Point Bar Research Articles

Recognizing genetically related depositional packages using 3D photogrammetric outcrop models in a fluvially dominated, tidally influenced meander-belt succession

Fluvio-tidal estuary deposits are characterized by abundant channel-associated dunes, compound dunes and point bar deposits. The delineation of boundaries between different point bars to identify genetically unrelated packages is difficult to assess, particularly where similarly dipping bars are superimposed on each other. This study uses an outcrop dataset of the McMurray Formation along the Christina River in NE Alberta, Canada, focuses on bedding relationships and the nature of sedimentary contacts pertaining to the two dominant channel-associated facies: 1) dune-scale, cross-bedded sandstone (CB) representing lower parts of estuary point-bar deposit or thalweg-associated dunes; and 2) inclined heterolithic stratified sandstone and mudstone (IHS) bedsets typically representing the middle and upper part of point bar deposits. This study lays a foundation for documenting and differentiating discrete channel deposits using sedimentological observations at the outcrop, photogrammetry, and surface-orientation analyses of the resulting 3D model. The results reveal the following findings: 1) the IHS units may be underlain by erosional surfaces, which may not be genetically associated with the underlying cross-bedded sandstone intervals; 2) the forward-accreted tidal compound dunes and laterally accreted fluvio-tidal point bars share similar facies characteristics, but are discernible using bedding orientation analysis; 3) these tidal compound dunes may be under-recognized in many tidally influenced estuary deposits; and 4) an inner estuary point-bar setting may be characterized by stacked small-scale point bars, or stacked lateral accretion sets of a single point bar. The result of this study provides a detailed view of facies architecture in a tide-influenced fluvial setting, and feasible solutions to the challenge of assigning genetic units in such environment.

The evolution of meandering and anabranching rivers in postglacial and loess landscapes of Europe

This study aims to explain the influence of sediments and landforms of postglacial and loess landscapes of Europe on processes forming meandering and anabranching rivers. Based on a literature review, sedimentary architecture, types and grain-size of deposits, and channel planform changes since the Late Pleniglacial were collected for extensive set of European rivers. These data were used to create a conceptual model explaining the evolution of meandering and anabranching rivers in both types of landscape. The present study shows that the inheritance of glacial and fluvioglacial landforms and sediments, and loess formation, influence types of processes forming anabranching and meandering rivers. Point bar accretion formed meandering rivers in postglacial zone whereas oblique accretion dominated in loess areas. Anabranching rivers of postglacial zone evolved through the formation of crevasse channels and meandering anabranches. Anabranching rivers of loess zone formed sustained bifurcations. Postglacial and loess rivers reacted differently to increased deposition and humidity in the Late-Holocene. Meanders of postglacial zone formed channel bars owing to increase in stream power and sediment load. In cases of flow energy decrease, and sustained upstream sediment delivery, they turned into anastomosing rivers. Anabranching rivers in ice-marginal valleys maintained its courses until hydro technical works in the 19th century. Low-energy meandering rivers of loess areas became wetlands owing to deposition of silts. High-energy meandering and anabranching rivers maintained the planforms throughout the Holocene. These findings need to be refined by detailed studies on the evolution of rivers in subarctic zone, and large rivers of Europe.

Delineation of stratigraphic traps within the basin floor fans of Miocene sedimentary sequences, offshore Indus, Pakistan using inverted acoustic impedance simulations

AbstractDeep‐water clastic settings frame major stratigraphic plays the world over. The advanced seismic interpretation tools provide prediction of accurate physical characteristics of undiscovered reservoirs, including their lithology, thickness, and porosity. The designed amplitude spectrum (DAS)‐based processing tool on Full spectrum seismic may yield a remarkable stratigraphy. This study deals with the prediction of thick and porous (possibly gas‐rich) litho‐facies using the DAS tool on high‐resolution seismal profiles within the offshore Indus Basin (OIB), SW Pakistan. The seismic and trace envelope magnitudes bound the demarcation of stratigraphic traps. The DAS processing tool on relative acoustic impedance inversion (RAI) magnitude demarcates the aggradational porous sandstone‐filled reservoirs, which are encased within a transgressive non‐porous shale‐filled channel‐levee system. The thickness predicted by band‐limited seismic acoustic impedance (AI) simulation for channels, point bars, and levees is 28, 27, and 24 m, respectively. The DAS‐based RAI processing on AI reservoir simulation accurately resolves the lenses of channel sandstone, point bars and levees, and confirms the channelized basin floor fans (BFFs) with an average 11, 34, 24, and 52 m thickness and a lateral extent between 10 and 25 km. The western zones have implications for basin development, which have accumulated the porous and thickest reservoir facies inside the aggradational parasequences of BFFs of Miocene sedimentary sequences. Hence, the presented scheme of exploration serves as a comparable example for exploring the hydrocarbon‐bearing plays inside OIB and global deep‐water depositional systems.

Depositional and thermal history of a continental, coal-bearing Middle Jurassic succession from Iran: Hojedk Formation, northern Tabas Block

AbstractDuring the early Bajocian, a conspicuous coal-bearing siliciclastic succession was deposited in the northern Tabas Bock, which is important for understanding the regional geodynamics of the Central-East Iranian Microcontinent (CEIM) as well as for the Jurassic coal genesis in this part of Laurasia. Sedimentary facies analysis in a well-exposed section of the lower Bajocian Hojedk Formation (Kalshaneh area, northern Tabas Block) led to the recognition of ten characteristic sedimentary facies and three facies associations, representing channels with point bars and floodplains of a Bajocian meandering river system. Modal analysis indicates that the mature quartz arenites and quartzo-lithic sandstones of the Hojedk Formation originated from the erosion and recycling of older, supracrustal sedimentary rocks on the Yazd Block to the west. The coal petrography and maturity show an advanced maturation stage, whereas the great thickness of these continental strata points to a pronounced extension-related subsidence in the northern Tabas Block. The rapid rate of differential subsidence can be explained by accelerated normal block-faulting in the back-arc extensional basin of the CEIM, facing the Neotethys to the south. Compared to the thick Jurassic, the post-Jurassic strata are relatively thin and played a limited role in the thermal history of the coal in the northern Tabas Block. A relatively high geothermal gradient in the tectonically highly mobile area of the northern Tabas Block and/or heating by regionally widespread Palaeogene intrusions were most probably the key drivers of the thermal maturation of the Middle Jurassic coals.

Distribution and sources of fluvial pollen in the middle reaches of the Yellow River in China and their relationship with vegetation and land use

Understanding the processes determining the composition of alluvial pollen assemblages and its relationship with watershed vegetation is a prerequisite for alluvial palynological study. Palynological analysis of a total of 45 river water samples collected from the middle reaches of the Yellow River and its major tributaries, identifies the distribution patterns, possible sources of pollen and relationship with the catchment vegetation. The results reveal that the pollen assemblages in the middle reaches of the Yellow River is dominated by herbaceous taxa, and the pollen is mainly derived from fluvial sources. Higher concentrations of the pollen tend to occur in the southern part of the study area. The Luo River is the main source of tree pollen in the Wei River Basin, while the Sanchuan River and Xinshui River are the main sources of tree pollen in the mainstream of the Yellow River. Herbaceous pollen mainly originates from the flood plain, and from channel bars and point bars, and there is no obvious relationship between herbaceous pollen and tributary inputs. The relative proportions of the various land use classes in the middle reaches of the Yellow River can be ordered as follows: grassland (GL) > cultivated land (CL) > forest (FO) > shrubland (SH) > water (WA). The herbaceous pollen of the Huangfuchuan River and Kuye River are closely related to the coverage of GL; cereal pollen is not fully representative of the CL coverage in the watershed; and the pollen of woody plants is extremely over-represented compared to the coverage of FO and SH in the watershed. Our results provide basic information about the sources of fluvial pollen and its indicative significance in the lower Yellow River and they are also potentially applicable to other major river basins.

Sharp change of the channel bar pattern within the river delta: Insights from modern Ganjiang River delta in Jiangxi province, China

Channel bars (midchannel bars or point bars) in river deltas present challenges to water transportation; meanwhile, they provide a source of building materials, habitats, and farmlands, and they could become targets in hydrocarbon reservoirs. Researchers focus on the channel bar pattern in rivers, while ignoring the channel bar pattern in distributary channels. We have analyzed a sharp change of the channel bar pattern from the river to the delta. The integration of remote map analysis, fieldwork, and a flume experiment has resulted in a quantified sharp change in the channel bar pattern in the Ganjiang River delta and revealed a hydrodynamic mechanism. The result finds that distributary channels develop much finer-grained, smaller-scale, less channel bars with the lower width-length ratio, compared to the upstream river. Distributary channels develop more point bars and fewer midchannel bars than the upstream braided river, and they develop fewer point bars than the upstream meandering river. Sharply weakening bank erosions in distributary channels lead to the formation of the sharp change in the channel bar pattern from the upstream river, due to backwater effect-induced sharp gentling of landform gradient. The backwater effect impedes bank erosions in the distributary channels, but it promotes bank erosions in upstream rivers, which, in turn, enhances the sharp change of the channel bar pattern. We provide insights into channel bars’ growth in modern river deltas and provide new facies models for the river-delta system.

Experimental investigation of flow pattern over a fully developed bed at a 60° river confluence in large floods

River confluences have a complex flow and sedimentation pattern that have vital influences on the hydraulic and bed morphology of river reach and the surrounding area. Confluences can be observed in waterways with various situations such as live bed conditions. This condition is a hydro-morphological situation with a high densimetric Froude number, i.e., bed load transport is supplied from upstream. According to the literature review, most of the experimental studies investigate the flow pattern on the flatbed and not on the developed riverbed, or/and in the low densimetric Froude number, or/and without supplying the sediment from upstream. Therefore, in the present study for the quantification of the flow pattern under these conditions, each developed bed was fixed with the cement blanket method in the laboratory. Then, the 3D velocity was measured at specific points at the confluence. The current study was designed to understand the flow pattern corresponding to the river bed behavior in the case of large floods. It is expected that the morphological features downstream of the confluence have a different pattern than the ones in the condition described in other literature. Thus, this paper describes briefly what are the different bed features and investigates the corresponding flow pattern. The results of the flow pattern on the developed bed show that all zones at the river confluence can be observed except the point bar due to the approximate equality of the mean longitudinal velocity of the separation zone and the main channel upstream of the confluence. Moreover, results show that by increasing the bedload ratio (sediment discharge to water discharge of the main channel of upstream of the confluence) from 0 to 3 × 10−4, flow deflection to the outer bank of the channel decreased down to 45%, the stagnation equivalent area decreased down to 2.5 times, and bed shear stress decreased down to 40%. Hence, the momentum of lateral flow decreased with increasing bedload. Besides, the recovery zone occurred at a longer distance after the confluence compared to the case without bedload. Hence, the location of the maximum velocity zone, vortices, and secondary flows changed downstream of the confluence, by changing the bed load value.

Comprehensive evaluation and reservoir classification in the Quan 3 Member of the Cretaceous Quantou Formation in the Fuxin Uplift, Songliao Basin

Continental tight oil sandstone reservoirs are developed in the Cretaceous Quentou Formation in the Songliao Basin, China. At present, there is still a lack of research on the reservoir microstructures, reservoir physical properties, and the division scheme of reservoir types in the Quan 3 Member of the Quanzhou Formation. Therefore, in this paper, taking the Quan 3 Member in the Fuxin Uplift Belt of the Songliao Basin as an example, the microscopic pore structure characteristics of tight oil sandstones have been systematically studied, and the classification standard of tight sandstones has been formulated. Furthermore, the sweet spots of the main production layers are predicted. The results show that the I sandstone group in the Quan 3 Member in the study area belongs to shallow water delta facies. Feldspar lithic fine sandstones are developed in the target layer, and calcareous sandstone is locally developed. Moreover, the mian pore types of the target layer include dissolved intergranular and intragranular pores, followed by primary intergranular pores, while micro-fractures are occasionally seen. According to the mercury intrusion test results, the pore-throat structures of the reservoir in the Quan 3 Member are divided into four types: 1) small-pore medium-throat type (point bar and delta distributary channel), 2) small-pore micro-throat type (point bar), 3) small-pore micro-throat type (natural levee), 4) micro-pore micro-throat type (river floodplain and inter-tributary bay). The lower limits of the physical properties of the effective reservoirs in the Quan 3 Member has been determined: the porosity is 10% and the permeability is 0.1 mD. Finally, combined with the study of the mercury intrusion curves, the physical properties and the sedimentary facies, the classification standard of the Quan 3 Member reservoirs was formulated. For the I sandstone group, the sweet spots of the Type I reservoirs are mainly developed in the Fuyu Oilfield in the southeast areas. The sandstones in this area suffered less compaction, and primary and secondary pores suffered from late dissolution are mainly developed.

Predictive geospatial model for arsenic accumulation in Holocene aquifers based on interactions of oxbow-lake biogeochemistry and alluvial geomorphology

The identification of arsenic-contamination hotspots in alluvial aquifers is a global-scale challenge. The collection and inventory of arsenic concentration datasets in the shallow-aquifer domain of affected alluvial basins is a tedious and slow process, given the magnitude of the problem. Recent research demonstrates that oxbow-lake biogeochemistry in alluvial plains, mobilization of geogenic arsenic, and accumulation in geomorphologically well-defined areas are interacting processes that determine arsenic-contamination locations. This awareness provides a tool to identify potential arsenic-hotspots based on geomorphological similarity, and thus contribute to a more robust and targeted arsenic mitigation approach. In the present study, a conceptual predictive geospatial model is proposed for the accumulation of dissolved arsenic as a function of interaction of oxbow-lake biogeochemistry and alluvial geomorphology. A comprehensive sampling campaign in and around two oxbow lakes in the Jamuna River Basin, West Bengal (India) provided water samples of the oxbow-lake water column for analysis of dissolved organic matter (DOM) and microbial communities, and groundwater samples from tube wells in point bars and fluvial levees bordering the oxbow lakes for analysis of the geospatial distribution of arsenic in the aquifer. Results show that abundant natural and anthropogenic (faecal-derived) recalcitrant organic matter like coprostanols and sterols in clay-plug sediment favours microbial (heterotrophs, enteric pathogens) metabolism and arsenic mobilization. Arsenic concentrations in the study area are highest (averaging 505 μg/L) in point-bar aquifers geomorphologically enclosed by partially sediment-filled oxbow lakes, and much lower (averaging 121 μg/L) in wells of levee sands beyond the oxbow-lake confinement. The differences reflect variations in groundwater recharge efficiency as result of the porosity and permeability anisotropy in the alluvial geomorphological elements, where arsenic-rich groundwater is trapped in point-bars enclosed by oxbow-lake clays and, by contrast, levee ridges are not confined on all sides, resulting in a more efficient aquifer flushing and decrease of arsenic concentrations.

Petrographic and Geochemical Analysis of Indus Sediments: Implications for Placer Gold Deposits, Peshawar Basin, NW Himalaya, Pakistan

Alluvial placer gold deposits that accumulate in streams across the globe are essentially allochthonous sedimentary deposits that are transported from their source to their location of deposition. The purpose of this study was to find placer gold deposits in alluvial sediments along the Indus River in the NW Himalaya of Pakistan. The investigated region was divided into five clusters based on river morphology. The research focused on mineralogical distribution, sediment source, gold transport distance, elemental composition, and gold concentration in river sediments. Throughout, during the deposition at point and channel bars, the mixed source of alluvial sediments was revealed by its mineralogical composition. However, the SEM analysis demonstrated that the gold grains had a high flatness index, indicating that they had been transported a significant distance. The elemental composition of several samples revealed a significant concentration of silicon dioxide, iron oxide, and alumina oxide transported from the Himalaya. The study of the trace elements indicated gold and related base metals with granitic provenance were transported from an acidic/granitic source. Based on gold concentration, it is demonstrated that the left riverbank (clusters C1, C2, and C3) has a higher concentration of gold deposits and higher potential for economic gold exploration than the right bank (clusters C4 and C5) due to the lower velocity of running water in the study area. The findings revealed that the studied area has good potential for commercial exploration of gold resources, and the workflow can be adopted in any region with a similar geological setting and morphology.

Identification and Quantitative Characterization of Point Bars in Subsurface Meander-River Belt, Taking Chengdao Oilfield in Bohai Bay Basin as an Example

Reservoir architecture is an important basis for studying the sedimentary evolution of underground reservoirs and the distribution of remaining oil. Taking meander-river reservoir of Guantao Formation in Chengdao Oilfield as an example, characteristics of the evolution of subsurface meander-belt deposits were studied by seismic sedimentology. Seismic lithology is performed using -90° phase wavelet and frequency fusions; seismic geomorphology is conducted on seismic stratal slices. Six meandering belts were defined in the target layer, and the sediment at the bottom is characterized by the transformation from “braided” river to “meandering” river. The width of meander-river belt has no correlation with the maximum thickness of meander-river belt. But it has obvious negative correlation differences in the minimum thickness of meander–river belt. With the increase of width of the meander-river belt, the minimum thickness of the drilled meander-river belt decreases as a whole. The forward model based on the shape of point bar reveals the seismic architecture characteristics formed by the superposition of sand bodies at different positions of point bars. According to these characteristics, the point bars in the meandering zone can be explained. In the Ng33, Ng42, and Ng45 sub-layers of the study area, the corresponding meander-belt widths where the point bar (or point bar connecting body) cannot be effectively identified by well logging and seismic data, are, respectively, 800, 800, and 500 m. At the same time, when the width of the meander belt is greater than 1000 m, three or more than three point bars (or point bar connecting body) can be basically identified in the meander belt. The width of the point bar segments in the meander belt of the three main sub-layers is mostly 300–400 m, and the maximum width of the point bar segments is about 550 m, while the scale of point bars in Ng45 sub-layer meander belt is relatively small. The quantitative characteristics of point bar debris and the determined location of SBM and SIA sand bodies provide limited and valuable data support for the formation and simulation of underground meandering rivers, which are also useful for the model of the target reservoir.

Preservation of exopolymeric substances in estuarine sediments.

The surface of intertidal estuarine sediments is covered with diatom biofilms excreting exopolymeric substances (EPSs) through photosynthesis. These EPSs are highly reactive and increase sediment cohesiveness notably through organo-mineral interactions. In most sedimentary environments, EPSs are partly to fully degraded by heterotrophic bacteria in the uppermost millimeters of the sediment and so they are thought to be virtually absent deeper in the sedimentary column. Here, we present the first evidence of the preservation of EPSs and EPS-mineral aggregates in a 6-m-long sedimentary core obtained from an estuarine point bar in the Gironde Estuary. EPSs were extracted from 18 depth intervals along the core, and their physicochemical properties were characterized by (i) wet chemical assays to measure the concentrations of polysaccharides and proteins, and EPS deprotonation of functional groups, (ii) acid-base titrations, and (iii) Fourier transform infrared spectroscopy. EPS-sediment complexes were also imaged using cryo-scanning electron microscopy. EPS results were analyzed in the context of sediment properties including facies, grain size, and total organic carbon, and of metabolic and enzymatic activities. Our results showed a predictable decrease in EPS concentrations (proteins and polysaccharides) and reactivity from the surface biofilm to a depth of 0.5 m, possibly linked to heterotrophic degradation. Concentrations remained relatively low down to ca. 4.3 m deep. Surprisingly, at that depth EPSs abundance was comparable to the surface and showed a downward decrease to 6.08 m. cryo-scanning electron microscopy (Cryo-SEM) showed that the EPS complexes with sediment were abundant at all studied depth and potentially protected EPSs from degradation. EPS composition did not change substantially from the surface to the bottom of the core. EPS concentrations and acidity were anti-correlated with metabolic activity, but showed no statistical correlation with grain size, TOC, depth or enzymatic activity. Maximum EPS concentrations were found at the top of tide-dominated sedimentary sequences, and very low concentrations were found in river flood-dominated sedimentary sequences. Based on this observation, we propose a scenario where biofilm development and EPS production are maximal when (i) the point bar and the intertidal areas were the most extensive, i.e., tide-dominated sequences and (ii) the tide-dominated deposit were succeeded by rapid burial beneath sediments, potentially decreasing the probability of encounter between bacterial cells and EPSs.

Planform architecture, meander evolution and grain‐size variability of a deltaic channel belt in the Rhine‐Meuse delta, The Netherlands

AbstractIn the unconstrained, low gradient setting of major delta plains, individual meander belts tend to function for relatively short periods of time due to repeated channel avulsion. Their short lifetime makes ‘deltaic’ channel belts suitable to study the products of steady meander evolution as the deposits and internal architectural elements preserved are often without complications of repeated bend cutoffs. This study investigated how sedimentary characteristics as preserved from subsequent stages of activity differ within the Stuivenberg channel belt. The Stuivenberg channel belt is a long‐studied example in the Holocene Rhine‐Meuse delta, The Netherlands, for which the meander evolution, i.e. geometry and dimensions through initiation, main activity and abandonment stages and durations of activity involved, was reconstructed. Mapping of the channel belt started from established coring based and LiDAR‐aided methods. Explorative approaches were used to assess active channel width at the onset of abandonment, and to reconstruct meander positions during earlier stages. The migration history of five consecutive meanders is revealed from convex and concave ridge‐and‐swale scrolls. Analysis identifies them to be the product of translation, expansion and rotation trajectories during a period of 800 years. Grain‐size composition throughout the sand body is interpreted given these positional contexts, with special attention to local coarsening of upper point bar facies in deltaic meander belts. The findings emphasize: (i) the need to separate abandonment stage from main activity stage when analysing three‐dimensional channel belt architectures; and (ii) the influence of meander evolution on lithological characteristics of initial stage versus mature stage parts of deltaic channel belt sands.

Bank and point bar morphodynamics in the Lower Jingjiang Reach of the Yangtze River in response to the Three Gorges Project

Bank and point bar morphodynamics in the Lower Jingjiang Reach of the Yangtze River in response to the Three Gorges Project

Integrated remote sensing and field-based approach to assess the temporal evolution and future projection of meanders: A case study on River Manu in North-Eastern India.

A common phenomenon associated with alluvial rivers is their meander evolution, eventually forming cutoffs. Point bar deposits and ox-bow lakes are the products of lateral bend migration and meander cutoff. The present study focuses on identifying the meanders of River Manu and their cutoffs. Moreover, this study compares the temporal evolution and predicts the progress of selected meanders of River Manu. In the present research, the Survey of India topographical map, satellite imagery, and geographic information system (GIS) technique were used to examine the evolution of the Manu River meander. Subsequently, a field visit was done to the selected cutoffs and meanders of River Manu to ascertain the present status and collect data. It has been observed that many cutoffs have undergone temporal changes, and their sizes have decreased. Some have become dried or converted to agricultural fields. The width of River Manu has decreased in all the selected bends from 1932 to 2017. The sinuosity index has changed from 2.04 (1932) to 1.90 (2017), and the length of the river has decreased by 7 km in 85 years (1932–2017). The decrease in length is evident from lowering the number of meanders. Uniformity coefficient and coefficient of curvature of the bank soil samples were calculated, indicating that the soil is poorly graded and falls under the cohesionless category. Based on cross-section analysis, sediment discharge, grain-size analysis of the bank material, channel planform change, and radius of curvature, it can be stated that almost all the selected bends have the probability of future cutoff. The highest probabilities were observed in bend 3 (Jalai) and bend 4 (Chhontail). This work is aimed to provide planners with decisions regarding the construction of roads and bridges in areas that show the huge dynamicity of river meandering.

Simulating Ecological Effects of a Waterway Project in the Middle Reaches of the Yangtze River Based on Hydraulic Indicators on the Spawning Habitats of Four Major Chinese Carp Species

The adaptability of fish to their habitats is closely related to river hydraulics. While navigation channel projects aim to improve the navigation conditions by adjusting the hydrodynamic force of local river sections, the impacts of these projects on the hydraulic indicators of habitats of the four major Chinese carp species (FMCCs) remain unclear. Taking the Daijiazhou reach in the middle reaches of the Yangtze River as a case study, a mathematical model for spawning suitability was established to simulate changes in these hydraulic indicators before and after the implementation of a navigation channel project. The optimal flow rate interval for the spawning of the FMCCs was 17,500–22,000 m3·s−1. After the navigation channel project was implemented, the habitat suitability index (HSI) and weighted useable area (WUA) increased across the spawning habitats of all FMCCs, indicating that the project implementation created more habitat space. The central bar (Chihugang central bar) became exposed during the dry season, with the HSI and WUA decreasing under low water flow but increasing under medium-low or higher water flow levels. At the Daijiazhou bar head floodplain, which remained unexposed during the dry season, the HSI and WUA increased after project implementation, providing more space for spawning and habitation for the FMCCs. For the low point bar with bank gullies (Lejiawan point bar), the implementation of the bar protection zone project restricted gully development, with the HSI and WUA decreasing for all FMCCs. Based on the above impacts of navigation channel projects on the hydrodynamic environment of fish habitats, this paper provides a reference for the optimization of navigation channel arrangement as well as for the restoration of fish habitats.

Analysis of Grain Morphology, Mineral Composition, and Ore Grade on Gold Placer Deposits in Bantimurung, Pangkep Regency, South Sulawesi, Indonesia

The information through social media shows that there is quite an intense placer mining activity by local residents in the Bantimurung area, Tondong Tallasa District, Pangkep Regency. This study as a preliminary research aims to determine the grain morphology characteristics of mineral composition and metal grade in gold placer deposits in the study area. The data collected were eight samples. The collected samples were prepared into thin section, polished and observed using a microscope to identify the mineral composition and grain morphology. The grades of Au metal and its associated metals consisting of Ag, Zn, Pb, and Cu in the placer samples were analyzed by the AAS method. Petrography shows abundant of quartz, plagioclase, biotite and pyroxene minerals it might be indication of mineralization of epithermal. Ore petrography shows pyrite present along the river, silver is also found quite a lot along the river. Meanwhile, covellite, magnetite, sphalerite, and garnet were found only slightly at the sampling station this mineral composition indicates that the source of the placer deposits was epithermal. The grain morphology of the thin-section observation shows that quartz dominant has a high sphericity with character of roundness tends to be very angular to sub-rounded from upstream to downstream of the river. Plagioclase tends to have sub rounded roundness and high sphericity. Biotite tends to have a high sphericity with roundness from upstream to downstream is very angular, then angular, then sub-rounded. Pyroxenes tend to have high sphericity with very angular and angular roundness. Au content is directly proportional to Cu and inversely proportional to Zn, Pb, and Ag. Statistically Au affects the content of Cu by 50.97%. It can be concluded that Au is genetically associated with Cu, however Au grains that were still attached to the mineral and had not been separated from other minerals so that it could not be seen visually. This can also indicate that the source of this placer deposit is not far from the study site. Au grade corelated with stream sediment types it is 97,86 ppm for channel bar and 94,16 ppm for point bar, based on this we conclude the downstream has higher grade of Au compare to the upstream.

RELATIONSHIP BETWEEN OVIPOSITION OF Podocnemis unifilis AND WATER LEVEL IN PERUVIAN AMAZONIAN FLOODPLAINS

In the Amazon floodplains, hydrological variability plays a crucial role by shaping the habitat, offering shelter and feeding or breeding areas. During the dry season, some fresh water turtles such as the yellow-spotted turtle (Podocnemis unifilis Troschel, 1848) use the sand banks at point bar areas as breeding sites, which must be available in time for the start of oviposition. In this study, we used altimetry-derived water level data from radar satellites combined with in-situ hydrological measurements to evaluate water level variations and relate them to oviposition starting dates (2003-2012) from Pacaya-Samiria National Reserve, Peru. Synchronous hydrological behavior was found between the major river stems (Ucayali and Marañon) and the inner rivers (Pacaya and Samiria), thus enabling the utilization of water level in the main river stem to correlate with oviposition in the inner rivers. Mean oviposition date was July 23nd with selection of a narrow water level range (92 masl ± 0.9 SD). Consistent shifts towards early/late oviposition were found for years with early/late dry season onset. Extreme biological shifts in terms of oviposition date onset, were identified for specific years (2004, 2010 and 2011) mainly for the extreme dry year of 2010.

Isotope compositions of dinosaur eggs and associated depositional settings in the Upper Cretaceous Huizhou Formation from the Qiyunshan area, Anhui Province, China: implications for paleoenvironmental reconstruction

ABSTRACT We analysed the stable isotope compositions of dinosaur eggshells and their associated depositional settings of the egg-bearing rocks in the Upper Cretaceous of the Qiyunshan area, Anhui Province, China. Data show that δ13C values for Similifaveoloolithus qiyunshanensis and Umbellaoolithus xiuningensis range between −5.94‰ and −3.55‰; this suggests that C3-type vegetation was consumed by dinosaurs with relatively high atmospheric CO2. δ18O values vary between −8.45‰ and −4.95‰, indicative of high temperature and low humidity within nesting areas. The lithological characteristics of the egg-bearing section evaluated in this study are dominated by red-brown fine sandy siltstone, correlating with pebbly medium-fine grained and medium-fine grained lithic sandstones. Grain size parameters, histograms, and sample probability cumulative curves are also all characterised by fine-grained sediments and suspension populations, likely indicative of floodplain and point bar environments. Therefore, the paleoclimate of the dinosaur nesting habitat was semiarid-to-arid based on food types as well as the colour and high Fe content of sediments. We suggest that this fluvial environment provided the best nesting and egg laying area for drought-adapted dinosaurs in the Upper Cretaceous of the Qiyunshan area and that the excavated nesting could be concluded in view of the periodic flooding events.

New evidence for avian and small non-avian theropod ichnotaxa from the Lower Cretaceous of Canada: Implications for theropod ichnodiversity

A diverse continental ichnofauna from the Lower Cretaceous (Aptian) Gething Formation occurs at the Ninesting Creek site in northeastern British Columbia. Vertebrate tracks including Wupus and Saurexallopus are inferred to represent medium-sized (footprint length ∼10 cm) tridactyl avian and larger (footprint length ∼15–17 cm), gracile, tetradactyl non-avian theropod trackmakers respectively. Shape, length-to-width and divarication ratios, suggest two morphotypes that are distinct from the poorly known, and infrequently-cited, Gething Formation ichnogenera Columbosauripus and Irenichnites (footprint lengths ∼12.5 and ∼15.0 cm respectively). This suggests a diverse theropod ichnofauna representing size classes which are quite distinct from the better-known large theropod ichnogenus Irenesauripus with footprint lengths in the range of ∼38.0–53.5 cm. Thus, current evidence suggests that the ichnodiversity of smaller avian and non-avian theropod tracks (footprint length ∼<15.0 cm) outnumbers large ‘megatheropod’ morphotypes by about 7:1. The implications of this distribution are consistent with recently proposed palaeoecological models. The assemblage also includes probable pterosaur tracks and distinctive arcuate compound Archaeonassa-Lockeia traces, attributed to freshwater unionid bivalves. The trace fossils comprise a composite Mermia-Scoyenia Ichnofacies assemblage. Palaeoenvironmentally the site represents the low energy margin of an open lake basin or floodplain pond, or a fluvial point bar.