Arkansas Stratigraphy Database

The Arkansas Paleozoic Stratigraphy Database, is the largest compilation of Paleozoic nomenclature of Arkansas. Included in this database are current, abandoned, and proposed lithostratigraphic names, along with each of their original citations, ages, type areas, type localities, type sections, primary reference sections, sub-division names (current, abandoned, and proposed), etymology, and a listing of the nomenclatorial history of each lithostratigraphic unit. Also included are two downloadable PDF files that illustrate the evolution of the stratigraphic nomenclature of the Ozark physiographic province in northern Arkansas (click here to download) and the Arkansas River Valley/Ouachita Mountain province (click here to download). The database is searchable based on name, status (abandoned, currently in use, or proposed), and age. Click the banner at the top to search the database. An example of a search result is below (click to enlarge).

Lithostratigraphy

Lithostratigraphy is the study of of stratigraphy based on lithology, differing from other stratigraphic studies such as chronostratigraphy (time), chemostratigraphy (chemistry), biostratigraphy (biology), among others. The lithology of Arkansas is dominantly sedimentary, such as sandstone, shale, and limestone, with some localized outcrops of Cretaceous igneous rocks. Divisions of lithostratigraphy are based on the characteristics of the rocks and contact boundaries that separate units from each other. Lithostratigraphic units are ranked based on prominence (i.e. regional exposure, also known as mappability): (from smallest to largest) bed, member (or lens, lentil, tongue), formation, group, and supergroup. Beds are the smallest unit and not commonly used in the Paleozoic stratigraphy of Arkansas. Members are typically more localized and defined on a distinct lithological characteristics as compared to the formation. Sometimes, these are termed lenses, lentils, or tongues. Formations are the most common rank and can also cover a large area, but do not necessarily need to be assembled into groups, or conversely, divided into smaller units. Like groups, formations can take the name of the dominant lithology (e.g. Fayetteville Shale) or if the formation is not comprised of a single dominant lithology, then it is given a name with "Formation" (e.g. Atoka Formation). Groups typically cover a very large area (such as several counties), and can be divided into formations that have a relationship across the area. Supergroups are assemblages of groups that, like groups, have an association with each other across a regional area. No supergroups are recognized in Arkansas. A lithostratigraphic unit may be carried across a region, such as state borders, and may change rank based on how well defined and mappable the unit is. 

Formality

Any unit may be formally or informally recognized; that is, they may or may not be recognized by an authoritative agency, such as the USGS or the Arkansas Geological Survey. If a name was written in a USGS or AGS publication with both parts of its name capitalized (e.g. Atoka Formation), then it is considered to be formally recognized (excluding pre-WWII era, during which time it was common to only capitalize the first part of the name and not the second [e.g. Atoka formation]). If the second part of the name is not capitalized, then it is considered to be an informal name. In the subsurface, the terminology is not well-defined and can differ from agency to agency or company to company. Thus, subsurface names are generally considered as informal.

Type localities

Type areas are regional areas where the lithostratigraphic unit was originally described in the publication that introduced the unit's name, such as Boone County. Type localities are local or specific areas where the unit was originally described and are commonly described, such as that mentioned above for the Cotter Dolomite. Sometimes, but not always described are type sections, which are specific locations where the unit was originally described along with a measured section in the original publication. Primary reference sections are equivalent to type sections, with the exception that a primary reference section is described after the original description was published and is explicitly proposed to be a type locality or primary reference section for a lithostratigraphic unit.

More info

This database is based on my Masters thesis, "Lost Names in the Paleozoic Lithostratigraphy of Arkansas", which itself was largely based on the USGS's Geologic Names Lexicon and John D. McFarland's "Stratigraphic Summary of Arkansas", along with the encouragement of Dr. Walt Manger. For more information regarding lithostratigraphic terminology, see the International Stratigraphic Guide and the North American Stratigraphic Code.

Only the Paleozoic nomenclature of Arkansas is available in this database. In the future, I'd like to include the Mesozoic and Cenozoic nomenclature, but I will require assistance to do so. Mesozoic nomenclature is in progress, but is currently on hold, while Cenozoic nomenclature requires assistance from those who are more familiar with pedostratigraphy (stratigraphy of soils/silts/sands).

A full list of references cited in the database are available here. Please notify me of any errors, typos, clarification issues, or updates at nm009@uark.edu.