New depositional models for Cretaceous source rocks

Conference · Mon Feb 01 04:00:00 EST 1993 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:6105952

Kauffman, E G; Villamil, T ^[1]

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1. Univ. of Colorado, Boulder (United States)

The Cretaceous marks one of the greatest periods of source rock development in geologic history, especially in coastal and epi-continental marine basins where the number, duration, and geographic extent of Corg-rich intervals exceeds that of oceanic basins. Large-scale factors regulating Cretaceous source rocks include sealevel, sedimentation rate/type, paleoclimate and marine thermal gradients, paleoceanography (circulation, stratification, chemistry, upwelling, nutrient supply), and surface water productivity. Marine dispositional settings favored as models for Corg concentration include silled and tectonically depressed basins, intersection of OMZ's with shallow continental seas, coastal upwelling, highly stratified shallow seas, and oceanic anoxic events (OAE's). All of these settings are thought to be characterized by stagnant, anoxic/highly dysoxic water masses above the sediment-water interface, and highly stressed benthic environments. This seemingly supported by fine lamination, spare bioturbation, high pyrite and Corg content of most source rocks. But high-resolution (cm-scale) sedimentologic, paleobiologic, and geochemical analyses of Jurassic-Cretaceous source rocks reveal, instead, dynamic benthic environments with active currents, episodically crowded with diverse life in event communities, and persistently characterized by longer term, low diversity resident benthic communities. These characteristics indicate rapidly fluctuating, predominantly dysoxic to oxic waters at and above the sediment-water interface for most Corg-rich black shales. A new model for source rock generation is proposed which retains the redox boundary at or near the sediment-water interface over large areas of seafloor, in part aided by extensive development of benthic microbial mats which may contribute up to 30% of the Corg to marine source rocks.

• OSTI ID: 6105952
• Report Number(s): CONF-930306--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 77:2
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
BLACK SHALES
CHEMISTRY
CRETACEOUS PERIOD
DEPOSITION
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
HYDROCARBONS
MESOZOIC ERA
MINERALS
ORGANIC COMPOUNDS
ORIGIN
PRODUCTIVITY
PYRITE
ROCKS
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SEDIMENTATION
SHALES
SOURCE ROCKS
STRATIFICATION
SULFIDE MINERALS
UPWELLING