Diverse depositional and geochemical signatures of the Frasnian-Famennian global event in western Thailand reveal palaeotethyan vs. Western Australian geotectonic affinities

Jolanta Dopieralska,Zdzislaw Belka,Peter Königshof,Grzegorz Racki,Agnieszka Pisarzowska

doi:10.1016/j.jaesx.2019.100010

Abstract

Two studied sections of the Frasnian-Famennian (F-F) boundary beds in western Thailand differ significantly in their depositional and geochemical characteristics. The highly condensed, monotonous Mae Sariang (MS) limestone succession generally corresponds to the event-chemostratigraphic pattern of the F-F biocrisis based primarily on German sections, and brief anoxic episodes are identifiable in trace-metal signatures (but neither organic-rich intercalations nor distinct volcanic signals). In the case of the Thong Pha Phum (TPP) site, two specific features are especially notable: (1) a δ13C positive excursion, comparable only with the peculiar Western Australian biogeochemical signature, and (2) elemental proxies that indicate exclusively oxic and probably largely oligotrophic conditions during both Kellwasser intervals. Therefore, the demonstrated biogeochemical and environmental differentiation confirms the totally different paleogeographic settings of the studied successions, as indicated previously by the Nd isotope composition of Late Devonian seawater. The distinctiveness of the TPP section clearly indicates its affinity with the Western Australian shelf successions, which are characterized by a well-known “atypical” biogeochemical and ecological signature. In terms of provenance, the siliciclastic fraction in the MS succession corresponds to continental margin. The Paleotethyan region was sourced by felsic-volcanic or granite-gneissic massifs. In the case of the TPP section, the continental margin, as well as the partly the continental island arc, are recorded in the detritus, predominantly derived from older, continental sedimentary-metasedimentary terrains. Therefore, the assumed Western Australian geotectonic assignment of TPP corresponds to the variable, partly recycled material supplied abundantly to the “Sibumasu depocenter” from adjoining granite-dominated Archean cratons.

Highlights

Folded and thrusted Upper Devonian strata are reported from a number of regions in Thailand (e.g., Savage et al, 2006; Fontaine et al, 2009; Thassanapak et al, 2017)
The highly condensed, monotonous Mae Sariang pelagic limestone succession generally corresponds to the worldwide F-F event pattern (Fig. 1)
Only briefly enduring anoxic conditions are identifiable in the key crisis timespan of the succession, which is devoid of dark, organic-rich intercalations (Savage, 2013)

Summary

Introduction

Folded and thrusted Upper Devonian strata are reported from a number of regions in Thailand (e.g., Savage et al, 2006; Fontaine et al, 2009; Thassanapak et al, 2017). This biotic crisis and the resulting disruption of the epeiric carbonate factory (in particular the total collapse of metazoan reefs) have been considered as representing a mass depletion of marine diversity resulting mainly from a reduced origination rate (see Racki, 2005; McGhee, 2013; Stanley, 2016) Both Thai sections lack diagnostic black KW-type lithology (time-specific facies sensu Walliser, 1984; Gereke and Schindler, 2012; see data from Vietnam in Komatsu et al, 2019; Königshof et al, 2017), but the occurrence of both KW intervals are indicated by positive carbon isotope excursions (Savage et al, 2006; Königshof et al, 2012; Savage, 2013). Is this relative uniqueness relevant to understanding the KW Crisis on regional and supra-regional Asiatic-Australian scales, but it has several implications for the global scenario

Material and methods

Mae Sariang

Thong Pha Phum

General comparative characteristics of Thai successions

Terrigenous input

Redox conditions and bioproductivity

Findings

Final remarks and conclusions