| The coastal loess in South Liaoning Province（Liaonan area）is locating at the easternmost edge of loess distribution in China,which better records the environmental evolution process of the eastern part of China.In this study,a typical coastal loess-paleosol sequence Xiajiahe section in the Liaonan area was investigated and selected as the research object.The geochemical,pedological,and Quaternary geological methods were used to reveal the pedogenic characteristics and their evolution of the typical loess-paleosol sequence by morphological observation,photoluminescence dating,elemental composition analysis,and basic physical and chemical properties.The results will deepen the understanding of peodogenic characteristics of deep loessal profiles in northeast coastal area,and lay a scientific foundation for studying the formation process of loess-paleosol sequences in Northeast China and deciphering their recorded environmental evolution information.The results show follows.（1）The Xiajiahe section was 1735 cm thick and had three gravel layers locating at 250cm,1382 cm and 1691 cm.It was a typical loess-paleosol sequence derived from wind deposits since 208.97±11.58 ka BP.It included a Holocene soil S0（48 cm thick,from13.00±0.81 ka BP to 0 ka BP）,a loess layer L1（660 cm thick,from 56.19±3.63 ka BP to13.00±0.81 ka BP）,a paleosol layer S1（492 cm thick,from 136.33±7.20 ka BP to 56.19±3.63ka BP）,a loess layer L2（362 cm thick,from 159.82±7.67 ka BP to 136.33±7.20 ka BP）,and a paleosol layer S2（173 cm thick,from 208.97±11.58 ka BP to 159.82±7.67 ka BP）.The section was predominant with sandy loam texture and blocky structure,and its color mainly ranged from 5YR to 7.5YR.The hue of paleosol layer was redder than the loess layer.The reddest soil layer appeared at 908～993cm in the paleosol layer S1.The paleosol layer mainly moderately developed,while the loess layer weakly developed.（2）The soil elemental composition of Xiajiahe section was dominated by Si O2,Al2O3and Fe2O3 with a total amount for more than 87%.The elemental contentswere sorted as to Si O2（71.60%）>Al2O3（11.83%）>Fe2O3（3.65%）>K2O（2.68%）>Na2O（1.74%）>Ca O（1.48%）>Mg O（0.99%）>Ti O2（0.63%）>Mn O（0.07%）>P2O5（0.05%）,and Ba（577.06μg/g）>Zr（326.39μg/g）>Sr（168.28μg/g）>Rb（94.27μg/g）>V（63.61μg/g）>Cr（50.96μg/g）>Zn（46.75μg/g）>Cu（17.38μg/g）>Ga（13.53μg/g）>Nb（11.18μg/g）>Co（10.38μg/g）>Th（8.27μg/g）.（3）The soil reddening rating index（RR）of Xiajiahe section ranged from 0 to 12,the chemical alteration index（CIA）ranged from 53.75 to 65.96,the chemical index of weathering（CIW）ranged from 63.22 to 76.31,the CPA index ranged from 76.73 to 86.09,the Na/K index ranged from 0.79 to 1.11,the K2O/Al2O3 index ranged from 20.50 to 28.56,Na2O/Al2O3 index ranged from 16.16 to 30.33,and Rb/Sr ranged from 0.50 to 0.74 and Ba/Sr ranged from 1.95 to 2.65.These indicated that the soil in the Xiajiahe section was basically in the primary chemical weathering stage,and the 908-993 cm soil layer reached the intermediate chemical weathering level.Combining with the A-CN-K chemical weathering triangle diagram,it indicated that the soils in the Xiajiahe section were basically in the stage of Ca and Na leaching,and a tendency of K depletion appeared in the 908-993 cm layer.（4）From 1735 to 1262 cm in the Xiajiahe section,the degree of soil development decreased from the bottom to the top;from 1262 to 908 cm,the degree of soil development started to increase and reached the strongest development intensity;from 908 to 445 cm,the degree of soil development started to decrease again;from 445 cm to the surface,the degree of soil development showed an increasing trend again.The degree of soil development was mainly influenced by temperature and precipitation,while sedimentary characteristics also showed certain contributions.When the degree of soil development became weaker,the corresponding climate showed a dry-cold trend;conversely,when the degree of soil development increased,the corresponding climate showed a humid-warm trend.The pedogenic characteristics of the typical loess-paleosol sequence in Liaonan had recorded four major climatic fluctuations since the Late Quaternary,from 208.97 ka BP to 152.11 ka BP,from 152.11 ka BP to 103.82 ka BP,from 103.82 ka BP to 24.27 ka BP,and from 24.27 ka BP to 0 ka BP.（5）Compared to pedogenic characteristics of typical loess-paleosol sequences from other regions in China,results showed that the chemical alteration index（CIA）values showed a trend of Zhangqiu（63.21）>Luochuan（61.66）>Liaonan（59.37）>Zhongliang（51.24）and the Na/K ratio for Zhongliang（1.48）>Liaonan（0.98）>Luochuan（0.96）>Zhangqiu（0.94）.The typical loess-paleosol sequences in Liaonan,Luochuan,Zhangqiu and Zhongliang areas were mainly at the primary chemical weathering stage,the strongest development intensity appreared in Zhangqiu and Liaonan as the moderate chemical weathering level,and the weakest level of soil development appeared in Zhongliang as the unweathered stage.Further correlation analysis of longitude,latitude,mean annual temperature,and mean annual precipitation data with soil development intensity showed that the temperature and precipitation influenced by latitude factors and sea-land location directly affected the developmental characteristics of the loess-paleosol sequence. |
