The influence of salt withdrawal subsidence on palaeosol maturity and cyclic fluvial deposition in the Upper Triassic Chinle Formation: Castle Valley, Utah   总被引：1，自引：0，他引：1  

SHANE J. PROCHNOW†  STACY C. ATCHLEY  THOMAS E. BOUCHER‡  LEE C. NORDT  MICHAEL R. HUDEC§ 《Sedimentology》2006,53(6):1319-1345

Integrated fluvial sequence stratigraphic and palaeosol analysis can be used to better reconstruct depositional systems, but these approaches have not been combined to examine halokinetic minibasins. This study characterizes the temporal and spatial patterns of lithofacies and palaeosols in a sequence stratigraphic framework to reconstruct a model of minibasin evolution and identify halokinetic influences on fluvial deposition. This research documents fluvial cycles and stratigraphic hierarchy, palaeosol maturity and apparent sediment accumulation rates in the Chinle Formation within the Big Bend minibasin. This study also uses palaeosols to help identify fluvial aggradational cycle (FAC) sets. The Chinle is divided into two hectometre‐scale (10² m) fluvial sequences, six decametre‐scale (10¹ m) FAC sets, and variable numbers of metre‐scale FACs depending on proximity to the minibasin. Ten pedotypes representing 225 palaeosol profiles are recognized. The pedotypes include palaeosols similar to modern Entisols, Inceptisols, Aridisols, Vertisols and Alfisols. A maturity index (1–5) is assigned to each pedotype to assess its variability in palaeosol development. Estimated palaeosol development time is used to approximate apparent sediment accumulation rates. Increased subsidence resulted in a greater number and thicker FACs, thicker FAC sets and fluvial sequence sections, and lithofacies associations reflecting more rapid sedimentation along the minibasin axis. Palaeocurrent indicators converge towards the minibasin axis and indicate that it formed and drifted through time. Relative palaeosol maturity is inversely related to stratal thickness, and decreases towards the minibasin where episodic burial by fluvial sediment was more frequent. Metre‐scale FACs are most abundant towards the minibasin axis, and locally have Entisols and Inceptisols developed upon their upper boundaries reflecting increased sediment accumulation rates. Areas outside the minibasin are characterized by fewer FACs that are associated with more mature palaeosols. Palaeosol‐derived apparent sediment accumulation rates are as much as two orders of magnitude greater within the minibasin than in marginal areas. The combined stratigraphic, palaeocurrent and palaeosol evidence is used to develop a model for the evolution of the Big Bend minibasin that illustrates the halokinetic affect on fluvial and landscape processes.  相似文献   

Carbonate dissolution revealed by silt grain-size distribution: comparison of Holocene and Last Glacial Maximum sediments from the pelagic South Atlantic     

MICHAEL FRENZ  RÜDIGER HENRICH 《Sedimentology》2007,54(2):391-404

The current issue of global warming and the role of the ocean in global exchange of CO₂ increases the interest in solid budgets of marine carbonate production and dissolution. The present study utilizes grain‐size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the South Atlantic for the Holocene and Last Glacial Maximum (LGM, 19–23 cal kyr BP). A decrease in grain size (e.g. sand content, mean grain size of coarse carbonate silt) indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils. The spatial grain‐size pattern suggests a threshold water depth below which a gradual grain‐size decrease becomes increasingly rapid. This water depth is considered as the sedimentary lysocline. For the Holocene time slice, a constant, gradual decrease of foraminifer carbonate of about 5–10% per 1000 m water depth above the lysocline gives evidence for supra‐lysoclinal dissolution. The water depth of the lysocline for the Holocene is tied to the interface of North Atlantic Deep Water and Antarctic Bottom Water (AABW) (ca 4100 m). Submarine ridges which restrict intrusion of AABW into the Angola Basin cause an asymmetry in carbonate preservation across the Mid‐Atlantic Ridge. The lysocline was reconstructed at ca 3100 m for the LGM. These data suggest that the ca 1000 m rise of the lysocline eradicated the Holocene east–west asymmetry.  相似文献   

TOWARDS A UNIFORM CONCEPT FOR THE COMPARISON AND EXTRAPOLATION OF ROCKWALL RETREAT AND ROCKFALL SUPPLY   总被引：1，自引：0，他引：1  

MICHAEL KRAUTBLATTER  RICHARD DIKAU 《Geografiska Annaler: Series A, Physical Geography》2007,89(1):21-40

Rates of rockwall retreat and rockfall supply are fundamental components of sediment budgets in steep environments. However, the standard procedure of referencing rockwall retreat rates using only lithology is inconsistent with research findings and results in a variability that exceeds three orders of magnitude. The concept proposed in this paper argues that the complexity inherent in rockfall studies can be reduced if the stages of (i) backweathering, (ii) filling and depletion of intermediate storage on the rock face and (iii) final rockfall supply onto the talus slopes are separated as these have different response functions and controlling factors. Backweathering responds to preweathering and weathering conditions whereas the filling and depletion of intermediate storage in the rock face is mainly a function of internal and external triggers. The noise apparent in backweathering rates and rockfall supply can be reduced by integrating the relevant controlling factors in the response functions. Simple conceptual models for the three stages are developed and are linked by a time‐dependent ‘rockfall delivery rate’, which is defined as the difference between backweathering and rockfall supply, thus reflecting the specific importance of intermediate storage in the rock face. Existing studies can be characterized according to their ‘rockfall delivery ratio’, a concept similar to the ‘sediment delivery ratio’ used in fluvial geomorphology. Their outputs can be qualified as trigger‐dependent rockfall supply rates or backweathering rates dependent on (pre‐)weathering conditions. It is shown that the existing quantitative backweathering and rockfall supply models implicitly follow the proposed conceptual models and can be accommodated into the uniform model. Suggestions are made for how best to incorporate non‐linearities, phase transitions, path dependencies and different timescales into rockfall response functions.  相似文献   

SEISMIC TESTING OF A BUILDING STRUCTURE WITH A SEMI-ACTIVE FLUID DAMPER CONTROL SYSTEM     

MICHAEL D. SYMANS  MICHAEL C. CONSTANTINOU 《地震工程与结构动力学》1997,26(7):759-777

This paper describes shaking table tests of a multi-storey scale-model building structure subjected to seismic excitation and controlled by a semi-active fluid damper control system. The semi-active dampers were installed in the lateral bracing of the structure and the mechanical properties of the dampers were modified according to control algorithms which utilized the measured response of the structure. A simplified time-delay compensation method was developed to account for delays within the control system. The results of the shaking table tests are presented and interpreted and analytical predictions are shown to compare reasonably well with the experimental results. © 1997 John Wiley & Sons, Ltd.  相似文献   

Late Devensian river and floodplain dynamics and related environmental change in northwest Europe,with particular reference to a site at Woolhampton,Berkshire, England     

PHILIP E. F. COLLINS  IAN M. FENWICK  D. MICHAEL KEITH-LUCAS  PETER WORSLEY 《第四纪科学杂志》1996,11(5):357-375

Marked fluctuations in Late-glacial climate are correlated with significant changes in river behaviour and floodplain environment across much of northwest Europe. Evidence from a new site in the Kennet Valley provides a rare comprehensive picture of varying fluvial regime and local vegetation during this interval. Chronological control for the site is provided by biostratigraphical and morphostratigraphical correlations with other sites in the region, and by radiocarbon dating of carefully selected material. Preservation of the sedimentary sequence was facilitated by its occurrence within a large depression in the underlying bedrock. The origin of this depression is uncertain, perhaps reflecting subsidence or scour. Following the Last Glacial Maximum, a nival regime braided river dominated by floods deposited sandy gravels under stadial conditions. A large channel infilled by fine sediments during the latter part of the Windermere Interstadial indicates a fall in flow competence at a time of increased floodplain vegetation, most notably the appearance of tree birch. Variations in sediments and vegetation suggest fluctuations in the floodplain environment, reflecting complex vegetation dynamics and possibly climate forcing. During the Loch Lomond/Younger Dryas Stadial, a nival, braided regime was re-established, accompanied by the disappearance of tree birch.  相似文献   

Production of mud‐grade carbonates by marine fish: Crystalline products and their sedimentary significance     

MICHAEL A. SALTER  CHRISTOPHER T. PERRY  ROD W. WILSON 《Sedimentology》2012,59(7):2172-2198

Recent work has established that marine teleost (bony) fish represent a prolific source of mud grade, mainly high‐Mg calcite, carbonate sediment by means of primary precipitation within the intestine. Previously documented crystalline products display a diverse array of morphologies, many unique in shallow tropical marine settings, and have a wide range of magnesium contents (from 18 to 39 mol% MgCO₃). This study utilizes scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction and liquid ion chromatography to provide a more extensive and expansive morphological, mineralogical and chemical characterization of the crystalline forms produced by a wider range of piscine functional groups (covering 21 different fish species common in The Bahamas). Several crystal morphologies not previously described in fish‐derived carbonates are documented, and chemical composition is found to be more variable than previously reported: in addition to high‐Mg calcites with >18 mol% MgCO₃, high‐Mg calcites with lower MgCO₃ contents and low‐Mg calcites are identified. From the expanded species range, MgCO₃ content in fish‐derived carbonates ranges from ca 0˙5 to > 40 mol%, and particle length is in the range 0˙1 to >50 μm (typically <2 μm for individual crystals). Amorphous Mg‐carbonates (with detectable CaCO₃ of <2 mol%) are also found to varying extent in the precipitates of many species. Dominant mineralogy and MgCO₃ content varies with producing species and crystal morphology (itself a species‐dependent variable). Given the very small grain size and often high MgCO₃ contents of these carbonates, interesting questions arise about their preservation potential. Thus, the extent to which carbonates produced by different species may follow different post‐excretion preservation pathways is considered.  相似文献   

Facies architecture of individual basin‐plain turbidites: Comparison with existing models and implications for flow processes     

PETER J. TALLING  LAWRENCE A. AMY  RUSSELL B. WYNN  CHRISTOPHER J. STEVENSON  MICHAEL FRENZ 《Sedimentology》2012,59(6):1850-1887

Current understanding of submarine sediment density flows is based heavily on their deposits, because such flows are notoriously difficult to monitor directly. However, it is rarely possible to trace the facies architecture of individual deposits over significant distances. Instead, bed‐scale facies models that infer the architecture of ‘typical’ deposits encapsulate current understanding of depositional processes and flow evolution. In this study, the distribution of facies in 12 individual beds has been documented along downstream transects over distances in excess of 100 km. These deposits were emplaced in relatively flat basin‐plain settings in the Miocene Marnoso Arenacea Formation, north‐east Italy and the late Quaternary Agadir Basin, offshore Morocco. Statistical analysis shows that the most common series of vertical facies transitions broadly resembles established facies models. However, mapping of individual beds shows that they commonly deviate from generalized models in several important ways that include: (i) the abundance of parallel laminated sand, suggesting deposition of this facies from both high‐density and low‐density turbidity current; (ii) three distinctly different types of grain‐size break, suggesting waxing flow, erosional hiatuses and bypass of silty sediment; (iii) the presence of mud‐rich debrites demonstrating hybrid flow deposition; and (iv) dune‐scale cross‐lamination in fine‐medium grained sandstones. Submarine sediment density flows in basin‐plain settings flow over relatively simple topography. Yet, their deposits record complex flow events, involving transformation between different flow types, rather than the simple waning surges often associated with the distal parts of turbidite systems.  相似文献   

A new atlas of temperature and salinity for the North Indian Ocean   总被引：2，自引：0，他引：2  

A CHATTERJEE  D SHANKAR  S S C SHENOI  G V REDDY  G S MICHAEL  M RAVICHANDRAN  V V GOPALKRISHNA  E P RAMA RAO  T V S UDAYA BHASKAR  V N SANJEEVAN 《Journal of Earth System Science》2012,121(3):559-593

  相似文献   

Comparative evolution of statewide Geographic Information Systems in Ohio     

MICHAEL N. DEMERS  PETER F. FISHER 《International journal of geographical information science》2013,27(4):469-485

Abstract

This paper describes four autonomous Geographic Information Systems operating at a statewide level in Ohio (USA). All were initiated at various times in the 1970s and 1980s. They are operated by branches of state government, namely the Department of Natural Resources, the Ohio Environmental Protection Agency, the Ohio Department of Transportation, and the Public Utilities Commission of Ohio. A critical review of the operations and institutional contexts of these four systems shows evolution from in-house software development to third party suppliers, from coarse resolution grid cells to high accuracy vector data, from large dedicated GIS staffs to application-specific users augmented by smaller GIS support staffs, and from agency-dependent databases to inter-agency database sharing as technology improves and user needs and databases increase.  相似文献   

A spatial analytical perspective on geographical information systems     

MICHAEL F. GOODCHILD 《International journal of geographical information science》2013,27(4):327-334

Abstract

The field of geographical information systems (GIS) is reviewed from the viewpoint of spatial analysis which is the key component of the familiar four-part model of input, storage, analysis and output Input is constrained by the limits of manual methods and problems of ambiguity in scanning. The potential for developments in output is seen to be limited to the query mode of GIS operation, and to depend on abandoning the cartographic model. Discussion of storage methods is organized around the raster versus vector debate and the need to represent two spatial dimensions in one. A taxonomy of GIS spatial analysis operations is presented together with a generic data model. Prospects for implementation are discussed and seen to depend on appropriate scales of organization in national and international academic research.  相似文献