Upper Eocene

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Upper Eocene

• John Ariail

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Introduction

• Roughly 55.8 million year ago
• Jacksonian Provenance
• Upper and lower components separated by
  discontinuity that can be trace from eastern
  Miss. To central S.C.
• Discontinuity from uplift of Piedmont and mild
  regression at lower Jacksonian boundary.
• Divided into Ocala and Barnwell groups

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Barnwell Group

• Clinchfield, Dry Branch, Tobacco Road Sandstone
  Formations
• Series of Upper Eocene near shore to coastal
  marine, sandy deposits in the Fall Line Hills
  area of central to eastern GA and western SC
• Grades downdip into Ocala Group
• Mainly quartz sand, smaller amounts of clay,
  limestone, chert, siliceous fossils, and small
  bone fossils such as fish teeth
• Highly permeable sands make up the Upper Three
  Runs Aquifer

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Barnwell Group

• Overlies Huber formation
• Has smectite clays versus kalonitic of Huber
  Formation
• Altamaha Formation (marginal marine) overlies
  Barnwell Group

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Clinchfield Formation

• Riggins Mill, Treadwell, Albion, Utley
  Limestone Members east of Ogechee River
• Basal sand deposit of Barnwell group
• Mainly medium-grained well-sorted unconsolidated
  calcareous fossiliferous sand.
• Overlies the Oconee Group

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Dry Branch Formation

• Twiggs Clay, Irwington Sand, Griffins Landing
  Member
• Overlies the Utely Limestone of Clinchfield Sand
  Formation
• Shallow water, marine depositional environment
  with giant oyster fossils present suggesting
  presence of near shore environment with fresh
  water input
• Three members interfinger suggesting near shore
  environment including bays, lagoons, beaches,
  tidal inlets, and oyster beds

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Tobacco Road Sandstone Formation

• Burrowed bioturbated, massive, poorly sorted,
  medium to coarse, pebbly, weathered sand
• Extends from Houston County to SC with a northern
  limit of the Fall Line
• Discontinuous bed of flat pebbles serve as marker
  for the basal contact with the Dry Branch
  Formation beneath it.
• Coastal marine, beach, to back barrier
  depositional environment
• Cross-bedded with presence of silicified sand
  dollars

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Ocala Group

• Ocmulgee, Tivola Limestone, Williston, Crystal
  River Formation
• In the subsurface underlies more than 4/5s of
  Georgia coastal plain

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Williston Crystal River Formations

• Recognized in Southwestern GA, Wayne County in
  Eastern GA
• Extends into Alabama
• Williston Formation correlated with Moodys Branch
  Formation in Alabama
• Williston - indurated, recrystalized limestone,
  less fossiliferous than lateral equivalent Tivola
  Limestone

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Williston Crystal River Formations

• Crystal River softer, less consolidated coarse
  fossiliferous limestone, foramifera rich
• Lateral equivalents of Tivola Ocmulgee
• Coincide with lower / upper Jacksonian boundary
• Limestone lithology indicates minor sea
  regression and restricted marine conditions on
  continental shelf

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Tivola Limestone

• Byrozoan-rich, coarse, bioclastic limestone
• Poor sorting of bioclastic debris
• Large fossils such as oysters byrozoans
• Areas have been removed by solution, leaving a
  brown clayey, cherty residium between Dry Branch
  Clinchfield Formations
• Grades laterally to the east north into the
  Twiggs member of Dry Branch Formation

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Ocmulgee Formation

• Extends from Houston Pulaski Counties east as
  far as Savannah River
• Slightly indurated, fossiliferous, very
  calcareous, granular limestone
• Facies change laterally into the Tobacco Road
  Sandstone
• Nearshore facies or subdivision of offshore Ocala
  Group
• Used to be referred to as Cooper Marl, but is not
  the lateral equivalent of Cooper Marl in South
  Carolina

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Conclusion

• Upper Eocene deposits extend south of the Fall
  Line
• Can be correlated from Mississippi to South
  Carolina
• Largely shallow marine depositional environment
• Dominated by a period of major transgression of
  the Jackson Sea with minor periods of regression
• Major deposits are limestone, sandstone,
  calcareous sandstone

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References

• Herrick, S.M., Counts, H.H., (1968). Late
  Tertiary Stratigraphy of Eastern Georgia. U.S.
  Geological Survey, Water Resources Division,
  Atlanta, Georgia.
• Herrick, S.M., (1971). Age and Correlation of
  the Clinchfield Sand in Georgia, Contributions
  To Stratigraphy. Geological Survey Bulletin
  1354-E.
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• Huddlestun, Paul F., Hetrick, John H., (1979).
  The Stratigraphy of the Barnwell Group of
  Georgia. Reprinted 1988 by the Georgia
  Geological Society.
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• Huddlestun, Paul F., Hetrick, John H., (1986).
  Upper Eocene Stratigraphy of Central and Eastern
  Georgia. Department of Natural Resources
  Environmental Protection Division Georgia
  Geologic Survey, Bulletin 95.
• Huddlestun, Paul F., Summerour, Joseph H.,
  (1996). The Lithostratigraphic Framework of The
  Uppermost Cretaceous And Lower Tertiary of
  Eastern Burke County, Georgia. Department of
  Natural Resources Environmental Protection
  Division Georgia Geologic Survey, Bulletin 127.
• Richards, Horace G., (1955). The Paleocene and
  Eocene of Geogia (Part 2 Upper Eocene). Georgia
  Geological Survey, Atlanta, Georgia.