Upper Triassic and Lower Jurassic Stratigraphy from Exploration Well L134/5-1, Oﬀshore Inner Hebrides, West Scotland

Home , Sea of the Hebrides

Journal of Micropalaeontology, 20: 155–168. 0262-821X/01 $15.00 2001 British Micropalaeontological Society Upper Triassic and Lower Jurassic stratigraphy from exploration well L134/5-1, oﬀshore Inner Hebrides, west Scotland

NIGEL R. AINSWORTH1 & IAN BOOMER2 139 De Tany Court, St Albans, Hertfordshire AL1 1TU, UK. ([email protected]) 2Department of Geography, University of Newcastle-upon-Tyne, Newcastle NE1 7RU, UK. ([email protected])

ABSTRACT – A thick (c.1368 m) Upper Triassic to Lower Jurassic sedimentary sequence from exploration well L134/5-1, offshore Inner Hebrides, has yielded a rich and diverse foraminiferal and ostracod microfauna. Many of the taxa have been previously described throughout northwest Europe. Poor preservation (often due to crushing and/or overgrowth) and low numbers preclude a complete taxonomic review of this material, although changes in the faunal composition, rates of faunal turnover and palaeoenvironmental analyses are discussed. This is the first published account of ostracod and foraminiferal assemblages from the Sea of Hebrides and they indicate that the sediments (argillaceous, arenaceous and carbonates) were deposited in a shelf-marine setting with environmental fluctuations that are possibly the result of local relative sea-level changes. J. Micropalaeontol. 20(2): 155–168, December 2001.

INTRODUCTION The Hebrides Basin is traversed by a number of northeast Exploration activity in the Hebrides Basin has remained very to southwest/north-northwest to south-southeast trending low compared to other regions within the United Kingdom Caledonian normal faults, which were reactivated during the continental shelf. To date (April, 2001) only three exploration Triassic. Along the northwest margins of each major basin are wells have been drilled, one in the North Minch Basin and two two significant faults: the Minch Fault and the Camasunary within the Sea of Hebrides. A large number (75) of shallow Fault. The southeast margins of both half-grabens appear, boreholes have, however, been drilled by the British Geological however, to be unfaulted. Numerous rock types occur within the Survey throughout the Hebrides Basin. British Petroleum drilled Hebrides Basin, including Proterozoic Torridonian sandstones the first of the three exploration wells (156/17-1) in the North and Moine Schists, Cambrian Durness Limestone, Devonian Minch Basin in 1989 (Fig. 1). This was followed by the first of Old Red Sandstone, Carboniferous sediments, Triassic New Red the two Sea of Hebrides wells, the onshore Upper Glen-1 well Sandstone, Jurassic sediments, Upper Cretaceous chalks, drilled by Pentex Oil in 1989 on the island of Skye. Chevron UK through Palaeogene igneous rocks and finally into Neogene drilled well L134/5-1 in the Sea of Hebrides, south of Skye and sediments (Fyfe et al., 1993). Within the deepest part of the Sea west of Rhum, within the Inner Hebrides, off the west coast of of Hebrides–Little Minch Basin over 2500 m of Permo-Triassic mainland Scotland. Chevron L134/5-1 was spudded in February through to Cretaceous sediments are recovered, of which over 1991 and plugged and abandoned in May 1991. It reached a 1494 m are Jurassic strata. total depth of 2472 m, terminating in Stornoway Formation sandstones of Triassic age. LITHOSTRATIGRAPHY This paper describes the Upper Triassic and Lower Jurassic Within the Hebrides Basin, thick extensive Lower Jurassic (Lias sediments and microfaunas (foraminifera and ostracods) from Group) sequences have been described from the onshore well L134/5-1. Particular emphasis has been placed on the regions, for example Skye has c.500 m of exposed Hettangian to microfossil taxa, because it is the first detailed published study of middle Pliensbachian sediments. The lithostratigraphical studies such faunas from this region. The paper describes the micro- of the Lias sequences of the Inner Hebrides commenced in 1897 faunas and their associated biostratigraphical and palaeoen- by Woodward, who subdivided these sediments into a lower vironmental implications. Poor preservation due to compaction Broadford Beds and the overlying Pabba Shales. Since this and heating of the surrounding sediments by igneous intrusions pioneering work, a large number of publications have discussed and/or low abundance preclude a complete taxonomic review of these sediments (including Buckman, 1920 (in Lee, 1920); this material. Although the palynological dataset for well L134/ Hallam, 1959; Howarth, 1956; Oates, 1978; Searl, 1992), culmi- 5-1 has not been used in this study, the authors have had access nating in the revision of the hebridean Lower Lias Group by to the company biostratigraphic report, and have noted that Hesselbo et al. (1998). The lithostratigraphy for the L134/5-1 much of the palynomorph biostratigraphic data complements well follows Hesselbo et al. (1998). the microfaunal age assignments for the well. GEOLOGY LITHOLOGY The Hebrides Basin can be subdivided into two distinct In well L134/5-1, 1368 m of strata were penetrated between the northeast–southwesterly half-grabens (Fig. 1); to the northwest, Upper Pliensbachian, Scalpa Sandstone Formation equivalent the Sea of Hebrides–Little Minch Basin and to the southeast, the and the Upper Triassic, Penarth Group (c. 494–1890 m depth). Inner Hebrides Trough (Morton, 1983, 1989). Separating these One Upper Triassic and six Lower Jurassic lithostrati- two half-grabens is the Skye High (Morton, 1965; Binns et al., graphic units are described using wireline log data (gamma ray, 1975; Harris, 1989, 1992; Fyfe et al., 1993; Hesselbo et al., 1998). resistivity and sonic velocity) and gross lithology (Fig. 2). A

155 N. R. Ainsworth & I. Boomer

mid-Late Pliensbachian (mid-ibex to upper margaritatus Zones) (Howarth, 1956; Oates, 1978; Hesselbo et al., 1998). The Scalpa Sandstone/Portree Shale formational boundary is placed at, or close to, the tenuicostatum/falciferum zonal boundary (Howarth, 1992).

Lithology. This formation is dominated by medium grey to dark grey, olive grey, locally silty, non-calcareous to calcareous claystones. Stringers of greyish orange and light olive grey, microcrystalline to sucrosic, dolomite and dolomitic limestone occur throughout. Traces of light olive grey to medium grey, argillaceous siltstone and silty sandstone occur towards the base. Disseminated pyrite occurs throughout this section.

Wireline log characteristics. The lower boundary is moderately sharp; deﬁned by an increase in gamma ray response and an associated increase in sonic velocity values, reﬂecting a lithological change to claystones. The interval is characterized by slightly serrated wireline log motifs with moderately low gamma ray responses and moderately high sonic velocities. The occurrence of sonic spikes indicates dolomite or dolomitic limestone stringers.

The Pabay Shale Formation: (659.5–1582 m, log) Age. Early Pliensbachian to Early Sinemurian in well L134/5-1. Onshore west Scotland, the Broadford Beds/Pabay Shale formational boundary is often poorly dated due to the absence of zonal/subzonal marker faunas. It is tentatively placed at the Early Sinemurian, bucklandi–semicostatum zone boundary (Hesselbo et al., 1998). Similarly the Blue Lias/Pabay Shale formational contact is diachronous. In Morvern (Loch Aline) the junction occurs at the bucklandi–semicostatum zonal boundary, while on South Mull the contact is questionably placed within the Early Sinemurian, semicostatum Zone.

Lithology. This formation is dominated by argillaceous sediments, comprising medium dark grey to dark grey, olive grey, in part silty, calcareous claystones. Infrequent beds of dark grey, non-calcareous siltstone and off-white, light olive grey, mica- Fig. 1. Location and structure of the Malin–Hebrides area, based on ceous, calcareous, silty sandstone occur towards the base. Rare Fyfe et al. (1993). stringers of light brownish grey and light olive grey, microcrystalline to sucrosic, limestone and dolomitic limestone are number of thin igneous intrusions are noted at and below also noted. Disseminated pyrite occurs throughout this section. 1250 m (the Pabay Shale Formation). All depths discussed below relate to wireline log data. Wireline log characteristics. The upper boundary is moderately sharp; defined by an increase in gamma ray response and an The Scalpa Sandstone Formation equivalent: (c.494 m, top not associated increase in sonic velocity values, reflecting a lithologi- seen, to 659.5 m, log) cal change to claystones. The lower boundary of the Pabay The sediments occurring within this interval in well L134/5-1 are Shale Formation is sharp; defined by a decrease in gamma ray envisaged to be lateral equivalents of the Scalpa Sandstone response and an associated increase in sonic velocity values, ff Formation of mainland west Scotland, di ering in their more reflecting a lithological change to interbedded limestone and argillaceous content (silty claystone/argillaceous siltstone) and, calcareous claystone. The Pabay Shale Formation is character- where recorded, the sandstones comprise finer-grained lith- ized by slightly serrated wireline log motifs with moderately low ologies. These lateral equivalent sediments are presumed to have gamma ray responses and moderately high sonic velocities. been deposited in a more distal to source setting. The Hallaig Sandstone Member equivalent: (1005–1097.5 m, Age. Late Pliensbachian in well L134/5-1. The Pabay Shale/ log) Scalpa Sandstone formational boundary is highly diachronous The sediments occurring within this interval are considered to be in mainland west Scotland, ranging in age from mid-early to a lateral equivalent to the Hallaig Sandstone Member of

156 Triassic/Jurassic micropalaeontology, Inner Hebrides

PALAEO- ENVIRON- MENT

Gamma Ray ILD Sonic Velocity FORAMINIFERA OSTRACODA (api) (ohms) (us) 0.00 50.00 0.20 20.00 60.00 0.00 AGE

CONTINENTAL

INNER SUBLITTORAL

TRANSITIONAL

BATHYAL

OUTER SUBLITTORAL

MEMBER FORMATION LITHOLOGY D. matutina, F. terquemi bicostata, F. terquemi sulcata plexus, M. prima prima, Ogmoconchella spp. (494m) S. sublaevis (506m) O. contracula, O. amalthei, O. aequalis, L. tenera tenuistriata (518m) O. pseudospina, N. (D.) firma (506m) B. liasica, M. prima ?interupta (530m) H. lincolnensis, F. brizaeformis, O. gruendeli, P. cf. etaulensis (518m) L. tenera pupa (549m) O. bispinosa, P. etaulensis (549m)

T. canningensis, D. terquemi (555m)

EQUIVALENT

SCALPA SANDSTONE

LATE PLIENSBACHIAN 659.5m G. ubiquita (664m) L. vestibulifera, O. amalthei form A (689m)

L. lanceolata (738m) V. mauritii, M. prima ?spinata (747m) G. ?klingleri, O. adenticulata (747m)

O. ?transversa (786m)

EARLY PLIENSBACHIAN D. varians hausleri (884m) E. foveolata (884m) O. mouherensis (896m) L. gottingensis (908m) Ektyphocythere spp., P. vermiculata (908m)

R. pachyderma “humilis” (933m) E. ?betzi, P. subaequalis (933m) O. danica, Cardobairdia sp. B, T. gryci (960m) P. cerasia (945m, swc) M. speciosa, M. prima rugosa (969m) E. frequens, G. bachi bachi (969m) M. prima praerugosa (975m, swc) A. siliceus, M. quadricostata (991m)

1,005m ?G. apostolescui (1,021m)

HALLAIG SST. EQUIVALENT 1,097.5m D. tenuistriata (1,105m, swc)

PABAY SHALE

LATE SINEMURIAN

R. margarita (1,273m, swc)

Consistent Ektyphocythere spp. (1,305m)

C. liasina, V. exarata (1,326m) K. ?sinemuriana (1,326m) I. tatei (1,335m)

I. cylindrica (1,370m, swc)

P. inaequistriata (1,449m, swc)

Influx squashed Haplophragmoides spp. (1,509m)

EARLY SINEMURIAN B. carinata undulata (1,544m, swc) Bairdia sp. 1 (1,559m, swc) R. ?planiconvexa (1,567m, swc) O. ?aspinata (1,582m, swc) 1,582m O. hagenowi, O. aspinata, O. michelseni (1,594m)

I. liassica (1,710m, swc) K. translucens (1,723m, swc)

BLUE LIAS

R. dreheri (1,754m, swc)

HETTANGIAN - 1,785m

EARLIEST SINEMURIAN

BROAD - FORD O. ?serratostriata (1,844m) PEN 1,845.5m RHT STO 1,861m Fig. 2. Wireline log characteristics and stratigraphic summary of the Upper Triassic–Lower Jurassic of exploration well L134/5-1.

157 N. R. Ainsworth & I. Boomer

Hesselbo et al. (1998). The sediments in well L134/5-1 are finer motif, reflecting the limestone–claystone interbeds. The gamma grained than their onshore counterparts, comprising mainly ray response for the Blue Lias Formation is slightly subdued siltstones/silty claystones, with rare fine-grained sandstones. compared to the overlying Pabay Shale Formation. They are considered to represent a more distal equivalent to the onshore Hallaig Sandstone Member sensu stricto. The Broadford Formation: (1785–1845.5 m, log) Onshore, this formation has been described as a shallow water Age. Late Sinemurian in well L134/5-1. In Raasay and Skye, the equivalent of the Blue Lias Formation. It comprises a succession Hallaig Sandstone Member has a maximum stratigraphic extent of littoral carbonate and arenaceous sediments, locally repre- of mid-Early to mid-Late Sinemurian (mid-semicostatum–lower sented by reefs and beach environments (Hesselbo et al., 1998). oxynotum Zones; Hesselbo et al., 1998). The lower parts of the sequence may yield reduced diversity marine faunas (Hallam, 1959). Lithology. This member is dominated by dark grey-brownish black, non- to slightly calcareous silty claystone and siltstone, Age. Early Hettangian in well L134/5-1. In the Hebrides Basin, while subsidiary off-white to light olive grey, very fine- to the Broadford Formation ranges from the Hettangian through fine-grained, micaceous, argillaceous sandstone occurs mid-way to the earliest Sinemurian (planorbis–bucklandi Zones; Hesselbo through the member. Disseminated pyrite occurs throughout. et al., 1998).

Wireline log characteristics. The upper boundary is sharp; Lithology. This formation is dominated by an interbedded defined by a slight decrease in gamma ray response and a sequence of claystones, limestones and sandstones. The clay- marked increase in sonic velocity values, reflecting a lithological stones are medium dark grey to dark grey, olive grey, locally change to siltstone. The lower boundary is sharp; defined by a light brownish grey, in part silty, slightly to very calcareous, slight increase in gamma ray response and a marked decrease in while the limestones comprise yellowish grey, light olive grey, sonic velocity, reflecting a lithological change to claystones. This medium brown grey, locally sandy, microcrystalline to sucrosic, member is characterized by a slightly bowed log profile, with the mudstones. Sandstone beds occur towards the base of the lowest gamma ray response and highest sonic velocity below the section, comprising off-white to greenish grey, very fine- to midpoint reflecting the most arenaceous part of the section. fine-grained, slightly argillaceous, calcareous sandstones.

The Blue Lias Formation: (1582–1785 m, log) Wireline log characteristics. The upper boundary is moderately The Blue Lias Formation interdigitates with the Broadford sharp; defined by a decrease in gamma ray response and an Formation in many of its more northerly outcrops of west associated increase in sonic velocity, reflecting a lithological Scotland (e.g. Ardnamurchan), while along its more southerly change to limestone. The lower boundary is sharp; defined by a outcrops (e.g. Mull) it occurs as a lateral equivalent of the decrease in gamma ray response and an associated decrease in Broadford Formation (Hesselbo et al., 1998). The Blue Lias sonic velocity, reflecting a lithological change to non-calcareous Formation is considered to be a deeper-water equivalent of the claystones. The Broadford Formation is characterized by an Broadford Formation. irregular, highly serrated log motif, reflecting the limestone, claystone, sandstone interbedding. Age. Earliest Sinemurian to intra-Hettangian in well L134/5-1. Where fully developed onshore west Scotland, the Blue Lias has The Penarth Group: (1845.5–1861 m, log) a maximum stratigraphic range of Hettangian to earliest Age. Rhaetian. Sinemurian (planorbis–bucklandi Zones). Lithology. This interval solely comprises medium light grey, Lithology. This formation is dominated by an interbedded dark grey/olive black, waxy, non-calcareous, claystones. These sequence of claystones and limestones. The former comprise sediments conformably overlie reddened limestones and calcar- medium dark grey to dark grey, olive grey, locally silty, slightly eous claystones of the Stornoway Formation at 1861 m (log). to very calcareous claystones, while the latter comprise yellowish grey, light olive grey, medium dark grey, microcrystalline and Wireline log characteristics. The upper boundary is sharp; sucrosic limestones. The claystones are increasingly lighter in defined by a decrease in gamma ray response and an associated colour and also more calcareous towards the base of the section. decrease in sonic velocity, reflecting a lithological change to Rare beds of off-white to light olive grey, very fine- to fine- non-calcareous claystones. This interval is characterized by grained, micaceous, argillaceous sandstone are also noted. serrated wireline log motifs with moderately high gamma ray responses and moderately low sonic velocities. Wireline log characteristics. The upper boundary is sharp; defined by a decrease in gamma ray response and an associated Intrusives increase in sonic velocity, reflecting a lithological change to interbedded limestone and calcareous claystone. The lower Palaeogene. A number of thin (<10 m), dusky yellowish green to boundary is moderately sharp; defined by a decrease in gamma dark greenish grey, crystalline, fine- to medium-grained dolerite ray response and an associated increase in sonic velocity, intrusions are noted within the interval between the Penarth reflecting a lithological change to limestone. The Blue Lias Group and the lower section of the Pabay Shale Formation. Formation is characterized by a regular, serrated ‘spiky’ log On wireline log criteria, they are identified by their low gamma

158 Triassic/Jurassic micropalaeontology, Inner Hebrides

LITHOST. AGE AGGLUTINATING FORAMINIFERA CALCAREOUS BENTHONIC FORAMINIFERA FORMATION MEMBER SYSTEM SUBSTAGE DEPTH (m) Trochammina spp. Ammobaculites spp. Bathysiphon spp. Haplophragmoides canui Haplophragmoides kingakensis Haplophragmoides lincolnensis Haplophragmoides spp. Recurvoides spp. Trochammina globigerinaeformis Trochammina canningensis Verneuilinoides mauritii Trochammina gryci Indet. Agglut. foraminifera Ammodiscus siliceus ?Rhizammina spp. Ammobaculites fontinensis Glomospira pattoni Ammodiscus asper Verneuilinoides liasina Verneuilinoides spp. Dentalina spp. Lenticulina varians Dentalina matutina Frondicularia terquemi bicostata Frondicularia terquemi sulcata form E Frondicularia terquemi terquemi Indet. polymorphinids Marginulina prima prima Nodosaria issleri Nodosaria spp. Planularia spp. Pseudonodosaria vulgata Saracenaria sublaevis Vaginulina listi Lenticulina spp. Lingulina tenera tenuistriata Brizalina liasica Eoguttulina liassica Marginulina prima interrupta Reinholdella spp. Dentalina glandulinoides Lingulina tenera tenera Frondicularia brizaeiformis Frondicularia terquemi sulcata form B Frondicularia terquemi sulcata form C Frondicularia terquemi sulcata form F Frondicularia terquemi sulcata form G Lingulina tenera pupa Nodosaria metensis Dentalina terquemi Frondicularia terquemi sulcata Nodosaria hortensis Marginulina prima spinata Dentalina varians hausleri Lenticulina gottingensis Reinholdella pachyderma "humilis" Marginulina prima rugosa Marginulinopsis speciosa Marginulina prima praerugosa Marginulinopsis quadricostata Nodosaria novemcostata Nodosaria mitis Dentalina tenuistriata Pseudonodosaria multicostata Reinholdella margarita Cyclogyra liasina Vaginulinopsis exarata Planularia inaequistriata Involutina liassica ?Reinholdella planiconvexa Reinholdella drehri SAMPLE TYPE Glomospirella spp. 494 DC 1 11 506 DC 3 4 13111162121141 518 DC 1 1 1 14 2 1 13 5 1 3 2 530 DC 71 1311 231?1?9 543 DC 1 1911 134 11 4 321 549DC12 12122 25 1321210 11 24 11123121 555 DC 1 1 5 3 18 1 2 5 2 12 2 1 1 1 1 567DC 2 412 152 151 ?1111 579 DC 1 591 DC 1 3 8 ?1 5 3 1 1 604 DC 1 3 1 1

LATE PLIENSBACHIAN 616 DC 1 628 DC 621 640 DC 1 5 1 SCALPA SANDSTONE EQUIVALENT 652 DC 3 664 DC 2 4 1 1 1 1 677 DC 12 1 689 DC 1 1 12 1 1 1 701 DC 713 DC 22 1 725 DC 1 21 738 DC 1 1211 747 DC 1 1 8 1 4 2 2 1 1 ?1 750 DC 762 DC 111 1 774 DC 786 DC 41 799 DC 811 DC 1 1 11 EARLY PLIENSBACHIAN 823 DC 2 1 835 DC 8 847 DC 860 DC 21 872 DC 884 DC 14 11 11 1 896 DC 6 12 908 DC 4 11 920 DC 6 1 933 DC 12211 1 111 945 SWC 2 74423215421 960 SWC 871411622 969 DC 2253111 3 1 6 11 51 141 3 ?11 975SWC 1 111 9 3 1 114 121 1125 991DC 21 8253 1 1 3 1 1 112 3151 1 1006 DC 1411212111?1 1021 DC 3 1 5 1 1 3 1 1 1036 SWC 211 1066 SWC 11

EQUIV. 1070 SWC

HALLAIG SST. 1089 SWC 12 1 1105 SWC 1 1 6 1 1 1 2 1 4 4 2 1

PABAY SHALE 1120 SWC 1 2 211 1138 SWC 1 1 1 11 LATE SINEMURIAN 1151 SWC 1 1 1 1 1 1 3 1 EARLY JURASSIC 1166 SWC 1 3 1 1 1181 SWC 5 2 2 2 3 4 1 1 1 1 1196 SWC 1 1 2 1 1213 DC 2 2 1 1 2 3 1227 SWC 22 1 ?1 211 1242 SWC 1 1 1 2 1 1 3 1 1259 DC 1 11 11 1273 SWC 1 5 8 1 7 20 1 2 3 1 1 6 1 1 2 1 3 1286 SWC 1 21 2 1305 DC 1 1 1 1 1 1320 DC 11 11 1326 DC 1 111 1335 DC 21 1352 SWC 1370 SWC 1111 12 1387 DC 11 1 1 1398 SWC 1 1 1408 DC 1 33 121 1417 SWC 11 13 1435 SWC 3 ?2 1449 SWC 1 6 3 5 2 8 1 1 1 2 3 2 2 1463 SWC 24 1 1 1 1478 SWC 13

EARLY SINEMURIAN 1494 SWC 2?1 1509 DC 50 2 1 2 5 1 ?1 1 5 1 1526 SWC 13 3 3 1544 SWC 5112 1 1559 SWC 11 5 1 21 1567 SWC 42 1582 SWC 50 1594 DC 12 11 1622 DC 1 1629 SWC 11 1646 DC 1653 SWC 1 11 261 1662 SWC 1 1676 DC 11 1 1 1692 DC 1 1

BLUE LIAS 1710 SWC 2 15 1723 SWC 3 ?1 1737 DC 1 114 1754 SWC 1768 DC 1 1779 SWC 1798 SWC 1 1814 SWC HETTANGIAN - EARLIEST SINEMURIAN 1836 SWC FORD

BROAD- 1844 DC PEN. TRI. RHT. 1860 SWC

Table 1. Stratigraphical occurrence of foraminifera in well L134/5-1. Samples types are either DC (ditch cuttings) or SWC (sidewall cores). The foraminifera are separated into agglutinating and calcareous benthonic taxa. ray responses and high sonic velocities, forming blocky log to be new; however, very poor preservation precludes a complete motifs. taxonomic review of this material (Tables 1–2). Since these data are mainly based on ditch-cuttings, emphasis is placed on the BIOSTRATIGRAPHY highest downhole occurrences (extinctions) of selected micro- A total of 100 taxa, comprising 11 agglutinating and 44 calcar- fossil taxa and major fossil assemblage changes. Numerous eous benthonic foraminifera, in association with 45 species of publications describe the Lower Jurassic microfaunas from the ostracod were recovered from 104 samples (42 sidewall cores UK and Ireland, and their adjacent oﬀshore areas. These and 62 ditch-cuttings samples). Eight samples were barren of include Ainsworth (1987, 1989a, b, 1990), Ainsworth & Horton both ostracods and foraminifera. Samples were analysed at (1986), Ainsworth et al. (1987, 1989, 1998), Barnard (1950, 1956, approximately 13 m intervals. A number of taxa are considered 1957, 1960), Boomer (1990, 1991), Boomer & Ainsworth (in

159 160 al 2. Table E.TI RHT. TRI. PEN. BROAD- AGE LITHOST. BLUE LIAS PABAY SHALE SCALPA SANDSTONE EQUIV. FORMATION FORD

HALLAIG SST. MEMBER EQUIV.

tairpia curneo srcd nwl 1451 ape ye r ihrD dthctig)o W sdwl cores). (sidewall SWC or cuttings) (ditch DC either are types Samples L134/5-1. well in ostracods of occurrence Stratigraphical EARLY JURASSIC SYSTEM

HETTANGIAN - EARLIEST SINEMURIAN EARLY SINEMURIAN LATE SINEMURIAN EARLY PLIENSBACHIAN LATE PLIENSBACHIAN SUBSTAGE 80SWC 1860 84DC 1844 SWC 1836 SWC 10 1814 SWC 1798 SWC DC 1779 2 1768 SWC DC 1754 1737 73SWC 1723 SWC DC 1710 1692 35D 1 1 1 5 1 2 1 1 1 1 ?1 1 2 DC 1676 SWC 1 1 1662 SWC DC 1653 1 1 2 1646 SWC 2 DC 1629 2 DC 1622 1 1594 SWC 1582 SWC 1567 SWC 1559 SWC 1544 SWC 1 1 DC 1526 1509 SWC 1494 SWC 1478 SWC 1463 SWC 1 1449 SWC 2 1435 SWC DC 1417 2 1408 SWC DC 1398 3 1387 SWC 7 1370 SWC 1 DC 13 1352 4 DC 1335 16 1326 DC DC 1320 1305 SWC 5 1286 SWC DC 1273 1259 SWC 3 1242 SWC DC 1227 1213 SWC 1196 SWC 1181 SWC 1166 SWC 1151 SWC 1138 SWC 9 1120 SWC 1105 SWC 1089 SWC 1070 SWC 1066 SWC 3 DC 1036 1021 DC 1006 9 C211122? 1 1 ?1 2 2 1 ?3 1 1 3121 1 1 1 1 2 3 1 1 1 4 1 1 2 1 1 1 2 2 ?2 1 1 1 ?1 1 ?22 1 2 1 ?1 DC 2 1 3 991 SWC DC 1 975 1 1 969 SWC 13 960 2 1 0 DC 945SWC 3 DC 933 1 DC 920 3 DC 908 1 DC 896 1 1 DC 884 1 DC 872 1 DC ?1 860 3 DC 847 DC 1 835 1 DC 2 823 3 DC 1 811 3 DC 799 1 DC 786 1 1 DC 774 1 DC 762 DC 750 1 DC ?1 747 1 DC 1 738 1 2 DC 725 DC 1 1 713 1 1 DC 701 1 4 DC 1 689 1 DC 677 1 1 2 DC 664 1 DC 5 652 8 DC 640 DC 628 2 5 DC 616 1 DC 604 DC 591 1 1 DC 579 DC 567 1 2 DC 555 1 DC 549 DC 543 DC 530 1 518 DC 506494 5115111 DC DEPTH (m)

SAMPLE TYPE

Ogmoconchella spp. Cardobairdia posteroprolata Nanacythere (Domeria) firma Ogmoconcha contractula Ogmoconcha spp. Ogmoconchella aequalis Ogmoconchella amalthei Ogmoconchella pseudospina Bairdia spp. Ogmoconchella gruendeli Pseudohealdia cf. etaulensis Pseudohealdia etaulensis Bairdia molesta Ogmoconchella bispinosa Indet. ostracods Isobythocypris spp. Gammacythere ubiquita Liasina vestibulifera

41116 14 1 11 111 Ogmoconcha amalthei form A Ogmoconchella cf. aequalis 1 2 2241 Pseudomacrocypris subtriangularis Liasina lanceolata Cytheropteron spp.

1 Gammacythere ?klingleri

1 Ogmoconchella adenticulata OSTRACOD 2 Ogmoconchella ?transversa

1 Ektyphocythere foveolata 121 2 11 1111271 1 1 3 1 21 1 Ogmoconchella mouhersensis 11 1 1 3121 2 5 1?21234 Ektyphocythere spp. A Pleurifera vermiculata

111 1 1 Isobythocypris elongata Pseudomacrocypris subaequalis Ektyphocythere betzi

01 50 3 2 28 11 1 1 Cardobairdia sp. B Ogmoconchella danica

1 1 Paracypris redcarensis Polycope cerasia Grammanicythere bachi bachi

173131404 Nanacythere spp. Ektyphocythere frequens .R isot .Boomer I. & Ainsworth R. N. ?Grammanella apostolescui

3 1 2 Ogmoconcha ?amalthei ?Cytherella spp. Kinkelinella ?sinemuriana

2 Isobythocypris tatei Isobythocypris cylindrica

11 Bairdia carinata undulata Bairdia sp. 1 ?1 71 11 6 621 25 2 47 21 950 Ogmoconchella aspinata 10 515 35 16 Ogmoconcha hagenowi Ogmoconchella michelseni Nanacythere (Goniocythere) minor Klinkelinella translucens Ogmoconchella serratostriata Triassic/Jurassic micropalaeontology, Inner Hebrides press), Brouwer (1969), Clark (1969), Colin et al. (1992), than the margaritatus Zone (Copestake & Johnson, 1989). In Copestake & Johnson (1984, 1989), Field (1968), Lord (1978), well L134/5-1, seven species are stratigraphically restricted to the Lord & Bown (1987), Malz & Lord (1976), Park (1987) and Late Pliensbachian. Throughout this interval the foraminiferal Partington et al. (1993). Further afield, references are made to assemblages are dominated by calcareous benthonic species, France (Apostolescu, 1959; Colloque sur le Lias Français, 1961; notably the Nodosariidae (Frondicularia terquemi sulcata plexus Bizon, 1960; Donze, 1967; 1985; Ruget, 1985; Ruget & Sigal, Bornemann, Lenticulina varians (Bornemann), Lingulina tenera 1967), Germany (Bartenstein & Brand, 1937; Drexler, 1958; plexus Borneman, Marginulina prima prima d’Orbigny), the Gründel, 1964; Harloff, 1993; Herrig, 1985; Klingler, 1962; Polymorphinidae and the Bolivinitidae (Brizalina liasica Klingler & Neuweiler, 1959; Malz, 1971, 1975), Holland (Terquem)). Agglutinating foraminifera only occur in small (Brouwer, 1969), Denmark (Norvang, 1957; Bang, 1968, 1971, numbers and are generally poorly preserved. Approximately 1972; Michelsen, 1975), Sweden (Norling, 1972; Sivhed, 1977, mid-way through this interval, there is a marked downhole 1980), offshore Norway (Malz & Nagy, 1989) and Portugal decrease in both diversity and abundance of the foraminifera. (Boomer et al., 1998; Exton, 1979; Exton & Gradstein, 1984; Many of the taxa occurring within this interval have been Ruget & Sigal, 1970). described throughout northwest Europe (see references listed To date (April, 2001), only Copestake & Johnson (1989) have above). published records of the Lower Jurassic foraminifera from the Hebrides Basin, from the Loch Aline area of Morvern, Mull Ostracoda. Eleven species of ostracod occur in the Late (Gribun) and Raasay. The Lower Jurassic ostracod faunas Pliensbachian. Highest downhole occurrences include Bairdia from the west coast of Scotland have been studied by Clark ?molesta Apostolescu, Cardobairdia posteroprolata Ainsworth, (1969), although, these data remain unpublished. Currently, this Isobythocypris spp., Nanacythere (Domeria) firma Herrig, material is being re-examined by one of the present authors Ogmoconcha amalthei (Quenstedt), O. contractula Triebel, (NRA). Ogmoconchella aequalis (Herrig), O. bispinosa (Gründel), O. pseudospina (Herrig), Pseudohealdia etaulensis Apostolescu Late Pliensbachian (494–664 m) and P. cf. etaulensis Apostolescu sensu Ainsworth. An age no younger than Late Pliensbachian (margaritatus Although many of these ostracod species are known to range Zone) is indicated on the highest downhole occurrence of the from the Early through to the Late Pliensbachian, none are calcareous benthonic foraminifera Dentalina matutina at thought to range into the Toarcian. Ostracod data from the (506 m). Confirmation of this age is indicated by the ostracod Fastnet Basin, North Celtic Sea and the Mochras Borehole Ogmoconcha contractula Triebel at 506 m and Haplo- suggested that only two of these species (Ogomoconcha phragmoides lincolnensis Copestake at 549 m. The former taxon contractula Triebel and Pseudohealdia cf. etaulensis Apostolescu is restricted to the Late Pliensbachian in the Mochras Borehole sensu Ainsworth) are stratigraphically restricted to the Late (Ainsworth et al., 1989; Boomer, 1990), while the latter taxon Pliensbachian (Ainsworth, 1987; Ainsworth et al., 1989; ranges no higher than the margaritatus Zone (Copestake & Boomer, 1990). In well L134/5-1, however, six taxa are restricted Johnson, 1989). to this interval. The Late Pliensbachian ostracod assemblages are not as abundant as the foraminiferal assemblages. Similar to Foraminifera. Thirty species of foraminifera –five agglutinating the foraminifera, a marked decrease in abundance occurs below taxa and 25 calcareous benthonic species – occur in the mid-interval, with the earliest part of the Late Pliensbachian Late Pliensbachian. Highest downhole occurrences include barren of ostracods. The assemblages within this interval are Haplophragmoides canui Cushman, H. lincolnensis Copestake, dominated by the Healdiidae, notably the genera Ogmoconcha H. kingakensis Tappan, Trochammina canningensis Tappan, T. and Ogmoconchella, with subsidiary Saipanettidae (Cardobairdia globigeriniformis Parker & Jones, Brizalina liasica (Terquem), posteroprolata Ainsworth). No samples contained the latest Dentalina glandulinoides Franke, D. matutina (d’Orbigny), Pliensbachian to earliest Toarcian ‘vallate forms’ of Ogmo- D. terquemi d’Orbigny, Eoguttulina liassica (Strickland), concha (of Malz, 1975) in this section. From the summary Frondicularia brizaeiformis Bornemann, F. terquemi bicostata completion log, first returns only began at 494 m, below the d’Orbigny, F. terquemi sulcata form B Barnard, F. terquemi setting of the 20 inch casing. The Late Pliensbachian assem- sulcata form C Barnard, F. terquemi sulcata form E Barnard, blages bear close similarities to those recorded elsewhere F. terquemi sulcata form G Barnard, F. terquemi terquemi in northwest Europe, especially with the dominance of the d’Orbigny, Lenticulina varians (Bornemann), Lingulina tenera Healdiidae. pupa (terquem), L. tenera tenera Bornemann, L. tenera tenuistriata (Norvang), Marginulina prima ?interupta (Terquem), M. prima prima d’Orbignyi, Nodosaria hortonensis Terquem, N. Early Pliensbachian (664–884 m) issleri Franke, N. metensis Terquem, Pseudonodosaria vulgata An Early Pliensbachian age is indicated by the highest downhole (Bornemann), Saracenaria sublaevis (Franke) and Vaginulina occurrence of the ostracod Gammacythere ubiquita Malz & Lord listi (Bornemann). at 664 m and the subsequent downhole occurrence of Ogmo- Many of the above foraminifera possess long stratigraphical concha amalthei ?form A Michelsen at 889 m. ranges, with their documented extinctions in the Toarcian. Only two species have their recorded extinctions within the Late Foraminifera. Nine species of foraminifera – 1 agglutinating Pliensbachian – Haplophragmoides lincolnensis Copestake and taxon and 8 calcareous benthonic species – occur in the Early Dentalina matutina (d’Orbigny) – both of which range no higher Pliensbachian interval. Highest downhole occurrences include

161 N. R. Ainsworth & I. Boomer

Verneuilinoides mauritii (Terquem) and Marginulina prima gottingensis (Bornemann), Marginulina prima praerugosa spinata Terquem. Norvang, M. prima rugosa Bornemann, Nodosaria metensis One taxon is stratigraphically restricted to the Early (Terquem), Marginulinopsis quadricostata (Terquem), M. Pliensbachian (Verneuilinoides mauritii (Terquem), while two speciosa (Terquem), Nodosaria mitis (Terquem & Berthelin), taxa do not occur below the Early Pliensbachian (Glomospirella N. novemcostata Bornemann, Pseudonodosaria multicostata spp., Brizalina liasica (Terquem)). Throughout this interval, (Bornemann), Reinholdella margarita (Terquem) and foraminifera are generally rare, of low diversity and are com- R. pachyderma ‘humilis’ Copestake. prized almost exclusively of calcareous benthonic taxa, notably Two of the above taxa indicate an age no younger than Late the Nodosariidae (Lenticulina varians (Bornemann)) and the Sinemurian (raricostatum Zone) – Dentalina varians hausleri Polymorphinidae. This marked decrease in foraminiferal diver- (Schick) at 884 m and Trochammina gryci Tappan at 960 m – sity within the Early Pliensbachian has also been described while Reinholdella pachyderma ‘humilis’ Copestake ranges no from a number of localities throughout England, including younger than mid-raricostatum Zone at 933 m (Copestake & Lincolnshire (Brouwer, 1969), Dorset (Barnard, 1950) and the Johnson, 1984, 1989). Reinholdella margarita (Terquem) is an Mochras Borehole (Copestake & Johnson, 1989). important marker species in the UK Early Jurassic, ranging no younger than the earliest Late Sinemurian (mid-obtusum Zone) Ostracoda. Fourteen species of ostracod occur in the Early to intra-Early Sinemurian (mid-semicostatum Zone) (Copestake Pliensbachian. Highest downhole occurrences include & Johnson, 1989). In well L134/5-1, its highest occurrence at Ektyphocythere foveolata (Michelsen), Gammacythere ?klingleri 1273 m (swc) is taken to indicate an earliest Late Sinemurian Boomer, G. ubiquita Malz & Lord, Liasina lanceolata (Aposto- (mid-obtusum Zone) age. Of the 41 taxa recorded, 12 are lescu), L. vestibulifera Gramann, Ogmoconcha amalthei ?form A stratigraphically restricted, while another 10 species do not Michelsen, Ogmoconchella adenticulata (Pietrzenuk), Ogmo- occur below the Late Sinemurian. The Late Sinemurian interval conchella cf.aequalis (Herrig) sensu Ainsworth, O. transversa is dominated by diverse and rich foraminiferal assemblages, (Gründel) and Pseudomacrocypris subtriangularis Michelsen. especially with respect to the calcareous benthonic taxa, notably The occurrence of Gammacythere ubiquita Malz & Lord the Nodosariidae (Dentalina matutina (d’Orbigny), D. terquemi indicates an Early Pliensbachian (davoei Zone) age at 664 m. d’Orbigny, Lenticulina varians (Bornemann), Lingulina tenera The presence of a tentatively identified specimen of Gamma- plexus Bornemann, Marginulina prima plexus d’Orbigny) cythere klingleri Boomer suggests an Early Pliensbachian (ibex and the Polymorphinidae. Although present, agglutinating Zone) age at 747 m, while the occurrence of a caved specimen foraminifera (Ammodiscus, Haplophragmoides and Trocham- (884 m) of Ektyphocythere foveolata (Michelsen) indicates the mina spp.) are generally very rare throughout the interval, but presence of lowermost Pliensbachian (?lower ibex–jamesoni they do become numerically significant within the middle part of Zones) sediments within the well section. Ogmoconcha amalthei this interval. ?form A Michelsen is also a marker taxon, restricted to the Early Pliensbachian (Michelsen, 1975). From the 14 taxa recorded in Ostracoda. Fifteen species of ostracod occur in the Late Sine- this interval, 8 are stratigraphically restricted, while another 4 murian. Highest downhole occurrences include Cardobairdia sp. species do not occur below the Early Pliensbachian. The assem- B Ainsworth, Isobythocypris elongata (Blake), E. ?betzi (Klingler blages are again dominated by the Healdiidae, notably the & Neuweiler), E. frequens (Ainsworth), Ektyphocythere spp., genera Ogmoconcha and Ogmoconchella, in association with Gramannicythere bachi bachi (Gramann), Ogmoconchella danica subsidiary Cytheracea such as Gammacythere. The faunas within Michelsen, O. mouhersensis (Apostolescu), Paracypris redcaren- this section are, however, generally sparser than those occurring sis (Blake), Pleurifera vermiculata (Apostolescu), Polycope in the overlying Late Pliensbachian. cerasia (Blake) and Pseudomacrocypris subaequalis Michelsen. The interval is marked by a number of taxa which do not Late Sinemurian (884–1326m) range above the Sinemurian/Pliensbachian boundary. These A Late Sinemurian age is denoted by the highest downhole comprise Cardobairdia sp. B Ainsworth, E. ?betzi (Klingler & occurrence of the calcareous benthonic foraminifera Dentalina Neuweiler), E. frequens (Ainsworth), Ogmoconchella danica varians hausleri (Schick) at 884 m. Although this taxon has a Michelsen and O. mouhersensis (Apostolescu). In the Mochras long stratigraphic range (Lower Sinemurian–Lower Toarcian), Borehole, Ogmoconchella danica Michelsen is restricted to the it is most commonly recorded from the Late Sinemurian, latest oxynotum–mid-raricostatum Zones, while O. mouhersensis raricostatum Zone (Brouwer, 1969; Copestake & Johnson, (Apostolescu) is restricted to the mid-obtusum–early rarico- 1989). Subsequent confirmation of this age is indicated by the statum Zones (Boomer, 1990). The occurrence of moderate occurrence of the ostracod Ogmoconchella mouhersensis numbers of Ektyphocythere spp. is a diagnostic feature of (Apostolescu) at 896 m. This taxon has a restricted stratigraphi- Sinemurian ostracod assemblages. Of the 15 taxa recorded, 10 cal range (upper obtusum–lower raricostatum Zones) in the are stratigraphically restricted, while 1 species does not occur Mochras Borehole (Boomer, 1990). below the Late Sinemurian. A marked change in the ostracod composition occurs at the Sinemurian/Pliensbachian boundary Foraminifera. Forty-one species of foraminifera – 6 agglutinat- with the highest downhole occurrence of moderate numbers of ing taxa and 35 calcareous benthonic species – occur in this the Cytheracea (Ektyphocythere spp.), in association with the interval. Highest downhole occurrences include Ammodiscus Healdiidae. The Late Sinemurian interval, is dominated by siliceus (Terquem), Trochammina gryci Tappan, Dentalina ten- moderately diverse assemblages, particularly the Cytheracea uistriata Terquem, D. varians hausleri (Schick), Lenticulina (Ektyphocythere spp. and Pleurifera vermiculata (Apostolescu)).

162 Triassic/Jurassic micropalaeontology, Inner Hebrides

Similar Upper Sinemurian assemblages, dominated by ornate 1567 m, swc) is characterized by sparse, low diversity faunas Cytheracea, are recorded throughout northwest Europe (see composed entirely of smooth taxa, notably Bairdia carinata references listed above). undulata Herrig, Bairdia. sp. 1 Ainsworth, Cardobairdia sp. B Ainsworth, Isobythocypris spp. and Pseudomacrocypris Early Sinemurian (1326–?1582 m, swc) subtriangularis Michelsen. A latest Early Sinemurian age is indicated by the highest Similar assemblages have been described by Ainsworth downhole occurrence of the calcareous benthonic foraminifera (1989a) and Ainsworth et al. (1987, 1989) from a number of Vaginulinopsis exarata (Terquem) and the ostracod Kinkelinella wells situated in both the North Celtic Sea Basin and Fastnet ?sinemuriana (Ainsworth) at 1326 m. The former taxon is strati- Basin. Comparable faunas are also known to occur in the more graphically restricted to the late semicostatum–early turneri oﬀshore regions of the English Channel Basin and the Southern Zones in west Scotland (Copestake & Johnson, 1989). North Sea (Ainsworth, pers. obs.).

Foraminifera. Twenty-five species of foraminifera – 4 agglutinat- Earliest Sinemurian–Hettangian (?1582–1844 m) ing taxa and 21 calcareous benthonic species – occur in the Early An age no younger than earliest Sinemurian (bucklandi Zone) is Sinemurian. Highest downhole occurrences include Ammodiscus indicated on the highest downhole occurrence of the ostracod asper (Terquem), Verneuilinoides liasina (Terquem & Berthelin), Ogmoconchella aspinata (Drexler) at 1582 m. The subsequent Cyclogyra liasina (Terquem), ?Involutina liassica (Jones), downhole occurrence of Ogmoconcha hagenowi Drexler and Lingulina tenera substriata (Franke) and Planularia inaequist- Ogmoconchella michelseni Ainsworth confirm this age at 1594 m. riata (Terquem), ?Reinholdella planiconvexa (Fuchs) and Vaginulinopsis exarata (Terquem). Foraminifera. Twelve species of foraminifera – 1 agglutinating The latest Early Sinemurian (lower tuneri Zone) is denoted by taxon and 11 calcareous benthonic species – occur in the earliest the occurrence of Vaginulinopsis exarata (Terquem) at 1326 m. Sinemurian to Hettangian interval. Notable occurrences include The presence of Planularia inaequistriata (Terquem) confirms an common Involutina liassica (Jones) and Reinholdella dreheri Early Sinemurian age at 1449 m (swc). This taxon has a short (Bartenstein). stratigraphical range (bucklandi Zone) in Morvern, west Involutina liassica (Jones) is a common constituent of the Scotland (Copestake & Johnson, 1989), however, in well L134/ foraminiferal fauna at 1710 m (swc). In the UK Early Jurassic, it 5-1 it is envisaged to have a less restricted range, extending into is often recorded in abundance within the latest Hettangian– the mid-Early Sinemurian. Of the 25 taxa recovered, 5 species earliest Sinemurian (late angulata–bucklandi Zones) (Copestake are stratigraphically restricted, while another 11 taxa do not & Johnson, 1989). In well L1343/5-1 its abundance is thought to occur below the Early Sinemurian. The Early Sinemurian can be represent its earliest stratigraphic occurrence (late angulata- divided into an upper interval (1326–1494 m, swc) characterized Zone). Of these 12 species only one taxon is stratigraphically by sparse foraminiferal assemblages (some specimens of which restricted (Reinholdella dreheri (Bartenstein)). The interval is are presumed cavings) and a lower interval (1509–1582m, swc) characterized by low diversity assemblages, with localized peak characterized by large numbers of poorly preserved Haplo- abundance levels of Haplophragmoides spp., Reinholdella spp. phragmoides spp., with subsidiary Nodosariidae (Lenticulina and Involutina liassica (Jones). Many of the taxa occurring varians (Bornemann)) and the Polymorphinidae. No direct within this section may be the product of cavings. faunal comparisons can be made with these Lituolidae- dominated assemblages; however, the calcareous benthonic Ostracoda. Ten species of ostracod occur in the earliest foraminifera are similar to those described from other sites in Sinemurian to Hettangian. Highest downhole occurrences in- northern Europe. clude Kinkelinella translucens (Blake), Ogmoconcha hagenowi Drexler, Ogmoconchella aspinata (Drexler), O. michelseni Ostracoda. Thirteen species of ostracod occur in the Early Ainsworth and O. ?serratostriata Ainsworth. Sinemurian. Highest downhole occurrences include Bairdia cari- The association of Ogmoconcha hagenowi Drexler, Ogmo- nata undulata Herrig, Bairdia sp. 1 Ainsworth, Isobythocypris conchella aspinata (Drexler), O. michelseni Ainsworth indicates cylindrica (Herrig), I. tatei (Coryell) and Kinkelinella ?sinemurian age no younger than earliest Sinemurian (bucklandi Zone) at ana (Ainsworth). 1594 m. All three taxa can often occur in profuse numbers. The All of the above ostracod taxa are envisaged to range later presence of specimens tentatively assigned to Ogmoconchella than the Early Sinemurian, with both Bairdia sp. 1 Ainsworth serratostriata Ainsworth at 1844 m suggests an earliest and Isobythocypris tatei (Coryell) occurring often in profuse Hettangian age. Six species are restricted to this interval. With numbers throughout the UK offshore (Ainsworth, 1989a, b; the exception of Ogmoconchella serratostriata Ainsworth, all of Ainsworth et al., 1987, 1989, 1998). Of the 13 species recorded, the other nine species decrease in abundance below c.1770 m. 4 taxa are stratigraphically restricted, while 1 species does not This is envisaged to be a function of lithology resulting in poor occur below the Early Sinemurian. Two distinct ostracod recovery from the indurated limestones of the Broadford assemblages are recognized during the Early Sinemurian. The Formation. The ostracod assemblages are dominated by large upper interval (1326–1408 m) is composed of moderately diverse numbers of the Healdiidae (notably Ogmoconcha hagenowi ostracod assemblages, comprising smooth-valved taxa such as Drexler and Ogmoconchella aspinata (Drexler)), with subsidiary Ogmoconchella, Isobythocypris, Cardobairdia and Paracypris,in Cytheracea (Kinkelinella translucens (Blake)). The Hettangian to association with moderate numbers of ornate Cytheracea (e.g. earliest Sinemurian ostracod assemblages recorded in well L134/ Ektyphocythere and Kinkelinella). The lower interval (1417– 5-1 are similar to contemporary assemblages described from

163 N. R. Ainsworth & I. Boomer

A. Ostracod B. Ostracod Diversity C. Foram Abundance D. Foram Diversity Abundance 0204060 05100 50 100 0102030 400 400 400 400

Late 600 600 600 600 Pliensbachian

Early 800 800 800 800 Pliensbachian

1000 1000 1000 1000

Late Sinemurian 1200 1200 1200 1200 Depth (m)

1400 1400 1400 1400 Early Sinemurian

1600 1600 1600 1600 Earliest Sinemurian - Hettangian 1800 1800 1800 1800 Rhaetian

2000 2000 2000 2000 Fig. 3. Changing diversity and abundance of foraminifera and ostracods with depth based on their highest downhole occurrences. (Graph A) Simple species abundance within the ostracods (points) with a 5-point moving mean (line). (Graph B) Simple species diversity within the ostracods (points) with a 5-point moving mean (line). (Graph C) Simple species abundance within the foraminifera (points) with a 5-point moving mean (line). (Graph D) Simple species diversity within the foraminifera (points) with a 5-point moving mean (line). other regions in northwest Europe, most of which are dominated simple species diversity, and includes a 5-point moving mean by the Healdiidae. This faunal assemblage is also charac- line which highlights the major patterns of change. For- teristic of contemporary horizons in the North Minch Basin aminiferal abundance is generally higher than the ostracods (Ainsworth, pers. obs.). throughout much of the studied interval, attaining a maximum of 71 specimens at 969 m. However, ostracods are more abun- PALAEOENVIRONMENTAL ANALYSIS dant within the Hettangian–earliest Sinemurian. Likewise The foraminiferal and ostracod assemblages occurring in well foraminiferal diversity is generally higher than the ostracods L134/5-1 are very similar to contemporaneous records described (with a maximum 24 taxa at 549 m), with a number of distinct from other areas in northwest Europe. The palaeoenvironmental cycles clearly visible. Figure 4 (graphs D and E) shows the reconstruction of the Hebridean area during the Early Jurassic percentage of agglutinating and calcareous benthonic foramini- (Hesselbo et al., 1998) places this exploration well at the fera present in each sample. Throughout much of the Early southern end of a NNE–SSW-trending depositional basin open- Jurassic, calcareous benthonic taxa are the prevalent group both ing seaward to the south, with major detrital sources to the west in diversity and abundance, dominated by the Nodosaridae (Hebrides Platform) and east (Scottish mainland). Given the (Dentalina, Lenticulina, Lingulina, Marginulina), the Polymor- relatively ﬁne-grained nature of many of the sediments occurring phidae and, to a smaller extent, the Bolivinitidae (Brizalina in well L134/5-1, the depositional environment is thought to liasica). Agglutinating foraminifera are less diverse and gener- have been more distal than the correlative sedimentary ally of moderate to rare abundance, dominated by Lituolidae sequences on Skye to the northwest, typiﬁed by a higher (Haplophragmoides spp.). A number of localized peaks of incidence of coarser-grained sediments (siltstones and sand- Haplophragmoides spp. occur, however, between 1509 m and stones). The microfossil assemblages support this palaeogeo- 1582 m (swc). graphical interpretation since they are all indicative of fully The ostracods also exhibit a number of distinct faunal marine conditions. There is little evidence of proximity to land changes throughout the Early Jurassic. Figure 3 (graphs A and or marginal marine conditions which would be indicated by the B) illustrates species abundance and species diversity, including ostracod taxa Darwinula or Lutkevichinella. the 5-point moving mean. Ostracod abundance is highest within Changes in the faunal composition of both foraminifera and the Hettangian–earliest Sinemurian, with numbers reaching 62 ostracods in well L134/5-1 are illustrated in Figures 3 and 4. specimens, whereas during the Early Sinemurian to Late From these data, a number of distinct events with characteristic Pliensbachian interval, totals do not exceed 35 specimens. assemblages have been noted. None of the data, however, have Ostracod diversity remains relatively low throughout the Early taken into account the weight of the unprocessed sample. Jurassic (never exceeding 8 taxa), however, again there are The foraminifera display a number of distinct changes. clearly a number of cycles. The percentage faunal composition Figure 3 (graphs C and D) illustrates species abundance and of the ostracod assemblages is illustrated in Figure 4, Graph A

164 Triassic/Jurassic micropalaeontology, Inner Hebrides

A. % Metacopina B. % Bairdiidae & C. % Cytheracea & D. % Agglutinated E. % Calcareous Cyprididae others Benthonic 0 50 100 0 50 100 0 50 100 0 50 100 0 50 100 400 400 400 400 400

Late 600 600 600 600 600 Pliensbachian

Early 800 800 800 800 800 Pliensbachian

1000 1000 1000 1000 1000

Late Sinemurian 1200 1200 1200 1200 1200 Depth (m)

1400 1400 1400 1400 1400 Early Sinemurian

1600 1600 1600 1600 1600 Earliest Sinemurian - Hettangian 1800 1800 1800 1800 1800 Rhaetian

2000 2000 2000 2000 2000 Fig. 4. Changing percentage patterns of foraminifera and ostracods with depth, based on their highest downhole occurrences. (Graph A) Percentage of metacopid ostracods recorded (points) with a 5-point moving mean (line). (Graph B) Percentage of the ostracod families (Bairdiidae and Cyprididae) recorded (points) with a 5-point moving mean (line). (Graph C) Percentage of ostracod superfamily Cytheracea recorded (points) with a 5-point moving mean (line). (Graph D) Percentage of agglutinating foraminifera recorded (points) with a 5-point moving mean (line). (Graph E) Percentage of calcareous benthonic foraminifera recorded (points) with a 5-point moving mean (line).

(Metacopina), Graph B (Bairdiidae and Cyprididae combined) microgastropods and bivalves occur in large numbers through- and Graph C (Cytheracea and others) which includes both the out this interval. A shallow, slightly deeper, low energy, well- Cladocopina and the Platycopina, both groups being extremely oxygenated open marine (inner to middle shelf) environment is rare. The Metacopina graph (Pseudohealdia, Ogmoconcha and envisaged. The occurrence of common specimens of Reinholdella Ogmoconchella) clearly illustrates the dominance of this group in dreheri at 1754 m (swc) suggests either a slight shallowing or a the earliest Jurassic interval (Hettangian to earliest Sinemurian), period of marine restriction. The high abundance of metacopid it should also be noted that the highest abundance of meta- ostracods within this interval and the low diversity and abun- copids coincides with the ostracod diversity peaks, illustrating dance of foraminifera (which occurs throughout northwest their importance within Early Jurassic ostracod assemblages. Of Europe) has been interpreted as the colonization of a transgres- the 80 samples that yielded ostracods, 56 contained metacopids sive sea by an opportunistic and successful group of organisms. and in all but 10 of those samples, the metacopids make up more The Lower Sinemurian can be subdivided into two units. The than half of all specimens, while 24 samples comprise more than lowermost part of the Pabay Shale Formation of intra-Early 80%. Sinemurian age is marked by large numbers of agglutinating The earliest sediments examined in this study (Rhaetian, foraminiferids (squashed Haplophragmoides spp.) occurring as Penarth Group) are devoid of microfaunas. From both litho- three distinct peaks. Calcareous benthonic foraminifera, notably facies evidence and palynological data (rare acritarchs and the Nodosaridae and the Polymorphinidae, occur in smaller abundant miospores) a marginal marine environment is sug- numbers. This is associated with a marked decline in the gested for these uppermost Rhaetian sediments. The succeeding ostracod faunas, especially with respect to the Metacopina. lowermost Jurassic sediments, the Broadford Formation of Although rare, the ostracod assemblages comprise mainly Hettangian age, yielded only small numbers of metacopid smooth-walled ostracods of the Bairdiidae and Cyprididae ostracods, in association with rare echinoderm debris. A shallow (Bairdia, Isobythocypris, Pseudomacrocypris and Cardobairdia). marine (inner shelf) environment is suggested, with deposition This association of faunal elements may suggest localized events occurring during the continuing marine transgression initiated of slightly reduced (dysaerobic) oxygen conditions upon the sea during the uppermost Rhaetian. The overlying Blue Lias ﬂoor, within a dominantly shallow marine (inner to middle Formation (Hettangian–earliest Sinemurian) yields low diversity shelf) environment. Bottom water conditions are envisaged to foraminiferal and ostracod faunas. The former is dominated have ameliorated during the latest part of the Early Sinemurian, by calcareous benthonic taxa, notably the Nodosaridae denoted by a marked increase in the ostracod faunas, notably (Lenticulina, Lingulina, Marginulina), with localized peaks of the ornate Cytheracea (Ektyphocythere). The foraminiferal the Involutinidae (Involutina liassica) and Epistominidae faunas, however, remain sparse both in diversity and abun- (Reinholdella dreheri). Ostracods are dominated by Ogmoconcha dance, with no particular group dominating the assemblages. An and Ogmoconchella spp. (albeit in low diversity), with subsidiary increase in calcareous benthonic foraminiferal diversity and Cytheracea (e.g. Kinkelinella translucens). Echinoderm debris, abundance occurs in the earliest part of the Late Sinemurian,

165 N. R. Ainsworth & I. Boomer suggesting moderate to good bottom water conditions, within an 25 inner to mid-shelf environment. The foraminiferal faunas are dominated by the Nodosaridae, notably Dentalina, Lenticulina, OSTRACODS 20 FORAMS Lingulina and Marginulina, reaching an abundance of 64 specimens at 1273 m. The ostracods mirror this increase in numbers within this early part of the Late Sinemurian, with the 15 assemblages again dominated by Ektyphocythere, in association with subsidiary smooth forms, notably Paracypris and Ogmo- 10 conchella. Within the early part of the Late Sinemurian, both Species diversity diversity and abundance of the calcareous benthonic fora- 5 miniferids and ostracods decreases; however, agglutinating foraminifera (Ammodiscus, Haplophragmoides and Tro- chammina) achieve numerical signiﬁcance, indicating some basin 0 0 20406080100 restriction within the inner to middle shelf environment. Simi- Specimen abundance larly the macrofaunas (bivalves, microgastropods and echino- Fig. 5. The number of specimens recorded is plotted against the number derm debris) are only recovered in small numbers, again of species for both foraminifera and ostracods in each sample. The suggesting dysaerobic bottom waters at this time. Microfaunal record for both groups indicates that the small samples investigated do recovery within the Hallaig Sandstone Member equivalent is not yield fully representative assemblages. It is commonly accepted that also poor. Deposition is envisaged to have been within a a sample of 300 individuals is required. The ostracods remain at particularly low diversity levels throughout, even in the most abundant shallow, inner shelf marine environment. The uppermost samples. Sinemurian sediments yield diverse and abundant macro- and microfaunas, with deposition in a well oxygenated inner shelf, shallow marine environment. The foraminiferal assem- chammina. Late Pliensbachian ostracods are moderately blages are dominated by calcareous benthonic taxa, notably common, again dominated by smooth-walled taxa, including the the Nodosaridae (Lenticulina, Dentalina, Lingulina and Cyprididae (Cardobairdia), and the Metacopina (Ogmoconcha, Marginulina), reaching a peak abundance of 71 specimens at Ogmoconchella and Pseudohealdia). Deposition of the 969 m and a peak diversity of 20 species at 991 m. Agglutinating Scalpa Sandstone equivalent is envisaged to have occurred taxa only comprise a tiny fraction of the total fauna. Ostracod within shallow (inner shelf) open marine, well oxygenated faunas also increase in both diversity and abundance towards environments, distal to an arenaceous source. the Sinemurian–Pliensbachian boundary, with up to 20 specimens. The assemblages are dominated by the ornate Cytheracea CONCLUSIONS (Ektyphocythere, Pleurifera, Grammanicythere), in association Exploration well L134/5-1 has yielded an extensive Triassic to with smooth forms, notably the Metacopina (Ogmoconchella). Lower Jurassic sequence, which contains a valuable biostrati- Microfaunal diversity and abundance dramatically decline graphical record permitting correlation with contemporaneous within the earliest Pliensbachian, suggesting restricted water sites throughout much of NW Europe. Although the Rhaetian circulation within an inner to mid-shelf environment. This is sediments were barren of microfaunas, the Hettangian to Upper supported by the occurrence of large numbers of micro- Pliensbachian yields a rich and diverse foraminiferal and ostra- gastropods within this interval. Midway through the Early cod fauna. A total of 100 taxa, comprising 11 agglutinating and Pliensbachian (top Pabay Shale Formation), conditions amelio- 44 calcareous benthonic foraminifera, in association with 45 rated, denoted by an increase in microfaunal recovery. Similar species of ostracod, are recorded. A number of taxa are envis- to the Late Sinemurian interval, the foraminiferal faunas almost aged to be new, however, poor preservation precludes a com- exclusively comprise calcareous benthonic taxa, dominated by plete taxonomic review of this material. Not surprisingly, many the Nodosaridae (Lenticulina, Marginulina) and the Polymor- of the microfaunal assemblages possess very strong similarities phinidae. Although generally rarer than the foraminifera, a to those described from the west coast of Scotland, the Mochras marked peak in ostracod abundance (35 specimens) occurs at Borehole, Fastnet and North Celtic Sea basins, as well as 747 m. The ostracods are dominated by the Metacopina, southern England and the various North Sea basins. Faunal notably Ogmoconcha, Ogmoconchella, in association with the comparisons can also be made further aﬁeld to those of France, ornate genus Gammacythere. A marked decline in microfauna, Germany, Portugal and Sweden. associated with large numbers of both echinoderm debris and The environment of deposition was entirely marine from the microgastropods, occurs within the basal part of the Scalpa earliest Hettangian through to the Late Pliensbachian, but a Sandstone equivalent of earliest Late Pliensbachian age. A combination of local tectonic controls and eustatic changes in shallow marine, partly restricted and/or shallow water environ- sea-level caused a number of abrupt changes in faunal diversity, ment is suggested. A marked increase in diversity and abun- turnover and assemblage composition. It has not been possible dance occurs within the latest Pliensbachian, with the to ascertain the relative impact of each of these dynamic foraminiferal assemblages dominated by rich calcareous processes upon the microbenthos. Figure 5 indicates that ostra- benthonic faunas, including the Nodosaridae (Dentalina, cod diversity remains low despite increasing sample size, Frondicularia, Lenticulina, Lingulina, Marginulina, Saracenaria) whereas the foraminiferal diversity increases with abundance. and the Bolivinitidae (Brizalina liasica). Although rare, aggluti- The Early Jurassic Hebrides microfossil record can be nating taxa are dominated by Haplophragmoides and Tro- summarized as follows.

166 Triassic/Jurassic micropalaeontology, Inner Hebrides

The Hettangian to earliest Sinemurian interval is character- biozonation for the English Channel and its adjacent areas. In ized by relatively high ostracod abundance dominated by the Underhill, J. R. (Ed.), Development, evolution and Petroleum Geology of the Wessex Basin Metacopina; this is a similar pattern to elsewhere in Europe. . Geological Society, London, Special Publi- cations, 133:87–102. The single Triassic sample examined is barren of ostracods Apostolescu, V. 1959. Ostracodes du Lias du Bassin de Paris. Revue de and foraminifera. L’Institut Francais du Pètrole, 14: 795–826. The Early Sinemurian marks a switch to low abundance Bang, I. 1968. Biostratigraphical investigations of the pre-Quaternary Cyprididae/Bairdiidae-dominated assemblages, with relatively in the Oresund boreholes mainly on the basis of foraminifera. In Larsen, G., Buch, A., Christensen, O. B. & Bang, I. (Eds), Oresund, high proportions of agglutinating foraminifera. This is fol- Helsingor–Halsingborgslinien, Geologisk Rapport,86–88. Rapport lowed by a period dominated by cytheracean ostracods. Danmarks Geologiske Undersøgelse. The Late Sinemurian witnesses two peaks in diversity and Bang, I. 1971. Jura aflejringerne I Ronde Nr1 (2103-2164M). Bio- abundance of both foraminifera and ostracods between the stratigrafi pa grundlag af foraminiferen. Danmarks Geologiske Undersøgelse depths 1000 m and 1300 m. These peaks are dominated by , 39:74–80. Bang, I. 1972. Jura biostratigrafi I Novling Nr1 pa grundlag af metacopine ostracods and calcareous benthonic foraminifera. foraminiferen. Danmarks Geologiske Undersøgelse, 40: 119–123. The Early Pliensbachian yields poor foraminiferal assem- Barnard, T. 1950. Foraminifera from the Lower Lias of the Dorset blages, but with a peak in ostracod diversity and abundance at Coast. Quarterly Journal of the Geological Society of London, 105: about 750 m; subsequently diversity and abundance of both 347–391. Barnard, T. 1956. Some Lingulinae from the Lias of England. groups falls sharply. Micropaleontology, 2: 271–282. The Late Pliensbachian interval is characterized by increas- Barnard, T. 1957. Frondicularia from the Lower Lias of England. ing biodiversity, dominated by metacopine ostracods and Micropaleontology, 3: 171–181. calcareous benthonic foraminifera. Barnard, T. 1960. Some species of Lenticulina and associated genera from the Lias of England. Micropaleontology, 6:41–55. Bartenstein, H. & Brand, E. 1937. Mikropaläontologische Unter- ACKNOWLEDGEMENTS schungen zur Stratigraphie des nordwestdeutschen Lias und The authors wish to acknowledge the co-operation of Chevron Doggers. Abhandlungen Herausgegeben von der Senckenbergischen Europe-London for permission to publish this paper, in particu- Naturforschenden Gesellschaft, 439:1–224. lar to David Lewis, Adrian J. Robinson and Lucy Williams. The Binns, P. E., McQuillin, R., Fannin, N. T. G., Kenolty, N. & Ardus, D. A. 1975. Structure and stratigraphy of the sedimentary basins in interpretations expressed in this manuscript are entirely the the Sea of the Hebrides and the Minches. In Woodland, A. W. responsibility of the authors. We wish to thank Dr Sylvie (Ed.), Petroleum and the Continental Shelf of North-West Europe, Crasquin-Soleau and the reviewers (Dr P. Copestake and 93–102. Applied Science Publishers, Barking. Prof. A. R. Lord) for their useful comments and constructive Bizon, G. 1960. Révision de quelques espèces-types de foraminiféres du Lias du Bassin Parisien de la collection Terquem. Revue de criticisms. Micropaléontologie, 3:3–18. Boomer, I. D. 1990. On Gammacythere klingleri Boomer sp. nov. Manuscript received 12 September 2000 Stereo-Atlas of Ostracod Shells, 17:77–80. Manuscript accepted 10 May 2001 Boomer, I. D. 1991. Lower Jurassic Ostracod biozonation of the Mochras Borehole. Journal of Micropalaeontology, 9: 205–218. Boomer, I. & Ainsworth, N. R. in press. Early Jurassic. In Athersuch, J., REFERENCES Keen, M. C. & Wilkinson, I. P. (Eds), A Stratigraphical Atlas of Ainsworth, N. R. 1987. Pliensbachian Ostracoda from the Fastnet British Ostracoda 2. British Micropalaeontological Society . Basin, offshore southwest Ireland. Bulletin of the Geological Survey of Boomer, I., Ainsworth, N. R. & Exton, J. 1998. A re-examination of the Ireland, 4:41–62. Pliensbachian and Toarcian Ostracoda of Zambujal, west-central Ainsworth, N. R. 1989a. Systematic description of new ostracod species, Portugal. Journal of Micropalaeontology., 17:1–14. in Rutherford, M. M. & Ainsworth, N. R. Micropalaeontological and Brouwer, J. 1969. Foraminiferal assemblages from the Lias of stratigraphical recognition of the Triassic/Jurassic boundary in the N. W. Europe. Verlandelingen der Koninklinjke Netherlandsche North Celtic Sea and Fastnet Basins. In Batten, D. J. & Keen, M. C. (Nederlandse) Akademie van Wetenschappen, Amsterdam. Afdeeling (Eds), Northwest European Micropalaeontology and Palynology, Natuurkunde, 25:1–48. 56–65. Ellis Horwood, Chichester. Clark, A. R. 1969. The Ostracoda of the Scottish Lias. PhD thesis, Ainsworth, N. R. 1989b. Rhaetian, Hettangian and Sinemurian Ostra- University of London. coda from the Fastnet Basin offshore Southwest Ireland. Bulletin of Colin, J.-P., Ionnoides, N. S. & Vining, B. 1992. Mesozoic stratigraphy the Geological Survey of Ireland, 4: 107–150. of the Goban Spur, offshore south-west Ireland. Marine and Ainsworth, N. R. 1990. Uppermost Rhaetian to lower Bajocian Ostra- Petroleum Geology, 9: 527–541. coda from the Porcupine, Slyne, Erris and Donegal Basins, offshore Colloque sur le Lias Francais 1961. Memoire du Bureau de Recherche West Ireland. Bulletin of the Geological Survey of Ireland, 4: 169–200. géologiques Miniéres 4. Ainsworth, N. R. & Horton, N. F. 1986. Mesozoic micropalaeontology Copestake, P. & Johnson, B. 1984. Lower Jurassic (Hettangian– of exploration well Elf 55/30-1 from the Fastnet Basin, offshore Toarcian) Foraminifera from the Mochras borehole, North Wales southwest Ireland. Journal of Micropalaeontology, 5:19–29. (U. K.) and their application to a worldwide biozonation. Benthos ’83. Ainsworth, N. R., O’Neill, M., Rutherford, M., Clayton, G., Horton, Second International Symposium on Benthic Foraminifera Pau, April N. F. & Penney, R. A. 1987. Biostratigraphy of the Lower Creta- 1983, 183–184. ceous, Jurassic and uppermost Triassic of the North Celtic Sea and Copestake, P. & Johnson, B. 1989. The Hettangian to Toarcian. In Fastnet Basins. In Brooks, J. & Glennie, K. (Eds), Petroleum Geology Jenkins, D. G. & Murray, J. W. (Eds), Stratigraphical Atlas of Fossil of North West Europe, 611–622. Graham & Trotman, London. Foraminifera 2, 129–189. British Micropalaeontology Society/Ellis Ainsworth, N. R., O’Neill, M. & Rutherford, M. M. 1989. Jurassic and Horwood Limited, Chichester. Upper Triassic Biostratigraphy of the North Celtic Sea and Fastnet Donze, P. 1967. Les Ostracodes du Sondage de Laneuveville-devant- Basins. In Batten, D. J. & Keen, M. C. (Eds), Northwest European Nancy (Lotharingen de la region type). Sciences de la Terre, 12:71–90. Micropalaeontology and Palynology,1–44. Ellis Horwood, Chichester. Donze, P. 1985. Lias Infe´rieur et Moyen. In Oertli, H. J. (Ed.), Atlas Ainsworth, N. R., Braham, W., Gregory, F. J., Johnson, B. & King, C. des Ostracodes de France. Bulletin des Centres de Recherches 1998. A proposed latest Triassic to earliest Cretaceous microfossil Exploration-Production Elf Aquitaine, Mémoires, 9: 101–117.

167 N. R. Ainsworth & I. Boomer

Drexler, E. 1958. Foraminiferen und Ostracoden aus dem Lias von Malz, H. 1971. Zur Taxonomie ‘glattschaliger’ Lias-Ostracoden. Siebeldingen/Pfalz. Geologisches Jahrbuch, 75: 475–554. Senckenbergiana Lethaea, 52: 433–455. Exton, J. 1979. Pliensbachian and Toarcian Microfaunas of Zambujal, Malz, H. 1975. Eine Entwicklungsreihe “vallater” Ogmoconchen Portugal: Systematic Paleontology. Geological Paper, 79:1–104 (Ostracoda) im S-deutschen Lias. Senckenbergiana Lethaea, 55: Carleton University, Ottawa. 485–503. Exton, J. & Gradstein, F. 1984. Early Jurassic stratigraphy and Malz, H. & Lord, A. R. 1976. Gammacythere n.g. (Ostracoda) and its micropalaeontology of the Grand Banks and Portugal. Geological occurrence in the Lower Jurassic of N.W. Europe. Senckenbergiana Association of Canada Special Paper, 27:13–30. Lethaia, 57: 249–263. Field, R. A. 1968. Lower Jurassic Ostracoda from England and Malz, H. & Nagy, J. 1989. Lower Jurassic ostracods from North Normandy. PhD thesis, University of London. Sea wells in the Norwegian Sector. Sonderdruck aus CFS-Courier, Fyfe, J. A., Long, D. & Evans, D. 1993. The Geology of the Malin– Forschungsinstitut Senckenberg, 113:61–75. Hebrides Sea area. United Kingdom oﬀshore regional report, HMSO Michelsen, O. 1975. Lower Jurassic biostratigraphy and ostracods of the for the British Geological Survey, London. Danish Embayment. Danmarks Geologiske Undersøgelse, 104:1–287. Gründel, J. 1964. Zur Gattung Healdia (Ostracoda) und zu einiger Morton, N. 1965. The Bearreraig Sandstone series (Middle Jurassic) of verwandten Formen aus dem unteren Jura. Geologie, 13: 456–477. Skye and Raasay. Scottish Journal of Geology, 1: 189–216. Hallam, A. 1959. Stratigraphy of the Broadford Beds of Skye, Raasay Morton, N. 1983. Palaeocurrents and palaeo-environment of part of the and Applecross. Proceedings of the Yorkshire Geological Society, 32: Bearreraig Sandstone (Middle Jurassic) of Skye and Raasay, Inner 165–184. Hebrides. Scottish Journal of Geology, 19:87–95. Harloﬀ, J. 1993. Ostracoden des Unter-Pliensbachiums in Baden- Morton, N. 1989. Jurassic sequence stratigraphy in the Hebrides Basin, Württenberg. Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie N. W. Scotland. Marine and Petroleum Geology, 6: 243–260. und Paläontologie), 191:1–215. Norling, E. 1972. Jurassic stratigraphy and foraminifera of western Harris, J. P. 1989. The sedimentology of a Middle Jurassic lagoonal Scania, southern Sweden. Sveriges Geologiska Undersokning, delta system: Elgol Formation (Great Estuarine Group), NW Afhandlingar och Uppsatser, 47:1–120. Scotland. In Whateley, M. K. G. & Pickering, K. T. (Eds), Deltas: Norvang, A. 1957. The Foraminifera of the Lias series in Jutland, Sites and Traps for Fossil Fuels. Geological Society, London, Special Denmark. Mededelingen Dansk, Geolisch Forening, 13:1–135. Publications, 41: 147–166. Oates, M. J. 1978. A revised stratigraphy for the western Scottish Lower Harris, J. P. 1992. Mid-Jurassic delta systems in the Hebridean basins: Lias. Proceedings of the Yorkshire Geological Society, 42: 143–156. thickness and facies distribution patterns of potential reservoir sand- Park, S.-M. 1987. The ostracod Zones and Subzones of the Lower bodies. In Parnell, J. (Ed.), Basins on the Atlantic Seaboard: Petroleum Jurassic in the southern North Sea Basin. Journal of the Paleontologi- Geology, Sedimentology and Basin Evolution. Geological Society, cal Society, Korea, 3:44–70. London, Special Publications, 62: 111–144. Partington, M. A., Copestake, P., Mitchener, B. C. & Underhill, J. R. Herrig, E. 1985. Zur taxonomie und evolution der netzberippten 1993. Biostratigraphic calibration of genetic stratigraphic sequences in Procytheridea-arten (Ostracoda) im Unteren Jura von Nordwest- und the Jurassic–lowermost Cretaceous (Hettangian to Ryazanian) of the Mittel Europa. Wiss. Z. Ernst-Moritz-Arndt-Univ. Griefswald, North Sea and adjacent areas. In Parker, J. R. (Ed.). Petroleum math-nat. wiss Reihe, 34:45–50. Geology of Northwest Europe: Proceedings of the 4th Conference, Hesselbo, S. P., Oates, M. J. & Jenkyns, H. C. 1998. The Lower Lias 371–386. Geological Society, London. Group of the Hebrides Basin. Scottish Journal of Geology, 34:23–60. Ruget, C. H. 1985. Les foraminiferes (Nodosariides) du Lias de l’Europe Howarth, M. K. 1956. The Scalpa Sandstone of the Isle of Raasay. Occidentale. Documents de la Laboratoire de geologie de Lyon, 94: Proceedings of the Yorkshire Geological Society, 30: 353–370. 1–273. Howarth, M. K. 1992. The ammonite family Hildoceratidae in the Lower Ruget, C. H. & Sigal, J. 1967. Les Foraminiferes du Sondage de Jurassic of Britain. Monographs of the Palaeontological Society. Laneuveville-devant-Nancy (Lotharingen de la region type). Sciences Klingler, W. 1962. Lias Deutschlands. Leitfossilien der Mikropaläon- de la Terre, 12:33–70. tologie. Gebru¨der Borntraeger, Berlin-Nikolasse, 73–122. Ruget, C. H. & Sigal, J. 1970. Le Lias Moyen de Sao Pedro de Muel II. Klingler, W. & Neuweiler, F. 1959. Leitende Ostracoden aus dem Communicacoes dos Servicos Geologicos de Portugal, 54:79–108. deutschen Lias B. Geologisches Jahrbuch, 76: 373–410. Searl, A. 1992. Sedimentology and early diagenesis of the Broadford Lee, G. W. 1920. The Mesozoic rocks of Applecross, Raasay and Beds (Lower Jurassic), Skye, north-west Scotland. Geological Journal, North-East Skye. Memoir of the Geological Survey for Scotland, 27: 243–270. Lord, A. R. 1978. The Jurassic, Part 1. (Hettangian–Toarcian). In Bate, Sivhed, U. 1977. A Lower Jurassic ostracode fauna in the Gantofta R. H. & Robinson, J. E. (Eds), A Stratigraphical Index of British brick pit, Skane, southern Sweden. Sveriges Geologiska Undersokning, Ostracoda 1: 189–212. Seel House Press, Liverpool. Afhandlingar och Uppsatser, 71:1–31. Lord, A. R. & Bown, P. R. 1987. Mesozoic and Cenozoic Stratigraphical Sivhed, U. 1980. Lower Jurassic ostracodes and stratigraphy of western Micropalaeontology of the Dorset Coast and Isle of Wight, Southern Skane, southern Sweden. Sveriges Geologiska Undersokning, 60:1–84. England. Field guide for the Twentieth European Micropalaeontologi- Woodward, H. B. 1897. Annual Report for 1896 of the Geological Survey cal Colloquium. British Micropalaeontological Society Field Guide, 1. and Museum of Practical Geology, 70.

168