| Holocene is the period of rapid development of human civilization, environmental change of this period has a very profound influence to the development of human society. A study of change law of Holocene is always an important part of global change, its research findings has important reference value to reconstruct the paleoclimate and ancient environment model in the past and predict the future evolution of the environment. Loess-paleosol sequence is formed from aeolian deposits and pedogenetic process under the alternately warm or cold weather and cyclical changes in the Quaternary, which is a good carrier of land information on global change study. Based on the extensive collection of domestic and foreign geologists and Quaternary environmental evolution progress, through detailed field investigation, this paper selects a TSG profile of the "Dali Man site" in Eastern Guanzhong as the research object, on the system research, we are trying to extract the environment and its evolution messages since Holocene.TSG profile is a typical Holocene loess-paleosol profile with continuous formation, intact conservation. In this paper, we make a systematic analysis of physical and chemical properties, such as magnetic susceptibility, grain size, carbonate content, pH, loss on ignition, and elements. On the distribution of these parameters and its Causes for in-depth analysis, we gain a wealth of information about Holocene environmental characteristics and its evolution of high-resolution information. Through comprehensive analysis and summary, the paper obtained the following understanding:(1) In TSG profile, complete stratigraphic section above the late Pleistocene, with the MSâ†'L0â†'S0â†'Ltâ†'L1 configuration. Stratigraphic sequence from top to bottom:MS,2.5Y8/4, silt texture, granular structure; L0,7.5YR7/4, silt texture, mass structure; S0,7.5YR6/4, silty clay texture, aggregate-mass structure; Lt,5YR6/3, silt texture, mass structure; L1, 7.5YR7/3, silt texture. This section completely records of the Holocene environmental change messages.(2) Compared loess with paleosol of TSG profiles, funding that different climate proxies show significantly different values, such as magnetic susceptibility, clay, loss on ignition, moisture water content, calcium carbonate, pH, they reflected different periods of pedogenetic environment in Holocene. The magnetic susceptibility, loss on ignition, clay and moisture water content of So in TSG profile showed high values, relatively low in loess; and calcium carbonate, coarse sand and pH value in S0 showed low, but high values in loess.(3) TSG Holocene loess-paleosol sequence has the typical characteristics of fractal structure. The fractal dimension values of the entire profile are between 2.5443 and 2.7123, whoes average of So was the largest (2.6713), Lt and L0 were 2.6318 and 2.6314. Fractal dimension curve with magnetic susceptibility, median grain size curve compared well, indicating that its changes reflect the evolution of the pedogenetic environment to some extent, we can used fractal dimension as a proxy indicator of climate, its high value indicates relatively warm climate and strong pedogenesis, low value indicates a relatively dry and cold climate and weak pedogenesis.(4) K/Na, Si-Al-Fe ratio, SiO2/(MgO+CaO), and residual coefficient of So in TSG profiles show significant high values, leaching factor displays low value, indicating that weathering function was strong during the formation of So, which is the most appropriate period of soil development; and accumulation of L0 and L1 relatively weak. CIA values of this profile reflects the distribution of the chemical weathering of So is highest degree, it is produced in the background with warm, humid climate conditions, while the weakest chemical weathering of L1; the diagram of CIA and K/Na also reflects the different degrees of chemical weathering of loess and paleosol, the weathering of intensity profile as follows:S0>L0>MS>Lt>L1.(5) The formation of TSG Holocene section, the geochemical behavior of the major elements Ca, Mg and Na showed a strong migration and leaching, Si and K showed weak enrichment characteristics, and the migration of Fe was not obvious. the activity and migration order of major elements:Ca> Na> Mg> Al> Fe> K> Si; trace elements of Cr, Sr and Pb had a strong migration, V and Ba were weak activity with slight migration changes, and As was expressed as enrichment, the migration change curves of Cr, Pb fluctuated, the migration order of trace elements:Sr> Ba> V> Ni> Cu> Zn> Rb> As.(6) Holocene pedogenetic environmental changes in the Eastern Guanzhong, the early Holocene, dry and cold environment, eolian deposits dominated, with weak pedogenesis, in this relatively dry climate conditions, mainly form Lt; To the stage of middle Holocene, the climate became warm and humid, weathering strong, clay and organic matter content increased, strong pedogenesis led some soluble elements migration of leaching downward, making some heavy metals elements in So was relatively rich, forming So; since the late Holocene, this area became relatively dry, pedogenesis had also been weakened, then transfer into accumulating loess mainly. |
PDF Full Text Request