排序方式： 共有14条查询结果，搜索用时 218 毫秒
1.
2.
Rabi Bastia M. Radhakrishna Suman Das Anand S. Kale Octavian Catuneanu 《Marine and Petroleum Geology》2010
The passive Eastern Continental Margin of India (ECMI) evolved during the break up of India and East Antarctica in the Early Cretaceous. The 85°E ridge is a prominent linear aseismic feature extending from the Afanasy Nikitin Seamounts northward to the Mahanadi basin along the ECMI. Earlier workers have interpreted the ridge to be a prominent hot spot trail. In the absence of conclusive data, the extension of the ridge towards its northern extremity below the thick Bengal Fan sediments was a matter of postulation. In the present study, interpretation of high resolution 2-D reflection data from the Mahanadi Offshore Basin, located in the northern part of the ridge, unequivocally indicates continuation of the ridge across the continent–ocean boundary into the slope and shelf tracts of the ECMI. Its morphology and internal architecture suggest a volcanic plume related origin that can be correlated with the activity of the Kerguelen hot spot in the nascent Indian Ocean. In the continental region, the plume related volcanic activity appears to have obliterated all seismic features typical of continental crust. The deeper oceanic crust, over which the hot spot plume erupted, shows the presence of linear NS aligned basement highs, corresponding with the ridge, underlain by a depressed Moho discontinuity. In the deep oceanic basin, the ridge influences the sediment dispersal pattern from the Early Cretaceous (?)/early part of Late Cretaceous times till the end of Oligocene, which is an important aspect for understanding the hydrocarbon potential of the basin. 相似文献
3.
Comment on Non‐unique stratal geometries: implications for sequence stratigraphic interpretations,by: P.M. Burgess and G.D. Prince,Basin Research (2015) 27, 351–365 
下载免费PDF全文
下载免费PDF全文 The non‐unique variability highlighted by Burgess & Prince (Basin Res. 2015, 27 , 351) (i.e. the origin and timing of maximum flooding surfaces, maximum regressive surfaces and subaerial unconformities; the process of topset aggradation in relation with the various types of shoreline trajectory; and the multiple controls that may affect the progradation and retrogradation of a shoreline) is irrelevant to the workflow of sequence stratigraphy. What is relevant is the observation of the unique stratal geometries that are diagnostic to the definition of all units and surfaces of sequence stratigraphy. In downstream‐controlled settings, these unique stratal stacking patterns relate to the forced regressive, normal regressive and transgressive shoreline trajectories. Multiple controls interplay during the formation of each type of stacking pattern, including accommodation, sediment supply and the energy of the sediment‐transport agents. This interplay explains the non‐unique variability, but does not change the unique criteria that afford a consistent application of sequence stratigraphy. Failure to rationalize the non‐unique variability within the context of unique stratal geometries is counterproductive, and obscures the simple workflow of sequence stratigraphy. 相似文献
4.
A Kaapvaal craton debate: Nucleus of an early small supercontinent or affected by an enhanced accretion event? 总被引：1，自引：1，他引：0
Patrick G. Eriksson Santanu Banerjee David R. Nelson Martin J. Rigby Octavian Catuneanu Subir Sarkar R. James Roberts Dmitry Ruban Mtimkulu N. Mtimkulu P.V. Sunder Raju 《Gondwana Research》2009,15(3-4):354-372
Incorporation of the Kaapvaal craton within a speculative Neoarchaean–Palaeoproterozoic supercontinent has long been debated, and this idea provides a potential solution to solving the apparently enigmatic provenance of the huge quantities of gold within the famous Witwatersrand auriferous deposits of Kaapvaal. Within a framework of a postulated Neoarchaean “Kenorland” (“northern”; present-day reference) supercontinent, we examine possible “southern” cratons that may have been contiguous with Kaapvaal: Pilbara, Zimbabwe, Dharwar, São Francisco, Amazon, Congo. Brief reviews of their basic geology and inferred evolution in syn-Witwatersrand basin times (c. 3.1–2.8 Ga) show no obvious support for any such supercontinental amalgamations. An alternative idea to explain a measure of gross similarity amongst several Neoarchaean cratons is through global events, such as a c. 3125–3000 Ma cratonic-scale erosive event interpreted for both Pilbara and Kaapvaal, and a much more widespread magmatic event at c. 2760–2680 Ma. We postulate that a global superplume event at c. 3.0 Ga included a plume beneath the Kaapvaal cratonic nucleus, thus halting any subduction around that terrane due to the thermal anomaly. Such a speculative global magmatic event is assumed to have enhanced production of juvenile oceanic crust at mid-ocean ridges, including those “offshore” of the thermally elevated Kaapvaal nucleus. Intra-oceanic obduction complexes may have built up fairly rapidly under such conditions, globally, and once the plume event had abated, “normal” plate tectonics would have resulted in composite (greenstone-tonalite, possibly also including granite) terranes accreting with nuclei such as Kaapvaal. This enhanced plume-related cratonic growth can be seen as a rapid accretion event. Formation of the envisaged ophiolite complexes possibly encompassed deformation-related first-order concentration of gold, and once accretion occurred around Kaapvaal's nucleus, from north and west (present-day frame of reference), a second-order (deformation-related) gold concentration may have resulted. The third order of gold concentration would logically have occurred once placer systems reworked detritus derived from the orogens along the N and W margins of Kaapvaal. Such conditions and placer gold deposits are known from many Neoarchaean cratons. The initial source of gold was presumably from the much hotter Mesoarchaean mantle and may have been related to major changes in Earth's tectonic regime at c. 3.0 Ga. The unique nature of Kaapvaal is probably its early stabilization, enabling formation of a complex flexural foreland basin system, in which vast quantities of placer sediments and heavy minerals could be deposited, and preserved from younger denudation through a unique post-Witwatersrand history. 相似文献
5.
Discrimination between wave‐ravinement surfaces and bedset boundaries in Pliocene shallow‐marine deposits,Crotone Basin,southern Italy: An integrated sedimentological,micropalaeontological and mineralogical approach 下载免费PDF全文
下载免费PDF全文 The lower Pliocene Belvedere Formation, cropping out in the Crotone Basin, southern Italy, exhibits a metre‐scale to decametre‐scale shallow‐marine cyclicity that shares features of both high‐frequency sequences linked to shoreline shifts and controlled by minor relative sea‐level and/or sediment supply changes, and sedimentological cycles unrelated to shoreline shifts. In order to better understand the high‐frequency sequence stratigraphic framework of this succession, an integration of sedimentological, micropalaeontological (micro‐foraminifera assemblages) and mineralogical (heavy mineral abundance) data is used. From a sedimentological/stratigraphic point of view, wave‐ravinement surfaces bounding high‐frequency sequences, and associated substrate‐controlled ichnofacies, are prominent in outcrop and document environmental and water‐depth changes, whereas bedset boundaries separating sedimentological cycles have a more subtle field appearance and are only associated with changes of environmental energy. Moreover, condensed deposits are present only above wave‐ravinement surfaces, and the high‐frequency sequences bounded by these surfaces have a thickness that is an order of magnitude greater than that of the bedsets. Micro‐foraminifera assemblages may change, and the content of heavy minerals usually increases, across wave‐ravinement surfaces, whereas both parameters do not change significantly across bedset boundaries. The abundance of heavy minerals is systematically higher, with respect to the underlying and overlying deposits, in the condensed shell beds that overlie wave‐ravinement surfaces. An integrated sedimentological, micropalaeontological and mineralogical approach represents a powerful tool to discriminate between wave‐ravinement surfaces bounding high‐frequency sequences and bedset boundaries, and in general to investigate at the intra high‐frequency sequence scale. This integrated approach is expected to be very useful in the study of potentially all shallow‐marine successions composed of small‐scale cycles, in order to delineate a detailed sequence stratigraphic framework and understand the factors that controlled the cyclicity. 相似文献
6.
Tectonic control on fluvial styles: the Balfour Formation of the Karoo Basin, South Africa 总被引：2，自引：0，他引：2
The Balfour Formation represents a fully fluvial succession of late Late Permian–earliest Triassic age which accumulated in the foredeep of the Karoo Basin during the overfilled phase of the foreland system. The lack of a coeval marine environment within the limits of the preserved Karoo Basin provides an opportunity to study the stratigraphic cyclicity developed during a time when accommodation was solely controlled by tectonics. The Balfour stratigraphy is composed of a succession of six third-order fluvial depositional sequences separated by subaerial unconformities. They formed in isolation from eustatic influences, with a timing controlled by orogenic cycles of loading and unloading. Sediment accumulation took place during stages of flexural subsidence, whereas the bounding surfaces are related to stages of isostatic uplift. The vertical profile of all sequences displays an overall fining-upward trend related to the gradual decrease in topographic slope during orogenic loading. At the same time, an upward change in fluvial styles can be observed within each sequence, from initial higher to final lower energy systems. The actual fluvial styles in each location depend on paleoslope gradients and the position of the stratigraphic section relative to the orogenic front. Proximal sequences show transitions from braided to meandering systems, whereas more distal sequences show changes from sand-bed to fine-grained meandering systems. The average duration of the Balfour stratigraphic cycles was 0.66 My, i.e. six cycles during 4 My. No climatic fluctuations are recorded during this time, with the long-term climatic background represented by temperate to humid conditions. 相似文献
7.
The Wheeler diagram is a type of chronostratigraphic chart and is one of the fundamental instruments available in the geologists' toolkit that is used to understand spatiotemporal relationships of strata. Over the last four decades, these diagrams have continued to improve due to advances in seismic technology. This article examines the historical developments behind Wheeler diagrams, not only stressing their merits, but also their pitfalls and the role that sequence stratigraphic principles have played in interpreting these diagrams. It is emphasized that the diagrams are only complete if one utilizes the thicknesses of a sequence stratigraphic unit (sequence, systems tracts) – a missing dimension that turns a 3D Wheeler diagram into 4D. The article also argues that the latter 4D diagrams represent the future for Wheeler diagrams. 相似文献
8.
Octavian G. Duliu Carmen Cristache Otilia A. Culicov Marina V. Frontasyeva 《Marine pollution bulletin》2009,58(6):827-831
The vertical distributions of five potential pollutants - Zn, As, Br, Sn, and Sb - were determined via epithermal neutron activation in the upper 50 cm of unconsolidated sediments from the Black Sea, which were collected 600 m below sea surface. This analysis demonstrated increasing concentrations towards the upper limits of sediments, which were greater than alert concentrations in the case of As and Br, and in accordance with Romanian Environment Regulations. The utilization of Chernobyl 137Cs as a time marker allowed for dating of this region to the last 100 years. 相似文献
9.
For a seismogenic area like Vrancea (Romania) with well-defined geometrical features of the seismicity production in space
and time, the numerical simulation of the earthquake generation process (e.g. cellular automaton) looks highly attractive.
The delimitation, as accurately as possible, of the geometrical features of the seismically active system in the Vrancea subcrustal
zone is essential to constrain the simulation modeling. As a first approximation, the seismicity pattern is close to a fault
plane NE–SW oriented, extended roughly vertically between 60 and 170 km depth. A characteristic median plane is defined by
minimizing the distance of hypocenters. The average distance of the hypocenters to the median plane is around 5 km. However,
a more detailed investigation of the geometrical configuration of seismicity indicates a fragmentation of the active body
located in the upper mantle in two segments. The seismicity pattern is well approximated by a planar distribution in each
segment. In the transition zone, between the upper and lower segment, the hypocenter distribution is more dispersed and shows
a disruption among the two planar segments, measured by about 9 km apart laterally one relative to the other. The two segments
hosted the major Vrancea events recorded in the last two centuries (for which we have available location of acceptable accuracy).
The narrow transition zone at about 100 km depth is interpreted as a weaker segment, possibly caused by a dehydration process
or by an infiltration of asthenosphere material from the back side of the South-Eastern Carpathian arc system. It is still
debatable if fragmentation in two seismically active segments reflects the existence of two neighbouring separate blocks (upper,
continental and lower, oceanic block) or a consequence of a breaking process separating a continental block into two parts.
The segmentation of the descending lithosphere and the edge effects are apparently stationary, at least for the time interval
since 1985 to the present, for which the earthquake catalogue is reliable (homogeneous). 相似文献
10.
The Calnistea catchment lies in the southern part of Romania in a region that has been confronted lately with serious water scarcity problems generated primarily by summer heat waves and long periods of drought. The high temperatures, excessive evapotranspiration and scant precipitation have a negative impact on water resources and especially on the river system, which is at the mercy of meteorological conditions, because all the streams in the area originate in the plain. Consequently, mean annual discharges are very low and more often than not, many rivers run dry. In order to avoid such an unwanted phenomenon people have built earth dams across the valleys thus creating chains of ponds, which are used to regulate the flow. Even so, however, most of the years the rivers look like mere threads of water oozing gently through their sediments. Under the circumstances, it is no wonder that irrigation systems are missing, which explains the low agricultural productivity. The most important asset of the region is the groundwater, as it represents the only source of drinking water for the population. Groundwaters are stored in superposed aquifers, most of them confined, generally having good hydrogeological properties. Water quality complies with the standards for drinking water and that is why groundwaters are used as such for domestic consumption. The problem is that in the past years, population increase has put more pressure on this resource and consequently water table sank. The growing depletion of groundwaters has brought about thirst, famine, poverty and despair, sad realities that local authorities are striving to control. Given this necessity the present study aims at making several proposals of what could be done on a short and middle term in order to increase the water supplies of the region and thus alleviate the people??s suffering. 相似文献