摘要:

SUMMARYBed forms arise by interaction between a fluid flow and the sediment transported over or close to the bed. The geometry of bed forms is two‐dimensional or three‐dimensional. Two‐dimensional bed forms generate two‐dimensional internal sedimentary structures and are adjusted to two‐dimensional flow‐vector fields. Three‐dimensional bed forms generate three‐dimensional internal sedimentary structures and are adjusted to three‐dimensional flow‐vector fields. Many shallow‐water flow systems observable today are each characterised by flow‐vector fields of unequal rank, and hence are hierarchically structured. Hierarchies of bed forms and internal structures which parallel the hierarchies of flow‐vector fields can also be established in the case of these flow systems. A single type of bed form or internal structure from an hierarchically structured flow system cannot specify that system fully with regard to either its directional or flow‐dynamic characteristics. An approach to palaeocurrent analysis that is more flexible and comprehensive than previously attempted

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01576.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYSand is being deposited in a meandering estuary separating Sapelo and Blackbeard Islands, Georgia, in the channel of the estuary and on two point bars associated with meanders. Sand is being eroded by the meandering channel from slightly lithified Pleistocene and unconsolidated Holocene strandline deposits, and is being redeposited by the ebb tidal currents. The estuary‐channel deposits are coarse grained and their grain‐size decreases down ebb current from the source outcrops. The point bars are elongated in the direction of the ebb current, and increase in grain‐size from their crests downward as they grade into the channel deposits. Festoon cross‐bedding and ripple marks on the point bars record the ebb direction, while elongate plant fragments are preferentially oriented normal to the bar elongation (current). Horizontally stratified muds and muddy sands are being deposited behind the bars, and contain a rich fauna (primarily annelids, arthropods, and molluscs). However, the fauna is represented in the deposits more by burrows and disturbed stratification than by preserved organisms. The sands of the bars and channel are biologically less productive, but the bioclastic content of the sediment

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01577.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYFour flume experiments have been performed in which the behaviour was investigated of a bed of fine silt under running water with and without an excess of material introduced into suspension.In the presence of excess material, bed features were formed in the tangential stress range 0.1<θ<0.4, and the bed was found to remain plane in the ranges 0<θF<0.1 and 0.4<θF<1.3. In the absence of excess material the stable condition over the entire range appeared to be that of the plane bed.Dual values of the threshold stress for grain movement were postulated to explain these results, and a relationship has been found between the magnitude of the tangential stress and the upstream slope of the featur

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01578.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY