The palynology of selected Ordovician localities in Scotland
Ordovician samples have been collected from various places from within three separate terranes in Scotland; the Highland Border Complex, the Southern Uplands and the Midland Valley. The samples have been palynologically processed and their assemblages studied with the aim of understanding some of the palaeoecological, biostratigraphical and thermal relationships of the three areas.Seventy one samples have been processed from nine localities of the Highland Border Complex and these have yielded fifteen species of chitinozoans in four genera, as well as indeterminate species of those genera. There are also five species of acritarchs in four genera as well as other microfossils. Black shales from the Complex yield the most diverse palynomorph assemblages, and were probably deposited from Arenig through to Caradoc although not necessarily at the same time in different parts of the basin. The preservation of palynomorphs appears to be better in the west of Scotland than in the east.From the Southern Uplands samples have been processed from Coldingham Bay and proved barren, from Barrhill the assemblages are poor, but from the Ordovician-Silurian bondary beds (C. peltifer to P. acuminatus Zones) at Dob's Linn they are quite diverse although abundance is very low, with forty three samples yielding thirty three species of acritarchs in eighteen genera, thirty one species of chitinozoans in thirteen genera and various other microfossils. The boundary cannot be delineated using the palynological assemblages, and although Tylotopalla sp. A and Ancyrochitina ancyrea Eisenack 1931 are common in most of the samples from the boundary the palynomorphs do not appear to mirror the changes that occur in the graptolite assemblages.From the Midland Valley samples have been processed from eight miscellaneous localities in the region of Girvan, giving very little biostratigraphical data, although one sample from Doularg Hill is dated as upper Arenig to lower Llanvirn. A section of twelve samples processed from the Mill and Shalloch Formations (D. complanatus and D. anceps Zones) at Woodland Point, Girvan, has yielded thirty five species of chitinozoans in twelve genera including a new species Angochitina woodlandensis and five new combinations; Belonechitina comma (Eisenack 1959), Belonechitina hirsuta (Laufeld 1967). Belonechitina micracantha (Eisenack 1931), Belonechitina schopfi subsp. americana (Taugourdeau 1965), and Belonechitina seriespinosa (Jenkins 1969). There are also forty seven species of acritarchs in twentyone genera, including two new species; Actinotodissus woodlandense, and Goniosphaeridium girvanense, and many scolecodonts. Spores are common and three species are recognised at Woodland Point. The samples are dated as Upper Ordovician and Calpichitina lenticularis (Bouche 1965) and Acanthochitina barbata appear to be important Upper Ordovician indicators, possibly being near-shore species as they are not found in rocks of the same age at Dob's Linn. Calpichitina lenticularis is very important in one sample and less so in all the others and it is suggested that it may be reworked. The palaeoecological picture at Woodland point shows an offshore situation in the Mill Formation, becoming more near-shore at the base of the Shalloch Formation and then more off-shore again.The palaeoecology of both Dob's Linn and Woodland Point are discussed and chitinozoans found to be more common in black shales than grey mudstones, although the acritarchs do not appear to be preferentially found in grey mudstones or black shales. Netromorph acritarchs are less common at Dob's Linn than was expected, but are very common at Woodland Point which may suggest that the sediments at Woodland Point were deposited more offshore than those at Dob's Linn but were more greatly influenced by turbiditic material. Sphaeromorph acritarchs at Woodland Point are very common and due to the variable thickness of the walls it is suggested that there is a mixing of near-shore and off-shore species, possibly by the turbiditic action mentioned above. Belonechitina is markedlymore important at Woodland Point than at Dob's Linn the reverse of which is true with Cyathochitina . The suggested reason for this is that Belonechitina is a near-shore species whilst Cyathochitina is an off-shore species. Veryhachium appears to become more important towards the end of the Ordovician, as a sample each from Woodland Point and Dob's Linn contain three species of this relatively rare genus, although the significance of this is not yet known.The sample from Dob's Linn and Woodland Point are compared with published works using the jacquard Coefficient and the results presented. The samples at Dob's Linn are compared with the Ordovician-Silurian boundary sediments elsewhere, and although different species are present at Dob's Linn and on Anticosti Island, and the abundance and diversity is lower at Dob's Linn, the boundary in Scotland has a much better palynomorph assemblage than was expected. The boundary assemblage presented here is quite similar to the one in Skane, Sweden.Finally the thermal history of the samples is discussed, and a general trend appears, with the samples from Girvan being the least altered, those from the Southern Uplands being moderately altered and finally the Highland Border Complex samples which have been subjected to temperatures probably between 200 and 300oC, and thus strongly altered.