Contour-current deposition, slumping, and erosion of crinoid-rich sediment drifts, blocks and boudins(?) across the faulted Early Mississippian seafloor in N Arkansas-SW Missouri-NE Oklahoma

C. Robertson Handford

Consulting Sedimentologist

Huntsville, Alabama

Accumulation of thick, crinodal carbonates and minor siliciclastics along the southern margin of North America, or Laurussia, during Early Mississippian time constructed one of the largest carbonate platforms ever documented.  They crop out as Kinderhookian-Osagean limestones and cherts across the Ozarks in north Arkansas, northeastern Oklahoma, and southwestern Missouri and extend westward into the subsurface of the Anadarko Basin, where they comprise the STACK reservoirs.

      Early studies (Harbaugh, 1957: Troell, 1962; and Anglin, 1966) identified numerous bioherms developed within the Lower Mississippian St. Joe outcrops (Bachelor-Compton-Northview-Pierson of Missouri) in NE Oklahoma. These and similar mounds in southwestern Missouri were subsequently interpreted as Waulsortian mounds by Manger and Thompson (1982) and Lane (1984).  More recently, several studies have proposed that (1) syndepositional tectonic activity influenced Kinderhookian-Osagean deposition (Mazzullo et al., 2011; Evans, 2012; Evans and Basssett, 2013), and (2) some previously interpreted mud mounds show evidence of mass transport processes (Chandler, 2001; Evans and Basssett, 2012; Mazzullo and Wilhite, 2015; Childress and Grammer, 2015). Additionally, Mazzullo and Wilhite (2015) proposed that foreland bulge uplift led to subaerial exposure and erosion of Lower Mississippian carbonates and that basinward thinning was not due to condensed sedimentation but by erosion and exposure over the crest of a foreland bulge uplift.

      The current study supports syndepositional tectonic activity as a major driver and proposes that deep outer-shelf contour currents account for depositional thickening/thinning and submarine erosion of St. Joe strata around and over major structural elements. Basinward-thinning of Lower Mississippian strata was controlled by juxtapositioning of contour-current deposition and erosion around regional fault-controlled sea-floor perturbations and condensed sedimentation in a relatively deep outer-shelf.  Support for a contour current hypothesis is provided by isopach patterns, stratal geometry of sediment waves along outcrops, and facies characteristics.  St. Joe limestones are typically thin-medium bedded, relatively continuous, include bi-gradational beds, Zoophycos and Thalassinoides, bottom-current ripples and flaser-lenticular bedding, all of which are common in contourites. Significant thickness variations correspond to the NE-SW, NW-SE trends of well-known basement fault zones (Fayetteville, Drakes Creek, Chesapeake, Bolivar-Mansfield fault zones).  Preliminary observations suggest that the following characteristics are more common along fault zones:

• 1.      sediment-wave amplitude,
• 2.      increased depositional dip-angles within sediment waves,
• 3.      stratal truncation by submarine erosion, and
• 4.      slumping and perhaps soft-sediment boudinage. 

Biography

Robert is a sedimentologist and stratigrapher in Huntsville, Alabama who received his MS from the University of Arkansas in 1969 and his PhD from LSU in 1976. For most of his professional career he worked at major petroleum company research labs and as a consultant.  His experience is global and he has investigated siliciclastic, evaporite, and carbonate depositional systems ranging from continental to deep marine.  Robert was  an AAPG Distinguished Lecturer in 1995 on carbonate sequence stratigraphy and he has received several SEPM and AAPG awards for poster and speaker presentations.