Stratigraphy of a flysch succession: the Ordovician of W Nithsdale, SW Scotland

Floyd, J. D.

doi:10.1017/s0263593300003278

Cited by 50 publications

(60 citation statements)

References 11 publications

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“…Early Ordovician ophiolite obduction was an extensive phenomenon at the Laurentian margin of Iapetus (Colman-Sadd et al 1992) and the subsequent erosion of the basic and ultrabasic rocks produced widespread late Ordovician greywackes rich in ophiolitic detritus. In the Southern Uplands these occur in the oldest, most northerly tectonostratigraphic tract (Floyd 1982). However, in view of the considerable strike extent of ophiolitic material, the juxtaposition with the Ballantrae Complex across the Southern Upland Fault may be fortuitous and should not be regarded as constraining lateral movement on that structure.…”

Section: The Southern Uplands Terranementioning

confidence: 99%

A regional geochemical assessment of some terrane relationships in the British Caledonides

Stone

Plant

Mendum

et al. 1999

SJG

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SynopsisRegional geochemical data have been systematically collected across the British Caledonides and interpreted, using single and multi-element image analysis, to provide geochemical constraints on terrane relationships. In the Hebridean Terrane, the Lewisian rocks show the characteristics of a large ion lithophile element (LILE) depleted lower crustal complex and seem unlikely to have been the source for the bulk of the overlying Torridonian clastic rocks. The psammite-dominated Moine Supergroup and the Dalradian rocks of the Grampian Group have closely similar evolved chemistries consistent with derivation from a higher crustal level than that of the currently exposed Lewisian complex. Across the Scottish Highland terranes the principal geochemical discontinuities coincide with the Moine Thrust Zone, the boundary between the Grampian Group and the Appin and Argyll Group Dalradian rocks, and the Highland Boundary Fault. The geochemical evidence provides little support for the Great Glen Fault as a significant terrane boundary. South of the Southern Upland Fault, which also coincides with a major geochemical discontinuity, a range of elements indicates division of the Southern Uplands terrane into northern and southern zones. These are transitional between the Orlock Bridge and Moffat Valley faults and reflect a change in sedimentary provenance during the early Silurian. Basic and ultrabasic elements, especially Cr, show exceptionally high levels over early Llandovery strata possibly indicating derivation from Iapetus Ocean crust obducted further NE as the Scandian Orogen was initiated. The geochemical characteristics of the southern part of the Southern Uplands Terrane continue into the Windermere Supergroup of the English Lake District, emphasising the continuity of mid-to late-Silurian deposition across the Laurentia-Avalonia (Iapetus) suture zone.

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Section: The Southern Uplands Terranementioning

confidence: 99%

A regional geochemical assessment of some terrane relationships in the British Caledonides

Stone

Plant

Mendum

et al. 1999

SJG

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“…Arc-style debris has been found in the coeval accretionary prisms in both the Southern Uplands (Floyd 1982;Smith et al 2001) and in Ireland (Morris 1987), confirming its former extent. Although the derivation of these deposits is sometimes contentious (Kelley & Bluck 1989;Phillips et al 2003), Kelling et al (1987), taking a considerable dataset, suggested sources mainly from the NW and NE.…”

Section: Later Ordovicianmentioning

confidence: 79%

Geotectonic evolution of Midland Scotland from Cambrian to Silurian: a review

Bluck

2013

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Synopsis During its Lower Palaeozoic history, the Midland Valley of Scotland was subject to compression from the blocks on either side, confirming the views of Kennedy (1958). Cambrian–Llanvirn-aged rocks of the Hebridean craton formed part of a passive margin, which extended to the ESE and is now replaced by the metamorphic complexes of the Moine and Dalradian. Both blocks had undergone metamorphism, uplift and shedding of their covers elsewhere. The ophiolitic part of the Highland Border Complex, which may be a continuation of the structurally foreshortened and rotated Ballantrae Complex, was obducted at c .490 Ma and may have interacted with rocks of the Hebridean passive margin. Ordovician rocks at Girvan are a small remnant of a one-time far larger forearc basin, which formed to the south of a major arc complex, originally situated in the Midland Valley and probably extending from somewhere in the North Sea to offshore Ireland and beyond. The Highland Border Complex includes rocks coeval with the Midland Valley arc at c .470 Ma that formed a back-arc basin. The Southern Uplands have converged on the Midland Valley, with the forearc sequence apparently missing in Scotland. Part of that convergence history is recorded in the Silurian conglomerates of the southern Midland Valley. Silurian sequences in this area contain conglomerates and breccias, derived from the south that record the presence of an igneous and possibly also a metamorphic complex in the region now occupied by the trench sequence of the Southern Uplands. It is suggested that the trench was later thrust over this source block and that the Southern Upland Fault forms part of that thrust sequence. The metamorphic complexes to the north, replacing the Hebridean passive margin, did not interact with the Midland Valley until Lower Devonian times. It follows that there was no mountain-building orogeny in Scotland, other than an arc, a sliver of trench, and numerous examples of crustal contraction by strike-slip and/or thrusting.

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“…However, re-valuation of the induration and petrography of the matrix (see below), together with the clast content and very high magnetic susceptibility, suggests that the unit is more likely to be a rudaceous facies within the Marchburn Formation (Floyd 1982). We propose that the Lamington Conglomerate Member (LAMN) is an integral part of the Marchburn Formation (MCHB), part of the Tappins Group (TAP).…”

Section: Introductionmentioning

confidence: 91%

The Lamington Conglomerate: further evidence for an ophiolitic source for the Ordovician Marchburn Formation, Northern Belt, Southern Uplands

Barron

Phillips

Floyd

2004

SJG

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Formerly regarded as an outlier of Lower Old Red Sandstone conglomerate within the Northern Belt of the Southern Uplands, the newly defined Lamington Conglomerate Member is now proposed to be an integral part of the Marchburn Formation (Tappins Group) of Ordovician (Caradoc) age. Pebbles and cobbles (up to 210 mm in size) are dominated by gabbroic and basaltic lithologies, with subsidiary amounts of tonalite, serpentinite, volcanic breccia and sedimentary lithic clasts. The matrix to the conglomerate is composed of a distinctive pyroxene-bearing sandstone. The member also has unusually high magnetic susceptibility, reminiscent of other units within the Tappins Group further to the SW, and consistently higher than any Old Red Sandstone conglomerate. The clast content supports an ophiolitic provenance for this part of the Marchburn Formation and is consistent with the overall petrography of the Tappins Group.

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Stratigraphy of a flysch succession: the Ordovician of W Nithsdale, SW Scotland

Cited by 50 publications

References 11 publications

A regional geochemical assessment of some terrane relationships in the British Caledonides

A regional geochemical assessment of some terrane relationships in the British Caledonides

Geotectonic evolution of Midland Scotland from Cambrian to Silurian: a review

The Lamington Conglomerate: further evidence for an ophiolitic source for the Ordovician Marchburn Formation, Northern Belt, Southern Uplands

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