Dinosaur Tracks And Environment Analysis Of The Upper Jurassic Tuchengzi Formation In Yanqing Global Geopark,Beijing

Yanqing county is located in the northwestern part of Beijing,and Yanqing Global Geopark is situated in the northern and southern mountainous areas of Yanqing.In 2011,a lot of dinosaur footprints in its Qianjiadian Scenic Area were found during the geoheritage investigation in preparation of application for the GGN membership,these dinosaur footprints are the first record in Beijing.However,the previous studies about the footprint-bearing strata(the third section of Tuchengzi Formation)are quite few.Therefore,the integrated study about dinosaur footprints and sedimentary environment is very important.Based on the detailed field investigation,using paleontological,petrological,sedimentary research methods,including the detailed measures of dinosaur footprints in field,indoor identification of dinosaur footprints,thin section analysis,and grain size distribution analysis,and detailed comparison in dinosaur footprint types,sedimentary environment and geological age with the Tuchengzi Formation in adjacent northern Hebei and western Liaoning,this paper obtains the following new results:1.The dinosaur footprints in the study area are belonging to the sauropod,theropod,and ornithopod tracks,and this paper considers that the previous possible thyreophoran footprints should be medium-sized sauropod tracks.At present,there are three major tracksites,yielding 193 footprints,including 105 sauropod footprints with 4 trackways,belonging to Brontopodus isp.,85 theropod footprints with 12 trackways,belonging to Grallator isp.,and 3 ornithopod footprints with 1 trackway,whose species is indeterminated,among them,the sauropod and ornithopod footprints are the first discovery in Tuchengzi Formation.2.According to the dinosaur footprint characteristics,sizes and distance between two tracks,this paper studies the possible dinosaur body length,moving speeds and their palaeoethology,indicating the body length of theropods ranges from 1.19 m to 1.82 m and the fastest running speed of 4.22 m/s;while the body length of sauropods is from 2.60 m to 8.19 m,and they walked slowly with the speed range from 0.45 to 0.57 m/s.Both are gregarious.The climate of Late Jurassic in Qianjiadian area is semiarid to arid based on the track assemblages and sedimentary rocks.3.The petrological analysis indicates that the third member of Tuchengzi Formation in the study area consists of terrigenous sandstone and tuffite.The dinosaur tracks preserved together with ripples,cracks,and burrows(Monocraterion isp.and Scoyenia isp.)indicate a shallow water.According to the grain size distribution analysis formula of depositional environment,with grain characteristic parameters,grain size frequency distribution histogram,the particle size of the cumulative curves,structural parameters scatter plots and CM Figures,the sedimentary environment of the third member of Tuchengzi Formation was a shallow lake,and the dinosaur tracks were formed in a lakeshore environment.4.Compared with the sedimentary environment,dinosaur track type and geological age of Tuchengzi Formation in northern Hebei and western Liaoning,the geological age of the third member of Tuchengzi Formation in the study area should be the Late Jurassic.