Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Late Cretaceous stratigraphy, Songliao Basin, NE : SK1 cores

Xiaoqiao Wan a,⁎, Jing Zhao a, Robert W. Scott b, Pujun Wang c, Zihui Feng d, Qinghua Huang d, Dangpeng Xi a a State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Xueyuan Lu 29, Beijing 100083, China b Department of Geosciences, University of Tulsa, Tulsa, OK 74104, USA c College of Earth Sciences, Jilin University, Changchun 130061, China d Exploration and Development Research Institute of Oil Field Corporation Ltd., Daqing, 163712, China article info abstract

Article history: The Songliao Basin is the largest Cretaceous oil and gas-producing lacustrine basin in China, with its greatest ae- Received 24 December 2011 rial extent in the middle Cretaceous. A coring program (SK1) has to date yielded 2485.89 m of continuous core Received in revised form 24 July 2012 (96.46% recovery) and provides significant material for Cretaceous research. The sequence of the core consists Accepted 22 October 2012 mainly of lacustrine sandstone, dark grey mudstone, shale and oil-shale. The Upper Cretaceous stratigraphic sec- Available online 1 November 2012 tion has been subdivided into the Quantou, Qingshankou, Yaojia, Nenjiang, Sifangtai and Mingshui formations in ascending order. Late Cretaceous microfossils are diverse and abundant. A detailed biostratigraphic study has Keywords: Late Cretaceous subdivided the sequence into high precision biozones: 21 ostracode assemblages, 10 phytoplankton assem- Biostratigraphy blages, 7 palynological zones and 4 charophyta assemblages, respectively. In addition, marine foraminifera Chronostratigraphy were first discovered from the basin. Three 206Pb/238Uagesandone40Ar/39Ar age were analysed. Ten local Songliao Basin magnetozones have been recognised in the SK1 (North), and two magnetozones have been indicated in the SK1 (South). Based on biostratigraphy, high-resolution magnetostratigraphy and SIMS U–Pb zircon analyses, the SK1 stratigraphy is correlated with Upper Cretaceous stages in the International Geologic Time Scale. The upper part of the Quantou Formation is the lower Turonian; the Qingshankou Formation is the upper Turonian–lower Coniacian; the Yaojia Formation is from the upper Coniacian to middle Santonian; the Nenjiang Formation is the upper Santonian to middle Campanian; the Sifangtai Formation is limited to the upper Campa- nian; and the Mingshui Formation is the uppermost Campanian to Maastrichtian. It is likely that the upper part of the Mingshui Formation belongs to the Paleocene, and the K/Pg boundary is within the Member 2 of the Mingshui Formation around the depth of 328 m by new micropalaeontologic and magnetostratigraphic data. © 2012 Elsevier B.V. All rights reserved.

1. Introduction stratigraphic section with samples appropriate for stratigraphical studies. In recent years, Chinese scientists have focused on the Creta- The Cretaceous non-marine deposits are extremely widespread in ceous events and achieved advantages over international communi- China and have been comprehensively studied (Gu, 1962; Huang, ties through studies of the Songliao Basin. To acquire a complete 1988, 1998; Ye and Zhong, 1990; Gao et al., 1994, 1999; Ye et al., 2002; Cretaceous stratigraphic record, a continuously cored hole has been Sha, 2007; Wan et al., 2007; Wu et al., 2007). The Songliao Basin is the drilled at Daqing Oilfield as an operator to various Cretaceous inves- largest Cretaceous oil–gas producing lacustrine basin in China, with the tigations. This coring project is a breakthrough in this research. The giant Daqing Oilfield situated in the central part of the basin. The basin deep core of 2485.89 m with a 96.46% recovery has been obtained is 700 km long from north to south, and 370 km wide from east to from two wells, respectively named the Songke Core-1 (North) west, covering an area roughly 260,000 km2 in Heilongjiang, Jilin and (SK1 (N)) and Songke Core-1 (South) (SK1 (S)) (Fig. 1). The north- Liaoning provinces in Northeast China. The lowermost sediments in the ern core reveals the upper part of the Upper Cretaceous sequence basin are the Upper Jurassic. The main sediment fill are Cretaceous sedi- and the southern core the lower interval. The former covers the in- mentary rocks overlain directly by Paleogene/Neogene or Quaternary terval from the uppermost Cretaceous to Member 2 of the Nenjiang deposits. The lake was at its greatest extent in the Late Cretaceous with Formation, and the latter from the Member 2 of the Nenjiang Formation continuous sediment deposition and witnessed the notable evolution to Member 2 of the Quantou Formation. The two cores are correlated by of terrestrial biotas. a key oil-shale marker bed, and together present a continuous Upper Extensive previous investigations of the Songliao Basin demonstrate Cretaceous lacustrine sequence that provides unique material for Creta- that no single existing corehole recovered the complete Cretaceous ceous research. The cored succession consists mainly of lacustrine sand- stone, dark grey mudstone, shale and oil-shale. It has been subdivided ⁎ Corresponding author. Tel.: +86 10 82321040. into the Quantou, Qingshankou, Yaojia, Nenjiang, Sifangtai, and Mingshui E-mail address: [email protected] (X. Wan). formations in ascending order.

0031-0182/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2012.10.024 32 X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43

215 70 216 30 216 90 correlation was based on the magnetochronology and SIMS zircon U–Pb chronology. Magnetostratigraphic samples spanned an inter- val of 26 cm in the north core and 21 cm in the south core. For SIMS U–Pb zircon analyses, three bentonite samples were collected China asin B from the south core and one tuffaceous siltstone layer from the north core (Deng et al., 2013–this issue). A feldspar 40Ar/39Ar age of 90 90 88.3 Ma was measured from a mugearite interbed in the corresponding 51 51 Songliao layer of Well Jin-6 which is close to the SK1 (South) by Wang et al. 0 100km (2009c). This age offers a reference to the SK1 chronostratigraphy.

Ne Daqing Sag 3. Lithostratigraphy of SK1 north and south cores

n jia n

30 30 The lacustrine Upper Cretaceous strata are well developed in the g Anda 51 SK1 (North) 51 Songliao Basin and provide complete lithostratigraphic sequence (Ye R et al., 2002; Wan et al., 2007). The China National Commission on ive Stratigraphy (2002) referred the lithostratigraphic sequence of Songliao r Basin as the Cretaceous nonmarine reference succession of China. The SK1 cores (N&S) penetrate a nearly complete Upper Cretaceous section, and have been described in centimetre scale (Cheng et al., 2009; Gao Well-SK1 Gulong 70 70 et al., 2009; Wang et al., 2009a,b). The present study subdivided the 50 50 cores according to the lithostratigraphic units that are widely used in the basin at both coreholes and outcrops. The formations are described City SK1 (South) from top to bottom as follows.

0 20 40km 3.1. SK1 (North) r 10 Songhua Rive 10 50 50 3.1.1. Upper Cretaceous to Paleocene 215 70 216 30 216 90

Fig. 1. Sketch map showing the localities of the SK1 (North and South). 3.1.1.1. The Mingshui Formation. This formation was named in the Mingshui County of Heilongjiang Province. The type section was based on the Ku3 core (E124°8′30″, N46°51′). These deposits contain diverse and abundant continental faunas and Member 2 of the Mingshui Formation — 420.17 m thick The member is floras (i.e., dinoflagellates, charophyta, ostracodes, conchostracans, bi- mainly composed of greenish grey, purple-red and greyish valves, gastropods, insects, fish and dinosaurs), as well as important black mudstone, greyish green gravel-bearing mudstone, coal and oil resources. The radiation and evolution of terrestrial biota greyish green muddy siltstone and greyish green sandstone will thus provide scientific evidence not only for stratigraphic correlation, with conglomerate intercalations. The top of the core is grey, but for palaeoclimate changes. This paper will focus on the dominant mi- purple and greyish green mudstones with a layer of grey silt- crofossil assemblages, magneto- and chronostratigraphic sequences in stone. order to provide a stratigraphical framework of East Asia. Member 1 of the Mingshui Formation — 152.7 m thick The member in- cludes interbedded purple-red with greyish green and grey mudstone; purple-red, black to grey sandy mudstone and 2. Material and methods greenish grey, dark grey muddy siltstone; and greyish green argillaceous siltstone of different thicknesses. For biostratigraphy, major lacustrine microfossil groups like ostra- code, charophyta, phytoplankton, spore and pollen have been studied. 3.1.1.2. The Sifangtai Formation — 237.4 m thick. The name of this for- Samples for ostracode and charophyta extraction were taken at 1 m in- mation is from the Sifangtai town of City, Heilongjiang Prov- tervals on average throughout the whole cores, with the exception for ince. The type section was based on the Ku3 core (E124°28′30″, sandstones in the Member 3 of the Quantou Formation. A total of 1000 N46°51′). samples were collected. Samples of 100 g dry weight were dispersed in It consists mostly of purple-red, greyish green, black to grey mud- deionised water for several weeks prior to sieving through a 100 μm stone and sandy mudstone; grey, greenish grey argillaceous siltstone; sieve. Ostracodes and charophytes were picked from the samples under and fine-medium grained sandstone and interbeds of grey sandstone a low-power binocular microscope. Many foraminiferal tests were picked and conglomerate. up from the samples in the lower Nenjiang Formation. This is the first dis- covery of marine fossils in the Songliao Basin. Microfossil studies were 3.1.1.3. The Nenjiang Formation. This formation was named in the carried out in the micropalaeontological laboratory of the China Universi- Nenjiang County of Heilongjiang Province. The type section was ty of Geosciences (Beijing). based on the DFT25 core (E125°15′, N45°42′). Samples collected for palynological study spanned an interval of Member 5 of Nenjiang Formation — 248.0 m thick Dark grey and 15–25 m in mudstones and siltstones and about 5–10 m in the coloured purple-red mudstone and silty mudstone; grey, greenish shaly segments. A total of 154 samples were processed for palynological grey and light purple argillaceous siltstone; and greenish analyses, 87 from the north core and 67 the south one. They were grey siltstone with gravel and sandy conglomerate. subjected to standard hydrochloric and hydrofluoric acid digestion in Member 4 of Nenjiang Formation — 204.6 m thick Black and greenish the laboratory. Palynomorph identification and counting were conducted grey mudstone and silty mudstone are dominant; others at the Nanjing Institute of Geology and Palaeontology. are dark grey muddy siltstone and grey siltstone interca- Lacustrine ostracodes, charophytes and palynomorphs are common lated with fine-medium grained sandstone. in the Songliao Basin; however, they are not directly integrated with ma- Member 3 of Nenjiang Formation — 106.5 m thick Black mudstone; rine biota that defines the Cretaceous stages. The chronostratigraphic greyish black sandy mudstone; and grey siltstone with X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43 33

interbeds of fine-grained sandstone and medium-gained of greenish grey, purple-red mudstone; greenish grey oily sandstone. silty mudstone; brownish grey oil-disseminated siltstone; Member 2 of Nenjiang Formation — 200.5 m thick The upper part is and brownish black oil-disseminated siltstone. composed of interbedded siltstone and mudstone of dif- Member 3 of the Quantou Formation — 43.67 m thick (not at base) It ferent thicknesses; dominated by greyish black mudstone, consists mostly of purple-red, greenish grey mudstone and silty mudstone and muddy siltstone interbeds; brownish silty mudstone intercalated with siltstone and argillaceous grey oil-stained siltstones in the middle; and greyish siltstone. black and black mudstones in the lower part. At the base is a black to brown oil-shale bed that is consistently dis- 4. Biostratigraphy of SK1 cores tributed in the Songliao Basin and is the key marker bed to correlate between the SK1 (N) and SK1 (S) cores. The SK1 cores yield abundant microfossils that enable us to make a complete biostratigraphic succession. Here we present biostrati- 3.2. SK-1 (South) graphic divisions based on ostracodes, charophytes, phytoplanktons, palynology, and foraminifera that have been studied in detail. 3.2.1. Upper Cretaceous 4.1. The assemblages of ostracodes 3.2.1.1. The Nenjiang Formation. Member 2 of the Nenjiang Formation — 56.96 m thick (not at top) Yellowish brown grey oil-bearing siltstones The previous studies of ostracodes in the Songliao Basin have de- overlying dark grey, brownish black mud- veloped a general biostratigraphic framework based on different stone and grey silty mudstone. The black coreholes (Gao et al., 1994; Hou et al., 2002; Ye et al., 2002). This re- to brown oil shale on the bottom is the search on the continuous SK1 (N&S) cores has discovered more than key bed to link the SK1 (N) core. 87 species and 25 genera of Ostracoda (Li et al., 2011). The taxonomy — Member 1 of the Nenjiang Formation 103.04 m thick Dark grey, and systematics of these fresh-water Ostracoda are based on previous greenish grey, black mudstone intercalated studies. Their evolutionary stages in the vertical stratigraphic profile with greyish black mudstone and yellowish define 21 fossil ostracode assemblages (Figs. 2, 3, and 4). grey marl. 1) Mongolocypris longicaudata assemblage is mainly present at a spe- 3.2.1.2. The Yaojia Formation. It was named near the Yaojia railway sta- cific horizon in the upper part of Member 4 of the Quantou Forma- tion of Dehui County, Heilongjiang Province. The type sections are lo- tion. Fossils are rare except for M. longicaudata, and a small number cated 2 km north to the station and the DSJ12 core (E125°14′, of Mongolocypris sp. and Cypridea sp. This assemblage is dominated N45°10′20″). by the Mongolocypris. Members 2 and 3 of the Yaojia Formation — 119.51 m thick Dark 2) Triangulicypris torsuosus–Triangulicypris torsuosus nota assem- grey, purple-red, greenish grey mudstone and sandy blage is present in the Member 1 of the Qingshankou Formation. mudstone; purple-red silty mudstone intercalated with It is dominated by two species: T. torsuosus with smooth shell or- light grey thin-bedded marl; purple-grey muddy sand- namentation and T. torsuosus nota with knobby shell ornamenta- stone; and greenish grey oily silty mudstone and brown- tion. Samples characteristically have low numbers of genera and ish grey siltstone with oil dissemination. species, and are also low in numbers of specimens. Member 1 of the Yaojia Formation — 50.95 m thick Dark grey, green- 3) Cypridea dekhoinensis–Cypridea gibbosa assemblage is located in ish grey mudstones in the upper part; below is mostly the lower part of Member 2 of the Qingshankou Formation. It is greenish grey silty mudstone; grey, greenish grey, oily dominated by eight Ostracoda species: Cypridea dekhoinensis, silty mudstone; and greyish yellowish brown, oily pelitic C. gibbosa, C. bistyloformis, C. tuberculata, C. unicostata, Triangulicypris siltstone with oil dissemination and interbedded with torsuosus, T. torsuosus nota,andT. fertilis with knobby and/or thorny yellowish brown siltstone rich in oil. shell ornamentation. The samples characteristically have moderate to high diversity and relative abundance. 3.2.1.3. The Qingshankou Formation. The name of this formation is 4) Cypridea nota–Sunliavia tumida assemblage is located in the from the Qingshankou Village of Nongan County, Jilin Province. The middle-upper part of Member 2 of the Qingshankou Forma- type sections are based on the outcrop NE of Qingshankou and the tion. The main Ostracoda species in this assemblage are: DWP4 core (E124°9′, N45°35′10″). Cypridea fuyuensis, C. nota, C. edentula, C. vicina, S. tumida, Members 2 and 3 of the Qingshankou Formation — 395.27 m Triangulicypris symmetrica, Kaitunia andaensis, Ziziphocypris thick The uppermost bed is composed of greenish grey mudstone rugosa,andLycopterocypris grandis mainly with smooth, or re- with purple-red silty mudstone. The upper interval is composed ticular shell ornamentation. High numbers of species and spec- of greenish grey, dark greyish green mudstone and light grey imens were found in the samples. muddy limestone. The composed of lower part is dark grey mud- 5) Cypridea edentula–Lycopterocypris grandis assemblage is mainly lo- stone and sandy mudstone with intercalations of yellowish grey cated in the upper part of Member 2 of the Qingshankou Forma- marl. tion. It is dominated by four species: Cypridea nota, C. fuyuensis, Member 1 of the Qingshankou Formation — 93.38 m thick Dark grey C. edentula,andL. grandis, mainly with smooth or reticular and black mudstone; greyish black silty mudstone, yellowish shell ornamentation. Samples characteristically have moderate grey marl and brownish black oil shale. numbers of species and specimens. 6) Cypridea fuyuensis–Triangulicypris symmetrica assemblage is mainly 3.2.1.4. The Quantou Formation. It was named near the Quantou rail- located in the lower part of Member 3 of the Qingshankou Forma- way station of Changtu County, Liaoning Province. The type section tion. It is dominated by two species: C. fuyuensis,andT. symmetrica, is located 3 km northeast to the station. mainly with smooth shell ornamentation. This assemblage has low Member 4 of the Quantou Formation — 84.05 m thick Dark grey number of species and specimens. mudstone and silty mudstone at the top; the upper part 7) Triangulicypris vestilus–Triangulicypris fusiformis–Triangulicypris is dominated by grey muddy siltstone, greyish yellowish pumilis assemblage is mainly located in the middle part of Member brown oily argillaceous siltstone; the lower part consists 3 of the Qingshankou Formation. Significant ostracode species in 34 X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43

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this assemblage are: Triangulicypris vestilus, T. fusiformis, T. pumilis, Formation. It is dominated by three species: Cypridea panda, Mongolocypris tera,andM. obscura. This assemblage is domi- Mongolocypris obscura,andM. tera, and it is characterised by nated by Triangulicypris,butmoreandmoreMongolocypris mixed shell size, smooth ornamentation, and a low species di- characterised by mixed shell size; smooth ornamentation is versity, but moderate to high number of total specimens. present in stratigraphically higher samples in this interval. This as- 9) Cypridea exornata–Cypridea dongfangensis assemblage is mainly semblage has moderate numbers of species and specimens. distributed in the Member 1 of the Yaojia Formation. It is dominat- 8) Cypridea panda–Mongolocypris obscura assemblage is mainly ed by four ostracode species: Cypridea exornata, C. dongfangensis, present in the upper part of Member 3 of the Qingshankou Mongolocypris infidelis and M. tera. Generally the specimens have X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43 35

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Fig. 4. Distribution of selected ostracodes in the SK1 (North).

preservation is similar to that in assemblage 9, but many speci- It contains a large variety of ostracode species, such as: Cypridea mens are red having been coated by iron from surrounding rock. anonyma, C. oblonga, C. maculata, Candona fabiforma, Ca. ovta, 11) Cypridea formosa–Cypridea sunghuajiangensis assemblage is locat- Advenocypris mundulaformis,andMongolocypris porrecta. Cypridea ed in the Member 3 of the Yaojia Formation. It is dominated by anonyma is dominant in the lower part of the assemblage with five species: Cypridea formosa, C. sunghuajiangensis, M. tabulata, large valves, but in the upper part, Candona with smaller valves be- Lycopterocypris retractilis,andZ. rugosa. Fossil preservation is simi- comes the main species. Samples characteristically have high num- lar to that in assemblages 8 and 9. bers of species and specimens. 12) Cypridea anonyma–Candona fabiforma assemblage is mainly 13) Cypridea gracila–Cypridea gunsulinensis assemblage mainly oc- found in the lower part of Member 1 of the Nenjiang Formation. curs in the upper part of Member 1 of the Nenjiang Formation. X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43 37

It is dominated by four species of Cypridea: C. gracila, C. gunsulinensis, Other species are Cypridea tuberculorostrata, Cypridea minuta, C. acclinia,andC. ardua, characterised by smooth ornamentation, Mongolocypris apiculata, Cypridea cavernosa, Timiriasevia ovata, swelled ventral valves and low numbers of species and specimens. Timiriasevia amoena, Renicypris bullata, Candoniella exial, Timiriasevia 14) Mongolocypris magna–Mongolocypris heiluntszianensis assemblage qingyuanangensis, Paracandona qiananensis, Mongolocypris is mainly found in black shale near the base of the Member 2 of kaitunensis and Mongolocypris subaequata. The fossils are well the Nenjiang Formation. It contains three species: Mongolocypris preserved, and the diversity and abundance are generally high. magna, M. heiluntszianensis,andCypridea spongvosa. Mongolocypris is characterised by large valves, up to 4 mm in the length. 4.2. Phytoplankton assemblages 15) Cypridea liaukhenensis–Cypridea bella assemblage is mainly found in the lower part of Member 2 of the Nenjiang Formation above the Previous works were concerned about the dinoflagellates from black shale with oil shale intercalations. Main fossils are: Cypridea different coreholes and made general reference to this study (Gao, liaukhenensis, C. stellata, Harbinia hapla, Ilyocyprimorpha sp., et al., 1992; Mao, et al., 1999; Li, et al., 2000). Based on the continuous Mongolocypris magna and M. heiluntszianensis.TheC. liaukhenensis records, ten Upper Cretaceous phytoplankton assemblages are domi- with thorny ornamentation is the dominant species. The number nated by dinoflagellates and are described in ascending order of specimens in this zone is low, but it contains a large number of according to the materials found in the SK1 (S&N): endemic species. 16) Periacanthella portentosa–Limnocypridea subscalariformis as- 1) The Granodiscus assemblage is distributed in Members 3 and 4 of semblage is in the upper part of Member 2 of the Nenjiang the Quantou Formation. The species Granodiscus granulatus was Formation in the SK1 (North) core. Its base is marked by the noted in some samples. first appearance of Periacanthella sp. at 1734 m in the SK1 2) The Dinogymniopsis–Granodiscus–Filisphaeridium assemblage (North) core. The dominant elements are P. portentosa, Strumosia occurs in the Member 1 of the Qingshankou Formation. The fos- sungarinensis, C. stellata, L. subscalariformis,andBicorniella sils Ilisphaeridium sp., Ranodiscus granulatus, Inogymniopsis bicornigera.OthersareC. spongvosa, Limnocypridea sunliaonensis, granulata and Dinogymniopsis tuberculata are characteristic of M. magna,andLimnocypridea dongbeiensis. The species in this as- this assemblage. semblage are characterised by ornamented carapaces with clavae, 3) The Kiokansium–Dinogymniopsis–Botryococcus assemblage occurs tuberclae and foveola. The diversity and abundance are relatively in Members 2 and 3 of the Qingshankou Formation. Dinoflagellate high. diversity is relatively high including Kiokansium declinatum, 17) Limnocypridea dilinensis–Limnocypridea nova assemblage occurs Kiokansium regulatum, Inogymniopsis spinulosa, Dinogymniopsis in the lower part of Member 3 of the Nenjiang Formation. The granulata and Dinogymniopsis tuberculata.Otherssuchas base is marked by the Last appearance of Periacanthella sp. at Sentusidinium bifidum, Sentusidinium minor, Atiacasphaera 1607 m. Dominant species are Limnocypridea dilinensis, L. nova, oligacantha, Ranodiscus granulatus and Errucosphaera sp. L. dongbeiensis and C. spongvosa. The fossil preservation is moder- Botryococcus braunii aremoreabundantinsomelayers. ate. Cypridea spongvosa and L. dilinensis are abundant and ac- 4) The Schizosporis–Campenia assemblage occurs in the Member 1 count for 80% of the total number of species. of the Yaojia Formation. Campenia sp. is abundant in this assem- 18) Strumosia inandita–Cypridea spongvosa assemblage occurs in the blage. The green algae Schizosporis reticulatus and Pediastrum interval from the upper part of Member 3 to the base of Member boryanum are also present. 4 of the Nenjiang Formation. Its base is indicated by the first ap- 5) The Pediastrum–Botryococcus assemblage occurs in Members 2 pearance of S. inandita at 1512 m, and the top by the last appear- and 3 of the Yaojia Formation. It is rich in Pediastrum boryanum ance of S. inandita. Dominant fossils are C. spongvosa, S. inandita, but Botryococcus braunii is rare. L. dilinensis, Limnocypridea harbinensis, M. heiluntszianensis, and 6) The Dinogymniopsis minor–Balmula assemblage occurs in Members Strumosia salebrosa. The most abundant species are S. inandita 1 and 2 of the Nenjiang Formation. Dinoflagellates are diverse and and M. heiluntszianensis. Cypridea spongvosa and L. dilinensis are the assemblage is characterised by abundant Dinogymniopsis minor also rich in certain layers. and Balmula spinosa. Other species are Batiacasphaera dictyophora, 19) The ostracodes are poorly preserved in the interval from Member Batiacasphaera henanensis, Dinogymniopsis tuberculata, Apteodinium 3 to the top of the Nenjiang Formation. Only poorly preserved granulatum, Sentusidinium bifidum, Eiosphaera hyaline and Campenia fossils like Cypridea spongvosa, C. liaukhenensis, Mongolocypris sp. magna, and M. heiluntszianensis have been found from the 7) The Dinogymniopsis–Chlamydophrella–Vesperopsis bifurcata as- lower part of this interval. Ostracodes are absent in the Members semblage occurs in Members 3 and 4 of the Nenjiang Formation. 4–5 of the Nenjiang Formation. Dinogymniopsis granulata. Dinogymniopsis tuberculata and 20) Talicypridea amoena–Eucypris cuneata assemblage occurs in the Dinogymniopsis torosa are relatively abundant. Horologinella lower part of the Sifangtai Formation. Its base is indicated by the sp., V. bifurcata and Chlamydophrella discreta are distinctive. appearance of Mongolocypris apiculata at 1010 m. Above the inde- Other members of this assemblage are Sentusidinium bifidum, terminate interval, the assemblage is totally composed of newly Sentusidinium minor, Filisphaeridium sp., Leiosphaera hyaline, appearing species. It is characterised by abundant Talicypridea Batiacasphaera oligacantha, Batiacasphaera dictyophora,and amoena. Other dominant species are Cypridea tuberculorostrata, Pediastrum boryanum. Cypridea triangula, Candonilla minuta, Mongolocypris apiculata, 8) The Pediastrum assemblage occurs in the Member 5 of the Nenjiang Cypridea cavernosa, Candona disjuncta, Altanicypris bianzhaoensis, Formation and is characterised by diverse Pediastrum,suchas Altanicypris obesa, Candona exilla, Mongolianella subaequata, Pediastrum boryanum, Pediastrum simplex and Pediastrum duplex. Metacypris kaitunensis,andEucypris cuneata. However, other algae are absent. 21) Talicypridea qingyuanangensis–Ziziphocypris simakovi assemblage 9) The Botryococcus–Pediastrum assemblage occurs in the Sifangtai is located in the interval from the upper part of the Sifangtai Formation and is characterised by low abundance and diversity, Formation to the middle part of Member 2 of the Mingshui Forma- and mostly including Botryococcus braunii, Pediastrum boryanum tion. Its base is marked by the appearance of T. qingyuanangensis and a small amount of Pediastrum simplex. at 838 m. More new elements appeared, such as Candona 10) The Tetranguladinium–Subtilisphaera–Botryococcus assemblage oc- glaber, T. qingyuanangensis,andCyclocypris calculaformis.Among curs in the Mingshui Formation and is dominated by Botryococcus them, Mongolocypris gigantea and Candona glaber are abundant. braunii. Among the dinoflagellates, Tetranguladinium cruciformis 38 X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43

and Subtilisphaera cf. circularis are the typical elements, while rare Although the diversity is lower, angiosperm pollen grains are relatively Pediastrum boryanum and Scenedesmus bifidus represent green abundant and include Alnipollenites, Juglanspollenites, Quercoidites and algae. Tricolpites.ThespeciesofCedripites and Piceapollis recorded from this zone are known only from Cenozoic deposits. 4.3. Palynological zonation 4.4. The assemblages of charophytes More research on Songliao palynology has provided large amount of data (Gao, 1982; Yu, et al., 1983; Gao, et al., 1999; Wan, 1999). Before the study on SK1, Wang, et al. (1985) studied charophytes From SK1, seven palynological biozones are defined based on the and offered a good reference to the present work. This study of first or last occurrences of the index taxa (Li et al., 2010). charophytes has been completed on samples from the SK1 (North), Zone 1 spans the interval from the Upper Quantou Formation to and the work on samples from the SK1 (South) is in progress. Four as- the lowermost Member 2 of the Qingshankou Formation in the SK1 semblages including 51 species of 27 genera have been recognised (South). It is defined on the basis of the occurrence of Quantonenpollenites, and described in ascending order as follows (Fig. 5). with secondary genera Cranwellia and Lythraites likely to occur in associ- – ation; their absence below 1783.7 m in the southern core may be due to 1) Atopochara ulanensis assemblage (1023.22 m 798.44 m) occurs in the poor productivity of the samples concerned. This zone spans all of the the Sifangtai Formation. Twenty-two species of 14 genera have Quantou Formation encountered in the borehole and the basal part of the been recognised. Among them, A. ulanensis, Euaclistochara mundula Qingshankou Formation. elliptica, Obtusochara altanulaensis and Hornichara anguanensis are Zone 2 includes the interval from Member 2 of the Qingshankou dominant elements. – Formation to the lowermost part of Member 2 of the Nenjiang Forma- 2) Raskyaechara gobica assemblage (798.44 m 629.15 m) is present tion in the SK1 (South). It is marked by several pollen taxa of biostrat- in the Member 1 of the Mingshui Formation. Fossil abundance is igraphic importance that first appear at its base at 1661.6 m in the relatively low. There are 19 species of 12 genera and it is dominat- southern core, which is within the lower part of the Qingshankou For- ed by R. gobica, Mesochara biacuta, Gobichara deserta and Sinochara mation. Associated species include Arecipites, Pterisisporites and praecursoria. – Sabalpollenites, but the most important is Borealipollis. Its typical, 3) Hornichara prolixa assemblage (328.77 m 299.74 m) is rich in elongate colpus-like exogerminals and multiple-layered exine with fossil charophytes and is in the Member 2 of the Mingshui Forma- a striate surface (Batten and Christopher, 1981) make it probably tion. There are 38 species of 21 genera in this assemblage. Among the best indicator of this palynological zone. them, Raskyaechara gobica, Gobichara deserta, Hornichara prolixa, Zone 3 encompasses the greater part of the Nenjiang Formation and Hornichara anguangensis mecilenta, and Turbochara specialis are the lowermost Sifangtai Formation. It is defined by the inception of dominant elements. – – triprojectate pollen referable to Aquilapollenites. Some 150 m higher 4) Grovesichara changzhouensis Neochara sinulata assemblage (328.77 m up the succession another representative of this group appears, namely 210.57 m) has relatively abundant charophyte fossils. It mainly occurs Translucentipollis. The triporate Momipites and Myricipites first appear in the upper part of the Mingshui Formation, and contains 30 species towards the middle of this zone. This zone encompasses the greater of 22 genera. Certain species are evolved from species in the lower stra- part of the Nenjiang Formation and the lowermost Sifangtai Formation. ta, and more Cretaceous species disappear from this assemblage. Some fi Zone 4 ranges from the lower Sifangtai Formation to the lower elements appear for the rst time in the assemblage that marks a new Member 1 of the Mingshui Formation and is characterised by the oc- phase of the biotic evolution. The new elements are Pechichara currence of Ulmipollenites and Ulmoideipites, and the absence of sp., Grovesichara changzhouensis, Neochara sinulata, Raskyella peckii, Lythraites. Above the abrupt decline in numbers at the top of Zone Stephanochara sp., and Restusochara sp. Among them, dominant spe- 3, Cyathidites remains scarce throughout the zone. A more significant cies are Neochara sinulata, Grovesichara changzhouensis, Restusochara change in composition is the greater abundance of angiosperm pol- daanensis, Gobichara deserta,andHornichara prolixa.Thesespecies len; they commonly comprise more than 15% of the palynomorph as- are 47% by numbers of specimens of the total assemblage. The semblage. The range of this zone coincides with all but the basal part appearance of some new genera like Neochara has stratigraphic of the Sifangtai Formation and also encompasses the lowermost implications to the K/Pg boundary (Wang et al., 1982; Huang, Mingshui Formation. 1988), which is characterised by its larger size, curved ornamenta- Zone 5 occurs in the upper part of Member 1 of the Mingshui For- tion on cellular spirals and apical rosette, and indicates a Paleocene mation and can be recognised by the first appearance of several gen- age. era in the northern core, including Integricorpus sp. and Kurtzipites trispissatus. Although the inception of Betpakdalina was recorded a lit- 4.5. Foraminiferal occurrence tle higher, the appearance of the first two and the association of all three genera is the basis upon which Zone 5 is recognised. This zone Many foraminiferal tests have been recovered from SK1 samples (Xi encompasses only some 90 m of the lower part of the Mingshui et al., 2011). In the present work, 9 species in eight foraminifer genera Formation. were found dominantly from Members 1 and 2 of the Nenjiang Forma- Zone 6 occurs in the lower part of Member 2 of the Mingshui For- tion in the SK1. Benthic foraminifera are Gavlinella sp., Anomalinoides mation and is marked by the initiation of Wodehouseia spinata. Some sp., Haplophragmoides sp., Pullenia sp., Karrorulina hokkaidoana and elements of the Normapolles group continue to occur sporadically, but Clavulinoides sp.; planktonic species are Archaeoglobigerina blowi not Complexiopollis. Other components of the assemblages of Zone 5 (Coniacian–Maastrichtian), Archaeoglobigerina cretacea (Coniacian– continue into this zone. The diversity of spore and pollen declines Maastrichtian), and Hedbergella flandrini (Upper Turonian–Santonian). above 360.6 m in the northern core, and most of the components of The main characteristics of the foraminifera are: (1) Foraminiferal test the assemblages in Zone 6 are no longer recorded above this depth. size ranges from 0.2 mm–0.5 mm, and a few agglutinated tests are up Zone 7 is located in the upper part of Member 2 of the Mingshui For- to 1 mm. Most of the foraminifera are calcareous including many mation. At the base most palynomorphs disappear and fossils are gener- planktonic specimens, and only a small number of agglutinated tests. ally rare, only Impardecispora, Momipites, Myricipites, Ulmipollenites and (2) Most of the foraminiferal tests are well preserved, and few are Ulmoideipites continue up to the top of the Mingshui Formation. pressed flat. In addition agglutinated tests and a few calcareous The diversity of the palynofloras is low, with gymnospermous tests have a brownish colour. (3) The abundance of foraminifera is Abietineaepollenites and Pinuspollenites being relatively common. relatively high, with more than 100 tests/100 g in several samples. X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43 39

sp.

.

sp.

sp.

sp

sp.

Age Strata

Depth

Hornichara anguangensismacilenta Hornichara

Euaclistochara mundula elliptica mundula Euaclistochara

Hornichara prolixa Hornichara Maedlerisphaeranana Aclistochara bransoni Mesocharasubtilis

Peckichara Peckichara peckii Raskyella

Hengyangochara jiaoshanpingensis Hengyangochara

Nemegtichara prima Nemegtichara

Latochara guangdongensis Latochara

Mesocharabiacuta Restusochara Croftiellahumilis Sinochara praecursoria Sinochara Restusocharadaanensis

Charitescretacea Maedlerisphaera

Aclistochara jilinensis Aclistochara

Gobichara rubra Gobichara jacobii Sphaerochara

Gobicharadeserta Aclistochara bransoniminor Aclistochara

Neochara sinulata Neochara

Mesochara qiananensis Mesochara

Sphaerochara parvula Sphaerochara Hornichara anguangensis Hornichara Nemegtichara actocara Nemegtichara Stephanochara

Latochara dongbeiensis

Turbochara specialis Turbochara

Mesochara fuyuensis Mesochara Grovesichara changzhouensis Songliaocharaheilongjiangensis

Mesochara shuangliaoensis Mesochara Grambastichara communis Grambastichara

Collichara taizhouensis Collichara

Grambastichara yuntaishanensis Grambastichara Grambastichara impolita Grambastichara Obtusocharaaltanulaensis 300 Obtusochara

350 Paleocene

400

Obtusochara lanpingensis Obtusochara

Raskyaecharagobica

Raskyaechara gobica songliaoensis gobica Raskyaechara

Raskyaechara deplanata Raskyaechara Raskyaechara costulata Raskyaechara

n 450

Member500 2

avoluta r

Formatio

Maastrichtian 550

600 Mesocha

Mingshui 650

a ulanensis

1

700

Atopochar

750 s s

Member

nsis e

n 800

a

sp. ni

m

850

a longiformi a Campa 900

ormatio rites guanping rites

F

Amblyochara Cha 950 Latochar

Obtusochara hailaerensi Obtusochara

1000

Sifangtai

Fig. 5. Distribution of selected charophytes in the SK1 (North).

The diversity of foraminifera is moderate, including the benthic cal- 6. Discussion careous foraminifera, agglutinated foraminifera and planktonic fora- minifera. (4) The foraminiferal fauna in the Songliao Basin is a 6.1. Stratigraphic sequence and correlation with International Geological typical marine fauna. (5) The foraminiferal fossils occur in several Time Table separate layers of the lower part of Members 1 and 2 of the Nenjiang Formation. Although a detailed biozonation has been defined for the SK1 cores, the zones are mainly non-marine and have local correlation utility. The age correlation of Cretaceous fluviatile and lacustrine de- 5. Chronostratigraphy of SK1 posits of intracontinental basins with Global Section and Stratotype Points (GSSP) marine reference sections is hampered by the absence The principle basis of the chronostratigraphy is magnetostratigraphy of common fossils. Only marine planktonic foraminiferal zones in and radiometric ages. Ten local magnetozones have been identified as the lower part of the Nenjiang Formation can be correlated with Chrons C34n to C29r (Fig. 6). Five with reversed polarity were named Santonian stage. However correlation of the lacustrine biozones with R1 (317.33–342.1 m), R2 (530.41–703.7 m), R3 (852.3–887.8 m), R4 Upper Cretaceous stages of the International Geological Time Scale (894.8–910.2 m), and R5 (1013.6–1736.6 m), and five with normal (GTS) is loosely constrained by the SIMS U–Pb zircon ages and local polarity were named N1 (342.1–530.41 m), N2 (703.7–852.3 m), magnetozones that correlate with C34n to C29n. N3 (887.8–894.8 m), N4 (910.2–1013.6 m), and N5 (1736.6–1800 m) Six pollen zones are defined for the Upper Cretaceous and one for the (Deng et al., 2013–this issue). Paleocene section in the SK1 cores (Fig. 6). The base Coniacian and base High-precision SIMS U–Pb ages have been analysed on bentonites Santonian are correlated within the Borealipollis zone. The base of the and tuffaceous siltstone layers intercalated in mudstones of lower Aquilapollenites zone is close to the base of the Campanian and the Qingshankou and lower Nenjiang formations. The three bentonite Kurtzipites and Wodehouseia zones are close to the base of the beds in the south core yield weighted mean 206Pb/238Uagesof91.4± MaastrichtianStageandareknowninthe Cretaceous epeiric Western In- 0.5 Ma at 1780 m depth, 90.1±0.4 Ma at 1673 m depth, and 83.7± terior seaway of North America (Nichols and Sweet, 1993). As in North 0.5 Ma at 1019 m depth, respectively (Deng et al., 2013–this issue). In America the K/Pg boundary is just above the extinction of Wodehouseia addition, a feldspar 40Ar/39Ar age of 88.3 Ma was measured from a species in the lower part of Chron C29r (Raynolds and Johnson, 2003); mugearite interbed in the corresponding layer of Well Jin-6 which is this boundary is placed between depths of −328 m and −336 m in the close to the SK1 (South) in distance (Wang et al., 2009c). SK1 north core. 40 X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43

A B C D E F G H I J Spore & pollen Phytoplankton Charophyte Ostracode Foraminifera

(ma) (ma) Grovesichara 250 Zone 7 changzhouensis Indeterminate interval Cedripites

Danian -Neocahra Piceapollis 65.5 300 sinulata C29r 65.58 350

400 C30n . 2 433.31 C30r

450 Zone 6 Fm C31n Tetr anguladinium- Hornicahara Wodehouseia 500 Subtilisphae ra- prolixa 68.74 spinata Botryococcus Talicypridea qingyuanangensis- Maastrichtian 550 Ziziphocypris simakovi Mings hui 600 C31r 70.6 70.2 650 Zone 5 Kurtzipites 71.07 700 trispissatus Raskychara 1 146.47 gobica 750 72.2 800 C32 Zone 4 Ulmipollenites 850 Ulmoideipi tes

orth) Botryococcus- Atopochara 230.33 900 73.62 Pediastrum ulanensis Talicypridea amoena- Eucypris cuneata 950 C33n

Sifangtai Fm. 1000 79.0 79.1 S K 11050 (N

1100

n 267.91 5 1150 Pedias trum

1200

1250 Indeterminate interval Camp ania 80.4 1300

Zone 3 1350 4 182.96 Aquilapollenites 1400 C33r Dinogymniopsis- Chlamydophrella- 1450 Vesperops is 81.6 bifurcata Strumosia inandita- 1500 Cypridea spangvosa Nenjiang Fm. 3 107.21 1550 Limnocypridea dilinensis- Limnocypridea nova 82.2 1600 Periacanthella portentosa- Limnocypridea 1650 subscalariformis 2 216.03 Cypridea liaukhenensis- 1700 Cypridea bella Dinogy mniopsis 83.0 Archaeoglobigerina minor-Balmula Mongolocypris magna- 1750 blowi 83.5 Mongolocypris heilun tszianensis 83.7 83.7 Archaeoglobigerina Cypridea gracila- cretacea, 1050 Cypridea gunsulinensis Hedbergella flandrini 1 103.04 Cypridea anonyma- Karrorulina 1100 Candona fabiforma hokkaidoana 84.5 Gavlinella sp. Cypridea formosa- Anomalinoides sp. 3 1150 Pediastrum- Cypridea sunghuajiangensis

Fm. Santonian Botryococcus Cypridea favosa- 125.30 1200 Mongolocypris tabulata 85.8 2 Cypridea exornata- ojia Schizosporis- 85.8 1250 Cypridea dongfangensis Campenia Ya 1 32.44 Cypridea panda- 86.2 Zone 2 1300 Mongolocypris obscura Borealipollis 1350 Triangulicypris vestilus- Triangulicypris fusiformis- Triangulicypris pumilis 1400

Coniacian Cypridea fuyuensis- 3 1450 Triangulicypris symmetrica C34n Kiokansium- 415.61 Dinogymniopsis- Cypri dea edentu la- 88.6 1500 88.3* Lycopt erocyp ris gran dis 2 Botryococcus

S K 1 (South) 1 K S 1550 Cypridea nota- Sunliavia tumida 1600 Cypridea dekhoinensis- 1650 Cypridea gibbosa Qingshankou Fm. 90.1 90.4 1700 Triangulicypris torsuosus- Dinogymniopsis- 81.41 Triangulicypris uronian 1 1750 Zone 1 Filisphaeridium torsuosusvar. nota

T 92.0 91.4 Quantonenpolle- 1800 nites-Cranwellia 95.10 4 Mongolocypris 1850 Granodiscus longicaudata 3 36.97 1900

Quantou F. Quantou X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43 41

These pollen zones correlate the stratigraphic interval from Member In general, we propose a tentative correlation of the lithostratigraphic 2 of the Nenjiang Formation up to the upper part of Member 2 of the units in the SK1 cores with stages of the International Geologic Time Mingshui Formation with the Campanian–Maastrichtian. The correlation Scale (Fig. 6). The top of Quantou Formation is in the lower Turonian; of this interval is confirmedbythebaseofChronC33rat−1736.6 m. The the Qingshankou Formation is the uppermost Turonian–lower Aquilapollenites zone ranges from Member 2 of the Nenjiang Formation Coniacian; the Yaojia Formation is from the upper Coniacian to mid- to the basal part of the Sifangtai Formation. The K. trispissatus zone dle Santonian; the Nenjiang Formation is from the upper Santonian spans from the middle to the upper parts of Member 1 of the Mingshui to middle Campanian stage; the Sifangtai Formation is limited to the Formation, and the W. spinata zone is in the Member 2 of the Mingshui upper Campanian; and the Mingshui Formation is the uppermost Formation and its top at −360 m is close to the K/Pg boundary. The Campanian to Maastrichtian. It is possible that the top part of the overlying interval yields poorly preserved pollen and is referred to the Mingshui Formation belongs to Paleocene. Cedripites piceapollis zone of Paleocene. The phytoplankton assemblage is dominated by dinoflagellates that 6.2. K/Pg boundary characterise ten assemblage biozones (Fig. 6). Some assemblages are composed of species known outside of the Songliao Basin and have In China, the Cretaceous/Palaeogene (K/Pg) boundary is document- well known stratigraphic ranges, but others are long ranging. Dinofla- ed from marine sediments in southern Tibet (Wan, 1988; Wan et al., gellate species are diverse in the Qingshankou Formation and Members 2000, 2002), but no well-preserved terrestrial biotic record crosses 1 through 4 of the Nenjiang Formation. One genus is known from the the boundary. In NE China, the Songliao and adjacent basins are poten- Quantou and Mingshui formations and none from the Yaojia Formation. tial areas for defining terrestrial criteria of the K/Pg boundary. In the The diverse assemblages suggest brackish to near marine waters during previous work, the boundary was placed in the Furao Formation the deposition of part of the Qingshankou and Nenjiang formations. above the Mingshui Formation (Li et al., 2004). Recent palynological Most species have rather long ranges. studies suggest that the boundary is below the Furao Formation but Upper Cretaceous to Paleogene charophytes are documented no exact data fix it. Our multi-disciplinary studies of the SK1 cores sug- in East Asia and a zonal scheme is developed (Karczewska and gest placing the K/Pg boundary in the upper part of the Mingshui Ziembinska-Tworzydlo, 1972, 1983). A major taxonomic turnover Formation. occurred among the charophytes during the Cenomanian–Santonian The charophyte record changes significantly from assemblage 3 when the Characeae replaced most species of Clavatoraceae to 4, although it is not a big extinction event. As mentioned above, (Martín-Closas, 2003). At the top of the Upper Cretaceous section some new elements appear in assemblage 4 such as Stephanochara, charophytes become an important microfossil group and divide the Pechichara, Neochara and Raskyella. Assemblage 4 is recognised by Sifangtai and Mingshui formations into four zones (Fig. 6). The K/Pg the greater abundance of Grovesichara changzhouensis which is boundary is picked at the boundary between the Hornichara prolixa widespread in China, and is considered to be Paleocene and early Eo- zone below and the Grovesichara changzhouensis–Neochara sinulata cene in age. More important is the appearance of Neochara in assem- above by correlating with the fossil occurrence in the Jiangsu and blage 4. It is generally agreed that the age of this genera is not older Guangdong provinces (Wang et al., 1982; Huang, 1988). than Paleocene (Wang, 1978; Ye et al., 1993). In addition to Paleo- East Asian Cretaceous ostracode assemblages are abundant, diverse cene elements, some Cretaceous species of Charities, Nemegtichara and widespread; a detailed biostratigraphic zonation is well established and Gobichara are also found with Paleocene species, but they are (Ye et al., 2002). Twenty Upper Cretaceous assemblage zones character- not abundant. We propose to use the evolutionary changes between ise the Quantou, Qingshankou, Yaojia, Nenjiang, Sifangtai, and the charophytes assemblages 3 and 4 to mark the K/Pg boundary at Mingshui formations in the SK1 cores (Fig. 6). Ostracode preservation about 328.77 m in the SK1 (N) core. and diversity are moderate in the lower part of the SK1 south section As noted above, the boundary between palynological Zones 6 and 7 is but improve in the upper section. The ostracode assemblage zones are defined by a dramatic reduction in palynomorph diversity and many correlated with Upper Cretaceous stages referring to the radiometric palynomorph species disappeared above this boundary. The palynologi- ages and magnetochrons mentioned above. cal data correlated Zone 6 with the Maastrichtian, and Zone 7 clearly has The Turonian/Coniacian boundary is correlated with the bound- a Cenozoic aspect with mainly angiosperm taxa of a more modern ap- ary between the C. nota zone below and the C. edentula zone above pearance (Li et al., 2010). However, the boundary between Zones 6 and in the Qingshankou Formation (Fig. 6).ThebaseoftheSantonianis 7 is also a lithological boundary. The reddish siltstone of the lower part demonstrated through the magnetochron and radiometric ages and of Zone 7 is rare for palynomorph fossils — the major palynofloral change alsoprojectedatthecontactoftheC. exornata and C. favosa in the towards the upper part of Zone 7. It is indicated that the K/Pg boundary is Yaojia Formation. The base of the Campanian correlates with the more or less higher than the base of Zone 7, and therefore, above the boundary between the C. gracila and M. magna zones at the contact depth of 360.6 m in the SK1 (N). between Members 1 and 2 of the Nenjiang Formation. The base of Magnetostratigraphic criteria suggest correlating the K/Pg boundary the Maastrichtian projects into Chron C31r, which is in the middle in the upper part of Member 2 of the Mingshui Formation (R1, 317.33– of the T. qingyuanangensis zone approximately at the base of Member 342.1 m in the SK1 north core), which is correlated with Chron C29r 2 of the Mingshui Formation. (Cande and Kent, 1995; Kuiper et al., 2008). The planktonic foraminifera A. blowi, A. cretacea and H. flandrini in the Based on the data obtained in the SK1 (N) core, we tentatively lower unit 1 of the Nenjiang Formation correlate with the uppermost place the K/Pg boundary above 360.6 m by palynology, at 328.77 m Turonian–Santonian stages. Benthic foraminifera found in the SK1 were by charophytes, and within the interval of 317.33–342.1 m by widely distributed in the upper Cretaceous strata (Kaiho et al., 1993). magnetostratigraphy. It is likely that the boundary is around 328 m According to global distribution of the above mentioned planktonic in general. Although the K/Pg boundary falls within the upper part foraminifera (Silva and Sliter, 2002), the Member 1 of the Nenjiang of Member 2 of the Mingshui Formation around the depth of 328 m Formation is restricted in the late Turonian to late Santonian. The by the new micropalaeontologic and magnetostratigraphic data, foraminifera-bearing beds are limited in the late Santonian by com- more data are necessary to accurately determine the position of the prehensive stratigraphic correlation of the SK1 (Fig. 6). K/Pg boundary in the Songliao Basin.

Fig. 6. Integrated stratigraphic frame of the SK1 (South and North) based on magnetostratigraphy, SIMS U–Pb age and biostratigraphy. A — Epoch; B — Formation; C — Member; D — Thickness; E — Interpolated boundary age; F — Core; G — Depth; H — Stratigraphic column; I — Polarity chron; J — SIMS zircon U–Pb and feldspar 40Ar/39Ar ages (*age from Well Jin-6). For legend see Figs. 2 and 3. 42 X. Wan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43

7. Conclusions Huang, R., 1988. Charophytes of Nanxiong Basin, Guangdong and its Cretaceous–Tertiary Boundary. Acta Palaeontologica Sinica 27 (4), 457–474 (in Chinese with English abstract). 1. The SK1 cored sequence consists mainly of lacustrine sandstone, Huang, Q.H., Chen, C.R., Wang, P.Z., Han, M.X., Li, X.J., Wu, D.Q., 1998. The Late Creta- ceous bio-evolution and Anoxic events in the ancient lake in the Songliao basin. dark grey mudstone, shale, and oil-shale. The section is subdivided Acta Micropalaeontologica Sinica 15 (4), 417–425 (in Chinese with English into the Quantou, Qingshankou, Yaojia, Nenjiang, Sifangtai, and abstract). Mingshui formations in ascending order. Kaiho, K., Fujiwara, O., Motoyama, I., 1993. Mid-Cretaceous faunal turnover of intermediate-water benthic foraminifera in the northwestern PacificOcean.Ma- 2. Upper Cretaceous microfossils are abundant and diverse in the SK1 rine Micropaleontology 23, 13–49. cores. A high resolution biostratigraphy divides the cored section Karczewska, J., Ziembinska-Tworzydlo, M., 1972. Lower Tertiary Charophyta from into 21 ostracode assemblages, 10 phytoplankton assemblages, 7 theNemegtBasin,GobiDesert.In:Kielan-Jaworowska,Z.(Ed.),ResultsPol- ish–Mongolian Palaeontological Expedition IV: Palaeontologia Polonica, 27, palynological zones, and 4 charophyta assemblages. Marine plank- pp. 51–81. tonic foraminifera were first discovered in the lower Nenjiang For- Karczewska, J., Ziembinska-Tworzydlo, M., 1983. Age of the Upper Cretaceous Nemegt mation and correlate with the upper Santonian stage. Formation (Mongolia) on charophytan evidence. Acta Palaeontologica Polonica 28, 137–146. 3. Based on biostratigraphy, high-resolution magnetostratigraphic and Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, P.R., Wijbrans, J.R., 2008. Syn- SIMS U–Pb zircon analyses of the SK1 cores, the top of Quantou For- chronizing rock clocks of Earth history. Science 320, 500–504. mation is the lower Turonian; the Qingshankou Formation is the Li, J., Mao, S.Z., Xu, Y., Qiao, X.Y., Wan, C.B., Yang, J.G., 2000. The late Cretaceous fl upper Turonian to middle Coniacian; the Yaojia Formation is from nonmarine dino agellates, acritarchs and sedimentary environment in the northern Songliao basin. Geoscience 14 (3), 267–272 (in Chinese, with English abstract). the upper Coniacian to middle Santonian; the Nenjiang Formation Li, X., Li, W., Chen, P., Wan, X., Li, G., et al., 2004. SHRIMP U-Pb zircon dating of the up- is the upper Santonian to middle Campanian; the Sifangtai Forma- permost Cretaceous Furao Formation near the Heilong River: an age closest to the – tion is limited to the upper Campanian; and the Mingshui Formation K/T boundary. Chinese Science Bulletin 49 (8), 860 862. Li, J., Batten, D.J., Zhang, Y., 2010. Palynological record from a composite core is the uppermost Campanian to Maastrichtian. It is likely that the top through Late Cretaceous early Paleocene deposits in the Songliao Basin, part of the Mingshui Formation belongs to the Paleocene Series. Northeast China and its biostratigraphic implications. Cretaceous Research 32, 1–12. Li, S., Xi, D., Jing, X., Huang, Q., Wang, Z., Wan, X., 2011. Upper Cretaceous ostracod biostra- Acknowledgements tigraphy of the CCSD-SK-1 (south) borehole, Songliao Basin. Acta Palaeontologica Sinica 50 (3), 330–343 (in Chinese, with English abstract). Mao, S.Z., Wan, C.B., Qiao, X.Y., 1999. Cretaceous nonmarine dinoflagellates from northeast Financial support was provided by the National Basic Research China. Grana 38, 1–18. Program of China (973 Program, NO. 2012CB822002), the National Martín-Closas, C., 2003. The fossil record and evolution of freshwater plants: a review. – Natural Science Foundation of China (Project NO. 41172037) and Geologica Acta 1, 315 338. Nichols, D.J., Sweet, A.R., 1993. 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