Diagenesis, dewatering, and source rock potential of Ordovician shales from the High Atlas, Morocco

Conference · Mon Aug 01 00:00:00 EDT 1988 · AAPG Bull.; (United States)

OSTI ID:5718291

Evans, I J

The Ordovician shales of the High Atlas are interpreted as shelf sediments. They contain uncommon thin, wave-rippled, fine sandstone layers which record rare high-energy event and are attributed to winter storm action. The shales coarsen upward and the sandstone horizons become more common toward the top of the sequence, reflecting increasing proximality up the sequence from an outer to a mid-shelf setting. In places the shales contain large ferroan carbonate concretions. These have been analyzed together with the shales to determine the diagenetic and dewatering history of the sequence. Comparison of the chemistry of the noncarbonate fraction within the concretions with that of the host shales has led to quantitative mass-transfer models for the system. These suggest the sequence was an important source of cementing components (e.g., Ca, Si) for adjacent potential reservoir rocks. Other elements (e.g., Al, Mg, K) have not moved out of the system; the shales were not therefore a source for authigenic aluminosilicates as is often supposed. The major transport/dewatering pathways were the interbedded storm-sandstone horizons. These are now extensively quartz cemented. Local synsedimentary faults were probably also important conduits. These results have important implications regarding the relationship between shale and sandstone diagenesis. The shales presently contain up to 1% TOC. In the study area, however, they are thermally postmature with respect to hydrocarbon generation. Equivalent rocks which have experienced less burial should be considered potential source rocks.

• Research Organization: Univ. of Reading (England)
• OSTI ID: 5718291
• Report Number(s): CONF-8809346-
• Journal Information: AAPG Bull.; (United States), Vol. 72:8; Conference: Mediterranean Basins conference and exhibition, Nice, France, 25-28 Sep 1988
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
MOROCCO
PETROLEUM DEPOSITS
SOURCE ROCKS
DIAGENESIS
MATURATION
ORDOVICIAN PERIOD
RESERVOIR ROCK
SANDSTONES
SHALES
AFRICA
DEVELOPING COUNTRIES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
MINERAL RESOURCES
PALEOZOIC ERA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
020200* - Petroleum- Reserves
Geology
& Exploration