Coastal sedimentary environments and sea-level changes

Abstract

A detailed knowledge of the 3-D arrangement and lateral facies relationships of the stacking patterns in coastal deposits is essential to approach many geological problems such as precise tracing of sea level changes, particularly during small scale fluctuations. These are useful data regarding the geodynamic evolution of basin margins and yield profit in oil exploration. Sediment supply, wave-and tidal processes, coastal morphology, and accommodation space generated by eustasy and tectonics govern the highly variable architecture of sedimentary bodies deposited in coastal settings. But these parameters change with time, and erosional surfaces may play a prominent role in areas located towards land. Besides, lateral shift of erosional or even depositional loci very often results in destruction oflarge parts ofthe sediment record. Several case studies illustrate some commonly found arrangements offacies and their distinguishing features. The final aim is to get the best results from the sedimentological analysis of coastal units. [RESUMO] o conhecimento detalhado do arranjo tridimensional e das relayoes laterais de facies nos depositos costeiros sao essenciais para definir, corn precisao, as variayoes do nivel do mar, em especial as flutuayoes de pequena escala. Estas fornecem dados uteis para 0 reconhecimento da evoluyao geodinamica das margens das bacias bem como para a pesquisa e explorayao de petroleo. 0 acarreio sedimentar, os processos ondulatorios e de mares, a morfologia costeira e 0 espayo de acomodayao gerado pela eustasia e pela tectonica sao os responsaveis pela arquitectura muito variavel dos corpos sedimentares depositados em arnbientes costeiros. Todavia, estes parametros variam no tempo, e as superficies de erosao podem ter papel importante nas areas proximas do continente. Alem disso, a deslocayao lateral da erosao ou mesmo lacunas sedimentares conduzem, corn frequencia, a destruiyao de parte significativa do registo sedimentar. Apresentam-se exemplos que ilustram alguns arranjos frequentes de facies e os seus parametros caracteristicos corn vista a obter os melhores resultados na analise sedimentologica das unidades costeiras.