scholarly journals Deformation–sedimentation feedback and the development of anomalously thick aggradational turbidite lobes: Outcrop and subsurface examples from the Hikurangi Margin, New Zealand

2021 ◽  
Vol 91 (4) ◽  
pp. 362-389
Author(s):  
Adam D. McArthur ◽  
Julien Bailleul ◽  
Geoffroy Mahieux ◽  
Barbara Claussmann ◽  
Alex Wunderlich ◽  
...  
Keyword(s):  
Feedback Mechanism ◽  
Structural Deformation ◽  
Turbidity Currents ◽  
Low Density ◽  
Oriented Growth ◽  
Flow Process ◽  
Marine Sedimentation ◽  
Thrust Belts ◽  
Distribution Of Resources ◽  
Partial Confinement

ABSTRACT Concepts of the interaction between autogenic (e.g., flow process) and allogenic (e.g., tectonics) controls on sedimentation have advanced to a state that allows the controlling forces to be distinguished. Here we examine outcropping and subsurface Neogene deep-marine clastic systems that traversed the Hikurangi subduction margin via thrust-bounded trench-slope basins, providing an opportunity to examine the interplay of structural deformation and deep-marine sedimentation. Sedimentary logging and mapping of Miocene outcrops from the exhumed portion of the subduction wedge record heavily amalgamated, sand-rich lobe complexes, up to 200 m thick, which accumulated behind NE–SW-oriented growth structures. There was no significant deposition from low-density parts of the gravity flows in the basin center, although lateral fringes demonstrate fining and thinning indicative of deposits from low-density flows. Seismic data from the offshore portion of the margin show analogous lobate reflector geometries. These deposits accumulate into complexes up to 5 km wide, 8 km long, and 300 m thick, comparable in scale with the outcropping lobes on this margin. Mapping reveals lobe complexes that are vertically stacked behind thrusts. These results illustrate repeated trapping of the sandier parts of turbidity currents to form aggradational lobe complexes, with the finer-grained suspended load bypassing to areas downstream. However, the repeated development of lobes characterized by partial bypass implies that a feedback mechanism operates to perpetuate a partial confinement condition, via rejuvenation of accommodation. The mechanism proposed is a coupling of sediment loading and deformation rate, such that load-driven subsidence focuses stress on basin-bounding faults and perpetuates generation of accommodation in the basin, hence modulating tectonic forcing. Recognition of such a mechanism has implications for understanding the tectono-stratigraphic evolution of deep-marine fold and thrust belts and the distribution of resources within them.

scholarly journals Fringe or background: Characterizing deep-water mudstones beyond the basin-floor fan sandstone pinchout

2020 ◽  
Vol 90 (12) ◽  
pp. 1678-1705
Author(s):  
Kévin Boulesteix ◽  
Miquel Poyatos-Moré ◽  
David M. Hodgson ◽  
Stephen S. Flint ◽  
Kevin G. Taylor
Keyword(s):  
Deep Water ◽  
Turbidity Currents ◽  
Stratigraphic Correlation ◽  
Low Density ◽  
Karoo Basin ◽  
Depositional Processes ◽  
Stratigraphic Architecture ◽  
Sand Supply ◽  
Stacking Pattern ◽  
Basin Floor

ABSTRACT Mud dominates volumetrically the fraction of sediment delivered and deposited in deep-water environments, and mudstone is a major component of basin-floor successions. However, studies of basin-floor deposits have mainly focused on their proximal sandstone-prone part. A consequent bias therefore remains in the understanding of depositional processes and stratigraphic architecture in mudstone-prone distal settings beyond the sandstone pinchouts of basin-floor fans. This study uses macroscopic and microscopic descriptions of over 500 m of continuous cores from research boreholes from the Permian Skoorsteenberg Formation of the Karoo Basin, South Africa, to document the sedimentology, stratigraphy, and ichnology of a distal mudstone-prone basin-floor succession. Very thin- to thin-bedded mudstones, deposited by low-density turbidity currents, stack to form bedsets bounded by thin packages (< 0.7 m thick) of background mudstones. Genetically related bedsets stack to form bedset packages, which are bounded by thicker (> 0.7 m thick) background mudstones. Stratigraphic correlation between cores suggests that bedsets represent the distal fringes of submarine fan lobe elements and/or lobes, and bedset packages represent the distal fringes of lobe complexes and/or lobe complex sets. The internal stacking pattern of bedsets and bedset packages is highly variable vertically and laterally, which records dominantly autogenic processes (e.g., compensational stacking, avulsion of feeder channels). The background mudstones are characterized by remnant tractional structures and outsize particles, and are interpreted as deposited from low-density turbidity currents and debris flows before intense biogenic reworking. These observations challenge the idea that mud accumulates only from hemipelagic suspension fallout in distal basin-floor environments. Thin background mudstones separating bedsets (< 0.7 m thick) are interpreted to mainly represent autogenically driven lobe abandonment due to up-dip channel avulsion. The thicker background mudstones separating bedset packages (> 0.7 m thick) are interpreted to dominantly mark allogenically driven regional decrease of sand supply to the basin floor. The recognition of sandstone-prone basin-floor fans passing into genetically linked distal fringe mudstones suggests that submarine lobes are at least ∼ 20 km longer than previously estimated. This study provides sedimentological, stratigraphic, and ichnological criteria to differentiate mudstones deposited in different sub-environments in distal deep-water basin-floor settings, with implications for the accurate characterization of basin-floor fan architecture, and their use as archives of paleoenvironmental change.

Multiple detachments of thin-skinned fold-and-thrust belts in the eastern Sichuan Basin, China

2020 ◽  
Author(s):  
Zhidong Gu
Keyword(s):  
Seismic Data ◽  
Sichuan Basin ◽  
Structural Deformation ◽  
Kinematic Evolution ◽  
Structural Style ◽  
Thrust Belts ◽  
Eastern Sichuan Basin ◽  
Fold And Thrust Belts ◽  
Eastern Sichuan ◽  
Stratigraphic Succession

<p>The eastern Sichuan Basin, South China, is characterized by approximately parallel thin-skinned fold-and-thrust belts with exposed narrow anticlines and wide synclines. The structural deformation, however, has remained controversial due to the previous poor seismic data. In this study, the new collected pre-stack long-offset 2D- and 3D seismic data have been applied, and a 200-km long cross section perpendicular to the fold-and-thrust belts has been constructed to analyze the structural style and geometric and kinematic evolution. The stratigraphic succession is composed of competent layers separated by three main incompetent layers being multiple detachments, which are the Cambrian evaporites, the Lower Silurian shales, and the Middle-Lower Triassic evaporites, respectively. The basal detachment, the Cambrian evaporites, played a dominant role in the structural deformation, above which the fold-and-thrust belts were generated, and the middle and top detachments accommodated the displacement during the deformation. The main structural styles are detachment folds, fault propagation folds, back thrusts and basement-involved folds. The evolution succession of the fold-and-thrust belts should be kink band, detachment folds, and sequential thrusts of the forelimb and backlimb of the folds. The style of deformation is dependent on the mechanical characters of stratigraphic succession, i.e., the thickness variation of competent and incompetent layers in the stratigraphic units.</p>

Deposition and alteration of volcaniclastic strata in two large, early Proterozoic iron-formations in Canada

1989 ◽  
Vol 26 (8) ◽  
pp. 1574-1585 ◽  
Author(s):  
Scott W. Hassler ◽  
Bruce M. Simonson
Keyword(s):  
High Density ◽  
Coarse Grained ◽  
Iron Formation ◽  
Turbidity Currents ◽  
Low Density ◽  
Early Proterozoic ◽  
Geothermal Gradients ◽  
Passive Margins ◽  
Iron Formations

The Gunflint Iron-formation of western Ontario and the Sokoman Iron-formation of the Labrador–Quebec geosyncline both contain interbeds of coarse-grained volcaniclastic detritus. Volcaniclastic beds in the Gunflint are typically less than a metre thick and display normal grading and other physical structures typical of high- and low-density turbidites. Similar volcaniclastic beds are present in the Sokoman, as well as thicker accumulations with structures indicative of deposition from high-density turbidity currents. The volcaniclastic detritus in both iron-formations consists largely of well-sorted vitric ash and lapilli with accessory holocrystalline grains and solitary feldspar crystals. Internal textures of the vitric grains, plus the presence of armored lapilli in the Gunflint, suggest they are products of hydroclastic eruptions. However the clasts in most beds are heterogeneous and well-rounded, indicating they are sedimentary rather than eruptive deposits. Quench textures, coalesced vesicles, and diabasic textures indicate that the volcaniclastics were originally basaltic in composition, but the rocks have been pervasively altered to iron-rich chlorite, calcite, and K-feldspar (Or98 Ab2 An0) with minor quartz and illite. In addition to being pseudomorphs after the original volcaniclastic textures within grains, these minerals also occur as interstitial and vesicle-filling cements. Fibrous rims of chlorite and poikilotopic to blocky calcite are the most abundant cement types. Cementation commenced early, inasmuch as some zones show little evidence of compaction. Patterns of cementation and alteration may indicate that geothermal gradients in such iron-formation basins were steeper than they are in the most closely comparable modern settings, namely passive margins.

scholarly journals A deep subaqueous fan depositional model for the Palaeoarchaean (3.46 Ga) Marble Bar Cherts, Warrawoona Group, Western Australia

2012 ◽  
Vol 149 (4) ◽  
pp. 743-749 ◽  
Author(s):  
NICOLAS OLIVIER ◽  
GILLES DROMART ◽  
NICOLAS COLTICE ◽  
NICOLAS FLAMENT ◽  
PATRICE REY ◽  
...  
Keyword(s):  
Mass Transport ◽  
Western Australia ◽  
Deep Sea ◽  
High Density ◽  
Turbidity Currents ◽  
Low Density ◽  
Depositional Model ◽  
Sea Fan ◽  
Pilbara Craton ◽  
Channel Systems

AbstractThe 3.46 Ga Marble Bar Chert Member of the East Pilbara Craton, Western Australia, is one of the earliest and best-preserved sedimentary successions on Earth. Here, we interpret the finely laminated thin-bedded cherts, mixed conglomeratic beds, chert breccia beds and chert folded beds of the Marble Bar Chert Member as the product of low-density turbidity currents, high-density turbidity currents, mass transport complexes and slumps, respectively. Integrated into a channel-levee depositional model, the Marble Bar Chert Member constitutes the oldest documented deep-sea fan on Earth, with thin-bedded cherts, breccia beds and slumps composing the outer levee facies tracts, and scours and conglomeratic beds representing the channel systems.

Random isn't real: How the patchy distribution of ecological rewards may generate “incentive hope”

2019 ◽  
Vol 42 ◽  
Author(s):  
Laurel Symes ◽  
Thalia Wheatley
Keyword(s):  
Natural Environment ◽  
Random Distribution ◽  
Spatiotemporal Distribution ◽  
Patchy Distribution ◽  
Distribution Of Resources

AbstractAnselme & Güntürkün generate exciting new insights by integrating two disparate fields to explain why uncertain rewards produce strong motivational effects. Their conclusions are developed in a framework that assumes a random distribution of resources, uncommon in the natural environment. We argue that, by considering a realistically clumped spatiotemporal distribution of resources, their conclusions will be stronger and more complete.

Application of Improved Voltage Compensation in the SEM to Imaging of Organic Materials

1973 ◽  
Vol 31 ◽  
pp. 444-445
Author(s):  
P.J. Killingworth ◽  
M. Warren
Keyword(s):  
Electron Beam ◽  
Organic Materials ◽  
Operating Parameters ◽  
Low Density ◽  
Beam Diameter ◽  
Incident Electron Beam ◽  
Specimen Material ◽  
Voltage Compensation ◽  
Selection Of ◽  
Scanning Electron

Ultimate resolution in the scanning electron microscope is determined not only by the diameter of the incident electron beam, but by interaction of that beam with the specimen material. Generally, while minimum beam diameter diminishes with increasing voltage, due to the reduced effect of aberration component and magnetic interference, the excited volume within the sample increases with electron energy. Thus, for any given material and imaging signal, there is an optimum volt age to achieve best resolution.In the case of organic materials, which are in general of low density and electric ally non-conducting; and may in addition be susceptible to radiation and heat damage, the selection of correct operating parameters is extremely critical and is achiev ed by interative adjustment.

Quantitative defect studies in semiconductor TEM samples prepared by low angle ion milling

1995 ◽  
Vol 53 ◽  
pp. 512-513
Author(s):  
L. Mulestagno ◽  
J.C. Holzer ◽  
P. Fraundorf
Keyword(s):  
Sample Preparation ◽  
Milling Time ◽  
High Density ◽  
Low Density ◽  
Ion Milling ◽  
High Quality ◽  
Variable Angle ◽  
Major Disadvantage ◽  
Induced Defects

Due to the wealth of information, both analytical and structural that can be obtained from it TEM always has been a favorite tool for the analysis of process-induced defects in semiconductor wafers. The only major disadvantage has always been, that the volume under study in the TEM is relatively small, making it difficult to locate low density defects, and sample preparation is a somewhat lengthy procedure. This problem has been somewhat alleviated by the availability of efficient low angle milling.Using a PIPS® variable angle ion -mill, manufactured by Gatan, we have been consistently obtaining planar specimens with a high quality thin area in excess of 5 × 104 μm2 in about half an hour (milling time), which has made it possible to locate defects at lower densities, or, for defects of relatively high density, obtain information which is statistically more significant (table 1).

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