, clay mineralogy and bulk-rock geochemistry. In the Lower Aptian part of the succession, quartz-rich sandstone facies is accompanied by high abundances of early diagenetic kaolinite, which is interpreted to reflect episodes of enhanced humidity and high meteoric flow-through. In contrast, the Late Aptian to Early Albian deposits are characterized by high abundances of detrital clay minerals (mica and chlorite) indicating the dominance of physical weathering processes in the source area, most probably related to low precipitation rates in conjunction with tectonically enhanced erosion. Palynological data show a strong dominance of Classopollis pollen associated with low pteridophyte spore abundances, suggesting warm semi-arid to arid palaeoenvironments. Changes in sedimentation patterns from varicoloured lagoonal marls to thick-bedded shallow-water carbonates are neither expressed in the spore-pollen assemblages nor in the distributions of clay minerals which both remain essentially stable throughout the Late Aptian to Early Albian. These relatively stable patterns are in contrast with various lines of evidence, predominantly from high-latitude areas, that suggest a significant cooling during this time interval. Our study demonstrates that terrestrial environments of low- to mid-latitude regions were not significantly affected by the Late Aptian - Early Albian “cold snap”.

Impact of aquacultures on the marine ecosystem: Modelling benthic carbon loading over variable depth

In order to be used within Environmental Impact Assessment study, we have developed a three-dimensional particle tracking model for prediction of benthic carbon loading (BCL) caused by fish farms. The model is based on stochastic differential equations for particle transport consistent with the well-known semi-empirical advection/diffusion equation. It requires only easily obtainable input data in the form of measured current record, the source location and a specification of local bathymetry. The model accounts for advection by long-term residual and tidal currents, turbulent diffusion, realistic bathymetry and variations in daily (monthly or yearly) emissions from fish farm. Here, we concentrate on the changes in sedimentation pattern caused by various bathymetric shapes. Examination of idealized cases reveals where and why we can expect the worst impact on benthic communities. For future reference, these results will be included into guidelines for fish farming.

Sedimentation and palaeogeography of the eastern part of the Paris Basin (France) at the Middle–Upper Jurassic boundary

The Middle–Upper Jurassic boundary corresponds to a period of far-reaching changes in sedimentation patterns related to alterations in the palaeoclimate and in the global carbon cycle. Marl deposits were laid down in the east of the Paris Basin at this time and ANDRA has selected these lithological units as the site for an underground study laboratory. The build-up of these marls is the result, among other things, of the area long having been a shelf and of more rapid subsidence from the Early Callovian to the Early Oxfordian. Changes are detected between areas on either side of the Vittel Fault from the onset of the mid-Oxfordian onwards. To cite this article: P.-Y. Collin, P. Courville, C. R. Geoscience ••• (••••).