Abstract

The inter-reef Ireton Formation of the Upper Devonian Woodbend Group of Alberta is essentially a calcareous shale with variable amounts of inter-bedded nodular limestones. Structures formed in limestone of the Ireton Formation vary from thin relatively undeformed beds to pinching and swelling ones, and finally to completely isolated lenses or nodules that are variously oriented. The nodules consist of finely granular lime (fine sand to very fine silt size) with minor quartz in the same grain size range as the calcite, and variable amounts of clay. All nodules are surrounded by finer grained less limey rock and display fine, peripheral, calcite-filled cracks. These structures are thought to be "sedimentary boudinage" formed by compaction. Thin limey beds sandwiched between more clayey and hence more plastic beds, are pulled apart by the laterally moving plastic beds when subjected to unconfined compaction near the depositional interface. Continued compaction under hydrostatic conditions further modifies these structures.

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