Stop 1 Huangshandian1.Content(1)Observation of overturned strata in the Huangshandian area.(2)Infer a large overthrust fault system from the stratigraphic relationships in the Huangshandian area.(3)Observe a large overturned fault and associated cleavage.2.Purpose(1)Based on the relationships in Huangshandian,fully understand the concept that“strata are the basis of structure analysis”.(2)Understand the stacking relations of the multi-phase structure.(3)Understand such structural phenomena as fold-thrust structure,folding layer,overturned fault and sheath fold.3.Main observationsStop ALocation:Western side of Huangshandian villageContent:(1)A ductile shear zone with layering occurs in the Tieling Fm.(Jxt)of the Jixian system and extends from Huangshandian village to the hillside behind Huangshandian elementary school,(2)overturned strata of Xiamaling,Tieling,Hongshuizhuang and Wumishan Formations.Description:Observe the thick-bedded dolomite of the Wumishan Fm.,the phyllite of the Hongshuizhuang Fm.,the dolomite of the Tieling Fm.,and metamorphic arenaoeous-pelitic rock at the base of the Xiamaling Fm.where they crop out along the path through Huangshandian village.In the Huangshandian area a large recumbent fold is made up of layers with a combination of strong strain and weak strain(Fig.3-11,Fig.3-12).A planar section of the stronger strain belt can be seen in laminated dolomite and oalcareous dolomite of the Tieling Fm.at the ohicken farm.Here,what appears to be bedding is actually intense flow cleavage,or penetrative cleavage.The deformation also formed some pencil structures and folds,and the rock has been mylonitized by strong shear.In outcrop,the fine-grained,dark and the coarse-grained light domains form a zone with the characteristics of rheomorphio struoture.On a larger scale,S and C foliations interweave to form a diamond network-node(Fig.3-11).Based on strain measurement in the XZ plane of this ductile shear zone,the deformational strength of the dolomite increased from edge to center.The ratio of minor axis and apical axis increases from 1 to 2 to 1 to 3.5.In the center of the belt,the rock is extremely sheared and the grain size is only about 10 micron（μm).The porphyroclasts have an asymmetrical structure,produced by rotation.These features of ductile deformation define extensional tectonic event Dl.Fig.3-11 Sketch of ductile shear zone with bedding in the chicken farm at Huangshandian,BaojinshankouThe Huangshandian fold-overthrust fault overprints the features formed by tectonic event Dl.The fold-fault system is exposed over an area of about 30 km2 and is made up of a recumbent anticline and a recumbent syncline,which together form a shovel-type thrust fault(Fig.3-12).On the overturned fold limb,the fault plane has been re-folded into a broad syncline.Looking into the distance from the north slope ditch behind the village,one can see the hinge zone of the large recumbent fold developed in strata of the Wumishan,Hongshuizhuang and Tieling Formation.The hinge trends in an ENE direction at 75°－80°，and the axial plane dips to the SSE.The thrust plane disappears under hill 628 m on the east side of the Huang Yuan Temple.Near the core of the anticline,stromatolites of the Wumishan Fm.have been strongly sheared,and are upside down,indicating that the strata are overturned.Along the road to the northwest,pods of folded dolomite with lamina of calcareous dolomite of the Tieling Fm.are well developed and show mineral lineations nearly parallel to the fold hinge.Muddy strata crop out in the core of the recumbent syncline where the foliation is entirely replaced by axial-plane cleavage D2.Fig.3-12 Huangshandian fold-thrust nappe structure(after Yan et al.,2006).Field photosA—and geological section; B—indicate the geometry and kinematics of this fold—thrust nappeRecent study(Yan et al.,2006)shows that the fault displacement gradually increases to the west of the observation point.The strata of Wumishan Fm.were pushed onto the strata of the Tieling Fm.,which forms the normal limb of the recumbent syncline.The greatest displacement was 2.75 km(Shan et al:1991).Stop BLocation:The hillside behind the Huangshandian elementary school.Content:Overturned stromatolites of the Wumishan Fm.Description:Pyramid stromatolites are developed in dolomite of the Wumishan Fm..Stromatolite cusps point to the underside and most cross the bedding plane at a high angle,which indicates that the strata are overturned.We can measure the strike-dip of the stromatolites and other structural elements.Stop CLocation:Penstock wall beside the southeast road of Huangshandian.Content:Connate deposit structure in the Wumishan Fm.Description:Thick-bedded dolomite of the Wumishan Fm.crops out at this location.It is only weakly deformed and its primary structures are well preserved.On the penstock wall,one can observe well-preserved water-escape structures and scour structures.Growth faults and disturbed bedding are obvious,showing that the connate deposit was unstable.The stromatolites in these rocks are erect and upward-facing.Stop DLocation:East flat-topped ridge of Huangyuan.Content:Sedimentary sequence and lithology of the Neoproterozoic Changlongshan and Jingeryu Fms.and some Paleozoic rocks.4.Questions for discussion(1)What are the characteristics of a fold-thrust structure?(2)How can one recognize syn-sedimentary growth faults?(3)How can one determine whether a sedimentary sequence is right side up or overturned?(4)How can one determine whether a folded layer is an anticline or syncline?Stop 2 Gushankou large recumbent fold1.LocationGushankou railway cut(Fig.3-13).2.Purpose(1)To observe the shape of a complicated fold at the Gushankou railway cut.(2)To recognize the associated structures in the fold and understand the structuralr elationships among the associated structures and the main fold.Fig.3-13 ⅡA-type recumbent fold in siliceous dolomitic marble and carbonaceous phyllite of the Wumishan Fm.,Gushankou railway cut(After Yan et al.,2006)A—a large-scale recumbent fold at Gushankou involving dolomite,limestone and phylite of the Wumishan formation(Jxw）;B—a sub-harmonic parallel fold(type IB)in competent dolomite,compared with type Ⅲ fold in incompetent phyllite(cf.Ramsay&Huber 1987);C—a ductile shear zone(inferred from several outcrops in Gushankou area),which has a top-to-the-southeast sense of shear;D—hinge zone of the large-scale recumbent fold at Gushankou involving dolomite,limestone and phyllite of the Wumishan formation(Jxw）;E—cleavages within the phyllite of the recumbent fold indicate a top-to-the-southeast sense of shear;F—Stereonet plot(lower hemisphere projection)of mineral lineations and S1 foliation fromuhe locality shown in E,indicating the southeast-northwest orientation of the principal strain(3)Sketch various parts of the outcrop.3.Main contentStop ALocation:The south hill tip at Gushankou railway cut.Content:Observe the overall character of the complicated fold on the north wall of the Gushankou railway cut.Description:Observe the complicated fold from SE to NW.Using the khaki-colored calcareous phyllite as an index bed,trace the outline of the fold.The fold has a long and gently dipping normal limb,and a short,steeply dipping overturned limb,and thus is a recumbent fold.Observe the character of the fold and then sketch the section carefully(Fig.3-13).Stop BLocation:Att he western part of the southern abrupt wall of the Gushankou railway cut.Content:Observe the small-scale structures.Description:(1)Observe the foliation and the minerall ineation,and measure their dip direction and dip angle.(2)Observe the recumbent fold and the refraction cleavage in the hinge zone of the fold.stop CLocation:Western part of the north abrupt wall at the Gushankou railway cut.Content:Observe the sub-fold and bedding fault.Description:(1)Observe the distribution ofthe“Z”“M”“S” type sub-folds,and measure their attitudes.(2)Observe the bedding fault,and confirm the character of the fault(according to the drag folds and the relationship to the fault surface and the cleavage in the fault zone).(3)Sketch the structural features with appropriate scale.Stop DLocation:Center of the north abrupt wall at the Gushankou railway cut.Content:Observe the cleavage and joint.Description:(1)Observe the refraction cleavage and the bending cleavage,and examine the relationship between cleavage dip angle(referring to the bed)and rock type.(2)Observe the fan-type and reverse fan-type cleavage in the hinge zone of the fold,and their relationship to the rock types.(3)Observe the relationship between cleavage and bedding.(4)Observe the torch-type joint combination.These joints represent brittle deformation,and overprint on the cleavage,which indicates brittle-ductile or ductile deformation.These joints have an echelon arrangement.Stop ELocation:South abrupt wall att he Gushankou railway cut.Content:Observe the mullion structure.Description:(1)Observe the strike and dip and the morphology of the mullion structure.Note that interlayered quartzite and phyllonite crop out here.The thick-bedded quartzite forms cylindrical folds with divisional cleavage,whereas the phyllonite forms cuspidal-circular folds with penetrative foliation.The combination of fold-type and foliation produces the mullion structure.(2)Sketch this outcrop.Stop FLocation:Eastern part of the north abrupt wall of the Gushankou railway cut.Content:Observe the sheath fold(Fig.3-14)and the stromatolites.Description:(1)Shape of the sheath fold.In the YZ section，“Ω”type and closed folds can be observed here,and a symmetric“Z”type fold can be seen in he XZ section.Fig.3-14 Sheath fold noses in the YZ and XZ sections,including a ductile shear zone occurring within the Wumishan Fm.at Gushankou(2)Character of the sheath fold hinge.Note that the minerall ineation is parallel to the hinge of the sheath fold.(3)Observe the stromatolites.Note that some workers consider these to be stromatolites,but others consider them to be sheath folds(Fig.3-14).4.Questions for discussions(1)How can we utilize the minor-scale structures to recognize the character of a large scale of fold?(2)Why is such a complicated fold present in the Gushankou area?(3)Why do variable lithologies in this structure show different deformation?Stop 3 The museum at the Peking man ruins(Fig.3-15)Purpose:Visit the museum of the Peking man to understand the process of human evolution and its significance.Fig.3-15 The museum att he Peking man ruins
