Middle Cambrian siliceous sponge-calcimicrobe buildups (Daegi Formation, Korea): Metazoan buildup constituents in the aftermath of the Early Cambrian extinction event

Abstract

Numerous decimetre- to metre-scale carbonate buildups dominated by siliceous sponges and the calcimicrobe Epiphyton are reported from the Middle Cambrian (Series 3) Daegi Formation of Korea. These siliceous sponge-Epiphyton buildups consist predominantly of grey micritic boundstones with dark clots and/or white clumps. The boundstones contain sponge spicule networks interpreted as the calcified remains of siliceous sponges. The white clumps and dark clots in the boundstones represent variously preserved Epiphyton. Siliceous sponges form constructional pore space and are commonly encrusted by Epiphyton. The sponges were probably the primary frame-builders, providing substrates for the attachment and subsequent growth of Epiphyton. Epiphyton is considered to be a binder when covering the surface of siliceous sponges, and a subordinate frame-builder when filling depositional voids created by siliceous sponges or growing on top of other Epiphyton growth bundles. The siliceous sponge-Epiphyton buildups of the Daegi Formation show similarities to previously described Late Cambrian (Furongian) anthaspidellid-calcimicrobe buildups from Iran and the USA. Together with recently reported examples from the Zhangxia Formation of eastern China, the sponge-Epiphyton buildups from Korea represent some of the oldest metazoan-calcimicrobe buildups, after the extinction of most archaeocyaths at the end of the Early Cambrian (Series 2). This implies that the incorporation of metazoans in Middle Cambrian (Series 3) carbonate buildups occurred much earlier than previously known. The buildup-forming siliceous sponges described in this study demonstrate that their role in Early Phanerozoic carbonate buildups has been grossly underestimated. (C) 2012 Elsevier B.V. All rights reserved.