Andrew C. Morton

Carboniferous sand provenance in the Pennine Basin, UK: constraints from heavy mineral and detrital zircon age data

Abstract The integration of heavy mineral analysis and detrital zircon age dating has enabled high-resolution differentiation and characterisation of Carboniferous sandstone provenance in the Pennine Basin of the UK. Heavy mineral data have identified a number of distinct mineralogical groups with different provenance histories and source-area compositions. Single-grain zircon dating on each mineralogical type has placed constraints on the geochronology of the various source terrains. This combination of mineralogical and isotopic data has led to the identification of four distinct source terrains and sediment transport pathways. During the Namurian, the majority of sediment was supplied from the north via the ‘Pennine delta’. The source region comprised a high-grade metasedimentary terrain with granitic intrusions. Zircon age data indicate that this lay within the part of Laurentia–Baltica affected by the Caledonian orogeny. Small amounts of sediment were shed northwards from the Wales-Brabant High, on the southern margin of the basin. Most of this was recycled from the Old Red Sandstone but some of it came directly from late Proterozoic igneous basement. Supply via the Pennine delta declined markedly in the Westphalian, with most of the Westphalian A and B being fed from the west. The western source mainly comprised pre-existing sediment, with variable contributions from ultramafic rocks. The precise location of this source remains conjectural: it is unlikely to be within the British Isles given the size and scale of the Westphalian fluvial systems, but the zircon age spectrum cannot be reconciled with derivation from the Appalachians–Newfoundland–Labrador area. Supply from the uplifting Variscan massif to the south became important in late Westphalian B times and continued into Westphalian D. Zircon age data indicate sourcing from Late Carboniferous granites and Cadomian and Icartian basement.

Insights into Cretaceous–Palaeogene sediment transport paths and basin evolution in the North Atlantic from a heavy mineral study of sandstones from southern East Greenland

Major changes in sandstone provenance occurred during the deposition of the Cretaceous–Eocene succession in Kangerlussuaq, southern East Greenland. These changes can be recognized on the basis of provenance sensitive heavy mineral parameters (apatite:tourmaline and rutile:zircon ratios and garnet geochemistry) and the SHRIMP U–Pb dating of detrital zircons. The results support the subdivision of the succession into three units separated by major unconformities spanning the Late Coniacian to Late Campanian and Late Maastrichtian to Early Eocene. Rifting during the deposition of the first unit (Aptian–Late Coniacian) led to rift flank uplift and resulted in the local sourcing of sediment. Thermal subsidence during the deposition of the second unit (Late Campanian–Late Maastrichtian) led to rift flank subsidence and sediment sourcing from outside the immediate region. Renewed rifting immediately preceding the third unit (Early Eocene) resulted in a return to local sediment sourcing. The basin morphology during the deposition of the second unit would have been more conducive for the long-distance transport of sediment into the adjacent Faroe–Shetland Basin than during deposition of the first and third units. The results provide a framework for the identification of Greenland-sourced material in the Faroe–Shetland Basin.

Understanding basin sedimentary provenance: evidence from allied phytogeographic and heavy mineral analysis of the Palaeocene of the NE Atlantic

The drilling of hydrocarbon exploration wells in the Faroe–Shetland Basin has provided an expanding sample resource that provides material for testing recently developed palynology-based sediment transport analysis. This technique has been verified by comparison with heavy mineral analysis; both approaches have been used to identify sediment sources and input points along the strike of the Palaeocene West Shetland Platform. Integration of heavy mineral and palynological data has provided a basis for understanding arenaceous and argillaceous sediment distribution and sourcing. In addition to a source from the western, Greenland side of the basin, four argillaceous and four arenaceous sedimentary sources have been identified along the strike of the West Shetland Platform. These vary in temporal and spatial distribution, and thus provide a history of sediment source evolution. This analysis supports a persistent difference in source between the Corona Basin and the Flett and Judd Sub-basins. Although source variation and overlap between basins is evident, transfer zones represent both conduits for and barriers to effective sediment transport. Both palynological and heavy mineral evidence identifies the former presence of Late Namurian–Westphalian strata on the West Shetland Platform, which were removed by subsequent erosion.

Correlation of Triassic sandstones in the Strathmore Field, west of Shetland, using heavy mineral provenance signatures

Abstract Integrated heavy mineral, mineral–chemical and zircon age data show that Triassic sandstones in the Strathmore Field result from the interplay of sediment derived from eastern and western sources. The Early Triassic Otter Bank Formation is interpreted as having a source on the British margin of the Faeroe-Shetland rift. Two main provenance components (recycled Devonian-Carboniferous Upper Clair Group in conjunction with Lewisian orthogneiss) were involved. The overlying Foula Formation (Middle-Late Triassic) was derived from high-grade metasedimentary/charnockitic basement rocks, interpreted as lying in the Nagssuqtoqidian belt of southern East Greenland on the opposite side of the rift. Zircon age data from the Foula Formation also provide evidence for an important Permian igneous event along the proto-northeast Atlantic rift. The switch in sediment supply from easterly-sourced to westerly-sourced detritus is the most clearly defined correlative event in the Triassic succession of the Strathmore Field. Variable supply from a subordinate zircon-rich component (probably of granitic origin) provides a basis for intra-Foula subdivision and correlation. The upper part of the Otter Bank Formation is characterised by a relatively high apatite/tourmaline ratio, believed to indicate the initial appearance of sediment from East Greenland. The construction of the correlation framework for the Triassic succession in the Strathmore Field depends crucially on identification and quantification of parameters that are sensitive to changes in provenance and insensitive to other processes that operate during the sedimentation cycle. This study demonstrates that ditch cuttings and core samples yield closely comparable heavy mineral data, indicating that construction of correlation frameworks can be readily achieved using ditch cuttings samples, although ideally cuttings data would benefit from calibration with core material.

The role of East Greenland as a source of sediment to the Vøring Basin during the Late Cretaceous

Provenance-sensitive heavy mineral criteria, mineral chemistry and detrital zircon age data show that there are strong links between Cretaceous sandstones in the Voring Basin and East Greenland areas. There are marked differences in the age spectra of detrital zircons from wells along the eastern margin of the Voring Basin (sandstone type K1) and those in the centre and west of the basin (sandstone type K2). The K1 sandstones have relatively simple zircon age spectra with largely Mid-Late Proterozoic zircons and a number of Caledonian age zircons. By contrast, the K2 sandstones have complex zircon age spectra, with Archaean, Early Proterozoic, Permo-Triassic and mid-Cretaceous zircons that are absent in the k1 sandstones. Some sandstones of Cenomanian and younger are from East Greenland share mineralogical features with the K2 sandstone type, having overlapping ranges of critical provenance sensitive parameters, such as RuZi, MZi and CZi, and similar types of detrital tourmalines and garnets. Detrital zircon age spectra from East Greenland samples include critical Archaean, Early Proterozoic and Permo-Triassic populations found in K2 sandstones. The zircon age data, therefore, provide support for sourcing of K2 sandstones from East Greenland. However, a source for the K2 sandstones to the cast of the Caledonian front in Scandinavia cannot be ruled out, neither can the recycling of older sediment previously transferred across the rift.

Volcanogenic impact on phytogeography and sediment dispersal patterns in the NE Atlantic

The Paleocene sedimentary sequences of the Faroe–Shetland Basin, northeast Atlantic, contain abundant palynomorphs (algae, pollen and spores). While one component of the palynoflora, the dinoflagellate cysts, has been used as the basis for biostratigraphical subdivisions of the succession, the terriginous palynoflora is the more abundant. This terriginous component was derived from two primary sources. The first, and most common source has an angiosperm palynoflora dominated by hickory types ( Momipites species), which occur in association with plane-types (various Tricolpites species) and Ginkgo . This palynoflora occurs commonly inmost Faroe–Shetland Basin wells throughout the early and mid-Paleocene succession. A second flora, which is restricted to early and mid Paleocene successions in the west of the basin, has an angiosperm component dominated by Cupuliferoipollenites and Cupuliferoidaepollenites species (broadly, ash and chestnut types). This Greenland Flora is confined to four main stratigraphical pulses in the early and mid-Paleocene, occurring more commonly in proximity to major transfer zones, and west of the Corona Ridge. This distribution pattern provides evidence of argillaceous sediment transportation from the west into the Faroe–Shetland Basin via major transfer zones. Comparison to palaeoclimatic interpretations dispute a relationship between climate change and westerly sediment input into the Faroe–Shetland Basin. Instead, a comparison is invited between pulses of igneous activity in the North Atlantic Igneous Province and sediment transfer from the uplifted eastern zone of the proto-North Atlantic rift.