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291.
Two-dimensional thermal-mechanical numerical models show that Rayleigh-Taylor-type (RT) gravitational removal of high-density lithosphere may produce significant surface deformation (vertical deflection 〉1000 m) in the interior of a continental plate.A reasonable range of crustal strengths and thicknesses,representing a variation from a stable continental interior to a hot orogen with a thick crust,is examined to study crustal deformation and the surface deflection in response to an RT instability.In general,three types of surface deflection are observed during the RT drip event:(1) subsidence and negative topography; (2) uplift and positive topography; (3) subsidence followed by uplift and inverted topography.One key factor that determines the surface expression is the crustal thickness.Models with a thin crust mainly show subsidence and develop a basin.In the thick crust models,surface expressions are more variable,depending on the crustal strength and depth of highdensity anomaly.With weak crust and a deep high-density anomaly,the RT drip is decoupled from the overlying crust,and the surface exhibits uplift or little deflection,as the RT drip induces contraction and thickening of the overlying crust.In contrast,with a strong crust and shallow anomaly,the surface is more strongly coupled with the drip and undergoes subsidence,followed by uplift. 相似文献
292.
Anne Marie Treguier Claire Gourcuff Pascale Lherminier Herle Mercier Bernard Barnier Gurvan Madec Jean-Marc Molines Thierry Penduff Lars Czeschel Claus Böning 《Ocean Dynamics》2006,56(5-6):568-580
Numerical models are used to estimate the meridional overturning and transports along the paths of two hydrographic cruises,
carried out in 1997 and 2002 from Greenland to Portugal. We have examined the influence of the different paths of the two
cruises and found that it could explain 0.4 to 2 Sv of difference in overturning (the precise value is model-dependent). Models
show a decrease in the overturning circulation between 1997 and 2002, with different amplitudes. The CLIPPER ATL6 model reproduces
well the observed weakening of the overturning in density coordinates between the cruises; in the model, the change is due
to the combination of interannual and high-frequency forcing and internal variability associated with eddies and meanders.
Examination of the -coordinate overturning reveals model–data discrepancies: the vertical structure in the models does not change as much as
the observed one. The East Greenland current variability is mainly wind-forced in the ATL6 model, while fluctuations due to
eddies and instabilities explain a large part of the North Atlantic Current variability. The time-residual transport of dense
water and heat due to eddy correlations between currents and properties is small across this section, which is normal to the
direction of the main current. 相似文献
293.
Marie Grace Pamela G. Faylona Claire E. Lazareth Anne‐Marie Smah Sandrine Caquineau Hugues Boucher Wilfredo P. Ronquillo 《Geoarchaeology》2011,26(6):888-901
Tridacnidae shells, a valuable archive of past environments, are common in the Balobok Rockshelter archaeological site on Sanga‐Sanga Island in the south Philippines. This site was occupied during the mid‐Holocene (ca. 5000–8800 14C yr B.P.), a period of Neolithic cultural expansion in the Philippines. This paper focuses on the preservation of two shell specimens, Hippopus hippopus and Tridacna maxima, unearthed from two mid‐Holocene layers within the rockshelter. The shells' mineralogy and microstructure (prismatic and crossed‐lamellar) were studied using micro‐Fourier transform infrared spectroscopy and scanning electron microscopy to determine if the samples were suitable as paleoenvironmental records. Both shells are still aragonitic but aragonite crystals of both microstructure types are partly dissolved. This dissolution, characteristic of meteoric water alteration, precludes their utility in paleoenvironmental geochemical studies. Nevertheless, these shells are abundant in archaeological sites in the region and may be better preserved in other depositional contexts; more studies on Philippine Tridacnidae shell diagenesis are needed. © 2011 Wiley Periodicals, Inc. 相似文献