Print this pageEarly Diagenesis of Delta Sediments - Origin and Role of Organic Acids
HUTCHEON, IAN, GRAHAM SIMPSON, and BRIAN RICKETTS
Pore fluids from fine grained sediments of the recent Fraser Delta in Vancouver, British Columbia, Canada have very high organic acid contents, up to 4,400 mg/L. The organic acid suite is dominated by propanoic acid, in marked contrast to deeper waters observed in sedimentary basins in which ethanoic acid typically dominates. In this sense, these waters are similar to those associated with coal bearing rocks. Carbonate minerals, either as cement or as bioclasts, are not common in the sediments of the Delta and, to some extent, the high organic acid concentrations may be responsible for this feature. The waters that contain high propanoic acid contents are associated with fine grained sediments in two relatively deep wells (35 m and 72 m) that are approximately 4 km onshore of the sea ward edge of the delta. Examination of these waters shows some of them to be far from saturation with respect to calcite.
Hydrogeological models of the modern delta can be combined with paleogeographic reconstruction to determine how the flow regime evolved through time. These models can then be considered in view of flow-transport models that contain pore fluid compositions, particularly high organic acid contents, observed in modern sediments. From these models the potential amount of calcite that can be dissolved by the flow of organic acid laden waters during the evolution of a delta during the early stages of diagenesis can be estimated.