Controls on ramp, platform and basinal sedimentation in the Dinantian of the Dublin Basin and Shannon Trough, Ireland

Abstract

In the Dublin Basin a Courceyan ramp phase of sedimentation was followed in the Chadian by tectonic break-up of the basin into distinct shallow-water platforms, on which production of carbonate sediments continued in considerable volume, and 'deep' basinal areas in which it ceased. Progradation of the platforms across these basinal areas was limited, and mainly confined to the dip-slope of hanging wall blocks; progradation across fault scarps was rare. In the Shannon Trough basement-fault control was evident in the distribution and migration patterns of volcanic centres in the Chadian to Arundian, but despite this, ramp sedimentation occurred throughout the Dinantian, evolving into a purely constructional large platform by late Dinantian time. There was no break-up of the basin as in the case of the Dublin Basin.The reason for the contrasting behaviour of the two basins is related to the rate of upwards movement of extensional faults relative to sedimentation rates. In the Dublin Basin these faults penetrated to the palaeosurface to form scarps by the late Chadian, and this topography survived into the Brigantian. In the Shannon Trough these faults failed to surface, but deep basement structures controlled the distribution of Dinantian volcanic centres which lie on a series of ENE-trending lineaments. These lineaments, which parallel the axis of the Shannon Trough, almost certainly mark the traces of active down-to-basin faults that controlled its half-graben structure.The basement rocks of the two basins are clearly of a different nature; the Dublin Basin is floored by basement of a much more heterogeneous nature than the Shannon Trough, the former lying south and the latter north of the putative Iapetus Suture line.

Biostratigraphy, sequence stratigraphy and gamma-ray spectrometry of the Tournaisian-Viséan boundary interval in the Dublin Basin

“…Although this is beyond the scope of the present paper, it is worth mentioning that the low diversity foraminiferal fauna lacking some foraminiferal guides and containing abundant and morphologically diverse Eblanaia and other Tournayellidae that characterize the latest Tournaisian occurs in Lane in shallow water heterozoan-photozoan (foramderm) carbonates of the Lane Formation (Strogen et al 1996). A similar association (bryonoderm extended) (Beauchamp 1994, James (Carannante et al 1988, Westphal et al 2010.…”

“…The bioclast association in the calciturbidites corresponds to the heterozoan-photozoan facies in the lowermost part and to the photozoan facies in most of the section. This change in the upper part of MFZ 9 approximately 15 m from the base of the section may correlate with the similar change to photozoan associations in the higher part of MFZ 9 approximately 60 m below the top of the section in Rush and may be connected with the growth of the carbonate platform (Somerville et al 1992a, Pickard et al 1994, Strogen et al 1996.…”

“…Ammonoids in Rush reported by Smyth (1951) correspond to Ammonellipsites-Fascipericyclus zone vuyst 2006). Both levels are characterized by an increase in moravamminids which may be connected with the reorganization from a ramp into platform -rimmed basin (Sommerville et al 1992, Pickard et al 1994, Strogen et al 1996. In the Lane section, the Lane Formation corresponds to the latest Tournaisian MFZ 8 foraminifer zone and the top of the section correlates with the latest part of MFZ 8, as already stressed by Devuyst (2006).…”

“…1) is one of several sedimentary basins in Britain and Ireland, which were controlled by Caledonian structures that were reactivated during the Lower Carboniferous (Phillips & Sevastopulo 1986, Nolan 1989, Pickard et al 1994, Strogen et al 1996. The Lower Palaeozoic basement is overlain unconformably by Lower Carboniferous rocks.…”

“…In the past the base has commonly been identified at an horizon substantially older than its true recent position (Sevastopulo & Wyse Jackson 2009). Moreover, the foraminiferal record in the latest Tournaisian-earliest Viséan has been rather poor (Jones & Somerville 1996). Mamet (1969) described Lower Carboniferous foraminiferal associations in the Rush section of the Dublin Basin but did not identify the base of the Viséan.…”