A reappraisal of the Dinantian floras at Oxroad Bay, East Lothian, Scotland. 2. Volcanicity, palaeoenvironments and palaeoecology

Abstract

The classic late Tournaisian plant-bearing locality at Oxroad Bay was investigated by detailed field mapping, lithological logging, studies of clast orientation, thin-section petrography and analyses of bulk geochemistry. The lithologically and structurally complex,c. 45 m-thick succession includes eight plant-bearing exposures (each consisting of up to 16 phytofossiliferous horizons) that have yielded 43 anatomically-preserved organ-species and 19 adpressed organ-species. All floral assemblages are allochthonouss.l.and demonstrate a wide range of preservation states. They occur in five successive facies (braided flood-plain, shallow volcanigenic lacustrine, terrestrial mass-flow/base-surge, shallow biogenic lacustrine, dominantly terrestrial reworked ashes) that reflect increasing influence of several basaltic tuff-ring volcanoes on an ocean-marginal lowland bordering the Southern Uplands Massif. The variable local climate reflected proximity to the proto-North Sea and eruptive seeding of the atmosphere with ash particles. Base-surges, seismically-initiated mass-flows and volcanically-induced wildfires restricted the development of mature soils and of edaphic climax communities. These disturbances created a sequence of mosaic palaeocatenas that supported a wide range of sub-communities at any one moment in time. At least some of the relativelyk-selected species that occupied the preceding, fluvially-dominated terrain were extirpated by the persistent volcanism, yielding to immigrants that were better pre-adapted to the unstable environment. Low levels of competition allowed non-adaptiven-selection, enhancing the establishment potential of evolutionary innovations.

Permineralized Cardiocarpalean Ovules in Wetland Vegetation from Early Permian Volcaniclastic Sediments of China

“…In Mitrospermum and Rhabdospermum a single vascular strand passes through the sclerotesta to the base of the nucellus where it divides in the major plane into two strands that pass through the sclerotesta, continuing distally towards the micropyle. Species of Mitrospermum also typically display a broad sarcotestal wing in the major plane of symmetry (Baxter 1971) that is less developed in Cardiocarpus, including C. dabiziae. Nucellangium Darrah is similar to Cardiocarpus in most respects, but the nucellus is much more extensively vascularized (Stidd and Cosentino 1976).…”

“…In overall size and shape, Cardiocarpus dabiziae is similar to C. magnicellularis Baxter and Roth although the latter species lacks the distinctive ellipsoidal glands present in the Chinese materials. Additional differences are that the sclerotesta of C. dabiziae comprises 3±5 rows of elongated thick-walled cells and also lacks the large peripheral cells of the outer sarcotesta seen in C. magnicellularis (Baxter and Roth 1954).…”

“…Bateman and Rothwell 1990;Bateman and Scott 1990). The palaeobotanical importance now given to sites within the Calciferous Sandstone relates to the comparatively high quality of plant preservation in which plants are permineralized in carbonate.…”

Phenotypic Plasticity of the Hydrasperman Seed FernTetrastichia bupatidesGordon (Lyginopteridaceae)

“…W. R. in 1983 and, from exposure A (Bateman and Rothwell 1990) of unit 3 (Bateman and Scott 1990;Bateman 1991) at Oxroad Bay, near Edinburgh, Scotland ( fig. 1).…”

“…In this article we describe 59 additional specimens of T. bupatides on the basis of more than 8,000 cellulose acetate peels and more than 500 thin sections that were collected at the classical cliff section at Oxroad Bay (Gordon 1938;Bateman and Rothwell 1990;Bateman and Scott 1990). These new specimens provide data that expand the range of variation of stelar rib number, secondary xylem production, trachied pitting patterns, and rachis forking patterns, and they display new characters including periderm formation, the presence of epidermal trichomes, internode length, and pinnule vascularization.…”