Print this pageSome Controlling Factors on the Sequence Stratigraphic Evolution of Mississippian Mud Mounds
DOROBEK, S. L, M. F. HOFFMANN, S. L. BACHTEL, and S. K. REID
The evolution of carbonate mud mounds within Mississippian strata from North America and elsewhere was Influenced by several critical factors, including: antecedent ramp profiles (the archetypal profile for Mississippian platforms), low to moderate amplitude sea-level fluctuations (probably typical of early Mississippian time), sediment types deposited in outer ramp environments adjacent to mounds (crinoidal grainstone to marly lime mudstone), sediment dispersal patterns, and changing relative sediment accumulation rates for adjacent non-mound facies over the course of "third-order" relative sea-level fluctuations (the typical maximum "lifetime" of Individual mounds).
Mud mound growth was commonly initiated during relative sea-level rise and deposition of third-order transgressive systems tracts. Along antecedent ramps with extremely low-angle profiles, mounds are distributed over outer ramp regions for 20 km or more (dip direction). During relative sea-level rise, adjacent non-mound facies accumulate at comparatively slow rates (typically less than 1-2 cm/kyr). These slow accumulation rates are indicative of the somewhat sediment-starved, outer ramp position of many mounds.
During later highstand to lowstand conditions, prograding carbonate sands to marly facies interfingered with or buried mud mounds. Sediment accumulation rates for these non-mound facies were an order of magnitude faster than during transgressive conditions and "competition" between mounds and adjacent facies for available accommodation became important. Mounds could continue forming if they were far enough down-dip or had built enough relief during transgressive conditions to keep from being buried by progradational highstand/lowstand facies.
Sediments supplied from shallow ramp environments also influenced mound evolution. Mounds tend to be smaller where adjacent and overlying facies are argillaceous, suggesting that turbidity of the water column may have terminated mound growth prior to burial by progradational facies.