CONTROLS ON MIDDLE TO LATE ORDOVICIAN SYNOROGENIC DEPOSITION IN THE SOUTHEASTERN CORNER OF LAURENTIA

• Main Author: Bayona, German
• Format: Others
• Published: UKnowledge 2003
• Subjects: Blountian orogeny|reactivation|Ordovician|peripheral foreland|inversion; Geology
• Online Access: http://uknowledge.uky.edu/gradschool_diss/364; http://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1367&context=gradschool_diss

Middle and Upper Ordovician strata in the southernmost Appalachians document initial collision along the southeastern margin of Laurentia during the Blountian orogeny, an early phase of the Taconic orogeny. Coeval drowning and exposure of different parts of the former platform and variations in stratal architecture have been attributed to tectonic and depositional loading along the collisional margin. Stratigraphic correlations, using a bentonite-graptoliteconodont time framework, a palinspastic map, and a map of subsurface basement structures, suggest that basement-fault reactivation, flexural subsidence, and eustasy variously controlled uplift, subsidence, and deposition at different sites within the peripheral foreland basin. This dissertation documents how pre-existing structures in the continental margin and interior affected subsidence, deposition, diagenesis, and composition of foreland strata, and deformation in tectonic loads. Stratigraphic correlations document an early episode of basementfault inversion in the distal foreland, and heterogeneous subsidence and provenance patterns in the middle and proximal foreland. Abrupt variations in depth of erosion of passive-margin strata and in thickness of distal foreland deposits coincide with the boundaries of the intraplate Birmingham graben. Inversion of the former graben increased the magnitude of erosion on inverted upthrown blocks; increased tectonic subsidence in adjacent blocks; supplied chert and quartz detritus to shallow-marine carbonate depocenters; and facilitated influx of meteoric water to aquifers in shallow-marine limestones. Tectonic subsidence of middle and proximal foreland deposits reflects local irregularities in the foreland subsidence and different rates of migration of the flexural wave along strike. Differential subsidence between embayments and promontories may have caused reactivation of transverse basement faults. Relief produced by reactivation of transverse basement faults and flexural normal reactivation of basement faults may provide sources for local conglomerates interbedded with deep-water shales. Differences in orogenicbelt deformation are reflected in provenance analyses that suggest exposure of dominantly feldspar-bearing basement rocks in the orogenic belt adjacent to the promontory and exposure of basement rocks and sedimentary cover in the orogenic belt adjacent to the embayment. Results of this study reveal the importance of considering the effects of pre-existing structures in the interpretation of along- and across-strike variations of foreland strata. Therefore, geodynamic modeling of the Blountian foreland basin needs to consider along-strike variations in the geometry of tectonic loads and reactivation of different basement structures.