Sedimentary deposits alluvial

Potassic - ultrapotassic lavas [ Pyroclastic flows, surges, lahars J Pyroclastic fall deposits 1 Volcano-sedimentary deposits j Limestones I Carbonate deposits j Alluvial conglomerates J Sandstones and calcarenites... 

Reductive dissolution of Fe oxyhydroxides holding sorbed As appears to explain the very large concentrations of As in water from wells drilled into alluvial sediments of the Brahmaputra and Ganges Rivers in Bangladesh and West Begal (Nickson et al 1998, 2000). Dissolved As has accumulated from the reduction of As-rich Fe oxyhydroxides formed upstream of the contaminated areas by weathering of As-rich base metal sulfides. The reduction is driven by sedimentary organic matter in the deposits. Release of As from oxidation of pyrite in shallow wells contributes little to the water contamination because any As(IV) released would be re-sorbed on Fe oxides formed in pyrite oxidation. 

Pimentel, N.L.V. (2002) Pedogenic and early diagenetic processes in Palaeogene alluvial fan and lacustrine deposits from the Sado Basin (south Portugal). Sedimentary Geology 148, 123-138. 

About 25% of the State of Sao Paulo is covered by outcrops of the crystalline basement. The remaining area is covered by sedimentary rocks of the Parana Basin and the small Tertiary basins of Sao Paulo and Taubate, plus other restricted zones of coastal sediments and alluvial deposits. 

The rocks of the Beacon Snpergronp of Gondwana are noteworthy becanse they were deposited on land rather than in the coastal ocean of Gondwana. hi addition, the sediment was deposited after plants and animals had made the transition from the ocean to life on land. Even more fortunate is the fact that the rocks of the Beacon Supergroup have preserved a record of the evolution of air-breathing tetrapods because the sediment that was deposited on alluvial plains was not removed by erosion even before it was lithified. For these reasons, the sedimentary rocks of the Beacon Supergroup can provide information that is not available in rocks that were deposited in the oceans at the same time. 

The climate of Antarctica during the Permo-Triassic was at least partly determined by its proximity to the geographic south pole which affected the average annual temperature and the duration of darkness during the winter. Nevertheless, the geological evidence indicates that sand and mud were deposited by liquid water that flowed freely across alluvial plains. In addition, h flora implies that the sedimentary rocks of the Victoria Group were deposited under temperate climatic conditions. 

Streams mobilize sedimentary materials through erosion, transport materials along with stream flow, and release them in a solid form during deposition. Deposits of stream-borne sediments are called alluvium. As conditions such as lowered stream velocity begin to favor deposition, larger, more settleable particles are released first. This results in sorting such that particles of a similar size and type tend to occur together in alluvial deposits. Much sediment is deposited in flood plains where streams overflow their banks. 

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