Microbial-, fusulinid limestones with large gastropods and calcareous algae: an unusual facies from the Early Permian Kh
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ORIGINAL ARTICLE
Microbial‑, fusulinid limestones with large gastropods and calcareous algae: an unusual facies from the Early Permian Khao Khad Formation of Central Thailand Chatchalerm Ketwetsuriya1,2 · Martin Nose2,3 · Thasinee Charoentitirat4 · Alexander Nützel1,2,3 Received: 13 March 2020 / Accepted: 7 July 2020 © The Author(s) 2020
Abstract The Early Permian (Kungurian) Khao Khad Formation of Central Thailand consists mostly of carbonates deposited on the western margin of the Indochina Terrane. This formation has yielded unusual microbial-fusulinid limestones with large gastropods which contribute most to the rock volume. With a height of more than 6 cm, the gastropods are amongst the largest Early Permian gastropods ever reported. Gastropods as major rock formers are rare in the Palaeozoic. This, and other recently reported invertebrate faunas from Thailand show that gastropods may dominate Permian fossil assemblages not only in diversity, but also regarding abundance and in some cases also regarding biomass. Besides gastropods, fusulinids, various calcareous algae, intraclasts and thick microbial-cyanobacterial (Girvanella and Archaeolithoporella) coatings and reticular microbial patches as well as thick inter- and intragranular radial fibrous cement crusts are present. The gastropods represent at least four species and belong probably to undescribed taxa. The fusulinid genus Pseudofusulina and Misellina (M.) termieri are reported from the Khao Khad Formation for the first time and indicate a Bolorian age. Calcareous algae are dominated by dasycladaceans followed by gymnocodiaceans and solenoporaceans. The studied limestone almost completely lacks metazoan reef builders such as corals and sponges. Likewise, brachiopods and bivalves are absent in the studied samples and echinoderms are very scarce. The carbonate is interpreted as product of shallow water, back-reef lagoonal platform community with a high productivity providing the large gastropods with sufficient food. However, conditions were too eutrophic for sessile filter feeders including metazoan reef builders. Keywords Khao khad formation · Large gastropods · Saraburi group · Dasyclads · Microbialites · Permian
Introduction The role of gastropods—one of the major marine invertebrate clades—in the vast Late Palaeozoic deposits of Southeast Asia has been poorly known until recently. Even the * Chatchalerm Ketwetsuriya [email protected] 1
Department of Earth and Environmental Sciences, Paleontology and Geobiology, Ludwig-MaximiliansUniversität München, Richard‑Wagner‑Str. 10, 80333 Munich, Germany
2
SNSB-Bayerische Staatssammlung für Paläontologie Und Geologie, Richard‑Wagner Str. 10, 80333 Munich, Germany
3
GeoBio‑Center, Ludwig-Maximilians-Universität München, Richard‑Wagner Str. 10, 80333 Munich, Germany
4
Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
other invertebrate fauna from that region is not particularly well studied. This hinders analyses of faunal distributions and
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