Hathaithip Thassanapak

Conodonts, radiolarians and ostracodes in the Permian E-Lert Formation, Loei Fold Belt, Indochina Terrane, Thailand

Conodonts are rare in the Permian carbonates of Indochina but abundant conodonts and ostracodes have been obtained from turbiditic limestones of the Permian E-Lert Formation along with radiolarians from overlying cherts, all deposited on the margins of the interplatform Nam Duk Basin. Conodonts are typically Tethyan and are very similar to faunas from Sicily and south China. They include Hindeodus gulloides, Pseudohindeodus oertlii, Mesogondolella siciliensis and Sweetognathus subsymmetricus which indicate a probable late Kungurian – Roadian age range although a Wordian age cannot be excluded. M. siciliensis, which has a high blade and small cusp supposedly typical of warm-water conodonts, is found in deep (<500 m) carbonate turbidites in Thailand and in very deep deposits in Oman and Sicily, but generally not in shallow-water tropical limestones in Thailand, Oman and Sicily. The chert sequence yields a radiolarian fauna consisting of 11 confidently assigned species of which Albaillella asymmetrica, A. sinuata, Tormentum delicatum and Latentifistula patagilaterata suggest a latest Kungurian – earliest Roadian age, deposited at a palaeodepth of c. 500 m. Ostracodes consist of 16 genera and 23 species which belong to Shivaella, Paraberounella, Carinaknightina, Paraparchites, Shemonaella, Bairdia, Cryptobairdia, Bairdiacypris?, Spinocypris, Pseudobythocypris, Baschkirina, Microcheilinella, Basslerella, Polycope and Cyathus, of which Shivaella elertensis sp. nov. Chitnarin is newly described. The ostracodes are a palaeoecologically mixed assemblage comprising external platform and deeper-water forms, suggesting that the limestone turbidites were deposited on the proximal part of the slope. Cyathus caperata and C. elliptica show a palaeobiogeographic link to south China.

Geochemistry of radiolarian cherts from a Late Devonian continental margin basin, Loei fold belt, Indo-China terrane

More than 42 species of well-preserved Upper Devonian radiolarians have been obtained from cherts and siliceous shales in four sections (Chom Noi, Phu Kham Phe (P), Phu Kham Phe (C) and Pha Samyod) from the NE Thailand sector of the Loei fold belt, Indochina terrane. They include Ceratoikiscum sp. cf. planistellare Foreman, Helenifore laticlavium Nazarov & Ormiston, Astroentactinia sp. cf. paronae (Hinde), Stigmosphaerostylus herculea (Foreman), S. pusilla (Hinde), S. cf. vulgaris (Won), Trilonche davidi (Hinde), T. echinata (Hinde), T. elegans Hinde, T. hindea (Hinde), T. palimbola (Foreman), T. vetusta Hinde, Polyentactinia polygonia Foreman, Spongentactinella sp. cf. windjanensis Nazarov, Archocyrtium sp.?, Palaeoscenidium sp., Triaenosphaera sp., and others. Radiolarian faunas from these sections indicate a range from lower Frasnian to Famennian. Analyses of rare earth, trace and major elements suggest that the Upper Devonian chert and siliceous successions from Loei were deposited in a continental margin environment near to a volcanic arc. These successions contain distinctive weak negative Ce anomalies with strong positive Eu anomalies which differ from Upper Devonian cherts reported from northern Thailand, the Truong Son fold belt (Laos) and from South China. Negative Ce anomalies and low to moderate Lan/Cen ratios imply proximity between the Chom Noi and Phu Kham Phe (C), which were deposited in more distal parts of the depositional basin than the Pha Samyod and Phu Kham Phe (P) samples. Most of the Pha Samyod and Phu Kham Phe (P) samples exhibit high continental-derived trace element levels including Cr, Zr, Hf, Rb, Th and in part V, which supports close proximity to terrigenous sources. Paleozoic stratigraphic sequences of the Loei fold belt and geochemical results suggest that the Upper Devonian deep marine sequences in the Loei fold belt were deposited within a rifted, continental-margin basin, possibly a back-arc basin and not in a large oceanic basin as has been previously suggested.

Palaeoenvironment and palaeogeography of Middle and Upper Devonian strata from the Loei fold belt, Indochina terrane (northeast Thailand)

Limestone and chert sections from the Loei fold belt in Loei Province, northeastern Thailand, have yielded Givetian to Famennian conodonts and Late Devonian radiolarian faunas. The mid-Devonian siliciclastic section containing an abundant benthic assemblage is interbedded with volcaniclastics and is replaced laterally, in places, by pillow basalts. This siliciclastic section is conformably overlain by argillaceous limestones, divided into two microfacies. The lime mudstone (MF1) and spiculite wackestone (MF2) which contains Polygnathus linguiformis linguiformis, Belodella resima and Icriodus arkonensis, indicating the lower Givetian, deposited in a quiet subtidal to deeper water environment. This argillaceous limestone is succeeded by upper Givetian bioherm containing a diverse stromatoporoid–coral fauna. Microfacies of bioherm consists mainly of crinoidal wackestone/packstone (MF3) deposited in a flank and stromatoporoid–coral framestone/bafflestone/rudstone (MF4) forming a core of bioherm. Continuing relative sea-level rise led to drowning of the bioherms and the deposition of condensed section of non-oceanic, continental margin oozes containing the radiolarians Trilonche chiangdaoensis, Trilonche echinata, Trilonche elegans, Trilonche hindea, Trilonche minax and others and the Famennian conodonts Palmatolepis triangularis, Palmatolepis werneri, Palmatolepis minuta minuta and Palmatolepis wolskae. The transgressive Middle to Upper Devonian strata ranging from fossiliferous sandstones through argillaceous limestone and bioherm to radiolarian cherts are broadly similar to sections in South China and in the Rhenohercynian belt of Germany. Deposition in a continental margin basin, possibly on thinned continental crust, such as a back-arc basin, is more likely than previous models that suggested deposition in and around seamounts within a major ocean basin.

Middle Triassic radiolarians from cherts/siliceous shales in an extensional basin in the Sukhothai fold belt, Northern Thailand

More than thirty species of radiolarians are described from maroon chert and siliceous shales from the Den Chai and Santisuk sections in the east of the Sukhothai fold belt. The fauna obtained from Den Chai comprises Muelleritortis cochleata cochleata, M. cochleata tumidospina, M. expansa, Triassocampe deweveri, T. coronata, T. scalaris, Annulotriassocampe companilis, A. multisegmantatus, A. sulovensis, Pseudostylosphaera coccostyla coccostyla, P. imperspicua, Canoptum inornatus, C. levis, Corum kraineri, Spongoserrula rarauana, Orbiculiforma karnica and others. The assemblage may be correlated with those reported in the Fang-Chiang Dao and Lumphun areas in the north of Thailand and in the Changning-Menglian belt of western Yunnan, South China and suggests a late Ladinian (Middle Triassic) age. The radiolarian fauna from the Santisuk Section comprises Muelleritortis cochleata cochleata, M. sp., Striatotrissocampe nodosoannulata, Triassocampe. deweveri, T. sp., Pseudogodia? sp., Pseudostylosphaera coccostyla coccostyla, Archaeocenosphera sp., Annulotriassocampe multisegmantis, Pseudostylosphaera sp., and others which indicates a late Ladinian age. Middle Triassic radiolarian chert and siliceous shale from Den Chai and Santisuk are interpreted as having been deposited in an extensional continental margin within the Sukhothai fold belt and not in the Devonian–Permian back-arc basin of the Nan suture. These deep marine sequences were deposited in a subsiding continental margin in the Lampang-Phrae Basin. We consider these sequences to be part of the Hong Hoi Formation (Anisian–Ladinian) of the Lampang Group which, in turn, may be compared to the Choushui Formation and other associated Middle Triassic formations in the Simao Basin of South China.

Early Permian radiolarians from the extension of the Sa Kaeo Suture in Cambodia – tectonic implications

A reconnaissance survey of part of western Cambodia has found quarries in and near the town of Pailin containing chert, basalt, volcaniclastic rocks, gabbro and serpentinite. Abandoned quarries contain chert and basalt clasts in a volcaniclastic matrix and may constitute a melange. A new, recently active, quarry contains these rock units in close and coherent contact but they lack the serpentinitic matrix of the Thung Kabin Melange of eastern Thailand. The rock units are in close contact and may best be described collectively as a dismembered ophiolite. The melange–ophiolite association constitutes a 3 km wide, 20 km long E–W belt separating a northern 200 km2 block of the mainly amphibolitic Pailin Crystalline Complex from a southern area of Triassic submarine fan siliciclastic rocks. The cherts yield the first documented radiolarian fauna from Cambodia and include a moderately well-preserved Asselian–Sakmarian age fauna consisting of Pseudoalbaillella sakmarensis, Pseudoalbaillella scalprata morphotype scalprata, Pseudoalbaillella sp. cf. P. simplex, Pseudoalbaillella u-forma morphotype II, Pseudoalbaillella sp. cf. P. elegans, Pseudoalbaillella sp. cf. P. lomentaria, Albaillella sp., Pseudoalbaillella spp., Trilonche? sp., Latentifistularia gen. et sp. indet. and Entactinaria gen. et sp. indet. The Pailin ophiolitic rocks, melange and volcanic rocks occur within a generally E–W-trending belt, which suggests that the Sa Kaeo Suture does not extend southeastwards paralleling the Thai–Cambodian border, nor extend under the Cardamom Mountains but, rather, extends eastwards into Cambodia and possibly then turns southwards along the strike of the Pursat–Kampot Fold Belt.