A modern analogue for the Lower Ordovician Obolus conglomerate of Estonia
Article Abstract:
The coast of Namibia is dominantly made up of shell fragments of the inarticulate brachiopod Discinisca. The situation is analogous to the occurrence of similar organisms in the phosphate-rich Obolus Conglomerate unit of the Ordovician Kallavere Formation in northern Estonia. Occurrence of phosphorite deposits in the Namibian coast is attributed to the upwelling of phosphite-rich water, the Benguela system, which encourages the abundance of organisms secreting phosphate rich shells. A similar paleo-upwelling system is being postulated to explain the Estonian deposits.
Publication Name: Geological Magazine
Subject: Earth sciences
ISSN: 0016-7568
Year: 1993
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Palaeomagnetism of Late Ordovician igneous intrusions from the northern Welsh Borderlands: implications to motion Eastern Avalonia and regional rotations
Article Abstract:
Palaeomagnetic studies of the rotations in Late Ordovician dolerites of the northern Welsh Basin and of Lower Palaezoic inliers of Eastern Avalonia indicate that the Breidden Hills Inlier has the maximum rotation. Local rotations about a bend in the Severn Valley Fault System cause fractures between the Breidden Hills Inlier and the neighboring Shelve Inlier and rotation of Late Ordovician fold axes. There is a rapid movement of the Avalonian Plate toward southern palaeolatitudes, as revealed by studies on Upper Ordovician.
Publication Name: Geological Magazine
Subject: Earth sciences
ISSN: 0016-7568
Year: 1995
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