Howe of Byth Quarry - locality, Cainozoic of north-east Scotland

From Earthwise
Jump to navigation Jump to search
Merritt, J W, Auton, C A, Connell, E R, Hall, A M, and Peacock, J D. 2003. Cainozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, sheets 66E, 67, 76E, 77, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland).

Contributors: J F Aitken, D F Ball, D Gould, J D Hansom, R Holmes, R M W Musson and M A Paul.

Howe of Byth Quarry[edit]

Glacial and glaciofluvial features and the distribution of glacigenic deposits on Sheet 97 Fraserburgh. P915374.

Howe of Byth gravel quarry (NJ 839 753) lies at the confluence of a broad north-east trending valley and a meltwater channel orientated north-west to south-east and which now drains the Moss of Fishrie (P915374). The site, on Sheet 97, is thought to provide evidence of the glaciation of north-east Scotland in both the Late and Middle Devensian (Hall et al., 1995b). The sequence at the site also includes peat of the Late-glacial (Windermere) Interstadial overlain by cryoturbated gravel laid down during the following Loch Lomond Stadial.

Correlation of lithostratigraphical units in north-east Scotland. P915347.

The lithostratigraphy of the site was first set up informally by Hall et al. (1995b), but many of the units have been renamed subsequently by Sutherland (1999) in order to adhere more closely to international lithostratigraphical guidelines. The new names have been incorporated into the regional lithostratigraphy only where appropriate (P915347). The original and new names are given in the table for comparison.

Lithostratigraphy at the Howe of Byth
New name Old name Age
Peat (unnamed) Peat (un-named) OIS 1
Todholes Gravel Bed (Banffshire Coast Drift Group) Todholes Gravels Loch Lomond Stadial
Thinfolds Peat Bed (Banffshire Coast Drift Group) Byth Peat Windermere Interstadial
Auchmedden Gravel Formation (Banffshire Coast Drift Group) Auchmedden Gravels OIS 2
Byth Till Formation (East Grampian Drift Group) Byth Till OIS 2
Howe of Byth Gravel Formation (Banffshire Coast Drift Group) Byth Gravels OIS 3 ?
Graphic logs and lithostratigraphy of representative sections at the Howe of Byth quarry (after Hall et al., 1995b). P915309.

The oldest deposit is the Howe of Byth Gravel Formation, up to 13 m thick (P915309), which rests on granite, psammite and weathered red arkosic sandstone bedrock. It consists mainly of quartzite cobbles, which show crude subhorizontal bedding and are derived from the local Devonian conglomerates, together with sparse lenses of imbricate pebble gravel and cross-bedded sand. Palaeocurrents were directed towards the south. Brown gravel-rich diamictons, with a silty sand matrix, occur in the upper part of the H owe of Byth Gravel For mation and thicken to the north. In 1997, new sections in the northern part of the quarry showed the unit to comprise up to 8 m of gravel and gravelly diamicton. The beds and lenses of quartzite gravel were discontinuous and 20 to 80 cm thick, dipping gently southwards. The diamicton units were reddish brown in colour and comprised sandy matrix-supported quartzite gravel. Erect pebbles were noted at two locations within these diamictons indicating cryoturbation. The pit had been extended northwards by 1999 and erect pebbles were also observed towards the top of the unit. The gravels could now be seen to occupy a broad depression in the bedrock surface and the lowest beds contained much soft red sandstone similar to the underlying bedrock. The gravels were heavily iron stained with much black ‘iron-pan’ in the upper 4 m or so. The diamictons were seen to be greenish grey in colour and some of them could be traced for over 200 m southwards.

Devensian–Weichselian events in Britain and south-west Fennoscandia. P915290.

The Howe of Byth Gravel Formation is interpreted as forming an ice-proximal fan, deposited by meltwater draining southwards, with associated debris flow activity. In the distal parts of the fan, lenses of imbricate gravel and cross-bedded sand suggest formation of ephemeral bars. Although the high- energy, ice-proximal nature of the formation implies that ice was present along the northern coast of Buchan, the only material of nondurable Moray Firth origin observed within it was a single clast of grey mudstone.

Luminescence dating has given ages of 45 ± 4 and 37 ± 4 ka BP for sands within the Howe of Byth Gravel Formation (Hall et al., 1995b). If correct, these imply that the formation is Middle Devensian in age. This is contemporary with the Skjonghelleren Glaciation of western Norway between 42 and 36 ka BP (Larsen et al., 1987) (P915290). However, the degree of weathering observed in 1999 may cast doubt on the dating results. Similar developments of iron-pan were present in the gravels at Tillybrex, near Ellon, which are probably pre-Devensian in age, and have been seen in the oldest gravel unit at Leys, likely to be of OIS 8 age (see below). A problem is that the gravels contain much Old Red Sandstone-derived iron oxide as coatings to clasts. This material is easily mobilised and can give the impression of prolonged weathering. It is noteworthy that the most advanced development of staining and pan is in the proximal part of the fan where Old Red Sandstone material is most abundant in the gravel.

Overlying the Howe of Byth Gravel is the Byth Till Formation. This freshlooking, reddish brown, massive, matrix-supported, silty sandy diamicton is up to 3 m thick, but averages 0.8 to 1 m. Clast lithology is dominated by quartzite, psammite and Devonian sandstone. The Byth Till has a strong west–east clast fabric. The distinctive lithology and fabric suggest that it was deposited by a different ice stream to that from which the Howe of Byth Gravel was derived. The Byth Till is placed in the East Grampian Drift Group and is probably of Late Devensian age.

In the northern part of the quarry, the Byth Till Formation is overlain by up to 3 m of quartzite cobble gravel, the Auchmedden Gravel Formation. In lithology, this unit resembles the Byth Gravel except that it is less weathered. Clast imbrication suggests deposition by meltwater flowing to the south from an ice front to the north; not obviously that which laid down the underlying Byth Till. The Auchmedden Gravel dates from the deglaciation phase of the last ice sheet, while ice remained to the north of the site.

Radiocarbon dates from Late-glacial sites in the district
Site Grid reference Laboratory number Age (years BP) Dated material and setting Reference
Rothes cuffing NJ 277 498 Beta 8653 11 110 ± 70 peat under remobilised till Appendix 1
Garral Hill, Keith NJ 444 551 Q-104 10 808 ± 230 peat under remobilised till Godwin and Willis (1959)
Garral Hill, Keith NJ 444 551 Q-103 11 098 ± 235 peat under remobilised till Godwin and Willis (1959)
Garral Hill, Keith NJ 444 551 Q-102 11 308 ± 245 peat under remobilised till Godwin and Willis (1959)
Garral Hill, Keith NJ 444 551 Q-101 11 888 ± 225 peat under remobilised till Godwin and Willis (1959)
Garral Hill, Keith NJ 444 551 Q-100 11 358 ± 300 peat under remobilised till Godwin and Willis (1959)
Woodhead, Fyvie NJ 788 384 SRR-1723 10 780 ± 50 peat under remobilised till Connell and Hall (1987)
Howe of Byth NJ 822 571 SRR-4830 11320 peat beneath gravel Hall et al. (1995)
Moss-side, Tarves NJ 833 318 I-6969 12 200 ± 170 peat under remobilised till Clapperton and Sugden (1977)
Loch of Park NO 772 988 HEL-416 10 280 ± 220 kettlehole infill Vasari and Vasari (1968)
Loch of Park HEL-417 11 900 ± 260 kettlehole infill Vasari and Vasari (1968)
Mill of Dyce NJ 8713 1496 SRR-762 11 550 ± 80 kettlehole infill Harkness and Wilson (1979)
Mill of Dyce NJ 8713 1496 SRR-763 11 640 ± 70 kettlehole infill Harkness and Wilson (1979)
Glenbervie NO 767 801 GX-14723 12 460 ± 130 peat under remobilised till Appendix 1
Glenbervie NO 767 801 SRR-3687a. (humic) 12 305 ± 50 peat under remobilised till Appendix 1
Glenbervie NO 767 801 SRR-368Th (humin) 12 340 ± 50 peat under remobilised till Appendix 1
Brinzieshill Farm NO 7936 7918 SRR-387 12 390 ± 100 peat under remobilised till Auton et al. (2000)
Rothens NJ 688 171 SRR-3803 10 680 ± 100 kettlehole infill Appendix 1
Rothens NJ 688 171 SRR-3804 11 640 ± 160 kettlehole infill Appendix 1
Rothens NJ 688 171 SRR-3805 11 760 ± 140 kettlehole infill Appendix 1

To the south, the Auchmedden Gravel thins and the Howe of Byth Gravel extends close to the surface. The Thinfolds Peat Bed, up to 1 m thick, lies within a shallow basin on the surface of the till. Pollen analysis shows typical Late-glacial (Windermere) Interstadial pollen assemblages. This dating is supported by a radiocarbon age determination of about 11.3 ka BP (SRR–4830) (See table) and by luminescence ages of 13 ± 1.4 and 14 ± 4 ka BP. Overlying the peat is a unit of cryoturbated gravel about 1 m thick, the Todholes Gravel Bed, and 1.3 m of Holocene peat (P915309).

Further notes taken on visits to the quarry in 1999 to 2000 are given in Hall and Connell (2000).

References[edit]

Full reference list