1 Modern and Ancient Orogenic Belts

Sunday, 18 March 2012
8:00 AM - 12:00 PM
Capital Rooms 2 & 3

CAMBRIAN-ORDOVICIAN SUCCESSIONS AND DETRITAL ZIRCON GEOCHRONOLOGY OF NORTH WALES AND NOVA SCOTIA: TERRANE INTERACTIONS BETWEEN GANDERIA AND MEGUMIA

Paper number: 1-10
Program: Symposia Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

The Harlech Dome and St. Tudwell's Peninsula, in North Wales, and the Meguma Terrane of southern Nova Scotia, in Atlantic Canada, preserve similar sedimentary successions of Cambrian age. All three areas display thick early Cambrian continentally-derived sandstone turbidites, overlain by early to middle Cambrian alternating mud-rich and sand-rich units in which manganese is concentrated. The manganiferous interval is everywhere marked by a diverse and abundant assemblage of trace fossils, including locally abundant Teichichnus. Above, the successions comprise anoxic, organic-rich turbidites, shallowing upward into paler, early Ordovician mudstone and siltstone with the graptolite Rhabdinopora. The succession at St. Tudwell's is the thinnest of the three and displays a shallowing event close to the base of the Furongian (upper Cambrian) marked by a disconformity.

Meguma detrital zircon assemblages display strong peaks in the late Neoproterozoic (common to many peri-Gondwanan terranes) and in the Paleoproterozoic (2.0 - 2.2 Ma), suggesting derivation from the Eburnean orogens of west Africa. Detrital zircons from the Harlech Dome reveal closely similar clusters of ages. Within the limited constraints of the available biostratigraphic and geochronologic data, major changes in environment occurred synchronously in the two successions in the Cambrian. The Cambrian successions in these areas show much greater similarity to each other than to adjacent successions in "Avalonia", suggesting proximity between the two terranes on the margin of Gondwana.

In the Ordovician the histories diverge. The highest parts of the Nova Scotian succession record shallowing conditions with shelf sedimentation extending through the Early Ordovician. In the Welsh successions a strong component of Mesoproterozoic zircon indicates that the basin was juxtaposed with Ganderia in the Monian/Penobscot events in the Early Ordovician. The succeeding history records arc/backarc volcanism that has no equivalent in Nova Scotia.