Estimation of Holocene bedload sedimentation rate in a paleo-drowned river-valley (Middle Harbour, Sydney estuary, Australia)

Middle Harbour is a drowned-river valley located adjacent to the larger Sydney estuary, Australia. Extensive, high-resolution seismic data were correlated with borehole, land use, topographical, and geological data to calculate the mass of genetically different sediment deposits in Middle Harbour. The Harbour follows a well-defined drowned river-valley structure featuring small fluvial bedload delta deposits in the upper reaches of the embayments, a deep, central extensive mud basin overlying transgressive basal accumulations and a large flood-tide delta at the entrance. Deposits of an estimated 5,094 t of bedload, 21,143 t of suspended sediment and 5,947 t of transgressive basal material located in the estuary provided sedimentation rates of 0.68 t y-1, 1.29 t y-1, and 2.86 t y -1 respectively. These rates, determined from measured accumulations, were surprisingly low and substantially smaller than modelled rates. However, low sedimentation rates for suspended material may be due to fine sediment escaping over the top of the marine tidal delta, which effectively traps all bedload material from exiting the Harbour. Results of this study indicate that Holocene bedload sedimentation in Middle Harbour was slow and regular until a rapid increase after urbanisation commenced in the catchment. Most pre-Holocene material was eroded from Middle Harbour during the Last Glacial period with sediment currently present in the estuary having been deposited since sea-level recovery.

Integrated geophysical and geochemical assessment of submarine groundwater discharge in coastal terrace of Tiruchendur, Southern India

Submarine groundwater discharge (SGD) study is essential for groundwater in coastal terrace at Tiruchendur. The famous Murugan Temple is located in the area and around 25,000 people who visit this temple use the SGD well water at NaaliKinaru (a small open well) as holy water and drink it. The rock and soil type are sandy clay, silt, beach sand, calcarenite, kankar, gneissic rock and charnockite in base rock. Megascopic identification method was used to identify the porous and permeable rocks such as calcarenite, sandstone and kankar to support to increase SGD flux. Grain size study was used to identify the paleo-coastal estuarine environment with sediment deposits in the terrace. The square array electrical resistivity method was used to study the subsurface geology and aquifer depth. The 2d ERT technique was used to identify the subsurface shallow perched aquifer of freshwater. The magnetotelluric survey method was used to scan the entire subsurface geological and tectonic uplift, coastal ridges, rock folded subsurface structural features of continental and oceanic tectonism. Darcy’s law was used to calculate the SGD flux rate in the above study area.

Tracking Recent DDT Contamination in a Northern New England Watershed

Research on declines in loon populations at Squam Lake, New Hampshire, U.S.A., point to multiple potential causes since 2005, including dichlorodiphenyltrichloroethane (DDT). This study narrows down sources of DDT in a small sub-watershed by focusing mainly on collecting and analyzing soil and sediment samples, achieving rapid source area determination of DDT. We find presence of p,p’ isomers of DDT and DDE in the Bennett Brook sub-watershed arising from long-term soil and sediment storage of applications 60 years ago, plus a concentrated and current source area at a former barn. Highest concentrations, 723 μg/kg p,p’-DDT and 721 μg/kg p,p’-DDE, occur in the soils adjacent to the barn’s foundation remnants. DDT exceeds that of the metabolite, DDE, in many soils around Bennett Brook, including but not limited to the barn site. In soils where DDT>DDE, we infer mechanisms that delayed breakdown of DDT over the last 60 years. A Pb-210 dated lake sediment core, collected near the outlet of Bennet Brook, shows continuous accumulation of p,p’-DDE and p,p-DDD after 1951. These residuals likely derived from multiple sources within the sub-watershed, including orchard soils, the barn site, and from mobilized sediment deposits following extreme floods in the watershed. Although the DDT residues fall below mandatory soil remediation levels for the State of New Hampshire, Bennett Brook sediments exceed sediment quality guidelines for protection of aquatic life. Crayfish collected in Bennett Brook have significantly higher concentrations of p,p’-DDE than crayfish collected elsewhere in Squam Lake.

Debris flows and debris floods occurrence in the Ribnishka River watershed (southern slopes of Ograzhden Mountain)

The Ribnishka River watershed, located on the southern slopes of Ograzhden Mountain is known for the repeated torrential events in the last few decades. In this paper, we represent a preliminary assessment of the debris floods and debris flows hazard in the Ribnishka River watershed. For this purpose, the topographic conditions in the watershed are considered, the source, transport, and deposition zones are characterized, as well as the observed sediment deposits in the river valley. The obtained results could be used in the development of risk management plans, but also provide new information on the development of debris floods and debris flows in this part of the country.

Delineation of sedimentary basin structure beneath the Banyumas Basin, Central Java, Indonesia, using ambient seismic noise tomography

Subsurface images of an area with a thick volcanic layer generally cannot be well-imaged with conventional seismic exploration (seismic reflection) due to seismic wave scattering. Another method is needed to obtain an accurate subsurface image in a thick volcanic layer area. In this study, we applied ambient noise tomography (ANT) to image the shear-wave velocity (Vs) structure in the Banyumas Basin, Central Java, Indonesia, which has relatively thick volcanic layers. We aimed to delineate the sediment deposits and the sedimentary thickness in this area through the utilization of ambient seismic noise. The application of cross-correlations from ambient seismic noise has been widely applied in numerous locations to obtain a greater understanding of subsurface structures. In this study, more than 1000 pairs of vertical component cross-correlations were used to estimate the Green's Function of the Rayleigh wave. The Neighbourhood Algorithm (NA) was utilized to invert the dispersion curves at 121 grid points which were used to obtain a vertical depth profile of 1D Vs. The Vs map results show that the low Vs tend to trend in a northwest–southeast direction associated with two areas: the Majenang low, and the Citanduy low. The presence of low Vs values corresponds with Middle Miocene–Pliocene sedimentary rocks. Meanwhile, the high Vs values in this area might correspond with Oligocene–Early Miocene volcanic products and Eocene sediment. Our study was also able to reveal the thickness of sedimentary rocks in the Banyumas sedimentary basin, which is believed to have hydrocarbon potential.

Subsurface Sediment Deposits of Tanjung Berikat Coast, Bangka, Determined from GPR Interpretation

Tanjung Berikat Coast in Central Bangka, is a part of the Southeast Asian tin belt. We conducted four Ground-Penetrating Radar (GPR) survey lines and 13 hand auger coring to understand sediment deposition and composition. Two similar units were determined from GPR lines BLG 01–BLG 03: Unit A at the top part, reflected by parallel and continuous reflector configuration, weak–strong electromagnetic wave. Underneath Unit A is Unit B, characterized by subparallel configuration, not continuous–chaotic, weak–medium electromagnetic wave. Unit B is absent in BLG 04. We identify another two units from BLG 04 and BLG 03, Unit C, characterized by subparallel reflector configuration, not continuous– chaotic, weak–strong electromagnetic wave. It exhibits distinctive modulating contact with Unit D. Unit D is characterized by chaotic reflector configuration, relatively stronger electromagnetic wave that might be correlated to the granite intrusion Tanjung Klabat. Sediment deposit is composed of fine–coarse sand, consisting mostly of clastic plutonic and clastic biogenic (coral and mollusk fragments), which increase downward. This indicates marine-fluvial influence, which suggests that sea-level changes strongly influence sedimentation process. Unit A from GPR is correlated to these sediment deposits, the other three units might be correlated to weathering of older insitu deposit.

High Resolution Correlation of Sequence Stratigraphy to Stipulate Further Hidrocarbon Prospect in A Mature Field : Case Study of Limau Field, South Sumatera Basin

The Limau Trend Structure is located in the South Sumatera Basin of Indonesia. The main reservoir in this field is the Talang Akar Formation which is deposited in a fluvial complex that changes gradually into a shallow marine depositional environment in a transgressive phase of 3rd order sequence. The sediment deposit was developed from the Late Oligocene to Middle Miocene. A high-resolution sequence stratigraphic interpretation of the 3rd to 4th order was interpreted from the subsurface data (core and well log) combined with the outcrop observation that resulted in a comprehensive input for building a geological model. Based on this framework, the transgressive phase series in each parasequence set produces restricted sediment deposits that have the potential for stratigraphic traps. On the other hand, the amalgamated sands of the regression phase will be related to the structural traps. The RMS amplitude volume from seismic multi attributes analysis shows that the facies is changing with the reservoir distribution. The seismic attributes such as VpVs indicate a hydrocarbon presence. The combination of all data reveals that the stratigraphic traps are the main trapping mechanism in the Limau field. The field development works are now focusing in the northern area, on the transgressive phase of the 4th order parasequence set. It composes of a fluvial complex cycle that has a high potential for a virgin geometrically restricted (lense shaped) reservoir rather than well-connected and sand-rich maximum regressive reservoir facies. This transgressive phase reservoir of parasequence set (4th order) at the Northern Belimbing Field was proven by 2 (two) recently drilled wells. Both wells showed very good hydrocarbon indications and produced oil with an initial rate of 174 bopd & 1265 bopd respectively. These results confirmed the oil prospectivity within the transgressive phase of the 4th order parasequence set at the Northern Limau Trend. The initial resources estimation in the Northern Belimbing Field contains 65 MMBO. This is very promising for the development of the Belimbing Field, Limau Trend.

Vermiculations in painted caves: New inputs from laboratory experiments and field observations

Vermiculations are aggregates of small particles commonly found on cave walls. They are a major concern for the conservation of painted caves, as they can potentially alter valuable prehistoric cave paintings. A previous rheological study of fine sediment deposits on cave walls revealed that this material can undergo a solid-to-liquid transition triggered by variations in the chemical composition of the water film on the wall. Such a transition could occur at the origin of vermiculations by allowing the sediment to flow under low mechanical stress. In this work, we provide quantitative information on the conditions leading to this transition and show the importance of the chemical composition of the water film on the cave walls. A complete understanding of the phenomenon will, however, require more field information. This includes monitoring of the evolution of vermiculations, for which we have developed a dedicated observation protocol. Based on the combination of photogrammetry and a geographic information system we were able to precisely map the walls of the Hall of Bulls in Lascaux cave from past and future photographs. To better understand the vermiculation process, pictures need to be taken regularly, and the chemical composition of the thin water film covering cave walls needs to be analyzed with a similar time step. The correlation between the evolution of vermiculations, the humidification phases of the walls, temperature changes and the chemical monitoring of the water film should shed new light on conditions triggering vermiculations.

Calibration, inversion and sensitivity analysis for hydro-morphodynamic models

The development of reliable, sophisticated hydro-morphodynamic models is essential for protecting the coastal environment against hazards such as flooding and erosion. There exists a high degree of uncertainty associated with the application of these models, in part due to incomplete knowledge of various physical, empirical and numerical closure related parameters in both the hydrodynamic and morphodynamic solvers. This uncertainty can be addressed through the application of adjoint methods. These have the notable advantage that the number and/or dimension of the uncertain parameters has almost no effect on the computational cost associated with calculating the model sensitivities. Here, we develop the first freely available and fully flexible adjoint hydro-morphodynamic model framework. This flexibility is achieved through using the pyadjoint library, which allows us to assess the uncertainty of any parameter with respect to any output functional, without further code implementation. The model is developed within the coastal ocean model Thetis constructed using the finite element code-generation library Firedrake. We present examples of how this framework can perform sensitivity analysis, inversion and calibration for a range of uncertain parameters based on the final bedlevel. These results are verified using so-called dual-twin experiments, where the `correct' parameter value is used in the generation of synthetic model test data, but is unknown to the model in subsequent testing. Moreover, we show that inversion and calibration with experimental data using our framework produces physically sensible optimum parameters and that these parameters always lead to more accurate results. In particular, we demonstrate how our adjoint framework can be applied to a tsunami-like event to invert for the tsunami wave from sediment deposits.