37 Tectonics

Wednesday, 11 March 2026
8:30 AM - 10:00 AM
RCC, 106

Comparing Lower Mississippian Carbonate Mud Mounds of southwestern Missouri and Northwestern Arkansas with Type Waulsortian Mounds of Wallonia, Belgium

Paper number: 37-4
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Abstract

Troell (1962) identified more than 30 carbonate mud mounds in southwestern Missouri and northwestern Arkansas that he interpreted as bioherms. The largest reported was 300 ft long and 30 ft thick in the St. Joe Limestone (Compton Limestone). That mound is located on Elk-O-Zar Road next to Elk River in the Noel 7.5-minute quadrangle. The lateral extent that we measured was 172 ft long and 24 ft thick; actual extent of draping beds above the main masses is nearer 300 ft, and overall thickness of the Compton is about 30 ft. The main part of the mound is lenticular and composed of a recrystallized lime mudstone. An overlapping upper mass rests above it on the west side. Both parts rest on carbonate and shale facies of the Compton, and tapered, downlapping beds attached to the masses pinch out in adjacent carbonate and shale facies. Work on the Elk-O-Zar mound is in progress.

Carbonate and shale facies, like that below and adjacent to Elk-O-Zar mound, also are recognized around mounds along Highway 59, Highway DD, Elk Springs Road, and the intensely studied mound on Highway 71 in the Jane 7.5-minute quadrangle. Geologic mapping of the Noel and Jane quadrangles, as part of the U.S. Geological Survey’s EDMAP program, has furthered our understanding of the origin of the mounds. Most are found on the downthrown sides of major faults and folds; only one (Hwy DD) appears to be associated with faulting at shallow depth below the Mississippian. Evans and Bassett (2013; 2022) interpreted the mounds as slide and slump masses, based on associated structures such as auto-brecciation, roll-up beds, syn-tectonic duplexes, and tension cracks in updip strata. Alternative interpretations have included biohermal reefs, dislocated reefs, and mass accumulations due to baffling or microbial binding of mud.

Evans visited the Wallonia in 2025 to examine the original and newly designated type localities of mud mounds at Waulsort, Anserreme, and Celles-Gendron near Dinant. Belgian localities show a much wider diversity of carbonate fabrics, which will require further study, but the prevailing paradigm suggests these are accumulations associated with baffling and binding, although some interpretations reflect structural deformation of the Sudetic phase of deformation during the Hercynian orogeny.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411573

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