A high-resolution micromorphological record of the Late Quaternary paleosols from Ganga—Yamuna interfluve: Stratigraphic and paleoclimatic implications

摘要

This study reports the micromorphological record of a continuous set of samples from paleosol-bearing intervals of two subsurface cores of ～ 50 m depth representing typical pedosedimentary sequences of the Ganga-Yamuna interfluve in the western Ganga Plains. Micromorphology (microstructures, rhi-zocretes, Fe-Mn features, pedogenic carbonate, illuvial clay coatings and relict pedofeatures) was used to characterize pedogenic processes in the 13 paleosols in the IITK core and the 10 paleosols in the Bhognipur core. Formation of these paleosols took place through incipient to moderate weathering on relatively stable surfaces of the Ganga-Yamuna interfluve over the last 100 ka. These paleosols range in character from simple ones having weakly developed pedofeatures to mature paleosols with strongly developed pedofeatures and are similar to modern Entisols, Inceptisols, Alfisols and Vertisols of the Ganga Plains. Pedosedimentary evolution in the two interfluve successions differs in terms of stratigraphic stacking of paleosols, types of paleosols, and heterogeneous nature of sediments. In the northern part, the IITK interfluve core is marked by a thick mature paleosol with a strongly developed argillic (Bt) horizon at 41-45 m depth and weakly developed paleosols in the remaining part of the core. The mature paleosol represents a major discontinuity when prolonged pedogenic activity took place on stable surfaces with little or no deposition. On the other hand, thin-simple-thick cumulic paleosols with weakly developed pedogenic features, even with some preservation of sedimentary laminations indicate short stratigraphic breaks in rapidly aggrading sediments. In the southern part, the Bhognipur core is marked by the heterogeneous nature of sediments with a predominance of cratonic sediments in the lower part and the Himalayan sediments in the upper parts. In contrast, the IITK core shows a Himalayan source throughout. The entire interfluve succession in the Bhognipur region is marked by rapid sedimentation and short pedogenic intervals of weakly developed paleosols excepting one mature paleosol with well-developed argillic (Bt) and vertic (Bss) horizons at 10-14 m depth. This mature paleosol possibly formed synchronously with a mature paleosol from the northern part of this interfluve. The mature paleosol in both the cores represents a major stratigraphic break of 8000-10,000 years when prolonged pedo-genesis occurred over large areas of the Ganga-Yamuna interfluve following regional degradation and local gullying in response to climate change from sub-humid to semi-arid conditions during the MIS 5-4 transition.