Staffin Bay Research Articles

Chapter 4. Sequence stratigraphy scheme for the Middle Jurassic of the North Sea area

Abstract This chapter describes Middle Jurassic second-order sequences J20 and J30, and their component third-order sequences, J22–J26 and J32–J36. The J22 sequence contains the major Intra-Aalenian Unconformity (‘Mid-Cimmerian’) across a wide area of the North Sea Basin and an equivalent event onshore UK. The base J24 (Lower Bajocian) is marked by the Rannoch Shale (Brent Group) and by the flooding of the Ollach Sandstone, Hebrides Basin. The base J26 (Upper Bajocian) ties to the Mid Ness Shale (Brent Group) and the base of the Upper Trigonia Grit Member, central England. The base J32 (Upper Bajocian) ties to the base of the Tarbert Formation, the base of the Great Oolite Group in central England and the base of the Great Estuarine Group, Hebrides Basin. The base J33 (Middle Bathonian) falls within the Tarbert Formation and the base of the Taynton Limestone, central England. The base J34 (uppermost Middle Bathonian) commonly falls at the top of the Brent Group. The base J36 (uppermost Bathonian) represents a major increase in marine influence, at the base of the Beatrice Formation, in the Inner Moray Firth and at the base of the Staffin Bay Formation, Hebrides Basin.

The Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System), at Flodigarry, Staffin Bay, Isle of Skye, Scotland, UK

Andrzej Wierzbowski, Marcin Barski, Angela L. Coe, Mark W. Hounslow, Bronisław A. Matyja, Gregory D. Price, Hubert Wierzbowski, John K. Wright, with contributions from Francois Atrops, Jacek Grabowski, Emanuela Mattioli, Nicol Morton, James G. Ogg, Federico Olóriz, Kevin Page, Horacio Parent, Piotr Przybylski, Guenter Schweigert, Anna Bertha Villaseñor. Episodes 2023;0:. https://doi.org/10.18814/epiiugs/2022/022046

Unravelling Middle to Late Jurassic palaeoceanographic and palaeoclimatic signals in the Hebrides Basin using belemnite clumped isotope thermometry

Clumped isotope based temperature estimates from exceptionally well-preserved belemnites from Staffin Bay (Isle of Skye, Scotland) reveal that seawater temperatures throughout the Middle-Late Jurassic were significantly warmer than previously reconstructed by conventional oxygen isotope thermometry. We demonstrate here that this underestimation by oxygen isotope thermometry was likely due to a) using the incorrect calcite thermometry equation for belemnite temperature reconstructions and b) by incorrectly estimating the seawater δ18O (δ18Osw) for the Hebrides Basin. Our data suggests that the fractionation factor for oxygen isotopes in belemnites from seawater was closer to that of slow-growing abiogenic calcites than that of other marine calcifying organisms. Our clumped isotope temperatures are used to reconstruct δ18Osw trends across the Callovian–Kimmeridgian in the Hebrides Basin. The δ18Osw varied significantly in the Hebrides Basin throughout this interval, possibly as a result of changing currents through the Laurasian seaway. Trends in temperature and δ18Osw are compared to published palaeoceanographic studies to shed light on changing palaeoceanography in the Tethyan and Boreal realms throughout the Middle–Late Jurassic.

Dinoflagellate cyst assemblages across the Oxfordian/Kimmeridgian boundary (Upper Jurassic) at Flodigarry, Staffin Bay, Isle of Skye, Scotland – a proposed GSSP for the base of the Kimmeridgian

Examination of seven ammonite-calibrated palynological samples across the Oxfordian/Kimmeridgian boundary in the Flodigarry sections at Staffin Bay, Isle of Skye, northern Scotland, has revealed dinoflagellate cyst assemblages in general terms in line with previous contributions. The sparse occurrence of Emmetrocysta sarjeantii, Perisseiasphaeridium pannosum and Senoniasphaera jurassica slightly above the proposed Oxfordian/Kimmeridgian boundary may be used as a palynological approximation of the base of the Kimmeridgian. The high abundance of tests resembling modern zygnemataceous chlorophycean alga Spirogyra in two samples above the Oxfordian/Kimmeridgian boundary horizon is probably associated with increased eutrophication and possible association with ‟green tides”. This bloom is proposed as a palynofloral proxy event for the boundary in the Flodigarry section. According to previous studies, various eutrophication events may have a correlation potential in Subboreal Europe.

Calcareous nannofossils from the uppermost Oxfordian and lowermost Kimmeridgian of Staffin Bay, Isle of Skye, northern Scotland

Twenty six samples from the sections at Flodigarry and Digg at Staffin Bay, Isle of Skye, northern Scotland, spanning the stratigraphical interval from the uppermost Oxfordian to the lowermost Kimmeridgian were examined for their calcareous nannofossil content. The study revealed the presence of an assemblage typical of the nannofossil zone NJ15 of the northern European zonation.

Notes on the evolution of the ammonite families Aulacostephanidae and Cardioceratidae and the stratigraphy of the uppermost Oxfordian and lowermost Kimmeridgian in the Staffin Bay sections (Isle of Skye, Northern Scotland)

Detailed study of all the ammonite collections gathered by the authors in the Staffin Bay sections has resulted in minor changes in the distribution of ammonite taxa, and slight modification of the position of the Oxfordian/Kimmeridgian boundary. Most significant is the discovery of Pictonia (Triozites) cf. seminudata which results in the placing of the stage boundary 0.16 m below the level formerly proposed. This study discusses the evolution of the Subboreal family Aulacostephanidae, and the Boreal family Cardioceratidae, indicating changes in the patterns of individual development in the evolution of both families in terms of heterochrony. The Oxfordian/ Kimmeridgian boundary interval shows major morphological changes in both ammonite families which were released from phylogenetic constraints by heterochrony, closely related to changes in environmental conditions.

Vascular plant biomarker distributions and stable carbon isotopic signatures from the Middle and Upper Jurassic (Callovian–Kimmeridgian) strata of Staffin Bay, Isle of Skye, northwest Scotland

The molecular and stable carbon isotopic composition of higher plant biomarkers was investigated in Middle to Upper Jurassic strata of the Isle of Skye, northwest Scotland. Aromatic hydrocarbons diagnostic of vascular plants were detected in each of nineteen sedimentary rock samples from the Early Callovian to Early Kimmeridgian interval, a succession rich in fossil fauna including ammonites that define its constituent chronozones. The higher plant parameter (HPP) and higher plant fingerprint (HPF) calculated from the relative abundance of retene, cadalene and 6-isopropyl-1-isohexyl-2-methylnaphthalene (ip-iHMN) exhibit several large fluctuations throughout the Skye succession studied. These molecular profiles contrast with both (1) the more uniform profiles previously observed in Jurassic successions, putatively of the same age, from other palaeogeographical settings, including the Carnarvon Basin, Western Australia and (2) the steady rise in global sea level during this interval. This suggests that the HPF profiles of Jurassic marine successions may not be reliable indicators of global climate change. Our results indicate that other factors such as local tectonism, resulting in changes to the relief and landscape of the hinterland, likely influenced the palaeoflora and the mode of transport of its detritus into adjacent marine depocentres. However, the Skye succession showed similar δ13C profiles of total organic carbon (TOC; comprising mainly fossil wood), the vascular plant biomarker retene and a predominant phytoplanktonic biomarker (phytane). The apparent isotopic relationship between terrigenous and marine-derived biomarkers supports a strong coupling of the atmosphere and ocean. The maximum isotopic excursion occurs in the Cardioceras cordatum ammonite biozone of the Early to Middle Oxfordian, which may be indicative of changes in atmospheric and oceanic levels of CO2.

Further observations on the Jurassic dinoflagellate cyst Gonyaulacysta dentata (Raynaud 1978) Lentin & Vozzhennikova 1990 emended Riding 2012

Gonyaulacysta dentata is a large and morphologically distinctive dinoflagellate cyst. It is confined to the Late Callovian to earliest Oxfordian (Peltoceras athleta to Quenstedtoceras mariae zones) interval of the Boreal Realm and the Subboreal Province in the northern hemisphere, and has therefore been interpreted as a cold water species. The holotype of G. dentata is from the Staffin Shale Formation of Staffin Bay, Isle of Skye, northwest Scotland and has been lost. Consequently another well-preserved specimen from the Staffin Shale Formation of the Isle of Skye is proposed as a neotype. The ventral and apical areas of G. dentata are characterised by discontinuous, low, smooth sutural ridges. However, the 5″/6″, 4′/6″ and 4′/1′ sutures on the ventral side of the epicyst are frequently indicated by relatively high denticulate crests. The 2″′/1p suture and the cingular sutures may also be developed on the ventral face. Conversely, the dorsal and lateral sutural crests, except in the apical area, are prominent and denticulate. G. dentata is present in East Greenland. Two specimens were recorded, as Gonyaulacysta eisenackii subsp. oligodentata, from the Late Callovian of Jameson Land. These are probably from the Olympen Formation, and not the Upper Vardekløft Formation as was originally stated. This occurrence is entirely consistent with the Boreal distribution of G. dentata. The range of G. dentata, the Callovian–Oxfordian transition, was characterised by significantly lowered palaeotemperatures. Several other dinoflagellate cyst species are also believed to be cold water taxa, and migrated south from the Boreal Realm into Europe at this time.

Speciation in the cardioceratinid ammonites of the Costicardia Subzone (Cordatum Zone) of the Oxfordian of Skye

Synopsis The Middle Callovian/Oxfordian/Early Kimmeridgian Staffin Shale Formation at Staffin Bay, Isle of Skye contains one of the most complete, fossiliferous successions through Oxfordian strata in Britain, with Cordatum Zone (Chronozone) strata very well developed. During several visits to Staffin over the last 40 years, the author has collected some eighty ammonites from the Cordatum Zone. Well-preserved cardioceratid ammonites are common in the Costicardia Subzone of the Cordatum Zone, and these are the subject of the present study. Cordatum Subzone ammonites are less common and less well preserved at Staffin and, consequently, more problematic for such detailed study. Detailed analysis of Cordatum Zone cardioceratids as a whole shows that it is likely that almost all these Costicardia Subzone cardioceratinids belonged to the one species Cardioceras costicardia biosp.; all other morphospecies of Cardioceras recognized by previous authors from this subzone are regarded here as varieties of C. costicardia biosp. Goliathiceras , however, is regarded here as a separate Lower Oxfordian cardioceratid genus.

Molecular organic geochemistry of a proposed stratotype for the Oxfordian/Kimmeridgian boundary (Isle of Skye, Scotland)

AbstractThe composition of the soluble organic matter of the Oxfordian–Kimmeridgian Flodigarry Shale Member (Isle of Skye, Scotland) is presented for the first time. A continuous succession of silty clays and nodular limestone beds is exposed on a rocky shore to the north of Staffin Bay. This succession is proposed as a potential stratotype of the boundary between the Oxfordian and Kimmeridgian stages. This paper points out the exceptional preservation and very low thermal degradation of the organic matter. Indeed, the molecular composition is characterized by the abundance of unsaturated biomarkers (hopenes and diasterenes) as well as undamaged bioterpenoids (ferruginol and sugiol). The abundance of long-chainn-alkanes characterized by an odd-over-even predominance reveals a dominant continental contribution. This is also attested to by the relatively high amounts of plant biomarkers (e.g. ferruginol, sugiol, cadalene and retene), which suggest a palaeovegetation largely composed of pinophytes, especially Cupressaceae, Taxodiaceae and Cheirolepidiaceae, on the nearest emerged lands. The water column of the depositional environment was oxic in its upper part and rather dysoxic in its lower part. The composition of the organic matter does not significantly change along the Flodigarry Shale Member. In other words, no evolutionary events or drastic change in palaeoenvironments can be deduced from the molecular content of these sedimentary rocks, and it does not allow us to support a precise location for the Oxfordian/Kimmeridgian boundary in the succession.

Isotopic signals from Callovian–Kimmeridgian (Middle–Upper Jurassic) belemnites and bulk organic carbon, Staffin Bay, Isle of Skye, Scotland

Abstract: The stable isotope data presented here significantly extend and expand upon previous isotopic investigations of the Middle to Late Jurassic interval. The belemnite samples collected from the Staffin Bay and Staffin Shale formations from the Isle of Skye, Scotland, yielded oxygen isotope values consistent with Callovian–Kimmeridgian palaeotemperatures of 6.7–20.6 °C. The carbon isotope data comprise one of the first moderately high-resolution investigations of the relationship between terrestrial δ 13 C org (predominantly fossil wood debris) and marine δ 13 C carb (belemnites) as derived from a geologically coeval record. The Staffin Bay data reveal a broad Early to Mid-Oxfordian positive carbon isotope excursion. The excursion maximum occurs in the cordatum Zone (British Boreal ammonite zonation), although high values persist into the tenuiserratum Zone. The correspondence between the marine and terrestrial records indicates a strong coupling of the ocean–atmosphere system and suggests that the total exchangeable carbon reservoir would have been affected at this time. The Mid-Oxfordian negative carbon isotope excursions identified in published Tethyan records and commonly attributed to methane release are not recorded in the Staffin Bay data, which may suggest that the Tethyan excursions do not represent fluctuations in the global carbon reservoir and that the fidelity of the methane hypothesis should be re-evaluated. Supplementary material: Isotopic and geochemical data are available at http://www.geolsoc.org.uk/SUP18339 .

The Sub-Boreal/Boreal ammonite succession at the Oxfordian/Kimmeridgian boundary at Flodigarry, Staffin Bay (Isle of Skye), Scotland

ABSTRACTThis paper describes extensive new collections of ammonites made bed-by-bed across the Oxfordian/Kimmeridgian boundary sequence in the Flodigarry sections at Staffin Bay on the Isle of Skye. The ammonites belong to the Sub-Boreal family Aulacostephanidae and the Boreal family Cardioceratidae, enabling recognition of both the current standard Sub-Boreal and Boreal ammonite zonations. In consequence, it is possible to make a close correlation of these two zonal schemes through the interval studied in Skye. The research has provided new palaeontological data at levels of precision that justify the proposal of the section at Staffin as the site of a potential Global Boundary Stratotype Section and Point (GSSP) for the Oxfordian/Kimmeridgian boundary.The traditional Oxfordian/Kimmeridgian boundary placed at the Pseudocordata/Baylei zonal boundary of the Sub-Boreal zonal scheme corresponds precisely to the Rosenkrantzi/Bauhini zonal boundary of the Boreal zonal scheme. This level is characterised by the appearance of the first Pictonia (Pictonia flodigarriensis sp. nov.) together with first Prorasenia, replacing an older assemblage of Ringsteadia–Microbiplices (Sub-Boreal). It is also characterised by the first occurrence of small-sized Amoeboceras (Plasmatites) spp., as well as large Amoeboceras schulginae Mesezhnikov (Boreal). An alternative level that may be considered as a potential GSSP is the boundary between the Bauhini Zone and the Kitchini Zone of the Boreal zonal scheme, characterised by first occurrence of Amoeboceras (Amoebites) of the A. bayi group. This level corresponds to the Planula/Galar subzonal boundary of the Sub-Mediterranean zonal scheme, and lies close to the currently accepted Oxfordian/Kimmeridgian boundary in the Sub-Mediterranean Province.

The Sub-Boreal/Boreal ammonite succession at the Oxfordian/Kimmeridgian boundary at Flodigarry, Staffin Bay (Isle of Skye), Scotland

The Sub-Boreal/Boreal ammonite succession at the Oxfordian/Kimmeridgian boundary at Flodigarry, Staffin Bay (Isle of Skye), Scotland

87Sr/86Sr and Sr/Ca Investigation of Jurassic mollusks from Scotland: Implications for paleosalinities and the Sr/Ca ratio of seawater

Measurements of 87 Sr/ 86 Sr, Sr/Ca, ! 18 O, and ! 13 C were performed on molluskan fos- sils from the Great Estuarine Group, Scot- land, to deduce paleosalinity patterns and hydrodynamic environments in this classic Jurassic marginal marine succession. Fos- sils are found as winnowed accumulations in shell beds that bear low-diversity assem- blages, consistent with deposition in a la- goonal paleoenvironment. Previous studies have concluded that estuarine mixing of seawater and freshwater took place based on correlated trends in ! 18 O and ! 13 C, most notably in the mussel Praemytilus strathair- densis from the Kildonnan Member. This interpretation is shown to be incorrect based on 87 Sr/ O, ! 13 C, and the Sr/Ca ratio. This is consistent with a lagoonal hydrology controlled more by seasonal changes in evaporation, precipitation, and flooding than by direct inputs of seawater or river- ine water transported over large distances. Lagoons containing the oyster Praeexogyra in the Duntulm Formation have similar in- ferred O and C isotope characteristics, but based on their 87 Sr/ 86 Sr ratios, they have a higher proportion of seawater than the Praemytilus lagoons of the Kildonnan Member. The data thus far suggest that many of the lagoonal environments in the Great Es- tuarine Group were nearly hydrologically closed, at least over the interval represent- ing the molluskan invasion of these habi- tats, rendering O and C isotopes unreliable proxies of paleosalinity. Because strontium isotopes are not directly affected by evap- oration of the lagoons, knowledge of marine and freshwater 87 Sr/ 86 Sr ratios, along with estimates of Sr concentration, are used to calculate the proportion of seawater in the brackish water mixture. Unio is nearly al- ways the most radiogenic taxon compared to other genera in closely adjacent sedimen- tary strata, confirming its freshwater affin- ity. The purported marine-brackish bivalve Tancredia yields a low paleosalinity of 4‰, only slightly more saline than Unio and Praemytilus at 1-3‰. The oyster Praeexo- gyra hebridica yields paleosalinities between 2‰ and 26‰, attesting to the wide salinity tolerance of this species. Thus far, only Neomiodon from the Dun- tulm and Staffin Bay formations show co- variant relationships between 87 Sr/ 86 Sr and Ca/Sr ratio that can be reconciled with a dynamic response to seawater-freshwater mixing. The slopes of these trends converge at 0.7068, which is close to the early Cal- lovian seawater composition of 0.7069. Us- ing values of DSr from modern aragonite se- creting mollusks, the Sr/Ca ratio of middle Jurassic seawater is constrained from the best correlated mixing line to be 5.4 0.6 millimoles/mole. In contrast, Sr/Ca ratios in the Great Estuarine Group lagoons and continental watershed range from 5.4 to 19.0. These are much higher than the av- erage value of 2.3 for modern rivers but typical of Sr/Ca ratios in rivers draining arid climate regions. The semirestricted hy- drodynamic regime inferred from the high seawater-like ! 18 O values and high but uni- form Sr/Ca ratios in many of the Great Es- tuarine Group mollusks is consistent with a seasonally dry, Mediterranean-style climate for the Middle Jurassic of Britain.

Organic facies of the Middle Jurassic of the Inner Hebrides, Scotland

An integrated optical (palynofacies) and bulk organic geochemical study has been undertaken in order to determine the controls on the organic facies of paralic Middle Jurassic Hebridean sediments. The total organic carbon (TOC) values are generally between 0.5 and 2.5%, but reach up to 3-4% in dark-coloured non-bioturbated shales within the Bearreraig Sandstone Formation and Lealt Shales Formation, and 6-8% in the Staffin Bay Formation. Hydrogen indices (HI) are mostly below 300, increasing to 400-500 in the aforementioned organic-rich intervals, and reaching 650-800 in the Kilmaluag Formation. The best overall source potential probably occurs in the brackish Lealt Shales Formation. Correlations between HI, TOC and the content of the freshwater alga Botryococcus (< or =9% of the kerogen), suggest that freshwater run-off may have led to stratification of the Middle Jurassic lagoons, and thus dysoxic-anoxic bottomwaters and better quantitative and qualitative preservation of the plankton-derived amorphous organic matter.

Marine palynomorphs from the Staffin Bay and Staffin Shale formations (Middle-Upper Jurassic) of the Trotternish Peninsula, NW Skye

Synopsis The Staffin Bay and Staffin Shale formations of Trotternish, Skye represent an important Middle–Upper Jurassic (Callovian–Kimmeridgian) reference section. The succession is 133 m thick, mudstone-dominated, and the Staffin Shale Formation is rich in zonal ammonite faunas. Both formations have yielded abundant palynofloras rich in marine microplankton. The Staffin Bay Formation is lowermost Callovian on both dinoflagellate cyst and regional evidence. Only one ammonite has been recorded from its uppermost division, the Belemnite Sands Member. Miospores dominate the Staffin Bay Formation and the relatively low diversity dinoflagellate cyst floras are consistent with a palaeoenvironmental interpretation of restricted, nearshore marine conditions. Dinoflagellate cysts and other marine microplankton are relatively abundant and diverse throughout the Middle Callovian to Lower Kimmeridgian Staffin Shale Formation, thereby indicating an open marine depositional setting. The stratigraphical distributions and relative proportions of the dinoflagellate cysts are largely consistent with those observed in England and elsewhere in northern Europe. Established dinoflagellate cyst zonal schemes can be applied to both formations. Certain species, however, exhibit minor stratigraphical differences in overall ranges. Wanaea acollaris Dodekova 1975, for example, is recorded in the Lower Oxfordian Dunans Clay Member (Staffin Shale Formation); the range top of this species was previously thought to be within the Upper Callovian. Certain species recorded in the Staffin Shale Formation are interpreted as being of Boreal affinity; these include Ambonosphaera? staffinensis ( Gitmez 1970 ) Poulsen & Riding 1992 , Paragonyaulacysta spp. and Gonyaulacysta dentata ( Raynaud 1978 ) Lentin & Vozzhenikova 1990.

Urda mccoyi (), an isopod crustacean from the Jurassic of Skye

Introduction Although they are abundant and widespread in modern marine and terrestrial habitats, isopods are found only rarely as fossils. The fragile nature of their integument, their environmental preference, and their small size reduces preservation potential. Thus, the discovery of a fossil isopod that extends the geological or geographic range warrants notice. This communication reports the first fossil isopod from Scotland and discusses its implications for the generic placement of a previously described species. A single, nearly complete and well-preserved fossil isopod was collected from the Oxfordian of Staffin Bay, northern Skye. Comparison of this specimen with type specimens, where possible, and illustrations of previously described fossil isopods suggests that it is morphologically similar to the type specimens of Palaega mccoyi [Carter, 1889][1], from the Upper Greensand (Albian: Cretaceous) of Cambridge, England and should be assigned to that species. Further, evaluation of the morphology of Palaega mccoyi, in the context of this study, requires that the species be reassigned to Urda Munster. Systematic description Order ISOPODA Latreille 1817 Suborder UNCERTAIN Family Urdidae Kunth 1870 Urda mccoyi (Carter, 1889) Fig. 2. Material. Unique three-dimensional specimen in calcareous concretion, GSE 15083, in collections of British Geological Survey, Edinburgh. Collected by James McCall of H.M. Geological Survey in June 1936, from ‘just below top red rib praecordatum ’ Subzone, of what is now termed the Dunans Clay Member of the Staffin Shale Formation (Sykes 1975), at Point 5 (Anderson and Dunham 1966, fig. 10; Wright 1973) in Staffin Bay, northern Skye (Fig. 1). . . . [1]: #ref-2

A new occurrence of Scottish plesiosaurian remains from the Island of Skye

The discovery of plesiosaurian remains in the Lower Callovian (Middle Jurassic) sediments of Skye, Scotland, represents the most northerly occurrence from the Hebrides. Other Hebridean localities from which Jurassic plesiosaurian remains have been recorded include the famous Hugh Miller’s Reptile Bed from the Upper Bajocian to Bathonian (Middle Jurassic) sediments of Eigg, and a more recent discovery from the Liassic (Lower Jurassic) of Raasay ([Martill 1985][1]). Plesiosaurian remains have also been found from the northeast of Scotland at Elgin (Upper Triassic) (Taylor and Cruickshank in press), Brora (Late Callovian to Early Oxfordian, Middle to Upper Jurassic) ([Clark in press][2]), and Eathie (Kimmeridgian, Upper Jurassic) ([Paton 1975][3]). On 2nd July 1992 N.C. was contacted by Dr. S. Rigby to inform him of the discovery (by F.N.) of vertebrate remains on Skye. As the bones were found on a loose boulder on the foreshore near Flodigarry [NG472 708], it is difficult to provide a precise lithostratigraphical position. A comparison between the faunal content (the abundance of bivalves and belemnites) and sedimentological characteristics of the boulder, suggests that it may correlate lithologically within the Belemnite Sands (Lower Callovian) of the Staffin Bay Formation ([Hudson and Morton 1969][4]). Lithostratigraphy The boulder was found close to locality 3, excursion 21 of Bell and Harris (1986) where the succession youngs to the west. The Staffin Bay Formation is well exposed at this locality allowing much detail of the section to be recorded (Fig. 1). The boulder consisted of a 60 cm-thick medium to coarse-grained sandstone containing. . . [1]: #ref-5 [2]: #ref-2 [3]: #ref-6 [4]: #ref-4

On the age of the Upper Ostrea Member, Staffin Bay Formation (Middle Jurassic) of north-west Skye

Synopsis The precise age, late Bathonian or early Callovian, of the Middle Jurassic Upper Ostrea Member (Staffin Bay Formation) of NW Skye, Inner Hebrides has proved controversial. Twelve samples from the type section at Dunans, Staffin Bay, Skye yielded palynofloras rich in miospores with subordinate proportions of marine microplankton. All the samples produced low diversity dinoflagellate cyst florules which include Meiourogonyaulax caytonensis, M. planoseptata, Mendicodinium groenlandicum and Rhynchodiniopsis cladophora and thus indicate an early Callovian age. The Upper Ostrea Member represents, therefore, the oldest Callovian strata in Scotland and is coeval with the Fleet Member of England. The Staffin Bay Formation, with marine macrofauna and microplankton, overlies the regressive Skudiburgh Formation (Great Estuarine Group) and this boundary has been deemed to be a genetic sequence boundary. This interpretation is consistent with current assessments of global eustasy.

Upper Jurassic pyroclastic rocks in Skye, west Scotland

DURING a systematic sampling of shale lithologies in the Jurassic beds of Skye, an examination was made of sections in the Staffin Shales1–3 in Staffin Bay. Two localities were visited, one immediately south of the landslip at point 6 (ref. 4) [NG470712] and the other at point 7 (ref. 2) [NG468715], Six shale samples were collected at the former section, representing the Kosmoceras jason and Erymnoceras coronatum zones (Middle Callovian), the Peltoceras athleta and Quenstedoceras lambertizones (Upper Callovian), and the Quenstedoceras mariae and Cardioceras cordatum zones (Lower Oxfordian). Four shale samples were collected from the section at point 7, representing the Ringsteadia pseudocordata zone (Up zoneper Oxfordian) and the Pictonia baylei, Rasenia cymodoce, and Aulacostephanus mutabilis zones (Lower Kimmeridgian).