The Xiangyang reticulate red clay section was newly sampled in high-resolution. The viewpoints different from the previous studies[17] are put forward after studying Munsell color values, weathering degrees, magnetic ...The Xiangyang reticulate red clay section was newly sampled in high-resolution. The viewpoints different from the previous studies[17] are put forward after studying Munsell color values, weathering degrees, magnetic parame-ters and stable carbon isotopic compositions of the section. They are as follows: (1) The curves of hue, DCB extracted iron (Fed), DCB extracted iron/total iron ratio (Fed/Fet), weathering index (BA) of the section show that the redness is not significantly correlated with the weathering degree of the layers though the uppermost yellow-brown-colored layer is relatively weakly weathered. The variation in hues of the section is possibly attributed to the change of hematite and goethite contents. It is insufficient to determine the existence of the multiple deposit-pedogenesis cycles in the section, like the loess-paleosol sequence in Chinese Loess Plateau, only by the color variation. (2) Magnetic susceptibility (c) values in the non-reticulate and weakly reticulate layers are high; but are quite low in the reticulate red clay layer. The former are more than ten times higher than the latter because of the leaching and collapse of superparamagnetic (SP) and stable single domain (SSD) magnetic particles during the plinthitic processes. Hence, c values in the section are not controlled by weathering and pedogenic processes, and no longer have clear paleoclimatic implication. It is not correct to prove the existence of the multiple deposit-pedogenesis cycles in the section using c curves. (3) The organic d 13C curve of the section illustrates the reduction of forests and increasing of C4 plants in the study area since the late stage of the Qua-ternary period. It could not prove the existence of the multi-ple deposit-pedogenesis cycles in the section either. (4) As a matter of fact, it is difficult to prove the existence of the mul-tiple deposit-pedogenesis cycles in the Xiangyang section like the loess-paleosol sequence in Chinese Loess Plateau using the evidence available currently.展开更多
文摘The Xiangyang reticulate red clay section was newly sampled in high-resolution. The viewpoints different from the previous studies[17] are put forward after studying Munsell color values, weathering degrees, magnetic parame-ters and stable carbon isotopic compositions of the section. They are as follows: (1) The curves of hue, DCB extracted iron (Fed), DCB extracted iron/total iron ratio (Fed/Fet), weathering index (BA) of the section show that the redness is not significantly correlated with the weathering degree of the layers though the uppermost yellow-brown-colored layer is relatively weakly weathered. The variation in hues of the section is possibly attributed to the change of hematite and goethite contents. It is insufficient to determine the existence of the multiple deposit-pedogenesis cycles in the section, like the loess-paleosol sequence in Chinese Loess Plateau, only by the color variation. (2) Magnetic susceptibility (c) values in the non-reticulate and weakly reticulate layers are high; but are quite low in the reticulate red clay layer. The former are more than ten times higher than the latter because of the leaching and collapse of superparamagnetic (SP) and stable single domain (SSD) magnetic particles during the plinthitic processes. Hence, c values in the section are not controlled by weathering and pedogenic processes, and no longer have clear paleoclimatic implication. It is not correct to prove the existence of the multiple deposit-pedogenesis cycles in the section using c curves. (3) The organic d 13C curve of the section illustrates the reduction of forests and increasing of C4 plants in the study area since the late stage of the Qua-ternary period. It could not prove the existence of the multi-ple deposit-pedogenesis cycles in the section either. (4) As a matter of fact, it is difficult to prove the existence of the mul-tiple deposit-pedogenesis cycles in the Xiangyang section like the loess-paleosol sequence in Chinese Loess Plateau using the evidence available currently.
