Middle Hettangian (Lower Jurassic) ammonites from Isle of Raasay, Inner Hebrides, and correlation of the Hettangian-lowermost Sinemurian Breakish Formation in the Skye area, NW Scotland

Morton, Nicol

doi:10.1144/sjg35020119

Cited by 4 publications

(3 citation statements)

References 21 publications

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“…In the case of the Hebrides Basin, NW Scotland, Amiri-Garoussi (1977) suggested that locally derived smectite-rich assemblages of the Hettangian-earliest Sinemurian Lower Broadford beds (now Breakish Formation;Morton 1999) were replaced upwards by a mixture of illite and kaolinite in the Sinemurian, because the smectite sources had been either depleted or buried beneath onlapping sediment. As in the Hebridean area, so in southern England the Hettangian and Sinemurian interval is characterized by onlap on Hercynian massifs such as the London Platform (Donovan et al 1979).…”

Section: Discussionmentioning

confidence: 99%

Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England)

Deconinck

Hesselbo

Debuisser

et al. 2003

Int J Earth Sci (Geol Rundsch)

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We present a dataset including clay mineralogy, gamma-ray spectrometry, organic matter content and magnetic susceptibility of the Hettangian to lowest Sinemurian successions of Dorset and Somerset, southern UK (Blue Lias Formation, Bristol Channel and Wessex basins). In both areas, the clay assemblages comprise predominantly detrital illite, kaolinite and illite/smectite mixed layers. Clays probably originated from the erosion of the Hercynian massifs, the relative proportions of kaolinite and illite being modulated by arid-humid climatic fluctuations. The organic matter (OM) content (types II to IV) ranges up to 12% in both areas. A clear stratigraphical trend in clay mineral assemblages is apparent in Somerset, whereas in Dorset sharp contrasts between adjacent horizons and a greater dilution by carbonate mask the long-term evolution. Correlations between both areas based on similar vertical trends in clay mineral abundance support the suggestion of a hiatus within the angulata Zone of the Dorset succession. As expected, the kaolinite/illite ratio correlates with the Th/K ratio deduced from gamma-ray spectrometry. However, significant departures from the correlation occur in OMrich intervals, suggesting that Th may be partly adsorbed on to OM particles. Surprisingly, high magnetic susceptibility correlates with abundant kaolinite, not with Ferich clays, indicating either that kaolinite is accompanied by a soil-inherited magnetisable phase (possibly iron oxide) or that illite-rich rocks are more strongly diluted by carbonate than are kaolinite-rich strata.

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Section: Discussionmentioning

confidence: 99%

Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England)

Deconinck

Hesselbo

Debuisser

et al. 2003

Int J Earth Sci (Geol Rundsch)

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“…The 14 plant‐bearing horizons identified within the Bearreraig Sandstone Formation span deposits extending from the middle of the Opalinum Zone of the Dun Caan Shale Member to the top of the Laeviuscula Zone in the Holm Sandstone Member (Fig. 1C; Morton and Hodson, 1995). The Bearreraig Sandstone Formation represents a succession of shallow marine sediments, into which fossil plants rafted from surrounding land areas (Bateman and Morton, 1994; Bateman et al, 2000).…”

Section: Methodsmentioning

confidence: 99%

Middle Jurassic evidence for the origin of Cupressaceae: A paleobotanical context for the roles of regulatory genetics and development in the evolution of conifer seed cones

Spencer

Mapes

Bateman

et al. 2015

American J of Botany

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Scitistrobus duncaanensis extends the fossil record for anatomically preserved seed cones of the Cupressaceae backward from the Upper Jurassic to the Aalenian Stage of the Middle Jurassic. The cone displays a previously unknown combination of characters that we regard as diagnostic for seed cones of early-divergent Cupressaceae and helps to clarify the sequence of structural changes that occurred during the transition from ancestral voltzialean conifers to morphologically recognizable Cupressaceae. Hypotheses of homology underpinning such transformational series can be tested by ongoing reciprocal illumination between the morphology of fossil taxa and the morphogenesis and developmental genetics of their extant crown-group relatives.

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“…The contact is obscured by approximately 10 m of dead ground at Neist Point, but the first exposed eruptive deposits comprise subaerial sheet lavas. The sedimentary rocks below the subaerial lavas are dominated by Middle Jurassic shallow marine siliciclastic sediments (Searl, 1994;Morton, 1999;Hesselbo and Coe, 2000) and estuarine strata with many coarse-grained facies, crossbedding sedimentary structures, and nonmarine shales (Morton, 1983;Harris, 1989). The subbasalt sediments have locally been extensively intruded by dolerite sheet intrusions.…”

Section: Onshore: Isle Of Skye Scotlandmentioning

confidence: 99%

Mafic intrusions, hydrothermal venting, and the basalt-sediment transition: Linking onshore and offshore examples from the North Atlantic igneous province

et al. 2017

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The emplacement of large intrusive complexes into sedimentary basins can have profound effects on host sedimentary rocks including deformation, thermal aureole metamorphic reactions, alteration of fluid-flow pathways, and the formation of associated hydrothermal vent complexes (HVCs). These processes can in turn have major implications for petroleum systems on the local and regional scale, and can contribute to global climate change due to the production and outgassing of greenhouse gases, such as CH 4 and CO 2 . Imaging these features and assessing their implications from seismic data beneath extrusive volcanic cover is challenging due to heterogeneities in the volcanic pile and at the basalt-sediment transition. We have evaluated combined field and laboratory petrophysical data from the Isle of Skye, Scotland, where we identify a seismic-scale example of extensive intrusions interacting with the base-basalt transition. We have also evaluated a unique onshore example of a linked sill and associated HVC cutting up through the lava sequence. We compare these field results with HVCs from reflection seismic data across the Vøring Marginal High, offshore Norway, where subbasalt saucer-shaped intrusions are also seen associated with HVCs cutting the lava sequence. Seismic imaging problems associated with the velocity heterogeneity of volcanic sequences, along with a historical lack of highquality 3D data in volcanic regions worldwide, is suggested as having largely precluded the identification of these features in the past. The under-representation of these hydrothermal vents in the literature has key implications for the future appraisal of intrusion-related outgassing effects on the global climate such as those related to the Palaeocene Eocene Thermal Maximum, along with subbasalt petroleum prospectivity where they may alter maturation and migration pathways.

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Middle Hettangian (Lower Jurassic) ammonites from Isle of Raasay, Inner Hebrides, and correlation of the Hettangian-lowermost Sinemurian Breakish Formation in the Skye area, NW Scotland

Cited by 4 publications

References 21 publications

Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England)

Environmental controls on clay mineralogy of an Early Jurassic mudrock (Blue Lias Formation, southern England)

Middle Jurassic evidence for the origin of Cupressaceae: A paleobotanical context for the roles of regulatory genetics and development in the evolution of conifer seed cones

Mafic intrusions, hydrothermal venting, and the basalt-sediment transition: Linking onshore and offshore examples from the North Atlantic igneous province

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