Sediment routing and recycling through multiple basins from Palaeozoic to Mesozoic times: a provenance study of the Devonian Old Red Sandstone of southern Ireland and neighbouring offshore Mesozoic basins
Fairey, Brenton J.
University College Cork
This study presents the first dataset of detrital zircon U-Pb ages from the Devonian Old Red Sandstone (ORS) in the Dingle and Munster Basins as well as the offshore Mesozoic North Celtic Sea Basin (NCSB), South Celtic Sea Basin (SCSB), Goban Spur Basin (GSB) and Fastnet Basin (FB). This large dataset is complimented by new detrital white mica Ar-Ar ages in both onshore and offshore basins as well as apatite U-Pb ages in the Dingle and Munster Basins. Previous work (Ennis et al., 2015; Soper and Woodcock, 2003) has indicated the possibility of recycling of Lower ORS (LORS) into the Upper ORS (UORS) due to mid-Devonian Acadian deformation and basin inversion. By exploring the possible sediment sources for each basin, the study aims to investigate the role of recycling in sediment provision to answer two main questions: 1)Does the UORS in southern Ireland represent large-scale recycling of LORS from the Dingle Basin? 2)Does the southern Irish ORS act as a major source of detritus for Triassic to Cretaceous sediments of the NCSB, SCSB, GSB and FB? Sedimentary rocks in the LORS have similar detrital zircon age distributions which are dominated by ca. 1.2 Ga zircons as well as late Neoproterozoic grains. These age distributions suggest a dominant contribution of detritus of Laurentian affinity as well as contributions from westerly and southerly derived Ganderian (peri-Gondwanan) detritus. Caledonian uplift of the area north of the Iapetus Suture would have allowed for a large contribution of Laurentian material. The majority of UORS samples contain very few late Neoproterozoic grains and are instead dominated by early Palaeozoic and ca. 1.1 Ga zircons. These detrital zircon age distributions represent recycling of northerly-derived Ordovician to Silurian sedimentary rocks of the Southern Uplands – Longford Down terrane, which are of Laurentian affinity, and not recycling of LORS as previously suggested. The western Toe Head and Old Head Sandstone Formations, which represent the transition from terrestrial ORS to Carboniferous marine environments, are dominated by zircons of Acadian (410-390 Ma) age as well as late Neoproterozoic zircons, suggesting a western offshore Acadian granite source. Clastic rocks of the eastern Old Head Sandstone Formation have a Laurentian provenance like that of the underlying UORS. Detrital apatite and white micas from the ORS indicate Late Caledonian (430-420 Ma) to Acadian sources which were generally not recorded by detrital zircon ages. The majority of samples in the offshore basins of southern Ireland have complex detrital zircon age distributions which indicate a mixture of sources. Most samples contain an abundance of late Neoproterozoic zircons of peri-Gondwanan affinity. Potential candidates for these zircons include Ganderia, Megumia, Avalonia and Cadomia but distinguishing between these is problematic – especially given the likely mixture of sources. The abundance of late Mesoproterozoic detrital zircons in some samples indicates the presence of a Laurentian source with the most likely delivery method for such zircons being recycling of UORS sedimentary rocks, simply due to their close proximity (forming the footwall to the NCSB) to the Mesozoic basins. Two detrital white mica samples have dominant Late Caledonian (~430 Ma) ages, one sample has mostly Acadian (~405 Ma) and one sample has a dominant late Neoproterozoic age. Thus, sediments in the southern Irish offshore basins were predominantly sourced from peri-Gondwanan terranes, Caledonian and Acadian granites and recycling of UORS sedimentary rocks.
Sedimentary provenance , Sediment recycling , Old Red Sandstone , Detrital zircon , U-Pb , Detrital apatite , North Celtic Sea Basin , Detrital mica
Fairey, B. J. 2017. Sediment routing and recycling through multiple basins from Palaeozoic to Mesozoic times: a provenance study of the Devonian Old Red Sandstone of southern Ireland and neighbouring offshore Mesozoic basins. PhD Thesis, University College Cork.