Two intriguing pluricolumnals (Crinoidea) from the Lower Palaeozoic of Powys and Shropshire

Complete fossils must be preferred to fragments for most palaeontological studies, but disarticulated specimens are nonetheless potential sources of noteworthy data. Two crinoid pluricolumnals are recorded from the lower Palaeozoic; informed discussion shows each is a basis for palaeobiological interpretation. Both are gracile and are probably belong to disparids. Floricrinus (col.) sp. is from the Silurian of Wenlock Edge, Shropshire, either from the Much Wenlock Limestone Formation (Wenlock) or, more likely, the Lower Elton Formation (Ludlow). This is the first crinoid from the Silurian of the British Isles with a pentapetaloid arrangement of the areola, a geometry common in the Middle-Upper Ordovician and higher in the geologic column. Pluricolumnal gen. et sp. indet. is from the Lower Llanvirn of Powys. One end of the otherwise straight specimen is tightly coiled. This is likely the proxistele, the most flexible region of the column, and the coiling occurred after the crown was lost by autotomy in response to an environmental disturbance.     

AbnormalSq behaviour

It is well-known that the amplitude and phase of theSq(H) variation show considerable variability from day to day. In this paper we consider one aspect of the phase variability—that associated with AQDs. AQDs (or abnormal quiet days) are defined as magnetically quiet days where the maximum excursion ofH at a mid-latitude station on the poleward side of the focus occurs outside the normal time range 0830–1330 LST. Such days exhibit properties, many of which appear quite distinct from the properties of the normalSq(H) variation. The properties of AQDs, and the proposals that have been made to explain them, are considered in detail. The consequences of these proposals and some problems which need to be addressed in order to obtain a fuller understanding of the dynamics of the ionosphere on AQDs are also discussed.     

Late Pleistocene Vertebrates and Other Fossils from Epiguruk, Northwestern Alaska

Sediments exposed at Epiguruk, a large cutbank on the Kobuk River about 170 km inland from Kotzebue Sound, record multiple episodes of glacial-age alluviation followed by interstadial downcutting and formation of paleosols. Vertebrate remains from Epiguruk include mammoth, bison, caribou, an equid, a canid, arctic ground squirrel, lemmings, and voles. Radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37,000 and 14,000 yr B.P. The late Pleistocene pollen record is dominated by Cyperaceae, with Artemisia, Salix, Betula, and Gramineae also generally abundant. The fossil record from Epiguruk indicates that the Kobuk River valley supported tundra vegetation with abundant riparian willows during middle and late Wisconsin time. Large herbivores were present during the height of late Wisconsin glaciation as well as during its waning stage and the preceding interstadial interval. The Kobuk River valley would have been a favorable refugium for plants, animals, and possibly humans throughout the last glaciation.     

Calcification, photosynthesis and growth of the bloom-forming coccolithophore, Emiliania huxleyi

Measurements were made of photosynthesis and calcification in a bloom of coccolithophores in the Gulf of Maine as well as in laboratory batch cultures of the Emiliania huxleyi strain 88E. The¹⁴C technique for measuring calcification was evaluated with calcifying and noncalcifying coccolithophore strains. Shipboard bloom observations showed physiological evidence of stratification between surface and deep populations within the surface mixed layer. Photosynthesis and calcification rates were enhanced within hours of addition of KNO₃ or nitrate-rich deep water (to the same final concentration). Such rates were strongly temperature dependent in laboratory cultures, decreasing over a factor of two from 15 to 20°C. Calcification was considerably less light-dependent than photosynthesis and consistently had a measurable dark rate. In culture, maximum calcification rates and degree of cell plating were limited to logarithmic growth phase. This was followed by rapid increase in the coccolith shedding rate 1 day prior to the onset of stationary phase which continued several days after cell division stopped. The regional significance of these features to total organic and inorganic carbon production as well as calcite burial is discussed.