Early syndepositional tectonics of East Greenland's Old Red Sandstone basin
East Greenland's Old Red Sandstone basin formed in the interior of a mega-continent created by the Caledonian collision of Baltica and Laurentia. The basin has been regarded as a typical late- to post-orogenic extensional basin, formed in a collapsing orogen. Cross-cutting faults that have extended the basin substrata have been explained as Riedel and anti-Riedel shears that formed during basin initiation, but no detailed structural analysis has been presented. Analysis of geometrical relationships between faults and folds, and their relative timing with respect to the syn-tectonic deposits suggest a new model for basin evolution. In eastern Greenland, orogenic collapse was initiated at least as early as c. 425 Ma. Thus, the preserved Devonian basins formed after c. 70 Ma of large-magnitude crustal extension. Thick successions of Mid-Devonian Old Red Sandstone were deposited in troughs controlled by orogen-parallel extension and east–west folding. Later north–south-trending extensional structures cut the basal deposits, as episodes of folding continued until Permian time. Folding continued for c. 175 Ma after the Caledonian continent–continent collision and it is thus unrealistic to suggest that internal Caledonian forces caused these ‘late Caledonian spasms’. However, the collapsed orogen may have been thermally weakened, and the region was thus probably vulnerable to external forces resulting from the continuing orogenies along the rim of the megacontinent.
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New Perspectives on the Old Red Sandstone
From the 1960s onwards, the Old Red Sandstone of both borders of the Atlantic Ocean has acted as a test-bed for the development of new ideas on the interpretation of fluvial, lacustrine and aeolian sedimentary rocks, and the investigation of tectonically-active basins. Much of the earlier reconnaissance work is now being reviewed in the light of further detailed field study, along with new developments in the understanding of the biostratigraphy, palaeobiology, geochronology, pedogenesis and tectonics.
Three general papers review recent work on the stratigraphical and chronological analysis of the Late Silurian, Devonian and Early Carboniferous strata, and summarize present understanding of the tectonics of the basins. These are then followed by twenty-seven contributions covering new work in Eastern USA, Canada, Ireland, Britain, Norway, Greenland and Spitsbergen.