Eolian dust activity studies on the arid Central Asia (ACA), one of the world's largest dust sources, are of great importance to the global climatic system. Grain size distributions (GSDs) can ...provide information on sediment sources, transport processes and sedimentary environments. As a result, GSD is the most frequently applied proxy in reconstruction of past eolian dust activities of the ACA using lake sediments. The GSD dataset for a core spanning the last ~850 years from Kuhai Lake on the northeastern Tibetan Plateau was unmixed by end-member analysis (EMA) for reconstruction of past eolian dust activities on the southeastern margin of the ACA. The results suggest that EM 2 and EM 3, which were added together to form an eolian dust activity proxy, represent the proximal eolian suspension and saltation loads, respectively. The fractional abundances of EMs suggest that siliciclastic materials in the studied core were mainly from eolian contributions. The occurrence of enhanced eolian dust activities within the cold Little Ice Age period together with the GSDs of EM 2 and EM 3 indicate that eolian dust activities on the southeastern margin of the ACA were basically governed by the Siberian High-produced Asian Winter Monsoon over the last millennium. At decadal to centennial scales, enhanced eolian dust activities generally correspond to warm periods with high total solar irradiance (TSI). Increased temperatures as the result of high TSI would have caused larger increases in evaporation than in precipitation, and hence deteriorated vegetation cover and increased dust sources availability.
•Eolian dust activity of the arid Central Asia was studied using a core of Kuhai Lake.•The HALS-NMF parametric algorithm of end-member analysis was applied.•Siliciclastic materials in the studied core are mainly from eolian contribution.•Eolian dust activity at centennial scale was governed by Siberian High.•Eolian dust activity at decadal scale was governed by total solar irradiance.
Recognition and interpretation of paleoclimate signals in sedimentary proxy datasets are time consuming and subjective. Acycle is a comprehensive and easy-to-use software package for time series ...analysis in paleoclimate research and education. It is designed to speed paleoclimate time series analysis, especially cyclostratigraphy, and to provide objective methods for estimating astrochronology. Acycle provides for detrending with multiple options to track and remove secular trends. A selection of power spectral analysis methodologies is offered for the detection of periodic signals. Many of the functions are specific to cyclostratigraphy and astrochronology that are not found in standard statistical packages. A specialized function is provided to assess the astronomical (Milankovitch) forcing of paleoclimate series and search for the most likely sedimentation rate by evaluating the correlation coefficient between power spectra of an astronomical solution and sedimentary proxy data. Sedimentary noise modeling (for past sea-level changes) is also provided in Acycle. As an example, Acycle is applied to a sedimentary proxy series from the cyclostratigraphy of the Paleocene-Eocene thermal maximum (PETM) in Core BH9/05 from the Paleogene Central Basin, Svalbard. Acycle detects significant astronomical forcing in the proxy series and relatively stable sedimentation rates during and after the PETM. Acycle runs in the MATLAB environment or as stand-alone software on Windows and Macintosh OS X, and is open-source software.
•Acycle is signal processing software for paleoclimate research and education.•Many of the functions are specific to cyclostratigraphy and astrochronology.•Acycle includes models for sedimentary noise and sedimentation rate.•A fully implemented graphical user interface facilitates operator use.
Initial porosity and permeability in deep-water systems are controlled by primary sedimentary texture and mineralogy. Therefore, understanding the sedimentary processes that control changes in ...primary texture is critical for improved reservoir quality predictions. A well-constrained, exhumed submarine lobe in the Jaca Basin, and a submarine channel-fill element in the Aínsa Basin, northern Spain, were studied to characterize the depositional reservoir quality in axial to marginal/fringe positions. Construction of architectural panels and strategic sampling enabled analysis of the spatial changes in textural properties, and their relationship to reservoir quality distribution. Samples were analyzed in thin-section to establish how depositional processes inferred from outcrop observations affect textural properties. Results show that high-density turbidites are concentrated in lobe- and channel-axis positions and exhibit good depositional reservoir quality. Lobe off-axis deposits contain high- and low-density turbidites and have moderate depositional reservoir quality. Conversely, low-density turbidites dominate lobe fringe and channel-margin positions and have relatively poor depositional reservoir quality. There is a sharp decrease in depositional reservoir quality between the lobe off-axis and lobe fringe due to: 1) an abrupt increase in matrix content; 2) an abrupt decrease in sandstone amalgamation; and 3) a decrease in grain-size. There is an abrupt increase in depositional reservoir quality from channel margin to channel axis corresponding to: 1) an increase in total sandstone thickness and amalgamation; 2) an increase in grain-size, 3) a decrease in matrix content. Rates of change of key properties are up to two orders of magnitude greater between channel-fill sub-environments compared to lobe sub-environments. Spatial variability in properties of discrete architectural elements, and rates of changes, provides input to reservoir models during exploration, appraisal, and development phases of hydrocarbon fields.
•Bed- and grain-scale properties mapped in individual architectural elements.•Sediment gravity flow-type controls depositional reservoir quality.•Process-based approach to reservoir quality aids prediction.
The Geology of Kuwait Abd el-aal, Abd el-aziz Khairy; Al-Awadhi, Jasem Mohammed; Al-Dousari, Ali
2023, 2022, 2022-11-21
eBook
Open access
This open access book contains a set of chapters covering all aspects of geosciences related to Kuwait and adjacent regions, including Iran, Saudi Arabia and the Arab Gulf states. It covers basic ...information about the geology including a wide range of geoscientific disciplines such as marine geology, structural geology, hydrogeology and geophysics related to the region. This book is aimed at researchers and students, as well as professionals in the field of hazard mitigation and petroleum exploration.
We present a hydroclimate synthesis of the southern Great Basin over the last two glacial-interglacial cycles focused on paleolakes in Death Valley (core DV93-1), Searles Valley (core SLAPP-SRLS17), ...Owens Valley (core OL92), and the Devils Hole cave. There is close agreement between the occurrence of lakes in Death Valley and the height of the water table in the Devils Hole (50 km east of Death Valley) during the last 200 kyr. Death Valley and Devils Hole have adjacent, partly overlapping, drainage areas and most likely did over the last 200 kyr. When the water table in the Devils Hole was above the threshold level of ∼5 m higher than the modern, permanent lakes existed in Death Valley. At water table elevations less than 5 m above the modern, ephemeral lakes, saline pans, and mudflats occurred in Death Valley. The close temporal agreement between inferred paleoenvironments from the sediments in the Death Valley core and the paleowater table elevation in Devils Hole suggests a common forcing and provides insight into climate variability in the southwestern United States over the last 200 kyr. Owens Valley and Searles Valley, which derived inflow waters from the Sierra Nevada via the Owens River, contain paleohydrologic records which match those from Death Valley and the Devils Hole in terms of timing and direction of water availability over the last 200 kyr, indicating a similar paleohydrologic history for the entire southern Great Basin region. Near the end of Marine Oxygen Isotope Stage 6 (MIS 6), 140 ka - 130 ka, Lake Manly in Death Valley became shallow and hypersaline, and ultimately dried up at 127.1 ka ±4.3 ka. The transition from glacial to interglacial vegetation, which involved the loss of Juniperus pollen and an increase in Quercus (oak) pollen, occurred in Death Valley core DV93-1 at 131.3 ka ±4.0 ka. Following the glacial to interglacial pollen shift, a large alkaline lake formed in Death Valley. Similar conditions (freshwater, high productivity, and a mixed, deeply oxygenated water column indicated by biomarkers) existed in Searles Lake between 135.3 +2.7/-2.9 ka and 130.1+2.7/-2.6 ka, also following the juniper-oak pollen transition. Sr isotopes in calcite and sulfate minerals (gypsum, glauberite, thenardite), and the rare occurrence of the sodium carbonate mineral northupite with a low 87Sr/86Sr ratio in core DV93-1, together with organic geochemical proxies from Searles core SLAPP-SRLS17, all suggest that at this time, late MIS 6 Lake Manly in Death Valley received alkaline water via spillover from Searles Valley into Death Valley through Panamint Valley. The hydrologic connection between Searles Valley, Panamint Valley, and Death Valley at Termination II (130 ka) is documented here for this system of pluvial lakes for the first time. The Devils Hole water table decreased to +6.5 m at 140.8 ka ±3.2 ka, rose briefly to +8 m at 137.6 ka ±0.5 ka, and then dropped 8 m by 120.36 ka ±0.45 ka, when it reached an elevation similar to the modern. The pluvial lakes in Death Valley and Searles Valley may have coincided with the rise of the Devils Hole water table at ∼137.6 ka ±0.5 ka years ago, although the age models for core DV93-1 and core SLAPP-SLRS17 during the end of MIS 6 carry large uncertainties.
•200,000 year paleohydrologic synthesis of southern Great Basin: Death Valley, Searles Valley, Owens Valley, Devils Hole cave.•New data from Death Valley: U-Th dates (halite) and 87Sr/86Sr ratios (carbonates and sulfates).•Close agreement between Death Valley paleoenvironments and water table elevations in Devils Hole.•Searles Lake overflowed into Death Valley via Panamint Valley near the end of MIS 6.
The Southern Hemisphere Westerlies (SHW) are a vital part of the Southern Hemisphere's coupled ocean-atmosphere system and play an important role in the global climate system. The SHW affect the ...upwelling of carbon-rich deep water and exchange of CO2 from the ocean to the atmosphere by driving the Antarctic Circumpolar Current. On seasonal to millennial timescales, changes in the strength and position of the SHW are associated with temperature and precipitation changes throughout the extratropical Southern Hemisphere. Understanding the behaviour of the SHW under different background climate states is important for anticipating its future behaviour and remains a subject of ongoing research. Terrestrial paleoclimate records from lake sediments are valuable for reconstructing past atmospheric change and records from the handful of sub-Antarctic islands provide the opportunity to develop datasets to document spatio-temporal patterns of long-term SHW behaviour. Here, we generate palynological, microcharcoal, and sedimentological reconstructions (including CT imagery, μXRF analysis, magnetic susceptibility, and loss-on-ignition) on lake sediments from the Kerguelen Islands (49°S) to constrain variability in Holocene vegetation, climate, and atmospheric circulation (SHW position). Due to the influence of the SHW on the Kerguelen Islands, the influx of long-distance transported (LDT) pollen and microcharcoal from southern Africa serve as proxies for the meridional position of the SHW. In contrast with the stable conditions that prevailed on the Kerguelen Islands over the past 8,600 cal yr BP, our findings reveal a highly dynamic Early Holocene period. Consistent with local palynological evidence of warmer conditions, a high influx of LDT pollen and charcoal from southern Africa suggest that the SHW core belt was located further south of the Kerguelen Islands during this time. Comparison against paleoclimate records from the surrounding region and beyond suggests that the inferred changes might be explained by changes to our planet's interhemispheric thermal gradient, triggered by North Atlantic cooling in response to melting of the last remnants of the Laurentide Ice Sheet.
•We study Holocene vegetation and atmospheric circulation on the Kerguelen Islands.•Southern Hemisphere Westerlies position is based on long-distance pollen transport.•Wind belt shifts coincide with changes in local temperature and precipitation.•Durin the Early Holocene the core wind belt was positioned south of the Kerguelen.•From 8,600 cal yr BP the core wind belt shifted northward of the Kerguelen Islands.
Time-elevation plots and chronostratigraphic diagrams are valuable for understanding and analyzing stratigraphy when time-elevation data, or some approximation of them, are available, for example in ...flume experiments, numerical models, and three-dimensional seismic reflection surveys. We developed a Python module called stratigraph, aimed at the reproducible analysis and visualization of stratigraphy, and we use it here to explore data from forward stratigraphic models of meandering channels, the eXperimental EarthScape (XES) facility XES-02 experiment, and two experiments that were conducted at the Tulane University Sediment Dynamics and Stratigraphy Laboratory. We use these tools to generate and visualize three-dimensional chronostratigraphic diagrams, compute maps of stratigraphic completeness and other stratigraphic attributes, and explore the nature of the erosional surfaces. We show that, using a 3D Wheeler diagram, it is possible to create maps of important stratigraphic attributes, in addition to the conventional thickness maps. There are six fundamental stratigraphic attributes that are direct consequences of a quantitative chronostratigraphic approach, as follows. (1) Sediments that were preserved after deposition have a thickness and (2) a duration; normalized by the total time, this duration of preserved deposition is called stratigraphic completeness. (3) The duration of deposition of sediment that was eroded later (called vacuity); (4) the thickness of these sediments is the eroded thickness. (5) At any given geographic location, erosion occurs some of the time, and the duration of these erosive periods is the fifth quantity. (6) Finally, it is quite common that neither significant deposition nor erosion takes place for some time and the duration of this stasis can be considered at every location. These maps give an overview of where erosion or deposition dominate in a source-to-sink system, and for how long; and they make it possible to quickly identify sites with both a high degree of stratigraphic completeness and a significant thickness.
•The history of fluid advection on the margin of Great Bahama bank was calculated.•Advection rates into the sediment column increased abruptly at 12.5 Ma.•This change in flux coincides with a ...significant change in platform structure.
The advection of seawater into the sediments deposited on the margins of Great Bahama Bank has been demonstrated to play in important role in ventilating the uppermost sediments, as well as supplying elements for diagenetic reactions deeper within the platform. Here, we implement a numerical model to calculate the rate of fluid advection at ODP Site 1003, using calcium isotopes as a tracer for fluid advection. A key parameter for this model, the rate of recrystallization of sediments, was constrained using the clumped isotope proxy. The model was tuned to existing datasets of clumped and carbonate calcium isotope measurements for this site. Results of this modeling effort indicate that, prior to ∼15 Ma, fluids were advected into the platform at a rate substantially lower than the present day. The rate of advection abruptly increased ∼13 Ma to a value greater than the present day. The increase in advective flux during the mid-Miocene coincides with a major reorganization of the platform from a ramp-like geometry to a steeper carbonate platform, indicating a change in the relative contributions of different mechanisms governing fluid flow on the platform margin and interior. This paper aims to explore the utility of using clumped and calcium isotopes to quantitatively reconstruct past fluid advection rates using this novel technique.
With the aim to better understand the timing and geological evolution of the late Cenozoic stratigraphic record of the onshore, western Valdés Basin in northeast Chubut province (Patagonia, ...Argentina), we perform sedimentological, stratigraphic, and zircon U–Pb geochronologic analyses. The study includes the terrestrial Early Miocene Trelew Member of the Sarmiento Formation, the shallow marine Early Miocene Gaiman Formation, the shallow marine to estuarine Late Miocene Puerto Madryn Formation, and the Plesitocene fluvial conglomerates of the Rodados Patagónicos. Based on our data set, together with the recognition of relevant stratigraphic surfaces, we divide the succession into stratigraphically bounded units and define three cycles of sedimentation. The Lower Cycle rests on top of Surface 1, which comprise a long hiatus including the entire Oligocene Epoch. This cycle is in turn divided into two subunits separated by the transgressive, ravinement Surface 2. The Lower Cycle is separated from the overlying Middle Cycle (=Puerto Madryn Formation) by the flat and regionally extensive Surface 3. Finally, the latter is separated from the Upper Cycle (=Rodados Patagónicos) by Surface 4, a complex surface at the base of gravel deposits forming several terrace levels. Maximum depositional ages calculated from 10 zircon U–Pb samples indicate the succession between surface 1 and 4 extends from 21.5 to 2.7 Ma (Aquitanian-Piacenzian). The Lower Cycle is restricted to the 21.5–16 Ma interval (Aquitanian-Burdigalian); the Middle Cycle between 12 and 2.7 Ma (latest Serravalian-Piacenzian), with most of the new and previous ages clustering in the Tortonian; whereas the Upper Cycle is restricted to the Pleistocene. Although most of the analyzed sediments show fresh volcanic glass particles, older zircon ages are dominant, representing detrital components with a dominant peak of Permian-aged grains, with subordinated Devonian, Jurassic, Cretaceous, and Paleogene peaks. We interpret the analyzed succession as a condensed section compared to the offshore Valdés Basin depocenter area. Sedimentation in the study area was controlled by periods of slow subsidence, probably related to thermal subsidence and sediment compaction in the depocenter. Two main sources of sediments for the analyzed succession are envisaged: one represented by explosive volcanism located either in the Andes or in the North Patagonian Massif, the other through erosion of older rocks surrounding the North Patagonian Massif where late Paleozoic plutonic rocks are abundant. Particularly for the Middle and Upper cycles, an increase in Mesozoic contribution suggests erosion from sediments of the Cañadón Asfalto Basin. The new ages and stratigraphic analyses here reported are of major relevance for the integration of the onshore and offshore stratigraphies of the Valdés Basin which is key to connect the geologic evolution of the Andean and passive margin areas of southern South America. They are also of major relevance for the calibration of fossil communities, particularly for the abundant and diverse marine vertebrates preserved in the Burdigalian Gaiman Formation.
•Zircon U–Pb ages and stratigraphic descriptions are provided for Neogene strata.•Results indicate three Neogene depositional cycles in the onshore Valdés Basin.•The Gaiman Formation is isotopically dated for the first time.•Late Paleozoic zircons are dominant, puzzling the provenance interpretations.
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