Nature and origin of rubbly limestone in the upper Silurian Read Bay Formation of Arctic Canada

The Upper Silurian Read Bay Formation of Somerset and Cornwallis Islands contains a very distinctive rock herein termed rubbly limestone. This rock, formed of hard 'lumps' and beds of limestone in a softer matrix can be divided into rubbly argillaceous limestone for those rocks with an argillaceous matrix, and rubbly mottled dolomitic limestone for those rocks with a dolomitic matrix. Detailed field, petrographic and paleontological analyses indicate that the rubbly limestones are probably the result of incipient subtidal lithification that occurred at a very early stage after deposition. The exact form of the rubbly limestone was controlled by the original nature of the sediment, the rate of sedimentation, the degree of early lithification and the degree of dolomitization. Lumps encrusted by bryozoans and tabulate corals and lumps with micritized upper and/or lower surfaces are rare. Most lumps show evidence of burrowing; however, in some cases there is evidence that the burrowers purposely avoided the lumps. These features suggest that lithification occurred near the deeper limits of burrowing and storm exhumation. Dolomitization preferentially followed the more permeable zones between the limestone lumps and apparently occurred at a very early stage in the diagenetic history of the rock.