ALONG-STRIKE DIACHRONEITY OF OUACHITA-MARATHON OROGENY

The trace of the late Paleozoic Ouachita-Marathon thrust belt mimics the outline of the pre-orogenic passive margin around the Ouachita and Marathon embayments of southern Laurentia. Passive-margin strata of both shelf and off-shelf deep-water facies are overlain by synorogenic clastic-wedge deposits, which are diachronous along strike.

Deposition of a thick succession of deep-water mud-rich turbidites (Tesnus Formation) began in the Marathon embayment in Early Mississippian time, before initiation of similar deposition (Stanley Shale) in the Ouachita embayment during Meramecian (early Late Mississippian) time. Progradation of synorogenic clastic sediment over the passive-margin shelf progressed from east to west along the Ouachita embayment, beginning in the Black Warrior foreland basin in Meramecian time and reaching the Arkoma foreland basin by Atokan (early Middle Pennsylvanian) time. Pennsylvanian synorogenic deposits overlap shelf strata in the Fort Worth, Kerr, and Val Verde basins. Subsidence of the Marathon foreland began in middle Pennsylvanian time, somewhat later than in the Ouachita (Arkoma) foreland.

In the Arkoma foreland basin, the facies succession and a decrease in sedimentation rates mark the end of orogeny in Desmoinesian (late Middle Pennsylvanian) time. Similarly, in the subsurface south of Ouachita thrust-belt outcrops, Desmoinesian to Permian shallow-marine clastic and carbonate facies overlie deformed pre-Desmoinesian Ouachita strata at a distinct angular unconformity. In contrast, final Marathon thrusting is documented by an angular unconformity in the middle of the Wolfcampian (lower Lower Permian) succession.

Along-strike, east-to-west progression of Ouachita-Marathon orogeny is generally recognized; however, in detail, the pattern of along-strike diachroneity is more complex. Heterogeneity of provenance indicators suggests multiple, composite arc terranes, including a Silurian-Devonian orogen and possibly older continental crust, along with obduction of oceanic crust. Along-strike diachroneity reflects accretion of multiple terranes around the embayments and promontories of southern Laurentia.