High Resolution Continuous Sedimentary Records Of

Geoscience Frontiers 6 (2015) 895e912

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Research Paper High resolution continuous sedimentary records of Upper Cretaceous obtained from the continental drilling (SK-1) borehole in Songliao Basin: Sifangtai and Mingshui Formations

Guodong Wang a,*, Rihui Cheng b, Pujun Wang b, Youfeng Gao c, Chengshan Wang d, Yanguang Ren e, Qinghua Huang e a Research Institute of Petroleum Exploration & Development-Northwest (NWGI), PetroChina, Lanzhou 730020, China b College of Earth Sciences, Jilin University, Changchun 130061, China c Research Center of Palaeontology & Stratigraphy, Jilin University, Changchun 130026, China d School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China e Institute of Exploration and Development of Daqing Oilﬁeld Company Ltd., Daqing, Heilongjiang 163712, China article info abstract

Article history: The Sifangtai and Mingshui formations were continuously cored in the SK-1n borehole (China Cretaceous Received 27 May 2013 Continental Scientific DrillingeSongKe1-the north borehole). The core is 767.96 m long, and the recovery Received in revised form is 94.7%. The ages of the formations range from middle Campanian to Danian. The sequence and process 26 January 2015 of lithology-lithofacies and cyclic stratigraphy were described in detail. Eight litho-types compose the Accepted 24 February 2015 Sifangtai Formation, and 15 litho-types compose the Mingshui Formation. Deposition was predominantly Available online 28 March 2015 in meandering river and lacustrine environments, including 10 microfacies in the Sifangtai Formation and 15 microfacies in the Mingshui Formation. The complete sequence is composed of 535 m-scale cycles Keywords: fi fi Sifangtai Formation and Mingshui (sixth-order cycle), 152 fth-order cycles, 42 fourth-order cycles and ve third-order cycles. The Formation centimeter-scale description of the section revealed some previously unknown horizons such as a special Sedimentary facies type of mudstone, marl, volcanic ash and favorable sand reservoirs in the formations. The new-found Cyclostratigraphy evidence is very important for the interpretation of the evolution of the basin, conditions such as lake SK-1n oxic events, the K/Pg boundary, tectonism in the late sag basin stage, and the reservoir-cap rock as- Middle Campanian-Danian semblages in the shallow stratigraphy. Songliao Basin Ó 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

1. Introduction Cretaceous disturbances occurred in various places on the earth (Ma et al., 2001). In recent years, the Ocean Drilling Program (ODP), Major geological events occurred during the Cretaceous period, Deep Sea Drilling Project (DSDP) have provided extremely valuable such as large-scale volcanic activities (Larson, 1991; Jones and continuous marine records for further study of the major geological Jenkyns, 2001), oceanic anoxic events (Schlanger and Jenkyns, events, and important results have been achieved. 1976; Jenkyns, 1980; Bralower et al., 1994), oceanic red beds and As an important part of the earth’s surface system, the conti- its oxic processes (Hu et al., 2005; Wang et al., 2005), biota major nents are difficult to study because of the lack of continuous sam- radiation and replacement (Leckie et al., 2002), Cretaceous normal ples. The Songliao Basin in northeastern China, which is one of the superchron (Helsley and Steniner, 1969; Cronin et al., 2001; Shi and largest non-marine petroliferous basins in the world, contains a Zhu, 2002; Zhao, 2005), and late Cretaceous extinction events complete Cretaceous sequence of terrestrial sediments. The Con- (Walliser, 1996). All of the above events may be related to tinental Scientific Drilling ProjectdSK-1 obtained continuous, high-resolution Cretaceous terrestrial strata and geological records with little negative impact in the Songliao Basin. The SK-1 wells comprised two boreholes, the SK-1n and SK-1s. The 944.23 m up- * Corresponding author. E-mail address: [email protected] (G. Wang). per Cretaceous section recovered in the SK-1s core extends from Peer-review under responsibility of China University of Geosciences (Beijing). the third member of the Quantou Formation to the second member http://dx.doi.org/10.1016/j.gsf.2015.02.003 1674-9871/Ó 2015, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC- ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 896 G. Wang et al. / Geoscience Frontiers 6 (2015) 895e912 of the Nenjiang Formation. The 1541.66 m section recovered in the cored SK-1n borehole (Gao et al., 2009) correlates the K2s deposi- SK-1n core extends from the second member of the Nenjiang For- tional period with the midelate Campanian (He et al., 2012; Scott mation to the lower part of the Paleogene Taikang Formation (Feng et al., 2012; Wan et al., 2013). et al., 2013). In 1961 the Comprehensive Research Brigade of Songliao Pe- The objective of this paper is to present the most complete and troleum Exploration Bureau, Ministry of Petroleum Industry, first detailed sedimentary geological data of the Mingshui and Sifangtai named the Mingshui Formation. The reference profile is located in formations to date. These detailed stratigraphic, sedimentary facies Mingshui County, Heilongjiang Province. At the first stratigraphic and cyclostratigraphic data lay a solid geological foundation for meeting held in Taikang in 1961, the original Keshan Formation was future research. redefined as the present second member of the Mingshui Forma- tion (The second general survey brigade of Ministry of Geology, 2. The detailed research history of the Mingshui and Sifangtai 1965) by the exploration headquarters of the Songliao Petroleum formations Exploration Bureau, and that definition is still in use. The Mingshui Formation is mainly distributed in the central and In 1937, the Japanese scholar, Horiuchi, named the outcrop western parts of the Songliao Basin, and it is absent in the eastern strata located near the Sifangtai station in Suihua County, Hei- part. It is thicker in the southern part of the basin than in the longjiang Province, the “Sifangtai layer” (Songliao petroleum northern part, and it is generally 200e400 m thick, with a survey brigade, 1960), which was composed of grayish green, maximum thickness of 617 m (Jilin Oilfield Petroleum Geology brownish red mudstones with siltstone and fine-grained sandstone group, 1993). In the northern part of the basin, the Mingshui For- interbeds. On this basis, in 1958, the Second Exploration Brigade of mation overlies the Sifangtai Formation with a parallel uncon- the Ministry of Geology established the “Sifangtai Formation” (The formable contact, and in the southern part the contact is second general survey brigade of Ministry of Geology, 1965). conformable. The top of the Mingshui Formation is an angular However, the name “Sifangtai layer” was still used in the “Mono- unconformity with the overlying strata. Its stratotype is the profile graphic study report of upper Cretaceous Fulongquan and its above in the Hei 2 well in Qianguo County, Jilin Province, where it is strata in Songliao Plain”, which was written by the fourth district 597.5 m thick. Its lower part is composed of gray-brown, gray, gray- team of the Songliao petroleum exploration brigade in 1959 (Guo black mudstone, silty mudstone, and siltstone, and its upper part is et al., 1959). The authors correlated the “Keshan layer”, “Beian greyish-green, reddish brown, gray purple mudstone, and silty layer” and “Sifangtai layer” near the northern Songhua River with mudstone with ostracods and bivalves. The northern reference the “Sifangtai layer” near the southern Songhua River and classified profile is the Ku3 hole in Duerbote County, Heilongjiang Province, the “Sifangtai layer” in the Tertiary. In the “Geological summery with a thickness of 378 m. The formation can be divided into two report of Songliao Plain in 1959” written by the Songliao petroleum members. The first member (lower part) consists of dark gray exploration brigade in 1960, the “Sifangtai layer” was renamed the mudstone, grayelight gray sandstone, and siltstone. The lower part “Sifangtai Formation” and was divided into three lithological of the second member is composed of reddish brown, grayish green members. In 1965, the Songliao petroleum exploration headquar- mudstone, gray, fine siltstone with black mudstone and sandy ters redefined the “Sifangtai Formation” that had been proposed by conglomeratic interbeds. The upper part of the second member is the Songliao petroleum exploration brigade in 1961 to include only composed of brownish red, grayish green mudstone with grey, light fi the lower lithological member, K2s, and defined the upper two grey, ne siltstone, and argillaceous sandstone interbeds (Compile members as the “Mingshui Formation”. Since 1961 the “Sifangtai team of Table of regional strata of Heilongjiang province volume, Formation” and “Mingshui Formation” have been used consis- 1979). The group is mainly exposed in the west bank of the Keyin tently; however, the geological age of the “Sifangtai Formation” has River, in the Mingshui and Kelai gullies in Suihua County, Hei- been controversial. longjiang Province. The stratotype of the K2s Formation is the Dorbet 3 hole in The Mingshui Formation is correlated with the Maastrichtian Heilongjiang Province, where it is 160 m thick (Compile team of Stage according to phytoplankton (Gao et al., 1992), spore/pollen Table of regional strata of Heilongjiang province volume, 1979). (Gao et al., 1994)andcharophytes(Wang et al., 1985). The Its lower part consists of brownish red, grayish green sandstone, Mingshui Formation depositional period is generally considered mudstone with sandy mudstone, and argillaceous sandstone in- as Maastrichtian for current oil and gas exploration activities. terbeds containing mud boulder and calcareous concretions; the The Mingshui Formation was continuously cored (Gao et al., upper part consists of brownish red, grayish green mudstone, silt- 2009) in the SK-1n borehole and the biostratigraphy, cyclo- stone, and contains calcareous concretions and ostracode fossil. The stratigraphy and magnetostratigraphic studies reveal that the reference profile in the southern basin is in the Hei 2 well, where Mingshui Formation depositional period is equivalent to late e the K2s Formation is 394 m thick (Compile team of Table of regional Campanian Danian (He et al., 2012; Scott et al., 2012; Wan et al., strata of Jilin province volume, 1978). The K2s Formation is mainly 2013). The Cretaceous/Paleogene boundary is projected between distributed in the central and western parts of the Songliao Basin, 342.1 and 317.33 m by magnetostratigraphic and biostratigraphic but it is only locally present in the eastern part of Suihua County. It data; a graphic correlation experiment projects the boundary is 200e400 m thick in the northern basin and 200e413 m in the approximately at 328 to 325 m (Scott et al., 2012; Wan et al., southern basin, and the depocenter is in the HeidimiaoeQian’an 2013). area. The K2s Formation unconformably overlies the Nenjiang Group, except locally where the contact is conformable. The 3. Detailed description on lithologic sequence Sifangtai/Mingshui contact is a parallel unconformity in the northern basin and a conformable contact in the southern basin. The cored interval of the K2s Formation in the SK-1n borehole is The age of the Sifangtai Formation has evolved. Palynologic 807.12e1021.60 m with a total thickness of 214.48 m, accumulative studies of charophytes (Wang et al., 1985; Scott et al., 2012; Wan core length of 209.02 m and core recovery of 97.5%. The Mingshui et al., 2013) correlated the K2s depositional period as Maas- Formation in the SK-1n borehole is 210.66e807.12 m, with a total trichtian. However, new biostratigraphic, cyclostratigraphic and thickness of 596.46 m, cumulative core length of 558.94 m and magnetostratigraphic data of the K2s Formation in the continuously core recovery of 93.71%, in which the first member of the Mingshui G. Wang et al. / Geoscience Frontiers 6 (2015) 895e912 897 is from 632.33 to 807.12 m, and the second member is from 210.66 body interbeds. The K2s Formation developed as meandering to 632.33 m (Suppl. Table). The entire formation has never been river deposits in the early and late depositional period and small cored continuously in older wells. Compared with previous corings scale, shallow lake deposits in the middle depositional period. of the two formations in the Songliao Basin, the SK-1n borehole is The formation is composed of coarse to fine to coarse-grained unprecedented in either core length or core recovery. At the same cyclic deposits from bottom to top. time, in accordance with the special requirements of the core The K2s Formation in SK-1n is composed of 15 different types of description of scientific exploratory wells, detailed core descrip- meter-scale lithology-lithofacies cycles that are grouped into three tion work was completed on site while drilling. In addition, the categories: normally graded, reverse graded and non-graded. The color code, geological description and other aspects followed in- normally graded category includes 11 meter-scale cycles, including ternational general principles and methods for scientific explor- channel lag-point bar (which means that the channel lag deposit atory well description, which have greatly improved the accuracy grades up into the point bar), channel lag-point bar-natural levee, and degree to which the original data can be internationally point bar-natural levee, point bar-natural levee-flood lake, compared. crevasse splay-flood lake, crevasse splay-flood plain, crevasse The detailed description of cored rock is expressed by two as- splay flood plain-flood lake, crevasse channel-crevasse splay-flood pects. One is a description on millennial time scales (deposition lake, crevasse channel-flood plain, flood plain-flood lake, and rate: 5e8.8 cm/ka, Gao, 2010). The minimal lamination thickness is upper shoreface bar. The reverse graded category includes three 5 cm, thus a layer will be an interlayer if it is less than 5 cm. types of meter-scale cycles, namely static water mudstone- However, the minimal lamination thickness of some special li- turbidity current, middle shoreface bar and lower shoreface bar. thologies, such as marl and volcanic ash, is 2 cm. Therefore, a layer The non-graded category includes one meter-scale cycle, namely will be an interlayer if it is less than 2 cm thick. The other aspect is a color type (e.g., light gray mudstone-greenish gray mudstone). The description of minor changes of sedimentary microfacies, such as pairs of lithologies make up a basic genetic cycle that can be changes in structures, contents, and colors (See Fig. 1). identified in meter-scale (Cheng et al., 2008). The 174 meter-scale cycles, 43 fifth-order cycles, 13 fourth-order cycles and two third- 4. Lithology, lithofacies and cyclostratigraphy order cycles have been identified in the K2s Formation of the SK- 1n well, in which three to four meter-scale cycles compose one Eight types of lithology and 31 rock colors have been identified fifth-order cycle, and three to four fifth-order cycles compose one in the K2s Formation. Statistics show (Fig. 2) that mudstone makes fourth-order cycle. up the greatest thickness percentage (29.43%) and siltstone The Mingshui Formation in the SK-1n borehole is composed of (23.29%) is second, followed by argillaceous siltstone (13.35%), 15 types of lithologies having 35 rock colors. Statistics show (Fig. 4) siltstone (13.29%), fine-grained sandstone (10.48%), and medium- that mudstone has the highest percentage thickness (39.87%), and grained sandstone (8.74%). Regarding the frequency of occur- siltstone has the second highest percentage thickness (24.00%), rence, mudstone is the most common (124), silty mudstone is the followed by silty mudstone (11.77%), fine sandstone (7.85%), argil- second most common (105), followed by siltstone (90), fine- laceous siltstone (7.76%), and medium sandstone (5.12%). Mudstone grained sandstone (70), argillaceous siltstone (67), and medium- has the highest frequency (304), and siltstone has the second grained sandstone (45). Regarding color, greenish gray (5G6/1, highest frequency (272), followed by silty mudstone (129), fine 5GY6/1) (88) is the most frequent, followed by light gray (N7) (78), sandstone (100), muddy siltstone (85), and medium sandstone grayish brown (5YR3/2) (44), and grayish red (10R4/2, 5R4/2) (43). (42). Medium light gray color (N6) has the highest occurrence As for the cumulative thickness of the strata corresponding to the frequency, followed by light gray (N7), greenish gray (5G6/1), and same color, greenish gray (5G6/1, 5GY6/1) strata are the thickest medium grey (N5). As for the cumulative thickness of the strata (34.09 m), followed by the light gray (N7) (25.21 m). The back- corresponding to the four color categories, the medium light gray ground of the Sifangtai Formation is greenish gray mudstone and strata are the thickest, the thickness of the strata in other three silty mudstone, light gray, fine-grained sandstone and siltstone, color categories are basically equal, and the strata of the four cat- grayish brown, silty mudstone and mudstone, grayish red, silty egories account for 60% of the total thickness. Medium light grey mudstone and mudstone, light reddish brown, argillaceous silt- mudstone, greenish gray mudstone, medium light grey siltstone, stone and mudstone, medium brown mudstone, and silty medium light grey argillaceous siltstone, silty mudstone, and me- mudstone. dium light grey, fine-grained to medium-grained sandstone have The K2s Formation is composed of two subfacies and 10 the highest frequency of occurrence. These lithologies are inter- microfacies (Cheng et al., 2009). The two subfacies represent bedded and constitute the depositional background of the Min- meandering rivers and shallow lakes, and the 10 microfacies gshui Formation. formed as channel-lag (Fig. 3a), point bar (Fig. 3b), natural levee Three types of subfacies (Cheng et al., 2009) have been (Fig. 3c), crevasse splays (Fig. 3d), crevasse channel (Fig. 3e), flood identified in the core of the Mingshui Formation: meandering plain (Fig. 3f), flood lake (a lake deposition of oxide color river, shallow lake and lakeshore. Fifteen depositional environ- mudstone formed after the splay in the overbank environment) ments are described as channel lag (Fig. 5a), point bar (Fig. 5b), (Fig. 3g), shoreface bar (Fig. 3h), turbidity current (Fig. 3i), and natural levee (Fig. 5c), crevasse splay (Fig. 5d), crevasse channel fl fl quiet-water mudstone (Fig. 3i). The lower part of the K2s For- (Fig. 5e), ood plain (Fig. 5f), ood lake (Fig. 5g), still water mation is red, coarse clastic deposits of meandering river chan- mudstone (Fig. 5h), lime mudstone (Fig. 5i), horeface bar (Fig. 5j), nels, and grain size gradually decreases upwards. The channel storm bed (Fig. 5k), sand flat (Fig. 5l), mudflat (Fig. 5m), turbidity sand body grades up into interbedded channel and flood basin flow (Fig. 5n), and gravity flow channel (Fig. 5o). Sedimentary deposits, and the proportion of flood basin deposits increases facies of the lower part of the first member of the Mingshui e upward. The middle part of the K2s Formation changes into Formation is meandering river and the middle upper part is shallow lake deposits from flood-basin deposits. The upper mid- shallow lake. The second member of the Mingshui Formation dle and upper parts of the K2s Formation developed as flood- consists of meandering river environment in the lower part, basin deposits composed of reddish brown and greenish gray, mainly river channel and embankment deposits, and shallow fine-grained clastic rocks, with a small number of channel sand lake in the middle part; meandering river (mainly flood plain 898 G. Wang et al. / Geoscience Frontiers 6 (2015) 895e912

Figure 1. Columnar section of high-resolution lithology, cyclostratigraphy and sedimentary facies of Mingshui and Sifangtai Formations (modiﬁed from Cheng et al., 2011 and Wang et al., 2011). * The GSA Rock-Color Code is from the Geological Society of America rock-color chart, which is a common criterion for drilling rock color descriptioninIODP (Songliao petroleum survey brigade, 1960). N1: black; N3: dark gray; N4: med. dark gray; N5: medium gray; N6: med. light gray; N7: light gray; N8: very light gray; 5G4/1: dark greenish gray; 5G6/1: greenish gray; 5G8/1: light greenish gray; 5G5/2: grayish green; 5Y4/1: olive gray; 5Y6/1: light olive gray; 5Y8/1: yellowish gray; 5Y5/2: light olive gray; 5Y7/2: yellowish gray; 5R4/2: grayish red; 5R6/2: pale red; 5R6/6: light red; 10R3/4: dark reddish brown; 10R5/4: pale reddish brown; 10R4/2: grayish red; 10R6/2: pale red; 10R4/6: moderate reddish brown; 5GY4/1: dark greenish gray; 5GY6/1: greenish gray; 5GY8/1: light greenish gray; 5GY5/2: dusky yellow green; 5GY7/2: grayish yellow green; 10GY5/2: grayish green; 5YR3/2: grayish brown; 5YR3/4: moderate brown; 5YR4/1: brownish gray; 5YR4/4: moderate brown; 5YR5/2: pale brown; 5YR6/1: light brownish gray; 5YR7/2: grayish orange pink; 10YR4/2: dark yellowish brown; 10YR6/2: pale yellowish brown; 5YR6/4: light brown; 5B5/1: medium bluish gray; 5RP4/2: grayish red purple. .Wn ta./Gocec rnir 21)895 (2015) 6 Frontiers Geoscience / al. et Wang G. e 912 899 Figure 1. (continued). 900 .Wn ta./Gocec rnir 21)895 (2015) 6 Frontiers Geoscience / al. et Wang G. e 912

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Figure 1. (continued).

deposits) and shallow lake deposits make up the upper part. The 5. Discussion and conclusions basic depositional environment of the Mingshui Formation is meandering river, accompanied by lake fluctuations. 5.1. Centimeter-scale portrayed continental red beds provide a The sedimentary sequence of the Mingshui Formation is possible standard profile for the study of the global late Cretaceous composed of multiple scales of lithology-lithofacies cycles. Twenty and Paleocene oxic event different types of meter-scale cycles in a total of three graded sequences (normally graded, reverse graded and non-graded) Red beds in the Sifangtai Formation are mainly distributed in have been identified. The normally graded sequence includes 13 nine intervals, 807.47e820.99 m, 825.11e840.19 m, types of meter-scale cycles, including channel lag-point bar, 850.91e869.74 m, 878.12e889.12 m, 893.34e907.57 m, channel lag-point bar natural levee, point bar-natural levee, point 940.46e943.36 m, 961.84e972.18 m, 981.00e991.04 m, and bar-natural levee-flood lake, crevasse splay-flood lake, crevasse 995.30e1020.66 m, respectively. The minimum interval thickness is splay-flood plain, crevasse splay-flood plain-flood lake, crevasse 2.9 m, and the maximum is 25.36 m. Red beds account for 57% of channel-crevasse splay-flood lake, crevasse channel-flood plain, the total thickness of K2s Formation and are mainly composed of flood plain-flood lake, sand flat-mud flat, upper shoreface bar, mudstone, silty mudstone, argillaceous sandstone, and siltstone of sand flat, and tempestite. The reverse graded sequence includes gray brown 5YR3/2), gray red (10R4/2,5 R4/2), reddish brown four types of meter-scale cycles, quiet-water mudstone - turbidite, (10R5/4), and medium brown (5YR3/4,5 YR4/4), which belong to quiet-water mudstone - gravity channel, middle shoreface bar, the flood deposits of meandering rivers in the early period of the and lower shoreface bar. The non-graded sequence includes two late Cretaceous (other examples of Maastrichtian red beds include types of meter-scale cycles, namely muddy limestone- quiet- the continental alluvial strata in the middle and northern parts of water mudstone and color cycle. 361 meter-scale cycles, 109 Peru (Javier et al., 1996), marine red beds that developed in the fifth-order cycles, 29 fourth-order cycles and three third-order Tibet SagaeGeelong region (Wan et al., 2005) and Romanian East cycles have been identified in the Mingshui Formation, among Carpathians (Melinte and Jipa, 2005). Red beds in the Mingshui which three to four meter-scale cycles comprise one fifth-order Formation are one of the world’s few examples of Maastrichtian cycle, and three to four fifth-order cycles comprise one fourth- continental red beds and provide a possible standard profile for the order cycle. study of the global late Cretaceous oxic event.

Figure 2. Occurrence frequency and thickness percentage of the drilling core lithology of the Sifangtai Formation. G. Wang et al. / Geoscience Frontiers 6 (2015) 895e912 909

Figure 3. Main lithology and sedimentary facies of Sifangtai Formation in SK-1n. aelight gray and grayish red sandy fine-grained argillaceous conglomerate, aligned mud gravels with calcareous concretions, poorly sorted, oblique bedding, deformation bedding, channel lag deposit, depth 1019.56 m. bepale red medium-grained sandstone, with a small amount of mud gravels, parallel bedding, point bar, depth 1017.36 m. cepale brown argillaceous siltstone, with siltstone strips, sand ripple bedding and climb bedding, intensive bioturbation, natural levee, depth 831.11 m. demedium gray siltstone, deformation ripple bedding, scour surface at the base, with 2 cm basal conglomerate, charring biological debris on the bedding plane, crevasse splay, depth 822.48 m. eelight gray calcareous siltstone, small scale trough cross bedding, scour surface at the base, crevasse channel, depth 824.10 m. fegrayish brown and greenish gray argillaceous siltstone, with a small amount of calcareous concretions, deformation bedding, bioturbation, flood plain, depth 856.94 m. gemedium brown mudstone, massive bedding, a small amount of cracks filled with calcite, few calcareous concretions, flood lake, depth 882.44 m. helight gray fine-grained sandstone, wave generated cross bedding, a small amount of aligned mud gravels at the base, nearshore bar, depth 927.41 m. iemedium dark gray mudstone, with light gray siltstone interlayer, horizontal bedding in mudstone and parallel bedding in siltstone, erosion surface developed at the bottom of siltstone, turbidite and mudstone of still water in shallow lake, depth 937.26 m.

Figure 4. Occurrence frequency and thickness percentage of the drilling core lithology of the Mingshui Formation. 910 G. Wang et al. / Geoscience Frontiers 6 (2015) 895e912

Figure 5. Plate showing main lithology and sedimentary facies of Mingshui Formation in SK-1n. aemedium light grey fine-grained sandstone, bearing aligned flat mud gravels with maximum diameter of 4 cm, massive bedding, scour surfaces at the bottom, channel lag deposition, depth 590.4 m. bemedium gray fine-grained sandstone, wavy bedding at the bottom, trough cross-bedding in the middle part, point bar, depth 585.31 m. cemedium light grey argillaceous siltstone, with siltstone strips and lens. wavy cross-bedding, lenticular bedding, wormhole structures, nature levee, depth 799.42 m. demedium grey siltstone, argillaceous conglomerate interbeds and mud strips in the middle and lower part, trough cross-bedding and deformed bedding, crevasse splay, depth 595.2 m. eemedium grey bearing gravel fine-grained sandstone, massive bedding, scour surface developed, crevasse channel, depth 422.41 m. fegreenish grey and greyish brown silty mudstone, with a few calcareous concretions, floodplain. depth 612.50 m. gemedium reddish brown mudstone, massive bedding, flood lake, depth 340.97 m. hemedium grey mudstone, horizontal bedding, mudstone of still water, depth 740.46 m. iegreenish grey mudstone interbedded with light olive grey marlite, ostracod fossil fragments developed in marlite, shallow lake marlite, depth 504.69 m. jelight grey siltstone, with a few mud strips, wave- generated cross-bedding and bioturbation structures, scales of bedding become larger upward, near-shore bar, depth 756.39 m. kedark greenish grey polygenic conglomerate (argillaceous gravel, quartz gravel, sand gravel), with maximum gravel diameter of 4 cm, poorly sorted, a few fossil fragments, cutting structure developed at the bottom, tempestite, depth: 721.06 m. lelight grey medium-grained sandstone, low angle cross-bedding, sandy beach, depth 673.56 m. megreenish grey silty mudstone, with calcareous concretions, massive bedding, mud flat, depth 668.38 m. nemedium grey mudstone interbedded with grey siltstone, wavy bedding in siltstone, scour surface developed at the bottom of siltstone, turbidite, depth 650.28 m. oemedium light grey silty calcareous concretion medium-grained conglomerate, massive bedding, deformed bedding in local, scour surface developed at the bottom, gravity channel, depth 267.75 m. G. Wang et al. / Geoscience Frontiers 6 (2015) 895e912 911

The MaastrichtianePaleogene red beds of the Mingshui For- river, which corresponded to the reduction of the accommodation mation are mainly distributed in two intervals, 271.25e303.75 and space. Therefore, the basin accommodation space in the direction 323.43e342.52 m, with thicknesses of 32.5 and 19.09 m, respec- towards the tectonic stress reduced by the lateral extrusion effect tively. The red beds mainly consist of reddish brown (10R4/6) causing the depocenter to be displaced far from the direction of the mudstone, deposited in flooded meandering rivers. These red beds extrusion. The meandering river and shallow lake subfacies alter- are also coeval with large sets of continental red beds formed in nated, reflecting the intermittent compressive stress’s control on alluvial plain environments that developed in central and northern the migration of the sedimentary facies belt and lateral shift of the Peru (Javier et al., 1996) and marine red beds of early Paleocene age depocenter. that developed in China’s south Tibet Zhada area (Wan et al., 2005). As one of the world’s few continental red beds from that period, the 5.4. Potential oil and gas reservoir-cap combinations in the upper centimeter-scale portrayed continental red beds in the Mingshui part of the Songliao Basin Formation could serve as a standard profile for the study of the global Paleocene oxic event. The coarsest lithology in the K2s Formation is mainly siltstone, fine-grained sandstone and medium-grained sandstone (Fig. 2). 5.2. K/Pg boundary in Songliao Basin Based on the occurrence frequency and cumulative thickness percentage, it can be seen that the individual beds of medium-grained The Songliao Basin is a large continental oil and gas bearing sandstone have a maximum thickness of 4 m, followed by fine- basin that has been explored and produced for more than half a grained sandstone and siltstone; the thick sandstone beds are century. During this time, because exploration has focused on the well sorted. As for the origins of the sandstones, the K2s sandstones oil and gas bearing layers from the Quantou to Nenjiang Forma- are mainly composed of meandering channel sandstone and tions, the Sifangtai Formation and the Mingshui Formation, which shoreface bar sandstone in a shallow lake. As for the vertical have poor oil and gas shows, have been relatively little studied. development, the meandering channel sandstone is mainly devel- Until recently in oil and gas exploration activities, the Cretaceous oped in the lower part of the K2s Formation and interbedded with and Paleogene boundary in the Songliao Basin generally have been mudstone and silty mudstone of the flood basin, forming several considered to be at the top of the Mingshui Formation, primarily sets of thick deposits. Shoreface-bar sandstones are concentrated in based on the regional angular unconformity between the Mingshui the middle part of the K2s Formation, with a total cumulative ’ and the Palaeogene Yi an formations (Yu et al., 1999; Lin et al., thickness of up to 30 m. The upper part of the K2s Formation is 2007). Because of the regional angular unconformity on the top mainly composed of mudstone, silty mudstone and argillaceous of the Mingshui Formation, it has long been thought that the K/Pg siltstone of meandering river and flood basin environments, with a boundary transition may not be preserved in the Songliao Basin. small amount of thin sandstone. These lithologies are a set of However, during the geological site selection and drilling design relatively stable regional cap rocks, with a total thickness of up to process for the SK-1n borehole, it was believed that the K/Pg 80 m or more. Oil and gas reservoir-seal conditions in the K2s boundary was quite probably in the second member of the Min- member are very prospective. gshui Formation. This hypothesis was based on the comparison of In the first member of the Mingshui Formation two sets of dark basin evolution, paleoclimate variations, and stratal development gray mudstone are developed from 721.46 to 748.51 m and from and preservation conditions in the Songliao and Jiayin basins. 643.65 to 660.07 m, with thicknesses of 27.07 and 16.42 m, Preliminary biostratigraphic (Scott et al., 2012; Wan et al., 2013), respectively. The corresponding sandstone layers are beach sand- magnetostratigraphic (Deng et al., 2013) and cyclostratigraphic stone and bar sandstone, respectively. In addition, thick mudstone research results for the Mingshui Formation in the SK-1n borehole interbedded with thick sandstone of fluvial facies and lacustrine show that the K/Pg boundary is located in the upper second facies provide good conditions for oil and gas reservoirs and seals member of the Mingshui Formation. The boundary is preserved in deposited during the late subsidence stage of the Songliao Basin. continuously deposited sediments of the second member of the This relationship has been proved by the recent discovery of oil and Mingshui Formation. Therefore, K/Pg boundary deposition may be gas from the first member of the Mingshui Formation on the preserved in Songliao Basin. Honggangzi and Salto structures (Hou et al., 2009).

5.3. Alternating tension and compression controlled the basin Acknowledgments deposition at the late depression stage of the Songliao Basin This work has been supported by the National Basic Research In the Mingshui Formation cores of the SK-1n borehole, small Program of China (Grant No. 2012CB822002), the National Natural fi synsedimentary normal faults are developed at the base of the rst Science Foundation of China (Grant No. 41202072) and the “Key fi member of the Mingshui Formation that display tensile stress eld Laboratory of Northeast Asia biological evolution and environment features. Subsidence caused by early tension expanded the lake of Ministry of Education” platform base construction project. fi basin area during deposition of the rst member of the Mingshui Thanks to all of the workers and researchers for their participation Formation and the depositional environment evolved from in the Chinese Cretaceous Continental Scientific Drilling Project. meandering river into shallow lake, which lasted until the end of deposition of the first member of the Mingshui Formation. Synse- Appendix A. Supplementary data dimentary normal faults developed in the basal part of the second member of the Mingshui Formation. Above the normal faulted Supplementary data related to this article can be found at http:// section the overlying section has reverse faults. These fault systems dx.doi.org/10.1016/j.gsf.2015.02.003 show that the basin experienced inversion from tension to compression from the early period of the second member of the Mingshui Formation. One type of reverse faults developed in the References large set of channel sands of the meandering river, representing a Bralower, T.J., Arthur, M.A., Leckie, R.M., Sliter, W.V., Allard, D.J., Schlanger, S.O., 1994. small accommodation space stage. Another type of reverse faults Timing and paleoceanography of oceanic dysoxia/anoxia in the Late Barremian developed in the transition from the shallow lake and meandering to Early Aptian (Early Cretaceous). Palaios 9, 335e369. 912 G. Wang et al. / Geoscience Frontiers 6 (2015) 895e912

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