Sediment Transport in Estuarine Areas
The Estuarine Sedimentation Research Group of King's College and Sir John Cass College has been studying the estuaries of the Thames, Medway and Taw-Torridge. Its members, who report some of their results here, have found that the sedimentary processes in the estuaries are varied and complex.
Solid phase partitioning of metals in managed retreat soils: field changes over the first year of tidal inundation.
Sequential extraction methods were used to determine the effect of saline inundation on partitioning behaviour of metals in soils at Orplands Managed Retreat site, Essex, UK. A suite of metals (Al, Ca, Cr, Cu, Fe, K, Li, Mn, Ni, Pb and Zn) were analysed in sequential extracts from samples of soil cores extracted immediately before breaching of sea walls in 1995 and 1 year after. Generally, partitioning of most metals was dominated by associations with the residual fraction and an absence of associations with the exchangeable fraction indicating a relatively uncontaminated environment. Changes in partitioning were predominantly limited to the top 8 cm of the soil profile where a decaying mat of vegetation from the pre-inundation surface resulted in high moisture contents and low redox potentials. In this zone, the predominance of metal associations with the residual fraction was replaced by associations with more labile fractions. In the surface layer deposited after breaching, Ca was dominantly associated with the carbonate fraction, which indicates biogenic import from adjacent estuarine sediments.
The Chenier Plain and Its Stratigraphy, Southwestern Louisiana
ABSTRACT The low coastal marshland of southwestern Louisiana is characterized by numerous relict beach ridges, or cheniers, which give the region its name. From analyses of cores along a north-south line of section through Creole, Louisiana, it has been possible to identify 4 faunal zones and 7 distinct sedimentary facies in the post-Pleistocene deposits which underlie the plain. The faunal zones, named after the dominant foraminifers, are: the Streblus, Streblus-Elphidium, Quinqueloculina and Trochammina zones. The sedimentary facies consist of varying proportions of sand, silt, and clay which, together with their contained faunas, clearly reflect the environments of deposition, including marsh, bay, mudflat, open gulf, and beach. The relict beaches or cheniers are lenticular sand and shell bodies similar to certain shoestring sands which commonly serve as oil reservoirs in older rocks; thus, they hold special interest for the petroleum geologist. The cheniers, which extend as uninterrupted coastwise ridges up to 30 miles in length, are biconvex in cross section and average about 600 feet across and about 7 feet in thickness. They rise from a few inches to more than 10 feet above the marsh. They are characterized by a smooth, generally arcuate seaward front and an irregular landward margin. These deposits rest on shallow gulf bottom sand and silty clay and are overlapped by organic marsh silt and clay. Should the ridges eventually be buried by such marsh deposits, they will form potential stratigraphic traps. A knowledge of the characteristic shape, trend, and dimensions of the chenier sands, and of their distinctive sedimentary and faunal properties should aid materially in identifying similar potential reservoirs in the subsurface.