AVALONIA

The rocks and the fossils seen in southeastern Newfoundland, southern New Brunswick, Nova Scotia, eastern Massachusetts and Rhode Island in North America and in England and Wales indicate that these areas represent a region which formed an independent small continent during the Cambrian termed Avalonia. The Cambrian-Ordovician faunas of Avalonia compose an Avalonian Faunal Province. The sedimentary cover sequence in these area indicates that Avalonia was an insular continent located in higher latitudes by the latest Proterozoic (Landing 1996). The preserved uppermost Proterozoic to lowest Cambrian sequences are limited to marginal platform areas, higher sequences are most complete in fault-bounded depocenters on the inner platform. The search for a stratotype of the Precambrian-Cambrian boundary (which has a unique importance because of the development of metazoan animals and its resultant first fossil record adequate for detailed evolutionary and biostratigraphical questions) ended in the southwestern Newfoundland sector of Avalonia. Here, composite sections span a great range across the Proterozoic-Cambrian boundary, staring with Late Proterozoic sequences qith a tillite (Gaskiers Formation), succeeded by volcaniclastics with Ediacaran fossils through to sediments with "algae" (vendotaenids) and various associations with progessively more complex trace fossils, to small shelly fossils assemblages and finally to trilobites (of the late Early Cambrian Callavia zone).
The the first appearence date (FAD) of Trichophycus pedum in the reference section at Fortune Head was chosen in 1991 by the International Subcommission on Cambrian Stratigraphy (through its Working Group on the Precambrian-Cambrian Boundary) the Global Stratotype Section and Point (GSSP) for the Precambrian-Cambrian boundary. Sections in England and Wales are of historic importance as the original type area of the Cambrian System of Sedgwick and Murchison (1835). The relatively rich late Early Cambrian to Late Cambrian faunas are, similarly to those of maritime Canada, pandemic and reflect biota of the outer detrital belt, in accordance with uniform shales which dominate the sequence.
 
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Global Stratotype Section and Point (GSSP) of the Proterozoic-Cambrian boundary
at Fortune Head, Southeastern Newfoundland.
The cliff exposes the lower part of the Chapel Island Formation.
Copyright (C) G. Geyer, 1997
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GSSP of the Proterozoic-Cambrian boundary
at Fortune Head, SE Newfoundland.
Dr. G. M. Narbonne points to the earliest occurrence of
Trichophycus pedum (formerly termed "Phycodes pedum"),
now the Golden Spike site.
Copyright (C) G. Geyer, 1997
Late Early Cambrian steeply dipping rocks of the
top of Random Formation (resitant sandstones to the left)
and base of Brigus Formation (calcareous rock with small shelly fossils
of Tommotian aspect and exceptionally rare trilobite fragments).
Between the formations is a major unconformity.
Little Dantzig Cove Brook, Southeastern Newfoundland
Copyright (C) G. Geyer, 1997
The classical Comley Quarry
at Comley, Welsh Borderlands, U.K.
Exposed in this small quarry are nearly all
Lower Cambrian lithostratigraphic units of this area.
The picture shows the layers dipping to the right
with the youngest, Protolenus Limestone on top.
Copyright (C) G. Geyer, 1997
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Typical Upper Cambrian deposits:
The Lingula Flags
at Whitesands Bay, St. David's Head, South Wales
Copyright (C) G. Geyer, 1997
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Further reading
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