Refined Paleoenvironmental Interpretation of Mississippian Oolites

Lenore P. Tedesco, Harold R. Wanless

Form and internal microstructure of both modern and ancient ooids vary with environmental setting - specifically in response to variations in the type, intensity and persistence of bottom agitation. The Mississippian oolitic sediment bodies of southern Indiana have geometric and petrologic characteristics that are similar to modern oolitic sediment bodies forming (a) in both tidal agitation and wind-wave-agitation settings and (b) in both persistently and intermittently agitated environments.

Modern oolitic sediments of the southeastern Bahamian archipelago form in wind-agitation as well as tidal-agitation settings. Tidal agitation settings include cross-bedded to bioturbated platform-margin shoals and banks. Wind agitation settings include agitated beaches, platform interior sand banks and the level-bottom platform interior. These wind-agitated settings produce stratified grainstones as strandplain deposits, cross-bedded to bioturbated grainstones on platform-interior banks and rippled to bioturbated level-bottom grainstones of the platform interior. Oolitic grains in persistently agitated tidal and wind settings form concentrically laminated spherical grains on tidal shoals, channels and beaches. Ooid size varies from fine to coarse with energy setting. Ooids in intermit ently agitated settings (shoal flanks; deeper platform interior) grow into irregular-shaped medium to coarse grains because boring, micritization, encrustation and aggregation modify grain surfaces during quiescence.

Mississippian oolites of southern Indiana, situated in the paleo-trade wind belt, display a spectrum of subtidal to strandplain environments that record persistent to intermittent agitation in both wind-wave and tidal settings. Integration of sediment body geometry, structures and grain microstructure is permitting refined paleoenvironmental interpretation within these widespread oolitic deposits.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995