Milankovitch climate cyclicity and its effect on relative sea level changes and organic carbon storage, Late Cretaceous black shales of Colombia and Venezuela

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

OSTI ID:5998198

Villamil, T; Kauffman, E G ^[1]

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

The Late Cretaceous Villeta Group and La Luna Formation shows remarkable depositional cyclicity attributable to Milankovitch climate cycles. Each 30-60 cm thick hemicycle is composed of a basal gray shale, a medial black, organic-rich shale, and an upper gray shale with a dense argillaceous limestone cap. Fourier time-series analysis revealed peak frequencies of 500, 100, and 31 ka (blending 21 and 42 ka data). ThiS cyclicity reflects possibly wet cooler (shale) to dry, possibly warm (limestone) climatic changes and their influence on relative sea level, sedimentation rates/patterns, productivity, water chemistry and stratification. Wet/cool hemicycles may produce slight lowering of sealevel, increased rates of clay sedimentation, diminished carbonate production, water stratification, increased productivity among noncalcareous marine plankton, and increased Corg production and storage. Dry/warm hemicycles may produce a slight rise in sealevel, and return to normal marine conditions with low Corg storage. Source rock quality may depend upon the predominance of wet over dry climatic phases. Differences between climate-forced cyclicity and random facies repetition, are shown by contrasting observed lithological patterns and geochemical signals with litho- and chemostratigraphy generated from random models. Accomodation space plots (Fischer plots) for cyclically interbedded black shale-pelagic limestone sequences, allowed prediction of facies behavior, shoreline architecture, and quantitative analysis of relative sea level. The synchroneity of Milankovitch cycles and changes in hemicycle stacking patterns, were tested against a new high-resolution event-chronostratigraphic and biostratigraphic framework for NW South America. Geochemical spikes and hemicycle stacking patterns occur consistently throughout the sections measured, supporting the correlation potential of cyclostratigraphy.

• OSTI ID: 5998198
• Report Number(s): CONF-930306-; CODEN: AABUD2
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 77:2; Conference: International congress of the American Association of Petroleum Geologists (AAPG), Caracas (Venezuela), 14-17 Mar 1993; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
03 NATURAL GAS
COLOMBIA
PALEOCLIMATOLOGY
SOURCE ROCKS
TIME-SERIES ANALYSIS
VENEZUELA
BLACK SHALES
CLIMATE MODELS
CLIMATIC CHANGE
FOSSILS
GEOCHEMISTRY
LIMESTONE
LITHOLOGY
PLANKTON
SEA LEVEL
SEDIMENTATION
SHALES
STRATIFICATION
WATER CHEMISTRY
AQUATIC ORGANISMS
CARBONATE ROCKS
CHEMISTRY
DEVELOPING COUNTRIES
GEOLOGY
LATIN AMERICA
LEVELS
MATHEMATICAL MODELS
MATHEMATICS
PALEONTOLOGY
PETROLOGY
ROCKS
SEDIMENTARY ROCKS
SOUTH AMERICA
580000* - Geosciences
030200 - Natural Gas- Reserves
Geology
& Exploration