Griesbachian and Dienerian (Early Triassic) ammonoids from the Salt Range, Pakistan

Abstract

Introduction The biotic recovery following the end-Permian mass extinction is an intensively studied topic, for which high accuracy and high precision time control is of paramount importance. Nekto-pelagic clades such as ammonoids and conodonts recovered very quickly compared to other marine clades (e.g. Brayard et al. 2006, 2009; Orchard 2007) and play the leading roles in dating of Lower Triassic marine sedimentary rocks. However, many studies addressing the recovery are based on insufficiently resolved palaeontological age controls. This is particularly the case for the Dienerian, where ammonoids and biochronology are still poorly understood (Jenks et al. 2015). A review of the current knowledge of Griesbachian and Dienerian ammonoids from the Salt Range is given in the foreword of this volume (Ware & Bucher 2018) to which the reader is referred. From 2007 to 2010, our research group carried out intensive field work in the Salt Range and the Surghar Range. Palynological and carbon isotope records have been recently published by Hermann et al. (2011a,b, 2012a,b) and Schneebeli- Hermann et al. (2012), oxygen isotopes from biogenic phosphates by Romano et al. (2013), Smithian ammonoids by Br€uhwiler et al. (2012) and bivalves of Smithian and Spathian ages by Wasmer et al. (2012). The present work focuses on Griesbachian and Dienerian ammonoids from four different areas in the Salt Range. It is based on abundant and well-preserved material sampled bed by bed. This new material provides the basis for a comprehensive revision of the taxonomy and biostratigraphy of Griesbachian and Dienerian ammonoids in the Salt Range, where all relevant sections are found. Because of the incomparable quality of the Dienerian ammonoid record of the Salt Range, this taxonomic and biostratigraphical re-investigation is an essential contribution to the Lower Triassic ammonoid zonation of the Northern Indian Margin and to the understanding of the Early Triassic biotic recovery.