Burrow preservation and diagenetic events: An example from the Late Carboniferous to Permian Kati Formation, Kinta Valley, Malaysia

The new insights into the Kati Formation include two members: the Tronoh Member and the Parit Member, in descending order. The Tronoh Member, as the parent rock and lower succession, comprises dark grey, bedded-to-massive shale intercalated with thin-bedded, fine-grained sandstone. The Parit Member, as a replacement origin and upper succession, contains hematite- and magnetite-beds. Two modes of burrow preservation are classified: Primary Preservation and Diagenetic Preservation. The primary preservation reflects tiering, and two styles are distinguished: deep tiering, marked by Chondrites and Thalassinoides; and shallow tiering, represented by Planolites and root traces. Based on the diverse styles of diagenetic preservation, three stages of diagenetic events are examined: (i) Early stage diagenesis: marks the replacement of Thalassinoides and root traces by hematite and magnetite, with both bedding surfaces and entire beds, mediated by bacterial iron mineralization. It occurs after colonization but before infilling of Thalassinoides, in which roots were altered following root disintegration. (ii) Mid-stage diagenesis: Occurs during Quaternary seafloor and coastline migration, forming secondary infill of yellowish-brown sandy siltstone from the overlying sediment in the voids of eroded Thalassinoides. Several eroded hematite- and magnetite-boulders from the Parit Member are redeposited. (iii) Late-stage diagenesis: marks recent to subrecent weathering processes, producing red stained shale, limonite- and goethite-replacement roots, eroded empty infill of Thalassinoides, and hematite- and magnetite-fragments lying on the unconformity surface, obscured burrows and mottled textures.