Anatomy, geometry and sequence stratigraphy of basin floor to slope turbidite systems, Tanqua Karoo, South Africa     

Stephen David Johnson  Stephen Flint  David Hinds  & H. De Ville Wickens 《Sedimentology》2001,48(5):987-1023

The Tanqua area of the Karoo basin, South Africa, contains five Permian deep-water turbidite fan systems, almost completely exposed over some 640 km². Reconstruction of the basin-fill and fan distributions indicates a progradational trend in the 450 m+ thick succession, from distal basin floor (fan 1) through basin-floor subenvironments (fans 2, 3 and 4) to a slope setting (fan 5). Fans are up to 65 m thick with gradational to sharp bases and tops. Facies associations include basin plain claystone and distal turbidite siltstone/claystone and a range of fine-grained sandstone associations, including low- and high-density turbidite current deposits and proportionally minor debris/slurry flows. Architectural elements include sheets of amalgamated and layered styles and channels of five types. Each fan is interpreted as a low-frequency lowstand systems tract with the shaly interfan intervals representing transgressive and highstand systems tracts. All fans show complex internal facies distributions but exhibit a high-frequency internal stratigraphy based on fan-wide zones of relative sediment starvation. These zones are interpreted as transgressive and highstand systems tracts of higher order sequences. Sandy packages between these fine-grained intervals are interpreted as high-frequency lowstand systems tracts and exhibit dominantly progradational stacking patterns, resulting in subtle downdip clinoform geometries. Bases of fans and intrafan packages are interpreted as low- and high-frequency sequence boundaries respectively. Facies juxtapositions across these sequence boundaries are variable and may be gradational, sharp or erosive. In all cases, criteria for a basinward shift of facies are met, but there is no standard 'motif' for sequence boundaries in this system. High-frequency sequences represent the dominant mechanism of active fan growth in the Tanqua deep-water system.  相似文献   

Tectonic controls on the development of a semi-arid alluvial basin as reflected in the stratigraphy of the Purilactis Group (upper cretaceous-eocene), northern Chile     

A.J. Hartley  S. Flint  P. Turner  E.J. Jolley   《Journal of South American Earth Sciences》1992,5(3-4)

The Upper Cretaceous-Eocene Purilactis Group of the north Chilean Precordillera consists of over 4100 meters of continental strata deposited in a retro-arc extensional basin. Deposited in an arid/semi-arid climate with no marine influence, the group comprises alluvial fan (51%), playa (35%), aeolian (8%), and lacustrine (6%) facies associations locally interbedded with volcaniclastic material. The basin-fill has an overall coarsening-upward profile and shows an increase in proximal fan facies up section, indicating basinward (eastward) fan progradation. Within the coarsening-upward profile, fan and playa facies are organized into: 1) large-scale (50–700 m thick) coarsening- (CU) and fining- (FU) upward cycles extending tens of kilometers, in which CU cycles represent tectonically induced (allocyclic) fan progradation during periods of decreased accomodation space (FU cycles reflect vertical aggradation and fan retreat during periods of increased accomodation space); 2) medium-scale cycles (15–50 m thick) extending up to 9 km, also representing tectonically induced fan progradation and retreat but superimposed on the larger scale cycles; and 3) small-scale, predominantly FU cycles (up to 15 m thick) extending only a few hundred meters and reflecting minor, autocyclically induced changes in sedimentation. Purilactis Group sediments were derived from a westerly (footwall) source of: 1) Upper Triassic to Lower Cretaceous sediments and volcanics (back-arc basin-fill), and 2) an andesite-dominated Upper Cretaceous volcanic arc sequence, unroofing of which is indicated by a systematic provenance change in the upper 500 meters of the group from dominantly andesitic to granodioritic detritus. Localized development of volcaniclastics in the uppermost part of the group — together with evidence of arc unroofing — indicates that arc activity, although synchronous, did not contribute significantly to the overall Purilactis basin-fill. Basin subsidence may have been influenced by thermal contraction related to cooling of the Late Cretaceous arc and/or isostatic uplift following arc unroofing, processes likely to result in relatively localized extension. A larger scale cause of extension may have resulted from the relatively slow convergence rates along the Andean margin during Late Cretaceous to Eocene times (< 55 mm/yr), which would have promoted subduction roll-back and, together with the slab pull force active at the subduction zone, resulted in the development of an extensional tectonic regime across the Andean margin.  相似文献   

Stratospheric ozone reduction,solar UV-B radiation and terrestrial ecosystems   总被引：13，自引：0，他引：13  

Martyn M. Caldwell  Stephan D. Flint 《Climatic change》1994,28(4):375-394

Stratospheric ozone reduction is occurring and will continue to increase in magnitude into the next century. Yet, the consequences for terrestrial ecosystems of the increased solar UV-B (280–320 nm) radiation resulting from total column ozone reduction are not understood. Based on studies of higher plant response to UV-B, several possible consequences for ecosystems include decreased primary production, altered plant species composition, and altered secondary chemistry with implications for herbivory, litter decomposition and biogeochemical cycles. However, like the assessment of increased atmospheric CO₂, extrapolation from studies with isolated plants to ecosystem function is very tenuous at best. Very few UV-B studies have dealt with multispecies systems. Most of the UV-B research in the past two decades (since the first suggestions of ozone reduction) has been conducted as short-term experiments in growth chambers and greenhouses where the unnatural spectral balance of radiation can lead to unrealistic conclusions. Technical difficulties in suitable measurement and manipulation of UV-B radiation also complicate the conduct of reliable experiments. This essay surveys and categorizes some 300 papers from the past 20 years on this subject, draws general conclusions from the research and offers some recommendations with respect to ecosystem consequences.  相似文献   

THREE-DIMENSIONAL, CROSS-SEMIVARIOGRAM CALCULATIONS FOR HYDROGEOLOGICAL DATA     

Jonathan D. Lstok  Richard M. Cooper  Alan L. Flint 《Ground water》1988,26(5):638-646

Abstract. Geostatistics is a powerful tool for the analysis of hydrogeological data, but few well-documented computer programs for performing the necessary calculations have been presented in the technical literature. This is especially true for applications that require either three-dimensional or multivariate analyses. This paper describes a FORTRAN subroutine, VARIO, that can be used to compute experimental direct- and cross-semivariograms from a set of sample data, for any specified direction in one-, two-, or three-dimensional space. The subroutine combines into groups those sample pairs that fall within predetermined angular tolerances of the specified direction. The number of sample pairs used to compute the value of the experimental semivariogram at each value of separation can be specified in four different ways, depending on the nature of the available data. Written in FORTRAN 77, VARIO can be used on any computer that supports a FORTRAN 77 compiler. Source code listing, user instructions, and example input and output data for VARIO are presented.  相似文献   

Glacial deposits | Richard P. Goldthwait (Editor), 1975. Vol. 21 of Benchmark Papers in Geology (R.W. Fairbridge,Editor). Dowden,Hutchinson, and Ross,Stroudsburg, Pa. (Distributed by John Wiley and Sons,New York), 464 pp., U.S. $29.00     

R.F. Flint 《Earth》1976,12(4):421-422

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Coastal ecosystem dynamics: Relevance of benthic processes     

R. Warren Flint 《Marine Chemistry》1985,16(4):351-367

It is believed that the ecological balance and productivity of marine coastal environments are directly related to nutrient supplies from various sources including riverine-estuarine-coastal exchange, upwelling, precipitation, nitrogen fixation, and nutrient regeneration. In south Texas coastal waters, where phytoplankton productivity is comparable to other high productive coastal areas, many nutrient sources are suspected, but are not equally important in supplying sufficient nutrients to drive coastal production dynamics. Nitrogen regeneration from the benthos is implicated from a 2.5-y study of the nutrient cycling processes important in contributing to production levels in these waters. Sediments of the south Texas coastal habitat appear to exhibit a sensitive coupling with overlying waters, where a strong negative correlation exists between the random periodicity of external supplies of ‘new’ nitrogen to the coastal system and the rate at which nitrogen is recycled by sediments. This pattern buffers these waters against extended periods of low input of nutrients from external sources. The development of a conceptual scheme for nutrient cycling in this coastal habitat has provided a more holistic framework from which we can derive an objective assessment of the importance of mechanisms in the system. All data collected so far suggest that the primary production of organic matter and passage through the benthic habitat of these coastal waters is an important pattern responsible for the continued maintenance of productivity in the south Texas coastal ecosystem.  相似文献   

Structural Evidence of Recent Activity of the Khatanga–Lomonosov Fault Zone in the Laptev Sea     

Baranov  B. V.  Flint  M. V.  Rimskiy-Korsakov  N. A.  Poyarkov  S. G.  Dozorova  K. A. 《Doklady Earth Sciences》2018,480(1):671-673

Doklady Earth Sciences - New structural data obtained by a geophysical survey during Cruise 69 of the R/V Akademik Mstislav Keldysh in 2017 indicate that the Khatanga−Lomonosov fault zone is...  相似文献   

Changes in the Radiation State of Bottom Sediments in Yenisei Gulf     

Miroshnikov  A. Yu.  Flint  M. V.  Dubinina  E. O.  Asadulin  En. E.  Shchuka  S. A.  Usacheva  A. A. 《Doklady Earth Sciences》2018,483(2):1582-1586

Doklady Earth Sciences - This paper reports on the results of radiation monitoring of bottom sediments in Yenisei Gulf for the period from 1995 to 2016. Clear positive trends in changing the...  相似文献   

Lateral variability in clinoform trajectory,process regime,and sediment dispersal patterns beyond the shelf‐edge rollover in exhumed basin margin‐scale clinothems          下载免费PDF全文

George E. D. Jones  David M. Hodgson  Stephen S. Flint 《Basin Research》2015,27(6):657-680

Sediment supply rate and accommodation regime represent primary controls on the depositional architecture of basin margin successions, but their interaction is commonly inferred from 2D dip profiles and/or with limited constraints on sedimentary facies. In this study, three parallel (>40 km long) 2D depositional oblique‐dip profiles from outcrops of the lower Waterford Formation (Karoo Basin, South Africa) have been correlated. This data set provides a rare opportunity to assess the lateral variability in the sedimentary process record of the shelf‐to‐slope transition for eight successive clinothems over a 900 km² area. The three profiles show similar shelf‐edge rollover trajectories, but this belies significant along‐margin variability in sedimentary processes and down‐dip sediment supply. The depositional architecture of three successive clinothems (WfC 3, 4 and 5) also show along‐shelf physiographic differences. The reconstructed shelf‐edge rollover position is not straight, and a westward curve to the north coincides with an area of greater sand supply to the slope beyond a shelf dominated by wave and storm processes. All the clinothems thicken northwards, indicating an along‐margin long‐term increase in accommodation that was maintained through multiple shoreline transits across the shelf. The origin of the differential subsidence cannot be discriminated confidently between tectonic or compaction processes. The interplay of basin margin physiography, differential subsidence rate and process regime resulted in significant across‐strike variability in the style and timing of sediment dispersal patterns beyond the shelf‐edge rollover. This study highlights the challenge for accurate prediction of the sediment partitioning across the shelf‐edge rollover in subsurface studies.  相似文献   

Transport and deposition of mud in deep‐water environments: Processes and stratigraphic implications     

Kvin Boulesteix  Miquel Poyatos‐Mor  Stephen S. Flint  Kevin G. Taylor  David M. Hodgson  Stephen T. Hasiotis 《Sedimentology》2019,66(7):2894-2925

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