Tectonic significance of mesofracture systems associated with the Lebanese segment of the Dead Sea transform fault     

P.L. Hancock  M.S. Atiya 《Journal of Structural Geology》1979,1(2):143-153

A 3000 m Jurassic-Cretaceous-Palaeogene succession dominated by carbonates is deformed by NNE trending open folds of Palaeogene age. Conjugate wrench faults and a system of normal faults extend the fold belt axially and probably evolved during anticlockwise rotation in a transpressive regime related to the oblique convergence of the African and Arabian plates across the Lebanese segment of the Dead Sea transform fault. Three sets and four systems of conjugate mesoscopic fractures, symmetrically orientated with reference to bedding and the plunge of the fold in which they are contained, resulted in minor axial elongation. Pressure solution on surfaces striking parallel to the fold belt locally achieved up to 50% shortening.The N30°E vertical Yammouné Fault Zone, which connects with the principal rift faults to the north and south, is accompanied by mesostructures which indicate that displacements were dominantly left-lateral and that the 1–2 km Zone is younger than the folds, possibly of Neogene age.  相似文献   

New constraints on the late Cenozoic incision history of the New River, Virginia     

Dylan J. Ward  James A. Spotila  Gregory S. Hancock  John M. Galbraith   《Geomorphology》2005,72(1-4):54-72

The New River crosses three physiogeologic provinces of the ancient, tectonically quiescent Appalachian orogen and is ideally situated to record variability in fluvial erosion rates over the late Cenozoic. Active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level. However, thick sequences of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation. We used cosmogenic ¹⁰Be exposure dating, aided by mapping and sedimentological examination of terrace deposits, to constrain the timing of events in this history. ¹⁰Be concentration depth profiles were used to help account for variables such as cosmogenic inheritance and terrace bioturbation. Fill-cut and strath terraces at elevations 10, 20, and 50 m above the modern river yield model cosmogenic exposure ages of 130, 600, and 600–950 ka, respectively, but uncertainties on these ages are not well constrained. These results provide the first direct constraint on the history of alluvial aggradation and incision events recorded by New River terrace deposits. The exposure ages yield a long-term average incision rate of 43 m/my, which is comparable to rates measured elsewhere in the Appalachians. During specific intervals over the last 1 Ma, however, the New River's incision rate reached 100 m/my. Modern erosion rates on bedrock at a prominent knickpoint are between 28 and 87 m/my, in good agreement with rates calculated between terrace abandonment events and significantly faster than 2 m/my rates of surface erosion from ancient terrace remnants. Fluctuations between aggradation and rapid incision operate on timescales of 10⁴− 10⁵ year, similar to those of late Cenozoic climate variations, though uncertainties in model ages preclude direct correlation of these fluctuations to specific climate change events. These second-order fluctuations appear within a longer-term signal of dominant aggradation (until 2 Ma) followed by dominant incision. A similar signal is observed on other Appalachian rivers and may be the result of sediment supply fluctuations driven by the increased frequency of climate changes in the late Cenozoic.  相似文献   

Tectonics of an early Proterozoic geosuture: The Halls Creek orogenic sub-province, northern Australia     

S.L. Hancock  R.W.R. Rutland 《Journal of Geodynamics》1984,1(3-5)

The exposed elements of the Lower Proterozoic orogenic belts of the Halls Creek sub-province, Northern Australia, lie in fault zones which have suffered repeated tectonic activity at various times through the Proterozoic and Phanerozoic. The Halls Creek and King Leopold orogenic domains subtend an angle of 80° and are characterized by linear late tectonic batholithic complexes several hundred kilometres long but only a few tens of kilometres wide, reminiscent of those in Phanerozoic Cordilleran orogenies. The associated superposed folding and high temperature metamorphism are more akin to those in Phanerozoic collision orogenies.The sub-province is analyzed in the wider context of the North Australian orogenic province which was deformed, metamorphosed and intruded by granitic plutons approximately 1900-1800 Ma ago. In this province the Archaen basement was extended and broken into a mosaic of blocks, some of which (now largely concealed by younger Kimberley and McArthur basin sediments) retained a more positive character and fed sediment to intervening regions (such as the Pine Creek Geosyncline) which suffered greater extension and subsidence, but which retained a thinned Archaean basement.The Halls Creek Group was deposited in a trough to the south-east of the Kimberley island continent, and deposition was probably broadly contemporaneous with, and continuous with, that in the Pine Creek geosyncline. A volcanic—fine grained clastic—carbonate phase of marine deposition, following basin formation, is represented by the Biscay Formation. During the later phase of basin evolution widespread flysch facies (Olympio Formation), partly derived from the island continent, was deposited and is now preserved in low grade zones on both sides of the main belt of high strain and upper amphibolite to lower granulite facies metamorphism which displays recumbent folding and nappe tectonics with fold axes oblique to the major faults.No island arc compex or paired metamorphic belts are present in the orogenic belts, and it is concluded that the lithospheric extension and subsequent convergence did not involve the generation of oceanic crust or B-subduction.In the Halls Creek domain vergence is south-easterly across all zones and is related to oblique convergence leading to limited A-subduction of the basinal area in the south-east beneath the island continent to the north-west, accompanied by left-lateral strike-slip or transform fault movements on the north-trending major faults. The convergence generated the associated high temperature metamorphism and plutonism on the leading edge of the lower plate.A phase of upright folding (with trends varying continuously form E-W in the King Leopold belt to NNE-SSW in the Halls Creek belt) intervenes between the main recumbent deformation and metamorphism (ca 1920 Ma ago) and the emplacement of the late tectonic granite batholiths (ca 1840 Ma ago) which are fault controlled.The province represents a distinctive type of linear Proterozoic ensialic orogeny, not explicitly identified previously, and it needs to be distinguished both from true collision orogenies of the Phanerozoic, involving a Wilson Cycle, and from the areally extensive Proterozoic orogenies with which it is associated. Its essential characteristics are due to convergence between a small continent and an ‘oceanic’ area underlain by thin continental crust, resulting in limited A-subduction of the latter prior to crustal shortening.  相似文献   

Referees for volume 5     

Paul Hancock  Tony Barber  Susan Treagus  Peter Hudleston  John Platt 《Journal of Structural Geology》1983,5(6):633

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A comparison of SRTM and high‐resolution digital elevation models and their use in catchment geomorphology and hydrology: Australian examples     

G. R. Hancock  C. Martinez  K. G. Evans  D. R. Moliere 《地球表面变化过程与地形》2006,31(11):1394-1412

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Revisiting the hypsometric curve as an indicator of form and process in transport-limited catchment     

Garry Willgoose  Greg Hancock 《地球表面变化过程与地形》1998,23(7):611-623

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Are multispecies models an improvement on single-species models for measuring fishing impacts on marine ecosystems?   总被引：13，自引：6，他引：7  

Hollowed  Anne B.; Bax  Nicholas; Beamish  Richard; Collie  Jeremy; Fogarty  Michael; Livingston  Patricia; Pope  John; Rice  Jake C. 《ICES Journal of Marine Science》2000,57(3):707-719

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The measurement and modelling of rill erosion at angle of repose slopes in mine spoil   总被引：2，自引：0，他引：2  

G. R. Hancock  D. Crawter  S. G. Fityus  J. Chandler  T. Wells 《地球表面变化过程与地形》2008,33(7):1006-1020

The process of rill erosion causes significant amounts of sediment to be moved in both undisturbed and disturbed environments and can be a significant issue for agriculture as well as mining lands. Rills also often develop very quickly (from a single rainfall event to a season) and can develop into gullies if sufficient runoff is available to continue their development. This study examines the ability of a terrestrial laser scanner to quantify rills that have developed on fresh and homogeneous mine spoil on an angle of repose slope. It also examines the ability of the SIBERIA erosion model to simulate the rill's spatial and temporal behaviour. While there has been considerable work done examining rill erosion on rehabilitated mine sites and agricultural fields, little work has been done to examine rill development at angle of repose sites. Results show that while the overall hillslope morphology was captured by the laser scanner, with the morphology of the rills being broadly captured, the characteristics of the rills were not well defined. The digital elevation model created by the laser scanner failed to capture the rill thalwegs and tops of the banks, therefore delineating a series of ill defined longitudinal downslope depressions. These results demonstrate that an even greater density of points is needed to capture sufficient rill morphology. Nevertheless, SIBERIA simulations of the hillslope demonstrated that the model was able to capture rill behaviour in both space and time when correct model parameters were used. This result provides confidence in the SIBERIA model and its parameterization. The results demonstrate the sensitivity of the model to changes in parameters and the importance of the calibration process. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Field evidence for the influence of weathering on rock erodibility and channel form in bedrock rivers   总被引：1，自引：0，他引：1       下载免费PDF全文

Charles M. Shobe  Gregory S. Hancock  Martha C. Eppes  Eric E. Small 《地球表面变化过程与地形》2017,42(13):1997-2012

Erosion processes in bedrock‐floored rivers shape channel cross‐sectional geometry and the broader landscape. However, the influence of weathering on channel slope and geometry is not well understood. Weathering can produce variation in rock erodibility within channel cross‐sections. Recent numerical modeling results suggest that weathering may preferentially weaken rock on channel banks relative to the thalweg, strongly influencing channel form. Here, we present the first quantitative field study of differential weathering across channel cross‐sections. We hypothesize that average cross‐section erosion rate controls the magnitude of this contrast in weathering between the banks and the thalweg. Erosion rate, in turn, is moderated by the extent to which weathering processes increase bedrock erodibility. We test these hypotheses on tributaries to the Potomac River, Virginia, with inferred erosion rates from ~0.1 m/kyr to >0.8 m/kyr, with higher rates in knickpoints spawned by the migratory Great Falls knickzone. We selected nine channel cross‐sections on three tributaries spanning the full range of erosion rates, and at multiple flow heights we measured (1) rock compressive strength using a Schmidt hammer, (2) rock surface roughness using a contour gage combined with automated photograph analysis, and (3) crack density (crack length/area) at three cross‐sections on one channel. All cross‐sections showed significant (p < 0.01 for strength, p < 0.05 for roughness) increases in weathering by at least one metric with height above the thalweg. These results, assuming that the weathered state of rock is a proxy for erodibility, indicate that rock erodibility varies inversely with bedrock inundation frequency. Differences in weathering between the thalweg and the channel margins tend to decrease as inferred erosion rates increase, leading to variations in channel form related to the interplay of weathering and erosion rate. This observation is consistent with numerical modeling that predicts a strong influence of weathering‐related erodibility on channel morphology. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Cumulative spatial impact layers: A novel multivariate spatio‐temporal analytical summarization tool     

Lucy Romeo  Jake Nelson  Patrick Wingo  Jennifer Bauer  Devin Justman  Kelly Rose 《Transactions in GIS》2019,23(5):908-936

Scientific inquiry often requires analysis of multiple spatio‐temporal datasets, ranging in type and size, using complex multi‐step processes demanding an understanding of GIS theory and software. Cumulative spatial impact layers (CSIL) is a GIS‐based tool that summarizes spatio‐temporal datasets based on overlapping features and attributes. Leveraging a recursive quadtree method, and applying multiple additive frameworks, the CSIL tool allows users to analyze raster and vector datasets by calculating data, record, or attribute density. Providing an efficient and robust method for summarizing disparate, multi‐format, multi‐source geospatial data, CSIL addresses the need for a new integration approach and resulting geospatial product. The built‐in flexibility of the CSIL tool allows users to answer a range of spatially driven questions. Example applications are provided in this article to illustrate the versatility and variety of uses for this CSIL tool and method. Use cases include addressing regulatory decision‐making needs, economic modeling, and resource management. Performance reviews for each use case are also presented, demonstrating how CSIL provides a more efficient and robust approach to assess a range of multivariate spatial data for a variety of uses.  相似文献