The Avalon Assemblage (Ediacaran, late Neoproterozoic) provides some of the oldest evidence of diverse macroscopic life and underpins current understanding of the early evolution of epibenthic communities. However, its overall diversity and provincial variability are poorly constrained and are based largely on biotas preserved in Newfoundland, Canada. We report coeval high-diversity biotas from Charnwood Forest, UK, which share at least 60% of their genera in common with ones in Newfoundland. This indicates that substantial taxonomic exchange took place between different regions of Avalonia, probably facilitated by ocean currents, and suggests that a diverse deepwater biota may already have been widespread at the time. Contrasts in the relative abundance of prostrate versus erect taxa likely record differential sensitivity to physical environmental parameters (hydrodynamic regime, substrate) and highlight their significance in controlling community structure.
The Oman -UAE ophiolite is the world"s largest ophiolite. It is divided into twelve separate fault-bounded blocks, of which the northern three lie wholly or partly in the United Arab Emirates (UAE). Extensive mapping has shown that the UAE blocks contain mantle and crustal sections which correspond to the classic "Penrose conference" ophiolite definition, but which are cut by a voluminous later magmatic sequence including ultramafic, mafic and felsic components. Samples from the later magmatic sequence are dated at 96.4 ± 0.3 Ma, 95.74 ± 0.3 Ma, and 95.2 ± 0.3 Ma; the early crustal section, which has not been dated directly, is thus constrained to be older than c.96.4 Ma.Petrological evidence shows that the early crustal section formed at a spreading ridge, but the later magmatic sequence was formed from hydrous magmas that produced different mineral crystallisation sequences to normal MORB. Mineral and whole-rock geochemical analyses show that the early crustal rocks are chemically similar to MORB, but the later *Manuscript Click here to download Manuscript: OphPaper_vfinalApr10. doc 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 magmatic sequence has chemical features typically found in supra-subduction zone (SSZ) settings. The ophiolite in the UAE thus preserves clear evidence for two stages of magmatism, an early episode formed at a spreading centre, and a later episode associated with the onset of subduction. Similar two-stage magmatism has been recognised in the Oman sector, but the UAE contains the most voluminous SSZ magmatism yet described from this ophiolite.
We present a revised lithostratigraphy for the Voltaian Supergroup of Ghana, based on a review of existing literature, interpretations of remotely sensed data and reconnaissance field survey of the Volta Basin. These strata thicken eastwards, to a maximum of between 5 and 6 km adjacent to the PanAfrican Dahomeyide orogen. They began to accumulate some time after about 1000 Ma, along the margin of an epicontinental sea. Initial sedimentation, comprising the age-equivalent Kwahu and Bombouaka Groups, shows a cyclical mode of deposition controlled by eustatic changes in sea-level that produced a range of nearshore marine, littoral and terrestrial environments. A major erosional interval was followed by deposition of the 3-4 km thick Oti-Pendjari Group. Basal tillites and associated sandy diamictons are correlated with the Marinoan (end-Cryogenian) glaciation, indicating a maximum depositional age of about 635 Ma. The overlying cap carbonates and tuffs were deposited within a shallow epeiric sea bordered by a volcanically active rift system. The main part of the group records the transition from a rifted passive margin to a fully developed foreland basin receiving marine flysch in the form of argillaceous strata interbedded with highly immature wacke-type sandstones and conglomerates. Maximum accommodation space was developed within a foredeep adjacent to the Dahomeyide belt. Towards the end of the orogenic phase, the foredeep succession became partially inverted and then was buried under coarse terrestrial, red-bed molasse of the Obosum Group
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