Palaeoenvironmental control on distribution of crinoids in the Bathonian (Middle Jurassic) of England and France

Bulk sampling of a number of different marine and marginal marine lithofacies in the British Bathonian has allowed us to assess the palaeoenvironmental distribution of crinoids for the first time. Although remains are largely fragmentary, many species have been identified by comparison with articulated specimens from elsewhere, whilst the large and unbiased sample sizes allowed assessment of relative proportions of different taxa. Results indicate that distribution of crinoids well corresponds to particular facies. Ossicles of Chariocrinus and Balanocrinus dominate in deeper-water and lower-energy facies,with the former extending further into shallower-water facies than the latter. Isocrinus dominates in shallower water carbonate facies, accompanied by rarer comatulids, and was also present in the more marine parts of lagoons. Pentacrinites remains are abundant in very high-energy oolite shoal lithofacies. The presence of millericrinids within one, partly allochthonous lithofacies suggests the presence of an otherwise unknown hard substrate from which they have been transported. These results are compared to crinoid assemblages from other Mesozoic localities, and it is evident that the same morphological ad-aptations are present within crinoids from similar lithofacies throughout the Jurassic and Early Cretaceous

A low diversity Sinuites gastropod community from the Floian, Early Ordovician, of South Wales

A low diversity Sinuites-dominated gastropod community is described from the Floian, Arenig Series, of the Llangynog Inlier, southwest of Carmarthen, South Wales. The abundant material comes from shallow-water siltstone and mudstone beds of the Bolahaul Member of the Ogof Hên Formation. The locality has an exceptionally diverse mollusc-dominated fauna (63.5% of the fauna), with gastropods constituting 6% and tergomyans 1% and echinoderms, arthropods and other fauna making up the rest. Except for one rare tergomyan mollusc, identified as Carcassonnella cf. vizcainoi, other tergomyans are described elsewhere. Nearly half of all gastropod specimens are represented by Sinuites ramseyensis. Three of the five taxa described are new: Mimospira llangynogensis sp. nov., Catalanispira prima sp. nov., and Ceratopea? moridunensis sp. nov. The assemblage compares best with those of contemporaneous high-latitude peri-Gondwana areas. Early Ordovician species of Carcassonnella are typically found in France, Iberia, Czech Republic, and Morocco, while species of Mimospira are found in Germany and Czech Republic, but also in Baltica where the main radiation took place later. Two of the oldest occurrences of Mimospira are from Avalonian Wales (Carmarthenshire and Anglesey). Catalanispira occurs later in Baltica and Laurentia in the late Middle and early Late Ordovician, when taxa from these areas start to appear in Wales and vice versa. The presence of Ceratopea?, a genus typical of Laurentia, is at odds with the biogeographic distribution of faunas at this time. Part of the observed distribution pattern may be explained by different latitudinal position and facies depths of Avalonia compared to Armorica, Bohemia, and Morocco. The species described herein are amongst the first Floian taxa of these groups formally described from this area and add significantly to the global Floian record

Examining the case for the use of the Tertiary as a formal period or informal unit

The ‘Tertiary’, omitted from IUGS-approved timescales since 1989, is still in common use. With the recent re-instatement of the Quaternary as a formal unit, the question arises as to whether the Tertiary too should be reinstated as a formal period, with the ‘Paleogene’ and ‘Neogene’ being downgraded to sub-periods. This paper presents arguments for and against this proposal, stemming from discussions by members of the Geological Society Stratigraphy Commission. It is intended to stimulate discussion of the topic in the wider community