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Lithofacies and sequence development on an Upper Devonian mixed carbonate-siliciclastic fore-reef slope, Canning Basin, Western Australia 总被引：1，自引：0，他引：1
ANNETTE D. GEORGE PHILLIP E. PLAYFORD† C. McA. POWELL P. M. TORNATORA‡ 《Sedimentology》1997,44(5):843-867
Detailed sedimentological and stratigraphical analysis coupled with conodont biostratigraphy of a fore-reef slope succession in the Napier Range (Napier Formation) is used to develop a depositional model and relative sea-level history for late Frasnian to late Famennian reef evolution in the Canning Basin of north-western Australia. Changes in sedimentary style on the slope, reflecting differing rates of carbonate production on the platform, are linked to third- and higher order relative sea-level fluctuations. Overlapping slope aprons accumulated along the base of a steep-walled platform margin. Coarse carbonate debris was deposited adjacent to the margin as talus breccias (via rockfall) and debris-flow breccias. Depositional slopes up to 45°, and locally steeper, are demonstrated using rotated geopetal cavity fills. The predominance of channel-filling lithofacies throughout the slope succession indicates the highly channelized nature of the aprons. The middle slope is dominated by sandy oolitic-peloidal turbiditic grainstones interpreted as sediment exported from an active platform. The turbidites and associated debris-flow breccias contrast with condensed carbonate intervals and deep-water, non-fenestral stromatolites that record times of very low platform production. Lower slope turbidites and associated intraclastic breccias indicate widespread redeposition of sediment eroded from lithified and semi-lithified limestones higher up the slope. Several third-order sequences are recognized in the fore-reef succession and these are composed primarily of transgressive and highstand deposits. Carbonate production was severely restricted in the early Famennian coinciding with development of onlapping siliciclastic aprons during a relative sea-level lowstand. Evidence for a subaerial exposure event is also preserved within the siliciclastic strata. Controls on sequence development are difficult to constrain. Although two sequence boundaries can be correlated with falls on the global sea-level curve, the reef complexes evolved in an active extensional regime and it is highly likely that tectonism, in conjunction with eustasy, controlled accommodation on the platform and therefore carbonate productivity. 相似文献
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Transport and accumulation of actinide elements in the near-shore environment: field and modelling studies 总被引：2，自引：0，他引：2
OLIVIA J. MARSDEN† LIAM ABRAHAMSEN† NICHOLAS D. BRYAN† J. PHILIP DAY† L. KEITH FIFIELD‡ CLARISSA GENT† PHILLIP S. GOODALL§ KATHERINE MORRIS¶ FRANCIS R. LIVENS 《Sedimentology》2006,53(1):237-248
Nuclear facilities in coastal locations often discharge low‐level liquid wastes into the sea and the radioisotopes in these discharges are of interest both in assessing possible environmental impacts and as tracers for coastal processes. The distributions of a range of artificial radionuclides, derived from the authorized discharges from British Nuclear Fuels (BNFL) Sellafield, have been determined in the sediments of an intertidal salt marsh in the Esk Estuary, Cumbria, UK. Where published discharge histories exist (for 137Cs, 238Pu, 239,240Pu and 241Am), the sediment core‐profile distributions of these radionuclides have been compared with the releases from Sellafield, and consistent values of the accumulation rate (0·226 ± 0·007 g cm?2 yr?1) are obtained. A quantitative model has been developed, describing association of radionuclides with suspended particulate material, which is then accumulated and mixed in an offshore mud patch before resuspension and deposition in the salt marsh. The model has been used to describe radionuclide distributions observed in both the mud patch and the salt marsh, and to identify isotopes for which post‐depositional remobilization or solution transport from the discharge point are important. The behaviour of the commonly studied isotopes (137Cs, 238Pu, 239,240Pu and 241Am) is similar to that observed at this and other nearby locations. The activation product isotope 236U is enhanced in these sediments over the natural baseline by four to eight orders of magnitude, and the results suggest that Sellafield‐derived uranium is comparably mobile to 137Cs in these sediments although the processes governing the behaviour of these two elements may be different. In situ production of 241Am by decay of its 241Pu parent has generated only 17% of the current sediment inventory of this isotope, insufficient to account for the increase over the last 20–25 years, and suggesting that the input material for these sediments is preferentially enriched in Am relative to Pu during transport from the offshore mud patch. The discharge history of 244Cm, which is unknown, has also been reconstructed from the sediment profile and the model. 相似文献
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ABSTRACT. The Toronto Star newspaper began rescuing poor children from the city's hottest, smokiest, and smelliest neighborhoods in 1901. The Fresh Air Fund, like park and playground planning, assumed that proximity to nature modified both health and behavior. Evoking transcendentalism—the idea that providential nature could move humanity into higher forms of existence—the Star sent children to the countryside near Toronto, albeit temporarily, assured of producing tangible health benefits. It also expected “nature” to convert the antibourgeois immorality of poor children into something more tolerable. 相似文献
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JIRI CHLACHULA ROB A. KEMP CATHERINE A. JESSEN ADRIAN P. PALMER PHILLIP S. TOMS 《Boreas: An International Journal of Quaternary Research》2004,33(2):164-180
Two high-resolution loess-palaeosol sections from the Ob Loess Plateau (Iskitim) and the Minusinsk Basin (Kurtak 33) provide new detailed information on the last interglacial climate variations and landscape development in the parkland-steppe zone of southern Siberia. The complete last interglacial sensu lato (130-74 ka BP) records of the two sites, documented by magnetic susceptibility, grain-size, CaCO 3 and organic carbon content as proxy climatic data, and supplemented by thin-section studies, indicate several short warm and very cold intervals correlated with OIS 5e-5a. A strongly continental warm climate culminated around the peak of the last interglacial sensu stricto (OIS 5e) and cooler conditions occurred during the following interstadial stages (OIS 5c and 5a), corresponding to shifts in palaeolandscape development with gradual replacement of parkland-steppe and mixed southern taiga by boreal forest. During stadial stages (OIS 5d and 5b), the palaeolandscape was transformed into a cold arid periglacial tundra-steppe. Evidence for a major cooling in Siberia during OIS 5d, corroborating the palaeolimnological record from Lake Baikal, is provided by deep frost-wedge casts distorting the OIS 5e chernozemic palaeosol, suggesting formation of permafrost shortly after the last interglacial climatic optimum. The pedosedimentary record, reflecting the effects of syndepositional pedogenic processes, attests to a dynamic climate pulsation during the last interglacial stage. 相似文献
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