The provenance of Western Irish Namurian Basin sedimentary strata inferred using detrital zircon U–Pb LA‐ICP‐MS geochronology

Abstract

The Western Irish Namurian Basin (WINB) preserves classic examples of basin floor sequences through to slope deposits and deltaic cyclothems. Despite over 50 years of research into the WINB, its sediment provenance remains highly contested. Sedimentological arguments, including palaeocurrent vectors and palaeoslope indicators have been invoked to propose a sediment source from the NW or the west (i.e. from within Laurentia). These same indicators have been subsequently reinterpreted to reflect a southern provenance. It is not clear from sedimentological arguments alone which interpretation more accurately reflects the infilling of the WINB. Regional-scale constraints on WINB provenance may be obtained with detrital zircon U-Pb geochronology.U-Pb LA-ICP-MS detrital zircon analysis was undertaken on samples from three sandstone units at different stratigraphic levels within the WINB siliciclastic sedimentary fill (Ross Formation, Tullig Sandstone, Doonlicky Sandstone). The samples are dominated by 500-700 Ma zircons, which can be correlated with Cadomian-Avalonian orogenic activity within terranes to the south of the WINB (Avalonia/Ganderia, Armorica and Iberia). In contrast, Eastern Laurentia, to the north of the WINB, was devoid of orogenic activity at this time. WINB samples also yield age populations younger than 500 Ma, and older than 700 Ma. These are not diagnostic of a particular source terrane and thus could be derived from terranes north and/or south of the WINB. WINB detrital zircon age spectra can be reconciled by an Avalonian or combined Avalonian-Laurentian provenance for WINB sedimentary strata. Further research is required in order to distinguish between these two possibilities.

The provenance of the Devonian Old Red Sandstone of the Dingle Peninsula, SW Ireland; the earliest record of Laurentian and peri-Gondwanan sediment mixing in Ireland

“…2) shows three broad peaks that correspond to major crust-forming events that contributed to the formation of Laurentia (Cawood et al 2007). These peaks occur in the Archean, Paleoproterozoic and Mesoproterozoic, recording essentially uninterrupted zircon production from 1.9 to 0.9 Ga. A major characteristic of detrital zircon distributions from this sector of the Laurentian continent is the absence of zircons of late Neoproterozoic age owing to the absence of an active margin on the Laurentian continent at this time (Pointon et al 2012). The Rhinns Complex on the island of Inishtrahull off the north coast of County Donegal and the Annagh Gneiss Complex in County Mayo form the exposed Proterozoic Laurentian basement in Ireland, and are also the oldest rocks exposed in Ireland.…”

“…Kernel density plots (bandwidth 20 Ma) of published detrital zircon ages from various potential source terranes (modified and expanded afterPointon et al 2012). Laurentia data from…”

High‐resolution X‐ray fluorescence profiling of hybrid event beds: Implications for sediment gravity flow behaviour and deposit structure

“…Detrital zircon analyses by Pointon et al . () suggest that the sediment source to the Clare Basin included peri‐Gondwana terranes such as extensions of Ganderia and Avalonia lying to the south‐west and possibly involved recycling via earlier Devonian‐aged Old Red Sandstone basins. Given the low‐grade metamorphic provenance, it is likely that illite, sericite and chlorite were the dominant detrital clays at the time of Ross deposition.…”

Variable character and diverse origin of hybrid event beds in a sandy submarine fan system, Pennsylvanian Ross Sandstone Formation, western Ireland

“…Basin filling and shallowing were driven by a copious supply of fine sand, silt and clay delivered by transcontinental rivers. Uranium–lead (U‐Pb) provenance data (Pointon et al ., ) suggest an Avalonian or mixed Avalonian–Laurentian source along the suture zone to the south‐west and west. The overall fine grain size and quartz arenitic composition of the sand is consistent with long transport distances and/or recycling of sand from earlier dominantly fine‐grained Avalonian sources.…”

“…The thicker and largely structureless Tb1 event beds were probably emplaced by high-density flows (Lowe, 1982;Kneller & Branney, 1995), whereas the thinner and better structured event beds (Tb5 and Tb6) were deposited by low-density turbidity currents (Mutti, 1977). The weak normal grading reflects the largely uniform finegrained texture of the sand supplied to the basin, a function of the large scale of the hinterland delivery system and the recycled provenance (Elliott, 2000a;Pointon et al, 2012). The limited development of sedimentary structures in the upper parts of many of the beds suggests that most deposition was from high-concentration near-bed layers and that the tail of the flows, whilst turbulent, had relatively low volumes of suspended sediment and low suspended load fallout rates.…”