根据野外调查和室内分析,确定了长武和西安地区第 5层古土壤的 Ca CO3和 Fe2 O3已迁出了古土壤,该层古土壤为酸性淋溶土壤。长武和西安第 5层古土壤剖面构型分别为 Bts- Cs- Cl-Bk- C型和 Bts- Cf- Cs- Cl- Bk- C型。该层古土壤底部之下发育了有 Fe2 O3淀积的深部风化层,表明当时风化作用至少已开始进入铁铝氧化物迁移的化学风化中期阶段。 Fe2 O3、 Ca CO3迁移特征、孢粉、粘土矿物和深部风化层等 6项指标显示距今 50 0 ka BP前后亚热带气候迁移到了黄土高原中部,当时年均降水量显著增加。

It is discovered through field investigations that the illuvium of CaCO 3 in the 5th layer of paleosol in Changwu and Xi’an does not get in touch with the bottom of clay grouting layer but lies in loess which is 0 5～2 3 m deep under the bottom of clay grouting layer, and the red ferruginous clay film also migrated to the mother loess It is indicated that CaCO 3 and Fe 2O 3 migrated out of the paleosol, the paleosol has the character of acid elevation and at least the weathering had already been in the middle of the chemical weathering process at that time The weathered loess layer (Cs) with ferruginous film and weathered loess layer (Cl) without ferruginous film were discovered under the bottom of the 5th layer of paleosol in Changwu and Xi’an, and the light red brown weathered loess layer (Cf) with ferruginous concretion was discovered under the bottom of 5th paleosol in Xi’an Generally, the content of CaCO 3 is less than 0 5% in weathered loess layers, and the content of clay grains, Fe 2O 3 and Al 2O 3 is higher in weathered loess layers than in the unweathered loess layer, which indicates that each of the weathered loess layer had experienced chemical weathering to a certain extent The material shows that the 5th layer of paleosol in Changwu and Xi’an has the character of subtropical soil and its profile construction is Bts Cs Cl Bk C in Changwu and is Bts Cf Cs Bk C in Xi’an The content of smalite takes 8% 9% in the clay film of the 5th layer of paleosol in Xi’an, the sporo pollen of some subtropical Liquidambar and Castanoposis appear in the paleosol in Changwu, which points out that the 5th paleosol developed in subtropical climate Six indexes, removed depth of Fe 2O 3 and CaCO 3, deep weathered loess layers and sporo pollen and so on, indicate that the subtropical climate migrated to the middle area of Loess Plateau at about 500 ka BP, mean annual precipitation was 850～900 mm in Changwu area and was about 1 100 mm in Xi’an area According to the obvious increase of the precipitation at about 500 ka BP and 100 ka BP ascertained by the author, after eliminating the effect of the new tectogenesis, it can be drawn that in interglacials which was obviously warmer than today.