Distribution of continental red paleosols and their forming mechanisms in the Late Cretaceous Yaojia Formation of the Songliao Basin, NE China

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Cretaceous Research 32 (2011) 244e257

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Cretaceous Research

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Distribution of continental red paleosols and their forming mechanisms in theLate Cretaceous Yaojia Formation of the Songliao Basin, NE China

Xuebin Du a,b,*, Xinong Xie a,b, Yongchao Lu a,b, Jianye Ren a,b, Shun Zhang c, Penglin Lang d, Tao Cheng e,Ming Su a,b, Cheng Zhang a,b

aKey Laboratory of Tectonics and Petroleum Resources, China University of Geosciences, Ministry of Education, Wuhan 430074, ChinabKey Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, Chinac Institutes of Exploration and Development of Daqing Oilfield Company Ltd., Daqing 163712, Chinad Zhanjiang Branch of CNOOC Ltd, Zhanjiang 524057, ChinaeBeijing Research Center of CNOOC, Beijing 100027, China

a r t i c l e i n f o

Article history:Received 10 November 2009Accepted in revised form 9 December 2010Available online 15 December 2010

Keywords:Red paleosolsYaojia formationSongliao basinLithologyStratigraphyCretaceous oceanic red bedsOceanic anoxic eventsSediment Geochemistry

* Corresponding author. China University of GeoTectonics and Petroleum Resources, Ministry of EdWuhan 430074, China.

E-mail address: [email protected] (X. Du).

0195-6671/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.cretres.2010.12.010

a b s t r a c t

Red paleosols accumulated in the Yaojia Formation of the Songliao Basin during the Late Cretaceous period,which are enclosed by underlying Qingshankou dark mudstones and overlying Nenjiang dark mudstones.According to core descriptions and lithological analyses, three types of redsols are recognized. Type A redpaleosol with a thickness of 4e15 m is characterized by a complete redsol succession and observed influvial, delta plain, lakeshore facies and shallow lacustrine environments. Type B paleosol is developed inflood plains of fluvial systems and interdistributary areas of delta plains, and is characterized by thin-bedded red mudstones. Type C paleosol is featured by large complete sets of red mudstones or siltymudstones with some celadon(¼pale grayegreen) mudstones, which are formed onshore or in shallowlacustrine facies in weak hydrodynamic and oxic conditions. Combined with the analysis of tectonics,paleoclimate and lake-level variation, it is shown that the type A paleosol is the result of strong pedo-genesis due to a relative long period exposure caused by the underthrust of Pacific plate beneath the Euro-Asian plate since 88Ma,while the other types of paleosols are the exposure products of the development ofrelatively stable lake facies. The variation in mudstone color and thickness of different kinds of redpaleosols can be a typical marker in the boundary of different sequence units.

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1. Introduction

A paleosol is a soil that formed on a landscape of the past (Ruhe,1965; Retallack, 1997, 2001). Soils and paleosols can form becauseof physical, chemical and biological modification of sediment androcks. The original research on paleosols was in the Quaternary andnow they have been found in all the strata as old as Precambrian(Kraus, 1999). Paleosols can be found in continental depositionalsettings such as alluvial, deltaic and palustrine. Paleosols can alsoappear in marine strata if the sea-level fell to expose marine sedi-ments (Willis and Behrensmeyer,1994; Driese et al., 1994; Therrien,2005). Typical geologic applications of paleosols range from thelandscape reconstruction to paleoclimatic studies (Lee et al., 2003).Paleosols can provide detailed insight into ancient landscapes andlandscape evolution because the spatial distribution of different

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paleosols reflects the particular landforms and the geomorphicprocesses that operated in the ancient landscape (Bown and Kraus,1987; Willis and Behrensmeyer, 1994; McCarthy and Plint, 1999).Paleosols are also being used to understand the ancient climaticregimes and atmospheric changes over geologic time (Driese et al.,1994). Moreover, paleosols can be used in stratigraphic analyses,and one of their more recent applications is to sequence stratig-raphy in which paleosols are considered as the mark of strati-graphic diastem or unconformity. Some workers have usedpaleosols to calculate short-term sediment accumulation rates,both qualitatively and quantitatively (Willis and Behrensmeyer,1994; Kraus, 1999) and some consider that paleosols can reflecta complex interplay between sedimentation, erosion and non-deposition (Ginat et al., 2002; Sheldon, 2005).

Cretaceous red beds are widely distributed in East Asia (Miki,1992). Most studies are concerned with the analysis of paleo-climate from Early Cretaceous to the Late Cretaceous; however,literature about sedimentology, stratigraphy and tectonic eventsduring Cretaceous time is scarce. Red paleosols of Late Cretaceousage have been observed in the Yaojia Formation in the Songliao

X. Du et al. / Cretaceous Research 32 (2011) 244e257 245

Basin, enclosed by underlying Qingshankou dark mudstones andoverlying Nenjiang dark mudstones (Du et al., 2008). The origin ofthe relatively thick red paleosols in the Songliao Basin is, however,the subject of debate. In this study, core descriptions of severalboreholes and lithological data collected from many boreholes areused to document the distribution of red paleosols in the SongliaoBasin, and to explore the likely origins of these paleosols.Geochemical analyses of rock samples are then used to quantita-tively examine the vertical variation in the composition. The

Fig. 1. (A) The location of the Songliao Basin in northeastern China, showing the Central Dregional section. (B) Distribution of basement deep faults, there are 13 fault zones and thSongliao Basin in NW-SE direction. Position of sections matches those in (A).

ultimate goal is to interpret more accurately the origin and predictthe location of red paleosols in this basin to allow more effectivestratigraphic correlation.

2. Geological setting

The Songliao Basin in northeastern China, with a length of750 km and width of 330e370 km and total area of 26 � 104 km2, isone of the largest Cretaceous continental rifts in the world (Fig. 1A).

epression and surrounding basin margins. The solid line indicates the location of theey show an “X”-shaped fault pattern. (C) The constructed regional section across the

X. Du et al. / Cretaceous Research 32 (2011) 244e257246

The area of Songliao Plain is bordered to the west by the Daxin’anChain, to the northeast by the Xiaoxin’an Chain and to the northeastby the Zhangguangcai Chain (Gao et al., 1994; Jiang et al., 2005;Zhou and Littke, 1999).

The Songliao Basin, comprising a central depression andsurrounding basin margins (Fig. 1A), is the most important oil-productive basin in China, with 53 oil and 27 gas fields so far in thebasin (Zhou and Littke,1999; Hou et al., 2009). The largest oil field isthe Daqing field in the central part of the basin (Fig. 1A). Based onthe characteristics of regional uplift and depression, the SongliaoBasin can be divided into six 1st-order structural units: the northplunge, the central depression, the northeast uplift, the southeastuplift, the southwest uplift and the west slope zones. The main oil-and gas-producing province is situated in the central depressionregion (Fig. 1A), including the Daqing placanticline, Qijia-Gulongsag, Sanzhao sag, Changling sag and Chaoyanggou terrace.

According to geological and geophysical analysis, four groups offaults controlled the construction and evolution of the basin. Theirstrikes are NNE-NE, NNW-NW, nearly EW and NS, with a predom-inance of faults of NNE-NW and NNW-NW (Fig. 1B). Faults of NNE-NE make up three main fault zones (F1, F2 and F3) and they areoften intersected by faults of NNW-NW strikes, forming an“X”-shaped fault pattern (Jiang et al., 2005) (Fig. 1B).

The AeB profile (Fig. 1C) reveals a “steer’s head” form of thebasin structure which is related to the stretching of the crust and

Fig. 2. Generalized geological column of the Songliao Basin. The litho

mantle followed by thermal subsidence involved in the formationof rift basins (White and McKenzie, 1988).

The Songliao Basin fill includes Jurassic, Cretaceous, Paleogeneand Neogene clastic deposits with a maximum thickness of about10,000 m, underlain by Palaeozoic metamorphic, magmatic rocksand volcanic rocks (Gao and Cai, 1997). Late JurassiceEarly Creta-ceous syn-rift deposits (syn-rifting tectonic sequence) include theUpper Jurassic Huoshiling Formation (J3h), the Lower CretaceousShahezi Formation (K1sh), Yingchenzi Formation (K1y) and Den-glouku Formation (K1d). These formations are composed ofvolcanic and volcaniclastic rocks as well as alluvial and lacustrinesediments. Late EarlyeLate Cretaceous post-rift deposits (post-rifttectonic sequence), with a thickness of 1000e3000 m, uncon-formably cover all the faulted sub-basins and prevail in the wholebasin; the Quantou Formation (K1q) consists of coarse clastic rocksof fluvial origin in the lower part and lacustrine mudstones in theupper part (Figs. 1C and 2).

The lacustrine sandstones, mudstones, and shales of the Qing-shankou (K1qn), Yaojia (K2y) and Nenjiang (K2n) formationscontain the majority of the oil source rocks, reservoir rocks andseals of the Daqing Oil field (Li et al., 1995). Unconformably over-lying the K2n, the Sifangtai (K2s) and Mingshui (K2m) formationsare mainly composed of siliciclastic rocks deposited in alluvial andshallow lacustrine environments during basin inversion. The upperpart of the basin is infilled with Tertiary and Quaternary fluvial

logy of the different stratigraphic units is described in the text.

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deposits. The Tertiary is mainly concentrated in the west of thebasin and was eroded at the eastern margin. A generalized strati-graphic column for the Songliao Basin is shown in Fig. 2.

The Yaojia Formation (K2y; Late Cretaceous Coniacian and San-tonian), themain research target in this study,was deposited duringthe post-rift thermal subsidence and compression shear stage(Fig. 2). It consists of sandstones, siltstones andmudstones formed influvial, deltaic, and shallow lacustrine environments with a thick-ness ranging from 17 m to 218 m. This stratum is separated by anunconformity surface (sequence boundary of T11) from the under-lying Qingshankou Formation. Based on the interpretation ofseismic profiles, the boundary is characterized by obvious trunca-tion and erosion of the underlying strata and overlap for the over-lying strata, especially in the West Slope, the Southeast Uplift andthe Central Uplift zones. At the bottom of the Yaojia Formation,scoured surfaces of fluvial facies and redsols in the marginal area ofthe basin directly contact with underlying gray black shale of the

Table 1Major element compositions in Yaojia Formation, Songliao basin.

Well depth Na2O MgO Al2O3 SiO2 P2O5 K2

Shu118 1575.79 2.91 1.90 15.86 59.27 0.15 3.Shu118 1576.69 4.25 1.21 16.25 66.56 0.11 2.Shu118 1578.00 3.85 1.89 17.29 63.97 0.10 2.Shu118 1579.00 4.20 1.63 15.93 66.40 0.10 2.Shu118 1580.00 3.95 1.47 16.02 66.58 0.10 2.Shu118 1582.00 4.21 1.11 16.99 65.29 0.19 2.Shu118 1583.00 5.20 0.62 12.82 74.90 0.06 1.Shu118 1583.70 4.55 1.40 16.12 66.65 0.09 2.Shu118 1584.70 3.94 0.92 14.50 72.08 0.05 1.Shu118 1585.42 4.34 0.98 14.07 70.87 0.07 1.Shu118 1586.12 4.65 1.10 16.14 68.48 0.07 2.Shu118 1586.92 3.72 0.89 12.64 60.94 0.16 1.Shu118 1587.22 4.00 1.20 16.73 66.35 0.08 2.Shu118 1590.83 4.95 0.81 12.53 74.06 0.05 0.Shu118 1592.23 4.06 0.94 15.63 68.68 0.03 2.Shu118 1592.33 3.81 1.10 16.74 66.74 0.06 2.Shu118 1595.03 3.92 1.34 16.34 65.57 0.09 2.Shu118 1595.80 4.71 0.35 10.27 73.37 0.04 0.Shu118 1596.40 4.26 1.43 15.52 62.08 0.22 2.Shu118 1596.80 5.42 0.63 12.68 73.10 0.05 0.Shu118 1597.03 4.62 1.38 17.05 66.29 0.10 2.Shu118 1597.80 4.12 1.39 15.72 67.85 0.10 2.Shu118 1598.50 2.38 1.84 17.95 57.09 0.18 4.Shu118 1601.20 2.72 1.68 16.66 61.61 0.14 3.Shu118 1603.20 2.91 1.75 16.53 62.55 0.14 3.Shu118 1604.50 1.49 1.73 11.60 41.77 0.23 2.

Shu102 1455.51 4.13 1.05 16.17 67.91 0.09 2.Shu102 1456.86 4.00 1.21 15.39 68.18 0.12 2.Shu102 1458.86 4.36 0.96 14.29 70.98 0.08 1.Shu102 1459.86 4.35 0.85 10.35 65.65 0.07 1.Shu102 1460.06 4.12 1.00 15.83 68.05 0.08 2.Shu102 1461.16 4.25 0.99 15.62 68.69 0.08 2.Shu102 1461.71 4.56 0.76 13.13 73.05 0.05 1.Shu102 1461.61 4.06 0.78 10.21 64.70 0.06 1.Shu102 1463.16 3.84 1.14 15.24 68.05 0.12 2.

Ao16-2 1284.83 2.12 2.58 17.50 55.40 0.15 4.Ao16-2 1285.83 1.77 2.82 18.20 53.92 0.14 4.Ao16-2 1286.83 2.71 2.23 18.19 60.16 0.13 4.Ao16-2 1286.93 2.63 2.07 16.58 60.54 0.18 3.Ao16-2 1287.93 1.67 3.96 14.91 47.07 0.21 3.Ao16-2 1288.33 3.18 1.80 15.69 66.34 0.11 3.Ao16-2 1288.73 2.26 2.42 15.07 57.28 0.16 3.Ao16-2 1291.53 1.76 2.70 17.45 53.38 0.23 4.Ao16-2 1291.73 2.62 2.16 16.64 61.60 0.13 3.Ao16-2 1293.33 1.74 2.66 14.41 49.30 0.23 3.Ao16-2 1293.63 1.97 4.87 13.08 45.48 0.25 3.Ao16-2 1294.23 2.04 4.69 13.37 46.98 0.20 3.Ao16-2 1294.53 1.88 3.33 13.72 47.65 0.27 3.Ao16-2 1295.80 2.24 2.26 18.05 57.29 0.22 4.Ao16-2 1296.71 2.60 2.10 17.75 59.16 0.11 4.

Qingshankou Formation. Significant erosion and exposure markerscan be observed in the central part of the basin, such as stagnantmuddy pebbles, mud-cracks, calcareous nodules, calcareous rhizo-concretions and strong biodisturbance. In the Yaojia Formation,fluvial-deltaic and lacustrine systems are dominant, showinga fining-upward sequence. Red paleosols occur widely in the UpperCretaceous Yaojia Formation (Du et al., 2008), especially at animportant unconformity of third-order sequence (i.e. the sequenceboundary of T11), and boundaries of parasequences.

3. Samples and analytical methods

In this study, core descriptions of more than 20 boreholes,lithological data collected from more than 200 boreholes and twosedimentary stratigraphic sections are used to document thedistribution of the Yaojia Formation red paleosols in the SongliaoBasin, and to explore the likely causes of these paleosols.

O CaO TiO2 MnO Fe2O3 FeO H2Oþ CO2

01 4.47 0.62 0.12 2.47 2.12 3.72 3.1317 0.50 0.79 0.02 1.71 1.55 3.39 0.1248 0.49 0.97 0.01 1.86 3.20 3.61 0.1218 0.50 0.84 0.02 2.22 2.70 2.97 0.1451 0.42 0.84 0.01 2.34 1.97 2.84 0.8089 0.69 0.89 0.03 3.73 0.83 2.84 0.1424 0.71 0.49 0.02 1.32 0.90 1.19 0.2220 0.43 0.98 0.02 2.57 1.98 2.75 0.1060 0.42 0.55 0.01 1.30 1.33 1.85 0.1282 0.52 0.52 0.01 1.28 1.08 2.28 0.1257 0.43 1.02 0.01 1.78 0.85 2.62 0.1268 7.98 0.65 0.56 2.39 0.77 1.71 5.6872 0.48 0.92 0.01 3.33 1.12 2.79 0.1093 0.91 0.42 0.04 1.31 1.65 1.55 0.3758 0.46 0.71 0.10 3.30 0.78 2.39 0.1480 0.44 0.87 0.02 3.61 0.78 2.70 0.1663 0.54 0.91 0.04 3.69 1.50 3.12 0.1468 4.82 0.29 0.29 0.19 0.50 0.89 3.1329 1.54 0.75 2.03 2.39 1.92 2.75 2.6499 2.40 0.42 0.13 0.47 1.02 1.29 1.1640 0.50 1.03 0.01 1.73 1.45 3.16 0.1266 0.69 0.85 0.02 1.83 1.40 2.83 0.2938 2.52 0.70 0.07 5.94 1.00 4.17 1.4785 1.97 0.70 0.09 4.29 1.17 3.67 1.2592 1.60 0.69 0.05 3.46 1.37 3.66 1.1869 17.70 0.44 1.05 2.42 1.10 2.87 14.49

40 0.55 0.89 0.01 3.47 0.67 2.42 0.0642 0.61 0.78 0.02 3.00 1.10 2.81 0.1294 0.59 0.74 0.02 2.49 1.05 2.10 0.1613 7.78 0.27 0.76 0.80 1.20 1.09 5.2929 0.56 0.87 0.02 3.82 0.70 2.35 0.1426 0.58 0.80 0.01 3.04 0.73 2.65 0.1279 1.14 0.39 0.05 1.61 0.95 1.61 0.5911 8.74 0.32 0.72 0.86 1.20 1.05 5.7864 0.67 0.80 0.02 3.64 0.82 2.57 0.20

15 4.58 0.74 0.07 3.19 1.83 4.32 3.1364 3.70 0.74 0.07 4.80 2.05 4.81 2.0915 1.94 0.68 0.03 2.29 1.65 4.10 1.5076 3.23 0.65 0.05 2.29 1.55 3.76 2.5166 8.50 0.59 0.39 4.95 1.82 3.72 8.3231 0.95 0.68 0.03 2.56 1.40 3.13 0.6151 5.43 0.64 0.11 3.59 1.43 3.38 4.5052 3.98 0.67 0.06 6.18 1.37 4.15 3.3389 2.50 0.67 0.04 2.76 1.32 3.78 1.6871 10.20 0.51 0.25 4.06 1.17 3.50 8.0338 10.25 0.50 0.54 3.18 1.82 3.31 11.1637 9.26 0.51 0.47 3.05 1.68 3.19 10.9745 10.35 0.53 0.33 3.99 1.38 3.27 9.6059 2.35 0.67 0.04 5.03 1.38 4.12 1.5719 2.10 0.65 0.03 4.36 1.50 3.91 1.33

X. Du et al. / Cretaceous Research 32 (2011) 244e257248

A total of 54 paleosol samples including discrete ellipticalcarbonate nodules and tubular nodules were collected from threeboreholes (Ao16-2, Shu118, and Shu102) (Fig. 1A, Table 1). Freshwhole-rock samples were crushed in a steel crusher and powderedto 200-mesh size using an agate mill. Major element analysis wascarried out using a Phillips PW1480 X-ray fluorescence spectrom-eter at the Hubei Institute of Experimental Geology in Wuhan,Hubei province, China. H2Oþ was determined by gravimetry andCO2wasmeasured by volumetry. Estimates of error are gained fromthe standard deviation (�1s) of multiple analyses of standard rocks.

4. Distribution of red paleosols

4.1. Classification

Based on core descriptions and lithological data from rockfragments, three types of red paleosols are recognized in the YaojiaFormation.

Type A red paleosol, as a marker of unconformity of third-ordersequence, is developed in the base of the First Member of the YaojiaFormation (K2y1) with a thickness of 4e15 m, characterized by

Fig. 3. The features of Type A red paleosol in Yaojia Formation, showing the vertical structuris obvious net-type structure in this type of paleosol.

a brick-red redsol layer. The complete succession comprises darkred mudstones and mauve or dark red blocky mudstones in theupper part, net-type mauve and grayish green mudstones inthemiddlepart, and celadon mudstones orsilty mudstone with irreg-ular calcareous rhizoconcretions or calcareous sandstones in thelower part (Fig. 3). The ostracod Candona sp. nov. occurs in theupper red-gray mudstones, while in the lower red mudstones withgraymottles, the ostracod Cypridea panda is found (Fig. 3). This kindof red paleosol is widely distributed in the area from the basinalmargins to the central basin, and can be observed in fluvial, deltaplain and lakeshore facies, but is absent from deeper lacustrineenvironments.

Type B red paleosol is developed in the flood plain of fluvialsystems and interdistributary areas of delta plains in the FirstMember (K2y1) and Second/Third Member (K2y2þ3) of the YaojiaFormation. This paleosol is characterized by thin-bedded redmudstones with some fluvial sandstone. In some cases, calcareoussandstones with ripple lamination are observed in the lower part.Scour surfaces can be seen at the bottom. Type B red paleosols aredistributed separately in the basin margins and northern parts ofthe basin (Fig. 4).

e and variation in rock color, lithology, paleontology and magnetic susceptibility. There

Fig. 4. The features of Type B red paleosol, occurred in flood plain of fluvial systems and interdistributary areas of delta plains. This paleosol is characterized by thin-bedded redmudstones with some fluvial sandstone. In some cases, calcareous sandstones with ripple lamination are observed in the lower part. Scour surfaces can be seen at the base.

X. Du et al. / Cretaceous Research 32 (2011) 244e257 249

Type C red paleosol is developed in the First Member (K2y1) andSecond/Third Member (K2y2þ3) of the Yaojia Formation, charac-terized by large complete sets of red mudstones or silty mudstoneswith some celadon mudstones or silty mudstones, or alternatingred mudstones and gray mudstones; they formed onshore or inshallow lacustrine facies under weak hydrodynamic and oxidisingconditions while sedimentary supply was dominated by mud(Fig. 5). This redsol is distributed in the middle and southeasternparts of the basin, with relatively thick developments in theSoutheast Uplift zone.

4.2. Distribution

The spatial distribution of the three types red paleosols wasascertained by the interpretation of two cross-well facies correla-tions (EeW, NeS) and a depositional facies map of the YaojiaFormation (Figs. 6e8).

In the two cross-well facies correlations, the type A red paleosol,only found in the lowstand systems tract (LST), occurs along thebottom boundary of the Yaojia Formation which is recognized asthe sequence boundary of T11; its thickness range is 4e15 m,

Fig. 5. The features of Type C red paleosol, which is distinguished by large complete sets of red mudstones or silty mudstones with someceladonmudstones or silty mudstones, oralternating red and gray mudstones, which are formed onshore or in shallow lacustrine facies under weak hydrodynamic and oxidated conditions while sedimentary supply wasdominated by mud.

X. Du et al. / Cretaceous Research 32 (2011) 244e257250

decreasing from the eastern, western and northern basinal marginsto the central depression. Type B red paleosol is founded in alluvialplain and delta plain environments and is often associated withchannels. The thickness of type B red paleosol is up to 10 m and it isonly present in some western and northern isolated areas such asthe West slope zone, Fuyu structure zone, Wuyuer sag, Keshan-Yilong anticline zone and Heiyupao sag. In contrast to the abovetwo kinds of red paleosols, type C red paleosol with 5e20 mthickness is concentrated in the central basin and developed innear-shore and lake environments (Figs. 6 and 7).

According to the analysis of sequence stratigraphy, type B and Cred paleosols are distributed not only in the lowstand systemstracts (LST), but also in the transgressive systems tracts (TST) and in

the highstand systems tracts (HST). Most of the type B red paleosolis found in the northern part of the basin with only a few occur-rences in the west in the LST period. Type C red paleosol, is found inthe mid-southern basin and in the eastern local area. The arealextent of type B red paleosol is large in HST, small in TST and largeagain in HST, while in the corresponding intervals the distributionof type C red paleosols shows little change (Fig. 8).

5. Genesis of red paleosols

The formation of red paleosols is controlled by climate, organ-isms, topographic relief, parent material and age (Retallack, 2001).Each of these mechanisms can undoubtedly, in an appropriate

Fig. 6. A west-east trending cross-well correlation showing spatial distribution of three types of red paleosols in the Yaojia Formation of the Songliao Basin. Type A red paleosol isalong the bottom boundary of the Yaojia Formation and decreases from the eastern, western and northern basinal margin to the central depression.

X. Du et al. / Cretaceous Research 32 (2011) 244e257 251

situation, affect soil-forming processes. In the Yaojia Formation,variation in mudstone color and thickness of different kinds of redpaleosols seems to be influenced mainly by paleoclimate, topog-raphy and time.

5.1. The formational background of red paleosols

5.1.1. TectonicsIn general, post-rift subsidence usually originated from thermal

cooling after earlier lithospheric thinning, but in the Songliao Basinthe post-rift regimehas been complicated byepisodic compressions(Feng et al., 2010). Significant transition from thermal cooling toa combination of thermal subsidence and compression commencedaround 88 Ma, coincident with the age of reorganization of Pacificplate movements (Fig. 9). Then submarine volcanic activity in thewest Pacific Ocean increased abruptly, the Izanagi Plate ceased ina short period, the Kula Plate formed and the extension of the mid-oceanic ridge accelerated; in particular the direction of subductionof the Izanagi plate and Euro-Asia plate changed from NNW toWNW (Ren et al., 2002; Kravchinsky et al., 2002; Otofuji et al., 2003;

Fig. 7. A north-south trending cross-well correlation showing spatial distribution of three typaleosols is similar to that shown in Fig. 6.

Stepashko, 2006) (Fig. 10). Consequently, the Songliao Basin beganto encounter compression from the Southeast. At that time, anunconformity of interface T11 occurred in the Songliao Basin. Afterthen, compression phenomena became more and more obvious(Fig. 9). Since the end of the Late Cretaceous (about 65 Ma), thebasin underwent strong inversion and folding under strongcompression due to the subduction of the Kula-Pacific plates (Renet al., 2002). Hence, the east part of the basin has been upliftedand eroded.

5.1.2. Paleoclimate and lake-level variationPeriodical changes of paleoclimate and lake-level variation

usually have important effects on depositional filling and sequencestratigraphy.

According to the analysis of paleontology and geochemicalcharacteristics, there are four distinct episodes of climate changesin the Cretaceous of the Songliao Basin (Gao and Cai, 1997). Duringthe deposition of the Shahezi-Yingcheng formations, paleoclimatewas warm and wet, changing to semi-dry to dry heat in DengloukuFormation times. In Qingshankou to Nenjiang formations times the

pes red paleosols in the Yaojia Formation of the Songliao Basin. The distribution of red

Fig. 8. Distribution map of red paleosols in the lowstand systems tract (LST). (A) the transgressive systems tract (TST). (B) and the highstand systems tract (HST). (C) in the YaojiaFormation of the Songliao Basin. From LST to HST, the area of Type B red paleosol is big-small-big while the distribution of C red paleosol does not show major changes.

X. Du et al. / Cretaceous Research 32 (2011) 244e257252

paleoclimate became moist and humid, but returned to a dry, hotpaleoclimate in the interval represented by the Mingshui toSifangtai formations. The paleoclimate during the deposition of theFirst Member of the Yaojia Formation was dry and hot, but later(Second/Third Member) became a little humid and warm.

Carbon and oxygen isotope variations can be used to indicatecyclic fluctuations of the lake-level. Generally, in the humid-warmclimate, d13C and d18O value show a reduced trend because of lake-level rise caused by precipitation recharge, but when the climatebecomes dry-hot, the values of d13C and d18O show increases withwater evaporation. From the First Member to the Second/ThirdMember of the Yaojia Formation, the values of d13C and d18O displayhigh-low-high variation, which suggests a complete down-up-down cycle of lake-level fluctuation coincident with the changes ofsystems tract (Fig. 11).

5.2. The forming mechanisms of red paleosols

Type A red paleosol developed in the topmost part of the Qing-shankou Formation is characterized by purple or red mudstones, inwhich well-developed pedogenic slickensides and medium-sizedped structures are common, and irregular calcareous nodules arecommonly present. The color of the mudstones is predominantlydark red. It is interesting to note that plentiful fossils are observed inthe redmottledmudstones (Fig. 3), suggesting that thehost depositsformed in shallow lake environments were gray or black-gray likethe underlyingmudstones without pedogenesis. But those depositshave been changed to be red sediments through strong pedogenesisdue to exposure for a relative long period.

The obvious difference between type A paleosol and the othersis the presence of net-type structure, which is composed of mauve

Fig. 9. Map of stratigraphic framework and tectonic evolution in the Songliao Basin. Gray bars indicate tectonic subsidence rate, whereas the open bars indicate total subsidence.CORB ¼ Cretaceous Oceanic Red Beds; OAEs ¼ Oceanic Anoxic Events; LAEs ¼ Lacustrine Anoxic Events; CCRB ¼ Cretaceous Continental Red Beds.

Fig. 10. Sketch map of the movement of the Izanagi plate and Euro-Asia plate in late Cretaceous (Stepashko, 2006).

Fig. 11. Carbon and oxygen isotope variations from the Quantou to Nengjiang formations in the Songliao Basin; data from Zhang and Wang (1994), Ye and Wei (1996) and Hu(2005).

X. Du et al. / Cretaceous Research 32 (2011) 244e257254

and grayish green mudstone. Through the comparison of chemicalcharacteristics, it was found that only Fe2O3 is higher in the mauvepart than in the grayish part; other elements do not show suchpartitioning (Fig. 12). This phenomenon demonstrates that Fe inmauve mudstones was redistributed by gradual permeation ofgroundwater during the uplift of strata in a moist environment, andthat the process continued for a long time.

Based on the chemical analysis of some typical examples fromAo16-2, Shu118 and Shu102, it is established that the formation ofthe red beds is a clear process of desilicification and allitization.With the accumulation of Al2O3 and Fe2O3, the SiO2 contentdecreases rapidly (Table 1 and Fig. 12). At the base of the red bedthere is significant addition of CaO and some irregular calcareousrhizoconcretions or calcareous sandstones are formed (Fig. 12).Therefore, along a regional unconformity at the base of the UpperCretaceous Yaojia Formation, corresponding to the Turonian-Con-iacian boundary (about 88 Ma), paleosols include thick, well-differentiated layers of rock enriched in ferric oxide, as evidencedby high magnetic susceptibility (Fig. 3).

Relatively thick types B and C paleosols occur at the boundariesof parasequences and formed in the top of overbank or avulsion andonshore or shallow lake deposits. The magnetic susceptibility inthese redsols is much less than that in the type A paleosol. Thinpurple or red mudstones are interbedded with silty mudstones.Weakly-developed slickensides and roots are common. The color ofthe mudstones is predominantly light red, which may indicaterelatively short periods of exposure. In general, thin paleosols occurin the flood plains of fluvial systems because of the alternation of

frequent overbank deposits in the northern part of the SongliaoBasin, and relative thick paleosols are observed in shallow lakedeposits in the southeastern part of the Songliao Basin due to thedevelopment of relatively stable lake facies.

6. Discussion

6.1. Implications for sequence stratigraphy

Paleosols can be used in stratigraphic analyses (McCarthy andPlint, 1999). The variation in mudstone color and thickness ofdifferent kinds of red paleosols can be valuable markers of theboundaries of different sequence units.

Type A red paleosol developed in the topmost part of theQingshankou Formation and in the bottom of the Yaojia Formationis characterized by net-type structure and irregular calcareousnodules indicating gradual oxidation coupled with groundwaterdissolution and redistribution of calcium due to uplift. With thegradual change of the underthrust angle of the Pacific plate to theEuro-Asian plate since 88Ma, the distinct regional characteristics oftype A red paleosol, slowly thinning from east to west in the Son-gliao Basin, show that eastern uplift was stronger than in the west.Meanwhile, seismic reflection images show that the boundarysurface between the Qingshankou and Yaojia formations is char-acterized by large scale truncation unconformity. We drawa conclusion that the type A red paleosol is a widespread third-order sequence boundary indicative of a long exposure time andoxidation process at the base of the Yaojia Formation.

Fig. 12. The chemical composition of Type A paleosol (samples collected from Ao16-2 well) showing the accumulation of Al2O3 and Fe2O3 and the decreasing of SiO2.

X. Du et al. / Cretaceous Research 32 (2011) 244e257 255

Type B and C red paleosols are found in the middle part of theYaojia Formation, characterizedbypureandcompact redmudstonesformed in flood plain or shallow lacustrine environments, whichdisplay features indicative of autochthonous deposits and oxidationduring deposition. As amarker of lake-level relative change, the twotypes of paleosols can be used to divide parasequences.

6.2. Comparison between continental red paleosols and CretaceousOceanic Red Beds

Three Oceanic Anoxic Events (OAEs) occurred during Aptian-Albian (OAE1), Cenomanian-Turonian boundary (OAE2) and Con-iacian-Santonian (OAE3) times, characterized by wide distributionof black shales which indicate wide ranges of changes in paleo-environment and paleoclimate (Wu et al., 2009). At the same time,Cretaceous Oceanic Red Beds (CORB) are observed in UpperCretaceous sediments and widespread occurrences are reported

from the lower Turonian onward (Melinte and Jipa, 2005; Wanget al., 2005; Hu et al., 2005, 2005). Most authors attributed thesimultaneous onset of CORB deposition in the Turonian toa fundamental change in the oxidation state of the ocean, whichreflects changes of paleoenvironment and paleoclimate in theocean (Wan et al., 2005;Wang et al., 2004, 2005; Li et al., 2009) andfollowed the period of extensive mid-Cretaceous black shaledeposition. According to the comprehensive analysis of deposits,paleontology, paleoenvironment and paleoclimate, the black shalesimply anoxic events and the oceanic red beds imply oxic environ-ments. The change from OAEs to CORB is thought to be the result oflarge scale magmatic activities in the Cretaceous (Zhang et al.,2007; Mitchell et al., 2008).

Similar changes are observed in the Cretaceous Songliao Basin.The paleontological and organic geochemical results provide a lotof evidence for two marine-lake connection events between theSongliao lake and the East Asiatic Ocean via the Yitong Graben

X. Du et al. / Cretaceous Research 32 (2011) 244e257256

during the Late Cretaceous; the Songliao lake can be considered asthe edge of the East Asiatic Ocean and shows similar changes to theEast Asiatic Ocean during that period (Gao et al., 1994; Ye and Wei,1996; Hou et al., 2000; Sha et al., 2008).

There is abundant special evidence to support the idea of twogreat anoxic events in the Songliao Basin after the marineconnection phases, including the deposition of organic-rich blackshale and oil shale, calcareous nannofossils in the lacustrinecondensed sections, isotopic evidence from authigenic minerals,the appearance of 28, 30-bisnorhopane which originates froma typical anoxic bacteria, and lower diasteranes content inmudstone (Zhang and Wang, 1994; Hou et al., 2000; Huang, 2007;Huang et al., 2007; Wang et al., 2007). These two lacustrine anoxicevents happened in the Songliao Basin during the deposition of theFirst Member of Qingshankou Formation (K2qn1) (100 Ma) and theFirst-Second members of the Nenjiang Formation (K2n1þ2)(83.5 Ma), corresponding to Albian-Cenomanian and Santonian-Campanian intervals (Gao et al., 1994; Hou et al., 2000; Sha et al.,2008). The great lacustrine anoxic events occurred after the inter-vals of connection to the ocean, so they lag behind the OAEs.

In addition, the continental red paleosols in the bottom of theYaojia Formation are of Coniacian age (88 Ma), developing betweenthe black sediments of K2qn1 and K2n1þ2; they suggest an oxicevent similar to CORB after the lacustrine anoxic episode of K2qn1in the Songliao Basin. The red continental sediments of the K2y andthe black sediments of the K2qn1 and K2n1þ2 may indicate thealternation of anoxic and oxic environments, similar to the redoxcycles recorded in Cretaceous marine strata. Then, it’s speculatedthere would be some relationship between the alteration of anoxic-oxic-anoxic event in the Songliao Basin and the alteration of theredox in Cretaceous ocean.

7. Conclusion

The Late Cretaceous Yaojia Formation in the Songliao Basincontains three types of continental red paleosols developed instrata that were deposited in alluvial plain, delta plain and onshoreor shallow lacustrine environments. Paleosols of Type A are char-acterized by a succession composed of a brick-red redsol layer withobvious dark red mud in the upper part, net-typed mauve andgrayish green mudstones in the middle and celadon mudstoneswith irregular calcareous rhizoconcretions or calcareous sand-stones in the lower part. Paleosol characteristics in such succes-sions may attributed to a long time of exposure and oxidationprocess in the base of the Yaojia Formation, resulting from upliftcaused by the underthrust angle of Pacific plate to Euro-Asian platesince 88 Ma, and can be used as a marker of a widespread third-order sequence boundary.

Paleosols of Type B, composed of thin-bedded red mudstonesand calcareous sandstones, are observed occasionally in the lowerpart, and the third paleosol (Type C) is characterized by largecomplete sets of red mudstones or silty mudstones with someceladon mudstones or silty mudstones. These two types of paleo-sols are developed in the middle strata of the Yaojia Formation andcan be used as indicators of lake-level changes.

Although diagenetic processes also have affected these paleo-sols, detailed work permits comprehension of formingmechanismsand the background. In spite of some differences in depositionalenvironments and lithology among the three types of paleosols, thevariation in mudstone color and thickness of different kinds of redpaleosols can be used as markers of boundaries of differentsequence units. The results are used to interpret more accuratelythe origin and predict the location of red paleosols to allow moreeffective stratigraphic correlation in this basin.

Acknowledgements

We express our sincere appreciation to the journal editor (Prof.David J. Horne) and both reviewers for their careful review andconstructive suggestions that significantly improved the paper. Thestudy is supported by the National Nature Sciences Foundation ofChina (NSFC) (No. 40872076), the Key Natural Science Foundation ofHubei Province (No. 2008CDA095), the Young Teachers ResearchFund for the Doctoral Program of Higher Education of China(No. 200804911520) and China’s Post-doctoral Science Fund(20090450184).Wewould like to thank theDaqingOilfield PetroleumExploration and Development Institute for partially supporting thiswork.

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