Fold amplification and parasequence stacking patterns in syntectonic shoreface carbonates

Abstract

Kinematic models for fault-related folding may be examined by estimating amplification and limb-tilt rates using the stratigraphies of syndeformational strata. The methodology behind such analyses is described with reference to a case study from the Maghrebian thrust belt of Neogene age from central Sicily. High biostratigraphic resolution is provided by Pliocene strata that were deposited across the Marcasita anticline during deformation. The coastal carbonate facies of the rocks record variations of relative base-level and tilt histories. Foraminifera and nannoplankton faunal assemblages, from interbedded and laterally continuous pelagic sediments, bracket the age of the strata, and sequence stratigraphic boundaries are used to correlate relative time lines through the depositional architecture. These chronostratigraphic data are incorporated into a depositional model to quantify the rates of uplift and sedimentation. Offlapping parasequences record progressive tilting of the fold limb. Regionally, other sections also show this offlapping relationship, but the rate of offlap varies, thus putting constraints on the uplift history across several profiles of the fold. Tilt rates for late Pliocene time, based on an astronomically calibrated time scale, are estimated at 1°/28 k.y., with uplift rates (relative to long-term sea level) of 1 m/k.y. The methodology may be applied to study along-axis variations in fold amplification or regional variations in deformation rate. The parasequence stacking patterns and their implied deformation rates are inconsistent with simple fault-bend fold and kink-band models. They are better explained by detachment folding and tightening of a preexisting anticline in conjunction with continued propagation of an underlying thrust.