Upper Ordovician-Lower Silurian shelf sequences of the Eastern Great Basin: Barn Hills and Lakeside Mountains, Utah

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5130183

Harris, M T ^[1]; Sheehan, P M ^[2]

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1. Univ. of Wisconsin, Milwaukee, WI (United States). Dept. of Geosciences
2. Milwaukee Public Museum, WI (United States). Dept of Geology

Detailed stratigraphic sections through Upper Ordovician-Lower Silurian shelf strata of the Eastern Great Basin were measured in two Utah localities, Barn Hills (Confusion Range) and Lakeside Mountains. Six major subfacies occur in these strata: mud-cracked and crinkly laminated subfacies, Laminated mudstone subfacies, cross-bedded grainstone subfacies, cross-laminated packstone subfacies, grainy bioturbated subfacies, muddy bioturbated subfacies, and thalassinoides burrowed subfacies. These occur in 1--10 m thick cycles in three facies: muddy cyclic laminite facies (tidal flats), cross-bedded facies (subtidal shoals), and bioturbated facies (moderate to low-energy shelf). The vertical facies succession, stacking patterns of meter-scale cycles, and exposure surfaces define correlatable sequences. The authors recognize four Upper Ordovician sequences (Mayvillian to Richmondian). An uppermost Ordovician (Hirnantian) sequence is missing in these sections but occurs basinward. Lower Silurian sequences are of early Llandoverian (A), middle Llandoverian (B), early late Llandoverian (C1--C3), late late Llandoverian (C4--C5), latest Llandoverian (C6) to early Wenlock age. In general, Upper Ordovician and latest Llandoverian-Wenlockian facies are muddier than intervening Llandoverian facies. The shift to muddier shelf facies in latest Llandoverian probably corresponds to the development of a rimmed shelf. The sequence framework improves correlation of these strata by combining sedimentologic patterns with the biostratigraphic data. For example, in the Lakesides, the Ordovician-Silurian boundary is shifted 37 m downward from recent suggestions. In addition, the sequence approach highlights intervals for which additional biostratigraphic information is needed.

• OSTI ID: 5130183
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CARBONATE ROCKS
DEPOSITION
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
GREAT BASIN
NORTH AMERICA
ORDOVICIAN PERIOD
PALEONTOLOGY
PALEOZOIC ERA
PETROLOGY
ROCKS
SEDIMENTARY ROCKS
SILURIAN PERIOD
STRATIGRAPHY
USA
UTAH