Waulsortian-Type Buildups and Resedimented (Carbonate-Turbidite) Facies, Early Mississippian Burlington Shelf, Central Missouri

Abstract

ABSTRACT The crinoidal carbonates of the Lower Mississippian (Osagean) Burlington Limestone in central Missouri consist of individual and multiple interconnected Waulsortian-type buildups and associated resedimented debris (carbonate-turbidite) facies. This association of Waulsortian-type buildups and turbidity-current sedimentation developed on the foreslope, toe-of-slope, and basinal near-toe-of-slope areas of the prograding Burlington Shelf. The Waulsortian-type buildups contain a core facies of dolomitized, bryozoan-crinoid, lime mudstone and a flank facies of symmetrically disposed, thin-bedded crinoidal packstone and grainstone. The core developed where bryozoan-crinoid thickets trapped carbonate fines of upslope (turbidity-current) origin. Lime-mud hardgrounds in the cores developed during prolonged breaks in the influx of lime mud. The flank beds developed by in situ disarticulation of indigenous crinoids and minor gravity-slide processes. The resedimented-debris facies are laterally continuous and normally graded grainstone and packstone. The beds show 1) a subdivision of Bouma intervals A and B; 2) coarse-tail grading; 3) scours, flutes, and load casts; 4) a generally random fabric except for crinoid-ossicle alignment in Bouma interval B; and 5) no articulation of crinoid stems or calyxes. These features, combined with the absence of infiltration textures, escape burrows, shell imbrication, and hummocky cross-stratification, are useful in distinguishing these resedimented beds from lag-suspension deposits of storm origin. The lower part of the Burlington (5-15 m thick) consists exclusively of Waulsortian-type buildup core and flank facies. These buildups rest on a thin, laminated dolomitic shale bed (starved-basin sediment) and represent basinal near-toe-of-slope deposition. The upper and middle parts of the Burlington Limestone, corresponding to foreslope and toe-of-slope depositional settings, consist of Waulsortian-type buildups and resedimented-debris facies. Considering approximate modern analogues, the resedimented debris probably came from various linear, near-shelf margin sources. The resedimented debris contains algal-bored grains from the shelf margin and foreslope biogenic grains and clasts.