U–Pb SHRIMP age for the Tuchengzi Formation, northern China, and itsimplications for biotic evolution during the Jurassic–Cretaceous transition
Huan Xu a, Yong-Qing Liu a,∗, Hong-Wei Kuang a, Xiao-Jun Jiang a, Nan Peng a,b
a Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, Chinab China University of Geosciences, Beijing 100083, China
Received 11 April 2012; received in revised form 28 July 2012; accepted 16 October 2012Available online 22 October 2012
bstract
The Late Jurassic–Early Cretaceous Tuchengzi Formation is widespread in North China. Its clastic deposits indicate a tropical, dry, and hotaleoclimate, different from the subtropical, humid, and seasonal climate in the early Middle Jurassic. The sudden environmental change from theiddle to Late Jurassic resulted in a rapid disappearance of the Yanliao/Daohugou Biota, with more than 90% of the species of the Yanliao/Daohugouiota dying out and replaced by the Early Cretaceous Jehol Biota. Eolian sandstones with large-scale cross-bedding occur within the uppermostart of the Tuchengzi Formation in North China. The sandstones are stratigraphically higher than the tuff previously dated as 139 Ma. We obtainedwo SHRIMP zircon U/Pb ages from the tuff beds. One sample was collected from the tuff in the basal Tuchengzi Formation in northern Hebei and
he other from the tuff intercalated in the eolian cross-bedded sandstones in the uppermost Tuchengzi Formation in western Liaoning. Our resultshow that 154 Ma is the oldest age constraint for the Tuchengzi Formation and 137 Ma is the youngest age estimate of the formation, providing ange constraint for the transition from the Yanliao Biota to the Jehol Biota.
2012 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.
During the late Mesozoic, a series of rift basins and volcan-sm appeared as a result of intraplate orogenies in northeasternhina (Ren et al., 2002; Wu et al., 2002; Zhang Y.Q. et al., 2004;hang J.H. et al., 2008; Ying et al., 2010). The Tuchengzi Forma-
ion consists of coarse-grained, purplish-red alluvial sediments,ndicating a tropical, dry, and hot climate with eolian depositsn a highland paleogeographical environment in the transitionaleriod from the Late Jurassic to the earliest Cretaceous duringhe transition between the Yanliao/Daohugou Biota (J2) (Zhang,002) and the Jehol Biota (K1) (Chen, 1999).
In the last two decades, exceptional fossils have been recov-red from the Early Cretaceous Jehol Biota in western Liaoning,
orthern Hebei, and southeastern Inner Mongolia in northeast-rn China, including early birds, feathered dinosaurs, mammals,terosaurs, amphibians, fish, insects, and flowering plants (Sun
t al., 1998; Xu et al., 1999; Ji et al., 2001, 2006a; Gaond Shubin, 2003; Wang et al., 2005; Meng et al., 2006;hou, 2006). Much less is known about the many equally
mportant Middle–Late Jurassic fossils belonging to the Yan-iao/Daohugou Biota from the same region, including the oldestnown feathered dinosaurs (Hu et al., 2009; Liu et al., 2012),wimming and flying mammals (Ji et al., 2006a; Meng et al.,006), pterosaurs with hair-like integument, lizards, fish, andbundant salamanders and insects. The recent fossil discover-es of the Yanliao/Daohugou Biota have extended the temporalistribution of feathered dinosaurs and helped to resolve theo-called temporal paradox that has perplexed paleontologiststudying the origin of birds (Xu et al., 2010; Zhou et al., 2010).
The Tuchengzi Formation has yielded rare plants (Zhengt al., 2001), dinosaur and bird tracks (Lockley et al., 2006;ullivan et al., 2009; Xing et al., 2009, 2011, 2012; Zhang et al.,012), a dinosaur (Chaoyangosaurus liaoxiensis; Zheng et al.,001), and some freshwater invertebrates (Shen and Chen, 1984;
ang et al., 2004; Wang and Li, 2008). More than 90% of the
enera and species from the formation died out (Ji et al., 2004,006b) before the Jehol Biota emerged in the earliest part of
he Early Cretaceous (Zhou, 2006). Determining the timing ofhe transition and replacement between the two biotas is a keyo understanding the paleoecology and biotic evolution. How-ver, despite the importance of this transition, its timing has beeneither well defined nor finely dated.
Large-scale cross-bedded eolian strata, indicative of highind deposits, are frequently found within the uppermost unitf the Tuchengzi Formation in northern China. As the eolianandstone of the Tuchengzi Formation is located at the top ofhe formation and above the tuff dated by Swisher et al. (2002),he age of the eolian sandstone and the youngest age of theuchengzi Formation are certainly younger than the previousate of 139 Ma (Swisher et al., 2002). A robust youngest age esti-ate for both the eolian sandstone and the Tuchengzi Formation
s necessary for reconstructing the geochronology of the biotand paleogeographic evolution. The Yanliao/Daohugou Biotand the Jehol Biota share a similar paleogeographic distribution,nd the transition between them was punctuated by a long inter-al of the dry, hot, and high-wind climate during the depositionf the Tuchengzi Formation.
The Tuchengzi Formation has been increasingly recognizeds stratigraphically and geologically important in the Meso-oic evolution of the regional tectonics of northern China (Het al., 1998, 1999; Davis et al., 2001; Cope, 2003; Davis, 2005).espite its importance in the Mesozoic evolution of the Yanshan
old and thrust belt, the relationship of the Tuchengzi Forma-ion to the regional tectonics of northern China remains unclear.ome researchers considered the Tuchengzi sedimentation to beelated to contractional tectonics (Zhao, 1990; He et al., 1998,999, 2007, 2008; Davis et al., 2001; Guo et al., 2002; Dengt al., 2003; Dong et al., 2007), whereas others have proposedhat the sedimentation occurred in an extensional environmentMa et al., 2002; Shao et al., 2003; Xu et al., 2011). Someesearchers favoring a contractional tectonic setting concludedhat the Tuchengzi sedimentation was syntectonic, synchronousith thrusting (Zhao, 1990; He et al., 1998, 1999, 2007, 2008;avis et al., 2001; Guo et al., 2002; Deng et al., 2003; Dong et al.,007). It has also been suggested that the Tuchengzi depositionepresents a period between major episodes of the Yanshanianeformation, thus implying a period of relative tectonic quies-ence; or that the Tuchengzi Formation was deposited during aajor transformational period by a compressive tectonic mecha-
ism to the extensional basins during the terminal Mesozoic (Lit al., 2003; Qu and Zhang, 2005; Sun et al., 2007). These dif-erent interpretations are partly due to the poor geochronologyf the Tuchengzi Formation.
Reliable radiometric ages for the Tuchengzi Formation areare because of the scarcity of volcanic rocks (or tuff). The lack ofossils in the Tuchengzi Formation makes it difficult to determinehe biochronological age. As a result, the age of this formation isontroversial and generally considered to have a late Middle toate Jurassic age of ca. 156–145 Ma based on K–Ar and Rb–Srges from overlying and underlying units (He et al., 1998, 1999).
n accurate age would also help to determine if the terrestrial J/Koundary, which is still controversial, belongs to this formation.revious age studies using 40Ar/39Ar and U/Pb methods wereocused mainly on the middle and upper units of the Tuchengzi
Ctap
21 (2012) 222–234 223
ormation or the top of the underlying Tiaojishan FormationSwisher et al., 2002; Liu J. et al., 2006; Zhang H. et al., 2008a,b,009; Chang et al., 2009).
Here, we report two newly obtained zircon U/Pb ages, onerom a sample collected from the tuff in the lowest part of theoucheng Formation in Weichang, northern Hebei, and the other
rom a tuff interbedded with the eolian cross-bedded sandstonesn the uppermost unit of the Tuchengzi Formation in Chaoyang,estern Liaoning, northeastern China. The purpose of this paper
s to provide a robust age estimate of the Tuchengzi Formation. reinforced geochronology for the Tuchengzi Formation and
elated geological implications will be discussed. Research onhe geochronology and calibration with paleontology, stratigra-hy, and sedimentology of the Tuchengzi Formation will greatlyncrease our knowledge of Mesozoic terrestrial ecosystems androvide high-precision age constraints for the transition betweenhe Yanliao Biota and the Jehol Biota.
. Geological background and geochronology
During the late Mesozoic, the sampling location and sur-ounding area (western Liaoning and northern Hebei) wereocated in the northeastern part of the North China Craton (Fig. 1)n a terrestrial environment at a paleolatitude of approximately5◦N (Smith et al., 1994). The late Mesozoic terrestrial strata ofortheastern China, in ascending order, are the Middle Jurassicaifanggou Formation (or the Jiulongshan Formation in Hebeirovince) and Tiaojishan Formation (or the Lanqi Formation
n Liaoning Province), the Upper Jurassic–Lower Cretaceousuchengzi Formation (or the Houcheng Formation in Hebeirovince), the Lower Cretaceous Zhangjiakou Formation, theabeigou Formation, the Yixian Formation, and the Jiufoutangormation, which are widely distributed in western Liaoning,orthern Hebei, and southern Inner Mongolia of northeasternhina (Fig. 1) and contain two well-preserved terrestrial bio-
as (the Yanliao/Daohugou Biota and the Jehol Biota). Both theaifanggou Formation and Lanqi/Tiaojishan Formation yield
ossils of the Yanliao/Daohugou Biota. The Jehol Biota occursn the Lower Cretaceous Zhangjiakou Formation, Dabeigou For-
ation, Yixian Formation, and Jiufoutang Formation.The Tuchengzi Formation is widely distributed in an east-
est trend in the northern part of North China (Fig. 1).eneralized lithologic associations and descriptions of theuchengzi Formation are similar across North China. Maxi-um thicknesses of the Tuchengzi Formation are approximately
400 m in Hebei Province, 2600 m in western Liaoningrovince, and 1400 m in Beijing Municipality (Xu et al., 2011)Fig. 2).
The Tuchengzi Formation rests unconformably on pre-esozoic units at Chicheng, northern Hebei, whereas elsewhere
t commonly overlies predominantly andesitic, trachyandesitic,nd pyroclastic rocks interbedded with clastic sedimentaryocks known as the Middle Jurassic Tiaojishan Formation (J2).
ontact relationships between the Tuchengzi Formation and
he underlying Tiaojishan Formation are generally describeds disconformable, but field observations in this study andreviously determined age relationships in most localities
224 H. Xu et al. / Palaeoworld 21 (2012) 222–234
north
iaTovcceHccgr
prvpsssimtpti
3
1ti
tipiswopt
2iTeivcsdsshF(1maaul
Fig. 1. Study area and regional distribution of the Tuchengzi Formation in
ndicate no significant break between the Tuchengzi Formationnd the underlying Middle Jurassic Tiaojishan Formation. Theuchengzi Formation is mainly overlain conformably, with anccasional angular unconformity (northern Hebei), by silicicolcanic rocks of the Early Cretaceous Zhangjiakou Formationonsisting mainly of felsic volcanic rocks and tuffs with inter-alated sediments with an approximate age of 144–135 Ma (Liut al., 2003; Zhang H. et al., 2008a,b and c, 2009) in northernebei, whereas in western Liaoning, there is an uncomformable
ontact with the overlying Early Cretaceous Yixian Formationomposed of variegated thick conglomerates and sandstonesrading up to mainly andesitic, trachyandesitic, and pyroclasticocks.
Sediments in the Tuchengzi Formation are coarse-grained,urplish-red alluvial deposits from mainly fan and braidediver facies interbedded with lacustrine facies and occasionalolcanic rocks and tuffs. The formation consists mainly ofurplish-red conglomerates with intercalated tuffaceous sand-tones, siltstones, and tuffs in the lower member, gray-purpleiltstones,sandstones, and conglomerates intercalated with sand-tones in the middle member, and gray-purple conglomeratesntercalated with green tuffaceous sandstones in the upper
ember, with occasional intercalations of andesitic, rhyolite,rachyandesitic, and pyroclastic rocks in the middle or upperart. Spectacular, giant, inclined cross-bedding is present at theop of the Tuchengzi Formation in a thousand-kilometer rangen northern areas of North China (Fig. 2, Table 1).
. Sample description and analytical procedures
◦ ′
One rhyolite tuff sample (Bed No. 4, 42 01.62 N,17◦40.41′E) was collected from the basal Tuchengzi Forma-ion in a measured section in Weichuang, northern Hebei, ands shown in Fig. 3. At this site, the Tuchengzi Formation has a
tpt
ern Hebei, western Liaoning, and southern Inner Mongolia, North China.
hickness of 1905 m and rests disconformably on the underly-ng Middle Permian sedimentary-volcanic rocks, consisting ofurplish-red sandstones, siltstones, and mudstones with alternat-ng felsic tuffs in the lower part of the section, conglomerates,andstones, and rhyolitic lavas in the middle, and conglomeratesith sandstone intercalations in the upper part of the unit. A bedf 31.4-m-thick rhyolitic tuff is intercalated in the lowermostart (Bed No. 4) of the Tuchengzi Formation and was sampledo provide an oldest age estimate of the Tuchengzi Formation.
The other rhyolitic tuff sample was collected from a.5-m-thick rhyolitic tuff horizon (42◦01.62′N, 117◦40.41′E)nterbedded with eolian sandstones in the top unit of theuchengzi Formation in Chaoyang, western Liaoning, north-astern China (Fig. 4). At this site, the Tuchengzi Formations 2000 m thick and disconformably contacts the underlyingolcanic rocks of the Middle Jurassic Tiaojishan Formation. Itonsists of purplish-red siltstones and mudstones in the lowerection, conglomerates interbedded with sandstones in the mid-le, and more conglomerates and sandstones, particularly eolianandstones with large-scale cross-bedding, intercalated with silt-tones and mudstones in the top unit. Because the stratigraphicorizon of the sampled tuff is located at the top of the Tuchengziormation and much higher than that sampled by Swisher et al.2002) and Zhang H. et al. (2008b), who reported ages between40 and 139 Ma, the tuff could provide a youngest age esti-ate of the Tuchengzi Formation. Furthermore, the estimated
ge will also provide an age constraint on the eolian sandstonend the occurrence of the high wind climate, and will thus beseful for reconstructing the paleoclimatic environment in theate Mesozoic in northern China.
Examination of petrographic thin sections revealed that
he tuff sample is fresh and contains phenocrysts of sanidine,lagioclase, biotite, zircon, and quartz. Fresh zircons from theuff sample were suitable for zircon SHRIMP U–Pb dating.
H. Xu et al. / Palaeoworld 21 (2012) 222–234 225
Fig. 2. Correlation of the Tuchengzi Formation, North China. 1, gneiss; 2, plagioclase gneiss; 3, andesite; 4, dacitic tuff breccia; 5, rhyolite; 6, andesitic breccia lava; 7,volcanic breccia; 8, tuff; 9, tuffaceous mud; 10, rhyolitic porphyry; 11, rhyolitic crystal tuff; 12, rhyolitic tuff; 13, coarse-grained conglomerate; 14, medium-grainedconglomerate; 15, fine-grained conglomerate; 16, sandy conglomerate; 17, pebbly coarse-grained sandstone; 18, coarse-grained sandstone; 19, medium-grainedsandstone; 20, fine-grained sandstone; 21, siltstone; 22, muddy siltstone; 23, mudstone; 24, shale; 25, limestone; 26, dolomite; 27, dolomitic limestone; 28, dinosauror bird tracks. References: [a] (Xing et al., 2009, 2011, 2012), [b] (Zhang et al., 2012), [c] (Sullivan et al., 2009), [d] (Zhang Y.Z. et al., 2004b; Fujita et al., 2007),[e] (Chen et al., 2006; Lockley et al., 2006). Ar3w, Neoarchean Wulashan Group; Ar1s, Paleoarchean Sanggan Group; O1y, Early Ordovician Yeli Formation; Jxw,Mesoproterozoic Wumishan Formation; J2t, Middle Jurassic Tiaojishan Formation; J2x, Middle Jurassic Xinmin Formation; (J3-K1)t1, lower part of the Late Jurassicto the Early Cretaceous Tuchengzi Formation; (J3-K1)t2, middle part of the Late Jurassic to the Early Cretaceous Tuchengzi Formation; (J3-K1)t3, upper part ofthe Late Jurassic to the Early Cretaceous Tuchengzi Formation; (J3-K1)t in columns (12)–(15) represent the remnant Tuchengzi Formation; K1l, Early CretaceousLisangou Formation; K1g, Early Cretaceous Guyang Formation; K1yj, Early Cretaceous Yanjiayao Formation; K1dl, Early Cretaceous Donglingtai Formation (equalto Zhangjiakou Formation); K1z, Early Cretaceous Zhangjiakou Formation; K1db, Early Cretaceous Dabeigou Formation; K1yx, Early Cretaceous Yixian Formation;K1, Early Cretaceous intrusive rocks.
226 H. Xu et al. / Palaeoworld 21 (2012) 222–234
Table 1Lithofacies and interpretation of sedimentary facies of the Tuchengzi Formation.
Lithofacies Descriptions of rock association Interpretations of facies
Massive conglomerate (Gm) Purplish red, medium-thick bedded or massive conglomerate, poorly sortedsubangular, sandy and muddy cement. Pebbles are 2–5 cm in diameter,maximum 30 cm, imbricated and mainly consist of andesite, gneiss,quartzite and carbonates
Alluvial fan, mud flow
Lenticular conglomerate (Gl)Gray or purplish red, conglomerate in medium lenticulars, not well sorted,subangular-subrounded, multicomponent pebbles, sandy cement
Lags, braided channel
Gray, conglomerate in small lens, poorly sorted, subrounded,multicomponent pebbles, sandy cement, interbeded with eoliancross-bedding sandstone
Channels in dry climate
Inclined bedding sandstone (Gp, Sp) Purplish red, medium or thick bedded pebble sandstone, not well sorted,subrounded with trough cross stratification
Bar, braided channel
Lenticular sandy conglomerate (Gl, Sl) Gray yellow, sandy conglomerate in small lens with fine grained sandstone,poorly or medium sorted, subangular-subrounded, multicomponent pebbles
Subaqueous distributary channel,fan delta
Coarse grained sandstone with crossbedding (Stg)
Gray, medium or thick bedded, coarse grained sandstone with trough crossstratification
Bar, braided channel
Lenticular coarse grained sandstone (Slg) Gray, coarse grained sandstone, lenticular, fingering with fine grainedsandstone
Subaqueous distributary channel,fan delta
Massive, medium grained sandstone(Sm)
Gray green, massive, medium grained sandstone, more lithological clastics Subaqueous channel, mouth bar,delta front
Medium, fine grained sandstone with crossbedding (Stm, Sts, Sws, Swm, Stm, Sws,Stm)
Gray yellow, medium or thick bedded pebbly medium or fine grainedsandstone, normal grading and trough cross stratifications (Stm, Sts)
Bar, channel
Gray green, medium bedded, fine grained sandstone with ripple and wedgebedding (Sws)
Shallow lake, bars of delta front
Gray green, medium or thick bedded, medium or fine grained sandstone,quartz up to 75–80%, well sorted with large scale trough crossstratifications, wedge cross beddings and ripple marks (Swm, Stm, Sws,Stm)
Eolian sandstone
Medium and fine grained sandstone withripple marks (Srm, Srs)
Yellow or gray purplish red, thin-medium bedded, medium-fine grainedsandstones, asymmetric ripple marks, wave length of 3–5 cm and waveheight of 1–2 cm, undulate ripple ridge
Point bar, channel
Light gray, medium and fine grained quartz sandstone, eolian ripple marks,ripple length of 10–15 cm and ripple height of 1–2 cm, straight ripple ridge
Eolian sandstone
Fine grained sandstone with rain prints(Srs)
Gray, medium-thick bedded, fine grained sandstone, rain prints andburrows
Purplish red, mudstone, calcareous and muddy siltstone, calcareousnodules, horizontal bedding
Shallow lake, delta front
L ded li
ZmMcaia(mgauCf
t2
dMs
aTMtwif
fa1ut1(fo
imestone, marl (Fbm) White gray, medium or thin bedhorizontal bedding
ircons were separated from samples using standard density andagnetic separation techniques at the Institute of Geology andineral Resources, Hebei. Zircon grains, together with the zir-
on U–Pb standard TEMORA (Black et al., 2003), were cast inn epoxy mount, which was then polished to section the crystalsn half for analysis. Zircons were documented with transmittednd reflected light micrographs as well as cathodoluminescenceCL) images to reveal their internal structures (Fig. 5), and theount was vacuum-coated with a 500-nm layer of high-purity
old. Under the guidance of zircon CL images, the zircons werenalyzed for U–Pb isotopes and U, Th, and Pb concentrationssing a SHRIMP II ion microprobe at the Beijing SHRIMPenter, Chinese Academy of Geological Sciences, Beijing,
ollowing the procedures reported by Liu D.Y. et al. (2006a).The U–Th–Pb isotopic ratios were determined relative
o the TEMORA standard zircon corresponding to 417 Ma06Pb/238U = 0.0668 (Black et al., 2003), and the absolute abun-
ances of U–Th–Pb were calibrated to the standard zircon257. Analyses of the TEMORA standard zircon were inter-
persed with unknown sample grains following the operating
zTo
mestone, gray medium bedded marl, Shallow or deep lake
nd data-processing procedures described by Williams (1998).he reference zircon was analyzed after every fourth analysis.easured compositions were corrected for common Pb using
he 204Pb method (Compston et al., 1984), and data processingas carried out using Isoplot (Ludwig, 2001). Uncertainties in
ndividual analyses are reported at the 1-sigma level; mean agesor pooled 206Pb/238U results are quoted at the 2-sigma level.
Zircons from the two rhyolitic tuff samples show crystalorms that are euhedral or long columnar with inherited coresnd fine crystallization growth texture mostly at sizes of about50–100 �m (Fig. 5). Sample 060815 exhibits low to highranium (1281–358 ppm) and thorium (4621–448 ppm) con-ent, yielding Th/U ratios from 1.55 to 3.73 (Table 2). Sample00724-3 shows low uranium (186–111 ppm) and thorium139–64 ppm) content and Th/U ratios from 0.73 to 0.49. Theseeatures are consistent with the zircons being magmatic inrigin (Compston et al., 1984). Thus, the interpretation of the
ircon U–Pb isotopic data (see Section 4) is straightforward.he obtained 206Pb/238U ages are interpreted as dating the timef crystallization of the zircons and, thus, the time of deposition
H. Xu et al. / Palaeoworld 21 (2012) 222–234 227
Fig. 3. Measured section of the Tuchengzi Formation at Weichang, Chengde, northern Hebei Province, North China. 1, purplish siltstone; 2, purplish gray medium-thick-bedded sandstone with siltstone; 3, purplish siltstone with gray sandstone; 4, white gray rhyolitic tuff; 5, purplish thick-bedded conglomerate with siltstone; 6,white gray rhyolite; 7, white gray rhyolitic breccia lava; 8, purplish medium-thick-bedded conglomerate; 9, purplish siltstone interbedded with lenticular conglomerate;10, purplish gray medium-thick-bedded conglomerate with purplish siltstone; 11, white gray rhyolite; 12, white gray rhyolitic tuff; 13, purplish medium-beddedconglomerate with siltstone; 14, purplish gray conglomerate interbedded with purplish siltstone; 15, purplish gray medium-bedded conglomerate and purplishs ne; (J3
C or int
oa
4
0gaamw1
fad
wdoRat
iltstone; 16, purplish gray medium-bedded conglomerate with purplish siltstoretaceous white gray rhyoliteporphyry; Qpm, Quaternary Malan Formation. (F
he web version of this article.)
f the host rocks. Zircon U–Pb age data from actual analysesnd data reduction procedures are given in Table 3.
. Analytical results and discussion
Total 206Pb/238U analytic results of 14 zircons from sample60815 yielded an age range of 148.5–156.9 Ma. One zirconave a youngest age of 148.5 Ma and the other 13 zircons yieldedn age interval of 151.2–156.9 Ma. Age data are all on a concord-
nt line (Fig. 6). All 14 zircons from 060815 yielded a weightedean 206Pb/238U date of 153.7 ± 1.1 Ma (2σ) (mean-squareeighted deviation, MSWD = 1.18). The 15 zircons from sample00724-3 contain an age population of 142.9–134.0 Ma, except
Sf1
Fig. 4. Sampled tuff intercalated in the topmost Tuchengz
-K1)tc, Late Jurassic to Early Cretaceous Tuchengzi Formation; K1��, Earlyterpretation of references to color in this figure legend, the reader is referred to
or one zircon of 267.7 Ma from wall rocks (Fig. 6). Age data arell on a concordant line and yield a weighted mean 206Pb/238Uate of 137.4 ± 1.3 Ma (2σ) (MSWD = 0.84) (Fig. 6).
The Tuchengzi Formation in northern Hebei Province andestern Liaoning Province was dated previously by various ageating methods (Fig. 7). He et al. (1998, 1999) reported agesf 156–145 Ma for the Tuchengzi Formation using K–Ar andb–Sr dates. Later, Swisher et al. (2002) reported an 40Ar/39Arge of 139 Ma from a tuff in “the topmost” Tuchengzi Forma-ion in Beipiao, western Liaoning. Cope (2003) reported a zircon
HRIMP U–Pb age of 156 Ma and an 40Ar/39Ar age of 152.6 Maor the base of the Tuchengzi Formation. A basalt K–Ar age of45 Ma from the upper Tuchengzi Formation was determined
i Formation, Chaoyang, western Liaoning Province.
228 H. Xu et al. / Palaeoworld 21 (2012) 222–234
F -3 ana RIMA alyze
bamtTeoaeattt
T1sirepd
F
FLa
ig. 5. Cathodoluminescence (CL) images of zircon from sampled tuff (100724nd Chaoyang, western Liaoning Province. (Circles indicate the locations of SHcademy of Geological Sciences. U/Th ratio in Tables 2 and 3 shows that all an
y Shao et al. (2003). Zhang et al. (2005) obtained Zircon U–Pbges of 136 and 140 Ma from the top of the Tuchengzi For-ation in northern Hebei. Zhang H. et al. (2008b) reported
hree zircon U–Pb ages between 147 and 142 Ma for the loweruchengzi Formation in northern Hebei. More recently, Changt al. (2009) published an 40Ar/39Ar age of 139 Ma for the topf the Tuchengzi Formation, which nearly coincides with theges from the same stratigraphic horizon obtained by Swishert al. (2002) and Zhang H. et al. (2005, 2008b). Although thebovementioned dates have provided a rough age estimate for
he Tuchengzi Formation, the confidence levels or errors forhese dates require further refinement. Ages for the bottom andhe top of the formation or the oldest and the youngest age of the
oet
ig. 6. Concordia plots of zircon SHRIMP U–Pb dating of tuffs from the Tuchengzi Foiaoning Province (100724-3). (Weighted mean ages are 2s analytical errors. Bar hen error range for each spot and age variation of analyzed spots in sample.)
d 060815) from the Tuchengzi Formation, Weichang, northern Hebei Province,P U–Pb dating, which were performed at Beijing SHRIMP II Center, Chinesed zircons are of magmatic origin.)
uchengzi Formation are particularly questionable (He et al.,998, 1999; Cope, 2003; Zhang H. et al., 2008b) and the datasethould be expanded. Furthermore, the eolian sandstones withnclined bedding distributed widely across northern China rep-esent a significant depositional event that may have affected thevolution of the terrestrial biota. These sandstones have not beenreviously described and dated. Therefore, current and furtherates for the Tuchengzi Formation are essential.
The current results indicate that the base of the Tuchengziormation is 153.7 ± 1.1 Ma, which is consistent, within error,
r slightly younger than the 156 Ma and older than the 152.6 Mastimated by Cope (2003). Field observations indicated thathere is no significant break between the Tuchengzi Formation
rmation, Weichang, northern Hebei Province (060815), and Chaoyang, westernights in inset are 2s. Common Pb corrected using measured 204Pb. Inset shows
H. Xu et al. / Palaeoworld 21 (2012) 222–234 229
ebei
aTpm1on(j(FzachosF
tezabtsa(esCla
ddozsspttfH2
NtJfs(amlcfihJ
dM
Fig. 7. Previous ages of the Tuchengzi Formation, northern H
nd the underlying Middle–Late Jurassic Tiaojishan Formation.herefore, the age of the top of the Tiaojishan Formation isreferred for constraining the basal age of the Tuchengzi For-ation. Davis et al. (2001) published two 40Ar/39Ar ages of
53.6 ± 3.8 Ma and 152.6 ± 0.3 Ma and one zircon U–Pb agef 153.3 ± 3.3 Ma for the top of the Tiaojishan Formation inorthern Hebei. Liu Y.Q. et al. (2006c, 2010) and Liu Y.X. et al.2006d) reported an age of 152 ± 2.6 Ma for the top of the Tiao-ishan Formation in Ningcheng, Inner Mongolia. Zhang H. et al.2008a, 2009) concluded that the youngest age of the Tiaojishanormation is no older than 153 Ma based on LA-ICP-MS U–Pbircon dating of the Tuchengzi Formation in western Liaoningnd northern Hebei. Thus, these previously determined ages areonsistent with an age of 153–154 Ma for the top of Tiaojis-an Formation, and are, within error, identical to the currentbtained age for the basal Tuchengzi Formation. Therefore, thistudy estimates the maximum age of 154 Ma for the Tuchengziormation.
The 40Ar/39Ar age of 139 Ma of Swisher et al. (2002) fromhe tuff at the top of the Tuchengzi Formation in Beipiao, west-rn Liaoning, the K–Ar age of 145 Ma (Shao et al., 2003), theircon U–Pb ages of 136 and 140 Ma (Zhang H. et al., 2008b),nd the 40Ar/39Ar age of 139 Ma of Chang et al. (2009) haveeen obtained from stratigraphic horizons lower than that ofhe eolian sandstone of the Tuchengzi Formation dated in thistudy; therefore, our result of 137.4 Ma is probably a more suit-ble estimate for the youngest age of the Tuchengzi FormationFig. 7). Meanwhile, this study implies that due to a high windnvironment at 137 Ma, large-scale inclined bedded eolian sand-tones were widely deposited in the northern areas of North
hina and a significant eolian geological event occurred on a
arge scale. The dry and high wind climate could have greatlyffected the terrestrial biota. Eolian sandstones are widely
hTb
Province and western Liaoning Xiao et al., 1994; Province.
istributed and well correlated from the east (eastern Shan-ong) to the west (northern Ordos Basin and middle Gansu)ver about a 2000 km range in North China during the late Meso-oic (Fig. 8). Statistical analysis of large-scale inclined beddinghowed that high winds prevailed, blowing from northwest tooutheast, in a geographic range between 25◦N and 41.2◦N. Theresent results, in combination with previous age estimates ofhe Early Cretaceous eolian sandstones of North China, indicatehat the age of the eolian sandstones is younger toward the westrom Kimmeridgian–Berriasian to Valanginian–Hauterivian andauterivian–Aptian (Meng, 1994; Huang, 2010; Tang et al.,008).
The Yanliao Biota (the equivalent Daohugou Biota iningcheng, Inner Mongolia) existed mainly before the deposi-
ion of the Tuchengzi Formation, in the Middle–Lower Jurassiciulongshan and Tiaojishan formations (Haifanggou and Lanqiormations in Liaoning), representing a subtropical, humid, andeasonal climate. The Yanliao Biota was first used by Hong1983) to refer to insect fauna from northern China and was laterdopted by Ren et al. (1995) to refer to the Middle Jurassic faunaainly from northern Hebei and western Liaoning. The Yan-
iao Biota included hundreds of insect species and many plants,onchostracans, ostracods, and bivalves. Important vertebrateossils have now been reported from the Tiaojishan Formationn the Daohugou area in Ningcheng, Inner Mongolia (the Dao-ugou Biota) and more recently from the Linglongta area inianchang, western Liaoning (Duan et al., 2009).
Like the Jehol Biota, the Yanliao/Daohugou Biota isistributed mainly in western Liaoning, southeastern Innerongolia, and northern Hebei, but some elements of the biota
ave a broader distribution in Central and East Asia. Theuchengzi Formation was deposited in a 20 Ma time intervaletween the Yanliao Biota and the Jehol Biota. Of the pollen
230 H. Xu et al. / Palaeoworld 21 (2012) 222–234
Fig. 8. Eolian sandstone and sedimentary facies in the Tuchengzi Formation, western Liaoning Province. A–G are outcrop photos of the Tuchengzi Formation,western Liaoning Province. A–C are outcrop photos of eolian sandstone with giant wedge shape cross-beddings, a, b, and c are sketches of A–C respectively; D ispurplish fine-grained sandstone or muddy siltstone of lacustrine facies; E is purple massive conglomerate in alluvial fan facies; F is purple red calcareous siltstoneof shallow lucustrine facies; G is purplish paleosoil. (For interpretation of references to color in this figure legend, the reader is referred to the web version of thisarticle.)
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/ Palaeow
orld 21
(2012) 222–234
231
Table 2SHRIMP U–Pb zircon age results of the basal Tuchengzi Formation, Weichang, northern Hebei Province.
Errors on individual spots are based on counting statistics and are at the 1σ level, but the average weighted ages are quoted at 2s or 72% confidence. Pbc and Pb* indicate the common and radiogenic portions,respectively. The common lead is corrected by assuming 206Pb/238U–208Pb/232Th age-concordance.
Table 3SHRIMP U–Pb zircon age results of the upper Tuchengzi Formation, Chaoyang, western Liaoning Province.
Errors on individual spots are based on counting statistics and are at the 1σ level, but the average weighted ages are quoted at 2s or 68.3% confidence. Pbc and Pb* indicate the common and radiogenic portions,respectively. The common lead is corrected by assuming 206Pb/238U–208Pb/232Th age-concordance.
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32 H. Xu et al. / Palaeo
ound in the Tuchengzi Formation, up to 86% is Classopol-is pollen (Zheng et al., 2001) and the percentage of conifernd pteridophyte pollen is low (below 2–3%), which sug-ests a hot, dry tropical and subtropical paleoclimate during itseposition. In contrast, pollen species in the middle Early Cre-aceous Dabeigou-Yixian-Jiufotang formations containing theehol Biota rapidly increased from 38 genera and 58 species inhe Dabeigou formation to 40 genera and 65 species in the Yix-an formation and 60 genera and 110 species in the Jiufotangormation. Among them, pollen of intermediate temperaturend humidity, especially Picea and Abies, prevail, indicating aountainous paleogeography with altitude of 2500 m above sea
evel.We favor the idea that the rise and decline of terrestrial
iotas is closely related with coeval paleogeography and pale-environments. With the closure of paleo-Asia Ocean in Lateermian–Early Triassic and the Mongolia-Okhotsk seaway iniddle–Late Jurassic (Chen et al., 2000; Mo et al., 2005; Li,
006; Lin et al., 2008; Li et al., 2009), an extensional environ-ent within the central Asia region, including the northern areas
f North China, and systems of rift basins widespread acrosshe region are infilled by products of intraplate bimodal mag-
atism and continental coarse-grained deposits. During Lateurassic–Early Cretaceous, a westward wind prevailed alonghe northern North China with great impact on the paleoecol-gy, resulting in a poor biota with rare fossils preserved in theuchengzi Formation. As shown in Fig. 2, most dinosaur tracksere preserved within the top unit (upper part or the topmost for-ation, (J3-K1)t3, (Lockley et al., 2006; Sullivan et al., 2009;ing et al., 2009, 2011, 2012; Zhang et al., 2012). Scatteredinosaur footprints of a few centimeters in length suggest that
phytophagous dinosaur of small body size lived at the timef the Tuchengzi Formation deposition. The high-wind climateight have adversely affected the paleoecology. The sudden
cological change from the Middle to Late Jurassic and the ear-iest Cretaceous led to massive reduction of the previous biotauring the deposition of the Tuchengzi Formation. This studyrovides a robust age constraint on the transition from the Yan-iao biota to the Jehol Biota and evidence on the changes in thealeogeography, paleoclimate, and paleoecology.
Distinctive bird tracks were reported from the topmost unitf the Tuchengzi Formation (Fig. 2), predating the famousixian Formation, which has produced a different avifauna inhaoyang, western Liaoning Province, and appear to repre-
ent different ichnotaxa and diverse avian ichnofaunas at thisime, suggesting that East Asian avian ichnofaunas are the mostiverse known during the Early Cretaceous (Lockley et al.,006). The precise age of the bird track-bearing beds here has noteen determined, but must be younger than 139 Ma. Firstly, birdrack-bearing horizon is within the topmost part ((J3-K1)t3) ofhe formation and immediately overlying the eolian sandstonesith large-scale inclined beddings horizons in the Tuchengziormation at the Yangshan track site, Chaoyang, western Liao-
ing. Secondly, current date of 137.4 Ma was obtained from theample of volcanic ash beds interbeded with eolian sandstones.evertheless, an age of 139.4 Ma (Swisher et al., 2002) yielded
rom tuff underlying aeolian sandstones, which is overlying the
C
21 (2012) 222–234
iddle member ((J3-K1)t2) of the Tuchengzi Formation andielding an age of ca.141 Ma (Zhang H. et al., 2008b). Thus,he bird tracks of the upper part of the Tuchengzi Formation arerobably of Early Cretaceous Valanginian age.
. Conclusions
Sediments in the Tuchengzi Formation (J3-K1) indicate arevailing tropical, dry, and hot paleoclimate at that time. Sud-en environmental change resulted in the disappearance of thearly biota during the deposition of the Tuchengzi Formation.e show that the U–Pb SHRIMP date of 154 Ma is the old-
st age constraint for the Tuchengzi Formation, nearly identicalo previously published ages for the top of the Tiaojishan For-
ation, suggesting that no significant hiatus exists between theuchengzi and underlying Tiaojishan Formation. It also implies
hat the disappearance or drastic reduction of the Yanliao Biotaccurred at 154 Ma to be replaced by elements of the later Jeholiota. Our date of 137 Ma represents the youngest age of theuchengzi Formation. This is the first attempt to provide an accu-ate age for the eolian deposit and to constrain the initial timef the prevailing west wind along the north rim of North Chinauring the studied period. The two isotopic dates suggest thathe Tuchengzi Formation was deposited between 154 Ma and37 Ma, when the paleoclimate and ecology changed dramati-ally, which possibly affected the evolutionary turnover betweenhe Yanliao and Jehol biotas. The bird tracks from the upper partf the Tuchengzi Formation are dated to be Early CretaceousValanginian).
cknowledgements
We thank Ms. Sun Liqin for her help during the labora-ory work and in processing the data for the zircon SHRIMP–Pb ages. Financial supports from the Natural Scienceoundation of China (90914003), the Foundation of Geologynstitute of CAGS (No. J1106), and the China Geology Survey1212010610421, 1212011085477) are gratefully acknowl-dged. Constructive reviews by Prof. Xiao-Qiao Wan and twononymous reviewers substantially improved the manuscript.
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