The Dalradian rocks of the south-west Grampian Highlands of Scotland

Tanner, Peter; Bendall, Charles A.; Pickett, Elizabeth; Roberts, John L.; Treagus, J. E.; Stephenson, David

doi:10.1016/j.pgeola.2012.07.008

Cited by 18 publications

(6 citation statements)

References 109 publications

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“…The Garvellachs have the advantage of complete exposure of the stratigraphy, together with scope for exploring lateral variations and the whole archipelago has been designated as a Site of Special Scientific Interest within the Geological Conservation Review (Tanner et al, 2013). Strata dip systematically SE ( Fig.…”

Section: Lithostratigraphymentioning

confidence: 99%

Tonian-Cryogenian boundary sections of Argyll, Scotland

Fairchild

Spencer²,

Ali

et al. 2018

Precambrian Research

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The Tonian-Cryogenian System boundary is to be defined at a GSSP (Global Boundary Stratigraphic Section and Point) beneath the first evidence of widespread glaciation. A candidate lies within the Dalradian Supergroup of Scotland and Ireland, which is least deformed and metamorphosed in Argyll, western Scotland. We present new stratigraphic profiles and interpretations from the Isle of Islay and the Garvellach Islands, update the chemostratigraphy of the Appin Group Tonian carbonates underlying the thick (ca. 1 km) glacigenic Port Askaig Formation (PAF) and demonstrate an environmental transition at the contact.The Appin Group forms a regionally extensive, >4 km-thick, succession of limestones, shales and sandstones deposited on a marine shelf. On Islay, the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure, oolite, stromatolitic dolomite and intraclastic microbial mounds. Significantly deeper erosion at the unconformity at the base of the overlying PAF is demonstrated in the southern section. Carbonate facies show a gradual decline in δ 13 C VPDB from +5 to +2‰ upwards.In NE Garbh Eileach (Garvellach Islands), a continuously exposed section of Appin Group carbonates, 70 m thick, here designated the Garbh Eileach Formation (GEF), lies conformably beneath the PAF. The GEF and the GEF-PAF boundary relationships are re-described with new sedimentological logs, petrological and stable isotope data. Interstratified limestone and dolomicrosparite with δ 13 C of -4 to -7 ‰ (a feature named the Garvellach anomaly, replacing the term Islay anomaly) are overlain by dolomite in which the isotope signature becomes weakly positive (up to +1 ‰) upwards. Shallow subtidal conditions become peritidal upwards, with evidence of wave and storm activity. Gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the GEF. The basal diamictite (D1) of the PAF is rich in carbonate clasts similar to slightly deeper-water parts of the underlying succession. D1 is typically several metres thick with interstratified sandstone and conglomerate, but dies out laterally. Scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft-sediment deformation is interbedded with carbonate below and above D1. Dolomite beds with derived intraclasts and gypsum pseudomorphs are found above D1 (or equivalent position, where D1 is absent).Published and new Sr isotope studies, including successive leach data, demonstrate primary Tonian 87 Sr/ 86 Sr values of 0.7066-0.7069 on Islay, decreasing to 0.7064-0.7066 in the younger GEF limestones on the Garvellachs, with 1700-2700 ppm Sr. Other typically Tonian characteristics of the carbonates are the Sr-rich nature of limestones, molar tooth structure, and dolomitized peritidal facies with evidence of aridity. Seabed surveys suggesting uniformly-dipping strata and shallow borehole core material illustrate the potential for extending the...

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Section: Lithostratigraphymentioning

confidence: 99%

Tonian-Cryogenian boundary sections of Argyll, Scotland

Fairchild

Spencer²,

Ali

et al. 2018

Precambrian Research

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“…between the conglomerate and the Easdale Slate were sampled at Lagg (National Grid Reference NR 588774), Inverlussa (NR 643865) and Black Mill Bay (NM 732087) on the islands of Jura and Luing ( Fig. 2; localities described by Anderton 1977;Baldwin and Johnson 1977;Tanner et al 2013).Selected samples were then prepared as polished thin sections and examined using an ISI ABT-55 scanning electron microscope with Link Analytical 10/55S EDAX facility. The carbon content of some of the samples was measured using a LECO CS225 elemental analyzer.…”

Section: Methods Of Study Black Sandstones From the Scarba Conglomermentioning

confidence: 99%

“…The deep water Easdale Slate passes laterally up-dip to, a coarse pebbly quartzose sandstone, the Scarba Conglomerate (Figs. 1, 2) The Scarba Conglomerate averages 450 m thick, and is attributed to a submarine fan environment, including mass-flow and turbidite deposits on a north-dipping palaeoslope (Anderton 1985, Tanner et al 2013. It fines northwards and upwards, and is gradational into the Easdale Slate.…”

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A Neoproterozoic petroleum system in the Dalradian Supergroup, Scottish Caledonides

Bata

Parnell

2013

JGS

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Petroleum systems occur in the Neoproterozoic in several parts of the world, based on organic-rich hydrocarbon source rocks deposited during late Neoproterozoic high sea level. The Dalradian Supergroup in Argyll, Scotland, shows evidence for coupled source rock and reservoir rock. The Easdale Slate and laterally up-dip Scarba Conglomerate in the Easdale Subgroup, Argyll Group, were deposited as deep water mudrocks and submarine fan coarse pebbly sandstone respectively. The Easdale Slate contains several percent organic carbon, rich enough to be a good source rock. The pore-space in the sandstones of the Scarba Conglomerate is infilled with carbonaceous matter that originated as an oil residue. Pyrite spatially associated with the oil residue may reflect microbial sulphate reduction, as occurs in many younger petroleum reservoirs. Despite greenschist facies metamorphism, the Easdale Subgroup records a hitherto unrecognized petroleum system, which adds to a global picture of late Neoproterozoic hydrocarbon generation.

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“…During the mid-Ordovician Grampian Orogeny, major fold systems were formed (Tanner et al, 2013). One of these is a set of mostly NE-plunging en echelon anticlinal folds collectively referred to as the Islay Anticline ( Fig.…”

Section: Study Areamentioning

confidence: 99%

Stable isotopes of oxygen and hydrogen in meteoric water during the Cryogenian Period

Skelton

Löwhagen

Fairchild

et al. 2019

Precambrian Research

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2019) Stable isotopes of oxygen and hydrogen in meteoric water during the Cryogenian Period. Stable isotopes of oxygen and hydrogen in meteoric water during the Cryogenian Period, Precambrian Research (2018), doi: https://doi. ABSTRACTWe measured  18 O and  2 H values of muscovite and carbonate mineral separates from metamorphosed carbonate-bearing mudstone layers in late Tonian to early Cryogenian strata, including Sturtian glacial deposits, which were deposited in a coastal setting at an approximate paleolatitude of 30-35S and now crop out on Islay and the Garvellach Islands, Scotland. From these values, we calculated  18 O and  2 H values of meteoric water that equilibrated with clay at diagenetic conditions which we infer were reached shortly after deposition (i.e. before the end of the Cryogenian Period) because sediment accumulation was rapid due to fast subsidence at that time.This calculation required removal of the effects of exchange with reservoir rocks, metamorphic volatilization and mixing with metamorphic fluids on  18 O and  2 H values. The values we calculated for meteoric water fall within the 2 ranges  18 O = -1 to -4 ‰ and  2 H = 0 to -23 ‰, respectively.These ranges are similar to present day values at equivalent latitudes. This finding is consistent with sediment accumulation in the Cryogenian Period having occurred in a climate similar to present day (Ice Age) conditions. This conclusion is not at odds with the Snowball Earth hypothesis because one of its predictions is that sediment accumulation occurred as the climate warmed at the end of panglaciation, a prediction supported by sedimentological evidence of multiple glacial advances and retreats in our study area and elsewhere.Highlights  Baseline  18 O and  2 H of Cryogenian meteoric water are similar to the present day. Snowball Earth episodes are associated with negative excursions from this baseline. Effects of post-depositional exchange can be removed from  18 O and  2 H records.

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The Dalradian rocks of the south-west Grampian Highlands of Scotland

Cited by 18 publications

References 109 publications

Tonian-Cryogenian boundary sections of Argyll, Scotland

Tonian-Cryogenian boundary sections of Argyll, Scotland

A Neoproterozoic petroleum system in the Dalradian Supergroup, Scottish Caledonides

Stable isotopes of oxygen and hydrogen in meteoric water during the Cryogenian Period

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