The karst profile at Yangjikan section

Keping

northwestern Tarim Basin

provides an excellent opportunity to evaluate the relative importance of reaction between fault bend fold-controlled uplift and meteoric water dissolution-controlled karstification during the middle and late Himalayan movement; and then the porosity caused by interlayer decollement under structural compression and dissolution was estimated

in line with the comprehensive study of petrographic

geochemical and fold disengaging analyses.The fold disengaging(simulated with VSD)facilitated the result of 0.2%-0.5% porous zones

accounting for 1/50-1/100 of the effective and actual empty-cavity rate.However

the porous zones have played a significant role in Darcy flow channel formation and karstification.The breccias related to mechanical fracture filling

calcareous tufas and megacrystalline calcites are well developed in the Yangjikan section karst reservoir.Compared to the surrounding rocks of the Dawangou Formation

the negative and linear correlation of δ

18

O(PDB)and δ

13

C(PDB)in the formation is distinct

and single-phase aqueous inclusions

typical products of meteoric water karstification

grew in the megacryst calcites within fractures and cavities.A successive tufa depositions from the lower to the upper section of karst profile

are characteristic of weakening negative depleted δ

13

O(PDB)

δ

18

O(PDB) and δ

34

S(V-CDT).The content of Al

2

O

3

Fe

2

O

3

MgO

K

2

O

and Na

2

O decreases from tufas to megacrystalline calcites to(long)cylindrical scalenohedron calcites

indicating a transition in climate conditions from semi-wet to humid

to semi-humid and then to drought

as well as changes of hydrodynamic conditions.Moreover

the karst cavern of 1.5m-2.0m high can be formed within less than 5ka under a hot humid and strong hydrodynamic condition

while it may take a longer time in semi-humid and drought climate.