Geology of the Troy, Miss., 7.5 Minute Topographic Quadrangle

Charles T. Swann and Jeremy J. Dew

Goals

The primary purpose of this investigation is to evaluate the stratigraphy as reported for Pontotoc County and to describe for the first time, the detailed stratigraphy for a portion of Chickasaw County. Secondary goals are to use the geological maps to evaluate the potential mineral resources for the area such as industrial minerals, identify any potential trapping mechanisms that could pool accumulations of natural gas or liquid hydrocarbons, and to provide a basic set of information to assist in the development of this area of Mississippi.

Status of Project

This project is complete. The details of the investigation are available in MMRI Open-file Report 09-2S. A digital version of the geological map is available through the MMRI web site. Funding for this project was provided by appropriations from the State of Mississippi.

Stratigraphy

Clayton Formation (Tertiary): The Clayton Formation is the basal stratigraphic unit of the Tertiary section in the map area. The Clayton outcrop belt is contained in the western half of the map and confined mostly to elongate ridge-top exposures. The exposed Clayton lithology typically consisted of massive, red, sandy, clay. The Clayton often contains varying amounts of glauconite in unweathered exposures and is probably the source of the red coloration in Clayton-derived soils (such as in the Redland Community and Redland Creek in the northwestern corner of the map), Iron oxide spheres and pellets appear associated with the highly weathered Clayton exposures. The Clayton may contain carbonates in the basal half of its section.

Prairie Bluff Chalk / Owl Creek Formations (Cretaceous): The Prairie Bluff Chalk and Owl Creek Formations are of different lithologies, but are stratigraphically equivalent units. This set of formations are bounded both above and below by unconformities. The upper contact is the well known Cretaceous - Tertiary boundary. The Owl Creek Formation is a clastic unit consisting of fossiliferous, fine-grained sands, silts and clays. The Prairie Bluff is a phosphatic chalk in its type section and is generally considered to be predominately calcium carbonate, although thin limestones and significant amounts of clastic-rich section have been assigned the Prairie Bluff name.

Ripley Formation (Cretaceous): The Ripley Formation was formally defined in 1860 for exposures in Ripley, Mississippi. The formation consists of four lithologic components that change along strike reflecting differing depositional environments. The Ripley Formation is recognized throughout the southeastern U.S.

  • Transitional Clay: The basal lithologic component of the Ripley Formation consists of 100 feet or more of clay with subordinate amounts of interbedded, fine-grained sand. The clay is locally fossiliferous (Figure 1).
  • Troy Beds: The Troy Beds (named herein) overly the transitional clay. It consists of calcareous sediments such as nodular limestone and marls and is approximately 50 feet thick. It is often abundantly fossiliferous and equivalent to the better known Coon Creek Tongue further north Figure 2).
  • Middle - Upper Ripley Sands: These sands overlie the Troy Beds and consist of medium- to coarse-grained, marine sands. The unit is typically sparsely fossiliferous. If the Chiwapa Sandstone is absent, this unit may be as much as 90 feet thick and comprises the upper-most Ripley stratigraphic component.
  • Chiwapa Sandstone: The Chiwapa Sandstone was formally named in 1958 for exposures in Pontotoc County. When present, it is the upper-most Ripley component. The Chiwapa consists of interbedded limestones, calcite-cemented sandstone, and calcareous sands. The thickness is highly variable, ranging from 0 to 50 feet. The Chiwapa is equivalent to the upper section of the Middle - Upper Ripley Sands and is often abundantly fossiliferous.


Figure 1: Jeremy Dew of the MMRI (front of photo) and George Phillips of the Mississippi Museum of Natural Sciences examine the bed of Tallabinnela Creek for Cretaceous fossils in the Ripley Formation.

Figure 1: Jeremy Dew of the MMRI (front of photo) and George Phillips of the Mississippi Museum of Natural Sciences examine the bed of Tallabinnela Creek for Cretaceous fossils in the Ripley Formation.

Figure 2: The Troy beds of the Ripley Formation can be abundantly fossiliferous. Pictured here is a fossil of Exogyra costata, a common Cretaceous oyster, in place in the marls of the Troy beds near Troy, Mississippi.

Figure 2: The Troy beds of the Ripley Formation can be abundantly fossiliferous. Pictured here is a fossil of Exogyra costata, a common Cretaceous oyster, in place in the marls of the Troy beds near Troy, Mississippi.

Mineral Resources

Hydrocarbons: Sediments in the subsurface Mississippian section, beneath the Cretaceous and Pennsylvanian section contain hydrocarbon accumulations of economic importance. Within the map area are the Goodfood Creek, Coleville, West Coleville, Van Vleet, Thelma, Bacon, and Troy Fields. These fields produce natural gas and, to a lesser extent, liquid hydrocarbons from the Lewis, Evans, Rea, Abernathy, or Carter sands.

Sands: Sands suitable for construction and road building are present in the study area with most of the existing sand pits in the Upper Ripley section. The thick Ripley sand section makes construction / road sand the most abundant industrial mineral. No sand was identified that would qualify as glass sand or specialty sands.

Groundwater: Groundwater resources are also an important aspect of the study area geology. The Ripley Formation forms the shallowest source of groundwater in the map area. In the Ripley outcrop belt, water wells may be as shallow as 30 feet, but water quality is often problematic (often excessive iron oxides). Water quality concerns have lead to some wells being drilled into the deeper Eutaw Formation at depths of as much as 1000 feet. Potentially small amounts of water could be derived from local sands in the younger Prairie Bluff / Owl Creek section and from the Clayton.

Educational Aspects

Three students (one undergraduate and two graduate students) from the University of Mississippi, Department of Geology and Geological Engineering assisted with various aspects of this project including field work.

Collaborators

Mississippi Museum of Natural Sciences
Mississippi State University Department of Geosciences
Mississippi Office of Geology



Contact Information

For more information, please contact Charles T. Swann
E-mail: cts@olemiss.edu
Phone: +1 (662) 915-7320
www.olemiss.edu/depts/mmri