Pleistocene clastic dykes in the King Valley, western Tasmania

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Abstract
Four types of Pleistocene clastic dykes are present in a variety of sediments in the King Valley. They include till dykes injected into bedrock fractures produced by overriding ice; gravel dykes in bedrock openings that appear to be eroded and stream‐filled bedding planes; gravel dykes in weathered limestone formed as fillings of dolines and solution tunnels; and gravel dykes in unconsolidated Pleistocene deposits. Gravel‐filled, wedge‐shaped structures in Pleistocene tills and outwash gravels are the most numerous dykes and most occur in three distinct swarms. The dykes of one swarm have along‐slope strikes and are formed on laminated glacial lake sediments that have been subjected to landsliding; the dyke structures apparently formed as tensions cracks caused by the landslides. The other two swarms have downslope strikes and are associated with sediments deposited in ice contact environments. Although these dykes resemble ice wedge casts, they probably formed syndepositionally by the collapse and deformation of the sediments as buried ice melted.