Upper Oligocene-Lower Miocene shallowing-upwardlacustrine sequences controlled by periodic and non-periodic processes(Ebro Basin, northeastern Spain)     

Arantxa Luzón  Angel González  Arsenio Muñoz  Belén Sánchez-Valverde 《Journal of Paleolimnology》2002,28(4):441-456

The lacustrine facies from two sections (Candasnos and Fraga) ofthe Oligocene-Miocene Torrente de Cinca lithostratigraphic Unit in thecentral part of the Ebro Basin (Spain) have been analysed to determine theinfluence of orbital parameters in lacustrine sedimentation. The unit ispredominantly composed of limestones and marls, and represents a shallowlacustrine freshwater system. The sedimentological features of the faciesstudied demonstrate that the lower part of the Candasnos section representsoffshore lacustrine subenvironments whereas the upper part, and the whole ofthe Fraga section, characterise marginal lacustrine areas. Series of stratalthickness variations of limestone, marl, and limestone/marl couplets fromboth sections have been analysed using spectral analysis. This shows thatinformation corresponding to periodic cycles only appears in the offshorefacies, that is to say, in the lower part of Candasnos section, and disappearsin the marginal facies where non-periodic cycles exist. Furthermore, thespectral analysis of the offshore facies highlights the existence of a peak inthe power spectrum with a period of around 7 (6.8 to 7.8) that can berecognised in the field as shallowing-upward lacustrine sequences.Magnetostratigraphic data from the Candasnos section allow us to establish atime span of 2,808 years for the limestone/marl couplet from the lower partof this section, and between 19,000 and 22,000 years for the periodic cycleidentified, thus representing the climatic precession cycle. Shallowingsequences from marginal areas do not correspond with any periodiccycle.  相似文献   

Some Aspects of Resource Uncertainty and Their Economic Consequences in Assessment of the 1002 Area of the Arctic National Wildlife Refuge     

Attanasi  Emil D.  Schuenemeyer  John H. 《Natural Resources Research》2002,11(2):109-120

Natural Resources Research - Exploration ventures in frontier areas have high risks. Before committing to them, firms prepare regional resource assessments to evaluate the potential payoffs. With...  相似文献   

A method to reduce the influence of ice-rafted debris on a grain size record from northern Fram Strait, Arctic Ocean   总被引：2，自引：0，他引：2  

H. Christian Hass 《Polar research》2002,21(2):299-306

The granulometric composition of terrigenous deep-sea sediments provides information on current speed if certain frame conditions are fulfilled. These include that current transport is the only transport process. At high latitudes this type of investigation is impaired due to the influence of ice-rafted debris (IRD) which contaminates the current-sorted grain size fractions. This study presents a new method that addresses this problem by setting the ice-rafted sand in relation to the silt of both current- and ice-transported origin. Deviations from the resulting regression function are then used to determine the behaviour of the silt mean grain size as a function of current speed largely independent from IRD bias. The study is based on sediments from the Yermak Plateau, Arctic Ocean, a region influenced by IRD brought with the south-headed Transpolar Drift and by north-directed bottom currents. The IRD correction results in displaying changes of current speed at much higher clarity; climate forcing of the currents becomes more evident. For example, the 8200 year cold event shows up as a major event in the corrected record whereas it is hardly visible in the original record.  相似文献   

Tectono-sedimentary processes along an active marine/lacustrine half-graben margin: Alkyonides Gulf, E. Gulf of Corinth, Greece     

M. R. Leeder  R. E. Ll. Collier  †  L. H. Abdul Aziz  M. Trout  †  G. Ferentinos  ‡  G. Papatheodorou‡  E. Lyberis‡ 《Basin Research》2002,14(1):25-41

ABSTRACT The Alkyonides half‐graben is separated from the Gerania Range to the south by active faults whose offshore traces are mapped in detail. The East Alkyonides and Psatha Faults have well‐defined, Holocene‐active tip zones and cannot be extrapolated from the onshore Skinos Fault into a single continuous surface trace. During the late Quaternary, catchments draining the step‐faulted range front have supplied sediment to alluvial fans along a subsiding marine ramp margin in the hangingwall of the Skinos Fault, to shelf ledge fans on the uplifting footwall to the East Alkyonides Fault and to the Alepochori submarine fan in the hangingwall of the latter. During late Pleistocene lowstand times (c. 70–12 ka), sediment was deposited in Lake Corinth as fan deltas on the subsiding Skinos shelf ramp which acted as a sediment trap for the adjacent 360 m deep submarine basin plain. At the same time, the uplifting eastern shelf ledge was exposed, eroded and bypassed in favour of deposition on the Alepochori submarine fan. During Holocene times, the Skinos bajada was first the site of stability and soil formation, and then of substantial deposition before modern marine erosion cut a prominent cliffline. The uplifting eastern shelf ledge has developed substantial Holocene fan lobe depositional sequences as sediment‐laden underflows have traversed it via outlet channels. We estimate mean Holocene displacement rates towards the tip of the Psatha Fault in the range 0.7–0.8 mm year^?1. Raised Holocene coastal notches indicate that this may be further partitioned into about 0.2 mm year^?1 of footwall uplift and hence 0.5–0.6 mm year^?1 of hangingwall subsidence. Holocene displacement rates towards the tip of the active East Alkyonides Fault are in the range 0.2–0.3 mm year^?1. Any uplift of the West Alkyonides Fault footwall is not keeping pace with subsidence of the Skinos Fault hangingwall, as revealed by lowstand shelf fan deltas which show internal clinoforms indicative of aggradational deposition in response to relative base‐level rise due to active hangingwall subsidence along the Skinos Fault. Total subsidence here during the last 58 kyr lowstand interval of Lake Corinth was some 20 m, indicating a reduced net displacement rate compared to estimates of late Holocene (< 2000 bp ) activity from onshore palaeoseismology. This discrepancy may be due to the competition between uplift on the West Alkyonides Fault and subsidence on the onshore Skinos Fault, or may reflect unsteady rates of Skinos Fault displacement over tens of thousands of years.  相似文献   

On the state of sublithospheric upper mantle beneath a supercontinent   总被引：2，自引：0，他引：2  

Jun Korenaga  Thomas H. Jordan 《Geophysical Journal International》2002,149(1):179-189

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A Bayes filter in Friedland form for INS/GPS vector gravimetry     

B. Schaffrin  J. H. Kwon 《Geophysical Journal International》2002,149(1):64-75

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Determining the magnetic field in the core–mantle boundary zone by non-harmonic downward continuation     

L. Ballani  H. Greiner-Mai  D. Stromeyer 《Geophysical Journal International》2002,149(2):374-389

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Non-smooth gravity problem with total variation penalization functional   总被引：1，自引：0，他引：1  

H. Bertete-Aguirre  E. Cherkaev  M. Oristaglio 《Geophysical Journal International》2002,149(2):499-507

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Bent-ray traveltime tomography and migration without ray tracing     

P. E. Ecoublet  S. C. Singh  C. H. Chapman  G. M. Jackson 《Geophysical Journal International》2002,149(3):633-645

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Gravity evidence for a larger Limpopo Belt in southern Africa and geodynamic implications   总被引：2，自引：0，他引：2  

R. T. Ranganai  A. B. Kampunzu  E. A. Atekwana  B. K. Paya  J. G. King  D. I. Koosimile  E. H. Stettler 《Geophysical Journal International》2002,149(3):F9-F14

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