New Perspectives in Basin Analysis

Part of the series Frontiers in Sedimentary Geology pp 431-444

Glaciation: An Uncommon “Mega-Event” as a Key to Intracontinental and Intercontinental Correlation of Early Proterozoic Basin Fill, North American and Baltic Cratons

  • Richard W. Ojakangas

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Glaciation was an uncommon “mega-event” during early Proterozoic time, with a glaciation well documented in North America. Glaciogenic units, including diamictites and finely laminated sediments with dropstones, are present in the Huronian Supergroup of Ontario, in the Marquette Range Supergroup of Michigan, in the Snowy Pass Supergroup of Wyoming, in northern Quebec, and in the Northwest Territories.

Glaciogenic deposits have been recognized recently on the Baltic Shield in the Sariolian Group of the Karelian Supergroup of Finland. Since they were first described, they have been noted at the same stratigraphichorizon at several other Finnish localities. To the east of Finland in Karelia, USSR, rocks at several localities that were earlier interpreted as tectono-sedimentary in origin have been reinterpreted as glaciogenic; these occurrences, sixteen in number, are located in the Sariolian Group as in Finland. The Finnish and Karelian occurrences are scattered over an area of 500 km by 300 km, suggestive of a large glaciated terrain.

The aforementioned supergroups have many similarities in lithology and sequence. Similarity of sequence may be a reflection only of similar environments of deposition in basins with a similar tectonic evolution, but when the sequence includes products of a widespread, uncommon sedimentary event (a “mega-event”), in this case a glaciation, then the case for chronocorrelation is strengthened. The chronocorrelation between the Huronian and Karelian Supergroups is further strengthened by the observation that both are cut by ca. 2,150 Ma mafic dikes and rest upon ca. 2,450 Ma igneous rocks.

This application of “mega-event correlation” is an example of “mega-event stratigraphy” in which glaciations can be used to subdivide a sedimentary sequence whose age is otherwise constrained only within broad limits. If the age of the overall sequence is constrained by radiometric data, the sequence can be subdivided on the basis of the mega-event(s) into pre-mega-event, mega-event, and post-mega-event strata. The recognition of depositional sequences within the overall sequence may make possible the interpretation of eustatic sea-level changes related to glaciation.