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Rhythmic Sedimentation in a Mid-Pennsylvanian Delta-Front Succession, Magoffin Member (Four Corners Formation, Breathitt Group), Eastern Kentucky: A Near-Complete Record of Daily, Semi-Monthly, and Monthly Tidal Periodicities

By
Rhonda M. Adklns
Rhonda M. Adklns
Department of Geological Sciences, 4044 Derring Hall, Virginia Tech, Blacksburg, Virginia 24061
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Kenneth A. Eriksson
Kenneth A. Eriksson
Department of Geological Sciences, 4044 Derring Hall, Virginia Tech, Blacksburg, Virginia 24061
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Published:
January 01, 1998

Abstract

The Magoffin Member of the Four Corners Formation (Breathitt Group) outcrops in eastern Kentucky as a predominantly coarsening-upward succession of rhythmically interstratified sandstone, siltstone, and mudstone with minor occurrences of limestone at its base. Primary sedimentary structures, trace fossils, vertical successions of facies, and sediment body geometries suggest that these rhythmically bedded sediments were deposited in a delta-front/distributary-mouth-bar setting. The overall thickness of the Magoffin Member is highly variable. Within the study area, it ranges in thickness from less than 25 m to greater than 40 m. Evidence indicates that in areas where the Magoffin Member is thickest, it tends to be sandier and contain rhythmite intervals that are thicker and more complete than in areas where it is thin. The member displays several orders of centimeter- to decimeter-scale cycles that are consistent with semi-diurnal, diurnal, semi-monthly, and monthly tidal periodicities. Halfsynodic (semi-monthly neap-spring-neap) and anomalistic (monthly) lunar periodicities are manifested by the systematic thickening and thinning of the shorter duration cycles. The rhythmite interval ranges in thickness from less than 5 m up to 20 m and records up to four months of deposition. Accumulation rates for the rhythmites typically ranged from 20–100 cm per neap-spring-neap event, but reached rates of over 30 cm per day in areas where the Magoffin Member is thickest and the most proximal deltaic facies are preserved. The nature of tidal bundling suggests that these rhythmites accumulated in a mixed, dominantly semi-diurnal tidal system where both lunar phases and lunar declination influenced tidal cyclicity.

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Contents

SEPM Special Publication

Tidalites: Processes & Products

Clark R. Alexander
Clark R. Alexander
Skidaway Institute of Oceanography Savannah GA
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Richard A. Davis
Richard A. Davis
University of South Florida Tampa FL
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Vernon J. Henry
Vernon J. Henry
Henry Georgia Southern University Statesboro GA
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SEPM Society for Sedimentary Geology
Volume
61
ISBN electronic:
9781565761834
Publication date:
January 01, 1998

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