We conducted a multichannel seismic reflection survey offshore Cape Roberts, Antarctica, and combined our findings with the results of the Cape Roberts International Drilling Project (CRP). This ...allows us to interpret Cenozoic tectonics in the southwest sector of the Ross Sea including the history of uplift of the Transantarctic Mountains (TAM) and subsidence of the Victoria Land Basin (VLB). Seismic stratigraphic sequences mapped offshore Cape Roberts arc tilted eastward and thicken into the VLB where they comprise more than half the fill seen on seismic records. Normal faults a few kilometers offshore cut these sequences and define a north trending rift graben. Drilling results from the CRP show that these strata are latest Eocene (?), Oligocene, and younger in age; much younger than previously inferred. We interpret this pattern to be due to an episode of E‐W extension and related subsidence that occurred across the major basins in the western Ross Sea during the early Cenozoic. The rift graben offshore and adjacent to Cape Roberts is bounded on the west by a major north trending fault zone. At Cape Roberts this fault system may have from 6 to 9 km of vertical separation. This fault system is part of a larger zone along the coastline in southern Victoria Land that accommodated uplift of the TAM in Oligocene time. We name it here the McMurdo Sound Fault Zone. A late Oligocene angular unconformity that is seen in seismic data and sampled by CRP drilling marks the end of east tilting of the stratigraphic sequences. We interpret this as the end of the main uplift of the TAM coinciding with a change from E‐W extension to NW‐SE oblique rifting at that time. Uplift of the TAM and subsidence in the VLB may be linked with seafloor spreading on the Adare Trough to the northwest of the Ross Sea between 43 and 26 Ma. This would imply a plate boundary between East and West Antarctica crossing through the western Ross Sea in Eocene and Oligocene time.
Sediments in the East China Sea Miller, J.H.; Bartek, L.R.; Potty, G.R. ...
IEEE journal of oceanic engineering,
10/2004, Letnik:
29, Številka:
4
Journal Article
Recenzirano
This paper describes measurements of sediments during the 2000-2001 Asian Seas International Acoustic Experiment in the East China Sea. A number of techniques were used to infer properties of these ...sediments, including gravity and piston cores, subbottom profiling using a water gun, long-range sediment tomography, and in situ measurement of conductivity. Historical data from echosounder records and cores showed two regions of surficial sediments in the experimental area: a silty area to the west and a sandy area to the east. The tomography, cores, and water-gun measurements confirm the two surficial sediment regions seen in the historical data and also indicate that the subbottom structure at the experimental site consists of a thin (0-3 m thick) layer of sandy sediment directly beneath the sea floor. Below this layer, there is an extensive package of sediment with relatively uniform acoustic attributes. Core analysis shows that the surface sediment layer varies in compressional wave speed from a low near 1600 m/s in the west side of the experiment area to 1660 m/s in the east side of the experiment area. Long-range sediment tomography inversions show a similar spatial variation in the surface layer properties. In addition, the layer thickness as determined from tomography is consistent with the estimates from subbottom profiling.
The far eastern continental shelf of the Ross Sea, Antarctica, has been relatively unexplored up to now. This region and western Marie Byrd Land are at the eastern limit of the Ross Sea rift, part of ...the West Antarctic rift system, one of the larger regions of extended crust in the world. The Ross Sea continental shelf west of Cape Colbeck and the Edward VII Peninsula in western Marie Byrd Land was investigated using marine geophysics during cruise 9601 of the research vessel ice breaker Nathaniel B. Palmer. The purpose was to determine the structural framework and tectonic history of the eastern border of the Ross Sea rift and to integrate this with what is known about western Marie Byrd Land. The region mapped is characterized by a passive margin with a flat overdeepened shelf cut by the north trending Colbeck Trough, an erosional feature formed in Miocene and later time by glacial downcutting that followed the locations of existing basement structures. Seismic sequences and unconformities identified in the Ross Sea were correlated into the Colbeck shelf area. The section comprises mostly undeformed glacial marine sequences of late Oligocene and younger age that are unconformably overlying late Early to Late Cretaceous and minor early Tertiary (?) faulted sequences. This unconformity is identified as RSU6, mapped elsewhere in the eastern Ross Sea. Two units are found below RSU6, each separated by an unconformity that is here named RSU7. These sequences fill north trending half grabens in the faulted basement and are interpreted as syn rift units. Unconformity RSU7 is correlated to the West Antarctic Erosion Surface mapped onshore in western Marie Byrd Land. The lack of thick early Tertiary sediments on the shelf suggests significant vertical tectonics. This onshore and offshore region was widely faulted in late Early and Late Cretaceous time, was high above sea level and was beveled by prolonged erosion, while subsiding steadily in Late Cretaceous and Cenozoic time. Subsidence was largely due to lithosphere cooling amplified later by glacial and sediment loading in Cenozoic time. Mylonites that have late Early Cretaceous cooling ages were dredged from the southeast wall of the Colbeck Trough. This finding and normal faults that we mapped in the eastern Ross Sea we attribute to detachment‐style extension in late Early Cretaceous time. This extension was directed subparallel to the trend of the present margin edge and occurred prior to the rifting of Campbell Plateau from Marie Byrd Land at ∼79 Ma. Cooling events onshore western Marie Byrd Land suggest the main extension began at ∼105 Ma. This is also the time of transition from subduction to extension elsewhere along the ancient Gondwana margin. Minor west tilting of the shelf during the late Cenozoic was the result of continued subsidence of the continental shelf along with possible uplift of western Marie Byrd Land associated with the Marie Byrd Land dome to the east. Early Tertiary extension in the western Ross Sea rift is not strongly reflected in the east side of the rift. A more robust correlation of the events here with the better known tectonic history on the west side of the Ross Sea rift awaits sampling and dating of the units we mapped on the Colbeck shelf.
Analyses by Barrett et al. (1989) of the stratigraphic sequences of the CIROS-1 drill core provided evidence of late Paleogene and early Neogene glacial advances and retreats that appear to correlate ...with the global eustatic curve of Haq et al. (1987). During Leg 2 of the
Polar Duke 90 (PD90) cruise in the Ross Sea approximately 650 km of highresolution seismic data were collected in McMurdo Sound with the main objective of facilitating regional correlation of stratigraphic events observed in the cores of the CIROS-1, DVDP-15, and MSSTS-1 drilling programs, and therefore providing an opportunity to test hypotheses on linkages between Cenozoic eustatic and Antarctic ice volume fluctuations.
Twenty unconformity-bound, seismic-stratigraphic sequences (labeled from top A to T) were identified in the McMurdo Sound PD90 data base. However, seismic data from the shallow shelf on which CIROS-1 was drilled show erosional surfaces at many levels, indicating a condensed section in this area. It is difficult to distinguish individual lithological units identified by Barrett et al. (1989) in the seismic data, but seismic units O, P and Q correspond to the upper Oligocene interval where they recognized 3 glacioeustatic events. These three sequences, totaling around 300 m in thickness, can be traced over a distance of almost 100 km. However, they lack the seismic characteristics of glacial facies identified by Anderson and Bartek (1992) and thus the significance of waxing and waning events suggested for upper Oligocene strata in CIROS-1 remains equivocal.
The younger sequences in the McMurdo Sound data base are largely Miocene (E-N), the oldest of these forming the upper 70 m in CIROS-1. These sequences can be traced 300 km north into the center of the Victoria Land basin, where they have seismic features characteristic of glacial facies. This suggests that ice sheets of continental scale (and hence large enough to affect eustasy) waxed and waned across the Ross Sea continental shelf at least 10 times during the Miocene. The data presented here for the Oligocene do not preclude similar ice sheet behavior, but are insufficient to test the hypothesis properly.
A quantitative approach was utilized to establish the nature of spatial and temporal variations of glaciomarine and subglacial seismic facies deposition in the Ross Sea. The Ross Sea is an excellent ...area to study Antarctic ice sheet volume variations because it receives ice sheet drainage from approximately 25% of the continent and it contains subsiding basins to preserve the stratigraphic record of the ice sheet volume fluctuations. This region receives most of the influence on deposition from the marine-based West Antarctic Ice Sheet which is believed to have been subject to catastrophic surges Hollin, J.T., 1962. On the glacial history of Antarctica. Journal of Glaciology, 4: 173–195. The Eastern Basin, in particular, has been subsiding, creating accommodation space in which to preserve the Plio-Pleistocene record of ice sheet fluctuations. Evidence from high-resolution seismic data in conjunction with DSDP Leg 28 drilling results are used to test hypotheses of paleo-ice sheet behavior. Here we present quantitative evidence for a dynamic polar style of glaciation (meaning that the ice sheets have had ‘dynamic’ or large ice volume change), not merely in the Plio-Pleistocene, but back to the Late Oligocene. High-resolution seismic data correlated to DSDP Sites 270–273 shows evidence of multiple ice sheet grounding events in central and eastern Ross Sea strata, a recipient of both West and East Antarctic Ice Sheets, from the Late Oligocene until the present. We suggest that the West and East Antarctic Ice Sheets are dynamic and have gone through a full spectrum of thermal states (temperate through polar) since the Late Oligocene and not necessarily in any particular preferred temporal order. Statistical analysis of the spatial distribution of seismic facies within ‘seismic cores’ indicates that tectonic influence on distribution of basal substrate is a significant contributor to spatial variability of subglacial depositional processes and therefore distribution of subglacial facies.
A new encapsulation technique to seal a vacuum-tube microcavity hermetically at low pressures, based on aluminium evaporation, is presented and its performance is compared to conventional ...low-pressure chemical vapour deposition (LPCVD) reactive sealing. The microdiode consists of an in-cavity recessed single-crystalline silicon cathode tip above which a polycrystalline silicon anode is suspended on a silicon-rich nitride layer. The diode cavity is cleared from the sacrificial oxide in buffered HF through the horizontal etch-access channels between the polysilicon anode and the silicon-rich nitride isolation layer. Vacuum sealing of the cavity using LPCVD polycrystalline silicon results in polysilicon deposits ( > 50 nm) inside the cavity, and thus in a non-acceptable degradation of the cathode-tip curvature. When sealing is performed using aluminium evaporation, no deposits inside the cavity are observed and pressures below 10 Pa can be expected. Applications of the technique presented are not restricted to micro vacuum diodes, but also include various type of hermetically sealed micromechanical structures, where deposits inside the sealed cavity are undesirable.
Piston cores collected from the Ross Sea continental shelf, Antarctica, were studied as part of a multi-scale analysis of glacial and glaciomarine stratigraphy and sedimentology. The objective of ...these analyses was to differentiate glaciomarine sediments from subglacially deformed tills. Results from analyses of microstructures, lithofacies and seafloor morphology indicate that glaciomarine and subglacially deformed sediments can be clearly distinguished and further characterized by variations in textural parameters. Overcompaction, as well as presence of stratification in sediments, are not considered critical criteria for distinguishing subglacial from glaciomarine deposits. Trough-shaped morphologies and fluted terrain strongly correlate with S-C and S-C-C- type shear-zone microstructures and indicate that subglacial deformation is an important process in these areas, confirming the presence of grounded ice on the shelf during formation of these landforms and deposits. Flat, smooth topographies, as well as (low-angle) slope environments, correspond to microfabrics which lack microscopic shear-zone geometries and contain dropstones, angular-sediment clasts, large-shell fragments and slight sorting in sandy layers, which imply ice-shelf or open-water conditions present during deposition.
The transition from the Eocene to the Oligocene epochs was the most significant event in earth history since the extinction of dinosaurs. As the first Antarctic ice sheets appeared, major extinctions ...and faunal turnovers took place on the land and in the sea, eliminating forms adapted to a tropical world and replacing them with the ancestors of most of our modern animal and plant life. Through a detailed study of climatic conditions and of organisms buried in Eocene-Oligocene sediments, this volume shows that the separation of Antarctica from Australia was a critical factor in changing oceanic circulation and ultimately world climate. In this book forty-eight leading scientists examine the full range of Eocene and Oligocene phenomena. Their articles cover nearly every major group of organisms in the ocean and on land and include evidence from paleontology, stable isotopes, sedimentology, seismology, and computer climatic modeling. The volume concludes with an update of the geochronologic framework of the late Paleogene.
Originally published in 1992.
ThePrinceton Legacy Libraryuses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
A new pixel detector for the CMS experiment was built in order to cope with the instantaneous luminosities anticipated for the Phase~I Upgrade of the LHC. The new CMS pixel detector provides four-hit ...tracking with a reduced material budget as well as new cooling and powering schemes. A new front-end readout chip mitigates buffering and bandwidth limitations, and allows operation at low comparator thresholds. In this paper, comprehensive test beam studies are presented, which have been conducted to verify the design and to quantify the performance of the new detector assemblies in terms of tracking efficiency and spatial resolution. Under optimal conditions, the tracking efficiency is \(99.95\pm0.05\,\%\), while the intrinsic spatial resolutions are \(4.80\pm0.25\,\mu \mathrm{m}\) and \(7.99\pm0.21\,\mu \mathrm{m}\) along the \(100\,\mu \mathrm{m}\) and \(150\,\mu \mathrm{m}\) pixel pitch, respectively. The findings are compared to a detailed Monte Carlo simulation of the pixel detector and good agreement is found.
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