Microbial-, fusulinid limestones with large gastropods and calcareous algae: an unusual facies from the Early Permian Khao Khad Formation of Central Thailand

Chatchalerm Ketwetsuriya,Thasinee Charoentitirat,Martin Nose,Alexander Nützel

doi:10.1007/s10347-020-00605-w

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.

Highlights

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
The investigated locality is situated at Khao Wong hill, Saraburi Province which is a part of the Khao Khad Formation of the Saraburi Group (Geological map data derived from DMR, Thailand) high-spired gastropods, fusulinids, dasyclads and microbes
The calcareous rocks of the Khao Khad Formation are at least locally rich in large, undescribed gastropods showing that this group was an important part of the Permian carbonate platform biota

Summary

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. The present paper reports and interprets an unusual Permian carbonate facies from Thailand that is rich in large,. The investigated locality is situated at Khao Wong hill, Saraburi Province which is a part of the Khao Khad Formation of the Saraburi Group (Geological map data derived from DMR, Thailand) high-spired gastropods, fusulinids, dasyclads and microbes. The calcareous rocks of the Khao Khad Formation are at least locally rich in large, undescribed gastropods showing that this group was an important part of the Permian carbonate platform biota. We describe a new unusual coarse grained rudstone facies from the Khao Khad Formation at Khao Wong Hill, Phra Phutthabat district, Saraburi Province, Central Thailand, characterized by large gastropods, fusuline foraminifers, calcareous algae, intraclasts, thick microbial-cyanobacterial coatings, microbialites as well as thick inter- and intragranular radial fibrous cement crusts.

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