Cyclicity in Silurian island-arc carbonates, Alexander terrane, Alaska

Conference · Mon Mar 01 00:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5579787

Kittredge, L E; Soja, C M ^[1]

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1. Colgate Univ., Hamilton, NY (United States). Dept. of Geology

Silurian carbonates from Alaska (Alexander terrane) record the evolution of a submarine platform during waning volcanism in an island arc. A detailed stratigraphic analysis of a 47 meter-thick sequence revealed the existence of cyclically repeated limestones: coral-stromatoporoid wackestones alternate with oncoid packstones and bioturbated, silty lime mudstones. The coral-stromatoporoid deposits are characterized by a low-diversity assemblage of dendroid corals, massive stromatoporoids, Atrypoidea brachiopods, and rare occurrences of biostromes associated with Solenopora, high-spired gastropods, and crinoids. Oncoids typically are 2-6 mm in diameter and form massive, meter-thick units. Coated grains are symmetrically developed, have a shell or algal nucleus, and are also a minor component of coral-stromatoporoid beds. These lithologic units form seven, shallowing-upwards cycles (parasequences) that range in thickness from 3-9 meters. Coral-stomatoporoid wackestones form the base of each cycle and grade upwards into oncoid packstones with silty, lime mudstones at the top. This succession of lithofacies within each cycle reflects an increase in energy levels from relatively deeper water environments to relatively shallower ones. The lack of abrasion in the corals and stromatoporoids suggests predominantly quiet-water conditions in shallow subtidal areas affected by periodic turbulence. Comparison with correlative sections in Alaska and lack of correspondence with global sea level curves suggest that the primary cause of cyclicity was tectonic perturbations with secondary eustatic effects. Cyclic deposition in peri/subtidal sites was terminated by rapid drowning of the carbonate platform during late Silurian orogenesis.

• OSTI ID: 5579787
• Report Number(s): CONF-9303211-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALASKA
GEOLOGIC DEPOSITS
CARBONATE ROCKS
PETROLOGY
STRATIFICATION
DEPOSITION
FOSSILS
GEOLOGIC HISTORY
PALEONTOLOGY
SEA LEVEL
SILURIAN PERIOD
STRATIGRAPHY
VARIATIONS
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGY
LEVELS
NORTH AMERICA
PALEOZOIC ERA
ROCKS
SEDIMENTARY ROCKS
USA
580000* - Geosciences