Micro- and megafloral remains of Namurian H-Gl zones from Zhongwei of ,

Wang Yongdong, Shen Guanglong & WUXiuyuan

Wang Yongdong, Shen Guanglong & Wu Xiuyl.lan 1996. Micro- and megafloraI remains of Namurian H-G. zones from Zhongwei of Ningxia, China. Palaeobotanist45 : 224-232.

Abundant micro- and megafloral remains of Namurian H-GI zones have been studied from the Hongtuwa Formation in Zhongwei, Ningxia, China. The former consists of 80 species of 45 genera, which 'can be subdivided into two miospore assemblages, i.e., Lycospora subtriquetra-Gansusi5pora mammilla (SM) Zone and Gardenasporltes pinnatus­ Microreticulatisporites concavus (PC) Zone. They are roughly correlative to the H Zone of Namurian A stage and R-G1 zones of Namurian B-C stages, respectively. The megafloraI remains include 23 species of 18 genera and is known as Mesocalamites cistiformis-Paripterisgiganteaassemblage. It is comparable with the Middle to Late Namurian flora ofthe North Qilian Mountains, China. Both micro- and megaplant fossils indicate that the Middle to Late Namurian flora in Zhongwei is dominated mainly hy Filices and Pteridospermopsida. Lycopsida and Sphenopsida occupy a subdominant position, while Cordaitopsida and Con­ iferopsida are not Significant. The present flora reflects the coastal plain and delta environments as well as a tropical-subtropical warm and humid palaeoclimate.

Key-words--Palynology, Plant megafossil, Namurian, Ningxia (China)

Wang Yongdong & Shen Guanglong, DepaT1ment o/Geology, NOT1hwestUniversity, Xi'an 710069, PR. China. Wu Xiuyuan, Institute o/Geology and Palaeontology, Academia Sinica, Nanjing 210 008, PR. China.

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THE Carboniferous System is widespread in the Huo et al.) 1989; Liu, 1990; Yang et al.) 1983; Yang, Ningxia Hui Autonomous Region, northwestern 1987; Wang et al.) 1992, 1995). However, there are China, which is one of the important coal-bearing few reports on Namurian palynology and strata. In recent years, biostratigraphic research palaeobotany from the same section in Ningxia has progressed greatly in this area (Liu et al.) 1988; region. WANG et al.-MICRO-AND MEGAFLORAL REMAINS OF NAMURIAN H-GI ZONES, CHINA 225

Zhongwei county is located in central Ningxia. 105· The Xiaheyan section is approximately 15 km south- • ° ' , i IYinc~uant-/INNER west of the county, at 105 5 E and 37° 25 N (Text-fig- .~ \ £~ONGOL1A 1). o J 6" ure The section is bounded by and r' Hcngshanbu..... Tengerli Desert in the north and by Mt. Xiangshan in CHINA the south. The Carboniferous strata (Namurian- 38· /1/ Qi~gtongXia0 Wuzhong ...... f38 • <:>, ,I I to Stephanian) in this section are well developed and , , \ ~ ) exposed, yielding abundant animal and plant fossils. _.r-._./ Several species of fossil plants have been recorded ~ • f'2 recently by Li et al. (993). The purpose of present ~_.- ~Ongning paper is to report both micro-and megafloral remains NINGXIA recovered in the lower rart of Upper Carboniferous & MLXiangshan Namurian stage, i.e., the Hongtuwa Formation in ? 2.0 40 6qlcm ~37. Zhongwei, and to discuss the assemblage zones, geological age and the floral characteristics. 105 0 106·

Text-figure I-A sketch map showing the geographical location of the GEOLOGICAL SE1TING AND STRATIGRAPHY Xiaheyan section in Zhongwei of Ningxia.

order with the geological age as Namurian E, Tectonically, Xiaheyan in Zhongwei lies at the Namurian H-Gl, Westphalian and Stephanian, eastern margin of the Caledonian Fold Belt in the North Qilian Moutains. It borders on the North China respectively (Wang et al., 1992). Plate in the east and North Qilian Fold Series in the The Hongtuwa Formation consists mainly of west, and os of the distinctive significance in tectonic greyish black shales with thin-bedded limestones and evolution. lenticules, with a maximum thickness of 170 m, yield­ The Carboniferous strata in Xiaheyan section ing conodonts, goniatites, fusulinids, spores and pol­ consist of clastic rocks with intercalations of lime­ len, as well as plant megafossils (Text-figure 2). stone and thin coal-beds, indicating an alternating Conodonts are : Declinognathodus noduli/erus, marine and non-marine succession. Four lithological Idiognathoides sulcatus, Neognthodus symmetricus, units, namely, the Jingyuan, Hongtuwa, Yanghugou Fusulinids: Eostaffella postmosquensis, Millerella and formations are recognized in ascending marblensis, Schubertella sphaen'ca var. staffelloides,

E I Age Goniatites LL.

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Text-figure 2-Slraligraphic column and vertical range of animal and planl fossils in the Hongruwa Formation, Zhongwei. 226 THE PALAEOBOTANIST

Goniatites: Anthracoceraspaucilobum, A. glabrum, SM Zone PC Zooe

Cancelloceras bisati, Gastrioceras montgomeryense, C1- 6 C1_ 1_ 1 C1- 1- 2 C.-II C:t.-12

Wiedeyocerasxiaheyianense, Physematitesglobosus, LeiOfnltfts Punclal;spon',es Pseudoschartymitesxiaheyianensis, P. ningxiaensis, r alfl",ospora Miospores : Lycospora subtriquetra-Gansusispora Gralll//atispontes Cycfogf"Onlspon'les mammilla (SM) Zone, Gardenasporites pinnatus­ /'t-/,crOrtlkfllall$porit(!S Dictyotrileus Microreticulatisporites concavus (PC) Zone; Triquitnlt'$ Tnpartite! Megaplants : Mesocalamites cistijormis-Paripteris SimozonOlnleres Stellozollotnletes gigantea assemblage. LycO,tpora Del/Josporiles The conodonts in the lower part of the Hongtuwa Cranispora Formation are dominated by the index fossil 1::ndOJporiles (;Oll.fIIJ"tporo Declinognathodus nodulijerus(Ellison et Graves) for .lItrt'mispvnln (,rraln"rodites the Namurian H Zone. Its first appearance in the strata Laevigtll0sponres Columimspontes has been regarded as the basal boundary ofthe Upper C,duporires Carboniferous. The upper part ofthe formation yields FlaM'''itts Vrsicaspora Idiognathoides sulcatus Higgins et Bouckaert and G(ln/t"lfr.fjpo,.,(e~ o~ 10 20 30-/, p,ryoJpor"~J Neognathodus symmetricus (Lane), which are often found in the R-GI zones of Namurian. The fusulinids are characterized by EostaJlelia Text-figure 3--Showing the percenl~gediagram of princip~1miospore genera from the Honb'1uwa Fonnation in Zhongwei. Ningxia SM postmosquensis Kireava, Millerella marblensis Zone: Lycmpora suhtriquetra-Gansusi~poramammilla; PC Zone: Thompson, and Schubertella sphaerica var. stajfel­ Ga rdenaspon·tespinnatu.I-Microreticulatispon'tes concat/us. loides. The first occurrence of M. marblensis in the xiaheyianensis Yang and P ningxiaensis Yang are strata has been taken as an auxiliary fossil indicator found in the upper part of the Hongtuwa Formation. for the recognition of the boundary line between the This part of the formation corresponds to the horizon Lower and Upper Carboniferous, while the other two of the conodonts Idiognathoides sulcastus and Neog­ species are also the common elements of Namurian. nathodussymmetricus, indicating Late Namurian (R­ About 8 species of fossil goniatite are identified G} Zones) age. in the Hongtuwa Formation in Xiaheyan (Yang et al., 1983; Yang, 1987). Amongst them, Anthracoceras paucilobum (Phillips) and A. globum Bisat occur in MICROFLORA both lower and upper parts of the formation. Others, such as Cancelloceras bisati Ruzhencev et Bogos­ Abundant fossil spores and pollen grains have lovskaya, Gastrioceras montgomeryense (Miller et been studied from the Hongtuwa Formation, which Gurley), Wiedeyoceras xiaheyianense Yang, comprise 80 miospore speCies belonging to 45 Physematites globosus Yang, Pseudoschartymites genera. According to the quantitative analysis CText-

PLATE 1 Figures in Plate 1 are X 600. indicated.

1. GranulalfSporitespirojonnfS Loose Cx-8-2-(6). II. Demospon'tessphaeroln'angularis Kosanke Cx-8-2(S).

2. Mlcroreliculaltsporiles concallUS Bunerworth et Williams Cx-ll­ 12-13. .li~poramammilla Gao Cx-23-1(4). (1). 14. Cirratriradites satumii (Ibrahim) Schopf, Wilson et Bentall Cx­ 3. Acanlholrileles echlnatus (Knox) Potonie et Kremp Cx-4- (3). 11-(8). 4. Lophotrileles microsaetosus(Loose) Poton;e et Kremp Cx-6-(4). 15-16. Tripartites In'linguiS (Horsl) Smith et Butterworth 15.Cx-8-2-(6l 5 Dlcl)X)lrileles birellculatus (Ibrahim) Smith et Butterworth Cx-S­ 16. Cx-6-(3). 2-(3), 17. Tripartites vetustu.>·Schemel Cx-6-(2). 6. Calamospora microrugosa (Ibrahim) Schopf, Wilson et Bentall IS. Laevigatospontes mediu.>·Kosanke Cx-8-2-(5l. Cx-8-2-(l0). 7-8. Lycospora sublriquetra (Luber) Potonie et Kremp Cx-8-2- (4). 19. CrassL\pora kosankei(Potonie et Kremp) flh~radw~jCx-3- (9). 9. SlenozonOlriletes triangulus Neves Cx-ll-(6). 20. Florinitessp. Cx-ll-(8). .10. Slmozonotril&lessinensfS Zhu Cx-3-(4). 21. Gartienaspon·tespinnatusKrusina Cx-11-(4). WANG et al.-MICRO_AND MEGAFLORAL REMAlNS OF NAMURIAN H-Gl ZONES, CHINA 227

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PLATE 1 228 THE PAIAEOBOTANIST figure 3), two assemblage zones have been estab­ (Clayton et al., 1977). Other species, such as Den­ lished as follows: sosporites sphaerotriangularis, Crassispora kosankei and Savitrisporites nux are also common in the 1. Lycospora subtriquetra-Gansusispora Namurian H Zone. Tripartites trilinguis and T. venus­ (SM) mammiUa Zone tus, which are the marker species for the Namurian E This assemblage zone occurs in the lower part of Zone in Western Europe, are also distributed in the the Hongtuwa Formation. It is marked by the Namurian H Zone in China (Gao, 1987). dominance of pteridophytic spores (97.7-100%), Simozonotriletes sinensis and Stenozonotriletes among which the most common species of azonolete rotundus are often found in greater number in the spores (53.8-55.9%) are. Leiotriletes spp., Namurian E Zone of Jingyuan, Gansu (Zhu, 1989, Granulatisporitesgranulatus Ibrahim, G. pirojormis 1993). However, their percentages are distinctly Loose, Cyclogranisporites pressoides Potonie et lower in the present SM Zone. Gansusisporites mam­ Kremp, Microreticulatisporites punctatus Knox, milla was first discovered in the Namurian H Zone of Acanthotriletes echinatus (Knox) Potonie et Kremp, Jingyuan, Gansu together with the acritarch Dictyotriletes bireticulatus(Ibrahim) Smith et Butter­ Tetraporina(Gao, 1987). worth and Punctatisporites aeran'us Butterworth et In general, the SM Zone of Xiaheyan, Zhongwei Williams. correlates with not only the SO Zone of Western The zonolete spores (38.5-43.3%) include Europe, but also with the SB Zone (Densosporites Lycospora subtriquetra (Luber) Potonie et Kremp, sphaerotriangularis-Dictyotriletes bireticulatus) in Gansusispora mammilla Gao, Simozonotriletes the Hongtuwa Formation of Jingyuan, Gansu as sinensis Zhu, S. labellatus Wang, Densosporites proposed by Zhu 0989, 1993). Therefore, the SM sphaerotriangularis Kosanke, Triquitrites spp. and Zone belongs to the Namurian A (goniatite H zone) occasional Stenozonotriletes rotundus (Wang) Zhu, age. This conclusion is in agreement with the age of Tripartites trilinguis (Horst) Smith et Butterworth, T. the conodont Declinognathodus noduliferus. vetustusSchemel and Crassispora kosankei (Poronie et Kremp) Bharadwaj. Cirratriradites saturni 2. Gardenasporites pinnatus­ (Ibrahim) Schopf, Wilson et Bentall and Microreticulatisporites concavus (PC) Zone Savitrisporites nux(Butterworth et Williams) Smith et Butterworth make their first appearance in this for­ The PC Zone stratigraphically is equivalent to the mation. The frequency ofoccurrence of other genera, upper part of the Hongtuwa Formation. It is also such as Endosporites, Radizonates, Rotaspora and characterized by the dominance of pteridophytic Reinschospora is less than 1 per cent. spores (77.8-84.4%), and by the gradual increase of Monolete spores 0.7-4.9%) and monosaccate gymnospermous pollen grains 05.6-22.2%). pollen grains (0-1.8%) are represented by The most common azonolete spores include Laevigatosporites and Florinites. In addition, some Microreticulatisporites concavus Butterworth et Wil­ acritarchs assigned to Tetrapon'na have been dis­ liams, Dictyotriletes bireticulatus (Ibrahim) Smith et covered in the SM assemblage. The dominant species Butterworth, Cyclogranisporites aureus Potonie et of SM Zone, Lycospora subtriquetra, is an index Kremp, Granulatisporites pirojormis Loose, G. miospore for the Namurian H Zone in Western granulatus Ibrahim, Punctatisporites minutus Europe (Clayton et al., 1977; Owens et al., 1977). Its Kosanke, and Leiotriletes sp. Calamospora sp., Con­ miospore assemblage belongs to the SO Zone uolutispora sp. and Gulisporites cochlearius Imgrund (Lycospora subtriquetra-Krauselisporites ornatus) make their first appearance.

PLATE 2 Figures are in natural size unless otherwise mentioned. 1,2. Reticalethopterisyuanii(Sze) ti, Shen et Wu. 2,)(3. 5 Panpteris otozamioides (Sze et Lee) Gathan 3. Linopteris maxima Shen, Gou el Liu. 6,7, 7a. Linopterisgermanii Giebel 7a, X5. 4,4a. Potoniea adiantiformis Zeiller 4a, X5. WANG et al.-MICRO-AND MEGAFLORAL REMAINS OF NAMURIAN H-Gj ZONES, CHINA 229

2

PlATE 2 230 THE PALAEOBOTANIST

The zonolete spores begin decreasing in the PC MEGAFLORAL REMAINS Zone (11.1-17.8%). The important taxa are Lycospora, Triquitrites, Densosporites, Crassispora kosankei, The megaplant fossils in the Hongtuwa Forma­ Simozonotn'letes lahellatus Wang, Ahrensisporites tion comprise 23 species belonging to 17 genera and guerickei (Horst) Potonie et Kremp, Cirratriradites, named it as Mesocalamites cistijormis-Paripteris Stenozonotriletesand Reinschospora Several species gigantea assemblage. The most common species in­ clude Lepidodendron tripunctatum Stockman et such as Tripartites trilinguis, T. vetustus, Mathieu, Lepidostrohophyllum sp., Stigmaria Simozonotriletes sinensis and Gansusispora mam­ rugulosa Gothan of Lycopsida; Sphenophyllum milla become rarer in this zone and some of them tenerrimum En., Mesocalamites cistijormis Stur, disappear at the top of the formation. Asterophyllites longijolius (Sternb.) Brongniart, Monolete spores begin increasing slightly (9.8­ Asterophyllites sp., and Calamostachys sp. of 13.3%) and are marked by Laevigatosporites and Sphenopsida; Eusphenopteris scrihanii Ammerom, Columnisporites. Another characteristic of the PC Rhodeopteridium sp., Pecopteris plumosa (Artis) Zone is the increase of disaccate pollen grains as­ Brongniart, Neuropterissp., Linopteris maxima Shen, signed to Gardenasporites pinnatus Krusina. It is Gou et Liu, 1. germarii Giebel, Paripteris gigantea more than 8 per cent in most slides. Some other (Sternb.) Gothan, P. kaipingiana (Sze), P. pollen, such as Florinites spp., Vesicaspora spp. and otozamioides (Sze et Lee) Gothan, Potoniea adian­ Pityosporites spp. also occur in this zone. tijormis Zeiller, Reticalethopteris yuanii (Sze) Li, The PC Zone is comparable to zones KV (Cras­ Shen et Wu and Trigonocarpus sp. of Filices or sispora kosankei- Grumosisporites varioreticulatus) Pteridospermopsida as well as Cordaites principalis and FR (Raistn'ckia julva-Reticulatisporites (Germar) Geinitz of Cordaitopsida. reticulatus) of Western Europe (Clayton et al., 1977) Most of these fossil plants are the important ele­ based on the following common species: ments of Namurian in Western Europe. Sphenophyl­ Microreticulatispon'tes concavus, Crassispora lum tenerrimum mainly occurs in Visean to Namuian kosankei, Ahrensisporites guerickei, Cirratn'radites A, and even reaches to Namuian C. It is also dis­ saturniand Lycosporaspp. The disaccate pollen Gar­ covered in]ingyuan and]ingtai areas of Gansu, China denasporites pinnatus is also a common species of (Li, Wu et al., 1993). However, other index fossil zones KM (Crassispora kosankei-Rugaspora minuta) plants of Namurian A, e.g., Eleutherophyllum wal­ and BP (Triquitrites hransonii-Lycospora pellucida) denhurgense (Stur) and E. drepanophycijormae in the Hongtuwa Formation in]ingyuan, Gansu (Zhu, Remy et Remy do not appear in Xiaheyan, Zhongwei. Mesocalamites cistijormis, which occurs mainly in 1993). Other comparable species in both PC Zone the middle-Late Namurian (H Zone) both in China and KM, BP zones include Crassispora kosankei, and other countries, has been regarded as an impor­ Punctatisporites mrmmus, Cyclogranisporites tant indicator for testing the boundary line between aureus, Ahrensisporites guerickei, Dictyotriletes Lower and Upper Carboniferous. Eusphenopterisdid hireticulatus, Lycospora spp. and Triquitrites spp. as not begin its development until the Namurian. well as the increase of Laevigatosporitesspp. and the Rhodeopteridium is also a common genus of decrease of Tnpartites spp, Simozonotn'letes and Namurian in Western Europe. Pecopteris plumosa Stenozonotriletes spp. Therefore, the geological age was reported in the lower part of the Oulong Bruke of the present PC Zone should be regarded as equal Group in Qinghai and the Hongtuwa Formation in to the R-Gl zones of Namurian B-C. Furthermore, the Gansu. The extremely rich Paripterisgigantea in this conodonts-Jdiognathoides sulcatus, Neognathodus assemblage is a frequent element of the Westphalian symmetricus, and the goniatites Cancelloceras his-ati, in the Euramerican Province, its lowest horizon so far Gasterioceras montgomeryense, Wiedeyoceras known outside China being the middle Namurian xiaheyianense, Physematitesglohosus, Pseudoschar­ Reticulcceras (R) Zone in France. In the present as­ tymites ningxiaensisand P. xiaheyianensis, also sup­ semblage, the neuropterid plants are dominated by port the palynological dating. the Parispermae. In addition to Paripteris, its sister WANG el ai-MICRa-AND MEGAFLORAL REMAINS OF NAMUR[AN H-GI ZONES, CHINA 231 genera Linopteris, Neuropteris and the fossil male DISCUSSION reproductive organ Potoniea are also discovered alongwith the seed fossil ihgonocarpus. It has been Among the microflora in Xiaheyan, most spores established that the first appeared horizon of belong to the Filices and pteridosperms, such as parispermous plants is lower in China than that in Leiotriletes, Cyclogranisporites, GranulatispOrites, Euramerican Province. They are mostly distributed in Microreticulatisporites, Triquitrites, Tripartites and the Namurian, some even in middle-Late Visean in Dictyotriletes, etc. They represent the highest per­ China. Therefore, Li Xingxue et al. (992) proposed centage (56%) in the assemblage. Lycopsid spores that the parispermous plants first appeared in China, including Lycospora, Crassispora, Densosporites and and then migrated and spread towards the Cirratriradites occupy the subdominant position. Euramerican Province. Furthermore, Linopteris with Spores of sphenopsids are represented by reticulate veins is quite abundant in Namurian E Zone Calamosporaand Laevigatosporites(part), while Cor­ in Jingyuan, Gansu, and greatly decreases in the daitopsids and coniferopsids are mainly represented Namurian H Zone. In Xiaheyan of Zhongwei, only by Florinites and Gardenasporites. As it is shown by two species, L. maxima and L. germarii have been both micro- and megaplant fossils, the present flora collected in the Hongtuwa Formation On the mher in Xiaheyan is mostly dominated by Filices and hand, specimens of Paripteris are dominant in this Pteridospermopsida; Lycopsida and Sphenopsida oc­ cupy the subdominant position, while gymnosperms formation, including P. gigantea, P. kaipingianaand (Cordaitopsida and Coniferopsida) are not very com­ P. otozamioides. This is identical with that of the mon. Hongtuwa floral assemblage in Jingyuan, Gansu (Li, Wu et al., 1993). According to the analysis of both marine and Moreover, the endemic element represented by non-marine fossils and lithological characteristics, the middle to Late Namurian palaeoecology in Zhongwei Reticalethopteris yuanii (Sze) Li, Shen et Wu is dis­ may be coastal plain or delta environments (Tong et covered in Xiaheyan, Zhongwei. This type of plant aI., 1994). The swamp vegetation represented by has long been regarded as Palaeoweichselia, a arborescent lycopsids, sphenopsids and herbaceous Westphalian C-D element. According to a recent pteridophytes was distributed in the coast swamp study by Li, Shen et al. (1993), the specimens assigned area. The pteridosperms possibly grew at the lower to Palaeoweichselia in China are, in fact, different hydro- and wet land of the swamp. Only a few from :hat of Europe. Therefore, a new genus, gymnosperms (cordaitopsids and coniferopsids) Reticalethopteris was proposed for the Chinese lived on the onshore plain or lower upland. The material. The geological duration of Reticalethopten's present flora indicates a tropical-subtropical warm yuanii known so far is restricted to middle-Late and humid palaeoclimate, which is favourable forthe Namurian in China. This conclusion is also supported formation of coal resources. The palaeomagnetic by Luo's recent report from Tianzhu, Gansu (Luo, data (Wu et aI., 1993) also support the palaeoclimatic 1993). conclusion. It is clear that the megaplant fossils in Xiaheyan, although not abundant, still represent middle-Late ACKNO~DGEMENTS Namurian (H-G1 zones) age. It is comparable with the floras of Jingyuan and Jingtai, Gansu of the same The authors are grateful to ProfessorJiang Dexin, geological age (Li, Wu et aI., 1993) based on the Professor Yang HUiqiu, Mrs DuJinerand Lei Changyu following species, Sphenophyllum tenemmum, of Institute of Geology, Academia Sinica and Paripterisgigantea, P. kaipingiana, P. otozamioides, to Professor Ouyang Shu of Nanjing Institute of Geol­ Linopteris maxima, Neuropteris sp., Mesocalamites ogy and Palaeontology, Academia Sinica for their cistijormis, Eusphenopteris scribanii, Rhodeop­ valuable advise and technical assistance. Special teridium sp., Pecopteris plumosa, Potoniea adian­ thanks are expressed to Associate Professor Li Keding tijormis, Reticalethopterisyuanii, Trigonocarpus sp., of Lanzhou University, Professor Wang Zhihao of Stigmaria rugo!usa and Cordaites principalis. Nanjing Institute of Geology and Palaeontology, 232 THE PAlAEOBOTANIST

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