scholarly journals Autochthonous v. accreted terrane development of continental margins: a revised in situ tectonic history of the Antarctic Peninsula

2015 ◽  
Vol 172 (6) ◽  
pp. 822-835 ◽  
Author(s):  
A. Burton-Johnson ◽  
T. R. Riley
Keyword(s):  
Antarctic Peninsula ◽  
Continental Margins ◽  
Tectonic History ◽  
History Of ◽  
The Antarctic

New trigonioid bivalves from the Early Jurassic to earliest Cretaceous of the Antarctic Peninsula region: systematics and austral paleobiogeography

1995 ◽  
Vol 69 (1) ◽  
pp. 66-84 ◽  
Author(s):  
Simon R. A. Kelly
Keyword(s):  
New Zealand ◽  
Antarctic Peninsula ◽  
Southern Africa ◽  
Late Jurassic ◽  
Early Jurassic ◽  
South Shetland Islands ◽  
Shetland Islands ◽  
Livingston Island ◽  
History Of ◽  
The Antarctic

New discoveries of trigonioid bivalves are documented from three areas in the Antartic Peninsula: the Fossil Bluff Group of Alexander Island, the Latady Formation of the Orville Coast, and the Byers Group of Livingston Island, South Shetland Islands. Eleven taxa are described, representing six genera or subgenera. The faunas are characterized by genera including Vaugonia (Vaugonia), the first Early Jurassic trigonioid recognized on the continent; Vaugonia (V.) and V. (Orthotrigonia?) in the Late Jurassic; and Iotrigonia (Iotrigonia), Myophorella (Scaphogonia), and Pterotrigonia (Pterotrigonia), which span the Jurassic–Cretaceous boundary, reaching the Berriasian stage. The following species are new: Pterotrigonia (P.) cramei n. sp., Pterotrigonia (P.) thomsoni n. sp., Vaugonia (V.) orvillensis n. sp., and V. (Orthotrigonia?) quiltyi n. sp. The faunas show affinities with those of New Zealand and southern Africa. Trigonioids characterize the shallower marine biofacies in the Jurassic of the Antarctic and reflect the principal shallowing events in the history of the region.

scholarly journals Electrical Resistivity of Ice from the Antarctic Peninsula, Antarctica

1984 ◽  
Vol 30 (106) ◽  
pp. 289-295 ◽  
Author(s):  
John M. Reynolds ◽  
J. G. Paren
Keyword(s):  
Antarctic Peninsula ◽  
Flow Line ◽  
Polar Regions ◽  
List Type ◽  
Electrical Measurements ◽  
Ice Shelf ◽  
Ice Shelves ◽  
History Of ◽  
Surface Ice ◽  
The Antarctic

AbstractGeoresistivity soundings have been carried out at four sites in the Antarctic Peninsula. The objective of the work was to investigate the electrical behaviour of ice from an area where substantial melting occurs in summer and from contrasting thermal regimes. Electrical measurements made at three sites along a flow line within George VI Ice Shelf reveal that:(a)the resistivity of deep ice is similar to that of other Antarctic ice shelves,(b)the resistivity of the ice-shelf surface, which is affected by the percolation and refreezing of melt water, is similar to that of deep ice and hence the ice is polar in character.A compilation of published resistivities of deep ice from polar regions shows that the range of resistivities is very narrow (0.4 –2.0) x 105Ω m between –2 and – 29°C, irrespective of the physical setting and history of the ice. Typically, resistivity is within a factor of two of 80 kΩ m at –20° C with an activation energy of 0.22 eV. In contrast, the resistivity of surface ice at Wormald Ice Piedmont, where the ice is at 0°C throughout, is two orders of magnitude higher and falls at the lower end of the range of resistivities for temperate ice.

scholarly journals In-situ aircraft observations of ice concentrations within clouds over the Antarctic Peninsula and Larsen Ice Shelf

2012 ◽  
Vol 12 (7) ◽  
pp. 17295-17345
Author(s):  
D. P. Grosvenor ◽  
T. W. Choularton ◽  
T. Lachlan-Cope ◽  
M. W. Gallagher ◽  
J. Crosier ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Particle Production ◽  
Supercooled Liquid ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Ice Shelf ◽  
Aircraft Observations ◽  
The Antarctic ◽  
Larsen Ice Shelf

Abstract. In-situ aircraft observations of ice crystal concentrations in Antarctic clouds are presented for the first time. Orographic, layer and wave clouds around the Antarctic Peninsula and Larsen Ice shelf regions were penetrated by the British Antarctic Survey's Twin Otter Aircraft, which was equipped with modern cloud physics probes. The clouds studied were mostly in the free troposphere and hence ice crystals blown from the surface are unlikely to have been a major source for the ice phase. The temperature range covered by the experiments was 0 to −21°C. The clouds were found to contain supercooled liquid water in most regions and at heterogeneous ice formation temperatures ice crystal concentrations (60 s averages) were often less than 0.07 l−1, although values up to 0.22 l−1 were observed. Estimates of observed aerosol concentrations were used as input into the DeMott et al., 2010 ice nuclei (IN) parameterisation. The observed ice crystal number concentrations were generally in broad agreement with the IN predictions, although on the whole the predicted values were higher. Possible reasons for this are discussed and include the lack of IN observations in this region with which to characterise the parameterisation, and/or problems in relating ice concentration measurements to IN concentrations. Other IN parameterisations significantly overestimated the number of ice particles. Generally ice particle concentrations were much lower than found in clouds in middle latitudes for a given temperature. Higher ice crystal concentrations were sometimes observed at temperatures warmer than −9 °C, with values of several per litre reached. These were attributable to secondary ice particle production by the Hallett Mossop process. Even in this temperature range it was observed that there were regions with little or no ice that were dominated by supercooled liquid water. It is likely that in some cases this was due to a lack of seeding ice crystals to act as rimers to initiate secondary ice particle production. This highlights the complicated nature of this process and indicates that the accurate representation of it in global models is likely to represent a challenge. However, the contrast between Hallett Mossop zone ice concentrations and the fairly low concentrations of heterogeneously nucleated ice suggests that the Hallet Mossop process has the potential to be very important in remote, pristine regions such as around the Antarctic coast.

INTERPRETING REACTION HISTORIES AND P-T-T PATHS FROM IN-SITU MONAZITE AND XENOTIME PETROCHRONOLOGY: IMPLICATIONS FOR THE TECTONIC HISTORY OF NEW ENGLAND

2020 ◽  
Author(s):  
Ian W. Hillenbrand ◽  
◽  
Michael L. Williams ◽  
Michael J. Jercinovic ◽  
Daniel J. Tjapkes
Keyword(s):  
New England ◽  
Tectonic History ◽  
History Of

scholarly journals Glacier Fluctuations in George VI Sound Area, West Antarctica (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 345 ◽  
Author(s):  
C.M. Clapperton ◽  
D.E. Sugden
Keyword(s):  
Antarctic Peninsula ◽  
Ice Age ◽  
List Type ◽  
West Antarctica ◽  
Ice Shelf ◽  
Scotia Sea ◽  
Field Evidence ◽  
Glacial Chronology ◽  
History Of ◽  
The Antarctic

George VI Sound lies between Alexander Island and the Antarctic Peninsula and is over 20 km wide and 500 km long. At present an ice shelf fills the sound and is nourished largely by ice from the Antarctic Peninsula which flows across the sound to ground against the coast of Alexander Island. Ice-free areas, comprising small nunataks and larger massifs, fringe both sides of the sound and contain evidence of the former glacial history of the area. This paper describes the field evidence in detail and uses geomorphological and sedimentary analyses to put forward a relative glacial chronology, constrained by two absolute dates. The chronology distinguishes: (1) a maximum state during which all ice-free areas were submerged by ice flowing into George VI Sound from both the Antarctic Peninsula and Alexander Island and thence along the sound as an ice stream. This occurred in the late Wisconsin and followed an interstadial or interglacial when George VI Sound was free of an ice shelf. (2) a valley-based stadial during overall deglaciation represented by pronounced marginal moraines on Alexander Island. (3) deglaciation to a stage where there was less landbased ice on Alexander Island than today. At this stage isostatic recovery was incomplete, relative sealevel was higher, and George VI Ice Shelf penetrated further into embayments on Alexander Island than at present. (4) probable disappearance of George VI Ice Shelf by 6.5 14C ka BP. (5) neoglacial readvance of local glaciers on Alexander Island to form three closely spaced terminal moraines and the growth of a new George VI Ice Shelf which was again more extensive than at present. (6) subsequent oscillations of both smaller Alexander Island glaciers and George VI Ice Shelf probably during the Little Ice Age. These fluctuations are similar to those in other sub-Antarctic Islands in the Scotia Sea and also in southern Chile.

Present-day in-situ stresses versus paleo-stresses for locating sweet spots in unconventional reservoirs

2013 ◽  
Vol 53 (1) ◽  
pp. 217 ◽  
Author(s):  
Hani Abul Khair ◽  
Dennis Cooke ◽  
Martin Hand
Keyword(s):  
Sweet Spot ◽  
Principal Stresses ◽  
Tectonic History ◽  
In Situ Stresses ◽  
Calculated Stress ◽  
History Of ◽  
Software Codes ◽  
Sweet Spots ◽  
Element Method

The effect of stresses on permeability is a combination of external stress and pore pressure. The authors examine if and how present-day in-situ stresses and the spatial distribution of permeable locations in the Moomba-Big Lake fields in the Cooper Basin are correlated. Image logs, well logs, and formation tests are analysed and the orientation and magnitudes of the three principal stresses are calculated. A 3D model was constructed and the calculated stress magnitudes and orientations were applied to the model using the software Poly3D. The resulting stress distribution in the present-day stress state showed a potential sweet spot in the Big Lake field, which is presently the location of a gas pool that forms, with the Moomba field, one-third of the gas reserve in SA. No potential sweet spots, however, are located in the Moomba area. The authors also used the finite element method (FEM) and the boundary element method (BEM) for modelling the behaviour of folds, fractures, and faults and for mimicking the tectonic history of the basin. Software codes Dynel3D and Traptester were used to examine the validity of geomechanical restoration techniques for locating sweet spots in the Moomba-Big Lake fields. The methodology attempts to reconstruct the present-day structural and geometrical placement and to predict fractures generated due to stresses released during past tectonic events. Predicted stresses succeeded in mapping the same sweet spot in the Big Lake field using both software codes. Accordingly, the present permeability and production rate is controlled by a combination of present-day and stored stresses.

The Deep Roots of Geology: Tectonic History of Australia Preserved as Mantle Anisotropy

2021 ◽  
Author(s):  
Caroline Eakin
Keyword(s):  
Seismic Anisotropy ◽  
Small Scale ◽  
Continental Margins ◽  
Geological History ◽  
Deep Roots ◽  
Geographical Patterns ◽  
Tectonic History ◽  
History Of ◽  
Mantle Anisotropy ◽  
Continental Interior

Abstract Australia is an old stable continent with a rich geological history. Limitations in sub-surface imaging below the Moho, however, mean that is unclear to what extent, and to what depth, this rich geological history is expressed in the mantle. Scattering of surface waves at ~150km depth by lateral gradients or boundaries in seismic anisotropy, termed Quasi-Love waves, offer potential new insights. The first such analysis for Australia and Zealandia shown here detects over 300 new scatterers that display striking geographical patterns. Around two-thirds of the scatterers are coincident with either the continental margins, or major crustal boundaries within Australia, suggesting deep mantle roots to such features. Within the continental interior such lateral anisotropic gradients imply pervasive fossilized lithospheric anisotropy, on a scale that mirrors the crustal geology at the surface, and a strong lithosphere that preserves this signal over billions of years. Along the continental margins, lateral anisotropic gradients may indicate either the edge of the thick continental lithosphere, or small-scale dynamic processes in the asthenosphere, such as edge-drive convection, tied to the transition from oceanic to continental crust/lithosphere.

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