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Cretaceous Research 57 (2016) 50e65

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Cretaceous Research

journal homepage: www.elsevier .com/locate/CretRes

Cretaceous sedimentary basins in Sichuan, SW China: Restoration oftectonic and depositional environments

Yingqiang Li, Dengfa He*, Longbo Chen, Qinghua Mei, Chuanxin Li, Li ZhangThe Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Accumulation Mechanism, The Ministry of Education, China University of Geosciences,Beijing 100083, China

a r t i c l e i n f o

Article history:Received 5 June 2014Received in revised form10 July 2015Accepted in revised form 21 July 2015Available online 25 August 2015

Keywords:Cretaceous sedimentary basinsRestorationSichuan BasinTectonoedepositional environmentTemporal-spatial evolution

* Corresponding author.E-mail addresses: yingqiangcugb@126.com (Y.

(D. He).

http://dx.doi.org/10.1016/j.cretres.2015.07.0130195-6671/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

This study documents sediment infill features and their responses to the tectonic evolution of theSichuan Basin and adjacent areas. The data include a comparison of field outcrops, well drillings, inter-well correlations, seismic data, isopach maps, and the spatial evolution of sedimentary facies. We dividedthe evolutionary history of the Sichuan Cretaceous Basin into three stages based on the following tec-tonic subsidence curves: the early Early Cretaceous (145e125 Ma), late Early Cretaceous to early LateCretaceous (125e89.8 Ma), and late Late Cretaceous (89.8e66 Ma). The basin underwent NWeSEcompression with northwestward shortening in the early Early Cretaceous and was dominated by al-luvial fans and fluviolacustrine sedimentary systems. The central and northern areas of the Sichuan Basinwere rapidly uplifted during the late Early Cretaceous to early Late Cretaceous with southwestwardtilting, which resulted in the formation of a depression, exhibited southwestward compression, and wascharacterized by aeolian desert and fluviolacustrine deposits. The tectonic framework is controlled by theinherited basement structure and the formation of NE mountains, which not only affected the clasticsupply of the sedimentary basin but also blocked warm-wet currents from the southeast, which changedthe climatic conditions in the late Late Cretaceous. The formation and evolution of Cretaceous sedi-mentary basins are closely related to synchronous subtle far-field tectonism and changes in climate anddrainage systems. According to the analysis of the migration of the Cretaceous sedimentation centers,different basin structures formed during different periods, including periods of peripheral mountainasynchronous thrusting and regional differential uplift. Thus, the Sichuan Cretaceous sedimentary basinis recognized as a superimposed foreland basin.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

The Cretaceous period is recognized as a key transitional periodof plate tectonic evolution in China and adjacent areas and as asignificant period during the Mesozoic intracontinental orogeny ofSouth China (Wu, 2006; Li, Zhang, Dong, & Li, 2012a; Li, Zhang,Dong, Johnston, 2014), during which large-scale taphrogenic andmagmatic activity occurred that generated the large “South ChinaExtensional Basin and Igneous Province” (Zhou, Sun, Shen, Shu, &Niu, 2006; Shu et al., 2009; Li, et al., 2014). This transition wasmainly manifested by the transition from northesouth divergenceto eastewest divergence during the Cretaceous (Wu, 2006).

Li), hedengfa282@263.net

Neogenic structures played a dominant role in the eastern region ofSouth China, and tectonic inheritance played a dominant role in thewest (Li, 1996; Wu, 2006). Previous research studies regardingCretaceous tectonics in South China have focused on the easternregion of South China (e.g., Shen et al., 2012; Hu et al., 2012; Wang,2013; Wang, et al., 2013a; Li et al., 2012a; 2014). However, due tosevere destruction, geologists have not considered complex tec-tonic evolution, wide deposition with subsequent erosion, or pooroil-gas accumulation conditions in the western region of SouthChina as priorities.

The Sichuan Basin is located in the western area of the SouthChina Block and represents this region. Reconstruction of theSichuan Cretaceous sedimentary basins, which are related to theMesozoic intracontinental orogeny, can provide significant clues tohelp reveal the Cretaceous temporal-spatial evolution of thetectono-depositional environment in the western part of the SouthChina Block. Regional uplift following the Cretaceous converted the

Y. Li et al. / Cretaceous Research 57 (2016) 50e65 51

eastern part of the Upper Yangtze into an erosional area (e.g., Yuanet al., 2010; Tang, Yan, Qiu, Gao, & Wang, 2013; Li & Shan, 2011).Currently, residual Cretaceous rocks only exist in the southern,western, and northwestern Sichuan Basin, which are characterizedby “gray beds” in the north and “red beds” in the south. Althoughmany researchers agree that the Sichuan Basin entered a shrinkingand decline stage at the beginning of the Cretaceous period, mostprevious studies that have focused on lithofacies paleogeography,paleostructure, paleoclimate, paleoenvironment, or sedimentarybasin properties have focused on the present-day residual basin(e.g., Chen,1987; Guo, Deng,&Han,1996;Meng,Wang,&Hu, 2005;Long, Chen, Lin, Xu, & Cheng, 2011; Geng, 2011). However, no in-tegrated studies have combined tectonics and sedimentology, andsystematic and dynamic research is lacking. Consequently, thefollowing questions must be answered: Did the Cretaceous hiatusin the eastern Sichuan Basin result from a lack of deposition in thelate depositional period or from complete erosion during the upliftperiod? How large was the Sichuan Basin in the Cretaceous? Whatwas the tectonic and depositional environment?

To answer these questions, our study attempts to reconstructSichuan Cretaceous sedimentary basins by interactively synthe-sizing available data. The data sets used in this study includecomparisons of abundant field outcrops, well drillings, inter-wellcorrelations, seismic data, isopach maps, and the spatial evolutionof sedimentary facies. Although preliminary in nature, our studyaims to provide a starting point for more comprehensive futurestudies.

2. Geological setting

2.1. Tectonic setting of the Sichuan Basin

The Sichuan Basin is located in centralesouthern Asia, in centralChina, and in the western area of the South China Block (Fig. 1),including the eastern Sichuan province and Chongqing City, and issurrounded by peripheral mountains (i.e., the Longmen Mts. in thewest, Qiyao Mts. to the east, Daba Mts. to the north and

Fig. 1. Location of the South China Block and its relationships with other tectonic uni

DaliangeDalou Mts. in the south) (Fig. 2) (e.g., Liu, Deng, Li, & Sun,2012a). Bounded by the current residual terrestrial stratigraphicboundary, the Sichuan Basin covers an area of 18� 104 km2, makingit one of the four largest basins in China.

The major landmasses in China began to converge during thelate Indosinian period (the Late Permian to Triassic) (Zhang, Meng,& Lai, 1995; Ma et al., 2004a). Together with the Laurasian andGondwanan continents, these landmasses converged to form Eur-asia, and the Chinese terrestrial basin formed (Ma et al., 2004a).During the Late Jurassic to Early Cretaceous, the Paleo-Pacific platewas subducted below the Eurasian plate toward the north-northwest (Northrup, Rovden, & Burchfiel, 1995; Zhou & Li,2000). The South China plate, the north part of the South ChinaSea plate and the East China Sea plate were subjected to obliquecollision and shear orogeny, and the Tibetan plate was extrudedeastward (Fig. 1). These movements subjected the southern area ofChina to multiple strong deformation episodes that formed theSouth China Yanshanian (Jurassic to early Early Cretaceous) intra-continental orogenic belt and the eastern Yanshanian “plateau” andresulted inwidespreadmagmatic intrusions and volcanic activity inthe southeast area and many strike-slip pull-apart basins (Zhou &Li, 2000; Wu, 2006; Chen et al., 2009; He et al., 2011; Wang, Fan,Zhang, & Zhang, 2013b). The tectonic framework of the SichuanBasin and adjacent areas is restricted to three directions (thenorthwest, northeast, and southeast), with structural inversionbetween the east and west. In the Late Cretaceous, the interactionsbetween the Neo-Tethys and the Pacific tectonic domains changedthe tectonic character of South China to eastern strike-slip exten-sion and western compressional thrusting, which resulted in theformation of a large number of extensional rifted basins in theMiddleeLower Yangtze and produced large-scale magmatic andhydrothermal activity in the east (Wang et al., 2013b).

2.2. Stratigraphy

The Sichuan Basin is a multi-cycle superimposed basin with amarine carbonate platform and a continental clastic rock system

ts. The box shows the location of the Sichuan Basin (edited after Li et al., 2012a).

Fig. 2. A sketched geological map showing the distribution of Cretaceous strata and major terranes. The locations of inter-well correlations AA0 , BB0 and cross-section CC0 (dottedlines) and some typical wells are shown in the map and have the following profile names: 1. Nanjiang Shahe; 2. Wangcang Changle; 3. Jian'ge Yaojia; 4. Well Chuanfeng 563; 5. WellChuanhe 100; 6. Well Chuanxiao 107; 7. Well Chuanwen 303; 8. Chongzhou Huaiyuan; 9. Qionglai Jiaguan; 10. Tianquan Jinmenguan; 11. Hongya Zhongshanping; 12. Leshan Dafosi;13. Yibin Sanhechang; 14. Yibin Jinping; 15. Hejiang Shizi; 16. Xishui Tucheng; W-1. Well Dayi 6; W-2. Well Dayi 7; W-3. Well Guankou 2; W-4. Well Baima 9; W-5. Well Baiqian 58.

Y. Li et al. / Cretaceous Research 57 (2016) 50e6552

deposited on the Yangtze paraplatform in South China (Wang,Zhao, Zhang, & Wu, 2002; Ma et al., 2004a; 2004b; He et al.,2011). The Cretaceous deposits known as “red beds” are charac-terized by terrestrial brickered clastic deposits with a thickness ofapproximately 3000 m and account for nearly 40% of the basin area(Guo et al.,1996;Wang et al., 2002). Red beds arewidely distributedalong the east side of the LongmenMts., along the south side of theNorth Daba Mts., and in the south and southwest regions of theSichuan Basin (Fig. 2). Cretaceous red beds are comparativelycomplete in the western Sichuan Basin but absent in the south andsouthwest Lower Cretaceous. The Lower Cretaceous only remainsin the north and northwest and the Upper Cretaceous is absent.Different regions use different nomenclature (e.g., Guo et al., 1996;Wan, Chen, & Wei, 2007; Meng, 2012; Cao, 2013) (Fig. 3).

2.3. The regional tectonic uplift events

It is generally accepted that the SongpaneGarze Belt has un-dergone at least two major orogenic events since the Mesozoic(Burchfield, Chen, Liu, & Royden, 1995; Arne et al., 1997;Harrowfield & Wilson, 2005; Zhou, Yan, Vasconcelos, Li, & Hu,2008; Roger, Jolivet, & Malavieille, 2010), the Late Triassiccompressional event related to convergence between the NorthChina, South China, and Qiangtang Blocks (Enkin, Yang, Chen, &

Courtillot, 1992; Roger et al., 2010; Yan, Zhou, Li, & Wei, 2011a)and the Paleogene to Neogene deformation related to the India-eAsia collision (Burchfield et al., 1995; Arne et al., 1997). In addi-tion, Roger, Malavieille, Leloup, Calassou, and Xu (2004) proposedthat a major tectonic decollement in the SongpaneGarze fold beltoccurred before the Early Jurassic. When accounting for severalpieces of geological evidence, we support the view that the uplift inthe Longmen Mts. mainly occurred around the Early Pleistocene(e.g., Kirby et al., 2002; Godard et al., 2009; Tang, Guo,& Qiao, 2011;Wang et al., 2012; Li et al., 2012b ; Tan, Lee, Chen, Cook,& Xu, 2014),with deformation progressively propagating northward and east-ward (Yin& Harrison, 2000). The Dabashan fold-thrust belt formedbefore the Late Cretaceous based on the preservation of the age-elevation relationships and the lack of distinct age changes acrossthe tectonic structures (Zhang et al., 2013a). The Daba Mts. beganforming in the Early Cretaceous (120e110 Ma) and experiencedrapid, steady, and accelerated periods of growth. In addition, theuplift dating shows progressively younger uplift with southwest-ward extension (Shen, Mei, Xu, Tang, & Tian, 2007). Tian et al.(2012a) proposed that the onset of exhumation in the Daba ShanForeland Basin began during AptianeAlbian time (~100e125 Ma).Rapid uplift processes occurred in the MicangeHannan dome atapproximately 90 Ma and 15 Ma (Tian et al., 2010; 2012b) andspread to the northern Sichuan foreland basin in theMideCenozoic

Fig. 3. Stratigraphic correlation of the Cretaceous period in the Sichuan Basin and adjacent areas. The Cretaceous stratigraphic correlation is modified after Guo et al. (1996), Wanet al. (2007), Meng (2012), and Cao (2013). The later ages are adjusted according to the International Chronostratigraphic Chart v2015/01. The locations of basins are shown in Fig. 2.

Y. Li et al. / Cretaceous Research 57 (2016) 50e65 53

(ca. 30 ± 5 Ma; Tian et al., 2012b). Since the Yanshanian, the effectsof subtle far-field tectonism in southeastern Sichuan producedconstant northwestward compression from west of Hunan, Hubei,and from eastern Chongqing to central Sichuan and formed base-ment decoupling, thick-skinned widely spaced synclines, thin-skinned widely spaced anticlines, and gentle folds (Yan, Zhou,Song, Wang, & Malpas, 2003). Apatite fission-track thermal his-tory simulations indicate that the time of strongest uplift wasapproximately 165 Ma in the Sangzhi synclinorium of the westernHunan and Hubei fault fold belt and 95e65 Ma in the Huaying Mts.(Mei, Liu, Tang, Shen, & Fan, 2010). Shen, Mei, and Xu (2009) re-ported that the eastern Sichuan Basin experienced two rapidcooling events (~100e70 and after ~15 Ma) since the Cretaceous.The first rapid cooling is associated with Mesozoic tectonic reac-tivation that began at 100 Ma and produced folds and faults in theeastern Sichuan Basin. Tang et al. (2013) proposed the existence of aCretaceous Pan-Yangtze Basin within the central South China Blockthat was partitioned by the exhumation of the Xuefeng Mts. (whichunderwent rapid denudation after ~84 Ma). In addition, the southand north Mayang basins were uplifted more slowly from 67 to84 Ma, respectively (Tang et al., 2013). Deng et al. (2013) suggestedthat rapid cooling and exhumation events occurred at 120e80 Maand 20e10 Ma across the Sichuan Basin and that the regionalapatite fission-track (AFT) age, regional AFT length, and regionalAFT erosion rates with the oldest ages at the center and progres-sively younger ages towards the southwest.

A comprehensive study of the tectonic uplifting of the Meso-eCenozoic in the Sichuan Basin indicated the following regionalvariations in the Sichuan Basin. Rapid uplift occurred in northernSichuan at 110e70 Ma (Fig. 4), a period of stabilization occurred inthe Paleogene and a period of uplift occurred in the Neogene. Thecentral Sichuan area exhibited slow uplift from 85 to 65 Ma (Fig. 4),with stable uplift in the Paleogene and accelerated uplift in theNeogene. Tectonic deformation of the eastern Huaying Mts.occurred from 120 to 70 Ma with characteristics of westwardprogressive younging (Fig. 4). The eastern Sichuan was upliftedrapidly from 85 to 65 Ma and continued to uplift slowly with theformation of a Jura-type fold belt. The end of subsidence in thesouthern Sichuan area occurred at approximately 90Ma, was stablefrom 90 to 50 Ma and was reactivated in the late Neogene.

3. Data and methodology

Lithology, stratigraphy, paleogeography, sedimentary facies, andtectonic subsidence have been used to account for the restoration

of the Sichuan Cretaceous sedimentary basins. The study approachpresented here is an integration of points (wells or measuredgeological sections), lines (cross sections), and planes (planforms)data (Chen et al., 2014) and provides new information regarding thetemporal and spatial evolution of the tectono-depositional envi-ronment. The data sets include a comparison of field outcrops, welldrillings, inter-well correlations, seismic interpretations, and sedi-mentary facies in the Sichuan Basin.

(1) Field outcrop data: Twelve columnar sections from NanjiangShahe, Wangcang Changle, Jian'ge Yaojia, ChongzhouHuaiyuan, Qionglai Jiaguan, Tianquan Jinmenguan, HongyaZhongshanping, Leshan Dafosi, Yibin Sanhechang, Yibin Jin-pingzhen, Luzhou Hejiang Shizi, and Guizhou XishuiTucheng (locality of each section is marked by triangles inFig. 2) were collected and interpreted using sedimentarysubfacies analysis based on lithofacies, grain size and sedi-mentary structures.

(2) Well data: Four wells, Chuanfeng 563, Chuanhe 100,Chuanxiao 107, and Chuanwen 303 (the location of each wellis marked by circles in Fig. 2), were described and interpretedusing sedimentary subfacies analysis based on logging data.Six wells with relatively complete logging data from theWestern Sichuan, Chuanwen 303, Dayi 6, Dayi 7, Guankou 2,Baima 9, and Baiqian 58 (their locations aremarked by circlesin Fig. 2) were selected to recover the Cretaceous subsidencehistory.

(3) Inter-well correlations: Two inter-well correlations, AA0 andBB0, were integrated with well data, and interpretations ofoutcrop sections were used for correlation, interpretationand sedimentology analyses. We partitioned the sedimen-tary facies in detail to clarify the spatial evolution of sedi-mentary facies with time.

(4) Seismic data: Seismic grid data (including 2-D seismic surveylines and 3-D pre-stack depth migration data) covering theentire basin and wells with synthetic seismograms wereused to trace the horizons and constrain the thickness of theCretaceous strata.

(5) Strata isopach maps: Isopach maps showing the currentthicknesses were defined using data from wells, measuredgeological profiles, and seismic profiles.

(6) Data from sedimentary facies with planar beds: Sedimentaryfacies with planar beds were defined using comprehensivedata from field outcrops, well drillings, inter-well correla-tions, and seismic interpretations.

Fig. 4. Sketch map showing the time of uplifting and space distribution of the Sichuan Basin and peripheral areas. Circles with different colors in the left corner legend show AFTdata results from different authors. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Y. Li et al. / Cretaceous Research 57 (2016) 50e6554

In this paper, the standard 1-D backstripping technique (e.g.,Watts & Ryan, 1976; Steckler & Watts, 1978; Watts, Karner, &Steckler, 1982; Scheck & Bayer, 1999) was employed to recon-struct basin subsidence during Cretaceous times. This techniquerestores the original thickness of sediment units by beginning fromthe lowest unit of a stratigraphic section and moving step by stepthrough the overlying units (Sclater & Christie, 1980).

Drilling information (unpublished data of the CNPC and Sino-pec) obtained during hydrocarbon exploration can be used tocompile the lithological compositions for each well in which thefractions of sandstone, siltstone, clay, and carbonates were previ-ously defined. The compaction corrections were conducted by us-ing the standard exponential relations of porosity versus depth andthe widely used North Sea basin lithological parameters proposedby Sclater and Christie (1980). The paleo-water depth was assumedto equal zero because deepwater formations were lacking; thus, theadditional water load can be ignored. Eustatic change correctionswere calculated from the long-term eustatic curve presented byHaq, Hardenbol, and Vail (1987). The ages of the Cretaceoussequence boundaries in the study area are listed in Fig. 3, and thelater ages are adjusted according to the International Chro-nostratigraphic Chart v2015/01.

To provide a clear image of the evolution of Cretaceous subsi-dence in the Western Sichuan Basin, subsidence curves from sixshallow wells were produced using Basin Mode 2009 and fit

together on a computer screen using CorelDRAW. We only calcu-lated “tectonic subsidence” curves that reflected the tectonic ordriving mechanisms of a basin (Bond & Kominz, 1984) because amirror-image relationship potentially occurred between the upliftof the longmen Shan thrust belt and the subsidence of the WesternSichuan foreland basin following ~60 Ma (Liu, Luo, Dai, Arne, &Wilson, 1996).

4. Results

4.1. Basin tectonic subsidence

The subsidence curves indicate that the western Sichuan Basinwas characterized by episodic subsidence in the Cretaceous period;thus, we divided the evolutionary history of the western SichuanCretaceous basin (extended to the whole basin) into three stages:

(1) Oscillating subsidence in the early Early Cretaceous(145e125 Ma): The rate of subsidence varies slightly indifferent areas and at different times with a short duration ofuplifting in the late stage (Fig. 5).

(2) Stable subsidence during the late Early Cretaceous to earlyLate Cretaceous (125e89.8 Ma) with an average subsidencerate of approximately 10 m/My (Fig. 5).

Y. Li et al. / Cretaceous Research 57 (2016) 50e65 55

(3) Rapid subsidence in the late Late Cretaceous (89.8e66Ma) atan average rate of ~30 m/My (Fig. 5).

4.2. Sediment infill features

4.2.1. Description of SWeNE inter-well correlationsAA0 is a SWeNE profile showing sedimentary filling (Fig. 6) from

Qionglai to Nanjiang (the location is shown in Fig. 2 AA’). Ninecolumnar sections or wells were joined together, and the Creta-ceous lithofacies and sedimentary fillings are described brieflybelow.

� Qionglai Jiaguan: The local lithostratigraphic subdivision con-tains the Jiaguan Fm. (Formation) (K1�2j) and Guankou Fm. (K2g)(Fig. 6). The Jiaguan Fm. of the Lower Cretaceous is 210 m thick,is characterized by mottled, thick conglomerate, sandy-conglomerates, conglomerates with salt, and contains poorlysorted and moderately rounded conglomerates with pebblediameters of 1e10 cm. The Jiaguan Fm. of the Upper Cretaceousis 140 m thick and consists of coarse sandstones in the upperpart and salt containing sandstones in the lower part. TheGuankou Fm. of the Upper Cretaceous is 800 m thick and con-tains a brown-red cyclothem with unequal siltstone andmudstone thicknesses and comparatively thick marlstones, fineconglomerates, gypsums (Fig. 7A), and salt layers (Fig. 7B).

� Chongzhou Huaiyuan: The Tianmashan Fm. (K1t) is 265 m thickand is characterized by thick conglomerates at the bottom thatconsist of cyclothem and unequal thicknesses of fine-sandstones, siltstones, and mudstones with increasing grainsizes with depth (Fig. 6). The Lower Cretaceous Jiaguan Fm. is353 m thick and is composed of red siltstones, sandstones,pebbly sandstones and conglomerates with trough crossbedding and characterized by fine-grains in a matrix of coarsegrains. The Upper Cretaceous Jiaguan Fm. is 194 m thick and hassimilar features and a finer grain size. The Guankou Fm. consistsof 85-m-thick conglomerates at the top with poorly sorted andmoderately rounded clasts.

Fig. 5. Tectonic subsidence curves of typical wells in the western Sichuan Basin. Everysolid line in the figure above represents the tectonic subsidence history of where a wellis located.

� Well Chuanwen 303: The Cretaceous strata, from bottom to top,are assigned to the Cangxi Fm. (K1c), Bailong Fm. (K1b), QiqusiFm. (K1q), Jiaguan Fm. (K1j and K2j), and Guankou Fm. (K2g)(Fig. 6). The Cangxi Fm. is 180 m thick and mainly consists ofgray or yellow pebbly sandstones and mudstones with crossbedding. The Bailong Fm. is 258 m thick and consists mainly ofsandstones and mudstones with horizontal bedding and ripplebedding. The Qiqusi Fm. is 216 m thick, and the lithofacies aresimilar to those of the Bailong Fm. The Jiaguan Fm. is composedmainly of brown-red or reddish sandstones with bimodal crossbedding and is 420 m thick. The Guankou Fm. consists mainly ofbrown mudstones and siltstones with interbeds of reddishlaminated sandstones. This formation is also a salt-bearing layerwith a thickness of up to 550 m.

� Well Chuanxiao 107: Only the Cangxi Fm. (K1c) and Bailong Fm.(K1b) of the Lower Cretaceous remained in this well (Fig. 6). TheCangxi Fm. consists mainly of gray sandstones and mudstonesinterbedded with some pebbly sandstone layers, except for a~65-m-thick layer of coarse-grained feldspathic pebbly sand-stones at its base. The Bailong Fm. is composed of gray fine-grained sandstones and mudstones with horizontal bedding.

� Well Chuanhe 100: The local lithostratigraphic subdivision ofthe Jianmenguan Fm. (K1jm) is ~750 m thick and containsdifferent lithofacies between the lower and upper sections ofthe lithologic log (Fig. 6). The lower portion is 255 m thick andmainly consists of mudstones and siltstones interbedded withsome sandstone layers. The upper part is composed of sand-stones interbedded with some siltstone and mudstone layers.

� Well Chuanfeng 563: The Jianmenguan Fm. (K1jm) is ~450 mthick and mainly consists of gray sandstones and siltstones withinterbeds of gray mudstone (Fig. 6).

� Jian'ge Yaojia: The local lithostratigraphic subdivision includesthe Jianmenguan Fm. (K1jm), Hanyangpu Fm. (K1h), and Jian'geFm. (K1jg) (Fig. 6). The Jianmenguan Fm. is > 400 m thick and ischaracterized by poorly sorted and moderately rounded con-glomerates with interbeds of sandstones (Fig. 7C). In addition,~100-m-thick mudstones and siltstones with interbeds oflaminated sandstones occur. Differences in the lithology andsedimentary structure occur among the lower, middle and up-per portions of the Hanyangpu Fm. The lower, 105-m-thickportion consists mainly of gray coarse sandstones and mottled,well-sorted and rounded conglomerates. The middle part is155 m thick and mainly includes mid-to fine-grained sand-stones with trough cross bedding and scour surfaces. The upperpart is 170 m thick and is characterized by gray siltstone withinterbedded mudstone and parallel bedding and ripple lami-nations. The lower part of the Jian'ge Fm. consists mainly of grayand fine conglomerates and coarse sandstones with troughcross bedding (Fig. 7D and D0). However, the grain-size of theupper part becomes fine and lateral accretion cross bedding isobserved.

� Wangcang Changle: The Cangxi Fm. (K1c), Bailong Fm. (K1b), andQiqusi Fm. (K1q) in the Lower Cretaceous occur in this section(Fig. 6). The Cangxi Fm. consists of 4 sequences graded fromcoarse at the bottom to fine at the top. The first sequence, whichis 95 m thick, is composed of reddish conglomerates withmoderately sorted and rounded clasts. The second sequence is~75 m thick and consists of interbeds of gray laminated sand-stones and gray-blue mudstones and boulder clay in thelowermost interbed. The third sequence is ~265 m thick andmainly consists of gray coarse sandstones interbedded with thinlaminated dark gray mudstones and gray-blue siltstones. Thefourth sequence is 110 m thick and mainly composed ofmudstone. The Bailong Fm. is 360 m thick, consists mainly ofwhiteegray sandstones interbedded with some siltstone and

Fig. 6. SWeNE depositional fillings of the Cretaceous in the Sichuan Basin (the location of the cross-section is shown in Fig. 2 AA0).

Y. Li et al. / Cretaceous Research 57 (2016) 50e6556

mudstone layers, and is characterized by the sandstones inmudstones in the sedimentary sequence. The Qiqusi Fm. is~110 m thick and mainly consists of whiteegray sandstones,siltstones, and mudstones interbedded with thick good sortedand rounded conglomerates.

� Nanjiang Shahe: The Jianmenguan Fm. (K1jm) and HanyangpuFm. (K1h) of the Lower Cretaceous remain in this section (Fig. 6).The Jianmenguan Fm. is > 500 m thick and contains four se-quences with alternating layers of coarse and fine lithology(Fig. 6). This section begins with well sorted and rounded3e10 cm diameter conglomerates with whiteegray coarsesandstones and dark-gray mudstones that become finer upwardwith interbedded sandstones and siltstones containing mudpebbles and overlain by ~300-m-thick coarse clastic sedimentswith characteristic mudstones in sandstones and the develop-ment of trough cross-bedding. The uppermost part of the Jian-menguan Fm. is ~100m thick and consists mainly of whiteegraysiltstones and mudstones. The sedimentary characteristics ofthe Hanyangpu Fm. are similar to those of the Jianmenguan Fm.,except for the fining-upward sequence in the uppermost part(Fig. 6).

4.2.2. Description of NWWeSEE inter-well correlationsBB0 is a NWWeSEE profile of sedimentary filling (Fig. 8) from

Tianquan to Xishui (the location is shown in Fig. 2 BB’). Eightcolumnar sections were joined together with the lithofacies andsedimentary fillings described below.

� Tianquan Jinmenguan: The Lower Cretaceous Jiaguan Fm. (K1j)consists of ~50 m thick well sorted and rounded conglomerates

overlain by interbedded siltstones and mudstones (Fig. 8) withlarge-scale trough cross bedding. Interbedded coarse sand-stones and mudstones characterize the Upper Cretaceous Jia-guan Fm. (K2j). The lower part of the Guankou Fm. (K2g) consistsof ~450-m-thick poorly sorted and moderately rounded con-glomerates with a maximum pebble diameter of 65 cm. Themiddle portion is composed of sandstones, siltstones andmudstones with thicknesses of ~200 m. The uppermost part ofthe section consists of horizontally bedded siltstones andmudstones that contain salt.

� Qionglai Jiaguan: This profile shows the intersection of the inter-well correlation section AA0 and BB0, which is described above.

� Hongya Zhongshanping: The Lower Cretaceous Jiaguan Fm.consists mainly of interbedded siltstones and mudstones withtrough cross-bedding and sorted and moderately roundedconglomerates at the bottom. The Upper Cretaceous Jiaguan Fm.is ~100 m thick and consists of red siltstones with thin, lami-natedmudstones (Fig. 8). The Guankou Fm. is up to ~750m thickand is dominated by brown-red mudstones with interbeds ofcomparatively thick marlstones, siltstones and shales.

� Leshan Dafosi: The Lower Cretaceous Jiaguan Fm. mainly con-sists of thick red sandstones with large-scale cross-bedding andsiltstones that are interbedded with thin brown-red mudstones.The Upper Cretaceous Jiaguan Fm. is ~200 m thick and is char-acterized by a set of brickered sandstones (Fig. 8). Notably, theLeshan Giant Buddha, which is famous worldwide, was carvedfrom this sandstone. The Guankou Fm. is >650 m thick,conformably overlies the Jiaguan Fm. and is mainly composed ofbrown or reddish mudstones and siltstones.

� Yibin Sanhechang: The Wotoushan Fm. (K1w), Daerdang Fm.(K2d), Sanhe Fm. (K2s) and Gaokanba Fm. (K2gk) were identified

Fig. 7. Typical outcrops and facies photographs. A. Brownish red mudstone with minor gypsum in dissolved pores and located in a Salt lake environment in the Guankou Formationsoutheast of Qionglai Jiaguan. B. Brownish red mudstone with argillaceous siltstone and glauberite in a Salt lake environment in the Guankou Fm., northeast of Qionglai Jiaguan. C.Thick, poorly sorted and moderately rounded conglomerates with interbeds of sandstones and a thickness of >400 m in an alluvial fan environment in the Jianmenguan Fm. Jian'geYaojia. D. (and its sketch map D0) Thick conglomerate with coarse sandstone and small cross-bedding developed in sandstone strata, in which the conglomerate is characterized bysub-rounded clasts with poor sorting and a clast size range from 5 to 30 cm in an alluvial fan deposit in the Jian'ge Fm. northeast of Jian'ge Yaojia. (For interpretation of thereferences to colour in this figure legend, the reader is referred to the web version of this article.)

Y. Li et al. / Cretaceous Research 57 (2016) 50e65 57

in this section with conformable contact relationships betweeneach (Fig. 8). The Wotoushan Fm. is ~90 m thick and mainlyconsists of red sandstones in a thinning- and fining-upwardsequence. The Daerdang Fm. is ~120 m thick with a set ofbrick-red, thick, massive, fine-grained feldspar-quartz sand-stones characterized by highly developed cross-bedding withthree-level interfaces and well-sorted, well-rounded grains(Fig. 9A and A0). The Sanhe Fm. is 156 m thick and consists of redsandstones interbedded with brown-red mudstones. The Gao-kanba Fm. is mainly composed of red or reddish sandstones withinterbeds of brown-red mudstones and is ~540 m thick.

� Yibin Jinpingzhen: This profile has the same nomenclature andsimilar sedimentary infilling features, including the Wotoushan

Fm., Sanhe Fm. and Gaokanba Fm., which are characterized bysandstone with calcareous concretions (Fig. 8), and the Daer-dang Fm., which is characterized by aeolian sand with contact-porous calcite cementation and highly developed cross-bedding.

� Luzhou Hejiang Shizi: The Wotoushan Fm. and Daerdang Fm.are the only formations in this profile (Fig. 8). The bottom of theWotoushan Fm. consists of ~210-m-thick red sandstones withcalcareous concretions that become finer upward into the ~300-m-thick sandstones or siltstones with interbeds of brown-redmudstones. The Daerdang Fm. is ~210 m thick and is charac-terized by red, thick, massive, fine-grained feldspar-quartzsandstones with well-sorted and well-rounded grains.

Fig. 8. NWWeSEE depositional fillings of the Cretaceous in the Sichuan Basin (the location of the cross-section is shown in Fig. 2 BB0).

Fig. 9. Typical outcrops and facies photographs. A. (and its sketch map A0) Brick-redfine-grained sandstone with large-scale aeolian cross-bedding in an aeolian desertenvironment in the Daerdang Fm. north of Yinbin Sanhechang. (For interpretation ofthe references to colour in this figure legend, the reader is referred to the web versionof this article.)

Y. Li et al. / Cretaceous Research 57 (2016) 50e6558

� Guizhou Xishui Tucheng: The Wotoushan Fm. is ~180 m thickand mainly consists of red sandstones with interbeds of brown-red mudstones. The Daerdang Fm. is ~220 m thick and mainlyconsists of brown-red mudstones with interbeds of red sand-stones and siltstones. The Sanhe Fm. and Gaokanba Fm. mainlyconsist of red fine-grained sandstones and brown-red mud-stones that become coarser with decreasing depth (Fig. 8).

4.3. Interpretations of tectonic and depositional environments

4.3.1. The early Early Cretaceous (the Berriasian to Barremian,145e125 Ma)4.3.1.1. Tectonic environment. The Longmen Mts. and the westernSichuan Basin inherited the deformation framework of the LateJurassic and the paleostructural framework of the MiddleeUpperYangtze area significantly changed (Wu, 2006). The Longmen Mts.continued to rotate counter-clockwise (Meng et al., 2005) as theywere uplifted towards the piedmont zone and the south segment(Li et al., 2012b). The middle and north segments of the LongmenMts. piedmont zone formed a flexural depression that was super-imposed on the Late Jurassic foreland basin (Meng et al., 2005).Together, these zones continued to evolve into a superimposedflexural basin. At the end of the early Early Cretaceous (approxi-mately 129e125 Ma), a short period of uplifting in the westernSichuan Basin resulted in varying degrees of denudation in theupper Tianmashan Fm. and produced small-angle disconformityand unconformity with the underlying Jiaguan Fm. Due to thecombined effects of strong southward thrusting in the forelandzone at the north edge of Yangtze and the northwestward move-ment of the fold belt of the Xuefeng Mts., a trumpet-shapedstructure developed in northeastern Sichuan. Because of thecontinued northward squeezing and obstruction of the clockwiserotation movement in the northwest and northeast, the SouthChina block was severely squeezed towards the north into the

Y. Li et al. / Cretaceous Research 57 (2016) 50e65 59

Qinling orogen (Meng & Zhang, 2000; Wang, Meng, Burchfiel, &Zhang, 2003; Meng et al., 2005). The northern area of Sichuanbecame a foreland basin (Fig. 10) under the influence of the Qinlingintracontinental subduction (Liu, Li, Liu, & Luo, 2006). Meanwhile,the Xuefeng Mts. and the adjacent areas to the east experiencedtensile deformation and NE strike-slip pull-apart basins began todevelop. Thus, initial opening and sedimentary infilling of theYuanma Basin occurred (Fig. 10) coevally with extensive EarlyCretaceous magmatism, volcanism and extensional doming inSouth China (Li et al., 2012a). The Sichuan intracratonic depressionbasin to subside gradually westward and fluviolacustrine faciesdeveloped steadily in the Xichang foreland basin while connectedwith the Sichuan Basin (Fig. 10). The development of these basins isa hallmark of the formation of an EeW structural inversionframework in the Yangtze area.

4.3.1.2. Depositional environment. The early Early Cretaceousdeposition has a maximum thickness of 1200 m and correspondswith the time of deposition of the Tianmashan Fm. Regional upliftduring the Late Jurassic. This deposition resulted in differentialerosion of the Penglaizhen Fm. followed by early Early Cretaceousdeposition overlapping various strata of the Penglaizhen Fm. in

Fig. 10. Map of the tectonicedepositional environment in the ear

many places and the subsidence center in the northwesternSichuan Basin and southern Xichang (Fig. 10). Controlled by theperipheral tectonic environment, post-orogenic denudation, andbasin tectonic subsidence, the Sichuan Basin received contributionsfrom major sediment source areas located to the west and north-west (the Longmenshan thrust belt) and a secondary sedimentsource area to the north (the Dabashan thrust belt) during adepositional period in the early Early Cretaceous (Fig. 10). Thus, thedistribution and depositional environment of the sedimentaryfacies is defined by the provenance system.

Alluvialefluvialelacustrine deposits developed in the westernSichuan Basin. The alluvial fan belt was distributed along the frontof the Longmen Mts., with layers overlapping lengthwise andtransversely skirting one another (Fig. 10). The well profiles ofChuanfeng 563, Chuanhe 100, Chuanxiao 107, and Chuanwen 303(Fig. 6) indicate that the central part of the western Sichuan Basinconsisted of a shallow lake deposit with a set of interbeddedsandstone and mudstone during this stage. The depositional envi-ronment becomes a meandering river towards the east (Fig. 10).Braided river deposits of superimposed layers of watercoursesandstone containing lentoid mudstone mainly occur north andnortheast of the Sichuan Basin. Without alluvial fan conglomerates,

ly Early Cretaceous in the Sichuan Basin and adjacent areas.

Y. Li et al. / Cretaceous Research 57 (2016) 50e6560

the deposits gradually became a meandering river alluvial plainsystem that featured sand beaches and flood plains towards thesouth. The fluvial-lacustrine facies of the early Early Cretaceous inthe southwestern Sichuan Basin was stable, and the Xichang Basinwas probably connected to it as a complete unit (Fig. 10). This unithad a distinct lengthwise bisectability and consisted of fluvialpositive rhythmite layers of coarse sandstoneesiltstone and purplemudstone in the bottom and lacustrine siltstone, fine sandstoneand dark mudstone in the top with grain size coarsening from eastto west. The Lower Cretaceous of Yuanma Basin unconformablyoverlies various layers of the Pre-Sinian, Paleozoic, and lowerMesozoic (Zheng, 1998; Zheng, Lou, Hou, & Chen, 1998; Ding, Liu,Lv, & Pan, 2007), of which the lithofacies consist of a set ofbrownish red-maroon conglomerates and sandstones interbededwith mudstones and the depositional environments were mainlythe alluvial plains of meandering rivers and lakes (Fig. 10).

4.3.2. The late Early Cretaceous to the early Late Cretaceous (theAptian to Turonian, 125e89.8 Ma)4.3.2.1. Tectonic environment. Influenced by the movement in thelate Yanshan period, tectonic compression from the Qinling spreadto the Sichuan Basin and resulted in rapid uplift in the north andnortheast parts of Sichuan (Shen et al., 2007; 2009) with south-westward tilting. This tectonic event ended continental depositionand resulted in a period of uplifting and weathering denudation.The sedimentary scope of the Late Cretaceous in the north and eastof Sichuan then shrank to the southwest, with the depositionalcenter migrated to the Qionglai area (Fig. 11). Next, the southwestSichuan foreland basin and south Sichuan foreland basin emerged,which compounded early subsidence, gradually progressed to-wards the southeast, and subsequently formed the southeastSichuan foreland basin. The tectonic regime of the Yuanma Basinchanged in the late Early Cretaceous to NWeSE compression andNEeSW extension, causing inversion of this extensional basin (Liet al., 2012a). A group of small, NE-trending analogous wedge-topbasins developed in the Enshi and Qianjiang areas among the foldbelts of widely spaced anticlines and synclines to the east of theQiyao Mts.

4.3.2.2. Depositional environment. The Jiaguan Fm. was depositedin the late Early Cretaceous to early Late Cretaceous-equivalent.Inversion of the basin framework was dominated by tectonicamalgamation along its peripheral tectonic zone and associatedintracontinental tectonisms and is important for providing sedi-ments and defining provenance systems. Three sediment sourceareas were defined, the south segments of the Longmenshan thrustbelt, the uplifting area of the Sichuan Basin, and the north segmentsof the Daloushan fold belt.

The strong thrusting of the southern segments of the LongmenMts. partially determined the development of two groups of allu-vial fans in front of the Longmen Mts. and centered west of Pen-gzhou and Qionglai, respectively (Fig. 11). Due to aridity andtorridness, the alluvial fan group west of Chengdu graduallychanged to desert depositional conditions in the southeast andthen to contiguous desert formed from the isolated and sporadicdeserts of the early stage (Tian, 1990; Jiang & Pan, 2005; Long et al.,2011; Geng, 2011) trending NWeSE along the Cheng-dueZigongeLuzhou line (Fig. 11). Large-scale aeolian cross beddingwith three-level interfaces (Yue & Ding, 1999) was observed in theDaerdang Fm. outcrop in the Yibin area, which was composed ofbrick-red, thick, massive, fine-grained mature feldspar-quartzsandstone with well-sorted and well-rounded grains (Fig. 9A andA’). This formation is a classic aeolian sand deposit with contact-porous calcite cementation (e.g., Kocurek, 1981; 1988; Ahlbrandt& Fryberger, 1982; Bristow & Mountney, 2013). The direction of

the paleowind indicated by the foreset bed was SW, from which acentral Sichuan Basin provenance was inferred (Fig. 11). The redcolor (in the web version) indicated that the aeolian sandstonesformed in an arid and torrid paleoclimate and are the same type ofsandstone that forms from lateral eolian dunes (Mountney, 2006;Bristow & Mountney, 2013). Due to the contributions of ancientwater systems in southeastern Chongqing, central Guizhou, easternLuzhou and southern Qijiang, a braided river depositional envi-ronment developed with sediments from south of the foldethrustbelt of western Hunan, Hubei, and eastern Chongqing (Fig. 11). Theother alluvial fan group west of Qionglai became a braided riverdepositional environment trending NEeSW and evolved into ameandering river sedimentary environment towards the south andsoutheast with the converging water systems of the westernSichuan Basin and Xichang Basin. The Yuanma Basin also inheritedthe tectono-depositional environment of the early Early Creta-ceous, meandering river and shallow lakes (Fig. 11).

4.3.3. The late Late Cretaceous (the Coniacian to Maastrichtian,89.8e66 Ma)4.3.3.1. Tectonic environment. Southeastward thrusting of theSongpaneGarze fold belt and northwestward squeezing of theXuefengshan fold belt resulted in strong folding and uplifting in theeast areas of Sichuan, which resulted in a series of NE-trendingorogens (Li, 2000; Yan, Hu, Lin, Santosh, & Chan, 2011b; Liu et al.,2012b), such as the Qiyao Mts. and Dalou Mts. The formation ofthese NE mountains not only affected the clastic supply to thesedimentary basins (Yan et al., 2011b) but also blocked the warmand wet air currents from the southeast, which altered the climaticconditions in the late Late Cretaceous. Furthermore, the constanteastward extension of the southwest Sichuan foreland basin andthe westward movement of the southeast Sichuan foreland basinwere compounded by the development of a superimposeddepression basin centered around the Zigong-Yibin area (Fig. 12).During this period, the Sichuan and Xicang basins sustained thebasin architecture formed in the depositional stage of the JiaguanFm. The NeS extension prevailed in the Late Cretaceous andcontrolled Late Cretaceous subsidence (Li et al., 2012a), whichresulted in the complete emergence of the Yuanma strike-slip pull-apart basin and gradual evolution into a separated foreland basin.The central Yangtze area experienced a comprehensive extensionalstructural transformation, and the NEetrending Jianghan rift basin(the location is indicated in Fig. 1), which represents the rift basingroup, formed and gradually developed into a basin and rangeprovince (Chen et al., 2009).

4.3.3.2. Depositional environment. The late Late Cretaceous isequivalent to the period when the Guankou Fm. was deposited inthe western Sichuan Basin. In the late Late Cretaceous, two majorsubsidence centers and one secondary subsidence center devel-oped (Fig. 12) due to superimposed coupling between the south-west and southeast Sichuan foreland basins. The main subsidencecenters are the southwest Sichuan foredeep, which is centered inYaan, and the southeast Sichuan foredeep, which is centered inGulin, with thicknesses of more than 1400 m and 800 m, respec-tively. The secondary subsidence center is a superimposeddepression in southern Sichuan that is centered in Yibin with apeak thickness of 800m. Large-scale alluvial fans were deposited infront of the southern segments of the Longmen Mts. Theconglomerate thicknesses at the ends of the fans are 400 m, 660 m,and 870 m, respectively, and rapidly become thinner towards theeast (Fig. 12). The conglomerate and coarse sandstone werereplaced by fine sandstone, siltstone, and mudstone. In theQionglai-Yaan area and eastward, the lithofacies gradually becomesbrownish-red fine sandstone, siltstone, and mudstone, and many

Fig. 11. Map of the tectonicedepositional environment in the late Early Cretaceous to early Late Cretaceous in the Sichuan Basin and adjacent areas.

Y. Li et al. / Cretaceous Research 57 (2016) 50e65 61

sets of thick stratiformmarlstone, dolomite limestone, gypsum, andglauberite are present with decreasing sedimentary thicknessesfrom west to east. Pollen assemblages contain abundant Schi-zaeoisporites, Classopollis, and Ephedripites, which indicate anextremely arid climate in the late Late Cretaceous (Wang et al.,2008). In southern Sichuan, the depositional environment varieddistinctly between the south and north (Fig. 12). The north mainlyexperienced braided river deposition that featured cycle depositionwith mud layers sandwiched between sand layers along theChengdueZigongeYibin and major provenances in the upliftingarea of Sichuan. The depositional environment along theLeshaneJunlianeXishui was chiefly a meandering river featurecycle deposition with sand layers sandwiched between mud layersand a secondary provenance in the central and northern Daloushanfold belt (Fig. 12). The tectono-depositional environments of theXichang Basin in the southwest and the Yuanma Basin in thesoutheast continuously evolved without great variations.

5. Discussion

During a long geological history, most sedimentary basinsexperience varying degrees of reformation and form “residual

basins”. Li, Lu, Liu, and Xu (2012c) proposed that a residual basincould be defined as the residual part of a sedimentary basin that hasbeen modified by postebasin formation. All of our original datapresented in this study were obtained from the Sichuan residualbasin and are original sedimentary records of the Cretaceoussedimentary basins. Concrete evidence that can be used to inves-tigate the tectonicedepositional environment of the Cretaceousremains lacking because Cretaceous sedimentary and stratigraphicrecords in eastern Sichuan are largely absent. Therefore, our studyattempts to reconstruct Cretaceous basins by combining contem-poraneous peripheral tectonic environments to provide evidence toevaluate previously stated hypotheses or develop alternative hy-potheses regarding the evolution of the Sichuan Cretaceous basins.

5.1. Sedimentary boundary of the Sichuan Cretaceous basin

Wepresent twomain lines of evidence to argue the view that thescope during the Sichuan Cretaceous sedimentary basin construc-tion period is much larger than the residual basin of the present dayand that themissing Cretaceous units of the eastern Sichuan are notdue to a lack of deposition during the construction period but resultfrom suffering multiple denudation events during the late uplift.

Fig. 12. Map of the tectonicedepositional environment in the late Late Cretaceous in the Sichuan Basin and in adjacent areas.

Y. Li et al. / Cretaceous Research 57 (2016) 50e6562

First, no large-scale magmatic or hydrothermal activity hasoccurred since the late Mesozoic; thus, the cooling events reflectthe uplift and denudation history. These uplift and denudationevents are coupled with the distribution of the Cretaceous residualstrata, which indicates that the sedimentary thickness and depo-sition range of the original Early Cretaceous strata were muchlarger than the Cretaceous residual strata. Second, the widelydistributed and exposed Jurassic units in eastern and centralSichuan experienced burial diagenesis that transformed sedimentdeposits to diagenetic materials, which indicated that a certainthickness of overlying sediments existed above the Jurassic strata.

5.2. Nature of Cretaceous sedimentary basins

The formation and evolution of the Cretaceous sedimentarybasins in Sichuan are affected by subtle far-field tectonism (Zhanget al., 2013b) and changes in climate and drainage systems (e.g.,Ratschbacher et al., 2003). Basin styles in south China exhibit arange, from stretching-rifted types in the east to compressional-depression types in the west. The nature of the basins iscontrolled by incomplete synchronized thrust nappes of peripheralorogenic belts and regionally disparate uplift events in the basin,

which result in Cretaceous rocks that contain many coarse-to me-dium-grained clastic rocks that were deposited in continental en-vironments and sourced from the erosion of mountain ranges(Fig. 13). Consequently, the Cretaceous sedimentary basin has thesame characteristics as a typical foreland basin with several stagesof thrusting and reworking.

The intracratonic depression basin with foredeep settlementfeatures in the early Early Cretaceous (Fig. 13A) subsequentlytransitioned to a converse foreland basin, which was characterizedby bidirectional provenance (Fig. 13B), and to a superimposedforeland basin with multi-phase late-stage superimposition(Fig. 13C). Thus, the Sichuan Cretaceous sedimentary basin could berecognized as a superimposed foreland basin. In the easternSichuan area (Guiyang to Enshi City), a series of NE-trendingintermontane basins with characteristics of a wedge-top depo-zone (e.g., Conti, Fontana, & Lucente, 2008; Gugliotta, 2011; 2012;Mazzoli, Szaniawski, Mittiga, Ascione, & Capalbo, 2012) devel-oped under the effects of westward or northwestward compressionamong the fold belts of widely spaced anticlines and synclines andwere superimposed or reworked during the Cretaceous period(Fig. 13). The Yuanma Basin is composed of a group of disperse SW-trending strike-slip pull-apart basins.

Fig. 13. Cross-section showing the evolution of tectonicedepositional environments of the Cretaceous in the Sichuan area (the location is shown in Fig. 2 as CC0).

Y. Li et al. / Cretaceous Research 57 (2016) 50e65 63

5.3. Some uncertainties

Defining the original boundaries of Cretaceous sedimentarybasins in Sichuan is important but very difficult because of asyn-chronous thrusting of peripheral mountains, regional differentialuplifting events, and post-orogenic denudation. Although weincorporated most of the available data interactively, our efforts donot guarantee an accurate estimate of the sedimentary basinboundary, especially in the early Early Cretaceous period. Thus,future research should focus on reconstructing the original sedi-mentary boundary during specific episodes of the basin's geologicalhistory.

Although the Sichuan Cretaceous sedimentary basin is definedas a foreland basin by solid studies, no direct evidence has beenfound that define themechanisms of the scattered basins (Guiyang-Enshi red basin, Xichang Basin, and Yuanma Basin) discussed in thispaper. However, our study provides a relatively reasonableassumption that is consistent with the tectonic background of thestudy area. Moreover, many types of conditions should be investi-gated to determine the nature of the basin. Our preliminary workaims to provide suggestions for future basin analyses or tectonicand sedimentary analyses.

6. Conclusions

(1) According to tectonic subsidence patterns in the westernSichuan Basin, we divided the evolutionary history of theSichuan Cretaceous basin into three stages, oscillating sub-sidence in the early Early Cretaceous (145e125 Ma), stablesubsidence during the late Early Cretaceous to early Late

Cretaceous (125e89.8 Ma), and rapid subsidence in the lateLate Cretaceous (89.8e66 Ma).

(2) The temporal-spatial evolution of the Cretaceous tecto-noedepositional environment in the Sichuan Basin and adja-cent areas is presented. The basin was subject to NWeSEcompressionwith northwestward shortening in the early EarlyCretaceous and was dominated by alluvial fan and fluviola-custrine sedimentary systems. The Longmenshan thrust belt isthemain sediment source area, and the Dabashan thrust belt isa secondary source area. The central and northern SichuanBasin was rapidly uplifted during the late Early Cretaceous toearly Late Cretaceous with southwestward tilting, whichdeveloped into a depression, exhibited southwestwardcompression, and was characterized by aeolian desert and flu-violacustrine deposits. The tectonic framework was controlledby the inherited basement structure, and the formation of NEmountains not only affected the material provision but alsoblockedwarm-wetcurrents fromthesoutheast,whichchangedthe climatic conditions in the late Late Cretaceous.

(3) The formation and evolution of the Cretaceous sedimentarybasins are closely related to synchronous regional tectonicuplifting events. Controlled by asynchronous thrusting ofperipheral mountains and regional differential upliftingevents, the Sichuan Cretaceous sedimentary basin is recog-nized as a superimposed foreland basin.

Acknowledgments

This research was financially supported by the National Scienceand Technology Major Project (2011ZX05008-001), the NationalNatural Science Foundation of China (40739906), and the National

Y. Li et al. / Cretaceous Research 57 (2016) 50e6564

Natural Science Foundation of China (412021471). We are verygrateful to the Editor-in-Chief Prof. E. Koutsoukos for hisconstructive comments and suggestions that significantlyimproved the original manuscript. We acknowledge Dr. AndreiKhudoley of St. Petersburg State University and another anonymousreferee for their critical and constructive comments. We thankSouthwest Company, Sinopec for kindly supplying drilling data, andwe also thank Chengdu University of Technology for supplying partof the outcrop data. Finally, we honor geologists at home andabroad for their remarkable work in Cretaceous research.

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