Sedimentation in an actively tilting half‐graben: sedimentology and stratigraphy of Late Tournaisian–Viséan (Mississippian, Lower Carboniferous) carbonate rocks in south County Wexford, Ireland

Abstract

The Wexford Basin (south‐eastern Ireland) is a NE–SW‐trending sedimentary basin containing carbonates and evaporites deposited during the Late Tournaisian and Viséan. Two separate depositional areas are defined on the basis of facies and facies associations. Sediments were deposited in inner ramp, lagoonal and peritidal environments near Rosslare, and in a more open‐marine, shallow‐ to moderately deep‐water, mid to outer ramp environment in the western area around Duncormick. Thick breccia deposits that occur in the Wexford Basin formed as a result of (i) fault movement that produced syn‐sedimentary debris flows in the Late? Chadian (Breccia type I); (ii) dissolution of anhydrite/gypsum and subsequent collapse of sedimentary strata (Breccia type II); and (iii) fracturing and brecciation of porous rock caused by the movement of high temperature, late diagenetic fluids along fault planes (Breccia type III). The NE–SW facies polarity displayed by both sedimentary successions was the result of NW–SE extension and the reactivation of the NE–SW‐trending Wexford Boundary Fault during the Chadian. Extension at the SE margin of the basin with downthrow to the NNW gave the basin a half‐graben character. Thickening of the debris flow deposits to the SW suggests that while the half‐graben was being tilted it also underwent a NE–SW block rotation due to an axial component of that normal fault.

The value of a combined approach: Innovative mineral exploration techniques in the Irish Zn-Pb orefield

“…The Tober Colleen Event began during the latest stages of Cruicetown Group deposition (during Supra-Waulsortian deposition) and was dominated by strong subsidence (rather than faulting). Previous tectonic interpretations of the Dublin Basin suggest that the Tournaisian was dominated by gentle subsidence and sagging, while most faults were produced as a result of Lower Viséan tectonism (Nolan, 1989;Strogen et al, 1990;Andrew, 1992;Pickard et al, 1992;Pickard et al, 1994;Strogen et al, 1995;Nagy et al, 2005).…”

Synsedimentary brecciation in the Eifelian (Middle Devonian) Baltic Basin: sudden catastrophe or diagenetic collapse?

“…, 2001). In addition, a carbonate sabkha has been described from marine marginal settings during the Late Tournaisian–Viséan in south County Wexford in Ireland, where the crackle‐ to mosaic‐breccia is associated with gypsum/anhydrite settings (Nagy et al. , 2005).…”