Bethany Falls Limestone (Missourian) Sedimentation and Diagenesis, Missouri and Kansas: ABSTRACT

Abstract

The Bethany Falls Limestone is a 15-30-ft-thick shelf deposit within lower Missourian rocks of the Mid-Continent region. In outcrop the lower Bethany Falls is typically an open-marine, faunally diversified, carbonate wackestone. The upper Bethany Falls consists of a wide variety of shallower water carbonate mudstone, wackestone, and grainstone. Cross-bedded oolitic grainstone and faunally restricted mudstone are perhaps the most distinctive rocks in the upper Bethany Falls. Cross-bed dip azimuths in the oolitic facies provide evidence that deposition resulted from 2 dominant current systems, one basically longshore drift toward the northwest and another essentially onshore tidal flow toward the north-northeast. The sequence of open-marine wackestone succeeded by shallower water limestone resulted from rapid transgression. As progradation built the sea floor into the zone of agitation, oolitic sand developed. These bars restricted circulation in many interbar and back-bar areas which became sites of the faunally restricted carbonate mud. Carbonate deposition ceased when progradation built to normal high tide. Color mottling, ubiquitous in most upper Bethany Falls mudstone and wackestone, is a diagenetic effect related to selective bleaching of the original medium-gray or grayish-tan color. The bleaching apparently follows areas of initially high permeability. The controlling paths are commonly burrows or churned areas, crumbly vugs resulting from bioturbation and other processes, and microfractures formed by slumping and shrinkage. Grain diminution or removal commonly accompanies the bleaching, and many of the bleached areas exhibit microslump and convergence of laminae. End_of_Article - Last_Page 869------------