http://orcid.org/0000-0002-4887-5274
Figures
Abstract
The largest lake transgression event (LTE) associated with lake anoxic events (LAE) and periodic seawater incursion events (SWIE) in the Songliao Basin, northeastern China, occurred during deposition of the Cretaceous Nenjiang Formation. The Yaojia-Nenjiang Formation boundary (YNB) marks the beginning of the LTE, as well as LAE and SWIE. However, there is an absence of direct radioisotopic dating, and therefore the age of the YNB, as well as the beginning of LTE, together with their relationship with other geological events, is strongly debated. Here we present a new SIMS U-Pb zircon age from the lowermost Nenjiang Formation. The bentonite bed located 9.88 m above the YNB of the X1-4 borehole was analyzed. Twenty-five analyses of 25 zircons were conducted, which produced a weighted mean age of 85.5±0.6 Ma (MSWD = 0.87). Based on the average sediment accumulation rate, the age of the YNB is suggested to be 85.7 Ma, indicating that the LTE began in the Early Santonian. The new ages provide a precise chronostratigraphic framework for climatic and geological events. Our new results imply that the beginning of the LTE, LAE and SWIE occurred almost simultaneously with short-term sea level rise, and probably had a close relationship with OAE3.
Citation: Xi D, He H, Yu Z, Huang Q, Hu J, Xu Y, et al. (2018) New SIMS U-Pb age constraints on the largest lake transgression event in the Songliao Basin, NE China. PLoS ONE 13(6): e0199507. https://doi.org/10.1371/journal.pone.0199507
Editor: Hao Cheng, Tongji University, CHINA
Received: April 8, 2017; Accepted: June 10, 2018; Published: June 26, 2018
Copyright: © 2018 Xi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper.
Funding: D.X. acknowledges support from the National Natural Science Foundation of China (Grant Nos. 41790452 and 41302008; http://www.nsfc.gov.cn/publish/portal1/), the National Basic Research Program of China (Grant No. 2012CB822002; http://www.most.gov.cn/eng/programmes1/200610/t20061009_36223.htm), and State Key Laboratory of Biogeology and Environmental Geology (Grant No. GBL21314; http://en.cug.edu.cn/Key_Laboratories/Key_Laboratories___Research_Centers.htm). J.H. acknowledges support from the National Natural Science Foundation of China (Grant No. 41372110; http://www.nsfc.gov.cn/publish/portal1/). H.H. acknowledges support from the National Natural Science Foundation of China (Grant Nos. 41425013 and 41688103; http://www.nsfc.gov.cn/publish/portal1/), and the Strategic Priority Research Program of the Chinese Academy of Sciences (http://english.cas.cn/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
The Cretaceous was one of the warmest periods in Earth history and is characterized by oceanic anoxic events (OAEs), intense volcanic activity, a long period of normal geomagnetic polarity (that is, the Cretaceous Normal Superchron (CNS)), and high sea level [1–6]. Paleoclimatic and paleoenvironmental changes in the Cretaceous ocean have been well studied, but there is relatively little information about the continental record and its associated localized climate changes. Cretaceous continental sedimentary records provide key evidence that can increase our understanding of how terrestrial systems respond to both regional- and global-scale environmental changes [7]. The Songliao Basin (SLB), in northeastern China, is one of the largest Cretaceous continental rift basins in the world [8–10] (Fig 1). The basin was a long-lived and mid-latitude lake basin that was located relatively close to the western Pacific Ocean during the Cretaceous [10–12], and was thus subjected to seawater incursions. The Cretaceous ocean system may have been connected to the SLB through either atmospheric processes or oceanic transgression onto continental margins [13,14]. Well-preserved Cretaceous lacustrine deposits in the basin provide a unique opportunity to study the Cretaceous paleoenvironment and paleoclimate, as well as geological events [11,12,14].
(map modified from GeoMapApp; http://www.geomapapp.org/) Locations of the X1-4 borehole (124°55'1''N, 46°25'43''E), the north core, SK-1(n) (46°12'44.22''N, 124°15'56.78''E), and the south core, SK-1(s) (45°34'14.42''N, 124°40'15.59''E).
The largest lake transgression event (LTE) in the region occurred during the Late Cretaceous, with dark mudstone, black shale and oil shale preserved in the Lower Nenjiang Formation (K2n), resulting in a large-scale lake anoxic event (LAE) [15]. During this event, the Songliao paleolake was also periodically inundated by seawater incursion events (SWIE) [16–23]; as such, the lower K2n units may have been affected by changes in both regional and global sea level [24]. Several workers have suggested that this large lake transgression in the SLB was related to an OAE [13,15,25], while others have challenged this view on the basis of the dissimilar timings for each event [26,27]. Recently, Wagreich et al. [28] proposed that the high lake level in the SLB might have been related to a short-term low point on the global sea-level curve. Eustatic changes in sea level during the Cretaceous have been reevaluated using a synthesis of global stratigraphic data [5], which can be used to interpret lake-level changes within the SLB. Detailed stratigraphic data and a precise geochronology allow an improved understanding of the paleoclimate and paleoenvironment that existed within the SLB during the Cretaceous, as well as their relationship with marine and continental rocks of the period.
The International Continental Scientific Drilling Project in SLB (SK-1) spanned the complete sequence of Upper Cretaceous strata [12,29]. Three U-Pb ages were previously obtained from the lower Qingshankou Formation (K2qn), and one from the lowermost member 2 of the Nenjiang Formation (K2n2) of the SK-1 [26,29]. However, no radioisotopic dating has yet been performed on units between the middle K2qn and Member 1 of the Nenjiang Formation (K2n1). The Yaojia Formation/Nenjiang Formation boundary (YNB) marks the beginning of the LTE, as well as LAE and SWIE, but its age is uncertain. The current age of the YNB was estimated to be 84.487 Ma based on magnetostratigraphy [30], U-Pb dating, and the average sediment accumulation rate; or 84.673 Ma based on cyclostratigraphy [27]. Consequently, the age of the YNB is debated, which hinders our understanding of the LTE, LAE, SWIE, as well as their relationship with global-scale climate, lake level and OAE3.
In this study, we report a new age from the lowermost K2n1 based on investigation of a bentonite layer located 9.88 m above the YNB that was obtained from borehole X1-4 in the Central Depression of the SLB (Fig 1). The significance of the new dating results is as follows. On the one hand, it provides new constraints on the YNB, and improves the chronostratigraphic framework of the lower part of K2n2 in SLB, which is important for understanding climate change during the early Santonian to early Campanian. On the other hand, as the lower K2n2 was subjected to SWIE, it was affected by both regional and global events. On the basis of this new chronostratigraphic framework, the local lake level, LAE and global sea level and OAE3 are well correlated.
Materials and methods
The Lower Nenjiang Formation (K2n1 to lower K2n2) of the X1-4 borehole (124°55'1''N, 46°25'43''E), which is located at Changyuan-Xingshugang area of SLB, has been investigated in this study. The Lower K2n is mainly composed of dark mudstone with a bentonite layer at the depth interval of 988.26–988.29 m, where a sample (XING988) was collected (Fig 2). Permits for collecting the sample were not required. The K2n1/K2n2 and K2y/K2n boundaries occur at depths of 892.67 m and 998.17 m, respectively. The sample XING988 used for U-Pb geochronological analysis were processed by conventional magnetic and density techniques in order to concentrate non-magnetic, heavy fractions. Zircon grains obtained from the samples were mounted in epoxy alongside zircon reference standard Plésovice [31] and Qinghu, which were all subsequently polished to half of their thicknesses so that their centers were exposed for isotopic analysis. All zircons were examined using transmitted and reflected light photomicrographs, as well as cathodoluminescence (CL) images in order to reveal their internal structures, and the mount was vacuum-coated with high-purity gold prior to secondary ion mass spectrometry (SIMS) analysis.
Fig 2 was created by CorelDRAW X8 (http://www.coreldraw.com/us/pages/free-download). Copyright (c) 2018 [Huaiyu He] and its licensors. All rights reserved.
Measurements of U, Th, and Pb were conducted using a Cameca IMS-1280 SIMS at the Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing. U-Th-Pb ratios and absolute elemental abundances were determined relative to the zircon standard 91500 [32], analyses of which were interspersed with those of unknown grains, using operating and data processing procedures similar to those described by Li et al. [33]. A long-term uncertainty of 1.5% (1 RSD) for 206Pb/238U measurements of the standard zircons was propagated to the unknowns [34], despite the measured 206Pb/238U error in any specific session having been around 1% (1 RSD) or less. Measured compositions were corrected for common Pb using non-radiogenic 204Pb. Corrections are sufficiently small to be insensitive to the choice of common Pb composition, and an average of present-day crustal composition [35] was used for the correction, assuming that it largely occurred as surface contamination introduced during sample preparation. Uncertainties of individual analyses in the data tables are reported at the 1σ level, and mean ages for pooled U/Pb and Pb/Pb analyses are given at the 95% confidence interval. SIMS U-Pb zircon data are presented in Table 1. Data reduction was carried out using the Isoplot Excel add-in v. 2.49 [36].
Results
Zircons from sample XING988 are mainly euhedral, transparent, colorless, 30–180 μm in length, and have length-to-width ratios between 1:1 and 4:1. Most grains exhibited oscillatory zoning in CL images (Fig 2) and inherited zircon cores were seldom observed. All analyses were conducted on portions of zircon with oscillatory zoning, which is interpreted as reflecting growth within magma. Twenty-five analyses of 25 zircons were obtained in sets of seven scans during a single analytical session. Measured uranium and thorium concentrations were in the ranges 295–945 ppm and 132–911 ppm, respectively, and Th/U ratio varied between 0.4 and 1.0. All analyzed 206Pb/238U ratios were consistent within the uncertainties associated with the analytical precision. Spot 15 (with distinguishable U-Pb isotopic compositions within analytical errors), gave a younger 206Pb/238U age of 77.6 ±1.5 Ma. The discordant U-Pb age may be due to the loss of radiogenic Pb. Elimination of this one analytical value left 25 grains which produced a concordant U-Pb age of 85.5±0.6 Ma (Fig 3) and a weighted mean 206Pb/238U age of 85.5±0.6 Ma (MSWD = 0.87). This age is interpreted as the best estimate of the timing of crystallization of sample XING988.
Ellipses on the analyzed zircon grains show the positions of U-Pb analytical sites.
Discussion
The Santonian through Early Campanian is an important period during which the global climate began to deteriorate, and numerous significant geological events occurred, such as OAE3, the termination of the CNS [2,28,37]. SIMS zircon analyses of intercalated bentonite layers located at depths of 1019 m (~6 m above K2n1/K2n2 boundary) in core SK-1(s) yielded U-Pb ages of 83.7±0.9 Ma [26]. More recently, U-Pb CA-ID-TIMS geochronology performed by Wang et al. [7] produced updated ages of 83.269±0.044 Ma. The U-Pb ages obtained by He et al. [26] using SIMS U-Pb technique, and those obtained by Wang et al. [7] using CA-ID-TIMS U-Pb technique overlap within uncertainties, but the CA-ID-TIMS analyses provide much greater precision [7]. Thus, we use the higher-precision CA-ID-TIMS U-Pb ages in core SK-1(s) [7] to calculate the age of the YNB. The total length of K2n1 in borehole SK-1(s) is 103.04 m [38], while in borehole X1-4 it is 105.5 m, implying that the sediment accumulation rates at both boreholes were very similar. Given that the bentonite layer from X1-4 is approximately 9.88 m above YNB, and using the ages of bentonite from the K2n2 of borehole SK-1(s) [7], we suggest that the average sediment accumulation rate for strata of the lower K2n1 in borehole X1-4 was ~45.5 m/Myr, and the age of the YNB is ca. 85.7 Ma. This indicates that the YNB might be older than the ages obtained from average sediment accumulation rate and astrochronological timescales [27,30]. Combining our new age for the YNB with ages of 85.7 Ma, and 83.269 Ma for strata at the depth of 1019 m within borehole SK-1(s) [7], the average sediment accumulation rate of K2n1 and the lower part of K2n2 of SK-1(s) is suggested to be ~44.9 m/Myr, indicating that the age of the K2n1/K2n2 boundary is ca. 83.4 Ma. This result provides a new age constraint on the astrochronological timescale and termination of the CNS. The previous astrochronological timescale indicated a duration of 0.791 Myr for K2n1 [27], roughly corresponding to two 405-kyr eccentricity cycles. However, our new finding suggests a duration of 2.3 Myr for K2n1, roughly corresponding to five and half 405-kyr eccentricity cycles. In addition, the previous termination of the CNS of SK-1 was estimated based on magnetostratigraphy, isotopic dating of K2n2, an astrochronological timescale, or on average sediment accumulation rates [7,26,27,30]. The new age provides a more reliable estimate for the average sediment accumulation rate of lower K2n of SK-1s, and thus may provide more reliable evidence for the termination of the CNS for future studies. Overall, the new ages provide a more precise chronostratigraphic framework which will contribute to a better understanding of the astrochronological timescale [27], termination of the CNS [26], carbon and oxygen stable isotope composition [39] and paleoclimate [12] of the SLB, as well as of their relationship with global events during the early Santonian to early Campanian.
Two large LTEs occurred in the SLB during the Late Turonian (lower K2qn) and Late Santonian–Early Campanian (lower K2n) [15]. The latter event is thought to have been the largest lake transgression to have occurred in the SLB and can be divided into two small stages (Fig 4): Lake transgression event a (LTE2a) during the deposition of lower K2n1 and b (LTE2b) of lower K2n2 [13]. During the Lake transgressions, the level of the lake increased and its area expanded [9,15], resulting in lake-wide anoxic events and the formation of productive source rocks for hydrocarbons [8,9,13,14,40–43]. Our new U-Pb age data indicate that the largest lake transgression events began in the Early Santonian at about 85.7 Ma (LTE2a at 85.7 Ma and LTE2b at 83.4 Ma), while two short-term high points on the sea-level curve occurred at 85.5 Ma and 83.2 Ma [5]. This suggests that the beginning of LTE2a, LTE2b, and the short-term rise in sea level occurred almost simultaneously, implying that the LTE documented in the region was closely related to global sea level changes. As the lake level rose and the lake area expanded, as a result of the high global sea level, the seawater likely entered into the Songliao paleolake on a periodic basis [24]. Consequently, a deep lake environment may have formed with oxygen-depleted bottom and brackish waters [14–15,44] resulting in the LAE, which would have provided favorable conditions for the formation of source rocks for hydrocarbons [13,24,43].
Data-point error ellipses are 2σ.
Although the relationship between ocean and continental climates during the Cretaceous has long been the subject of intense interest, there is still uncertainty regarding global OAEs and LAE of the SLB. OAE3 occurred during the Coniacian-Santonian [45,46], and the Western Interior Seaway records the classical OAE3, with high organic carbon contents during the Coniacian-Santonian [47]. The Cretaceous SLB has been well correlated and compared with the Western Interior Seaway [42]. Based on a floating orbital time scale, Locklair et al. [48] recognized three peaks in organic carbon content during the OAE3 interval, with middle Coniacian, early Santonian and Santonian/Campanian ages. The LAE2 of SLB is closely related to early Santonian OAE3 in terms of age. This may be because both were affected by the relatively high sea level of the Pacific Ocean and the high primary productivity during this period [12–14]. The SWIE of the SLB had the effect of linking the ocean and land together. The relationship between limno-eustasy or aquifer-eustasy has been proposed as a means of studying the Cretaceous climate and ocean circulation [28,49]. From such a perspective, this result implies that there may have been a close relationship between lakes and the ocean during the Cretaceous.
Conclusions
We have presented a new SIMS U-Pb zircon age from a bentonite bed located 9.88 m above the YNB of the X1-4 borehole. Twenty-five analyses of 25 zircons were obtained which produced a weighted mean age of 85.5±0.6 Ma (MSWD = 0.87). The largest LTE began in the Early Santonian at about 85.7 Ma (LTE2a at 85.7 Ma and LTE2b at 83.4 Ma), while two short-term high points on the sea-level curve occurred at 85.5 Ma and 83.2 Ma. Our new results imply that the beginning of LTE, LAE and SWIE occurred almost simultaneously with a short-term sea level rise, and that they probably had a close relationship with OAE3.
Acknowledgments
We thank Dr. Jan Bloemendal for polishing the manuscript. We thank the Editor, Gina Alvino, Su-Chin Chang and an anonymous reviewer for their assistance and insightful comments, which helped us to improve this article.
References
- 1. Schlanger SO, Jenkyns HC. Cretaceous oceanic anoxic events: cause and consequence. Geologie en Mijnbouw. 1976; 55: 179–84.
- 2.
Skelton PW, Spicer RA, Kelly SP, Gilmour I. The Cretaceous World. UK: Cambridge University Press; 2003.
- 3. Hay WW, Floegel S. New thoughts about the Cretaceous climate and oceans. Earth-Science Reviews. 2012; 115: 262–272.
- 4. Hu XM, Wagreich M, Yilmaz IO. Marine rapid environmental/climatic change in the Cretaceous greenhouse world. Cretaceous Research. 2012; 38: 1–6.
- 5. Haq BU. Cretaceous eustasy revisited. Global and Planetary Change. 2014; 113: 44–58.
- 6. Sames B, Wagreich M, Wendler JE, Haq BU, Conrad CP, Melinte-Dobrinescu MC, et al. Review: Short-term sea-level changes in a greenhouse world—A view from the Cretaceous. Palaeogeography Palaeoclimatology Palaeoecology. 2016; 441: 393–411.
- 7. Wang TT, Ramezani J, Wang CS, Wu HC, He HY, Bowring SA. High-precision U–Pb geochronologic constraints on the Late Cretaceous terrestrial cyclostratigraphy and geomagnetic polarity from the Songliao Basin, Northeast China. Earth and Planetary Science Letters. 2016; 446: 37–44.
- 8.
Yang WL. Petroleum Geology of Songliao Basin. Beijing: The Petroleum Industry Press; 1985. (In Chinese with English abstract).
- 9. Feng ZQ, Jia CZ, Xie XN, Zhang S, Feng ZH, Cross TA. Tectono-stratigraphic units and stratigraphic sequences of the nonmarine Songliao basin, northeast China. Basin Research. 2010; 22: 79–95.
- 10. Wang PJ, Mattern F, Didenko NA, Zhu DF, Singer B, Sun XM. Tectonics and cycle system of the Cretaceous Songliao Basin: An inverted active continental margin basin. Earth-Science Reviews. 2016; 159: 82–102.
- 11. Gao Y, Ibarra DE, Wang CS, Caves JK, Chamberlain CP, Graham SA, et al. Mid-latitude terrestrial climate of East Asia linked to global climate in the Late Cretaceous. Geology. 2015; 43: 287–290.
- 12. Wang CS, Feng ZQ, Zhang LM, Huang YJ, Cao K, Wang PJ, et al. Cretaceous paleogeography and paleoclimate and the setting of SKI borehole sites in Songliao Basin, northeast China. Palaeogeography Palaeoclimatology Palaeoecology. 2013; 385: 17–30.
- 13. Cao HS, Kaufman AJ, Shan XL, Cui H, Zhang GJ. Sulfur isotope constraints on marine transgression in the lacustrine Upper Cretaceous Songliao Basin, northeastern China. Palaeogeography Palaeoclimatology Palaeoecology. 2016; 451: 152–163.
- 14. Xi DP, Jansa L, Wan XQ, Zhang YY. Late Cretaceous paleoenvironment and lake level fluctuation in the Songliao Basin, northeastern China. Island Arc. 2011; 20: 6–22.
- 15. Huang QH, Chen CR, Wang PZ, Han MX, Li XJ, Wu DQ. The Late Cretaceous bio-evolution and Anoxic events in the ancient lake in the Songliao basin. Acta Micropalaeontologica Sinica. 1998; 15: 417–425 (In Chinese with English abstract).
- 16.
Gu ZW, Yu JS. Cretaceous bivalves of the region of Songhuajiang and Liaohe Rivers in Northeast China. Beijing: Science Press; 1999. (In Chinese with English abstract).
- 17. Zhang MM, Zhou JJ, Liu ZC. The age and depositional environment of the Cretaceous fossil fish bearing strata of the Northeast China. Vertebrata Palasiatica. 1977; 15: 194–198 (In Chinese).
- 18. Gao RQ, He CQ, Qiao XY. A new genus and species of cretaceous dinoflagellates from two transgressive beds in the Songliao Basin, northeast China. Acta Micropalaeontologica Sinica. 1992; 31: 19–30 (In Chinese with English abstract).
- 19. Hou DJ, Li MW, Huang QH. Marine transgressional events in the gigantic freshwater lake Songliao: paleontological and geochemical evidence. Organic Geochemistry. 2000; 31: 763–768.
- 20.
Wang PJ, Liu WZ, Shan XL, Bian WH, Ren YG, Du XD, et al. Depositional Events: Introduction, Example, Application. Changchun: Jilin Science and Technology Press; 2001. (In Chinese with English abstract).
- 21. Xi DP, Wang XQ, Feng ZQ, Li S, Feng ZH, Jia JZ, et al. Discovery of Late Cretaceous foraminifera in the Songliao Basin: Evidence from SK-1 and implications for identifying seawater incursions. Chinese Science Bulletin. 2011; 56: 3433–3436.
- 22. Huang YJ, Yang GS, Gu J, Wang PK, Huang QH, Feng ZH, et al. Marine incursion events in the Late Cretaceous Songliao Basin: constraints from sulfur geochemistry records. Palaeogeography Palaeoclimatology Palaeoecology. 2013; 385: 152–161.
- 23. Hu JF, Peng PA, Liu MY, Xi DP, Song JZ, Wan XQ, et al. Seawater incursion events in a Cretaceous paleo-lake revealed by specific marine biological markers. Scientific Reports. 2015; 5: 9508, pmid:25946976
- 24. Xi DP, Cao WX, Huang QH, Do Carmo DA, Li S, Jing X, et al. Late Cretaceous marine fossils and seawater incursion events in the Songliao Basin, NE China. Cretaceous Research. 2016; 62: 172–182.
- 25. Wan XQ, Li G, Chen PJ, Yu T, Ye DQ. Isotope stratigraphy of the Cretaceous Qingshankou Formation in the Songliao Basin and its correlation with Marine Cenomanian Stage. Acta Geologica Sinica. 2005; 79: 150–156 (in Chinese with English abstract).
- 26. He HY, Deng CL, Wang PJ, Pan YX, Zhu RX. Toward age determination of the termination of the Cretaceous Normal Superchron. Geochemistry Geophysics Geosystems. 2012; 13: Q02002,
- 27. Wu HC, Zhang SH, Jiang GQ, Hinnov L, Yang TS, Li HY, et al. Astrochronology of the Early Turonian–Early Campanian terrestrial succession in the Songliao Basin, northeastern China and its implication for long-period behavior of the Solar System. Palaeogeography Palaeoclimatology Palaeoecology. 2013; 385: 55–70.
- 28. Wagreich M, Lein R, Samese B. Eustasy, its controlling factors, and the limno-eustatic hypothesis–concepts inspired by Eduard Suess. Austrian Journal of Earth Sciences. 2014; 107: 115–131.
- 29. Wan XQ, Zhao J, Scott RW, Wang PJ, Feng ZH, Huang QH, et al. Late Cretaceous stratigraphy, Songliao Basin, NE China: Sk1 cores. Palaeogeography Palaeoclimatology Palaeoecology. 2013; 385: 31–43.
- 30. Deng CL, He HY, Pan YX, Zhu RX. Chronology of the terrestrial Upper Cretaceous in the Songliao Basin, northeast Asia. Palaeogeography Palaeoclimatology Palaeoecology. 2013; 385: 44–54.
- 31. Jiří S, Košler J, Condon DJ, Crowley JL, Gerdes A, Hanchar JM, et al. Plešovice zircon—A new natural reference material for U–Pb and Hf isotopic microanalysis. Chemical Geology. 2008; 249, 1–35.
- 32. Wiedenbeck M., Alle P, Corfu F, Griffin WL, Meier M, et al. Three natural zircon standards for U-Th-Pb, Lu-Hf, trace-element and REE analyses. Geostandards Newsletter. 1995; 19, 1–23.
- 33. Li XH, Liu Y, Li QL, Guo CH, Chamberlain KR. Precise determination of Phanerozoic zircon Pb/Pb age by multicollector SIMS without external standardization. Geochemistry Geophysics Geosystems. 2009; 10: Q04010,
- 34. Li QL, Li XH, Liu Y, Tang GQ, Yang JH, Zhu WG, et al. Precise U-Pb and Pb-Pb dating of Phanerozoic baddeleyite by SIMS with oxygen flooding technique. Journal of Analytical Atomic Spectrometry. 2010; 25: 1107–1113.
- 35. Stacey JS, Kramers JD. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters. 1975; 26: 207–221.
- 36.
Ludwig KR. Users manual for Isoplot/Ex rev. 2.49. Berkeley Geochronology Centre Special Publication. 2001; No. 1a, 1–56.
- 37. Huber BT, Norris RD, MacLeod KG. Deep-sea paleotemperature record of extreme warmth during the Cretaceous. Geology. 2002; 30: 123–126.
- 38. Gao YF, Wang PJ, Wang CS, Ren YG, Wang GD, Liu WZ, et al. Well site selecting, core profile characteristics and distribution of the special lithology in CCSD—Sk-1s. Acta Geologica Sinica. 2008; 82: 669–675 (in Chinese).
- 39. Chamberlain CP, Wan XQ, Graham SA, Carroll AR, Doebbert AC, Sageman BB, et al. Stable isotopic evidence for climate and basin evolution of the Late Cretaceous Songliao basin, China. Palaeogeography Palaeoclimatology Palaeoecology. 2013; 385: 106–124.
- 40. Bechtel A, Jia JL, Strobl SAI, Sachsenhofer RF, Liu ZJ, Gratzer R, et al. Paleoenvironmental conditions during deposition of the Upper Cretaceous oil shale sequences in the Songliao (NE China): Implications from geochemical analysis. Organic Geochemistry. 2012; 31: 76–95.
- 41. Wang PJ, Chen SM. Cretaceous Volcanic reservoirs and their exploration in the Songliao Basin, Northeast China. AAPG Bulletin. 2015; 99: 499–523.
- 42. Wang CS, Scott RW, Wan XQ, Graham SA, Huang YJ, Wang PJ, et al. Cretaceous climate changes recorded in Eastern Asian lacustrine deposits and North American Epieric sea strata. Earth-Science Reviews. 2013; 126: 275–299.
- 43. Feng ZH, Fang W, Li ZG. Depositional environment of terrestrial petroleum source rocks and geochemical indicators in the Songliao Basin. Science in China Series D. 2011; 54: 1304–1317.
- 44. Wang L, Song ZG, Qin Y, George SC. Paleosalinity significance of occurrence and distribution of methyltrimethyltridecyl chromans in the Upper Cretaceous Nenjiang Formation, Songliao Basin, China. Organic Geochemistry. 2011; 42: 1411–1419.
- 45. Jenkyns HC. Geochemistry of oceanic anoxic events. Geochemistry Geophysics Geosystems. 2010; 11: Q03004,
- 46. Wagreich M. “OAE 3”–regional Atlantic organic carbon burial during the Coniacian–Santonian. Climate of the Past. 2012; 8: 1447–1455.
- 47. Sageman BB, Meyers SR, Arthur MA. Orbital timescale and new C-isotope record for Cenomanian-Turonian boundary stratotype. Geology. 2006; 34: 125–128.
- 48. Locklair RE, Sageman BB, Lerman A. Marine carbon burial flux and the carbon isotope record of Late Cretaceous (Coniacian–Santonian) Oceanic Anoxic Event III. Sedimentary Geology. 2011; 235: 38–49.
- 49. Wendler JE, Wendler I, Vogt C, Kuss J. Link between cyclic eustatic sea-level change and continental weathering: evidence for aquifer-eustasy in the Cretaceous. Palaeogeography Palaeoclimatology Palaeoecology. 2016; 441: 430–437.