"The upper Mississippian Fayetteville Formation in northern Arkansas is primarily a calcareous black shale, but in some localities the upper one third to one half of the formation is made up of alternating black shales and limestones. Comparable lithologies have been suggested by some (Hallam, Ricken, Kent, and Sujkowski) to have been created by the diagenetic segregation of carbonate from calcareous shale.
Petrographic thin section analysis reveals that the lowest limestone beds of the rhythmic upper Fayetteville are made up almost entirely of microspar and all fossil material is recrystallized, even to the point of obliteration in some cases. The intervening calcareous shales contain generally smaller but better preserved fossils and are usually somewhat dolomitic. Faunal differences between the limestones and shales were observed. The limestones and shales immediately below the rhythmic part of the section are generally much more fossiliferous and more phosphatic than the rhythmic lithology.
The organic material present is amorphous and most likely algal in origin. Hydrocarbon analysis indicates that oil generation has occurred and that free or adsorbed hydrocarbons are present in the rock.
Evidence of diagenetic segregation such as destruction of fossils in shaley beds, lateral variation in limestone bed thickness, and lack of correlation between carbonate rhythms and sedimentary or faunal variations was not found. Primary structures and faunal variations suggest that a change in the depositional environment initiated deposition of the rhythmic lithology, and that periodic changes in sediment deposition created the rhythmic lithology"--Abstract, pages ii-iii.
Spreng, Alfred C., 1923-2012
Laudon, Robert C.
Hanna, Samir B.
Geosciences and Geological and Petroleum Engineering
M.S. in Geology and Geophysics
University of Missouri--Rolla
ix, 92 pages
© 1987 Edith Ann Starbuck, All rights reserved.
Thesis - Restricted Access
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Starbuck, Edith Ann, "A petrographic investigation of the rhythmically bedded upper Fayetteville Formation (Mississippian) in northern Arkansas" (1987). Masters Theses. 4333.