Triassic carbonate submarine fans along the Arabian platform margin, Sumeini Group, Oman     

KEITH F. WATTS 《Sedimentology》1988,35(1):43-71

ABSTRACT The Sumeini Group formed along the passive continental margin slope that bounded the northeastern edge of the Arabian carbonate platform. With the initial development of this passive continental margin in Oman during Early to Middle Triassic time (possibly Permian), small carbonate submarine fans of the C Member of the Maqam Formation developed along a distally steepened slope. The fan deposits occur as several discrete lenticular sequences of genetically related beds of coarsegrained redeposited carbonate (calciclastic) sediment within a thick interval of basinal lime mudstone and shale. Repeated pulses of calciclastic sediment were derived from ooid shoals on an adjacent carbonate platform and contain coarser intraclasts eroded from the surrounding slope deposits. Sediment gravity flows, primarily turbidites with lesser debris flows and grain flows, transported the coarse sediments to the relatively deep submarine fans. Channel erosion was a major source of intraformational calcirudite. Two small submarine fan systems were each recurrently supplied with calciclastic sediment derived from point sources, submarine canyons. The northern fan system retrogrades and dies out upsection. The southern fan system was apparently longer-lived; calciclastic sediments in it are more prevalent and occur throughout the section. The proximal portions of this fan system are dominated by channelized beds of calcirudite which represent inner- to mid-fan channel complexes. The distal portions include mostly lenticular, unchannelized beds of calcarenite, apparently mid- to outer-fan lobes. Carbonate submarine fans appear to be rare in the geological record in comparison with more laterally continuous slope aprons of coarse redeposited sediment. The carbonate submarine fans of the C Member apparently formed by the funnelling of coarse calciclastic sediment into small submarine canyons which may have developed due to rift and/or transform tectonics. The alternation of discrete sequences of calciclastic sediment with thick intervals of ‘background’ sediment resulted from either sea-level fluctuations or pulses of tectonic activity.  相似文献   

Laos and the making of a 'relational' resource frontier   总被引：1，自引：0，他引：1  

KEITH BARNEY 《The Geographical journal》2009,175(2):146-159

This paper seeks to reconsider the contemporary relevance of the resource frontier, drawing on examples of nature's commodification and enclosure under way in the peripheral Southeast Asian country of Laos. Frontiers are conceived as relational zones of economy, nature and society; spaces of capitalist transition, where new forms of social property relations and systems of legality are rapidly established in response to market imperatives. Customary property rights on the resource frontier can be seized by powerful actors in crucial political moments, preparing the territorial stage for more intensive phases of resource commodity production and accumulation. Relational frontier space is understood through the work of geographers such as Doreen Massey, who views the production of space as 'constituted though the practices of engagement and the power-geometries of relations'. In Laos, a twenty-first century resource frontier is being driven by new corporate investments in natural resources, and a supporting array of land reform programmes. The paper focuses on both the material and representational aspects of the production of the resource frontier, through policy and discourse analysis, and village level research in Laos' Khammouane province. By rethinking a dualist and hierarchical-scaled imaginary of frontier places, both rural people and local ecologies are shown to be key actors, in a complex, relational reproduction of frontier zones. An emerging Lao spatial and political assemblage – a form of 'frontier-neoliberalism'– is shown as producing dramatic changes in socio-natural landscapes, as well as new patterns of marginalisation and livelihood insecurity for a vulnerable rural population.  相似文献   

Terrace scarp deflation as a renewable source for eolian sediments in an arctic periglacial setting     

KEENE SWETT  KEITH MANN 《Polar research》1987,5(1):45-52

Glacial, glaciofluvial, and glaciolacustrine sediments deposited by the retreating Vibekes Glacier are being actively reworked into sand dunes and loess sheets on the tops of glaciofluvial terraces down-valley from Vibekes Glacier and Vibekes So. Active permafrost precludes trenching below 0.5 to 1.0 meters. However, sedimentary structures, deflationary and abrasion features in shallow and surface deposits are visible. Although an armored pavement inhibits sediment deflation on the horizontal terrace surfaces, a combination of fluvial erosion, mass-wasting, and eolian processes on terrace scarps provides a continuing source of sand- and silt-size materials for redeposition.  相似文献