Glacial sediments and erosional pavements near the Cambrian—Precambrian boundary in western Henan Province, China

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Abstract
Exceptionally well-preserved glaciated pavements and a variety of glacigenic sediments comprising the Luoquan Formation in Henan Province, central China, are believed to have formed close to the Cambrian–Precambrian boundary. They may therefore be younger than the better known Sinian tillites representing the Changan and Nantuo ice ages. They perhaps belong to a distinct glacial epoch that is recorded elsewhere in China and in other continents, but for which there is less evidence than for earlier Late Proterozoic glacial periods. Lithofacies represented in the Luoquan Formation are massive diamictite (signifying deposition as lodgement or melt-out till), bedded diamictite (waterlain till or glaciomarine/glaciolacustrine sediments with dropstones), rhythmites with dropstones (glaciolacustrine or fjord deposits, possibly varves), tabular conglomerates and sandstones (outwash, deltaic or sub-aqueous mass-flow deposits), lens-shaped breccia deposits (sub-aqueous mass-flow deposits) and gravel-sand wedges (frost contraction crack infillings). The glaciated pavements reveal well-preserved striations, grooves (often intersecting), 'plastically moulded' forms, crescentic gouges and steps. On a regional scale the linear features are of variable orientation, but they indicate a dominant ice flow direction towards the southeast. All this evidence points to upland glaciation with erosion followed by deposition in a terrestrial glacial and glaciolacustrine environment.