The effects of surface area, grain size and mineralogy on organic matter sedimentation and preservation across the modern Squamish Delta, British Columbia: the potential role of sediment surface area in the formation of petroleum source rocks

Surface sediment samples were collected from the Squamish River Delta, Brit ish Columbia, in order to determine the role of sediment surface area in th e preservation of organic matter (OM) in a paralic sedimentary environment. The Squamish Delta is an actively prograding delta, located at the head of Howe Sound. Bulk total organic carbon (TOC) values across the Squamish Delta are low, r anging from 0.1 to 1.0 wt.%. The carbon/total nitrogen ratio (C-org/N) rang es from 6 to 17, which is attributed to changes in OM type and facies varia tions. The < 25-mum fraction has TOC concentrations up to 2.0 wt.%, and a C -org/N ratio that ranges from 14 to 16. The 53-106-mum fraction has higher TOC concentrations and Corg/N ratios relative to the 25-53-mum fraction. Th e C-org/N ratio ranges from 9 to 18 in the 53-106-mum fraction and 5.5-10.5 in the 25-53-mum fraction. Surface area values for bulk sediments are low (0.5-3.0 m(2)/g) due to the large proportion of silt size material. Good co rrelation between surface area and TOC in bulk samples suggests that OM is adsorbed to mineral surfaces. Similar relationships between surface area an d TOC were observed in size-fractionated samples. Mineralogy and elemental composition did not correlate with TOC concentration. The relationships between surface area, TOC and total nitrogen (TN) can be linked to the hydrodynamic and sedimentological conditions of the Squamish Delta. As a result, the Squamish Delta is a useful modern analogue for the formation of petroleum source rocks in ancient deltaic environments, where TOC concentrations are often significantly lower than those in source rocks , formed in other geological settings. (C) 2001 Elsevier Science B.V. All r ights reserved.