Lake Fills Research Articles

The Chilean Laja Lake: multi-objective analysis of conflicting water demands and the added value of optimization strategies

Abstract Water scarcity leads to conflicts over water allocation. Laja Lake in Chile is a natural lake, which was formed by a volcanic barrier. Outflow from the lake is created by seepage through the barrier and via a controllable artificial outlet, which adds reservoir characteristics to the lake. Hydroelectric power stations have been built at both outlets. Downstream, water is diverted into irrigation canals, and the Laja River forms the Laja Falls, a popular tourist attraction. The previous operating policy preferred the most upstream water user and was found to be inadequate because the lake level decreased over long term. The current reservoir operation policy was established through stakeholder negotiations. This study investigated whether optimization (using Non-Dominated Sorting Genetic Algorithm II) can further improve the operation of Laja Lake while maintaining a fair balance between stakeholder groups. The results were compared with the stakeholder agreement and the previous policy. The main difference is in the spring, when Laja Lake fills up before the irrigation season starts. The optimization strategy prioritizes hydropower generation during this period, resulting in reduced storage. Ultimately, optimization proves to be a valuable tool for identifying trade-offs and exploring different scenarios in water management.

Geomorphological Processes in the Central Kamchatka Depression (the Kamchatka Peninsula, Ne Pacific) During the Last 30 Ka

The paper presents a reconstruction of geomorphological processes in the Central Kamchatka Depression (CKD) since 30 ka, including the global LGM time. Major geomorphological processes of this period included the evolution of volcanic edifices accompanied by steady tectonic submergence. Glaciers that originated from volcanic edifices were greatly affected by both climatic forcing and the eruptive history of their host volcanoes.
 The most prominent geomorphological feature of the studied time was a giant paleolake filled the CKD. The reassessed extent and timing of glaciation and volcanism provided the possible lake fill and discharge model due to the evolution of a piedmont glacier originating from the Old Shiveluch Volcano edifice. The lake discharge likely was gradual and started some 19 ka during the cold settings of LGM, and therefore did not have a climatic origin. The most possible trigger of the discharge is the change in ice supply from the highly active Shiveluch Volcano due to large sector collapses. During the Holocene, the ongoing tectonic submergence of the CKD have been preventing the complete drainage of this paleolake. Even now, an enormously wide floodplain of the Kamchatka River hosts a lacustrine system with a total area of water surface comparable to the largest lakes of the peninsula.

Sedimentology of the Jura Molasse: Miocene tidal clastics and freshwater carbonates from the Tramelan-2 Borehole, NW Switzerland

The Tramelan-2 borehole (Canton Bern, Switzerland) continuously cored a 275.60 m sequence of Palaeogene to Neogene sediments, providing a rare opportunity for sedimentological analysis of the Jura Molasse. Lithostratigraphy, sedimentary facies and heavy minerals allow correlation with the classical Swiss Molasse. Evidence for clastic input from Alpine and non-Alpine sources is consistent with deposition at the northern feather edge of the Molasse Basin. Grey sandstones at the base of the succession are tentatively interpreted as fluvial facies of the Lower Freshwater Molasse (USM). These are overlain by erosively-based conglomerates, interpreted as winnowed storm lags of locally-derived clasts and distantly-sourced Alpine material at the transgressive base of the Upper Marine Molasse (OMM). Above this, a range of plane-laminated and cross-bedded bioclastic sandstones are interpreted as the deposits of a meso- or macrotidal flat or estuarine complex. Facies evolution in the upper OMM records a series of stacked regressive cycles within an overall upward trend of reducing current energy, reflecting a transition from offshore to nearshore shallow marine environments. The unconformably overlying Upper Freshwater Molasse (OSM) passes upwards from micaceous siltstones and marls into a series of freshwater carbonates, dominated by lacustrine limestones which are arranged in repeated regressive cycles, each capped by organic-rich horizons. The middle part of the carbonate interval comprises palustrine limestones with pedogenetic fabrics recording periodic subaerial exposure. Stable isotope signatures from the palustrine facies reflect subaerial pedogenetic overprint, while the lacustrine carbonates record cyclical variations in δ13C which may reflect increases in organic material during progressive lake fill and/or an increased influence of aquifer waters during flooding events. The Jura Molasse onlapped a Mesozoic carbonate pediment hosting a regional karst system which remained active at least until the Burdigalian transgression on footwall highs bounding the Delémont Basin, and locally into the Langhian near Tramelan. This configuration controlled subsequent deposition of OSM carbonates which onlapped erosional and potentially early tectonic relief, and were deposited in groundwater-fed seasonal lacustrine/palustrine environments, where the karstic aquifer controls on seasonal hydrology appear to have been comparable to Caribbean freshwater carbonate wetland systems today.

The environmental history of the oxbow in the Luciąża River valley – Study on the specific microclimate during Allerød and Younger Dryas in central Poland

The vicinity of the Rozprza archaeological site (central Poland) has been the area of a series of palaeoecological studies tracking the environmental history of the Luciąża River valley up to ca. 13,200 cal. BP. Numerous subfossil palaeomeanders of different sizes have been discovered in the valley floor. Here, we present the first results of multiproxy research on the paleo-oxbow lake fill, one of the oldest in the region. The wide range of palaeoecological analyses resulted in reconstructions of vegetation history, climatic, hydrological and habitat changes. The studied oxbow was an aquatic ecosystem with diverse invertebrate fauna until the end of Younger Dryas when it transformed into a limno-telmatic habitat. The sediment composition indicates active denudation processes and several episodes of turbulent hydrological conditions. Such an increased river activity could have caused flooding, resulting in an allochthonous matter supply to the oxbow lake in Late Vistulian. Environmental changes were strictly related to the regional features of the catchment, the transformation of soils, and the hydrogeological conditions. The chironomid- and pollen-inferred climatic reconstructions indicate periods of high and low continentality. The chironomid record indicates relatively cool summer conditions in the Allerød, especially ca. 13,000 cal. BP, possibly related to the Gerzensee Oscillation. On the other hand, a distinct increase of summer temperatures in Younger Dryas (up to 16 °C) was recorded. Such a situation was also confirmed in some other studies from the region, suggesting that it might be the effect of some specific, local palaeoclimatic conditions.

Major and trace elements in mid-Eocene lacustrine oil shales of the Fushun Basin, NE China: Concentration features and paleolimnological implications

Mid-Eocene tectonic subsidence of the pull-apart Fushun Basin, NE China accommodated an up to 300-m-thick oil shale succession within the lacustrine Jijuntun Formation (Lutetian). Based on sedimentary records and bulk element geochemistry, accumulation of this oil shale succession is modeled to evaluate the principal controls on enrichment patterns of organic matter (OM) and trace metals in lacustrine organic facies. The Jijuntun Formation, consisting primarily of massive oil shale and interbedded siltstone and sandstone that grade rapidly upward into well-laminated oil shale, records an overall evolution from lacustrine–deltaic facies associations to profundal facies associations. Sedimentological characteristics of the oil shale succession display a gradual change of moderately overfilled to balanced-fill lake fill mode, consistent with the up-section drop in siliciclastic inputs reflected by detrital proxies like decreased Si/Al and K/Na ratios. Variations in the sedimentary fill states are accompanied by increasing hydrographic restriction of the Jijuntun paleo-lake, in agreement with low Mo/TOC (consistently <0.54 × 10−4), Mo depletions (average ~1 ppm), and slight U deficiencies (average <2 ppm). Slightly elevated (V + Cr)/Al values in the oil shale suggest reduced oxygen contents in the sediment column relative to oxic bottom waters. The up-section decrease in both FeT/Al and Mn/Al ratios further reveals a shift in bottom-water redox state toward less oxidizing conditions throughout deposition of this oil shale succession. In response to such a change in redox, reactive Fe–Mn shuttling across the chemocline could become intense and facilitate P recycling in water masses, resulting in the coupled Fe–Mn–P enrichments. Euphotic zones of this paleo-lake likely had moderate to high primary and export productivity, supported by the magnitude of enrichments of total organic carbon (TOC) and P nutrient as well as increasing TOC to P ratios. Aerobic respiration of sinking organic particles should occur at the sediment–water interface to reduce benthic O2 levels in the paleo-lake. However, greater aerobic remineralization of labile OM was required to consume relatively more dissolved oxygen during deposition of the lower relative to upper oil shale succession. Hence, different degrees of aerobic OM remineralization are responsible for the contrast in TOC contents between the lower (avg. = 4.7 wt%) and upper (avg. = 12.0 wt%) Jijuntun Formation.

Quantifying species’ geographic range changes: conceptual and statistical issues

AbstractGeographic range is an important metric used to evaluate species’ environmental relationships. Additionally, a very small or rapidly shrinking range may indicate elevated extinction risk. However, a species does not fully occupy its range in the way a lake fills a basin and is instead best thought of as a cloud of points rather than an area per se. Samples of species presence or abundance are subject to issues of both inherent detectability and stochastic detectability due to sample locations in space and time. In addition, populations fluctuate in space and time. These factors mean that the population centroid, range area, and range margin are not deterministic. Examples from the literature demonstrate that multidirectional range changes are ubiquitous due to stochastic effects. Confounding factors, particularly due to human activities such as land use change, also complicate inference about range changes. Herein, statistical tests for centroid and margin changes in the context of stochastic fluctuations of clouds of points and sample error are demonstrated. Scale‐dependent area analysis and tests for range area change are presented along with tests for responses at the community level (suites of species). This test allows for evaluation of change in spatial pattern for patchy populations with or without outliers. Geographic range change can reliably be tested with statistics based on distributions of clouds of observed points rather than bounded areas per se, if potential confounding is taken into account.

Tentative integration of paleoseismic data from lake sediments and from nearby trenches: the central section of the Boconó Fault (northern Venezuela)

The right-lateral strike slip Boconó Fault (Mérida Andes, northern Venezuela) accommodates an important part of the South-American Plate northern transform boundary. Along its central portion, preserved post-LMG lake fills are intersected by two surface-reaching active traces which could be trenched just beside. Outcropping and cored lacustrine sedimentary archives are combined with trench data in order to achieve a Holocene paleoseismicity record for a 7 km-long segment. For lakes sediments, several types of sedimentary “events” were taken into account as co-seismic: mass wasting on deltaic foreset, liquefaction and slumping, reflected tsunami effects, re-suspension, abrupt change in sedimentary dynamics and sources, abrupt emptying and lake surface changes. Time coincidences between two lacustrine archives and two trenches can be proposed for the last 10 kyr BP. Among a total of 24 events, 13 events are detected in two sites, 3 events in 3 sites. 9 possible correlations concern separate traces while 4 concern the same trace; a relay between the activity of the two traces is also deduced. This combination of surveys both reinforces and completes the trenches results, leading to a better knowledge of local to regional seismic hazard. Nevertheless, the total information results probably incomplete and/or biased. The co-seismic origin of lacustrine fills disturbances evidenced but the associated archive is incomplete and/or biased due to: changing recording potential through time, possible impacts by strong distant earthquakes. Trenches data appear to fill lacustrine “gaps” but with a number of events possibly overestimated if all ruptures and associated 14C data are considered as representing separated earthquakes.

Stratigraphy and internal structure of wind‐dominated barrier islands (dune and machair) of the Outer Hebrides, Scotland

AbstractThe barrier islands that fringe the western shore of the Outer Hebrides are globally unusual in that they are developed on a planated bedrock (strandflat) surface. They also contain the most extensive area of machair (a distinctive vegetated sandy plain) in the British Isles. This paper presents the first investigation of the internal structure and morphology of these barrier islands and investigates the controls on their structure. The barriers form extensive (300‐1000 metres wide) but thin (1.5‐2 m) surficial deposits typically resting on bedrock. In areas where depressions exist in the bedrock, and where sediment supply permits, transgressive dunes underlie the machair. A distinctive machair facies of sub‐horizontal, undulating reflections, which are laterally continuous over tens of metres is the dominant component of the barriers at each site. This reflects episodic deposition of windblown sand up to the level of the water table. Thereafter any additional sand is transported through the system to accumulate in topographic lows as lake fills, or on topographic highs as ‘high machair’. Eight radar facies were identified, the extent and presence of which vary between the study sites. Bedrock topography and sediment supply are interpreted as the dominant controls on variability in barrier structure. © 2019 John Wiley &amp; Sons, Ltd.

Estudio de metales pesados en el lago de Ilopango, El Salvador

El lago Ilopango está localizado entre tres departamentos de El Salvador: San Salvador, Cuscatlán y La Paz. De acuerdo con Arévalo y Castañeda (2012), el lago recarga acuíferos, almacena agua, controla inundaciones en la región y ofrece recursos pesqueros y belleza escénica para el turismo y la recreación. Sin embargo, en 2015, a través de la gestión pública, inició la extracción de agua del lago para abastecer la capital salvadoreña (Videla, 2015). Por tal razón, en esta investigación se estudió la presencia y concentración de elementos contaminantes como parte de un monitoreo de la calidad del agua para el consumo humano. Se hizo un muestreo simple en seis puntos del lago, distinguidos como: A, B, C, D, E y F. Estas muestras se analizaron mediante un inductor de plasma acoplado por emisión de espectroscopia óptica (ICP-OES 3300 XL). Entre los resultados se encontró evidencia de elementos contaminantes como: arsénico (As), berilio (Be), cadmio (Cd), selenio (Se), talio (Tl) y plomo (Pb). Sin embargo, estos elementos contaminantes sobrepasaron los límites permitidos para el uso y consumo humano que establece la Agencia de Protección Ambiental de Estados Unidos.Revista ciencia, cultura y sociedad Vol. 4 No. 1 enero-junio 2017; 7-14

Modeling meander morphodynamics over self‐formed heterogeneous floodplains

AbstractThis work addresses the signatures embedded in the planform geometry of meandering rivers consequent to the formation of floodplain heterogeneities as the river bends migrate. Two geomorphic features are specifically considered: scroll bars produced by lateral accretion of point bars at convex banks and oxbow lake fills consequent to neck cutoffs. The sedimentary architecture of these geomorphic units depends on the type and amount of sediment, and controls bank erodibility as the river impinges on them, favoring or contrasting the river migration. The geometry of numerically generated planforms obtained for different scenarios of floodplain heterogeneity is compared to that of natural meandering paths. Half meander metrics and spatial distribution of channel curvatures are used to disclose the complexity embedded in meandering geometry. Fourier Analysis, Principal Component Analysis, Singular Spectrum Analysis and Multivariate Singular Spectrum Analysis are used to emphasize the subtle but crucial differences which may emerge between apparently similar configurations. A closer similarity between observed and simulated planforms is attained when fully coupling flow and sediment dynamics (fully‐coupled models) and when considering self‐formed heterogeneities that are less erodible than the surrounding floodplain.

Improving age-depth models of fluvio-lacustrine deposits using sedimentary proxies for accumulation rates

Lacustrine fills, including those of oxbow lakes in river floodplains, often hold valuable sedimentary and biological proxy records of palaeo-environmental change. Precise dating of accumulated sediments at levels throughout these records is crucial for interpretation and correlation of (proxy) data existing within the fills. Typically, dates are gathered from multiple sampled levels and their results are combined in age-depth models to estimate the ages of events identified between the datings. In this paper, a method of age-depth modelling is presented that varies the vertical accumulation rate of the lake fill based on continuous sedimentary data. In between Bayesian calibrated radiocarbon dates, this produces a modified non-linear age-depth relation based on sedimentology rather than linear or spline interpolation.The method is showcased on a core of an infilled palaeomeander at the floodplain edge of the river Rhine near Rheinberg (Germany). The sequence spans from ∼4.7 to 2.9 ka cal BP and consists of 5.5 m of laminated lacustrine, organo-clastic mud, covered by ∼1 m of peaty clay. Four radiocarbon dates provide direct dating control, mapping and dating in the wider surroundings provide additional control. The laminated, organo-clastic facies of the oxbow fill contains a record of nearby fluvial-geomorphological activity, including meander reconfiguration events and passage of rare large floods, recognized as fluctuations in coarseness and amount of allochthonous clastic sediment input. Continuous along-core sampling and measurement of loss-on-ignition (LOI) provided a fast way of expressing the variation in clastic sedimentation influx from the nearby river versus autochthonous organic deposition derived from biogenic production in the lake itself. This low-cost sedimentary proxy data feeds into the age-depth modelling. The sedimentology-modelled age-depth relation (re)produces the distinct lithological boundaries in the fill as marked changes in sedimentation rate. Especially the organo-clastic muddy facies subdivides in centennial intervals of relative faster and slower accumulation. For such intervals, sedimentation rates are produced that deviate 10–20% from that in simpler stepped linear age-models. For irregularly laminated muddy intervals of the oxbow fill – from which meaningful sampling for radiocarbon dating is more difficult than from peaty or slowly accumulating organic lake sediments – supplementing spotty radiocarbon sampling with continuous sedimentary proxy data creates more realistic age-depth modelling results.

Planform architecture, stratigraphic signature and morphodynamics of an exhumed Jurassic meander plain (Scalby Formation, Yorkshire, UK)

AbstractModern fluvial meander plains exhibit complex planform transformations in response to meander‐bend expansion, downstream migration and rotation. These transformations exert a fundamental control on lithology and reservoir properties, yet their stratigraphic record has been poorly evaluated in ancient examples due to the lack of extensive three‐dimensional exposures. Here, a unique exhumed meander plain exposed to the north of Scarborough (Yorkshire, UK) is analysed in terms of architecture and morphodynamics, with the aim of developing a comprehensive model of facies distribution. The studied outcrop comprises tidal platforms and adjacent cliffs, where the depositional architecture of un‐tilted deposits was assessed on planform and vertical sections, respectively. In its broader perspective, this study demonstrates the potential of architectural mapping of extensive planform exposures for the reconstruction of ancient fluvial morphodynamics. The studied exhumed meander plain is part of the Scalby Formation of the Ravenscar Group, and originally drained small coastal incised valleys within the Jurassic Cleveland Basin. The meander plain is subdivided into two storeys that contain in‐channel and overbank architectural elements. In‐channel elements comprise expansional and downstream‐migrating point bars, point‐bar tails and channel fills. Overbank elements comprise crevasse complexes, levées, floodplain fines and lake fills. The evolution of the point bars played a significant role in dictating preserved facies distributions, with high flood‐stage nucleation and accretion of meander scrolls later reworked during waning flood‐stages. At a larger scale, meander belt morphodynamics were also a function of valley confinement and contrasts in substrate erodibility. Progressive valley infilling decreased the valley confinement, promoting the upward transition from prevalently downstream migrating to expansional meander belts, a transition associated with enhanced preservation of overbank elements. Strikingly similar relations between valley confinement, meander‐bend transformations and overbank preservation are observed in small modern meandering streams such as the Beaver River of the Canadian prairies and the Powder River of Montana (USA).

Physical and Biological Factors Affecting Mercury and Perfluorinated Contaminants in Arctic Char (&lt;i&gt;Salvelinus alpinus&lt;/i&gt;) of Pingualuit Crater Lake (Nunavik, Canada) + Supplementary Appendices (See Article Tools)

Pingualuk Lake fills a deep crater in the Parc National des Pingualuit on the Ungava Peninsula (Nunavik, Canada) and is isolated from nearby surface waters. The main objectives of this study were to determine and compare the concentrations of two atmospherically derived contaminants, mercury and perfluorinated chemicals (PFCs), in the lake water column and fish of Pingualuk Lake and to assess the physical and biological factors influencing contaminant concentrations. Mercury concentrations in arctic char muscle tissue were comparable to those of char in other Arctic lakes, while the total amount of PFCs was below reported levels for remote lakes in the Arctic and elsewhere. Stable isotope and stomach content analyses were made to investigate the feeding ecology of the Pingualuk Lake arctic char population and indicated the possibility of multiple feeding groups. Genetics characteristics (MH and mtDNA) of fish from Pingualuk Lake revealed that this population is likely distinct from that of nearby Laflamme Lake. However, both arctic char populations exhibit differential variation of their allele families. Physical characteristics determined for Lake Pingualuk revealed that the water column was inversely stratified beneath the ice and extremely transparent to visible and ultraviolet radiation. The highest mercury concentrations (3 – 6 pg mL-1 TH g) occurred just beneath the ice surface in each lake. Pingualuk Lake, given its near pristine state and exceptional limnological features, may serve as a most valuable reference ecosystem for monitoring environmental stressors, such as contaminants, in the Arctic.

Spatial and Temporal Distribution of Sand-Containing Basin Fills in the Holocene Rhine-Meuse Delta, the Netherlands

The quantitative significance of coarse-grained deposits in the overbank realm, such as crevasse-splay deposits, has not been studied at the delta scale or at the Holocene timescale. Such knowledge would be beneficial for understanding and explaining sediment distribution in delta plains. This study addresses delta-scale distribution of sand-containing basin fills and their sand-body proportion variability, based on eight valleywide cross sections in the Holocene Rhine-Meuse delta in the Netherlands. We found that sand-containing basin fills form 7.1% of the fluviodeltaic wedge, of which splay deposits are most frequently observed midway between the delta apex and the coast. Organic-clastic lake fills and bay-head delta deposits, in contrast, are limited to the distal delta plain. Over four successive periods (between 9000 and 800 cal yr BP), the largest proportions of splay deposits remain at 50–150 km downstream of the upstream-shifting delta apex. We show that intermediate floodbasin widths (between 3.1 and 3.6 km in the Holocene Rhine-Meuse delta) yield the highest proportions of splay deposits. High rates of base-level rise and wide floodplains both facilitate the creation of accommodation, which in turn provides conditions for peat-forming wetlands in which organic-clastic lake fills can develop. The results show that sand bodies form 26%–30% of sand-containing basin fills. This proportion is shown to be controlled by, among other variables, channel planform and superelevation of the trunk channel and substrate composition. We conclude that potentially large volumes of nonchannel sand bodies exist in distal delta plains. They constitute up to 39% of the reservoir volume in the distal Rhine-Meuse delta and yield relatively high connectedness ratios.

Seismic geomorphology and sedimentology of a tidally influenced river deposit, Lower Cretaceous Athabasca oil sands, Alberta, Canada

The bitumen of the Lower Cretaceous McMurray Formation in Alberta arguably represents one of the most important hydrocarbon accumulations in the world. In-situ development relies on heat transfer through the reservoir via horizontal steam injection wells placed 4 to 6 m (13–20 ft) above horizontal producers near the base of the sandstone reservoirs. Given this technology, understanding the distribution of the resource is paramount for a successful development program. Sedimentary facies provide a direct control on bitumen distribution and recovery. Most facies models developed to describe and predict sedimentary units of the McMurray Formation consider fluvial, estuarine, and/or deltaic depositional settings. In-situ development, however, requires a particularly high-resolution sedimentologic interpretation. High-quality three-dimensional seismic reflection data and extensive drill cores from acreage located approximately 50 km (31 mi) south of Fort McMurray provide important insights into the sedimentologic organization of reservoir and nonreservoir deposits in the upper one third (40 m [131 ft]) of the reservoir interval. Geomorphologic characteristics of the strata observed in seismic time slices reveal that a fluvial depositional setting was prevalent. Ichnologic and palynologic data, as well as sedimentary structures suggestive of tidal processes, indicate a marine influence in the upper reaches of a fluvial system characterized by channels that were 390 to 640 m (1280–2100 ft) wide and 28 to 36 m (92–118 ft) deep. The complex stratigraphic architecture consists of a mosaic of large-scale depositional elements, including abandoned channels or oxbow lake fills, point bars associated with lateral accretion, point bars associated with downstream accretion, counter point bars, and sandstone-filled channels. Reservoir deposits are primarily associated with point bars and sandstone-filled channels.

SEQUENCE STRATIGRAPHY OF DINOSAUR LAKE: SMALL SCALE FLUVIO-DELTAIC STRATAL RELATIONSHIPS OF A DINOSAUR ACCUMULATION AT THE AARON SCOTT QUARRY, MORRISON FORMATION, SAN RAFAEL SWELL, UTAH

Stratal geometries, cyclical stacking patterns, and taphonomic analysis of the Aaron Scott Quarry in the Jurassic Morrison Formation indicate that sediments accumulated within a prograding fluvio-deltaic lacustrine system. Sediments were deposited during the progressive fill of a large lake. Stratal geometries and stacking patterns display relationships similar to larger-scale deltaic sequences caused by fluctuations in base level. Stratigraphic, paleontologic, and sedimentologic analysis indicates that water-volume-driven, base-level changes were responsible for the accumulation and preservation of the assemblage. The assemblage accumulated during a lowering of base level during the late stages of an overall fall caused by drought and was buried by a rapid rise at the end of the drought. Fluvio-deltaic lake fill consists of numerous off-lapping beds of sparsely bioturbated, coarsening-upward mudstone capped by thin, bioturbated silty mudstones. Erosional surfaces dip to the west and cut older mudstone parasequences. Retrogradation, aggradation, and progradation of strata typify stratigraphic trends above the erosion surface. Coarse braided stream sands cap off successive sequences as accommodation is filled prior to the next lowstand and sequence boundary incisement. The quarry is a large, taxonomically diverse deposit formed by the concentration of animals at the margins of a lake during a drought. Animals congregated near the banks as smaller watering holes dried. Bone locations and orientations indicate reworking by fluvial and wave currents. Vertical preservational trends indicate accumulation over a period of years. Trace fossil, lake invertebrate distributions, and sedimentological evidence indicate that periodic establishment of oxygen stratification within lake waters may have contributed to conditions favorable for bone preservation.

Soil loss assessment in the Tasik Chini catchment, Pahang, Malaysia

The Universal Soil Loss Equation (USLE) model is used to estimate average soil loss generated from splash, sheet, and rill erosion in agricultural plots at the Tasik Chini catchment. Use of the USLE has recently been extended for predicting soil loss and plan control practices in agricultural catchment by the effective integration of Geographic Information Systems (GIS) based on procedures to estimate the factor values in a grid cell basis. This study was performed to predict the soil erosion risk by the USLE/GIS methodology for planning conservation measures in the site. Rainfall erosivity (R), topographic factor (LS) and land cover management factor (C) values for the model were calculated from rainfall data, topographic and land use maps. Soil was analyzed for the soil erodibility factor (K). Soil samples were selected from the eleven soil series around the Tasik Chini area. A total of 55 samples were collected from the eleven soil series namely Tebok, Lating, Serdang, Kuala Brang, Kedah, Bungor, Kekura, Malacca, Rasau, Prang and Gong Chenak. Physical properties such as particle size distribution, texture, hydraulic conductivity and organic matter content (OM) were analyzed in order to support the erosion rate analysis. Results shows that five soil series have low rates of soil loss, i.e. Tebok, Lating, Bungor, Kekura and Gong Chenak series, having an average soil loss of 0.65, 0.10, 1.61, 4.23 and 0.53 ton/ha/year, respectively. Two soil series have moderate rates of soil erosion namely Serdang and Prang series (average of 47.41 and 41.10 ton/ha/year, respectively). Two soil series with moderately high rates of soil loss are Kuala Brang and Rasau soil (average of 57.16 and 57.93 ton/ha/year, respectively). Malacca Series has high rate of soil loss, ranges from 21.44 to 348.7 or average of 130.26 ton/ha/year. Kedah soil series has very high soil loss, ranges from 79.99 to 319.75 or average of 180.49 ton/ha/year. This high erosion rate is expected to generate higher sedimentation rate into the Tasik Chini water body, elevating the lake fills and eventually forming an extinct lake.

Late Quaternary palaeohydrological changes in the large playa Lake Frome in central Australia, recorded from the Mg/Ca and Sr/Ca in ostracod valves and biotic remains

The last 42,000 years of hydrological history of Lake Frome, a large playa located in the arid part of northern South Australia, which is hypersaline and most often dry today, is reconstructed using a combination of ostracod assemblages, other microfossil remains, and the trace elemental composition of the selected halobiont ostracod species of Diacypris and Reticypris. The Mg/Ca and Sr/Ca of ostracod valves from 2 cores relate to significant hydrological changes that affected the lake over time. The reconstruction of the Sr/Ca of the lake’s waters, based on the Sr/Ca of ostracod shells, shows that when the lake fills the waters originate mostly from runoff, not from hypersaline waters located below the lake or the surrounding aquifers. The Last Glacial Maximum saw gypsum deflation from the lake. Prior to 25K yBP, Frome had a stable hydrological regime, permanent water and low salinities, with occasional freshwater conditions between 42 and 33K yBP. From 25 to 20.3K yBP, salinities fluctuated and ephemeral conditions operated. After that, until ∼14.8K yBP, a brine pool was located below the lake and was therefore under a different hydrological regime. Between 13 and 11.2K yBP, wet conditions occurred, but such conditions were not seen again during the Holocene.

Architecture and Facies Distribution of Organic-Clastic Lake Fills in the Fluvio-Deltaic Rhine-Meuse System, The Netherlands

Abstract Lakes are prominent features in distal zones of delta plains. Organic-clastic lake fills may form in these lakes, which include gyttja and lacustrine deltas. Understanding of the geometrical properties, the facies distribution, and the origin of organic-clastic lake fills is limited. Knowledge of their development and composition, however, will improve our fundamental understanding of both sediment distribution in and evolution of distal delta plains. Furthermore, organic-clastic lake fills potentially form connectors in hydrocarbon reservoirs. This study aims to describe and explain the characteristics of organic-clastic lake fills and thereby to contribute to the understanding of delta evolution, especially of distal delta plains. A field study conducted in the Schoonhoven and Angstel–Vecht areas, located in the distal part of the Rhine–Meuse delta, the Netherlands, indicates that organic-clastic lake fills developed in peat-bounded lakes after an avulsion initiated fluvial sedimentation. The characteristics of organic-clastic lake fills, such as geometry, sedimentary facies, and sedimentation rates, were both qualitatively and quantitatively determined by cross sections, geomorphogenetic maps, and logs. The results show that in the Angstel–Vecht area as much as 30% of the fluvial-sand volume is stored in organic-clastic lake fills. This contrasts to the general notion that overbank deposits do not contain significant portions of sand. Further, the lacustrine setting often results in vertically bounded sediment bodies that include gyttja and underlies clastic depositional facies, which show a prominent coarsening-upward succession. It is concluded that the presence of organic-clastic lake fills enlarges the reservoir capacity of ancient fluvio-deltaic successions as they contribute to the reservoir volume and also can form connectors between isolated channel-belt sand bodies.

Plio-Pleistocene climate change and the onset of aridity in southeastern Australia

Extreme global climate change in the Late Neogene is well known. In Australia, climate changed from wet conditions in the Late Neogene to the arid conditions that characterize much of the continent today. We constrain the nature and timing of the onset of aridity in southeastern Australia by detailed stratigraphic analysis of palaeo megalake Bungunnia. The demise of the megalake has previously been thought to herald the onset of arid climatic regimes and the sedimentary record of this event has become a proxy-type section for understanding Plio-Pleistocene climate in southern Australia. Our investigations of this sedimentary record reveal regionally extensive and correlatable aeolo-lacustrine quartz silts that represent a major and previously unrecognised step in the aridification of the continent, prior to the demise of the megalake. The age of the aeolo-lacustrine silts is constrained to be around 1.4 Ma to 1.5 Ma, just prior to the middle Pleistocene transition. The silts are preserved in a record of maximum lake fill and not long after their deposition the lake began to contract. Our data show that the youngest lake sediment, the Bungunnia Limestone, is diachronous and preserved on at least 5 distinct terraces, ranging over more than 20 m in elevation. The terraces are interpreted to represent downcutting events during arid conditions, while the sediments on each terrace represent deposition during wet periods. The mineralogy of the limestone preserved on these terraces changes from calcite, aragonite and dolomite dominated at higher elevations to gypsum and magnesite dominated on the lower terraces, providing a unique record of the increasing amplitude of arid climatic cycles. These observations suggest that the onset of aridity in southern Australia was progressive and step-wise, beginning significantly earlier than previously suggested.