Sedimentology and characteristics of dispersed organic matter in Tertiary Niger delta: origin of source rocks in a deltaic environment
Organic matter in Tertiary strata of the Niger delta is mainly a mixture of types II and III kerogen as defined by pyrolysis, has a high pristane/phytane ratio (> 1%), and is composed of the macerals vitrinite and minor liptinite. The main palynofacies are structured woody material, opaque organic matter, cuticles, pollen and spores, and minor amorphous organic matter. The geochemistry, petrology, palynofacies, and distribution data indicate a predominantly terrestrial and detrital source of the organic matter irrespective of facies, formation, or age. The distribution and abundance of the organic matter are related to both the age of the strata and depositional environment. The most significant variation is the decline in mean total organic carbon (TOC) content from late Eocene (2.2% TOC) to Pliocene strata (.90% TOC) and an associated general decline in pyrolysis-defined hydrogen index (HI) and pristane/phytane ratio. The variation in organic matter with depositional environments, and environmental depth zones (defined by foraminiferal assemblages) is significant, although less important than variation due to age. The highest TOC and HI values occur in nonmarine swamp, marsh, and floodplain deposits, reflecting proximity to the organic source. Paradoxically, no rich source rocks occur in the Tertiary succession in the Niger delta and, as conventionally measured, the strata have little or no oil-generating potential. The poor quality of the source rocks has been more than compensated for by their great volume, by the excellent migration routes provided by the interbedded permeable sands, and possibly by the relatively rapid rate of maturation. Niger delta type of source rock, although an end member in terms of general source rock composition, appears to be relatively typical of Tertiary deltas. 19 figures.
- Research Organization:
- Univ. of British Columbia, Vancouver (Canada)
- OSTI ID:
- 6634244
- Journal Information:
- AAPG Bull.; (United States), Vol. 72:3
- Country of Publication:
- United States
- Language:
- English
Similar Records
Foraminiferal biostratigraphy, depositional environments and hydrocarbon source rock potential of sediments from five wells in the western offshore region of the Niger delta, Nigeria
Multivariate statistical analyses of palynodebris from the Middle Miocene of the Niger Delta and their environmental significance
Related Subjects
NIGERIA
PETROLEUM DEPOSITS
SOURCE ROCKS
MATURATION
CARBONACEOUS MATERIALS
KEROGEN
MACERALS
OPTICAL PROPERTIES
PERMEABILITY
POROSITY
PYROLYSIS
TERTIARY PERIOD
AFRICA
BITUMINOUS MATERIALS
CENOZOIC ERA
CHEMICAL REACTIONS
DECOMPOSITION
DEVELOPING COUNTRIES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
MATERIALS
MINERAL RESOURCES
ORGANIC MATTER
PHYSICAL PROPERTIES
RESOURCES
THERMOCHEMICAL PROCESSES
020200* - Petroleum- Reserves
Geology
& Exploration