Ripley Sands' Providence, Eutaw, and Blufftown Formations

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Ripley Sands. Providence, Eutaw, and Blufftown
Formations

• Lithology, Characteristics, etc.

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Ripley Formation Backgroud

• Cretaceous strata was first recognized by Sir
  Charles Lyell on his second trip to North America
• E.W. Hilgard proposed the name Ripley in 1860 to
  distinguish strata in Tippah County, Mississippi
  that lays between the Rotten Limestone that he
  encountered, which is now given the name Selma
  Chalk, and lignite formation, now know as the
  Porters Creek Clay.

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Ripley Background

• The Cretaceous strata of the Ripley was first
  divided into the Eutaw Group and the Ripley Group
• The Eutaw Group includes the Tuscaloosa and Eutaw
  Formation, and the Ripley Group is known as the
  Ripley Formation and the Prarie Bluff Chalk
• In 1909 the Ripley Formation was subdivided into
  the Lower Marl (Blufftown), Middle Sand
  (Cusetta), Upper Marl ( Renfroe), and the Upper
  sand (Providence)
• The Renfroe Formation was later dropped, and
  known as the Perote Formation, which is situated
  between the Cusetta and the Providence Formation

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Ripley Formation

• The extent of the beds that the Ripley have been
  named extend from Twiggs County, in central
  Georgia to central Alabama
• The Selma chalk interrupts the formation
  synchronously, forming the top of the Upper
  Cretaceous between central Alabama, and Houston
  County, Mississippi
• Selma Chalk also occurs in Cretaceous
  stratagraphic units extending from Tennessee to
  Georgia

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Ripley History

• The extent of the Ripley Formation was better
  defined after paleontology studies better defined
  the limits of the formation and the subdivisions
  are still being redefined
• Sediments of the Ripley Formation and Providence
  Sand were deposited during the Maestrichtian,
  meaning the latest Cretaceous (65-70 Mya.)
• During this period transgressive-regressive
  deposition cycles occurred
• Sedimentary cycles throughout the Upper
  Cretaceous represent a period of rapid
  transgression followed by progradation (sediments
  build in the basin in areas of progradation)
• Progradation- The accumulation of sequences by
  deposition in which beds are depostited
  successively basinward because sediment supply
  exceeds accommodation. The shoreline migrates
  into the basin during episodes of progradation,
  known as regression

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Extent of the Ripley Formation

• The entire Ripley Formation extends from Northern
  Alaska, through the Central USA, down to South
  Georgia, then up through the northern U.S. to the
  southern part of Greenland
• Towards the east of Georgia, and east of the
  Chattahoochee basin, the Ripley Formation is
  thought to be around one thousand feet, and thins
  in Georgia, where it becomes a littoral sand
  (littoral sand- sand transported by erosion),
  then thins to 400 feet in Wickcliffe, Kentucky,
  and has been measured to be 50 feet in Cairo,
  Illinois according to well logs
• In Georgia, outcrops of the Ripley are known to
  be between ten to fifteen miles wide

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Composition of the Ripley Formation

• In Georgia, the Ripley is predominately massively
  bedded dark grey to greenish black marine sands
  of mainly calcareous, micaceous, pyritiferous,
  glauconitic, and argillaceous, depending on the
  conditions of sedimentation in different parts of
  the Ripley Sea
• Some contain enough fossils to be considered
  Marls (metamorphosed limestone)

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Eutaw Formation

• In west Georgia, it is characterized by facies of
  estuarine origin
• The central deposits are dominated by mud shales
• It is exposed in Columbus, Georgia and have
  fine-grained sand beds that reflect deposition
  during long occuring or intense storms, thus
  showing hummocky cross-stratification
• The Eutaw is mildly bioturbated, including funnel
  and disk-shaped structures, back-filled
  cylindrical burrows, and escape structures, and
  are composed of a diverse assemblage of trace
  fossils, which include assemblages of
  Ophiomorpha, Asterosoma, and Planolites.
• These ichnofossils occur mainly occur in mud, and
  can be attributed to deposit feeders that
  colonized the sands.

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