Structural and fluid evolution of Saraburi Group sedimentary carbonates, central Thailand: A tectonically driven fluid system John Warren a, * , Christopher K. Morley b, d , Thasinee Charoentitirat a , Ian Cartwright c , Prueksarat Ampaiwan b , Patcharin Khositchaisri b , Maryam Mirzaloo a , Jakkrich Yingyuen b a Dept of Geology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand b PTTEP, EnCo, Soi 11, GGS, Vibhavadi Rangsit Road, Chatuchak, Bangkok 10900, Thailand c School of Geosciences, Monash University, Victoria, Australia d Department of Geological Sciences, Chiang Mai University, 239 Huay Kaew Road, Chiang Mai 50200, Thailand article info Article history: Received 19 August 2013 Received in revised form 21 December 2013 Accepted 24 December 2013 Available online 3 January 2014 Keywords: Thrust Veins Stable isotopes Indosinian Saraburi Karst abstract A stable isotopic study, focused on calcite cements, vein-fill calcite and various bioclasts was conducted on variably deformed and thrusted Lower and Middle Permian carbonates of the Saraburi Group. Samples were collected in quarry faces across 3 areas in the SaraburieLopburi region of central Thailand. Stable isotope crossplots (carbon and oxygen), using texture-aware isotope samples, defined variable, but related, fluid-cement histories, which are tied to regional burial and then orogenic overprints driven by the Indosinian (Triassic) orogeny. This was followed by telogenetic overprints, driven by late Cenozoic uplift. The studied carbonates were deposited along the western margin of the Indochina Block, where they were deposited as isolated calcareous algal, sponge and fusilinid-rimmed platforms on highs bound by extensional faults. The platform areas passed laterally and vertically into more siliciclastic dominated sequences, deposited in somewhat deeper waters within probable fault-bound lows. Regional post- depositional mesogenetic fluid-rock re-equilibration of the isotope values in ongoing calcite pre- cipitates occurred until the matrix permeability was occluded via compaction and pressure solution. This regional burial regime was followed by collision of the Indochina and Sibumasu blocks during the Indosinian (Triassic) blocks, which drove a set of structurally focused (thrust-plane related) increasingly warmer set of fluids through the studied sequences. The final diagenetic overprint seen in the isotopic values of the latest calcite cements occurs in a telogenetic (uplift) setting driven by Cenozoic tectonics and isostatic uplift. Integration of isotope data with its structural setting establishes a clear separation in fluid events related to two time-separate tectonic episodes; its fluid chemistry defines the Permo-Triassic closure of the Paleotethys and its subsequent reactivation during the Tertiary collision of India and Asia. The CeO covariant plot fields in the Permian carbonates of central Thailand are so distinct that it is possible to use their signatures to separate burial from meteoric cements in drill cuttings and hence recognise equivalent subsurface unconformities and likely zone of porosity development in possible “buried hill plays in Thailand. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Fluid flow and fluiderock interactions in fold and thrust belts are of considerable interest for determining a better understanding of their structural and tectonic development, as well as fluid dis- tribution in relation to mineral exploitation, and the trapping of hydrocarbons. Syntectonic veins record evidence for fluid flow during deformation, and provide important data about the stress and strain state during episodes of deformation (e.g. Lacombe, 2010; Beaudoin et al., 2012) as well as information about the origin and temperature of the fluids (e.g. Hudson, 1977; Dietrich et al., 1983; Kirschner et al., 1995; Beaudoin et al., 2011; Lacroix et al., 2014). Syntectonic veins commonly represent responses to accommodation of minor deformation during folding (e.g. Evans and Fischer, 2012; Beaudoin et al., 2011, 2012), and shortening by pressure solution (Dietrich et al., 1983), while others record sig- nificant fluid migration, particularly along major thrusts (e.g. Travé et al., 1998; Badertscher et al., 2002; Wiltschko et al., 2009). Fluids precipitating minerals in these veins may originate as single or mixed sources from depth, the formation, or meteorically. The analysis of stable oxygen and carbon isotopes is one key element in * Corresponding author. Tel.: þ66 (0)22352464. E-mail addresses: jkwarren@ozemail.com.au (J. Warren), chrissmorley@gmail. com (C.K. Morley). Contents lists available at ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo 0264-8172/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpetgeo.2013.12.019 Marine and Petroleum Geology 55 (2014) 100e121