Abstract

A combination of facies analysis and the identification of dropstones as well as striated and faceted clasts in diamictites and associated sedimentary rocks from the Hamersley Province confirms earlier suggestions of their glacial origin. Ten lithofacies, comprising two diamictite, four sandstone, and four fine-grained facies, have been identified and arranged into three glaciomarine facies associations. Massive diamictite interbedded with laminated siltstone in the southern part of the province is interpreted to have been deposited peripheral to the margin of rapidly melting tidewater glaciers emanating from more extensive ice cover in highlands to the south. Distal diamictites, sandstones, and laminated siltstones preserved north of the Hardey syncline were deposited from sediment gravity flows, sediment plumes, and rain-out from rare icebergs. Background marine sedimentation consisted of banded iron formation and siltstone. Using these glacial deposits as an event marker, it can be shown that ∼2000 m of turbidites and shallow-marine sedimentary rocks in the Turee Creek Group, on the southern margin of the Hamersley Province, are lateral facies equivalents of as much as 400 m of banded iron formation and mudrock to the north. This correlation demonstrates the markedly asymmetric nature of subsidence in the McGrath trough, which has previously been interpreted as a foreland basin with an orogenic margin to the southwest. New geochronologic data constrain the age of these glacigenic deposits to 2.45–2.20 Ga, which is within the range of present constraints for similar deposits in North America, Fennoscandia, and South Africa. Available paleomagnetic data suggest low-latitude (5°–11°) glaciation for the North American, South African, and West Australian deposits.

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