Implications of calcite twin style in midcontinent carbonate rocks of the LaSalle anticlinal belt, Illinois Basin

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5770441

Qi, S L; Marshak, S ^[1]

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1. Univ. of Illinois, Urbana, IL (United States). Dept. of Geology

Standard strain gage'' analysis of twinning in calcite was completed on oriented samples from localities in the northernmost extension of the LaSalle anticlinal belt in the Illinois Basin. Units examined included Ordovician and Pennsylvanian bioclastic dolomitic calcarenites and limestones. These strata have been affected by outcrop-scale low-amplitude folding and reverse faulting. Preliminary results indicate that penetrative strain magnitudes associated with the twinning are low. The majority of twins observed in the Ordovician units are thick twins, and within the ordovician units the number of twins is low. Locally, thick twins pinch out toward the edge of a grain and/or taper to thin twins midway along the width of the grain. Within a very small percentage of the grains, the trace of the twin planes is continuously curved into an open arc. The majority of twins in the Pennsylvanian units are noticeably thinner than those of Ordovician units, suggesting a possible change in twin characteristics with stratagraphic level. Observed features of twinning in the Ordovician strata are comparable to borderline high temperature features of twinned calcite reported by Ferrill (1991), suggesting that twinning strain in the LaSalle anticlinal belt developed at temperatures of approximately 150-200 C. Such temperatures are higher than would be expected for shallow platform carbonate strata on the margin of an intracratonic basin, and are compatible with models in which formation of the twins was synchronous with regional hot-brine migrations linked to the Alleghanian orogeny. Heat transferred to shallow strata by these brine migrations may have effectively weakened midcontinent carbonate rocks, thereby permitting twinning to develop even though differential tectonic stresses were low.

• OSTI ID: 5770441
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALCITE
TWINNING
ILLINOIS BASIN
PALEOTEMPERATURE
BRINES
CARBONIFEROUS PERIOD
COMPARATIVE EVALUATIONS
ENVIRONMENTAL TRANSPORT
ORDOVICIAN PERIOD
OROGENESIS
RESERVOIR TEMPERATURE
STRAINS
CARBONATE MINERALS
EVALUATION
GEOLOGIC AGES
MASS TRANSFER
MINERALS
PALEOZOIC ERA
580000* - Geosciences