MEGUMA.HTM

Donald Kenney (donaldkenney@gmail.com)
Last Update: Thu Oct 8 01:17:56 2020

Introduction

Introduction

The Meguma Terrane consists of marine sedimentary rocks in Southern Nova Scotia that appear to have been deposited in the sea off the continent of Gondwana in the Early Paleozoic. Fossils are scarce, but those identified do not resemble those of the North American core (Laurentia) until after the two regions fused in the Mid-Paleozoic.

Background

The Meguma Terrane is the furthermost outboard of the various surviving regions appended to North America ("Laurentia") late in the Paleozoic. The terranes were appended during the closing of the ocean that lay between the ancient continents of Laurentia and Gondwana in the late Precambrian and the first half of the Paleozoic. Meguma is composed of marine sediments and represents a small portion of the Rheas sea bottom that once existed between the Micro-continent of Avalonia and the Continent of Gondwana (Roughly the modern West Coast of Africa or possibly the Modern North West coast of South America). The Rheas ocean was created when Avalonia separated from Gondwana in the late Precambrian. It eventually closed in the late Paleozoic when Gondwana collided with Laurentia which had been accumulating areas of sea bottom, volcanic island arcs and the micro-continents of Avalonia and Baltica throughout much of the Paleozoic as the Iapetus and Rheas Seas closed.

Location

Meguman sediments are found only in the Southern half of the province of Nova Scotia. The line from Cape Chignecto on the West to Canso on the East represents the course of the Minas (Cobequid-Chedabucto) Fault Zone. Rocks immediately North of the zone are Avalonian. Those to the South are Meguman. It is currently believed that the two rock sequences evolved separately and were later forced into contact along the fault. It is believed that the Meguma Terrane extends Subsurface to the Southern Grand Banks and to Cape Cod. In general, the Northwestern edge of the region is Carboniferous or Early Mesozoic, The central strip is Lower Paleozoic with a lot of intrusives, and the Southeast part is Lower Paleozoic with minor intrusives.

Rocks

The rocks in Southern Nova Scotia consist of a mixture Upper Paleozoic intrusives intruded into Lower Paleozoic sediments and meta-sediments. The meta-sediments have been studied for many decades because of the presence of extensive Gold deposits dating to around 370Ma in metamorphosed Cambrian shales. The Meguman sedimentary sequence consists of a thick sequence of Cambrian and early Ordovician turbide deposits -- shales and sandstones overlain by thinner Middle and Upper Paleozoic beds. Ichnofossils are reportedly common throughout. Body fossils reportedly are rare becoming more common as the rocks get younger. At least one bed containing shelly fossils is reported from Early Middle Cambrian sandstones. The Ordovician rocks are dated from (rare?) Graptolites and Acritarchs. The Silurian beds are dated from Graptolites and body fossils. The Devonian Torbrook formation is said to contain relatively numerous body fossils. It is hypothesized that Meguman sediments younger than Early Ordovician consist of material recycled from the older Cambrian-Ordovician Meguma Supergroup. The total thickness of Meguman sediments is estimated to be 23 km, but no single sequence of exposures reveals the entire group.

Rocks are separated into groups mostly of shale and sandstone with rare volcanic tuff, limestone, or conglomerate. The Meguma Supergroup is exposed in the South. The younger Annapolis Supergroup is found in the Northwest. The general sequence is Goldenville (9km Cambrian-Lower Ordovician), Halifax (12.4km Middle Ordovician), Whiterock (Upper Ordovician 260m), Kentville (Silurian 900m), New Canaan (Upper Silurian 1000m), Torbrook(Devonian 1100m), Horton (Carboniferous)

The actual welding of Gondwana to North America took place during the late Devonian Acadian Orogeny. During the accretion, the Cambrian through Early Devonian beds were warped into parallel ridges (synclines) perhaps 15km peak to peak and many tens of km in length. Subsequent erosion has largely removed the peaks of the synclines leaving the Meguma rocks exposed in parallel North-South bands.

Younger rocks in the Northern part of the area include the Carboniferous Horton Group. These rocks which presumably date to times after the merger of Avalonia and Laurentia and are similar to rocks of similar age in other nearby terranes.

Localities

No recommended localities. Examine the fossil list for Nova Scotia. All Devonian and older localities in the Southern half of the province will be Meguman.