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Waldron and White declared that the manganese rich sedimentary rocks of Nova Scotia and Wales are Cambrian. They discovered that these rocks were deposited in a deepwater turbidite basin called Megumia and not on the Avalonian shelf. We found that the geo-chronological data does not conflict with the Early Ordovician deposition age for manganese rich sedimentary rock of the Rheic suture. This region included Nova Scotia and northern Wales. They said that “Megumia” is part of the Avalonian plate and manganese rich rocks formed on its shelf.
They performed a coticule study and found that occurrences of coticules andMn-rich sedimentary rocks are exposed in Megumia and Avalonia, as well. The two greats stated that Meguma is part of the Avalonian plate. They tested their hypothesis by investigating a few samples distributed along the Rheic suture. They used the geological map of Nova Scotia. They realized that the lithostratigraphy, which had been shown in these maps, indicated it was possible that the deposition of the coticule-bearing Halifax Formation possibly started in the latest Cambrian. However, most of its sedimentary rocks constitute Lower Ordovician deposits. This stratigraphic information validated their assumption that the deposition age of the coticule-bearing strata of the Meguma Supergroup is roughly coeval to the biostratigraphically well-constrained strata of the Ardennes.
If the stratigraphic order is undisturbed, the occurrence at different levels inside the Halifax Formation would indicate that the Mn enrichment occurred over a longer period which means the latest Cambrian to Early Ordovician. Thus, for our approach, which began from the biostratigraphically well-constrained occurrences and the geochemically well-investigated incidents of the Ardennes, and which was further studied to compare their geochemical signatures with deposits in areas that are less well characterized.
We found that the rifting of the margin of Gondwana, eventually led to the separation of Avalonia and the opening of the Rheic Ocean. This redistributed these matures rocks into the developing rift. These rocks kept redepositing to a height of several thousand meters and made latest Cambrian to Ordovician sedimentary rocks. These high rocks deposited in a short time and inherited the geochemical signatures of their protoliths. They figured that this geochemical signature is found throughout Variscan Europe to the south of the Rheic suture in sandstones and intercalated less mature sedimentary rocks of latest Cambrian to early Ordovician age. It is interesting to note that this geochemical signature can also be found in sedimentary rocks of Nova Scotia.
Waldron and White mentioned that the European occurrences of Palaeozoic coticules are hosted by sedimentary rocks that have been deposited, including the Welsh occurrences on Avalonian crust. They said that they didn’t use their sedimentological investigations as there was evidence for deposition of Halifax formation on the shelf. We noticed the thick turbidite sequences inside the Meguma Zone require enormous subsidence that is in contrast to the depositional environment of Avalonia. Referring to a segmented shelf they said, the turbidites of the Goldenville Formation, which is in the Meguma Zone, may represent the final filling of a channel incised in the Avalonian shelf which was finally overlain by a prevailing muddy shelf facies of the Halifax Formation. Hence, it can be concluded that the term Avalonian shelf can be safely used.