Lower Jurassic Foraminifera from the Llanbedr (Mochras Farm) Borehole, North Wales, UK

Abstract

ABSTRACT The complete, fully cored Lower Jurassic (Hettangian, Sinemurian, Pliensbachian, Toarcian) succession from the Llanbedr (Mochras Farm) Borehole, North Wales, the thickest known British section, has yielded a diverse and well preserved foraminiferal fauna, comprising 270 species and subspecies which are described and illustrated. An additional nine taxa, not encountered at Mochras, are also described. This typical European Boreal Atlantic foraminiferal fauna is dominated by members of the Lagenida, with the Ceratobuliminoidea, Miliolida, Spirillinina, Involutinina, Buliminida and Textulariida as important accessory groups. The Ceratobuliminoidea and Miliolida are unusually diverse, with Reinholdella and Ophthalmidium being notably abundant. The presence of the Family Oberhauserellidae is significant. A benthonic foraminiferal biozonation scheme for the Lower Jurassic, comprising 16 biozones and tied to the standard ammonite-based chronostratigraphy, is described in detail. It is recognizable across the northern European Boreal province, and is applicable to subsurface hydrocarbon exploration of the UK continental shelf and onshore Europe. Three new genera (Duoplanum, Extonia and Haynesella) are described as well as 19 new species (Citharina sherringtoni, Duoplanum inaequale, D. leve, Glomospirella liassica, Lagena? haeusleri, L. semisulcata, Lagenammina pseudofusiformis, L. tangentia, Loxostomum liassicum, Marginulina turneri, Neobulimina bangae, Nodosaria pseudoclaviformis, Ophthalmidium strictum, Reinholdella? mochrasensis, R. robusta, Reussoolina? lacrimaforma, Semiinvoluta excelsa, Tubinella pseudoinornata and Vinelloidea lordi), and 10 new subspecies (Berthelinella involuta striata, Ichthyolaria terquemi bamardi, I. terquemi mediumcostata, Lenticulina varians barnardi, Loxostomum liassicum liassicum, L. liassicum teres, Ophthalmidium macfadyeni tenuiloculare, Paralingulina cernua ssp. A, Reinholdella margarita dorsoplana and R. pachyderma humilis). Two further species are renamed as Nodosaria whittakeri and Paralingulina paranodosaria.