Late Cretaceous Stratigraphy, Songliao Basin, NE China: SK1 Cores
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Palaeogeography, Palaeoclimatology, Palaeoecology 385 (2013) 31–43 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Late Cretaceous stratigraphy, Songliao Basin, NE China: 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 Daqing Oil Field Corporation Ltd., Daqing, Heilongjiang 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 Suihua 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.