Biostratigraphy and structure of Richmond group rocks in the Rairoa River—mount Heslington area, Nelson

Abstract A map of the Wairoa River‐Mount Heslington area is presented, in which Garden Formation (new formation), Problematica Shellbed (new fomation name), Max Sandstone (new formation), Heslington Conglomerate (new formation), Mount Wellington Sandstone, and Richmondiana Shellbed (new formation name) are shown as formations within Richmond Group, Murihiku Supergroup. The formations comprise 610 m of siltstone, sandstone, conglomerate, shellbed, and tuff exposed in sections along Wairoa River and on the slopes of Mount Heslington. The succession is repeated in the limbs of the isoclinal Heslington Syncline which appears to be non‐plunging. The syncline lies north‐west of Eighty‐eight Fault and is itself faulted. Faunas allow recognition of Oretian, Otamitan, and Warepan stages (Upper Triassic). Stages in the evolutionary development of athyridid and spiriferinide brachiopods and the occurrence of gregarious bivalves allow refined correlation with formational units in sequences in the Southland and Kawhia synclines. Heslington Syncline appears to have an extended sequence for part of late Otamitan time. Comments on the nature and location of early fossil collections are included in an appendix.