Post-Last Glacial Maximum evolution of a “fjord-type” lake based on high-resolution seismic data: the Lago Roca/Acigami (southern Tierra del Fuego,Argentina/Chile)     

Donaldo Mauricio Bran  Jorge Gabriel Lozano  Dario Civile  Emanuele Lodolo  María E. Cerredo  Alejandro Tassone  Luca Baradello  Maurizio Grossi  Juan Vilas 《第四纪科学杂志》2020,35(3):396-409

Lago Roca/Acigami is a “fjord-type” lake located in the southernmost part of South America, in the proximity of the Beagle Channel. A high-resolution seismic survey was carried out to analyse the seismic stratigraphy of the lake and to shed some light on the post-Last Glacial Maximum history of the area. Six seismic units were recognised, and their nature and depositional context were interpreted using seismic stratigraphy and acoustic facies analysis. A buried large ridge was identified within the glacial unit (SU1), interpreted as a frontal moraine that indicates a stabilisation phase. After retreat of the glacier from the basin, the trough was flooded by meltwater and a lake developed (SU2). The seismic facies, from bottom to top, depict a transition from ice-contact (SU2; SU3) to ice-distal proglacial conditions (SU4). A thick draping unit (SU5) marks a marine transgressive event and the instauration of a fjord environment in the basin. The marine transgression was a rapid event preceded by a fall in the lake level that caused an erosional unconformity. During the fjord phase the sedimentation remained controlled by meltwater discharge. Sea level fall, and subsequent disconnection from the Beagle Channel was accompanied by a progradation of the glaciofluvial deltaic sediments and the occurrence of several mass-wasting deposits (SU6). © 2019 John Wiley & Sons, Ltd.  相似文献   

Mercury: Absence of crystalline Fe²⁺ in the regolith     

Faith Vilas 《Icarus》1985,64(1):133-138

Reflectance spectra of terrain on Mercury containing both smooth plains and intercrater plains were obtained using a charge-coupled device spectrograph on 24 November 1984. The composite spectrum covers the 0.53- to 1.02-μm spectral range with a resolution of 17 Å. Absorption features due to telluric H₂O absorption are clearly mapped around 0.73, 0.82, and 0.93 μm. No evidence exists in the new spectrum for the proposed orthopyroxene absorption centered near 0.9 μm seen in older spectra of this terrain. The surface material is probably highly reduced, with any iron present in metallic form. Based upon the new spectrum, a history of heavy micrometeoroid bombardment of the Mercurian surface is suggested, resulting in a surface regolith primarily comprised of agglutinates.  相似文献   

Pangea, the geoid, and the paths of virtual geomagnetic poles during polarity reversals     

H. Vizn  M. Mena  J.F. Vilas 《Journal of South American Earth Sciences》1992,6(4)

The elongated distribution of virtual geomagnetic poles (VGPs) of South American Jurassic units has been interpreted as reflecting: 1) the behavior of the Earth's magnetic field (EMF), and 2) apparent polar shift of the South American plate before the breakup of Gondwana. New paleomagnetic data do not support the latter. We analyze these Jurassic VGPs together with those of other Pangean continents, considering a model based on the following assumptions: 1) Pangea was assembled over the present African-Atlantic geoid high; 2) the hotspot framework has not been significantly deformed over the last 200 Ma; 3) the present geoid matches the present topography of the core mantle boundary (CMB); 4) the overall topography of the CMB remains unchanged for long periods of time. We plotted Jurassic VGPs of Pangean continents, previously returned to a fixed-hotspot framework, on a map of the present topography of the CMB. The VGPs seem to follow the trend of regions of increased CMB seismic velocities. When a polarity reversal was registered by a Jurassic unit, the path of the VGPs was channeled on zones that have been observed in translational paths for the last 10 Ma.  相似文献   

Gas-charged sediments in the Ría de Arousa: Short- to long-term fluctuations?     

R. Diez  S. García-Gil  R. Durn  F. Vilas 《Estuarine, Coastal and Shelf Science》2007,71(3-4):467-479

Repeated surveys at control sites in the gas accumulation fields from the Ría de Arousa (Galicia, NW Spain) have shown that the top of the acoustic turbidity fluctuates vertically. The vertical movement of gas fronts is more apparent in the gas fields located in the outer ría, where fluctuations of up to 1.5 ms (1.1 m) have been detected. At the inner ría, the depth to the top of the gas horizons varied between 0.5 and 1 ms (40 to 80 cm). Short-term (diurnal) fluctuations associated with the hydrostatic pressure variations of the water column during a tidal cycle have been identified as the most likely factors to explain fluctuations of gas fields in the outer ría. At the inner ría, gas fields are affected by these short-term pressure changes superimposed on long-term temperature and salinity variations of bottom water masses. This combination produces a different pattern of variation in gas fields from the inner and the outer ría. Prominent pockmarks and acoustic plumes have also been monitored throughout the three seismic surveys. Many of these pockmarks exhibit active characteristics, including the observance of plumes of escaping fluids and sediment.  相似文献   

Beach morphodynamics forcements in oiled shorelines: Coupled physical and chemical processes during and after fuel burial     

Bernabeu AM  Nuez de la Fuente M  Rey D  Rubio B  Vilas F  Medina R  González ME 《Marine pollution bulletin》2006,52(10):1156-1168

In November 2002, the sinking of the Prestige oil tanker off the Galician coast (N.W. Spain) caused the largest ecological catastrophe in the history of Spain, affecting the coast called the 'Costa da Morte' (Galicia, N.W. Spain). This work is focused on the study of the oil contamination of the intertidal area of two beaches located on this stretch of coast. The study of twenty cores extracted from both beaches has identified fuel embedded in the sedimentary column up to a depth of 2.38 m (this being the maximum depth of extraction). This, along with the presence of oil below the groundwater indicates the existence of a new factor which determines the burial of oil: the morphodynamic behaviour of the beach. Furthermore, this morphodynamic variation conditions the physical appearance of the buried oil. Four different types have been identified: tar-balls (cm), particles (mm), oil coatings on sediment grains and on emulsion, with distribution patterns conditioned by the degree of wave exposure. The analysis of the information obtained have permitted the development of a conceptual model of the burial and oil evolution in the sedimentary column in relation to wave exposure, and thus to the morphodynamic variability of the beach.  相似文献   

Palaeomagnetism and K-Ar ages of triassic igneous rocks from the Ischigualasto-Ischichuca Basin and Puesto Viejo Formation,Argentina     

Daniel A. Valencio  JoséE. Mendía  Juan F. Vilas 《Earth and Planetary Science Letters》1975,26(3):319-330

The palaeomagnetism of Middle Triassic (224 ± 5 m.y.) igneous rocks from the Ischigualasto-Ischichuca Basin (67°40′W, 30°20′S) was investigated through 86 oriented hand samples from 11 sites. At least one reversal of the geomagnetic field has been found in these rocks. Nine sites yield a palaeomagnetic pole at 239°E, 79°S (α₉₅ = 15°, k = 13).The K-Ar age determinations of five igneous units of the Puesto Viejo Formation give a mean age of 232 ± 4 m.y. (Early Triassic). The palaeomagnetism of six igneous units of the Puesto Viejo Formation (68°W, 35°S) was investigated through 60 oriented samples. These units, two reversed relative to the present magnetic field of the Earth and four normal, yield a pole at 236°E, 76°S (α₉₅ = 18°, k = 14).Data from the Puesto Viejo Formation indicate, for the first time on the basis of palaeomagnetic and radiometric data, that the Illawarra Zone, which defines the end of the Kiaman Magnetic Interval, extends at least down to 232 ± 4 m.y. within the Early Triassic. The palaeomagnetic poles for the igneous rocks of the Ischigualasto-Ischichuca Basin and Puesto Viejo Formation form an “age group” with the South American Triassic palaeomagnetic poles (mean pole position: 239°E, 77°S; α₉₅ = 6.6°, k = 190). The Middle and Upper Permian, Triassic and Middle Jurassic palaeomagnetic poles for South America would define a “time group” reflecting a quasi-static interval (mean pole position: 232°E, 81°S; α₉₅ = 4°, k = 131).  相似文献   

Pollution in intertidal sediments of San Simón Bay (Inner Ria de Vigo,NW of Spain): total heavy metal concentrations and speciation     

Alvarez-Iglesias P  Rubio B  Vilas F 《Marine pollution bulletin》2003,46(4):491-503

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Paleosecular variations recorded by Holocene-Pleistocene sediments from Lake El Trébol (Patagonia, Argentina)     

M.A. Irurzun  C.S.G. Gogorza  M.A.E. Chaparro  J.M. Lirio  J.F. Vilas  A.M. Sinito 《Physics of the Earth and Planetary Interiors》2006,154(1):1-17

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Palaeomagnetism of the Silurian Lipeón formation, NW Argentina, and the Gondwana apparent polar wander path     

C. M. Conti  A. E. Rapalini  J. F. Vilas 《Geophysical Journal International》1995,121(3):848-862

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Palaeomagnetism of a sequence of Upper Palaeozoic-Lower Mesozoic red beds from Argentina     

Ana M. Sinito  Daniel A. Valencio  Juan F. Vilas 《Geophysical Journal International》1979,58(2):237-247

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