Clinoform geometry,geomorphology, facies character and stratigraphic architecture of a sand‐rich subaqueous delta: Jurassic Sognefjord Formation,offshore Norway          下载免费PDF全文

Stefano Patruno  Gary J. Hampson  Christopher A.‐L. Jackson  Tom Dreyer 《Sedimentology》2015,62(1):350-388

The integration of core sedimentology, seismic stratigraphy and seismic geomorphology has enabled interpretation of delta‐scale (i.e. tens of metres high) subaqueous clinoforms in the upper Jurassic Sognefjord Formation of the Troll Field. Mud‐prone subaqueous deltas characterized by a compound clinoform morphology and sandy delta‐scale subaqueous clinoforms are common in recent tide‐influenced, wave‐influenced and current‐influenced settings, but ancient examples are virtually unknown. The data presented help to fully comprehend the criteria for the recognition of other ancient delta‐scale subaqueous clinoforms, as well as refining the depositional model of the reservoir in the super‐giant Troll hydrocarbon field. Two 10 to 60 m thick, overall coarsening‐upward packages are distinguished in the lower Sognefjord Formation. Progressively higher energy, wave‐dominated or current‐dominated facies occur from the base to the top of each package. Each package corresponds to a set of seismically resolved, westerly dipping clinoforms, the bounding surfaces of which form the seismic ‘envelope’ of a clinoform set and the major marine flooding surfaces recognized in cores. The packages thicken westwards, until they reach a maximum where the clinoform ‘envelope’ rolls over to define a topset–foreset–toeset geometry. All clinoforms are consistently oriented sub‐parallel to the edge of the Horda Platform (N005–N030). In the eastern half of the field, individual foresets are relatively gently dipping (1° to 6°) and bound thin (10 to 30 m) clinothems. Core data indicate that these proximal clinothems are dominated by fine‐grained, hummocky cross‐stratified sandstones. Towards the west, clinoforms gradually become steeper (5° to 14°) and bound thicker (15 to 60 m) clinothems that comprise medium‐grained, cross‐bedded sandstones. Topsets are consistently well‐developed, except in the westernmost area. No seismic or sedimentological evidence of subaerial exposure is observed. Deposition created fully subaqueous, near‐linear clinoforms that prograded westwards across the Horda Platform. Subaqueous clinoforms were probably fed by a river outlet in the north‐east and sculpted by the action of currents sub‐parallel to the clinoform strike.  相似文献   

Mapping optical ray trajectories through island wake vortices     

Christopher G. Nunalee  Ping He  Sukanta Basu  Jean Minet  Mikhail A. Vorontsov 《Meteorology and Atmospheric Physics》2015,127(3):355-368

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Factors contributing to a decadal oscillation in South African rainfall     

Mark R. Jury 《Theoretical and Applied Climatology》2015,120(1-2):227-237

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Analysing uncertainties in climate change impact assessment across sectors and scenarios     

Calum Brown  Evan Brown  Dave Murray-Rust  George Cojocaru  Cristina Savin  Mark Rounsevell 《Climatic change》2015,128(3-4):293-306

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Projected changes in diverse ecosystems from climate warming and biophysical drivers in northwest Alaska     

Mark Torre Jorgenson  Bruce G. Marcot  David K. Swanson  Janet C. Jorgenson  Anthony R. DeGange 《Climatic change》2015,130(2):131-144

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Primitive Ordovician (Floian) echinoderms from Sandu,Guizhou Province,South China,and their significance     

Christopher R. C. Paul  Stephen K. Donovan  Lucy A. Muir  Joseph P. Botting  Jih‐Pai Lin  Yuandong Zhang 《Geological Journal》2016,51(1):143-156

Pelmatozoans diversified primarily during the Middle and Late Ordovician Period, with Early Ordovician records being much more limited, resulting in many gaps in our knowledge of the early stages of their diversification. Dissociated pelmatozoan ossicles have been found abundantly in one section in the Tonggao Formation (Tetragraptus approximatus Biozone, Floian, Early Ordovician). Most of the ossicles are thecal plates and stem ossicles from hemicosmitoid and glyptocystitoid cystoids. Thecal plates of ‘Cheirocrinus’ sp., Polycosmites sp., and other plates of uncertain affinity are described. A different ossicle type, Pentagonopentagonalis (col.), may represent crinoid remains; this would be one of the earliest occurrences of the class. The thecal ossicles and columnals are all considered, as both sets of data are desirable to determine the most complete estimate of generic diversity. The echinoderm ossicles may have been transported in from shallower water palaeoenvironments and clusters of ossicles may represent coprolites or regurgitates. Estimates of Early Ordovician palaeogeography that place this site at 30°S or near the palaeoequator are supported by the physiological requirements of the primitive echinoderms described herein. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Amplitude Variation with Offset Responses Modeling Study of Walkaway Vertical Seismic Profile Data at CO2 Geological Storage Site, Ketzin, Germany     

YANG Can  Sayed Hesammoddin KAZEMEINI  FAN Wenfang  Christopher JUHLIN  LIU Dameng 《《地质学报》英文版》2011,85(5):1118-1126

An important component of any CO2 sequestration project is seismic monitoring for tracking changes in subsurface physical properties, such as velocity and density. Different reservoirs have different amplitude variation with offset (AVO) responses, which can define underground conditions. In the present paper we investigate walkaway vertical seismic profile (VSP) AVO response to CO2 injection at the Ketzin site, the first European onshore CO2 sequestration pilot study dealing with research on geological storage of CO2. First, we performed rock physics analysis to evaluate the effect of injected CO2 on seismic velocity using the Biot-Gassmann equation. On the basis of this model, the seismic response for different CO2 injection saturation was studied using ray tracing modeling. We then created synthetic walkaway VSP data, which we then processed. In contrast, synthetic seismic traces were created from borehole data. Finally, we found that the amplitude of CO2 injected sand layer with different gas saturations were increased with the offset when compared with the original brine target layer. This is the typical class III AVO anomaly for gas sand layer. The AVO responses matched the synthetic seismic traces very well. Therefore, walkaway VSP AVO response can monitor CO2 distribution in the Ketzin area.  相似文献   

Malargüe Group (Maastrichtian–Danian) deposits in the Neuquén Andes,Argentina: Implications for the onset of the first Atlantic transgression related to Western Gondwana break-up     

B. Aguirre-Urreta  M. Tunik  M. Naipauer  P. Pazos  E. Ottone  M. Fanning  V.A. Ramos 《Gondwana Research》2011,19(2):482-494

The discovery of marine to brackish and fresh-water carbonates in the inner Agrio fold-and-thrust belt at Pichaihue, Neuquén, Argentina, located to the west of the Andean orogenic front, imposes important constraints on the paleogeography of the first Atlantic transgression in the Neuquén Basin related to the break-up of Western Gondwana. The constraints on the timing and areal extent of these deposits shed light on the early uplift history of the southern Andes. These limestones are part of the Maastrichtian–Danian Malargüe Group, which was previously only known from its exposures in the extra-Andean area, representing foreland basin deposits. The presence of stromatolites, oncoids, serpulids, bivalves and gastropods as well as silicified stems of macrophytes indicates a shallow marine, partially brackish environment associated with non-marine deposits. These strata are interfingered with and overlie distal tuffs and proximal pyroclastic flows, whose geochemical characteristics point to a magmatic arc source. SHRIMP U–Pb dating of volcanic zircons of these tuffs yielded an age of 64.3 ± 0.9 Ma that confirms the correlation to the Maastrichtian–Paleocene marine transgression from the Atlantic Ocean. The change in the paleoslope of the basin from Pacific Ocean transgressions to this Atlantic transgression is related to the uplift and deformation of the Agrio fold-and-thrust belt. The Pichaihue Limestone is unconformably deposited on volcanic agglomerates which in turn unconformably overlie Early Cretaceous deposits. Based on these data, it is confirmed that the Cretaceous uplift of the Andes was episodic at these latitudes, with a first pulse in the Cenomanian and a second one in pre-Maastrichtian times. The episodic uplift is also related to an eastward migration of the thrust front and the volcanic arc, related to a previously proposed shallowing of the subduction zone. These episodes were controlled by the Western Gondwana break-up and the beginning of absolute motion of South America toward the west.  相似文献   

The Growth of Estuarine Resources (Zostera marina, Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians, Cyprinodon variegatus) in Response to Nutrient Loading and Enhanced Suspension Feeding by Adult Shellfish     

Charles C. Wall  Bradley J. Peterson  Christopher J. Gobler 《Estuaries and Coasts》2011,34(6):1262-1277

While many coastal ecosystems previously supported high densities of seagrass and abundant bivalves, the impacts of overfishing, eutrophication, harmful algal blooms, and habitat loss have collectively contributed to the decline of these important resources. Despite improvements in wastewater treatment in some watersheds and subsequent reduced nutrient loading to neighboring estuaries, seagrass and bivalve populations in these locations have generally not recovered. We performed three mesocosm experiments to simultaneously examine the contrasting effects of nutrient loading and historic suspension-feeding bivalve densities on the growth of eelgrass (Zostera marina), juvenile bivalves (northern quahogs, Mercenaria mercenaria; eastern oysters, Crassostrea virginica; and bay scallops, Argopecten irradians), and juvenile planktivorous fish (sheepshead minnow, Cyprinodon variegatus). High nutrient loading rates led to significantly higher phytoplankton (chlorophyll a) levels in all experiments, significantly increased growth of juvenile bivalves relative to controls with lower nutrient loading rates in two experiments, and significantly reduced the growth of eelgrass in one experiment. The filtration provided by adult suspension feeders (M. mercenaria and C. virginica) significantly decreased phytoplankton levels in all experiments, significantly increased light penetration and the growth of eelgrass in one experiment, and significantly decreased the growth of juvenile bivalves and fish in two experiments, all relative to controls with no filtration from adult suspension feeders. These results demonstrate that an appropriate level of nutrient loading can have a positive effect on some estuarine resources and that bivalve filtration can mediate the effects of nutrient loading to the benefit or detriment of different estuarine resources. Future ecosystem-based approaches will need to simultaneously account for anthropogenic nutrient loading and bivalve restoration to successfully manage estuarine resources.  相似文献   

A conceptual framework of groundwater flow in some crystalline aquifers in Southeastern Ghana     

Sandow Mark Yidana  Samuel Ganyaglo  Bruce Banoeng-Yakubo  Thomas Akabzaa 《Journal of African Earth Sciences》2011,59(2-3):185-194

A conceptual groundwater flow model was developed for the crystalline aquifers in southeastern part of the Eastern region, Ghana. The objective was to determine approximate levels of groundwater recharge, estimate aquifer hydraulic parameters, and then test various scenarios of groundwater extraction under the current conditions of recharge. A steady state groundwater flow model has been calibrated against measured water levels of 19 wells in the area. The resulting recharge is estimated to range from 8.97 × 10^?5 m/d to 7.14 × 10^?4 m/d resulting in a basin wide average recharge of about 9.6% of total annual precipitation, which results in a basin wide quantitative recharge of about 2.4 million m³/d in the area. This compares to recharge estimated from the chloride mass balance of 7.6% of precipitation determined in this study. The general groundwater flow in the area has also been determined to conform to the general northeast–southwest structural grain of the country. The implication is that the general hydrogeology is controlled by post genetic structural entities imposed on the rocks to create ingresses for sufficient groundwater storage and transport. Calibrated aquifer hydraulic conductivities range between 0.99 m/d and over 19.4 m/d. There is a significant contribution of groundwater discharge to stream flow in the study area. Increasing groundwater extraction will have an effect on stream flow. This study finds that the current groundwater extraction levels represent only 0.17% of the annual recharge from precipitation, and that groundwater can sustain future increased groundwater demands from population growth and industrialization.  相似文献