Paleogene lake deep water sedimentary facies in the northern zone of the Chezhen Sag, Bohai Bay Basin, China

This study researches an important genetic type of Paleogene sublacustrine fan deposits in widely developed glutenite bodies in the northern Chezhen Sag. The Paleogene sublacustrine fans in the Bohai Bay Basin are primarily distributed in Es3 (The third member of Paleogene Shahejie Formation). There are many sedimentary types in Chezhen depression, but understanding of the reservoir is too limited to support a development strategy. Therefore, a detailed study on the core characteristics, sedimentary structure, sedimentary microfacies and reservoir properties has been completed in order to reduce uncertainty. It is confirmed that the sublacustrine fan deposits are mostly characterized by a positive cycle of upward thinning, and the base is composed of conglomerate supporting conglomerate and massive gravel sandstone, which reflect the sedimentary characteristics of traction and gravity currents. Finally, the influence of sedimentary process on properties was assessed by establishing the correlation between microfacies and reservoir physical parameters, such as porosity, permeability, detrital particle. It is revealed that the sublacustrine fan glutenite body formed in the deep depression period is interspersed with deep- to semi-deep lake source rocks. The superior source–reservoir–caprock combination is one of the most important exploration targets in the northern zone.

Glacial carbon cycle changes by Southern Ocean processes with sedimentary amplification

Recent paleo reconstructions suggest that increased carbon storage in the Southern Ocean during glacial periods contributed to low glacial atmospheric carbon dioxide concentration (pCO2). However, quantifying its contribution in three-dimensional ocean general circulation models (OGCMs) has proven challenging. Here, we show that OGCM simulation with sedimentary process considering enhanced Southern Ocean salinity stratification and iron fertilization from glaciogenic dust during glacial periods improves model-data agreement of glacial deep water with isotopically light carbon, low oxygen, and old radiocarbon ages. The glacial simulation shows a 77-ppm reduction of atmospheric pCO2, which closely matches the paleo record. The Southern Ocean salinity stratification and the iron fertilization from glaciogenic dust amplified the carbonate sedimentary feedback, which caused most of the increased carbon storage in the deep ocean and played an important role in pCO2 reduction. The model-data agreement of Southern Ocean properties is crucial for simulating glacial changes in the ocean carbon cycle.

The Characteristics Of Shoreface Deposits And The Reservoir Implication Of Seulimum Formation, Aceh Besar

The shoreface deposits study commonly conducted to characterize the reservoir's physical properties carried out by surface geological data. The physical properties focused on pore space conditions controlled by sedimentary process and tectonic settings in Seulimum Formation. The method used as descriptive analysis and previous study of the area interested. The geological data showed shoreface environmental deposits that can be divided into two types of environmental deposits they are middle shoreface and upper shoreface deposits. These environmental deposits are proven by some features such as bioturbation with an abundant presence of Ophiomorpha in the second stop sites (total 5 stop sites). The first stop site indicates two kinds of environmental deposits by coarse sandstones and mudstones dominated facies presence in the specific beds. Mudclast and hummocky structures also present in the field observation that concludes complex environmental deposits during the quaternary period the formation. Based on characteristics of facies could suggest those sediment products deposited on shallow marine. These wave-dominated coasts generally have an excellent reservoir potential effect on shoreface sands that are laterally continuous and were orientated parallel to the shoreline.

Late-Holocene palaeoenvironmental reconstruction from a lake in the Amazon Rainforest-Tropical Savanna (Cerrado) boundary in Brazil using a multi-proxy approach

As an ecotone, the region between the Amazon Rainforest and Tropical Savanna (Cerrado) biomes is, by definition, more susceptible to climate change. Therefore, understanding palaeoenvironmental dynamics is essential to address the future responses of such transition areas to climatic fluctuations. In this context, we present a new sediment record for the Late-Holocene retrieved from Barro-Preto, currently an oxbow lake located in an ecotone at the southern Brazilian Amazon border. Our multi-proxy data include carbon and nitrogen isotopes, as well as bulk TOC, chlorophyll derivatives, grain-size and microcharcoal analyses, all anchored on a radiocarbon-dated chronology. The sedimentary process recorded at the Barro-Preto Lake responded to both local and regional climate dynamics. It was influenced by river excursions associated to local responses to precipitation changes by the activation of the palaeochannel connecting the main-stem river and the Barro-Preto lake. This activation was evidenced by the presence of different colour lithology laminations accompanied by coarser sediments and also by climate conditions known to influence the Amazon region. Depositional processes linked to lake dynamics and different oxbow lake cycle stages were also important to explain the changes verified in the Barro-Preto record, endorsing the use of this lake formation for palaeoclimatic reconstructions. The record indicated a rising humidity trend, reflected by a progressive increase in lacustrine productivity, in accordance to other studies carried out in the Amazon region concerning the Late-Holocene, associated with a more southward displacement of the Intertropical Convergence Zone. Despite this rising humidity trend, dry episodic events during the Late-Holocene were evidenced by charcoal data, also coherent with regional Amazon studies, albeit exhibiting increased intensity, suggesting that the transitional nature of the environment might have influenced susceptibility to fires.

Late Quaternary aggradation and incision in the headwaters of the Yangtze River, eastern Tibetan Plateau, China

River aggradation or incision at different spatial-temporal scales are governed by tectonics, climate change, and surface processes which all adjust the ratio of sediment load to transport capacity of a channel. But how the river responds to differential tectonic and extreme climate events in a catchment is still poorly understood. Here, we address this issue by reconstructing the distribution, ages, and sedimentary process of fluvial terraces in a tectonically active area and monsoonal environment in the headwaters of the Yangtze River in the eastern Tibetan Plateau, China. Field observations, topographic analyses, and optically stimulated luminescence dating reveal a remarkable fluvial aggradation, followed by terrace formations at elevations of 55−62 m (T7), 42−46 m (T6), 38 m (T5), 22−36 m (T4), 18 m (T3), 12−16 m (T2), and 2−6 m (T1) above the present floodplain. Gravelly fluvial accumulation more than 62 m thick has been dated prior to 24−19 ka. It is regarded as a response to cold climate during the last glacial maximum. Subsequently, the strong monsoon precipitation contributed to cycles of rapid incision and lateral erosion, expressed as cut-in-fill terraces. The correlation of terraces suggests that specific tectonic activity controls the spatial scale and geomorphic characteristics of the terraces, while climate fluctuations determine the valley filling, river incision and terrace formation. Debris and colluvial sediments are frequently interbedded in fluvial sediment sequences, illustrating the episodic, short-timescale blocking of the channel ca. 20 ka. This indicates the potential impact of extreme events on geomorphic evolution in rugged terrain.

The Plantation's Outsides: The Work of Settlement in Kalimpong, India

While the colonial and contemporary economy of Bengal's Himalayan foothills is most often associated with the tea plantations of Darjeeling and the Dooars, the small farms of nearby Kalimpong were also a key space in which colonial agents and missionaries worked to “settle” the mountainous terrain. Focused on Kalimpong, this article traces the trajectory of one technology of settlement, agricultural extension, from the late 1880s to the early 1940s. It highlights agricultural extension's racialized and gendered politics, as well as its implication in a long-term project that merged material (i.e., food) provision with social reproduction (i.e., childrearing, kin-making). Agricultural extension created a patchwork of relatively biodiverse small farms that historical and contemporary accounts describe as a “green belt”: a socio-ecological outside to the plantation monocultures that dominate the hills. British governors attempted to use non-plantation space for multiple ends. In this sense, their work might be termed “biopolitical,” in that it was geared toward supporting and amplifying the life chances of certain human bodies and certain botanical species. Through a series of experiments, colonial agents made calculated choices about which of these forms of life should be made to flourish, and which might be allowed to perish. Importantly, settlement, as a set of intertwined projects, did not unfold in a coherent or deliberately sequential manner. Settlement was, and continues to be, a sedimentary process.

Using Logging and Seismic Data to Identify Boundaries Between Different OWC Units in a Deepwater Carbonate Reservoirs

At least three very different oil-water contacts (OWC) encountered in the deepwater, huge anticline, pre-salt carbonate reservoirs of X oilfield, Santos Basin, Brazil. The boundaries identification between different OWC units was very important to help calculating the reserves in place, which was the core factor for the development campaign. Based on analysis of wells pressure interference testing data, and interpretation of tight intervals in boreholes, predicating the pre-salt distribution of igneous rocks, intrusion baked aureoles, the silicification and the high GR carbonate rocks, the viewpoint of boundaries developed between different OWC sub-units in the lower parts of this complex carbonate reservoirs had been better understood. Core samples, logging curves, including conventional logging and other special types such as NMR, UBI and ECS, as well as the multi-parameters inversion seismic data, were adopted to confirm the tight intervals in boreholes and to predicate the possible divided boundaries between wells. In the X oilfield, hundreds of meters pre-salt carbonate reservoir had been confirmed to be laterally connected, i.e., the connected intervals including almost the whole Barra Velha Formation and/or the main parts of the Itapema Formation. However, in the middle and/or the lower sections of pre-salt target layers, the situation changed because there developed many complicated tight bodies, which were formed by intrusive diabase dykes and/or sills and the tight carbonate rocks. Many pre-salt inner-layers diabases in X oilfield had very low porosity and permeability. The tight carbonate rocks mostly developed either during early sedimentary process or by latter intrusion metamorphism and/or silicification. Tight bodies were firstly identified in drilled wells with the help of core samples and logging curves. Then, the continuous boundary were discerned on inversion seismic sections marked by wells. This paper showed the idea of coupling the different OWC units in a deepwater pre-salt carbonate play with complicated tight bodies. With the marking of wells, spatial distributions of tight layers were successfully discerned and predicated on inversion seismic sections.

An Integrated Reservoir Predicting Approach with Geological Constraints from Stratigraphic Forward Modeling of the Miocene Fan Delta in Albert Basin, Uganda

Reservoir prediction is a core area of research in oilfield exploration and development, and it is generally constructed on a combination of well data, seismic attributes or inversion. However, reservoir prediction in sparse well areas poses great challenges due to insufficient well control. If the quality of seismic data is poor, the spatial distribution characteristics of reservoirs cannot be effectively characterized through inversion or attribute analysis, which seriously affects the prediction accuracy. This paper proposes a new method to solve the difficulty in reservoir prediction of oilfields with sparse data and poor quality seismic cube, which evolves from depositional models, forward stratigraphic modeling (FSM) to geocellular modeling. First, based on the comprehensive analysis of core, seismic, grain size, heavy minerals, dip data, it is believed that a special fan delta developed in the Miocene strata in the south of Albert Basin. The reservoirs are dominated by distributary channels, which are in medium-coarse grains, and the provenance is from the southwest to flowing to the northeast. The formation thickness of the stratum decreases from the boundary fault to the direction of the basin. Then, the input parameters of FSM modeling are quantitatively expressed based on the sedimentary model research, including model boundary conditions, basic input information, sediment supply and transportation. FSM results were used to quantitatively characterize the deposition process. The FSM simulation results are compared with the depositional model and well data to verify the reliability. Finally, the shale content model in FSM results is resampled to the geocellular grids and used as the constraint for facies model and property model in geological modeling. This model is used for well pattern design and optimization. This new approach integrates the conceptual depositional model with quantitative FSM results. It improves the accuracy of reservoir prediction and provides a new technical workflow for reservoir characterization. Furthermore, it helps to obtain more insight into the sedimentary process and reduces the risk of oilfield exploration and development.

Stratigraphy and sedimentary process in a closed-basin lake in Central Italy during the Anthropocene

<p>Shallow and closed lakes are affected by meteorological and climate variations and are especially sensitive to the change in their hydrological balance. In central Italy, there is the fourth-largest lake of the country, the Trasimeno Lake, whose water level has undergone various fluctuations over the centuries with alternation of flood and drought periods because of its shallow depth and the absence of natural outflows [1].</p><p>Sediment archives are used as information records to study chemical, physical, and biological environmental variations and changes in the hydrological budget driven by climatic fluctuations, but this is particularly complicated in shallow lakes due to the multiple perturbative phenomena. A robust study depends on the ability to obtain valid high-resolution geochemical data from lake sediments.</p><p>We conducted high-resolution geochemical analysis on three sediment cores about 1 meter long each, collected in Lake Trasimeno. We sectioned at 1  or 2 cm interval, which provided a detailed characterization of the significant changes in lacustrine processes that occurred in the basin during the Anthropocene (~last 150 years) [2], combining quantitative chemical (ICP-OES) and semi-quantitative (XRD and SEM) investigations. Geochemical variables are used as paleolimnological proxies to reconstruct past lake events that occurred within the water column. In particular, we report the study of the endogenic precipitates characteristic of the Trasimeno sediments, whose precipitation processes have been influenced by water fluctuations and anthropogenic impacts.</p><p>Given the strong presence of water fluctuations, the investigation period was divided into three distinct phases related to the lake's hydrometric state and characterized by sedimentary compounds of different nature. The endogenic carbonate compounds of calcite (commonly present in the Trasimeno sediments) contain a different Mg percentage during the different hydrometric phases. The lake sediments are particularly rich in Mg-calcite due to both water level changes and biological effects. Moreover, co-precipitation of non-crystalline Ca-P compounds (e.g., apatite type) has been detected during a hydrometric phase characterized by high microorganisms activity. Precipitation processes were triggered in Trasimeno by the growth of nutrient discharge into the lake (since the 1970s) and are currently studied for their importance in controlling eutrophication phenomena.</p><p>In conclusion, our findings show that rapid lake responses to water fluctuations and climate variations were transcribed within the sedimentary stratigraphic archives, which underlines their value and high quality in paleoenvironmental and paleohydrological reconstruction.</p><p>References:</p><p>[1] Frondini, Dragoni, Morgantini, Donnini, Cardellini, Caliro, Melillo, and Chiodini (2019). An En-dorheic Lake in a Changing Climate: Geochemical Investigations at Lake Trasimeno (Italy).Water, 11(7):1319.</p><p> [2] Gaino, E., Scoccia, F., Piersanti, S., Rebora, M., Bellucci, L. G., and Ludovisi, A. (2012). Spiculerecords of Ephydatia fluviatilis as a proxy for hydrological and environmental changes inthe shallow Lake Trasimeno (Umbria, Italy). Hydrobiologia, 679(1):139–153.</p>