Sand Sequences Research Articles

Dating post-LGM aeolian sedimentation and the Late Palaeolithic in Central Yakutia (northeastern Siberia)

Central Yakutia is a large region in northeastern Siberia characterized by extensive permafrost, large river valleys, mountain glaciers, and large massifs of aeolian sands; the geological history of the region is complex and, at present, poorly constrained. In recent years, it has been shown that aeolian sands cover up to 60% of large parts of Central Yakutia. This paper presents the results of luminescence dating of aeolian sedimentation at the Diring Yuriakh Palaeolithic site located in the middle reaches of the Lena River. Field studies identified several thick units of aeolian sand, which cover an old deflation surface with Late (Duktai culture) and Early Palaeolithic (Diring culture) artefacts. The reliability of the OSL chronology was assessed by comparison of ages based on the optically stimulated luminescence from quartz and the infra-red stimulated luminescence from potassium-rich feldspars; these age pairs are in good agreement, implying that at least the quartz grains were sufficiently bleached before sedimentation. We obtained OSL ages that reflect three periods of accumulation between the LGM and the Holocene: ∼21 ka, 15-14 ka, and 12.5–10 ka. These periods of accumulation broadly coincide with global cooling episodes during the Last Glacial Maximum, the Older Dryas, and the Younger Dryas, with some extension into subsequent warmer intervals, whereas the intervening intervals without preserved sediments are taken to reflect dune stability during warmer periods. The sand on the terraces, sourced from alluvial bars in the river channel, was blown up the valley slope during cold and dry periods when the vegetation cover was sparse. When the climate warmed, the vegetation took some time to spread, and so the accumulation of aeolian sand on the high terraces continued into the warm periods. We also infer periods of deflation (wind erosion) that occurred before 21 ka and between 20 and 15 ka, presumably due to increased aeolian activity and localized remobilization of sediment. The new OSL chronology shows that the younger artefacts located at the cape of Diring Yuriakh, belonging to the Late Palaeolithic Duktai culture, are older than 15 ka. The new ages also show that the post-LGM aeolian sand sequences at Diring Yuriakh are correlated with the regionally developed subaerial Dolkuma Formation.

Sedimentary Evolution Laws and Main Controlling Factors of the Nenjiang Formation in the Songnan Da’anbei Area, China

Shallow-water deltas serve as a critical area for the exploration and development of terrestrial lacustrine oil and gas reservoirs. Current research on oil and gas exploration and development in China’s terrestrial lacustrine basins primarily focuses on their delta front facies zones. Despite extensive discussions on the sedimentary characteristics of shallow-water deltas by predecessors, there is a lack of comprehensive analysis on the combined effects of dynamic factors such as climate change, lake level fluctuations, and sediment supply. This paper, through a detailed examination of 12 core samples and integrating data from 493 exploratory, appraisal, and development wells in the study area, establishes a stratigraphic correlation framework using well–seismic integration techniques. It identifies two main sedimentary facies types in the southern Da’anbei area of the Songliao Basin: shallow-water deltas and lake facies, which can be further subdivided into four sub-facies and nine microfacies. Two depositional models for the shallow-water deltas of the Southern Songliao Nenjiang Formation are established: a deeper water background with channel-river mouth bar sequences forming the delta front framework and a shallower water background with channel-sheet sand sequences forming the delta front framework. This paper also discusses the controlling effects of paleoclimate, sediment supply, and lake level changes on sedimentary evolution, providing a scientific basis for the exploration of lithologic oil and gas reservoirs in the Nenjiang Formation of the study area and the deployment of horizontal wells.

Nigerian Case Study Explores Drilling Through Shales Below Depleted Sands

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 217195, “Drilling Through Shales Below Depleted Sands: Case Study of a Niger Delta HP/HT Gas Development Well,” by Stella Ogbodu, SPE, Bart Tichelaar, and Chibueze Amadi, SPE, Shell, et al. The paper has not been peer reviewed. _ Choosing the right casing depth is a key step in executing high-pressure/high-temperature (HP/HT) wells in the geologically complex Niger Delta. In the wells of Astra East Field, a casing shoe was set in a homogeneous shale of approximately 200 ft vertical thickness located between overlying heavily depleted sand and underlying overpressured sand. The question remained, however, as to what depth the casing shoe should be set to minimize the risk of kicks or wellbore instability and losses. To address this issue, wireline log data and drilling observations from other wells in the same field were analyzed and evaluated. Introduction The Astra East field was planned to provide feedstock gas. The field is in the Central Swamp depobelt of the Niger Delta and is 90 km west of Port Harcourt. More than 40 wells have been drilled in the field to date. A regional shale layer at approximately 11,400 ft subsea caps the regional top of overpressure in this field. This approximately 200-ft-thick shale layer vertically segments the field into two pressure regimes: a near-hydrostatic regime above it and an overpressured regime below. In other words, this shale layer acts as a regional pressure seal. Historically, oil and gas production has focused on the reservoirs above this regional seal, resulting in pressure depletion to pore-pressure values below hydrostatic in some of the reservoirs. Of the wells drilled in the field, only a handful penetrate the deeper overpressured section below the regional pressure seal and have faced various drilling challenges. Location and Geology of the Study Area The Astra East study interval is part of the Agbada formation, a paralic sequence of sands and shales up to 4 km thick in the central parts of the basin. Three lithostratigraphic subdivisions exist in the delta: the prodelta Akata shale formation, the paralic deltaic Agbada formation, and the continental Benin formation. These units represent an overall regressive, progradational stratigraphy. Depletion History and Drilling Performance The produced reservoir that sits immediately above the regional pressure seal is the C reservoir. Because hydrocarbon production from the C reservoir began more than 50 years ago, reservoir pressure gradient has depleted from approximately 5,150 psi before production to subhydrostatic. During the last 20 years, this depletion has remained relatively constant at approximately 1,660 psi below hydrostatic. The underlying, unproduced D reservoir is not depleted and is, in fact, at its virgin pressure, which is overpressured at approximately 3,035 psi above the hydrostatic pressure. This implies that the approximately 200-ft-thick intrareservoir shale between C and D reservoirs holds a large differential pore pressure of approximately 4,700 psi for the last 20 years. In fact, because the aquifer of the C reservoir was hydrostatic at virgin conditions, a large pressure differential was in place across this intrareservoir shale (between C and D reservoirs) even before production started.

Non-pollen palynomorph assemblages in mid- to late Holocene wetland deposits and their palaeoenvironments of deposition: Microfossil signatures in sediment sequences of the Yangtze Delta coastal lowlands, East China

Fluvial processes such as sediment deposition within drainage channels and seasonal overbank flooding, and fluvial events such as occasional high intensity floods all leave particular sedimentary signatures in terms of their lithology and also in their contained microfossil assemblages, which represent different environments of deposition. Over several thousand years the Yangtze River in eastern China has developed a coastal lowland plain around its delta that is mainly composed of stacked fluvial sediment facies, but also includes many marine or estuarine layers in some areas, as well as deposits of limnic and semi-terrestrial pool, marsh and mire origin, some of which are highly organic. The fluvial facies are dominantly clastic sequences of sands, silts and clays that reflect a range of deposition from quiet water to high energy conditions and in varying water depths, mainly governed by fluvial input from the Yangtze and the many other, smaller, rivers and streams of the deltaic lowland. The limnic and marshland sediments reflect autochthonous deposition in a range of freshwater wetland types of varying water depth, from lake through marsh/fen to surface peatland. Allied to lithological and pollen data, non-pollen palynomorph spore assemblages and abundances within these complex sedimentary sequences, particularly from algal communities, provide signatures of floodplain wetland depositional history and hydrodynamic patterns. We have used groupings of these microfossil data to characterise the sedimentary facies of the lower Yangtze coastal plain and to reconstruct hydrological history across the area at a range of spatial scales. Fluctuations in the relative taxa abundances are good indicators of changes in water levels at the site scale from surface waterlogging through reedswamp and fen to deeper open water. While some changes seem to be site specific, the data show flooding and increased water depths that correlate with known phases of climatic deterioration.

Primary source of titanomagnetite ores at the Orokolo Bay placer deposit: Implications for petrogenesis

AbstractCoastal and river sand sequences of Holocene age at Orokolo Bay in Papua New Guinea are host to secondary titanomagnetite ore deposits. The resource developer (Mayur Resources) declares a measured orebody of 139 million tons at grades of 11.35% Fe, 1.94% Ti, and 712 ppm Zr. Orokolo Bay is located near the boundary between the Papuan Thrust and Fold Belt and the Aure Fold Belt. This region is characterized by sedimentary rocks of the Papuan Basin, which are intruded and overlain by a diverse array of magmatic intrusive and volcanic rocks, ranging from mafic alkaline to felsic calc‐alkaline types related to arc–continent collisions in the Cenozoic. The Vailala and Purari rivers located to the east and west of Orokolo Bay, respectively, are the main sediment pathways. Earlier provenance studies have suggested that the deposited sediments mainly come from the erosion of volcanic rocks found within the catchments of these two rivers. However, these studies did not specifically identify the primary source of the Fe‐Ti ores within this region. Here, we report on a potential primary source of the Fe‐Ti ores by examining the occurrence and chemical compositions for detrital titanomagnetites, and associated pyroxene and amphibole minerals. The purpose of this was to discern specific attributes of the primary source for its identification. Lithic sediments comprised of magnesio‐hornblende (Mhbl), tschermakaite (Tsr) and magnesio‐hastingsite (Mhst) amphiboles, clinopyroxene (Cpx), and Fe‐Ti oxide minerals dominate the heavy sands. Feldspar is more abundant than quartz, and Cr‐spinel is rare. Two primary titanomagnetite types were categorized based on their homogeneous grain textures and TiO2 content, Tmt1 (average 28 wt% TiO2) and Tmt2 (average 7 wt% TiO2). Pleonaste exsolutions and zircon inclusions distinguish Tmt1 from Tmt2, while apatite and quenched glass inclusions occur in both. A portion of both primary titanomagnetites exhibits hydrothermal overprinting, this subset was categorized as Tmt3 (average 12.5 wt% TiO2). Fe‐Ti oxides are associated with Cpx and amphiboles as inclusions, and as pseudomorphs in opacitic amphiboles. Tmt1 coexists predominantly with Mhst‐Tsr but also appears less frequently with Mhbl and Cpx. Tmt2 occurs almost exclusively with Mhbl and Cpx. Titanomagnetite chemistry is low in Cr, Mg, and V content suggesting crystallization from evolved melts. Tmt3 is shows enriched Si, Ca, Al, and Mg concentrations that are characteristic of late‐stage fluids derived from calcareous rocks. Amphibole and Cpx chemistry indicate they were derived from a subalkaline source magma of arc affinity. Fe‐Ti thermobarometry reveals Tmt1 (990 to 967°C, −0.51 to −0.18 ΔNNO) formed at higher temperatures and in less oxidized conditions than Tmt2 (834 to 689°C, 0.33 to 3.2 ΔNNO). Amphibole thermobarometry reveals Mhst‐Tsr and Mhbl formed under similar conditions as Tmt1 and Tmt2, respectively. The lack of Cr‐spinel, olivine, and the abundant occurrence of zircon and Mhbl indicate an evolved subalkaline source characterized by felsic rocks related to arc magmatism. The only volcanic source which aligns with these characteristics is Mount Yelia within the Vailala River catchment. Compositional variation between Tmt1 and Tmt2 titanomagnetites and associated silicate minerals is attributed to heterogeneous temperature and ƒO2 conditions within the melt during crystallization. The provenance of Ti‐rich titanomagnetite ores from sources related to arc magmatism indicates the potential of other areas associated with arc activity in Papua New Guinea to host secondary deposits rich in Fe‐Ti ores.

Electro-sequence valorization of specific enablers of aquifer vulnerability and contamination: A case of index-based model approach for ascertaining the threats to quality groundwater in sedimentary beds

This work was set up to appraise the quality of groundwater within a newly established university using index-based techniques and the intention is to generate vulnerability potential maps that can guide in avoiding vulnerable aquifer systems. The study used geo-electrical technology to evaluate the lithological sequence of the hydrogeological units and their first-and second-order geo-electric properties, as well as the geochemical constituents of groundwater. The results showed that the hydrogeological units are composed of sequences of sands, including fine to gravelly sands minimally laced with sandy clay, according to the results of geo-electrical technology. Layers 2 and 3 were accessible by the twenty VES (V1-V20) in which current gained access to designated economic and prospective aquifer systems. The aquifer systems considered have resistivity values ranging from 26.3 to 3576.5Ωm and mean value of 832.97Ωm. The five vulnerability models deployed showed very high spatial variability and moderate negative and positive binary correlations, construed to be due to subjectivity in the weight-rate assignment. The coefficients of variation (CV) from sensitivity analysis (SA) indicated variation in the vulnerability index due to topography (9.7%) and the impact of the vadose zone (4.3%), which are marginally higher than the 1.6% displayed by other parameters. The groundwater displayed WHO's disallowed concentrations of heavy ions, and the SA indicated that CV for the groundwater geochemical contamination is variably high in cadmium ions (140.9%) followed by manganese ions (132%) and copper ions (88. 2%) across the wells. The moderately variable contribution distributions across the wells are nickel ions (48.8%), lead ions (41.6%), chromium ions (39.8%) and iron ions (35.0%). All the geophysical and geochemical indices affirm that the groundwater is vulnerable and contaminated and therefore requires monitoring and management.

Sedimentology and Mineralogy of Sedimentary Sequences in Nanim Field in the Niger Delta basin, Nigeria.

A total of nineteen ditch cuttings from the sedimentary sequence of Nanim Field, were subjected to both sedimentological and mineralogical analysis with the aim of investigating the mineralogical composition of the studied section (1810 m - 2650m) in the study area. The shale samples were grinded, pulverized and sieved with less than 75μm and analyzed using X-ray diffraction techniques (XRD) for mineralogical composition. Results of the sedimentological analysis, suggests four lithofacies made up of sandstone, shaly sand, shale and sandy shale in he studied section. The studied section has been interpreted as a shallow marine environment  divided into two broad lithofacies sequences made up of beach sand (1810 m - 2290 m.) and upper shoreface (2300 m – 2650m) respectively. The beach sand sequences comprises thick sands, brownish, grey to black, fine to coarse grained, whereas the upper shoreface sequence is essentially a heterogeneous sequence of alternating sand medium to very fine grained sand and shale - grey. Results from the XRD analysis shows that the mineralogical composition of the basal part (upper shoreface) of the studied section is characterized by kaolinite a dominant in sediments of fluviatile environments and is known to concentrate in many near-shore sediments (shallow marine) with a decrease in abundance from the shoreline as other clay minerals increase basinward.

Reef growth and carbonate sedimentation at the southernmost Pacific reefs

Lord Howe Island and Balls Pyramid are located at the latitudinal limit of coral reef formation in the Tasman Sea, with the fringing reef on the western margin of Lord Howe Island considered to be the southernmost coral reef in the Pacific. An extensive submerged fossil reef occurs on the shelf around Lord Howe Island. Mapping of the shelf surrounding Balls Pyramid, 24 km south of Lord Howe Island, has revealed a comparable submerged mesophotic reef system in 30–50 m water depth supporting scattered live coral colonies. Radiocarbon dating of coral extracted from limestone cores on the fossil reef reveals that accretion occurred during the early Holocene (10,100–8800 cal. Years BP), concurrent with the first phase of Holocene accretion around Lord Howe Island. The timing of fossil coral growth on the shelves of the two islands indicates that the reefs have been drowned by rising sea level. The fossil reef around Balls Pyramid is a give-up reef that was unable to keep pace with sea level. After its demise, carbonate sediment production continued across the shelf with sands and gravels that have accumulated in basins and channels, between the submerged fossil reef structures. Vibrocores record a fining upward sequence of sands overlying rhodoliths and angular carbonate gravels. The coral reef around Lord Howe Island persisted a little longer (∼7000 cal. Years BP) and has accreted into shallower water (∼25 m). The reef here was able to backstep to form the modern fringing reef. Although similar benthic habitats characterise both shelves, availability of suitable accommodation space on Lord Howe Island enabled deposition of sequences of eolianite during successive Late Quaternary highstands, and the development of a modern fringing reef and lagoon over eroded basalt, and late Pleistocene reef and eolianite. Antecedent topography has provided a first-order control on establishment and persistence of reef habitats during post-glacial sea-level rise, and the relative extent of past reef structures and eroded bedrock outcrops has constrained coral reef accretion at this latitudinal limit.

Three-Dimensional Geological Modeling of the Shallow Subsurface and Its Application: A Case Study in Tongzhou District, Beijing, China

Three-dimensional (3D) geological models are currently needed and used independently for urban development. The main difficulty in constructing a 3D geological model of a shallow subsurface is to determine the stratigraphic distribution. Highly variable properties and geometries of geological units beneath lead to difficulty. It is key to find a practicable and efficient way to construct a model in practical work. This study takes Tongzhou District (Beijing) as a case; 476 boreholes (40 newly drilled and 436 existing engineering boreholes) were utilized combined with the cross-section method to construct an integrated 3D geological model. The framework and analyses contributed to the following applications: (1) High-quality information from new boreholes and existing engineering boreholes were used to define stratigraphy and build cross-sections. (2) The resulting geological model (up to 50 m beneath Tongzhou area) shows many details of the shallow subsurface. This includes 10 major layers which were grouped into three cyclothems representing cyclic sequences of clay, interbedded silt, sand, and gravel with variable quantities of lenses. (3) The new model was used as a tool to visualize the depth and geometry variations below ground and to characterize a large variety of properties (for example, the compression modulus analyzed in this paper) that each unit contains, and then to evaluate the underground geological conditions. (4) An analysis of a dynamic monitoring model based on the resulting 3D model indicated that the geological units (sand and silty clay) at depths between 30 m and 40 m, with an average vertical deformation of 0.97 mm, from July 2019 to September 2020, are suitable for underground construction, from the perspective of vertical stability in the study area. Monitoring models that take time into consideration based on a 3D framework will be further explored.

Sedimentation and erosion at Majuli Island, Assam, India: analysis of paleo-depositional environment

ABSTRACT The World’s one of largest inhabited river-made island Majuli, developed in response to depositional processes of large sediment load carried by the Bramhaputra River and Subhansari River from the Himalayan hinterland. But, for decades it has been going through a significant rate of erosion, which is severely threatening the existence of the island and its rich cultural heritage. These erosional processes result in exposure to island depositional records and provide an opportunity to study these sedimentary deposits. This paleo depositional record is very well analysed by adopting the methodology of facies identification and their relationship diagram. A total of 18 exposed outcrop sections are studied with detailed sedimentological documentation, facies identification and symbols assigned to facies. Then calculations and tabulations are carried out for Facies Relationship Diagram (FRD) along with the construction of the sequence model, which provides a lateral and vertical lithofacies association developed in the entire island sequentially. On the basis of validation of obtained data through field survey and analysis of more vertical profiles, we study the correlation between existing bank erosion and dominated sedimentary facies at Majuli Island. This analysis results in two facies sequences: one mud-dominated and the other sand-dominated facies. The Massive Mud and Massive Sand beds are represented as the main facies between these two sequences. Therefore, mud-dominated sequence represents the Flood Plain deposit, whereas the sand-dominated sequence represents Bar and Channel deposits. This study also reveals that sedimentary sequences developed by the Bramhaputra River are mud dominated, while that of the Subhansiri River is both mud and sand sequences. This reflects the differential source to sink transport of sediments, as the Bramhaputra River carries sediment load for a longer distance than the Subhanshiri River. This study also reveals that areas of sand-dominated facies show higher erosion than mud-dominated facies. Therefore, the sedimentary record of the Subhansiri River is more vulnerable to erosion.

Characterizing groundwater salinity patterns\xa0in a coastal sand aquifer\xa0at Magilligan, Northern Ireland,\xa0using geophysical and geotechnical methods

Tidal forcing influences groundwater flow and salt distribution in shallow coastal aquifers, with the interaction between sea level variations and geology proving fundamental for assessing the risk of seawater intrusion (SI). Constraining the relative importance of each is often confounded by the influences of groundwater abstraction and geological heterogeneity, with understanding of the latter often restricted by sampling point availability and poor spatial resolution. This paper describes the application of geophysical and geotechnical methods to better characterize groundwater salinity patterns in a tidally dominated ~ 20 m thick sequence of beach sand, unaffected by groundwater abstraction. Electrical resistivity tomography (ERT) revealed the deposit to consist of an upper wedge of low resistivity (< 3 Ωm), reaching over 8 m thick in the vicinity of the low water mark, overlying a higher resistivity unit. Cone penetrometer testing (CPT), and associated high-resolution hydraulic profiling tool system (HPT), coupled with water quality sampling, revealed the wedge to reflect an intertidal recirculation cell (IRC), which restricts freshwater discharge from a relatively homogeneous sand unit to a zone of seepage within the IRC. The application of CPT and HPT techniques underscored the value of geotechnical methods in distinguishing between geological and water quality contributions to geophysical responses. Survey results have permitted a clear characterization of the groundwater flow regime in a coastal aquifer with an IRC, highlighting the benefit of combining geophysical and geotechnical methods to better characterize shallow SI mechanisms and groundwater flow in coastal hydrogeological environments.

Grain size analysis of the latest Quaternary Kordofan Sand of Central Sudan: Depositional environment and mode of transportation

Grain size analysis is a powerful tool for determining the depositional environment. Grain size analysis for 48 samples from four sections along a 280 km long, nearly north–south-trending transect, has been conducted in the mainly Holocene Kordofan Sand in the Kordofan Region of Central Sudan. In these sections, this part of the Kordofan Sand comprises three pedosedimentary sequences. The lower sequence (∼13–10 kyr) has been pedogenized during the African Humid Period and ends up farther West with lacustrine or palustrine carbonates. The middle sequence (∼6–3 kyr) is represented by sand with low degree of pedogenesis and corresponds to the African Humid Period. The upper sequence was deposited after a hiatus lasting from ∼3.3 to 1.1 ka BP, and constitutes the present-day surficial deposits, showing little or no pedogenesis. Spatial grain size distribution and mode of transport show a southward fining trend, indicating that the sandy sediments were transported from north to south. This interpretation is supported by the results of mean grain size – sorting, and sorting – skewness interrelations, which provided a linear relationship. Vertical variation in grain size distribution in the studied sections shows variable energy over time in the north and constant, low energy in the south. The dominance of saltation as a transport mode confirms that the studied sediments were deposited in aeolian environment. The low sorting degree, the presence of coarse grains, and the still active transverse dunes and barchans in the North, indicate that the Late Pleistocene part of the Kordofan Sandstone is submitted to reworking until now. Consequently, the mainly Holocene sand sequences were fed both by distal, fine-grained Saharan material and by proximal, coarser-grained sand proceeding from the Late Pleistocene aeolian dunes.

Electrical Resistivity Sounding for Groundwater Investigation around Enugu Metropolis and the Environs, Southeast Nigeria

This report evaluates the use of electrical method and borehole data to investigate the subsurface to delineate the groundwater potential in Enugu metropolis and the environs, south-eastern Nigeria other than rely only on resistivity method which could lead to interpretation error. Integrating these 2 data sets is key in this study. The study area is located in the Anambra Basin and is underlain by Nkporo/Enugu Shale which is overlain by the Mamu Formation. It is bounded by Latitudes 6°2 0'00"N to 6°30'00"N and Longitudes 7°25'00"E to 7°35'00"E and covers surface area of about 342 m2. Thirty-one vertical electrical soundings (VES) were carried out across the area using the Schlumberger electrode array with current electrode separation from 2 to 500 m to identify the depths and resistivity values of the identified geo-electric layers. Through data analysis using WinResist software, the apparent resistivity, thicknesses and depths and the thicknesses of the aquifers were generated. The resistivity and depths were modelled to generate resistivity map and depth map. The resistivity of the aquiferous zone within the study area varied from 20.55 - 427.8 ohm-m at depths of between 10.7 - 40.05 m. Depth to the water table appears to be shallow at the south western part of the map. The interpreted geo-electric layers show a sequence of lateritic top soil, shale, sand and shale. The frequency distribution of the VES curves generated shows the presence of 3 to 5 layers with HK type as the highest. Also, a 2D model was generated using the correlation of VES to VES data and borehole data to VES data to show the underlying stratigraphy beneath the study area as well as the direction of ground water flow. Result of the VES curve analysis reveals that the sub-surface is underlain by three lithological layers namely: lateritic top soil, shale, sand and shales with NW direction of groundwater flow from the 2D model. Groundwater prospective zones can be seen along NW, SW and central parts of the study area which have low resistivity values.

Evidences of early to mid-Holocene land–sea interactions and formation of Wetlands of Central Kerala in the south west coast of India

Coastal wetlands are seen in the central part of the SW coast of Kerala, India at Muriyad, Thrissur (∼15 km orthogonal to the present day coast towards inland) and form a part of Vembanad kol. These wetlands are sheltered by well-developed beach ridges in the west and lateritic uplands towards east between the latitudes and longitudes of 10°20‘-10°30‘N and 76°10‘-76°20‘E respectively. The present study aims to find the evidences of early Holocene transgression in the area and constrain its chronology using optically stimulated luminescence (OSL) as well as radiocarbon dating. The general stratigraphy of the wetland section shows estuarine sandy clay at the bottom, followed by one meter thick peat unit, overlain by lacustrine clay and colluvial sediments. The fluvial sequences were devoid of peat deposits and comprised of clay and sand sequences having large fossil tree logs. OSL age of a sand layer (7.0 ± 1.0 ka) below the peat unit as well as the radiocarbon ages of peat (between 7920–7740 and 7410–7180 Cal years BP) itself indicates that the unit was formed between 8 and 7 ka BP. The peat accretion shows an average rate of 1.74 mma-1. The pollen analysis of the peat unit demonstrates that peat was formed from Rhizophoraceae mangrove plants, implying close proximity of the study area to the shore line. Dominance of wet evergreen forest taxa in the non-mangrove pollen of the peat indicates wet climatic conditions in the area. The occurrences of fossil wood stumps in upright position and large tree trunks buried in the fluvial succession show that the trees were buried in-situ in the growth position/ during the transportation by flood waters in the fluvial sequence. The fluvial unit in the wetland stratigraphy shows evidences of enhanced SW monsoon in the area, causing large scale floods, submergence of forests and destruction of large trees during 5710–5610 and 6880–6750 Cal years BP.

Superimposed secondary alteration of oil reservoirs. Part II: The characteristics of biomarkers under the superimposed influences of biodegradation and thermal alteration

Petroleum biomarkers could be altered to varying extents under the influence of biodegradation and thermal alteration in reservoir, and their respective influence has been well documented. However, the superimposed influence of successive biodegradation and thermal alteration has not been systematically studied so far. In this study, a sequence of crude oils and oil sands that are of identical origin but at different biodegradation levels from the Liaohe Basin of China were artificially matured via closed-system pyrolysis. The distributions of biomarkers such as steranes and hopanes in the variably biodegraded oil samples and in their pyrolyzates at varying artificial thermal maturities were compared. The results showed that the presence of normal (n-) alkanes in crude oil does not necessarily excludes the possibility of previous moderate–severe biodegradation as n-alkanes can be further generated under advanced thermal stress. Besides, biomarkers in the oils that have suffered superimposed alterations could be derived not only from the modifications of free biomarkers in the oils, but also from the release of biomarkers bound in the asphaltenes. The mix of these two sources complicated the biomarker profiles in this type of oils. Most source related parameters based on steranes and tri-, tetra- and penta-cyclic terpanes seem to be reliable only when the oil reservoir has suffered biodegradation not beyond moderate level and the maturity of the crude oil is below 0.91 Easy%Ro. The TT23/(TT23 + TT24) ratio, however, was found to remain constant even after severe biodegradation and thermal alteration, making it applicable in oil-source correlation in superimposed oil reservoirs. In addition, isomerization-based maturity parameters such as methylphenanthrene index of crude oils are reliable if subsequent thermal alteration reached above 0.91 Easy%Ro despite prior moderate–severe biodegradation, because the related isomerization reactions would approach the same level observed for the non-biodegraded oil after subsequent thermal alteration.

Long-term African dust delivery to the eastern Atlantic Ocean from the Sahara and Sahel regions: Evidence from Quaternary paleosols on the Canary Islands, Spain

Africa is the most important source of dust in the world today and dust storms from that continent frequently deposit sediment on the nearby Canary Islands. Many investigators have inferred African dust inputs to Canary Islands paleosols based only on the presence of quartz. However, some local rocks do contain this mineral, so quartz alone is insufficient proof of dust deposition. Further, it is not known whether the Sahara Desert or the Sahel region is more important as a dust source. We address these issues by study of sequences of Pleistocene aeolian sands on the islands of Lanzarote and Fuerteventura. Aeolian sands are composed mostly of marine carbonate minerals and locally derived volcanic minerals. They date from the early-middle Pleistocene to the Holocene. Trace element geochemistry shows that the soils formed from both locally derived basalt and African dust. Major element geochemistry and clay mineralogy indicate that dust additions to the Canary Islands likely come from both the Sahara and Sahel. Dust delivered from the Sahel indicates that droughts in that region have had a history extending through much of the Quaternary. Accretionary-inflationary profile development, from dust accretion, is evident in the upward growth of Canary Islands paleosols.

Integrating Resistivity Techniques for Optimum Groundwater Exploration and Development within a Hotel Facility in Osogbo, Southwestern Nigeria

This work is an attempt to combine dipole-dipole profiling and vertical electrical sounding techniques of electrical resistivity methods to investigate the groundwater potential within the premises of a 3-star hotel facility in Osogbo, Nigeria by delineating the geoelectric layers, delineating the low resistivity layers, determining the lithologies and hence, delineating the groundwater bearing zones. The five vertical electrical sounding data were collected along two pre-surveyed dipole-dipole traverses at right angle to each other beside the fences of the premises using the ABEM SAS 300c terrameter. The observed data were interpreted quantitatively using curve matching and computer-assisted iteration method using the WinResist and Dipro software. The results of the inversion show that the lithology comprises of the top soil and an intermittent sequence of sand and lateritic clay having varying resistivity and thickness. The aquiferous layer was observed to be located at a depth of 23 m to 25 m due to the low resistivity and high thickness of the aquiferous layer. The result of the 2-D imaging closely correlates with the result of the vertical electrical sounding. Thus, combining these techniques in groundwater investigation has achieved similar result as the Werner technique and has reduced ambiguity and error in positioning for drilling.&#x0D; Keywords: Resistivity, Groundwater Exploration, Dipole-Dipole

Carbon Storage Resource Assessment of the Mid-Atlantic U.S. Offshore Region

Carbon capture and storage (CCS) is a critical technology for ensuring a range of clean energy options are available to meet future energy demands. Offshore storage can be linked to large point-sources of carbon dioxide (CO2) while avoiding many of the logistical difficulties and potential risks encountered when siting onshore projects, especially in densely populated areas of the East Coast of the United States. Offshore storage along mid-Atlantic region was studied under the U.S. Department of Energy (DOE) funded Mid-Atlantic U.S. Offshore Carbon Storage Resource Assessment Project (MAOCSRAP) and as a subtask under the Midwest Regional Carbon Sequestration Partnership (MRCSP). The assessment was conducted as a technical collaboration between Battelle, Rutgers University, Lamont-Doherty Earth Observatory at Columbia University, state geological surveys of Delaware, Maryland and Pennsylvania, United States Geological Survey-Woods Hole Coastal and Marine Science Center, and Harvard University. Major objectives were to complete a systematic carbon storage resource assessment of the of the mid-Atlantic offshore coastal region from the Georges Bank Basin (GBB) through the Long Island Platform (LIP) to the southern Baltimore Canyon Trough (BCT), examine offshore storage risk factors, and engage industry and regulatory stakeholders through development of a Road Map to assist future project planning and implementation. Various publicly available data sets, such as seismic data, well-logs, and core data, were integrated to define geologic characteristics of candidate storage sites and calculate prospective CO2 storage resources for Cretaceous- and Jurassic-age sandstone sequences of the mid-Atlantic offshore sub-regions. The combined dataset helped to identify and map potential storage zones within sequences of the Logan Canyon, Missisauga, and Mohawk formations, as well as the regionally extensive caprock comprised of the Dawson Canyon shale. Prospective storage resource estimates and formation-specific storage efficiency values were calculated with static volumetric and dynamic methods. Regional-scale estimates range from 150 to 1136 gigatonnes (Gt) for the combined storage zones, with high estimated storage resource (≥ 2.4 megatonnes [Mt] CO2/km2) occurring in the northern BCT near the Great Stone Dome (GSD) structure. Results of local scale simplified dynamic reservoir simulation in the GSD indicate that injection rates of 1 Mt CO2/year may be sustained within the time and pressure constraints assumed for a commercial storage project. An initial, qualitative assessment of technical risk factors present in mid-Atlantic offshore areas was conducted. Overall, the mid-Atlantic offshore area benefits from the large spatial extent, thick sequences of sands, lack of previous oil and gas wellbores, and distance from populated development. Geomechanical stability, reservoir variability, and soft sediment deformation were identified as moderate risk factors in some areas. No highly critical risk factors were identified that would impede CO2 storage along the study areas. Input and participation from government, industry, and environmental groups helped to address next steps needed for future CCS project planning and implementation in the study region. Recommended near-term actions are to develop site screening through advanced geologic modeling, implement stakeholder outreach and risk mitigation strategies, identify industry and research goals, and develop regulatory pathways. Recommended mid-term actions are to validate subsurface properties with new data, conduct a cost-benefit analysis, and develop a monitoring, verification, and accounting (MVA) plan. Long term-recommended actions are to implement a plan for large-scale CCS operations using the previous findings, conduct site design, permitting, and construction, and upscale infrastructure. This project represents an important first step by completing a high-level CO2 storage resource assessment and building the knowledge infrastructure necessary to support the development of full-scale offshore carbon storage.

A tsunamigenic delta collapse and its associated tsunami deposits in and around Lake Sils, Switzerland

Large lacustrine mass movements and delta collapses are increasingly being considered as potential tsunamigenic sources and therefore hazardous for the population and infrastructure along lakeshores. Although historical reports document tsunami events in several lakes in Switzerland, and although the propagation of lake tsunamis has been studied by numerical wave modeling, only little is known about on- and offshore lacustrine tsunami deposits. In Lake Sils, Switzerland, a large prehistoric mass-movement deposit originating from the Isola Delta with a minimum estimated volume of 6.5 × 106 m3 and a basinal thickness of > 6 m in the seismic record has been identified by previous studies and radiocarbon dated to around 700 Common Era. Here, we combine (i) comprehensive sedimentological investigation of sediment cores recovered from the on- and offshore settings, (ii) mineralogical fingerprinting of the inflows from key catchments to characterize sediment provenance, and (iii) numerical tsunami modeling, to test the hypothesis of a tsunamigenic delta collapse in Lake Sils. We observe a clastic event deposit consisting of coarse-grained, fining-upward sand overlying an organic-rich peat deposit in the shallow water. This layer thins and fines landward on the coastal plain. Toward the deeper water (20–40 m), the deposit transforms into a thicker and more heterogeneous sediment package with multiple sequences of fining-upward sand and a well-pronounced clay cap at the top. Radiocarbon dating of the peat underlying the event deposit yields a maximum age of 225–419 calibrated Common Era. The tsunami models, which indicate wave heights reaching up to 5 m, simulate areas of inundation that coincide with the location of event deposits. Based on our results, we propose that the historically undocumented Isola Delta collapse generated a basin-wide tsunami that inundated the lakeshore, transporting large amounts of unconsolidated sediment along the lakeshore toward the coastal plain and into the deeper lake basin.

Lithology and Fluid discrimination of Sody field of the Nigerian Delta

The lithology and fluid discrimination of an onshore Sody field, of the Niger Delta was studied using gamma ray, resistivity and density logs from three wells in the field in order to evaluate the field’s reservoir properties. Two reservoir sands (RES 1 and RES 2) were delineated and identified as hydrocarbon bearing reservoirs. The petrophysical parameters calculated include total porosity, water saturation and volume of shale. The results obtained revealed that the average porosity of the reservoir sands, range from 21% to 39%, which is excellent indicator of a good quality reservoir and probably reflecting well sorted coarse grain sandstone reservoirs with minimal cementation. Water saturation is low in all the reservoirs, ranging from 2% to 32%, indicating that the proportion of void spaces occupied by water is low, and implying high hydrocarbon saturation. The crossplot discriminated the reservoirs lithologies as sand, shaly sand and shale sequences, except well Sody 2 which differentiated its lithologies as sand and shale sequences and distinguished the reservoirs’ litho-fluids into three, namely; gas, oil and brine. These results suggest that the reservoirs sand units of Sody field contain significant accumulations of hydrocarbon.&#x0D; Keywords: Reservoir, porosity, net-to-gross, impedance, lithology