Organic deposits, Quaternary, Cainozoic of north-east Scotland

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From: 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).

Organic deposits

Peat

Deposits of basin peat in the district occur mostly within the sites of former lochans. Commonly, the peat contains tree boles and other woody fragments as well as the partially decomposed, acidic remains of sedges, reeds, rushes, Sphagnum and heather. Most raised peat mosses are a fraction of the original size because of their exploitation for fuel in historical times. Today, many deposits barely average even one metre in thickness, but they remain waterlogged and would partially regenerate in time. Many peaty hollows have been partly, if not completely infilled with boulders carted off the fields. Others have provided sites for dumping waste materials. Peat resources are discussed in Chapter 2 and the locality and extent of the main deposits are listed in Table 5.

Many basins are ice-scoured hollows in bedrock, such as Harestone Moss (NJ 932 195), which is underlain by ultra-basic igneous rocks north-east of Belhelvie (Map 9), and those formed on granite around New Pitsligo and Strichen (Map 6), which contain significant resources of peat. Many small basins are kettleholes in glaciofluvial sands and gravels or morainic deposits, such as large parts of Red Moss (NJ 747 014) and Leuchar Moss (NJ 788 047), on Sheet 76E Inverurie. The majority of basins, however, are ice-moulded hollows in till; abundant examples occur on Sheet 76E, for example Skene Moss (NJ 757 107) and Braigies Moss (NJ 758 047). They are also common on Sheet 87W Ellon (for example the Moss of Belnagoak (NJ 880 428) and Elrick Moss (NJ 954 418)), on Sheet 86E Turriff (for example between Cuminestown and the Ythan gorge) and on Sheet 77 Aberdeen (for example Burreldale Moss (NJ 829 239) and several mosses in the vicinity of Westfield (NJ 946 207)). Deposits of peat rest on raised marine and glaciomarine clays within hollows between Kinloss and Lossiemouth on Sheet 95 Elgin.

Some of the most extensive spreads of low-lying blanket peat in the district rest on particularly clayey and impermeable deposits of till, such as those of the Banffshire Coast Drift Group beneath Rora Moss (NK 045 515) and St Fergus Moss (NK 055 536) (Map 7), and several mosses around New Pitsligo (Map 6). Peat has developed on stiff red till of the Logie-Buchan Drift Group at Lochlundie Moss, 5 km south-west of Cruden Bay on Sheet 87E Peterhead.

Hill peat is most extensive on the granite outcrops in the south of the district, where tree roots and stumps, particularly of Scots pine, are very common. Blanket peat covers parts of Bennachie and the Hill of Fare on Sheet 76E Inverurie and on hilly areas underlain by the Mount Battock granite on Sheet 66E Banchory, where it is relatively thick and widespread. For example, up to 4 m of peat overlying decomposed granite is exposed beside a forestry track on the south-west side of Kerloch (NO 697 879). Other spreads include those on the flaggy quartzites forming the Hill of Stonyslacks, 8 km south of Buckie on Sheet 95 Elgin, and the Moss of Fishrie, on Old Red Sandstone sandstones and shales between Gardenstown and New Byth, on Sheet 96E Banff. Small spreads occur on Bracklamore and Windyheads hills to the south of Pennan, on Sheet 97 Fraserburgh, which are formed of Old Red Sandstone breccias and conglomerates.

Blanket hill peat is also widespread on the relatively high ground of central Buchan formed by the ‘Buchan Ridge’ and the Hill of Longhaven, which lie to the south-west of Peterhead (Map 7). This ground is either underlain by the clayey, kaolinitic deposits of the Buchan Gravels Formation, or on bedrock that has commonly decomposed to sandy kaolinitic clay (Chapter 3).

Woody peat deposits probably developed extensively around the coasts of north-east Scotland in the early to mid-Holocene, prior to the ‘Main Postglacial’ marine transgression, when most were destroyed by coastal erosion. However, some deposits have survived in sheltered situations, such as beneath the alluvium of the Water of Philorth, 3 km southeast of Fraserburgh (Map 4; Appendix 1). Remnants of this so-called Boreal forest are exposed on the foreshore in Burghead Bay at low tide (Map 1). Remnants of older peat deposits formed during the Windermere Interstadial are more sparse (Tables 7; 8; Appendix 1 Rothens, Mill of Dyce, Loch of Park, Glenbervie, Howe of Byth). Deposits of early Devensian age or older are even rarer (Appendix 1 Crossbrae, Moss of Cruden, Burn of Benholm).

Shell marl

Thin, discontinuous spreads of freshwater shell marl interbedded with basin peat and fluviatile silt overlie raised marine deposits around Loch Spynie, 4 km northnorth-east of Elgin (Map 1). A 35 cm-thick bed of shell marl resting on Late-glacial marine clay was formerly visible in a brick pit situated in another alluvial depression at Gilston (NJ 206 662), nearby.

References

Full reference list