GeoResJ最新文献

For 30 years, the initial sedimentation following the opening of the western Central Atlantic has been considered to be of Middle Callovian age (approximately 164.5 Ma) based on the biochronostratigraphical estimation for the basal sedimentary unit of the borehole from Site 534A of the Deep Sea Drilling Program (DSDP). That age has been used in kinematic models of the opening of the Central Atlantic. A reconsideration of the available biochronostratigraphical data and correlation of the δ¹³Ccarb record from Site 534A with those from the Tethyan and North Atlantic records suggest that the initial sedimentation at Site 534A is, in fact, of Middle Oxfordian age (approximately 160.6 Ma). The high biostratigraphic similarity among the basal sedimentary units of the boreholes at DSDP Site 534A and Ocean Drilling Program Site 801C in the Western Pacific suggest the same age for both sites. The Middle Oxfordian δ¹³Ccarb records from the different sites covary, marking the same palaeoenvironmental changes, although such an agreement was not previously acknowledged. A combination with additional data proposes that Middle Oxfordian age corresponds to the precise date of the opening of the Hispanic Corridor between the Atlantic and Pacific oceans.

This study aims at developing an internally consistent 3D network of brittle structures for the Kevitsa open pit Ni–Cu sulphide mine hosted by a Palaeoproterozoic mafic-ultramafic layered intrusion. The used approach involves compilation of depth and data-dependent three-dimensional geological sub-models at smaller depths, and their subsequent correlation with rock quality data, and reflection seismic structural models at greater depths. The work aims at bridging the characteristic gaps within and between the used geological–geophysical datasets, caused by the variable scales, coverages and resolutions. The second aim of the work is to provide a tectonic model explaining the generation of the major brittle structures within the area. The used data include digital elevation models, fracture and rock quality data from drill holes and 3D-photogrammetry, and seismic interpretations from previous investigations. The results show that the most distinct fracture zones dip gently towards WNW, steeply towards SE and sub-vertically, with NNW-SSE strikes. The gently WNW-dipping fracture zone shows the largest spatial extent and is clearly recognisable in all the source data sets. A kinematic model containing the gently WNW-dipping structures as major thrust zones, and smaller structures as second order structures is inferred. This work shows how surface and sub-surface data from various sources and depths are successfully integrated into high confidence structural models, which can be used as input data in future slope stability studies of the Kevitsa open pit.

First attention is offered to encrusting foraminifera existing in the Miocene reefal deposits of Wadi Gharandal (Sinai, Egypt). The detected encrusting foraminifera are confined to typical reefal limestone development. They belong mainly to the acervulinid, planorbulinid and homotrematid groups; dominated entirely by Tayamaia and Gypsina. Moreover, other forms include Neoplanorbulinella, Planolinderina, Borodinia, Discogypsina, Ladoronia, Sphaerogypsina and Sporadotrema. Besides, they inhabit different paleoenvironments; reef-flat, fore-reef and back-reef lagoonal conditions. This encrusting assemblage shows close paleobiogeographic affinity to the West Pacific region that locates at the same paleolatitudinal position. Consequently, such strong affiliation and copious faunal exchange certainly require direct and short distance connection and water inroad of an assemblage likely indicative for warm temperate to tropical settings. Therefore, the prior marine connection that dubiously proposed by Rögl (1999) in the Early Oligocene, extending north of India, west-east direction from eastern Mediterranean passing through east Iran and expanded directly across Asia to West Pacific is proposed to be the best direct and shortest water connection to the W. Pacific realizing this rigorous faunal similarity. On consequence, this connecting sea is thought to continue open even during Aquitanian and its closure had started in Early Burdigalian time. This closure is synchronous with the analogous restriction of the central basins of Iran which is considered the entry passage to W. Pacific across the proposed connecting sea. The results significantly provide an evidence for interruption also during the Early Burdigalian.

The Graham Bank is a broad and relatively shallow relief located off the SW coast of Sicily. This area hosts, among other submarine edifices, the ephemeral Ferdinandea Island, created in 1831 by an explosive eruption - the only well-documented event occurred in the study area - and rapidly dismantled by erosional processes. In the Graham Bank and its vicinity, three red coral deposits have been discovered and extensively exploited commercially during the last part of the 19th century, and were quickly depleted after discovery, since no living coral populations survived or repopulated the area after geological events that caused the massive die off. The coral deposits lay on a muddy sea-floor alongside some volcanic reliefs, and consisted of mostly dead corals, intermingled with volcanic and biogenic debris. Here, we describe these deposits and propose a model for their evolutionary history through palaeoecological analyses of their faunistic content, radiocarbon dating, Remotely Operated Vehicle sea-floor observations, and seismic profiles. Overall presented data suggest that these deposits have accumulated primarily (or even partially) as a consequence of volcanic activity dislodging living (or dead) corals from the steep flanks of volcanoes on which they lived. Periodic collapses of the friable pyroclastic walls of these edifices and landslides may have been triggered by repeated submarine eruptions, possibly associated with small earthquakes.

The South America Loess plateau covers a large part of Argentina. In this country, the Balcarce Hills represent at the moment a poorly studied area from a stratigraphic and paleoenvironmental point of view. This area is located in an intermediate place between other zones with a greater data density; for this reason, the geochronological and environmental knowledge of this area is key to a better regional understanding of Argentine loess formation mechanisms. For these purposes, Paleomagnetism, Rock Magnetism and chemical analyses were used as the main supports for this study. Two stratigraphic sections in the Balcarce area were studied. Both sections have lithostratigraphic units in common which allow to correlate them. Three lithostratigraphic and six pedogenetic cycles were recognized. The two younger lithostratigraphic units were deposited during the Brunhes Chron (< 0.781 Ma) while the oldest unit during Matuyama Polarity Chron (0.781 - 2.588 Ma). Towards the base of the oldest unit, normal polarity levels were recorded and they referred to Olduvai (1.778 - 1.945 Ma). The youngest reversal, assigned to the Brunhes-Matuyama Boundary (BMB), was found in the paleosoil of the top of oldest lithostratigraphic unit. This is very important because it allows to correlate it with other paleosols in the BMB of Argentina. With regards to magnetic signature, this is relatively homogeneous along the profiles and corresponds mainly to ferrimagnetic minerals, as titanomagnetites and probably maghemite in the paleosols. The magnetic grain size would dominantly be SD and the low coercivity fine to ultrafine particles increase in the pedogenetic horizons (A, Bw and Bt). The source rocks giving rise to the observed magnetic contribution seem to have been relatively constant in the last 1.9 Ma. In a first approach, the susceptibility values recorded in the sediments of Balcarce are higher than in areas located further north from the pampean loess plateau, but lower than those in the south. The mentioned differences would be linked to both the distance and the mineral composition of the source rocks.

Lime stabilization has been widely used in civil engineering to improve soils properties. A major shortcoming of lime is that it increases the soil brittleness. Thus, the aim of this research is to study the effect of lime along with geogrids on unconfined compressive strength (UCS) and modulus of elasticity (E_s) of the stabilized soil. Atterberg limits, XRF, and pH tests were performed to determine the optimal percentage of lime. Then, different percentages of lime were added to the soil to study strength, stress, and strain of specimens using UCS tests. Also, the effect of inclusion of geogrid on the lime stabilized soil was studied by adding four layers of geogrid in the soil at constant intervals. By increasing the percentages of lime, brittleness index, UCS, and E_s increased and deformability index decreased. Moreover, applying geogrids led to increasing deformability and failure strain. Based on SEM tests, an addition of lime caused fewer voids led to increasing UCS and E_s. A phenomenological model was used to develop equations for predicting UCS, E_s, brittleness, and deformability indexes for the stabilized soil. The results showed that there was a good correlation between the measured values and the estimated values given by the predicted equations.

The Lower Vindhyan (Semri) Group is largely composed of thick unmetamorphosed and undeformed sedimentary sequences of Late Palaeoproterozoic age. A detailed geochemical and palynological study has been carried out for the black shale lithounits of the Arangi and Kajrahat Limestone formations exposed near Chopan town, Sonbhadra district, Uttar Pradesh for evaluating their hydrocarbon potential and thermal maturity. The organic geochemical findings are mainly based on proximate analysis, ultimate analysis and Rock-Eval pyrolysis and indicates that the studied shale samples of both the formations have, due to high maturity, only a fair to poor hydrocarbon potential. Organic-walled microfossils recovered indicate high thermal maturity of the organic matter based on Acritarch Alteration Index (AAI) which is consistent with elevated T_max and very low hydrogen index (HI) values. Thus, only a low potential for generation of dry gaseous hydrocarbons remains for these highly matured samples, whereas the original kerogen type can be either type I or II.

Proper water resources management cannot be achieved without accessing comprehensive data, suitable resources exploitation programs, and quantified forecasts of water resources. Thus, it is necessary to develop new forecasting models of water resources. Autoregressive integrated moving average (ARIMA) models (classified as time series models) and artificial neural network models have performed well in forecasting linear and non-linear stream flow, respectively. In this paper, a hybrid method was used to evaluate the accuracy of daily flow forecasts through using the capabilities of ARIMA model and nonlinear auto regressive model with exogenous inputs (NARX). Moreover, the efficiency of forecasters such as North Atlantic oscillation (NAO) (as a large scale climate signal) was analyzed for flow forecasts. The forecasting results which compared using proposed error index (IIFFE) to assess mean absolute relative error (MARE), time to peak, and peak flow of forecasted flow. The results showed that forecasting accuracy was enhanced by using the hybrid model. It also displays that using rainfall as a forecaster has the most prominent influence on the increasing forecasting accuracy, while the accuracy is not achieved by using NAO singular or together with rainfall data. Finally, the proposed hybrid model decreased the IIFFE index from 1.25 (achieved by the best ARIMA forecast) to 0.36 and improved the accuracy daily flow forecasting considerably which enhance real time optimal operation of reservoirs.

The concept of superficial structure relates to surficial deformations that are determined neither by tectonic deformation nor by surface geomorphic processes sensu stricto. This work addresses two mechanisms leading to structural surface disturbances in the Lutetian strata of the Eocene plateaux of the eastern Paris Basin. Firstly, mechanical release which is associated with stress-relief during Quaternary valley downcutting. It results in lateral spreading of the middle Lutetian limestone, and subsequent sub-erosion of underlying sands may cause valley-side cambering. Secondly, ghost-rock karstification in the phreatic zone which is leading to surficial collapse of the upper Lutetian cover. Geological structure (thickness and porosity of the middle Lutetian limestone) and valley-side slopes stratigraphy (position of the upper Ypresian sand) control the spatial distribution of these processes. Ghost-rock karstification, conditioned by tectonic joints is confined to the west; to the east, cambering processes occur where upper Ypresian sand aquifer and alluvial aquifer are connected. During the Quaternary, periglacial conditions account for cambering processes and also for a second phase of karstification within an aquifer perched in the active layer, and from mechanical release joints. Resultant morphological features are then inherited and cambering is even a fossil process where upper Ypresian sand crops out above the valley floor. Consequently, large-scale landforms, derived from the superficial structure, are essentially inactive.

The ice wedges are considered as key subjects for ¹⁴C aging of yedoma, as there are no any exchange processes between the environment and the ice wedges. Syngenetic sediments contain allochthonous organic admixtures which originated at a distance from its present position. The main problem of radiocarbon dating within permafrost is the uncertain reliability of the ¹⁴C ages. To establish the age of ice wedge formation the strategy for the most authentic radiocarbon age selection for syngenetic sediments is considered on the base of a model of yedoma accumulation and distribution of reversal material by flood and aeolian transport. The re-working of organic material discussed in terms of cyclic syngenetic sedimentation of yedoma.

The advantages and the complications of ¹⁴C dating of organic inclusions from ice wedges by the accelerator mass spectrometry (AMS) are discussed applying to the search of true age organic material, which is simultaneous to ice-wedge formation. Radiocarbon ages of different organic materials from the same samples are compared, it is demonstrated that the difference between ages of the fractions from the ice wedges consists of about 9 kyr in Seyaha ice-wedge complex in Yamal Peninsula and about 5 kyr in Bison yedoma, Kolyma River valley. The principle of the choice of the youngest ¹⁴C age from the set and from the layer is proposed for yedoma.