Analytical Model for the Palaeoenvironmental Evolution of the Nihewan Beds

In this paper, the evolutional characteristics of palaeoclimate and oxidation-reduction conditions as well asacidity-alkalinity environment are discussed by means of the step-regression, cluster, optimal partitioning andcorrelation analyses of CaCO_3, C / P_2O_5, Fe~(2+) / Fe~(3+), pH and Eh values, taking the Xiaodukou section in theNihewan basin as an example. The CaCO_3, C / P_2O_5 and pH were calculated respectively using the optimalpartitioning method. Thus five cold zones and six warm zones as well as five reduction and six oxidation zoneswere distinguished. Then the inductive method was used to produce four numerical groups: 8.10, 8.3-8.4,8.6-8.7 and 8.9-8,97. The above-mentioned results are respectively based on CaCO_3 content, C/P_2O_5 andpH values. From Fig. 3, Tables 1 and 2 it can be seen that the Nihewan Beds were formed mainly under a re-duction and slightly alkaline environment of cold climate, with pH values of 8.3-8.4. Fig. 3 shows that bed 35is approximately near the boundary between the Brunhes and Matuyama polarity epochs, 0.73 Ma in age; bed26 is roughly near the Jaramillo event (base), 0.97 Ma in age; bed 18 coincides roughly with themagnetostratigraphic boundary of 2.00 Ma (?). Bed 13 may be the Pleistocene-Pliocene boundary, 2.48 Ma inage. Thus geochemical zones Ⅰ, Ⅱ, Ⅲ and Ⅳ include respectively cold zones 1; 2 and 3; 4; and 5.

Analytical Model for the Palaeoenvironmental Evolution of the Nihewan Beds

Abstract In this paper, the evolutional characteristics of palaeoclimate and oxidation-reduction conditions as well as acidity-alkalinity environment are discussed by means of the step-regression, cluster, optimal partitioning and correlation analyses of CaCO₃, C / P₂O₅, Fe²⁺ / Fe³⁺, pH and Eh values, taking the Xiaodukou section in the Nihewan basin as an example. The CaCO₃, C / P₂O₅ and pH were calculated respectively using the optimal partitioning method. Thus five cold zones and six warm zones as well as five reduction and six oxidation zones were distinguished. Then the inductive method was used to produce four numerical groups: 8.10, 8.3–8.4, 8.6–8.7 and 8.9–8.97. The above-mentioned results are respectively based on CaCO₃ content, C/ P₂O₅ and pH values. From Fig. 3, Tables 1 and 2 it can be seen that the Nihewan Beds were formed mainly under a reduction and slightly alkaline environment of cold climate, with pH values of 8.3–8.4. Fig. 3 shows that bed 35 is approximately near the boundary between the Brunhes and Matuyama polarity epochs, 0.73 Ma in age; bed 26 is roughly near the Jaramillo event (base), 0.97 Ma in age; bed 18 coincides roughly with the magnetostratigraphic boundary of 2.00 Ma (?). Bed 13 may be the Pleistocene-Pliocene boundary, 2.48 Ma in age. Thus geochemical zones I, ?, IH and IV include respectively cold zones 1; 2 and 3; 4; and 5.