New Early Cretaceous palynology of the Southeastern Khorat Plateau, Northeastern Thailand: palaeobotanical, palaeoclimatic, and palynophytogeographical implications

2025  47  15 geodiversitas Geodiversitas est une revue en flux continu publiée par les Publications scientifiques du Muséum, Paris Geodiversitas is a fast track journal published by the Museum Science Press, Paris Les Publications scientifiques du Muséum publient aussi / The Museum Science Press also publish: Adansonia, Zoosystema, Anthropozoologica, European Journal of Taxonomy, Naturae, Cryptogamie sous-sections Algologie, Bryologie, Mycologie, Comptes Rendus Palevol Diffusion – Publications scientifiques Muséum national d’Histoire naturelle CP 41 – 57 rue Cuvier F-75231 Paris cedex 05 (France) Tél. : 33 (0)1 40 79 48 05 / Fax : 33 (0)1 40 79 38 40 [email protected] / http://sciencepress.mnhn.fr © Publications scientifiques du Muséum national d’Histoire naturelle, Paris, 2025 ISSN (imprimé / print) : 1280-9659/ ISSN (électronique / electronic) : 1638-9395 Directeur De la publication / Publication director : Gilles Bloch, Président du Muséum national d’Histoire naturelle réDacteur en chef / editor-in-chief : Didier Merle réDacteur associé / associate editor: Sylvain Charbonnier assistant De réDaction / assistant editor : Emmanuel Côtez ([email protected]) Mise en page / Page layout : Emmanuel Côtez coMité scientifique / scientific board : Christine Argot (Muséum national d’Histoire naturelle, Paris) Beatrix Azanza (Museo Nacional de Ciencias Naturales, Madrid) Raymond L. Bernor (Howard University, Washington DC) Henning Blom (Uppsala University) Gaël Clément (Muséum national d’Histoire naturelle, Paris) Ted Daeschler (Academy of Natural Sciences, Philadelphie) Cédric Del Rio (Muséum national d’Histoire naturelle) Gregory D. Edgecombe (The Natural History Museum, Londres) Ursula Göhlich (Natural History Museum Vienna) Jin Meng (American Museum of Natural History, New York) Brigitte Meyer-Berthaud (CIRAD, Montpellier) Zhu Min (Chinese Academy of Sciences, Pékin) Isabelle Rouget (Muséum national d’Histoire naturelle, Paris) Sevket Sen (Muséum national d’Histoire naturelle, Paris, retraité) Stanislav Štamberg (Museum of Eastern Bohemia, Hradec Králové) Paul Taylor (The Natural History Museum, Londres, retraité) couverture / cover : Réalisée à partir des Figures de l’article/Made from the Figures of the article. Geodiversitas est indexé dans / Geodiversitas is indexed in: – Science Citation Index Expanded (SciSearch®) – ISI Alerting Services® – Current Contents® / Physical, Chemical, and Earth Sciences® – Scopus® Geodiversitas est distribué en version électronique par / Geodiversitas is distributed electronically by: – BioOne® (http://www.bioone.org) Les articles ainsi que les nouveautés nomenclaturales publiés dans Geodiversitas sont référencés par / Articles and nomenclatural novelties published in Geodiversitas are referenced by: – ZooBank® (http://zoobank.org) 641 GEODIVERSITAS • 2025 • 47 (15) © Publications scientifiques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com KEY WORDS Thailand, Sao Khua Formation, palynological assemblage, Valanginian, humid subtropical climate, Eastern Tethys Province. Yan ZHANG Xiao SHI College of Earth Sciences, Jilin University, Changchun 130061 (China) [email protected] (corresponding author) Sylvie BOURQUIN Univ. Rennes, CNRS, Géosciences Rennes – UMR CNRS 6118, F-35000, Rennes (France) Wenchun GE College of Earth Sciences, Jilin University, Changchun 130061 (China) Chuanbiao WAN Exploration and Development Research Institute of Daqing Oilfield Company Ltd., Daqing 163712 (China) [email protected] (corresponding author) Pradit NULAY Office of Mineral Resources Region 2, Department of Mineral Resources, Ministry of Natural Resources and Environment, Khon Kaen (Thailand) Submitted on 29 June 2024 | accepted on 10 November 2024 | published on 25 September 2025 New Early Cretaceous palynology of the Southeastern Khorat Plateau, Northeastern Thailand: palaeobotanical, palaeoclimatic, and palynophytogeographical implications urn:lsid:zoobank.org:pub:0AECD667-E640-4D93-AF6A-475951D76EE8 Zhang Y., Shi X., Bourquin S., Ge W., Wan C. & Nulay P. 2025. — New Early Cretaceous palynology of the Southeastern Khorat Plateau, Northeastern Thailand: palaeobotanical, palaeoclimatic, and palynophytogeographical implications. Geodiversitas 47 (15): 641-657. https://doi.org/10.5252/geodiversitas2025v47a15. http://geodiversitas.com/47/15 ABSTRACT The Khorat Plateau, situated in northeastern Thailand and extending partially into Laos and Cambodia, was a thriving ecosystem during the Early Cretaceous. It harboured a diverse array of vertebrate fauna, including freshwater hybodont shark-like fish, actinopterygian fishes, turtles, crocodilians, theropod and sauropod dinosaurs, as well as bivalves. However, not many studies were focused on the flora of this ecosystem. This study focuses on palynological findings from the Sao Khua Formation in the southeastern Khorat Plateau. A total of 74 species from 43 genera were identified, forming an assemblage characterised by Punctatisporites-Dicheiropollis-Classopollis. Based on recent radiometric dating of detrital zircon grains, the Sao Khua Formation is as assigned to an age no younger than the mid to late Valanginian. As the result, the key taxa found in this formation have been calibrated and the age of the palynological assemblage is therefore Valanginian. The assemblage was dominated by pollen of Cheirolepidiaceae together with diversity of pteridophyte spores, suggesting a humid subtropical climate with periodic arid seasons. Comparative analysis with other palynological provinces places this area within the Eastern Tethys Province of the Pan-Tethys Realm. 642 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. et al. INTRODUCTION The Khorat Plateau is a vast plateau region situated in northeastern Thailand. Covering an approximate area of 155 000 square kilometres, this expanse is distinguished by its flat and arid terrain. The saucer-shaped plateau is divided by the Phu Phan Mountains into two basins: the northern Sakhon Nakhon Basin and the southern Khorat Basin. (Fig. 1). The Khorat Basin, one of the largest and well-exposed continental sedimentary basins in southeastern Asia, spans across eastern Thailand, western Laos, and northern Cambodia. The Early Cretaceous strata of the Khorat Basin, collectively known as the Khorat Group, comprise five formations (Fig. 1): thePhu Kradung Formation (Fm), Phra Wihan Fm, Sao Khua Fm, Phu Phan Fm and Khok Kruat Fm in ascending order (Racey& Goodall 2009). The Khorat Group has yielded a plethora of vertebrate fossils, including selachians, actinopterygians, sarcopterygians, temnospondyl amphibians, turtles, crocodyliformes, pterosaurs, non-avian dinosaurs, and birds (Manitkoon etal. 2022). Among them, the Sao Khua Fm is famous for its abundant dinosaur fossils. Tetanuran non-avian theropods were found in the Sao Khua Fm, including the metriacanthosaur Siamotyrannus Buffetaut, Suteethorn& Tong, 1996, spinosaurid “Siamosaurus” Buffetaut& Ingavat, 1986, a possible second spinosaurid taxon “Phu Wiang spinosaurid B”, megaraptoran Phuwiangvenator Samathi, Chanthasit& Sander, 2019, and coelurosaurian Vayuraptor Samathi, Chanthasit& Sander, 2019, ornithomimid Kinnareemimus Buffetaut, Suteethorn& Tong, 2009, an undetermined carcharodontosaurid from Phu Wang, and an undetermined tetanuran, and at least two sauropods, including the somphospondylan Phuwiangosaurus Martin, Buffetaut& Suteethorn, 1994, and an undetermined MOTS CLÉS Thaïlande, Formation Sao Khua, assemblage palynologique, Valanginien, climat subtropical humide, Province de l’est de la Téthys. taxon (Tucker etal. 2022, and references therein). The authors also dated the Sao Khua Fm, from detrital zircon grains, as no younger than middle to late Valanginian. Moreover, palynological fossils have been documented from the continental sediments of the Early Cretaceous, helping to determine the palynoflora of the Khorat Group formations (Racey& Goodall 2009). However, only twelve genera of spore and pollen fossils were found at the Sao Khua Fm (Racey etal. 1996; Racey& Goodall 2009). To address this gap, a detailed palynological study was conducted on five samples from the upper section of the Sao Khua Fm in Nam Yuen city, northeastern Thailand (Fig. 1). The new palynological data studied here provide valuable information to complete the regional palynostratigraphy and facilitate the reconstruction of the palaeovegetation and palaeoclimate of this area. GEOLOGICAL SETTING The Khorat Group (Fig. 2) represents the largest red-bed sequence on the Korat Plateau, but the age of each formation within the group remains controversial due to the absence of index fossils. The lowermost Phu Kradung Fm may extend into the Jurassic Period, whereas the Phra Wihan, Sao Khua, Phu Phan, and Khok Kruat formations are dated as “Early Cretaceous” (Racey etal. 1996; Carter& Moss 1999; Meesook 2000; Carter& Bristow 2003; Hasegawa etal. 2010). The Sao Khua Fm is primarily composed of conglomeratic sandstone, siltstone, and claystone, as well as numerous palaeosol layers (Tucker etal. 2022). Facies analysis and architectural studies reveal that the sedimentation of Sao Khua Fm occurred within a floodplain setting fed by large meandering bedload-rich channels (Tucker etal. 2022). Multiple types RÉSUMÉ Nouvelles données palynologiques du Crétacé inférieur du sud-est du Plateau du Khorat, nord-est de la Thaïlande : implications paléobotaniques, paléoclimatiques et palynophytogéographiques. Le plateau de Khorat, situé dans le nord-est de la Thaïlande et s’étendant partiellement au Laos et au Cambodge, était un écosystème prospère durant le Crétacé inférieur. Il abritait une variété importante d’espèces de vertébrés, incluant des poissons d’eau douce ressemblant à des requins hybodontes, des poissons actinoptérygiens, des tortues, des crocodiliens, des dinosaures théropodes et sauropodes, et des bivalves. Cependant, peu d’études se sont concentrées sur la flore de cet écosystème. Cette étude se concentre sur les découvertes palynologiques de la Formation Sao Khua dans le sud-est du Plateau de Khorat. L’assemblage palynologique, composé de 74 espèces réparties en 43 genres, est caractérisé par Punctatisporites-Dicheiropollis-Classopollis. Sur la base d’une datation radiométrique récente de grains de zircon détritiques, la Formation de Sao Khua n’est pas considérée comme plus jeune que le Valanginien moyen ou supérieur. Ainsi, les taxons clés trouvés dans cette formation ont été calibrés et l’assemblage palynologique est donc d’âge valanginien. Cet assemblage était dominé par des grains de pollen de Cheirolepidiaceae, ainsi que par une diversité de spores de fougères, impliquant un climat subtropical humide avec des saisons arides périodiques. L’analyse comparative avec les autres provinces palynologiques permet de considérer que cette région se situait dans la Province orientale de la Téthys, au sein du Domaine pan-téthysien. 643 Early Cretaceous Palynology from Northeastern Thailand GEODIVERSITAS • 2025 • 47 (15) LAOS KHORAT PLATEAU Bangkok Trat CAMBODIA Sakhon Nakhon River Mekong Maha Sarakham Nakhon Ratchasima Dongrek Nakhon Thai 14° 16° 18°N 104°102°E Khao Phra Wihan Phu Phan Uplift Gulf of Thailand Ko Kut Quaternary Maha Sarakham & Phu Thok Fms Phu Phan & Khok Kruat Fms Phra Wihan & Sao Khua Fms Pre-Cretaceous 100 km Palynomorph samples N Phu Kradung Range fig. 1. — Synthetic geological map of eastern Thailand (after Meesook 2011). 644 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. et al. of palaeosols were identified in this formation. Based on the characteristics and geochemical data of these palaeosols, palaeoclimate conditions suggest a predominantly stable humid subtropical climate, with a mean annual temperature of approximately 17-20°C and a mean annual precipitation of around 1000-1400mm per year (Tucker etal. 2022). Based on radiometric dating of detrital zircons (via LA-IPC-MS), these authors considered that the middle part of the Sa Khua Fm was deposited no later than 133.8 ± 1.8 Ma (late Valanginian) and that the overlying Phu Phan Fm no later than 132.4 ± 2.0 Ma (lower Hauterivian). Consequently, the Sao Khua Fm is considered as no later than midto late Valanginian. The outcrop from which the samples were collected is located 11.8 kilometres from Nam Yuen City, near the borders of Thailand, Laos, and Cambodia (Fig. 1). In this area, only the yellow-green siltstone at the top of the Sao Khua Fm crops out in a small valley near a temple, which located at 14°21’31”N, 105°12’34”E (Fig. 2). It is overlain by the reddish-brown calcareous, conglomeratic sandstone attributed to the base of the Phu Phan Fm, with a conformable contact between the two formations (Racey& Goodall 2009; Meesook 2011). Most of this area is a military restricted zone because it lies at the junction of Thailand, Myanmar, and Cambodia. MATERIAL AND METHODS A total of five palynological samples were collected from the yellow-green siltstone and mudstone beds of the Sao Khua Fm in Nam Yuen City (Figs. 1, 3A). Each sample was spaced 40cm apart and identified as sk21, sk22, sk23, sk24, and sk25 from bottom to top. Plant macro-remains (Fig. 3B) can be observed within the yellow-green mudstone layer. Each 50g sample was crushed into grains smaller than 0.5cm in diametre and subjected to treatment with HCl (10%) for 24hours due to the high calcareous content, followed by HF (36%) for 48hours, then treated with HCl (37.5%) for 24hours again. To separate the organic residue from minerals and isolate the palynomorphs, a ZnCl-mixed KI heavy liquid with a density of 2.2g/cm³ along with an 8µm sieve were used. Subsequently, the slides containing the palynomorph samples were examined under a Leica DM4000B microscope. Image processing was conducted using CorelDraw software. The botanical affinities of spores and pollen found in the Sao Khua Fm were summarized according to findings reported in previous studies and listed in Table 1. All samples and slides are currently housed at the Research Center of Paleontology and Stratigraphy, Jilin University, China. Sandstone Unconformity Interbedded claystone, salt, gypsum, anhydrite and potash. Sandstone, medium to coarse; conglomerate, siltstone & claystone, red-brown. Sandstone, conglomeratic sandstone and conglomerate, Sandstone, conglomerate, siltstone and claystone, red-brown, silcretes & palaeosols. Sandstone, medium-coarse, conglomerate, siltstone and claystone, red-brown. Sandstone, fine-medium grained, conglomeratic sandstone, white-grey, medium-coarse, cross-bedded. conglomerate, white-grey. ? Tert. Cretaceous Jurassic ? Phu Thok Fm Maha Sarakham Fm Khok Kruat Fm Phu Phan Fm Sao Khua Fm Phra Wihan Fm Phu Kradung Fm 1000 m Evaporites Sandstone & conglomerate Siltstone Claystone Palynomorphs Khorat Group Upper Cretaceous Lower Cretaceous fig. 2. — Cretaceous stratigraphic column in the Khorat Plateau, NE Thailand (after Meesook 2011). 645 Early Cretaceous Palynology from Northeastern Thailand GEODIVERSITAS • 2025 • 47 (15) table 1 . — Palynomorphs identified in the Sao Khua Fm, with their botanical affinities and climate signal. References: 1, Abbink et al. 2004; 2, Alvin 1982; 3, Atfy et al. 2019; 4, Balme 1957; 5, Balme 1995; 6, Boulter & Windle 1993; 7, Couper 1958; 8, Dettmann 1963; 9, Dettmann 1986; 10, Dettmann et al. 1992; 11, Filatoff 1975; 12, Friis et al. 2004; 13, Guignard et al. 2009; 14, Harris 1979; 15, Hubbard & Boulter 1997; 16, Ji 1994; 17, Van Konijnenburg-Van Cittert 1971; 18, Van Konijnenburg-Van Cittert 1993; 19, Krutzsch 1963; 20, Li 1984; 21, Liu et al. 2024; 22, Mander 2011; 23, Rodríguez-Barreiro et al. 2024; 24, Santos et al. 2022; 25, Song et al. 1986; 26, Song et al. 1999; 27, Traverse 2007; 28, Trevisan 1971; 29, Volkheimer et al. 2009; 30, Weerakoon et al. 2021; 31, Weyland & Krieger 1953; 32, Wheeler et al. 2022; 33, Yang et al. 2007; 34, Ziaja 2006. Symbol: *, grains less than 10. Abbreviation: Gr., Grains. Taxa sk22 sk23 sk24 sk25 Climate signal Botanical affinityGr. Gr. % Gr. % Gr. Ferns spore – 50 31.06 72 19.89 – – – Foraminisporis wonthaggiensis (Cookson & Dettmann) Dettmann, 1963 – 1 0.62 – – – Warm and wet Sphagnaceae (8, 19, 33) Foraminisporis asymmetricus (Cookson & Dettmann) Dettmann, 1963 – – – 1 0.28 – Warm and wet Sphagnaceae (8, 19, 33) Densoisporites sp. – – – 1 0.28 – Warm and wet Pleuromeaceae/Selaginellaceae (5, 27, 31) Foveosporites sp. – – – 2 0.55 – Warm and wet Selaginellaceae (4, 5) Neoraistrickia sp. – – – 2 0.55 – Warm and wet Lycopodiaceae/Selaginellaceae (8, 10) Verrucosisporites granatum (Bollkh.) Gao & Zhao, 1976 – – – 1 0.28 – Warm and wet Selaginellaceae (27, 33) Verrucosisporites obscurilaesuratus Pocock, 1962 – – – 1 0.28 – Warm and wet Selaginellaceae (27, 33) Verrucosisporites scitulus Yu & Zhang, 1982 – – – 1 0.28 – Warm and wet Selaginellaceae (27, 33) Verrucosisporites sp. – 3 1.86 – – – Warm and wet Selaginellaceae (27, 33) Leptolepidites cf. psarosus Norris, 1969 – 1 0.62 – – – Warm and wet Lycopodiaceae (6, 11) Leptolepidites verrucatus Couper, 1953 – – – 1 0.28 – Warm and wet Lycopodiaceae (6, 11) Punctatisporites sp. – 19 11.8 12 3.31 – Warm and wet Lepidocarpaceae (5) Calamospora sp. – 1 0.62 – – – Warm and wet Lycopodiaceae, Equisetales (5, 11) Apiculatisporites sp. – 1 0.62 – – – Hot and wet Lycopodiaceae, Selaginellaceae (11) Baculatisporites sp. – – – 1 0.28 – Warm and wet Pteridophyta, Osmundaceae (11) Osmundacidites sp. – – – 1 0.28 – Warm and wet Osmundaceae (5, 6, 7, 11) Biretisporites potoniaei Delcourt & Sprumont, 1955 – 4 2.48 1 0.28 – Warm and wet Hymenophyllaceae (23) Biretisporites punctatus Wan & Sun, 2014 – – – 1 0.28 – Warm and wet Hymenophyllaceae (23) Biretisporites sp. – 2 1.24 1 0.28 – Warm and wet Hymenophyllaceae (23) Converrucosisporites minimus Yu & Miao, 1983 – – – 2 0.55 – Hot and wet Dicksoniaceae (5) Cicatricosisporites cf. paucistriatus Han, 1983 – – – 1 0.28 – Hot and wet Anemiaceae (23) Cicatricosisporites cf. potomacensis Brenner, 1963 – – – 1 0.28 – Hot and wet Anemiaceae (23) Cicatricosisporites cf. pseudoaurifer (Bolkh.) Li,1959 – – – 2 0.55 – Hot and wet Anemiaceae (23) Cicatricosisporites cf. subrotundus Brenner, 1963 – – – 1 0.28 – Hot and wet Anemiaceae (23) Cicatricosisporites cuneiformis Pocock, 1964 – – – 1 0.28 – Hot and wet Anemiaceae (23) Cicatricosisporites minutaestriatus (Bolkh.) Pocock, 1964 – 1 0.62 – – – Hot and wet Anemiaceae (23) Cicatricosisporites paucistriatus Han, 1983 – 1 0.62 1 0.28 – Hot and wet Anemiaceae (23) Cicatricosisporites solidus (Pu & Wu) Jia, 1986 – – – 1 0.28 – Hot and wet Anemiaceae (23) Cicatricosisporites sp. – 4 2.48 5 1.38 – Hot and wet Anemiaceae (23) Concavissimisporites emarcidus Yu,1984 – 2 1.24 – – – Hot and wet Lygodiaceae (23) Concavissimisporites punctatus (Delcourt & Sprumont) Brenner, 1963 – – – 6 1.66 – Hot and wet Lygodiaceae (23) Concavissimisporites verrucosus Delcourt & Sprumont,1955 – – – 1 0.28 – Hot and wet Lygodiaceae (23) Impardecispora apiverrucata (Couper) Venkatachala, Kar & Raza, 1969 – – – 4 1.1 – Hot and wet Cyatheaceae (1, 24) Impardecispora cf. breve (Martynova) Yu, 1989 – 1 0.62 2 0.55 – Hot and wet Cyatheaceae (1, 24) Klukisporites sp. – 2 1.24 – – – Hot and wet Lygodiaceae (23) Matonisporites?– – – 1 0.28 – Hot and wet Gleicheniaceae (23) Schizaeoisporites sp. – – – 3 0.83 – Hot and dry Schizaeaceae (25, 26) Todisporites major Couper, 1958 – 1 0.62 – – – Warm and wet Osmundaceae (11, 24) Todisporites sp. – 1 0.62 – – – Warm and wet Osmundaceae (11, 24) Trilobosporites sp. – – – 1 0.28 – Hot and wet Schizaeaceae (3, 11, 24, 29) Pterisisporites minor Li, 1984 – – – 1 0.28 – Hot and wet Pteridaceae (20) Pterisisporites undulatus Sung & Zheng in Sung & Li, 1976 – – – 3 0.83 – Hot and wet Pteridaceae (20) Cyathidites australis Couper,1953 – 3 1.86 1 0.28 – Hot and wet Cyatheaceae (23) Cyathidites minor Couper, 1953 – 1 0.62 – – – Hot and wet Cyatheaceae (23) Deltoidospora irregularis (Pflug) Sung & Tsao, 1976 – – – 1 0.28 – Hot and wet Dipteridaceae, Matoniaceae (5, 6, 7, 13, 18, 22) Deltoidospora sp. – – – 1 0.28 – Hot and wet Dipteridaceae, Matoniaceae (5, 6, 7, 13, 18, 22) Dictyophyllidites sp. – – – 2 0.55 – Hot and wet Dipteridaceae, Matoniaceae (6, 7, 11, 13, 18) Undulatisporites sp. – – – 1 0.28 – Hot and wet Ophioglossaceae (25) Laevigatosporites gracilis Wilson & Webster, 1946 – – – 2 0.55 – Warm and wet Ophioglossaceae (25) Tenuicontactosporites cretacius Han, 1983 – 1 0.62 – – – Hot and wet Unknown 646 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. et al. RESULTS The palynological recovery was excellent, four of the five samples (sk22, sk23, sk24, sk25) yielded spores and pollen grains. Notably, samples sk23 and sk24 showed diverse palynological richness, totalling 80 species and 46 genera (Table 1, Figs. 4-6). The composition of both sk23 and sk24 showed striking similarity, leading to the recognition of the Punctatisporites-Dicheiropollis-Classopollis assemblage. This assemblage is characterized by a predominance of gymnosperm pollen (68.32-80.11%), a low presence of pteridophyte spores (19.89-31.68%), and the absence of angiosperm pollen. Noteworthy gymnosperm pollen include Dicheiropollis Trevisan, 1971 (50.31-59.39%), Classopollis Pflug, 1953 (9.12-9.32%), as well as common types like Araucariacites Cookson ex Couper, 1953 (1.38-3.73%), Cycadopites Wode - house, 1933 (1.86-3.31%), and Taxodiaceaepollenites Kremp ex Potonié, 1958 (0.28-2.48%). Additionally, sporadically appearing types include Exesipollenitessp., Jugella rallus Yu, 1984, Jugella sp., and Callialasporites trilobatus (Balme) Sckh Dev, 1961. Among pteridophyte spores, Punctatisporites Potonié& Gelletich, 1933 are the most abundant (3.3111.80%), followed by Cicatricosisporites Potonié& Gelletich, 1933 (3.59-3.73%). Other significant types present in the assemblage encompass Trilobosporites sp., Impardecispora cf. breve (Martynova) Yu, 1989, Impardecispora apiverrucata (Couper) Venkatachala, Kar& Raza, 1969, Schizaeoisporites sp., Densoisporites sp., Foraminisporis wonthaggiensis (Cookson& Dettmann) Dettmann, 1963, Foraminisporis cf. Asymmetricus (Cookson& Dettmann) Dettmann, 1963, Concavissimisporites emarcidus Yu, 1984, Concavissimisporites punctatus (Delcourt& Sprumont) Brenner, 1963, Leptolepidites cf. psarosus Norris, 1969, Leptolepidites verrucatus Couper, 1953, Pterisisporites minor Li, 1984, Pterisisporites undulatus Sung& Zheng in Sung& Li, 1976, Klukisporitessp., Foveosporites sp., among others. Taxa sk22 sk23 sk24 sk25 Climate signal Botanical affinityGr. Gr. % Gr. % Gr. Gymnosperms pollen – 111 68.94 290 80.11 – – – Araucariacites australis Cookson, 1947 – 6 3.73 2 0.55 – Warm, semiaridsemihumid Araucariaceae (5, 9, 17) Araucariacites sp. – – – 3 0.83 – Warm, semiaridsemihumid Araucariaceae (5, 9, 17) Callialasporites dampieri (Balme) Sukh Dev, 1961 – 1 0.62 – – – Warm, semiaridsemihumid Araucariaceae (5, 6, 11, 15, 17) Callialasporites trilobatus (Balme) Sckh Dev, 1961 – – – 1 0.28 – Warm, semiaridsemihumid Araucariaceae (5, 6, 11, 15, 17) Psophosphaera grandis Bolkhovitina, 1956 – – – 1 0.28 – Warm, semiaridsemihumid Araucariaceae (16) Psophosphaera undata (Bolkhovitina) Zhang,1978 – – – 2 0.55 – Warm, semiaridsemihumid Araucariaceae (16) Psophosphaera sp. – – – 1 0.28 – Warm, semiaridsemihumid Araucariaceae (16) Classopollis sp. *15 9.32 33 9.12 *Hot and arid Cheirolepidiaceae (7, 14, 34) Dicheiropollis etruscus Trevisan, 1971 – 81 50.31 215 59.39 *Hot and arid Cheirolepidiaceae (28) Concentrisporites leptos Yu & Zhang, 1982 – – – 2 0.55 – Cool and semihumid Cupressaceae (1, 2, 24) Concentrisporites opimus Yu & Zhang, 1982 – – – 2 0.55 – Cool and semihumid Cupressaceae (1, 2, 24) Concentrisporites sp. – – – 3 0.83 – Cool and semihumid Cupressaceae (1, 2, 24) Perinopollenites limatus Lu & Wang, 1983 – – – 2 0.55 – Cool and semihumid Cupressaceae (1, 2, 24) Exesipollenites sp. – – – 1 0.28 – Cool and semihumid Cupressaceae (1, 2, 24) Taxodiaceaepollenites sp. – 5 3.11 1 0.28 – Cool and semihumid Cupressaceae (1, 2, 24) Pinuspollenites minutus (Zakl.) Sung & Zheng,1978 – – – 1 0.28 – Cool and semidry Pinaceae (5) Pinuspollenites sp. – – – 1 0.28 – Cool and semidry Pinaceae (5) Podccarpidites sp. – – – 1 0.28 – Cool and humid Podocarpaceae (25, 30) Cycadopites elongatus (Balkh.) Zhang, 1978 – – – 1 0.28 – Hot and semiarid Cycadales, Bennettitales, Ginkgoales (5, 11) Cycadopites sp. – 3 1.86 11 3.04 – Hot and semiarid Cycadales, Bennettitales, Ginkgoales (5, 11) Eucommiidites sp. – – – 4 1.1 – Hot and semiarid Cycadales, Gnetales (32) Jugella rallus Yu, 1984 – – – 1 0.28 – Arid Ephedrales, Gnetales (12, 21) Jugella sp. – – – 2 0.55 – Arid Ephedrales, Gnetales (12, 21) Caytonipollenites sp. – – – 1 0.28 – Warm and wet Caytoniaceae (25) Total * 161 – 362 100 * Table 1. — Continuation. 647 Early Cretaceous Palynology from Northeastern Thailand GEODIVERSITAS • 2025 • 47 (15) DISCUSSION Age of the pAlynoAssemblAge And sAo KhuA fm The age of the Sao Khua Fm has been discussed for several decades (Tucker etal. 2022, and references therein). Recently, U/Pb datings on detrital zircons recovered from the middle part of this formation and the overlying Phu Phan Fm allowed assigning the Sao Khua Fm to a mid to late Valanginian age (Tucker etal. 2022). This well-defined chronostratigraphy established with radiometric methods allows to calibrate the biostratigraphical ranges of some key palynological taxa of the Early Cretaceous. The Punctatisporites-Dicheiropollis-Classopollis assemblage contains a variety of taxa with stratigraphical significance, such as Cicatricosisporites Potonié& Gelletich, 1933, Trilobosporites Potonié, 1956, Impardecispora Venkatachala, Kar& Raza, 1969, Schizaeoisporites Potonié ex Delcourt& Sprumont, 1955, Densoisporites Dettmann, 1963, Foraminisporis Krutzsch, 1956, Concavissimisporites Delcourt& Sprumont, 1955, Leptolepidites Couper, 1953, Pterisisporites Sun& Zheng, 1976, Klukisporites Couper, 1958, Foveosporites Balme, 1957, Exesipollenites Balme, 1957, and Jugella Mchedlishvili& Shakhmundes, 1973. However, many of them have longranging stratigraphical occurrences. The main key species of the Punctatisporites-DicheiropollisClassopollis assemblage studied here is Dicheiropollis etruscus Trevisan, 1971. First identified by Trevisan (1971) in the Berriasian-Barremian Biancone Fm in Tuscany, Italy, Dicheiropollis etruscus has been found in various regions across Africa (Libya, Egypt, Morocco, Senegal, Ivory Coast, Gabon, Cameroon, Congo, Angola, Sudan, Chad, and South Sudan), South America (Venezuela, Brazil), and Asia (Yemen, Thailand, Cambodia, and China). Its predominant presence in the Berriasian-lower Barremian worldwide designates it as a valuable marker species for the Berriasian-lower Barremian stage in the northern Gondwana region (Fig. 7). Initially discovered in Barremian deposits in northern Morocco (Hoculi 1981), subsequent findings have also revealed the presence of Dicheiropollis etruscus during the Berriasian-early Aptian age interval, co-occurring with angiosperms such as Clavatipollenites hughesii, Stellatopollis sp., Retimonocolpites sp., Afropollis zonatus Doyle, Jardiné& Doerenkamp, 1982, and Afropollis operculatus Doyle, Jardiné& Doerenkamp, 1982, and Afropollis operculatus (Gübeli, 1984). In the lower part of the Abu Gabra Fm in the Muglad Basin, South Sudan, Dicheiropollis etruscus has been identified with angiosperm pollen species like Afropollis zonatus, Retimonocolpites variplicatus Schrank& Mahmoud, 1998, and Stellatopollis densiornatus (Lima) Ward, 1986. The studies by Eisawi etal. (2012) and Cole etal. (2017) respectively determined the age of this palynological assemblage to be Berriasian-Barremian and Berriasian-lower Barremian. The evolutionary development stage of angiosperm pollen in this assemblage aligns closely with that of the angiosperm pollen found in conjunction with Dicheiropollis etruscus in northern Morocco (Gübeli etal. 1984), indicating that its geological age likely extends to the lower Aptian. Notably, Dicheiropollis etruscus has been observed together with dinoflagellate cysts in the upper Hauterivian-lower Barremian marine deposits in Libya and Egypt (Uwins& Batten 1988; Deaf etal. 2016), and in Yemen (Racey& Goodall 2009), its presence in marine deposits has been related to a timeframe ranging from upper Valanginian-lower Barremian, as determined by dinoflagellate cysts and acritarchs. In summary, while Dicheiropollis etruscus may have originated as early as the Late Jurassic and continued to the lower Aptian of the Early Cretaceous, its primary prevalence aligns with the Berriasian-lower Barremian. AB Phu Phan Fm Phu Phan Fm Sao Khua Fm Sao Khua Fm fig. 3. — A, Outcrop of the upmost of the Sao Khua Fm in Nam Yuen City; B, Cupressinocladus Seward, 1919 (the pen is 15 cm in length). Photos: Xiao Shi. 654 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. et al. characterized by a notable presence of Dicheiropollis etruscus, alongside various species of Classopollis, and typical pollen taxa, such as Araucariacites, Inaperturopollenites, Ephedripites, and Eucommiidites, among others. Bisaccate conifer pollen is rare, with a low percentage of spores, which is consistent with the typical flora of the Northern Gondwana province (or Dicheiropollis etruscus/Afropollis Province). Consequently, this assemblage represents a significant component of the flora within the Pan-Tethys Realm, situated in the southernmost part of the Eastern Tethys Province. Acknowledgements We thank Prof. Jianguo Li for helpful discussion and constructive suggestions for the manuscript. The authors thank Dr. S. 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Submitted on 29 June 2024; accepted on 10 November 2024; published on 25 September 2025.