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

2025  47  15 geodi e si as Geodi e si as es une e ue en lux con inu publiée pa les Publica ions scien i iques du Muséum, Pa is Geodi e si as is a as ack jou nal published by he Museum Science P ess, Pa is Les Publica ions scien i iques du Muséum publien aussi / The Museum Science P ess also publish: Adansonia, Zoosys ema, An h opozoologica, Eu opean Jou nal o Taxonomy, Na u ae, C yp ogamie sous-sec ions Algologie, B yologie, Mycologie, Comp es Rendus Pale ol Di usion – Publica ions scien i iques Muséum na ional d’His oi e na u elle CP 41 – 57 ue Cu ie F-75231 Pa is cedex 05 (F ance) Tél. : 33 (0)1 40 79 48 05 / Fax : 33 (0)1 40 79 38 40 [email p o ec ed] / h p://sciencep ess.mnhn. © Publica ions scien i iques du Muséum na ional d’His oi e na u elle, Pa is, 2025 ISSN (imp imé / p in ) : 1280-9659/ ISSN (élec onique / elec onic) : 1638-9395 Di ec eu De la publica ion / Publica ion di ec o : Gilles Bloch, P ésiden du Muséum na ional d’His oi e na u elle éDac eu en che / edi o -in-chie : Didie Me le éDac eu associé / associa e edi o : Syl ain Cha bonnie assis an De éDac ion / assis an edi o : Emmanuel Cô ez ([email p o ec ed]) Mise en page / Page layou : Emmanuel Cô ez coMi é scien i ique / scien i ic boa d : Ch is ine A go (Muséum na ional d’His oi e na u elle, Pa is) Bea ix Azanza (Museo Nacional de Ciencias Na u ales, Mad id) Raymond L. Be no (Howa d Uni e si y, Washing on DC) Henning Blom (Uppsala Uni e si y) Gaël Clémen (Muséum na ional d’His oi e na u elle, Pa is) Ted Daeschle (Academy o Na u al Sciences, Philadelphie) Céd ic Del Rio (Muséum na ional d’His oi e na u elle) G ego y D. Edgecombe (The Na u al His o y Museum, Lond es) U sula Göhlich (Na u al His o y Museum Vienna) Jin Meng (Ame ican Museum o Na u al His o y, New Yo k) B igi e Meye -Be haud (CIRAD, Mon pellie ) Zhu Min (Chinese Academy o Sciences, Pékin) Isabelle Rouge (Muséum na ional d’His oi e na u elle, Pa is) Se ke Sen (Muséum na ional d’His oi e na u elle, Pa is, e ai é) S anisla Š ambe g (Museum o Eas e n Bohemia, H adec K álo é) Paul Taylo (The Na u al His o y Museum, Lond es, e ai é) cou e u e / co e : Réalisée à pa i des Figu es de l’a icle/Made om he Figu es o he a icle. Geodi e si as es indexé dans / Geodi e si as is indexed in: – Science Ci a ion Index Expanded (SciSea ch®) – ISI Ale ing Se ices® – Cu en Con en s® / Physical, Chemical, and Ea h Sciences® – Scopus® Geodi e si as es dis ibué en e sion élec onique pa / Geodi e si as is dis ibu ed elec onically by: – BioOne® (h p://www.bioone.o g) Les a icles ainsi que les nou eau és nomencla u ales publiés dans Geodi e si as son é é encés pa / A icles and nomencla u al no el ies published in Geodi e si as a e e e enced by: – ZooBank® (h p://zoobank.o g) 641 GEODIVERSITAS • 2025 • 47 (15) © Publica ions scien i iques du Muséum na ional d’His oi e na u elle, Pa is. www.geodi e si as.com KEY WORDS Thailand, Sao Khua Fo ma ion, palynological assemblage, Valanginian, humid sub opical clima e, Eas e n Te hys P o ince. Yan ZHANG Xiao SHI College o Ea h Sciences, Jilin Uni e si y, Changchun 130061 (China) [email p o ec ed] (co esponding au ho ) Syl ie BOURQUIN Uni . Rennes, CNRS, Géosciences Rennes – UMR CNRS 6118, F-35000, Rennes (F ance) Wenchun GE College o Ea h Sciences, Jilin Uni e si y, Changchun 130061 (China) Chuanbiao WAN Explo a ion and De elopmen Resea ch Ins i u e o Daqing Oil ield Company L d., Daqing 163712 (China) [email p o ec ed] (co esponding au ho ) P adi NULAY O ice o Mine al Resou ces Region 2, Depa men o Mine al Resou ces, Minis y o Na u al Resou ces and En i onmen , Khon Kaen (Thailand) Submi ed on 29 June 2024 | accep ed on 10 No embe 2024 | published on 25 Sep embe 2025 New Ea ly C e aceous palynology o he Sou heas e n Kho a Pla eau, No heas e n Thailand: palaeobo anical, palaeoclima ic, and palynophy ogeog aphical implica ions u n:lsid:zoobank.o g:pub:0AECD667-E640-4D93-AF6A-475951D76EE8 Zhang Y., Shi X., Bou quin S., Ge W., Wan C. & Nulay P. 2025. — New Ea ly C e aceous palynology o he Sou heas e n Kho a Pla eau, No heas e n Thailand: palaeobo anical, palaeoclima ic, and palynophy ogeog aphical implica ions. Geodi e si as 47 (15): 641-657. h ps://doi.o g/10.5252/geodi e si as2025 47a15. h p://geodi e si as.com/47/15 ABSTRACT The Kho a Pla eau, si ua ed in no heas e n Thailand and ex ending pa ially in o Laos and Cambo- dia, was a h i ing ecosys em du ing he Ea ly C e aceous. I ha bou ed a di e se a ay o e eb a e auna, including eshwa e hybodon sha k-like ish, ac inop e ygian ishes, u les, c ocodilians, he opod and sau opod dinosau s, as well as bi al es. Howe e , no many s udies we e ocused on he lo a o his ecosys em. This s udy ocuses on palynological indings om he Sao Khua Fo ma ion in he sou heas e n Kho a Pla eau. A o al o 74 species om 43 gene a we e iden i ied, o ming an assemblage cha ac e ised by Punc a ispo i es-Dichei opollis-Classopollis. Based on ecen adiome ic da ing o de i al zi con g ains, he Sao Khua Fo ma ion is as assigned o an age no younge han he mid o la e Valanginian. As he esul , he key axa ound in his o ma ion ha e been calib a ed and he age o he palynological assemblage is he e o e Valanginian. The assemblage was domina ed by pollen o Chei olepidiaceae oge he wi h di e si y o p e idophy e spo es, sugges ing a humid sub- opical clima e wi h pe iodic a id seasons. Compa a i e analysis wi h o he palynological p o inces places his a ea wi hin he Eas e n Te hys P o ince o he Pan-Te hys Realm. 642 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. e al. INTRODUCTION The Kho a Pla eau is a as pla eau egion si ua ed in no h- eas e n Thailand. Co e ing an app oxima e a ea o 155 000 squa e kilome es, his expanse is dis inguished by i s la and a id e ain. The sauce -shaped pla eau is di ided by he Phu Phan Moun ains in o wo basins: he no he n Sakhon Nakhon Basin and he sou he n Kho a Basin. (Fig. 1). The Kho a Basin, one o he la ges and well-exposed con inen al sedimen a y basins in sou heas e n Asia, spans ac oss eas e n Thailand, wes e n Laos, and no he n Cambodia. The Ea ly C e aceous s a a o he Kho a Basin, collec i ely known as he Kho a G oup, comp ise i e o ma ions (Fig. 1): hePhu K adung Fo ma ion (Fm), Ph a Wihan Fm, Sao Khua Fm, Phu Phan Fm and Khok K ua Fm in ascend- ing o de (Racey& Goodall 2009). The Kho a G oup has yielded a ple ho a o e eb a e ossils, including selachians, ac inop e ygians, sa cop e ygians, emnospondyl amphibians, u les, c ocodyli o mes, p e osau s, non-a ian dinosau s, and bi ds (Mani koon e al. 2022). Among hem, he Sao Khua Fm is amous o i s abundan dinosau ossils. Te anu an non-a ian he opods we e ound in he Sao Khua Fm, including he me iacan hosau Siamo- y annus Bu e au , Su ee ho n& Tong, 1996, spinosau id “Siamosau us” Bu e au & Inga a , 1986, a possible second spinosau id axon “Phu Wiang spinosau id B”, mega ap o an Phuwiang ena o Sama hi, Chan hasi & Sande , 2019, and coelu osau ian Vayu ap o Sama hi, Chan hasi & Sande , 2019, o ni homimid Kinna eemimus Bu e au , Su ee ho n& Tong, 2009, an unde e mined ca cha odon osau id om Phu Wang, and an unde e mined e anu an, and a leas wo sau opods, including he somphospondylan Phuwiangosau us Ma in, Bu e au & Su ee ho n, 1994, and an unde e mined MOTS CLÉS Thaïlande, Fo ma ion Sao Khua, assemblage palynologique, Valanginien, clima sub opical humide, P o ince de l’es de la Té hys. axon (Tucke e al. 2022, and e e ences he ein). The au ho s also da ed he Sao Khua Fm, om de i al zi con g ains, as no younge han middle o la e Valanginian. Mo eo e , palynological ossils ha e been documen ed om he con inen al sedimen s o he Ea ly C e aceous, helping o de e mine he palyno lo a o he Kho a G oup o ma ions (Racey& Goodall 2009). Howe e , only wel e gene a o spo e and pollen ossils we e ound a he Sao Khua Fm (Racey e al. 1996; Racey& Goodall 2009). To add ess his gap, a de ailed palynological s udy was conduc ed on i e samples om he uppe sec ion o he Sao Khua Fm in Nam Yuen ci y, no heas e n Thailand (Fig. 1). The new palynological da a s udied he e p o ide aluable in o ma ion o comple e he egional palynos a ig aphy and acili a e he econs uc- ion o he palaeo ege a ion and palaeoclima e o his a ea. GEOLOGICAL SETTING The Kho a G oup (Fig. 2) ep esen s he la ges ed-bed sequence on he Ko a Pla eau, bu he age o each o ma ion wi hin he g oup emains con o e sial due o he absence o index ossils. The lowe mos Phu K adung Fm may ex end in o he Ju assic Pe iod, whe eas he Ph a Wihan, Sao Khua, Phu Phan, and Khok K ua o ma ions a e da ed as “Ea ly C e aceous” (Racey e al. 1996; Ca e & Moss 1999; Meesook 2000; Ca e & B is ow 2003; Hasegawa e al. 2010). The Sao Khua Fm is p ima ily composed o conglome a ic sands one, sil s one, and clays one, as well as nume ous pal- aeosol laye s (Tucke e al. 2022). Facies analysis and a chi- ec u al s udies e eal ha he sedimen a ion o Sao Khua Fm occu ed wi hin a loodplain se ing ed by la ge meande ing bedload- ich channels (Tucke e al. 2022). Mul iple ypes RÉSUMÉ Nou elles données palynologiques du C é acé in é ieu du sud-es du Pla eau du Kho a , no d-es de la Thaïlande : implica ions paléobo aniques, paléoclima iques e palynophy ogéog aphiques. Le pla eau de Kho a , si ué dans le no d-es de la Thaïlande e s’é endan pa iellemen au Laos e au Cambodge, é ai un écosys ème p ospè e du an le C é acé in é ieu . Il ab i ai une a ié é impo an e d’espèces de e éb és, incluan des poissons d’eau douce essemblan à des equins hybodon es, des poissons ac inop é ygiens, des o ues, des c ocodiliens, des dinosau es hé opodes e sau opodes, e des bi al es. Cependan , peu d’é udes se son concen ées su la lo e de ce écosys ème. Ce e é ude se concen e su les décou e es palynologiques de la Fo ma ion Sao Khua dans le sud-es du Pla eau de Kho a . L’assemblage palynologique, composé de 74 espèces épa ies en 43 gen es, es ca ac é isé pa Punc a ispo i es-Dichei opollis-Classopollis. Su la base d’une da a ion adiomé ique écen e de g ains de zi con dé i iques, la Fo ma ion de Sao Khua n’es pas considé ée comme plus jeune que le Valanginien moyen ou supé ieu . Ainsi, les axons clés ou és dans ce e o ma ion on é é calib és e l’assemblage palynologique es donc d’âge alanginien. Ce assemblage é ai dominé pa des g ains de pollen de Chei olepidiaceae, ainsi que pa une di e si é de spo es de ougè es, impliquan un clima sub opical humide a ec des saisons a ides pé iodiques. L’analyse compa a i e a ec les au es p o inces palynologiques pe me de considé e que ce e égion se si uai dans la P o ince o ien ale de la Té hys, au sein du Domaine pan- é hysien. 643 Ea ly C e aceous Palynology om No heas e n Thailand GEODIVERSITAS • 2025 • 47 (15) LAOS KHORAT PLATEAU Bangkok T a CAMBODIA Sakhon Nakhon Ri e Mekong Maha Sa akham Nakhon Ra chasima Dong ek Nakhon Thai 14° 16° 18°N 104°102°E Khao Ph a Wihan Phu Phan Upli Gul o Thailand Ko Ku Qua e na y Maha Sa akham & Phu Thok Fms Phu Phan & Khok K ua Fms Ph a Wihan & Sao Khua Fms P e-C e aceous 100 km Palynomo ph samples N Phu K adung Range ig. 1. — Syn he ic geological map o eas e n Thailand (a e Meesook 2011). 644 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. e al. o palaeosols we e iden i ied in his o ma ion. Based on he cha ac e is ics and geochemical da a o hese palaeosols, pal- aeoclima e condi ions sugges a p edominan ly s able humid sub opical clima e, wi h a mean annual empe a u e o app oxima ely 17-20°C and a mean annual p ecipi a ion o a ound 1000-1400mm pe yea (Tucke e al. 2022). Based on adiome ic da ing o de i al zi cons ( ia LA-IPC-MS), hese au ho s conside ed ha he middle pa o he Sa Khua Fm was deposi ed no la e han 133.8 ± 1.8 Ma (la e Valangin- ian) and ha he o e lying Phu Phan Fm no la e han 132.4 ± 2.0 Ma (lowe Hau e i ian). Consequen ly, he Sao Khua Fm is conside ed as no la e han mid- o la e Valanginian. The ou c op om which he samples we e collec ed is loca ed 11.8 kilome es om Nam Yuen Ci y, nea he bo - de s o Thailand, Laos, and Cambodia (Fig. 1). In his a ea, only he yellow-g een sil s one a he op o he Sao Khua Fm c ops ou in a small alley nea a emple, which loca ed a 14°21’31”N, 105°12’34”E (Fig. 2). I is o e lain by he eddish-b own calca eous, conglome a ic sands one a ibu ed o he base o he Phu Phan Fm, wi h a con o mable con ac be ween he wo o ma ions (Racey& Goodall 2009; Meesook 2011). Mos o his a ea is a mili a y es ic ed zone because i lies a he junc ion o Thailand, Myanma , and Cambodia. MATERIAL AND METHODS A o al o i e palynological samples we e collec ed om he yellow-g een sil s one and muds one beds o he Sao Khua Fm in Nam Yuen Ci y (Figs. 1, 3A). Each sample was spaced 40cm apa and iden i ied as sk21, sk22, sk23, sk24, and sk25 om bo om o op. Plan mac o- emains (Fig. 3B) can be obse ed wi hin he yellow-g een muds one laye . Each 50g sample was c ushed in o g ains smalle han 0.5cm in diame e and subjec ed o ea men wi h HCl (10%) o 24hou s due o he high calca eous con en , ollowed by HF (36%) o 48hou s, hen ea ed wi h HCl (37.5%) o 24hou s again. To sepa a e he o ganic esidue om mine als and isola e he palynomo phs, a ZnCl-mixed KI hea y liquid wi h a densi y o 2.2g/cm³ along wi h an 8µm sie e we e used. Subsequen ly, he slides con aining he palynomo ph samples we e examined unde a Leica DM4000B mic oscope. Image p ocessing was conduc ed using Co elD aw so wa e. The bo anical a ini ies o spo es and pollen ound in he Sao Khua Fm we e summa ized acco ding o indings epo ed in p e ious s udies and lis ed in Table 1. All samples and slides a e cu en ly housed a he Resea ch Cen e o Paleon ology and S a ig aphy, Jilin Uni e si y, China. Sands one Uncon o mi y In e bedded clays one, sal , gypsum, anhyd i e and po ash. Sands one, medium o coa se; conglome a e, sil s one & clays one, ed-b own. Sands one, conglome a ic sands one and conglome a e, Sands one, conglome a e, sil s one and clays one, ed-b own, silc e es & palaeosols. Sands one, medium-coa se, conglome a e, sil s one and clays one, ed-b own. Sands one, ine-medium g ained, conglome a ic sands one, whi e-g ey, medium-coa se, c oss-bedded. conglome a e, whi e-g ey. ? Te . C e aceous Ju assic ? Phu Thok Fm Maha Sa akham Fm Khok K ua Fm Phu Phan Fm Sao Khua Fm Ph a Wihan Fm Phu K adung Fm 1000 m E apo i es Sands one & conglome a e Sil s one Clays one Palynomo phs Kho a G oup Uppe C e aceous Lowe C e aceous ig. 2. — C e aceous s a ig aphic column in he Kho a Pla eau, NE Thailand (a e Meesook 2011). 645 Ea ly C e aceous Palynology om No heas e n Thailand GEODIVERSITAS • 2025 • 47 (15) able 1 . — Palynomo phs iden i ied in he Sao Khua Fm, wi h hei bo anical a ini ies and clima e signal. Re e ences: 1, Abbink e al. 2004; 2, Al in 1982; 3, A y e al. 2019; 4, Balme 1957; 5, Balme 1995; 6, Boul e & Windle 1993; 7, Coupe 1958; 8, De mann 1963; 9, De mann 1986; 10, De mann e al. 1992; 11, Fila o 1975; 12, F iis e al. 2004; 13, Guigna d e al. 2009; 14, Ha is 1979; 15, Hubba d & Boul e 1997; 16, Ji 1994; 17, Van Konijnenbu g-Van Ci e 1971; 18, Van Konijnenbu g-Van Ci e 1993; 19, K u zsch 1963; 20, Li 1984; 21, Liu e al. 2024; 22, Mande 2011; 23, Rod íguez-Ba ei o e al. 2024; 24, San os e al. 2022; 25, Song e al. 1986; 26, Song e al. 1999; 27, T a e se 2007; 28, T e isan 1971; 29, Volkheime e al. 2009; 30, Wee akoon e al. 2021; 31, Weyland & K iege 1953; 32, Wheele e al. 2022; 33, Yang e al. 2007; 34, Ziaja 2006. Symbol: *, g ains less han 10. Abb e ia ion: G ., G ains. Taxa sk22 sk23 sk24 sk25 Clima e signal Bo anical a ini yG . G . % G . % G . Fe ns spo e – 50 31.06 72 19.89 – – – Fo aminispo is won haggiensis (Cookson & De mann) De mann, 1963 – 1 0.62 – – – Wa m and we Sphagnaceae (8, 19, 33) Fo aminispo is asymme icus (Cookson & De mann) De mann, 1963 – – – 1 0.28 – Wa m and we Sphagnaceae (8, 19, 33) Densoispo i es sp. – – – 1 0.28 – Wa m and we Pleu omeaceae/Selaginellaceae (5, 27, 31) Fo eospo i es sp. – – – 2 0.55 – Wa m and we Selaginellaceae (4, 5) Neo ais ickia sp. – – – 2 0.55 – Wa m and we Lycopodiaceae/Selaginellaceae (8, 10) Ve ucosispo i es g ana um (Bollkh.) Gao & Zhao, 1976 – – – 1 0.28 – Wa m and we Selaginellaceae (27, 33) Ve ucosispo i es obscu ilaesu a us Pocock, 1962 – – – 1 0.28 – Wa m and we Selaginellaceae (27, 33) Ve ucosispo i es sci ulus Yu & Zhang, 1982 – – – 1 0.28 – Wa m and we Selaginellaceae (27, 33) Ve ucosispo i es sp. – 3 1.86 – – – Wa m and we Selaginellaceae (27, 33) Lep olepidi es c . psa osus No is, 1969 – 1 0.62 – – – Wa m and we Lycopodiaceae (6, 11) Lep olepidi es e uca us Coupe , 1953 – – – 1 0.28 – Wa m and we Lycopodiaceae (6, 11) Punc a ispo i es sp. – 19 11.8 12 3.31 – Wa m and we Lepidoca paceae (5) Calamospo a sp. – 1 0.62 – – – Wa m and we Lycopodiaceae, Equise ales (5, 11) Apicula ispo i es sp. – 1 0.62 – – – Ho and we Lycopodiaceae, Selaginellaceae (11) Bacula ispo i es sp. – – – 1 0.28 – Wa m and we P e idophy a, Osmundaceae (11) Osmundacidi es sp. – – – 1 0.28 – Wa m and we Osmundaceae (5, 6, 7, 11) Bi e ispo i es po oniaei Delcou & Sp umon , 1955 – 4 2.48 1 0.28 – Wa m and we Hymenophyllaceae (23) Bi e ispo i es punc a us Wan & Sun, 2014 – – – 1 0.28 – Wa m and we Hymenophyllaceae (23) Bi e ispo i es sp. – 2 1.24 1 0.28 – Wa m and we Hymenophyllaceae (23) Con e ucosispo i es minimus Yu & Miao, 1983 – – – 2 0.55 – Ho and we Dicksoniaceae (5) Cica icosispo i es c . paucis ia us Han, 1983 – – – 1 0.28 – Ho and we Anemiaceae (23) Cica icosispo i es c . po omacensis B enne , 1963 – – – 1 0.28 – Ho and we Anemiaceae (23) Cica icosispo i es c . pseudoau i e (Bolkh.) Li,1959 – – – 2 0.55 – Ho and we Anemiaceae (23) Cica icosispo i es c . sub o undus B enne , 1963 – – – 1 0.28 – Ho and we Anemiaceae (23) Cica icosispo i es cunei o mis Pocock, 1964 – – – 1 0.28 – Ho and we Anemiaceae (23) Cica icosispo i es minu aes ia us (Bolkh.) Pocock, 1964 – 1 0.62 – – – Ho and we Anemiaceae (23) Cica icosispo i es paucis ia us Han, 1983 – 1 0.62 1 0.28 – Ho and we Anemiaceae (23) Cica icosispo i es solidus (Pu & Wu) Jia, 1986 – – – 1 0.28 – Ho and we Anemiaceae (23) Cica icosispo i es sp. – 4 2.48 5 1.38 – Ho and we Anemiaceae (23) Conca issimispo i es ema cidus Yu,1984 – 2 1.24 – – – Ho and we Lygodiaceae (23) Conca issimispo i es punc a us (Delcou & Sp umon ) B enne , 1963 – – – 6 1.66 – Ho and we Lygodiaceae (23) Conca issimispo i es e ucosus Delcou & Sp umon ,1955 – – – 1 0.28 – Ho and we Lygodiaceae (23) Impa decispo a api e uca a (Coupe ) Venka achala, Ka & Raza, 1969 – – – 4 1.1 – Ho and we Cya heaceae (1, 24) Impa decispo a c . b e e (Ma yno a) Yu, 1989 – 1 0.62 2 0.55 – Ho and we Cya heaceae (1, 24) Klukispo i es sp. – 2 1.24 – – – Ho and we Lygodiaceae (23) Ma onispo i es?– – – 1 0.28 – Ho and we Gleicheniaceae (23) Schizaeoispo i es sp. – – – 3 0.83 – Ho and d y Schizaeaceae (25, 26) Todispo i es majo Coupe , 1958 – 1 0.62 – – – Wa m and we Osmundaceae (11, 24) Todispo i es sp. – 1 0.62 – – – Wa m and we Osmundaceae (11, 24) T ilobospo i es sp. – – – 1 0.28 – Ho and we Schizaeaceae (3, 11, 24, 29) P e isispo i es mino Li, 1984 – – – 1 0.28 – Ho and we P e idaceae (20) P e isispo i es undula us Sung & Zheng in Sung & Li, 1976 – – – 3 0.83 – Ho and we P e idaceae (20) Cya hidi es aus alis Coupe ,1953 – 3 1.86 1 0.28 – Ho and we Cya heaceae (23) Cya hidi es mino Coupe , 1953 – 1 0.62 – – – Ho and we Cya heaceae (23) Del oidospo a i egula is (P lug) Sung & Tsao, 1976 – – – 1 0.28 – Ho and we Dip e idaceae, Ma oniaceae (5, 6, 7, 13, 18, 22) Del oidospo a sp. – – – 1 0.28 – Ho and we Dip e idaceae, Ma oniaceae (5, 6, 7, 13, 18, 22) Dic yophyllidi es sp. – – – 2 0.55 – Ho and we Dip e idaceae, Ma oniaceae (6, 7, 11, 13, 18) Undula ispo i es sp. – – – 1 0.28 – Ho and we Ophioglossaceae (25) Lae iga ospo i es g acilis Wilson & Webs e , 1946 – – – 2 0.55 – Wa m and we Ophioglossaceae (25) Tenuicon ac ospo i es c e acius Han, 1983 – 1 0.62 – – – Ho and we Unknown 646 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. e al. RESULTS The palynological eco e y was excellen , ou o he i e samples (sk22, sk23, sk24, sk25) yielded spo es and pol- len g ains. No ably, samples sk23 and sk24 showed di e se palynological ichness, o alling 80 species and 46 gene a (Table 1, Figs. 4-6). The composi ion o bo h sk23 and sk24 showed s iking simila i y, leading o he ecogni ion o he Punc a ispo i es-Dichei opollis-Classopollis assemblage. This assemblage is cha ac e ized by a p edominance o gymno- spe m pollen (68.32-80.11%), a low p esence o p e idophy e spo es (19.89-31.68%), and he absence o angiospe m pol- len. No ewo hy gymnospe m pollen include Dichei opollis T e isan, 1971 (50.31-59.39%), Classopollis P lug, 1953 (9.12-9.32%), as well as common ypes like A auca iaci es Cookson ex Coupe , 1953 (1.38-3.73%), Cycadopi es Wode - house, 1933 (1.86-3.31%), and Taxodiaceaepolleni es K emp ex Po onié, 1958 (0.28-2.48%). Addi ionally, spo adically appea ing ypes include Exesipolleni essp., Jugella allus Yu, 1984, Jugella sp., and Callialaspo i es iloba us (Balme) Sckh De , 1961. Among p e idophy e spo es, Punc a ispo i es Po onié& Gelle ich, 1933 a e he mos abundan (3.31- 11.80%), ollowed by Cica icosispo i es Po onié& Gelle ich, 1933 (3.59-3.73%). O he signi ican ypes p esen in he assemblage encompass T ilobospo i es sp., Impa decispo a c . b e e (Ma yno a) Yu, 1989, Impa decispo a api e uca a (Coupe ) Venka achala, Ka & Raza, 1969, Schizaeoispo- i es sp., Densoispo i es sp., Fo aminispo is won haggiensis (Cookson& De mann) De mann, 1963, Fo aminispo is c . Asymme icus (Cookson& De mann) De mann, 1963, Conca issimispo i es ema cidus Yu, 1984, Conca issimispo i es punc a us (Delcou & Sp umon ) B enne , 1963, Lep ole- pidi es c . psa osus No is, 1969, Lep olepidi es e uca us Coupe , 1953, P e isispo i es mino Li, 1984, P e isispo i es undula us Sung& Zheng in Sung& Li, 1976, Klukispo- i essp., Fo eospo i es sp., among o he s. Taxa sk22 sk23 sk24 sk25 Clima e signal Bo anical a ini yG . G . % G . % G . Gymnospe ms pollen – 111 68.94 290 80.11 – – – A auca iaci es aus alis Cookson, 1947 – 6 3.73 2 0.55 – Wa m, semia id- semihumid A auca iaceae (5, 9, 17) A auca iaci es sp. – – – 3 0.83 – Wa m, semia id- semihumid A auca iaceae (5, 9, 17) Callialaspo i es dampie i (Balme) Sukh De , 1961 – 1 0.62 – – – Wa m, semia id- semihumid A auca iaceae (5, 6, 11, 15, 17) Callialaspo i es iloba us (Balme) Sckh De , 1961 – – – 1 0.28 – Wa m, semia id- semihumid A auca iaceae (5, 6, 11, 15, 17) Psophosphae a g andis Bolkho i ina, 1956 – – – 1 0.28 – Wa m, semia id- semihumid A auca iaceae (16) Psophosphae a unda a (Bolkho i ina) Zhang,1978 – – – 2 0.55 – Wa m, semia id- semihumid A auca iaceae (16) Psophosphae a sp. – – – 1 0.28 – Wa m, semia id- semihumid A auca iaceae (16) Classopollis sp. *15 9.32 33 9.12 *Ho and a id Chei olepidiaceae (7, 14, 34) Dichei opollis e uscus T e isan, 1971 – 81 50.31 215 59.39 *Ho and a id Chei olepidiaceae (28) Concen ispo i es lep os Yu & Zhang, 1982 – – – 2 0.55 – Cool and semihumid Cup essaceae (1, 2, 24) Concen ispo i es opimus Yu & Zhang, 1982 – – – 2 0.55 – Cool and semihumid Cup essaceae (1, 2, 24) Concen ispo i es sp. – – – 3 0.83 – Cool and semihumid Cup essaceae (1, 2, 24) Pe inopolleni es lima us Lu & Wang, 1983 – – – 2 0.55 – Cool and semihumid Cup essaceae (1, 2, 24) Exesipolleni es sp. – – – 1 0.28 – Cool and semihumid Cup essaceae (1, 2, 24) Taxodiaceaepolleni es sp. – 5 3.11 1 0.28 – Cool and semihumid Cup essaceae (1, 2, 24) Pinuspolleni es minu us (Zakl.) Sung & Zheng,1978 – – – 1 0.28 – Cool and semid y Pinaceae (5) Pinuspolleni es sp. – – – 1 0.28 – Cool and semid y Pinaceae (5) Podcca pidi es sp. – – – 1 0.28 – Cool and humid Podoca paceae (25, 30) Cycadopi es elonga us (Balkh.) Zhang, 1978 – – – 1 0.28 – Ho and semia id Cycadales, Benne i ales, Ginkgoales (5, 11) Cycadopi es sp. – 3 1.86 11 3.04 – Ho and semia id Cycadales, Benne i ales, Ginkgoales (5, 11) Eucommiidi es sp. – – – 4 1.1 – Ho and semia id Cycadales, Gne ales (32) Jugella allus Yu, 1984 – – – 1 0.28 – A id Ephed ales, Gne ales (12, 21) Jugella sp. – – – 2 0.55 – A id Ephed ales, Gne ales (12, 21) Cay onipolleni es sp. – – – 1 0.28 – Wa m and we Cay oniaceae (25) To al * 161 – 362 100 * Table 1. — Con inua ion. 647 Ea ly C e aceous Palynology om No heas e n Thailand GEODIVERSITAS • 2025 • 47 (15) DISCUSSION Age o he pAlynoAssemblAge And sAo KhuA m The age o he Sao Khua Fm has been discussed o se e al decades (Tucke e al. 2022, and e e ences he ein). Recen ly, U/Pb da ings on de i al zi cons eco e ed om he middle pa o his o ma ion and he o e lying Phu Phan Fm allowed assigning he Sao Khua Fm o a mid o la e Valanginian age (Tucke e al. 2022). This well-de ined ch onos a ig aphy es ablished wi h adiome ic me hods allows o calib a e he bios a ig aphical anges o some key palynological axa o he Ea ly C e aceous. The Punc a ispo i es-Dichei opollis-Classopollis assemblage con ains a a ie y o axa wi h s a ig aphical signi icance, such as Cica icosispo i es Po onié& Gelle ich, 1933, T ilo- bospo i es Po onié, 1956, Impa decispo a Venka achala, Ka & Raza, 1969, Schizaeoispo i es Po onié ex Delcou & Sp u- mon , 1955, Densoispo i es De mann, 1963, Fo aminispo is K u zsch, 1956, Conca issimispo i es Delcou & Sp umon , 1955, Lep olepidi es Coupe , 1953, P e isispo i es Sun& Zheng, 1976, Klukispo i es Coupe , 1958, Fo eospo i es Balme, 1957, Exesipolleni es Balme, 1957, and Jugella Mchedlish ili& Shakhmundes, 1973. Howe e , many o hem ha e long- anging s a ig aphical occu ences. The main key species o he Punc a ispo i es-Dichei opollis- Classopollis assemblage s udied he e is Dichei opollis e uscus T e isan, 1971. Fi s iden i ied by T e isan (1971) in he Be iasian-Ba emian Biancone Fm in Tuscany, I aly, Dichei- opollis e uscus has been ound in a ious egions ac oss A ica (Libya, Egyp , Mo occo, Senegal, I o y Coas , Gabon, Came oon, Congo, Angola, Sudan, Chad, and Sou h Sudan), Sou h Ame ica (Venezuela, B azil), and Asia (Yemen, Thai- land, Cambodia, and China). I s p edominan p esence in he Be iasian-lowe Ba emian wo ldwide designa es i as a aluable ma ke species o he Be iasian-lowe Ba emian s age in he no he n Gondwana egion (Fig. 7). Ini ially disco e ed in Ba emian deposi s in no he n Mo occo (Hoculi 1981), subsequen indings ha e also e ealed he p es- ence o Dichei opollis e uscus du ing he Be iasian-ea ly Ap ian age in e al, co-occu ing wi h angiospe ms such as Cla a ipol- leni es hughesii, S ella opollis sp., Re imonocolpi es sp., A opollis zona us Doyle, Ja diné& Doe enkamp, 1982, and A opollis ope cula us Doyle, Ja diné& Doe enkamp, 1982, and A opollis ope cula us (Gübeli, 1984). In he lowe pa o he Abu Gab a Fm in he Muglad Basin, Sou h Sudan, Dichei opollis e uscus has been iden i ied wi h angiospe m pollen species like A opol- lis zona us, Re imonocolpi es a iplica us Sch ank& Mahmoud, 1998, and S ella opollis densio na us (Lima) Wa d, 1986. The s udies by Eisawi e al. (2012) and Cole e al. (2017) espec- i ely de e mined he age o his palynological assemblage o be Be iasian-Ba emian and Be iasian-lowe Ba emian. The e olu iona y de elopmen s age o angiospe m pollen in his assemblage aligns closely wi h ha o he angiospe m pollen ound in conjunc ion wi h Dichei opollis e uscus in no he n Mo occo (Gübeli e al. 1984), indica ing ha i s geological age likely ex ends o he lowe Ap ian. No ably, Dichei opollis e uscus has been obse ed oge he wi h dino lagella e cys s in he uppe Hau e i ian-lowe Ba emian ma ine deposi s in Libya and Egyp (Uwins& Ba en 1988; Dea e al. 2016), and in Yemen (Racey& Goodall 2009), i s p esence in ma ine deposi s has been ela ed o a ime ame anging om uppe Valanginian-lowe Ba emian, as de e mined by dino lagella e cys s and ac i a chs. In summa y, while Dichei opollis e uscus may ha e o igina ed as ea ly as he La e Ju assic and con inued o he lowe Ap ian o he Ea ly C e aceous, i s p ima y p e a- lence aligns wi h he Be iasian-lowe Ba emian. AB Phu Phan Fm Phu Phan Fm Sao Khua Fm Sao Khua Fm ig. 3. — A, Ou c op o he upmos o he Sao Khua Fm in Nam Yuen Ci y; B, Cup essinocladus Sewa d, 1919 ( he pen is 15 cm in leng h). Pho os: Xiao Shi. 654 GEODIVERSITAS • 2025 • 47 (15) Zhang Y. e al. cha ac e ized by a no able p esence o Dichei opollis e uscus, alongside a ious species o Classopollis, and ypical pollen axa, such as A auca iaci es, Inape u opolleni es, Ephed ipi es, and Eucommiidi es, among o he s. Bisacca e coni e pollen is a e, wi h a low pe cen age o spo es, which is consis en wi h he ypical lo a o he No he n Gondwana p o ince (o Dichei opollis e uscus/A opollis P o ince). Consequen ly, his assemblage ep esen s a signi ican componen o he lo a wi hin he Pan-Te hys Realm, si ua ed in he sou he nmos pa o he Eas e n Te hys P o ince. Acknowledgemen s We hank P o . Jianguo Li o help ul discussion and cons uc i e sugges ions o he manusc ip . The au ho s hank D . S. Mullin o p oo eading he English con en . 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