A Preliminary investigataton on the variations of weathering coeffici-ent in heavy minerals

the ratio of feldspar/quartz of detrital minerals andtheir relationship with stratigraphy and major structures at deep well No.10 in the Xian depression of Wei river basin are presented here.The weathering coefficient curve of the deep well can obviously be devid-ed into three sections:The first section shows the assemblage of unstableminerls

correspond to the first assemblage of heavy minerals and the 1st velocity layer of the seismic logging

represents the Quaternary.The Second section shows the alternation of unstable and stable mineral assemblage coin-cident with the second and the third assemblages of heavy minerals and the 2nd-4th velocity layers

represnts the Pliocene.The third section is the stable mineral assemblage intercalated with small amount of unstable mine-ral assemblage correspond to the fourth and fifth assemblage of heavy mine-rals and the 5th-9th velocity layers

represents the Miocene.According to the curves of the weathering coefficient and the surface evidence

the Ganhe formation in the well

w hich had been divided intolower Tertiary

should be considered as the early Miocene

because of thefacts that the upper Tertiary in this well has not been penetrated yet.The variation of the coefficient curve shows us:This region has beenmainly subjected to subsidence and the sediments of river and lacustrine facieshave been deposited during the Miocene;in the age of Pliocene

the crustalmovement has been stengthened

a large amount of unstable minerals indicatsthat the uplifted weathering denudation has been strengthened;during the Quaternary

this region has been elevated violently and weathered intensely

the content of unstably mineral has been predominated.All these facts coin-cided with the tectonic activity of this region.The weathering coefficient in all orthr wells of southern Xian depres-sion has the consistency and almost may de correlated.