Semiquantitative and statistical analysis of bioturbate textures, Sequatchie Formation (Upper Ordovician), Georgia and Tennessee, USA

Semiquantitative and statistical analyses of bioturbate textures from the Upper Ordovician Sequatchie Formation of Georgia and Tennessee utilized: (1) bioturbate‐texture categories as indicators of a nearshore‐offshore gradient in bioturbation; (2) bioturbate‐texture intervals as a measure of variation of original bioturbation in differing paleoenvironments; and (3) transitions among bioturbate‐texture categories as a general guide to depositional rates.

Lithofacies define riverine‐estuary and offshore‐shelf facies. Un‐bioturbated and very slightly bioturbated intervals predominate in facies of the upper reaches of the estuarine system, whereas intensely bioturbated intervals are more common in facies of the lower reaches and offshore shelf. Mean thicknesses and variances of unbioturbated intervals decrease from the upper reaches to offshore facies, which correspond with an offshore increase in bioturbation. High probabilities of transitions from unbioturbated to very slightly bioturbated intervals in facies from upper and lower reaches may support physical evidence of rapid deposition by river floods or storms.

Some factors must be considered in order to distinguish actual differences in bioturbation between stratigraphic sections; the most important may be postdepositional compaction, which can alter original thicknesses of bioturbated intervals. Although sections examined may have undergone differential compaction, the differences in patterns of bioturbation are deemed as actual differences reflective of their respective paleoenvironments. However, some of the semi‐quantitative methods used in this study have limited value in interpreting paleoenvironments, and may not offer any more information than standard outcrop descriptions.