Print this pageNumerical Investigation on Sediment Texture - Organic Content Relationship and Sequence Type Influence
CAZANACLI, DAN
Numerical data were obtained analyzing more than one hundred thin sections processed from Oligocene cores taken from 14 wells located in an elongated foreland basin bordering the Southern Carpathians (Romania). These are marine terrigenous deposits with a high organic productivity.
The following parameters could be accurately quantified: largest particle size, percentage of fine sediment (silt and clay), and percentage of immature organic matter. Statistic confirmatory techniques applied to the entire data set reveal a spatial variation from north to south but no clear relationship between the parameters. Only for the fine sediments there is a relationship between the organic content and the largest particle size. Correlation between percentage of fine sediment and organic content is extremely poor.
Using electric-log and seismic data a central section was divided into major depositional cycles. Each cycle consists of a fine grained transgressive sequence (high level), and a coarser sequence mainly progradational (low level). When data were analyzed separately important differences resulted. High level sequences show a weak relationship between textural parameters and organic content. In contrast, the low level sequences display a strong correlation between organic content and the largest particle size. A correlation between organic content and the fine fraction percentage is also present.
The explanation advanced is that during the high level transgressive periods organic matter preservation is helped by the bottom anoxic regime, whereas during the low level periods preservation is strongly controlled by sediment texture, especially by organic matter-clay sorptive interactions.