scholarly journals Thrusting and debris entrainment in a surging glacier: Bakaninbreen, Svalbard

1996 ◽  
Vol 22 ◽  
pp. 241-248 ◽  
Author(s):  
Michael J. Hambrey ◽  
Julian A. Dowdeswell ◽  
Tavi Murray ◽  
Philip R. Porter
Keyword(s):  
Tectonic Evolution ◽  
Sedimentary Facies ◽  
Shear Zones ◽  
Hot Water ◽  
Important Process ◽  
High Angle ◽  
Glacier Surface ◽  
Structural Investigations ◽  
Fine Grained ◽  
Drill Stem

Bakaninbreen, a 17 km long glacier terminating in fjord waters in central Spitsbergen (77°45′ N, 17°20′E), began to surge between the springs of 1985 and 1986. By summer 1994 the surge front had reached a position 3 km from the terminus and had almost ceased propagation. Structural investigations were undertaken to characterise the tectonic evolution of this thermally complex surge-type glacier, and the role played by thrusting and its effect on debris entrainment. Much of the glacier surface, particularly within and below the surge front, displayed transverse high-angle thrusts, defined by discrete fractures bounded by coarse clear ice. Some fractures were associated with a film of mud, whereas in others a discrete laver of diamicton, with interstitial ice several decimetres thick, was evident. Within the surge front, and genetically related to the thrusts, was a number of shear zones several metres wide. These were defined by fine-grained ice that was the product of the grinding up of crystals during shear (mylonitization). Three main sedimentary facies are associated with the thrusts: mud, gravelly mud and clast-rich muddy diamicton. The diamicton has the character of basal glacial debris: grain-size distribution ranging from clay to cobble size, clasts with a predominance in the sub-angular and sub-rounded classes, and striated and faceted clasts. Hot-water drilling through the glacier revealed several englacial layers above the surge front, and debris brought up on the drill stem suggests a basal origin. At least some of these englacial layers are probably the sub-surface continuations of the thrusts. The observed facies indicate that the glacier is moving over a soft, deformable bed and that thrusting is an important process in transferring debris to the surface, especially when the surge front is propagating down-glacier.

scholarly journals Thrusting and debris entrainment in a surging glacier: Bakaninbreen, Svalbard

1996 ◽  
Vol 22 ◽  
pp. 241-248 ◽  
Author(s):  
Michael J. Hambrey ◽  
Julian A. Dowdeswell ◽  
Tavi Murray ◽  
Philip R. Porter
Keyword(s):  
Tectonic Evolution ◽  
Sedimentary Facies ◽  
Shear Zones ◽  
Hot Water ◽  
Important Process ◽  
High Angle ◽  
Glacier Surface ◽  
Structural Investigations ◽  
Fine Grained ◽  
Drill Stem

Bakaninbreen, a 17 km long glacier terminating in fjord waters in central Spitsbergen (77°45′ N, 17°20′E), began to surge between the springs of 1985 and 1986. By summer 1994 the surge front had reached a position 3 km from the terminus and had almost ceased propagation. Structural investigations were undertaken to characterise the tectonic evolution of this thermally complex surge-type glacier, and the role played by thrusting and its effect on debris entrainment. Much of the glacier surface, particularly within and below the surge front, displayed transverse high-angle thrusts, defined by discrete fractures bounded by coarse clear ice. Some fractures were associated with a film of mud, whereas in others a discrete laver of diamicton, with interstitial ice several decimetres thick, was evident. Within the surge front, and genetically related to the thrusts, was a number of shear zones several metres wide. These were defined by fine-grained ice that was the product of the grinding up of crystals during shear (mylonitization). Three main sedimentary facies are associated with the thrusts: mud, gravelly mud and clast-rich muddy diamicton. The diamicton has the character of basal glacial debris: grain-size distribution ranging from clay to cobble size, clasts with a predominance in the sub-angular and sub-rounded classes, and striated and faceted clasts. Hot-water drilling through the glacier revealed several englacial layers above the surge front, and debris brought up on the drill stem suggests a basal origin. At least some of these englacial layers are probably the sub-surface continuations of the thrusts. The observed facies indicate that the glacier is moving over a soft, deformable bed and that thrusting is an important process in transferring debris to the surface, especially when the surge front is propagating down-glacier.

scholarly journals Structures within the surge front at Bakaninbreen, Svalbard, using ground-penetrating radar

1997 ◽  
Vol 24 ◽  
pp. 122-129 ◽  
Author(s):  
Tavi Hodson ◽  
Daniel L. Gooch ◽  
Graham W. Stuart
Keyword(s):  
Ground Penetrating Radar ◽  
Shear Zones ◽  
Hot Water ◽  
Important Process ◽  
Glacier Surface ◽  
Basal Ice ◽  
Extensive Region ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Ground Penetrating

Bakaninbreen, Svalbard, started to surge during 1985–86, and developed a surge front up to 60 m high. Associated with down-glacier propagation of this surge front was the formation of shear zones and thrust faults, some of which revealed basally derived debris at the glacier surface. Hot water drilling and sampling of basal material showed the glacier bed to be soft sediment more than 1 m thick. A high-resolution ground-penetrating radar (GPR) survey at 100 MHz was conducted along three 500 m lines parallel to glacier flow on the surge front. The aims were to investigate the internal geometry of the thrust features, and the processes of entrainment of basal debris into bulk glacier ice. A strong linear reflector was seen on the survey, but it is about 15–20 m above the bed as identified from drilling depths. It probably represents the upper interface of a layer of debris-rich basal ice. Several extensive englacial reflectors were interpreted as debris-laden emergent thrust features, varying in thickness from 0.1 to 1.1 m. These features were mapped at the glacier surface, and drilling and sediment sampling verified the interpretation. Other englacial features included regions of incipient thrusting at the basal reflector, and an extensive region of scattering up to 30 m above the basal reflector that we interpret as folds, or blind thrusts that terminate englacially. Our results clearly demonstrate the potential of GPR for mapping internal glacial structure, and suggest that thrusting is an important process by which sediment is incorporated into glacier ice in the highly compressive region at the surge front.

scholarly journals Structures within the surge front at Bakaninbreen, Svalbard, using ground-penetrating radar

1997 ◽  
Vol 24 ◽  
pp. 122-129 ◽  
Author(s):  
Tavi Hodson ◽  
Daniel L. Gooch ◽  
Graham W. Stuart
Keyword(s):  
Ground Penetrating Radar ◽  
Shear Zones ◽  
Hot Water ◽  
Important Process ◽  
Glacier Surface ◽  
Basal Ice ◽  
Extensive Region ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Ground Penetrating

Bakaninbreen, Svalbard, started to surge during 1985–86, and developed a surge front up to 60 m high. Associated with down-glacier propagation of this surge front was the formation of shear zones and thrust faults, some of which revealed basally derived debris at the glacier surface. Hot water drilling and sampling of basal material showed the glacier bed to be soft sediment more than 1 m thick. A high-resolution ground-penetrating radar (GPR) survey at 100 MHz was conducted along three 500 m lines parallel to glacier flow on the surge front. The aims were to investigate the internal geometry of the thrust features, and the processes of entrainment of basal debris into bulk glacier ice.A strong linear reflector was seen on the survey, but it is about 15–20 m above the bed as identified from drilling depths. It probably represents the upper interface of a layer of debris-rich basal ice. Several extensive englacial reflectors were interpreted as debris-laden emergent thrust features, varying in thickness from 0.1 to 1.1 m. These features were mapped at the glacier surface, and drilling and sediment sampling verified the interpretation. Other englacial features included regions of incipient thrusting at the basal reflector, and an extensive region of scattering up to 30 m above the basal reflector that we interpret as folds, or blind thrusts that terminate englacially. Our results clearly demonstrate the potential of GPR for mapping internal glacial structure, and suggest that thrusting is an important process by which sediment is incorporated into glacier ice in the highly compressive region at the surge front.

Structural and metamorphic evolution of the Ambin massif (western Alps): toward a new alternative exhumation model for the Briançonnais domain

2007 ◽  
Vol 178 (6) ◽  
pp. 437-458 ◽  
Author(s):  
Jerome Ganne ◽  
Jean-Michel Bertrand ◽  
Serge Fudral ◽  
Didier Marquer ◽  
Olivier Vidal
Keyword(s):  
Tectonic Evolution ◽  
Large Scale ◽  
Regional Scale ◽  
Shear Bands ◽  
Shear Zones ◽  
Western Alps ◽  
Ductile Deformation ◽  
Movement Direction ◽  
Lower Grade ◽  
Structural Investigations

Abstract The basement domes of the central part of western Alps may result either from a multistage tectonic evolution with a dominant horizontal shortening component, an extensional behaviour, or both. The Ambin massif belongs to the “Briançonnais” domain and is located within the HP metamorphic zone. It was chosen for a reappraisal of the tectonic evolution of the Internal Alps in its western segment. Structural investigations have shown that Alpine HP rocks were exhumed in three successive stages. The D1 stage was roughly coeval with the observed peak metamorphic conditions and corresponds to a non-coaxial regime with dominant horizontal shortening and north movement direction. Petrological observations and P-T estimates show that the exhumation process was initiated during D1, the corresponding mechanism being still poorly understood. The D2 stage took place under low-blueschist facies conditions and culminated under greenschist facies conditions. It developed a retrogressive foliation and pervasive shear-zones at all scales that locally define major tectonic contacts. D2 shear zones show a top-to-east movement direction and correspond actually to large-scale detachment faults responsible for the juxtaposition of less metamorphic units above the Ambin basement and thus to a large part of the exhumation of HP rocks toward the surface. D2 shear zones were subsequently deformed by D3 open folds, large antiforms (e.g. the Ambin dome) and associated brittle-ductile D3 shear-bands. The D1 to D3 P-T conditions and P-T path of the blueschists occurring in the deepest part of the Ambin dome, was estimated by using the multi-equilibrium thermobarometric method of the Tweeq and Thermocalc softwares. Peak pressure conditions, estimated at about 14–16 Kb, 500oC, are followed by a nearly-isothermal decompression that occurred concurrently with the major D1–D2 change in the ductile deformation regime. Eastwards, the Schistes Lustrés units exhibit a similar geometry on top of the Gran Paradiso dome but exhibit opposite D2 movement direction. Lower-grade units are lying above higher-grade units, the shear zones occurring in between being similar to Ambin’s D2 detachments. Thus at regional scale, the D2 detachments seem to form together with the Ambin shear-zones, a network of conjugate detachments. Such a pattern suggests that the exhumation history is mostly controlled by a D2+D3 crustal-scale vertical shortening resulting in the thinning of the previous tectonic pile formed during D1. The slab-break off hypothesis may explain such an extensional behaviour within the western Pennine domain. It is suggested that the thermo-mechanical rebound of the residual European slab initiated between 35 and 32 Ma the fast exhumation of the previously thickened orogenic wedge (stack of D1 HP slices). It was immediately followed by a collapse of the wedge that may correspond to the E-W Oligocene extensional event responsible for the opening of rifts in the West European platform.

scholarly journals Hot water drilling in the firn layer of Greenland's percolation zone

2020 ◽  
pp. 1-4
Author(s):  
Neil Humphrey ◽  
Joel Harper ◽  
Toby Meierbachtol
Keyword(s):  
Hot Water ◽  
Small Field ◽  
Glacier Surface ◽  
Drill Stem ◽  
Rapid Access ◽  
Structural Framework ◽  
Water Saturated ◽  
Percolation Zone

Abstract The intermixed thermal and structural framework of cold firn, water-saturated firn and ice layers in Greenland's percolation zone can be challenging to penetrate with core drills. Here, we present our experiences using a hot water drill for research on the firn layer of the percolation zone. We built and deployed a lightweight and easily transportable system for drilling a transect of ~15 cm diameter boreholes through the full firn column thickness, to depths exceeding 100 m. An instrumented drill stem provides a scientific measurement of the firn properties while drilling. The system was successful at gaining rapid access to the firn column with mixed wet and cold conditions, was easily transported to the site and across the glacier surface, and required a small field crew to operate. The boreholes are well suited for in situ investigations of firn processes in Greenland percolation zone.

scholarly journals Mudrock Microstructure: A Technique for Distinguishing between Deep-Water Fine-Grained Sediments

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 653
Author(s):  
Shereef Bankole ◽  
Dorrik Stow ◽  
Zeinab Smillie ◽  
Jim Buckman ◽  
Helen Lever
Keyword(s):  
Grain Size ◽  
Deep Water ◽  
Sedimentary Facies ◽  
X Ray Diffraction ◽  
Weak Current ◽  
Large Area ◽  
Fine Grained ◽  
Mean Size ◽  
The Mean ◽  
Water Facies

Distinguishing among deep-water sedimentary facies has been a difficult task. This is possibly due to the process continuum in deep water, in which sediments occur in complex associations. The lack of definite sedimentological features among the different facies between hemipelagites and contourites presented a great challenge. In this study, we present detailed mudrock characteristics of the three main deep-water facies based on sedimentological characteristics, laser diffraction granulometry, high-resolution, large area scanning electron microscopy (SEM), and the synchrotron X-ray diffraction technique. Our results show that the deep-water microstructure is mainly process controlled, and that the controlling factor on their grain size is much more complex than previously envisaged. Retarding current velocity, as well as the lower carrying capacity of the current, has an impact on the mean size and sorting for the contourite and turbidite facies, whereas hemipelagite grain size is impacted by the natural heterogeneity of the system caused by bioturbation. Based on the microfabric analysis, there is a disparate pattern observed among the sedimentary facies; turbidites are generally bedding parallel due to strong currents resulting in shear flow, contourites are random to semi-random as they are impacted by a weak current, while hemipelagites are random to oblique since they are impacted by bioturbation.

Filling process and filling characteristic analysis of Paleogene Baxian sag in Bohai Bay basin, China

2020 ◽  
pp. 1-21
Author(s):  
Zili Zhang ◽  
Xiaomin Zhu ◽  
Ruifeng Zhang ◽  
Sheng Fu ◽  
Jing Zhang
Keyword(s):  
Tectonic Evolution ◽  
Oil And Gas ◽  
Sedimentary Facies ◽  
Flood Plain ◽  
Alluvial Fan ◽  
Evolution Process ◽  
Bohai Bay ◽  
Characteristic Analysis ◽  
Sequence Boundaries ◽  
Lake Basins

In addition to core, logging, and other previous research results, this paper determines the fault development and tectonic evolution process of the Baxian sag with the Paleogene rift stage based on 3D seismic data. The Paleogene tectonic evolution of the sag can be divided into three episodes and six evolution stages, and three types of faults are identified: intensely active normal, active normal, and weakly active normal. One first-order sequence, three second-order sequences, and fourteen third-order sequences of the Paleogene Baxian sag were created, and fifteen sequence boundaries were recognised. According to the rifting background and sedimentary facies development characteristics of each episode, five combination types of the depositional system associations were identified, including alluvial fan-fluvial and braided-delta-lacustrine in an early rifting episode, delta-lacustrine and nearshore subaqueous fan-lacustrine in the middle rifting episode, and fluvial-flood plain in the late rifting episode. Six response models of filling and the evolution process in Paleogene Baxian sag were concluded. The multi-episodes tectonic cycles of faulted lake basins resulted in complex paleogeomorphology and variable provenance supply, forming abundant sequence structure patterns and different filling and evolution processes of faulted lake basins. The stable rifting stage is favourable to form and preserve high-quality source rock, and develop various sedimentary facies and sandbody types, which is a potential area for exploration of a lithologic stratigraphic oil and gas reservoir.

scholarly journals Recrystallization of ice enhances the creep and vulnerability to fracture of ice shelves 

2021 ◽  
Author(s):  
Meghana Ranganathan ◽  
Brent Minchew ◽  
Colin Meyer ◽  
Matej Pec
Keyword(s):  
Grain Size ◽  
Ice Sheet ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Model Parameters ◽  
Localized Deformation ◽  
Ice Shelves ◽  
Fine Grained ◽  
Initiation And Propagation ◽  
Rapid Deformation

<p>The initiation and propagation of fractures in floating regions of Antarctica has the potential to destabilize large regions of the ice sheet, leading to significant sea-level rise. While observations have shown rapid, localized deformation and damage in the margins of fast-flowing glaciers, there remain gaps in our understanding of how rapid deformation affects the creep and toughness of ice. Here we derive a model for dynamic recrystallization in ice and other rocks that includes a novel representation of migration recrystallization, which is absent from existing models but is likely to be dominant in warm areas undergoing rapid deformation within the ice sheet. We show that, in regions of elevated strain rate, grain sizes in ice may be larger than expected (~15 mm) due to migration recrystallization, a significant deviation from solid earth studies which find fine-grained rock in shear zones. This may imply that ice in shear margins deforms primarily by dislocation creep, suggesting a flow-law exponent of n=4 in these regions. Further, we find from existing models that this increase in grain size results in a decrease in tensile strength of ice by ~75% in the margins of glaciers. Thus, we expect that this increase in grain size makes the margins of fast-flowing glaciers less viscous and more vulnerable to fracture than we may suppose from standard model parameters.</p>

scholarly journals The internal structure and composition of a plate boundary-scale serpentinite shear zone: The Livingstone Fault, New Zealand

2019 ◽  
Author(s):  
Matthew S. Tarling ◽  
Steven A. F. Smith ◽  
James M. Scott ◽  
Jeremy S. Rooney ◽  
Cecilia Viti ◽  
...  
Keyword(s):  
New Zealand ◽  
Internal Structure ◽  
Shear Zone ◽  
Plate Boundary ◽  
Shear Zones ◽  
East Side ◽  
Local Dispersion ◽  
Fine Grained ◽  
Shear Sense ◽  
Tectonic Settings

Abstract. Deciphering the internal structural and composition of large serpentinite-dominated shear zones will lead to an improved understanding of the rheology of the lithosphere in a range of tectonic settings. The Livingstone Fault in New Zealand is a > 1000 km long terrane-bounding structure that separates the basal portions (peridotite; serpentinised peridotite; metagabbros) of the Dun Mountain Ophiolite Belt from quartzofeldspathic schists of the Caples or Aspiring Terranes. Field and microstructural observations from eleven localities along a strike length of c. 140 km show that the Livingstone Fault is a steeply-dipping, serpentinite-dominated shear zone tens to several hundreds of metres wide. The bulk shear zone has a pervasive scaly fabric that wraps around fractured and faulted pods of massive serpentinite, rodingite and partially metasomatised quartzofeldspathic schist up to a few tens of metres long. S-C fabrics and lineations in the shear zone consistently indicate a steep Caples-side-up (i.e. east-side-up) shear sense, with significant local dispersion in kinematics where the shear zone fabrics wrap around pods. The scaly fabric is dominated (> 98 vol %) by fine-grained (≪ 10 μm) fibrous chrysotile and lizardite/polygonal serpentine, but infrequent (

A petrographic study of the Rotliegendes Sandstone reservoir (Lower Permian) in the Rough Gas Field

Clay Minerals ◽  
1986 ◽  
Vol 21 (4) ◽  
pp. 459-477 ◽  
Author(s):  
M. W. Goodchild ◽  
J. H. McD. Whitaker
Keyword(s):  
Sedimentary Facies ◽  
Mineral Dissolution ◽  
Lower Permian ◽  
Secondary Porosity ◽  
Gas Field ◽  
Thin Sections ◽  
Fine Grained ◽  
Groundwater Movement ◽  
Marked Variability ◽  
Sandstone Reservoir

AbstractThe diagenetic history of the Rotliegendes Sandstone reservoir in the Rough Gas Field was studied using thin-sections, XRD analyses and SEM. The Rotliegendes comprises a sequence of fine-grained fluvial sheet-flood sandstones and coarse, gravelly, low-sinuosity channel sandstones, with thin aeolian interbeds, overlain by a sequence of aeolian dune and interdune sandstones. Early, environmentally-related diagnesis (eogenesis) shows a marked variability with sedimentary facies. Within aeolian sandstones, poikilotopic anhydrite and fine, rhombic dolomite are preserved. Fluvially-derived sandstones typically contain infiltrated detrital clays and early authigenic mixed-layer clays, together with coarse, framework-displacive dolomite. Feldspars show varying degrees of alteration within all facies. These eogenetic features reflect patterns of groundwater movement during the Rotliegendes and early Zechstein. Mineral dissolution and precipitation were controlled by the chemistry of the groundwaters. Burial diagenetic (mesogenetic) features are superimposed on eogenetic cements. Authigenic clays have been converted to illitic clays. In addition, mesogenetic chlorite has formed and quartz and strongly ferroan dolomite cements are recognized. These minerals may be related to clay diagenesis within the underlying Carboniferous Coal Measures. Early, framework-supporting anyhdrite, and both phases of dolomite, have been partially dissolved, creating secondary porosity. This is attributed to the action of acidic porewaters, generated by the maturation of organic material within the Carboniferous. Post-dissolution kaolinite, gypsum and minor pyrite infill secondary pores. Gas emplacement from the Late Cretaceous onwards effectively halted further diagenetic reactions.

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