Sequences In China Research Articles

A loess-paleosol dating method

Based on the non-diachronic nature of loess- paleosol sequences, a paleosol dating method is suggested. Based on this method, the extant drainage system of the Yellow River was found to be 1.67-1.45 Ma old. During its existence, six fluvial terraces and two alluvial plains were formed. In the deposits of this time interval, studied in 400 sections, 33 cycles were identified in the sequence built of aquatic sediments and paleosol. Correlation of loess, paleosol, and aquatic sediment sequences of China and other regions points to a 0.4 Ma periodicity in the hydrologic regime and in the denudational processes. This periodicity might be related to global climatic changes due to changes of orbital parameters of the Earth.

Paleoclimates and monsoon variations interpreted from micromorphogenic features of the Baoji paleosols, China

A full climatic interpretation of the loess-paleosol sequence in China that covers the last 2.5 Ma nearly continuously has been restricted because the soils in the oldest loess unit — the Wucheng Loess — spanning about 1.2–2.5 Ma are not distinct enough to ensure accurate recognition and subdivision in the field. Recently, the authors investigated the Baoji loess-paleosol sequence in the southern-most part of the Loess Plateau where 37 paleosols were clearly defined, including those of the Wucheng Loess. Based on macro- and micromorphological observations, the major pedogenic processes involved in the formation of the Baoji paleosol are believed to be carbonate eluviation and illuviation, clay translocation, pseudogleization and rubification. The diagnostic B horizons of the 37 soils are classified into four types — Bw or weak Bt, moderate Bt, strong Bt and very strong Bt. The Holocene soil at Baoji contains a moderately developed Bt, which is interpreted to have formed under steppe-forest vegetation. Most of the soils with Bt horizons to the Holocene soil are interpreted to be developed under forest and/or steppe-forest environments. Primary carbonates in most of the loess beds have been leached with the loess beds acquiring weak to strong granular structures. The loess is subdivided into four types — massive, weakly weathered, moderately weathered and strongly weathered. They are believed to have mainly accumulated under steppe environments. Variations of monsoonal rain exhibit frequent and wide oscillations over the last 2.5 Ma documented by alternations of loess and paleosol units. The oscillatory pattern appears to be a function of the time interval considered.

The record and stratigraphie implications of organic-walled microfossils from the Ediacaran (terminal Proterozoic) of South Australia

AbstractTwo assemblages of organic-walled microfossils have been recognized in drillcore samples from the late Proterozoic Rodda Beds in theeastern Officer Basin, South Australia. The fossils include tube-like remains and large, simple and sculptured acritarchs. Lithostratigraphic studies and seismic information, in conjunction with previous (albeit limited) acritarch finds, allow local correlation of the Rodda Beds with Ediacaran or terminal Proterozoic sequences in the northern Adelaide Fold Belt (site of the nominated Ediacaran stratotype). The new palynofloras are comparable withacritarch assemblages in the Amadeus Basin of central Australia, and suggest tentative correlations with sequences in China and the U.S.S.R. The presence of isotopically heavy marine carbonate in the lower fossiliferous horizons of the Rodda Beds (σ13CPDB= +3 to +6%0) is consistent with isotopic data from the equivalent interval in China. In contrast, the upper fossiliferous strata occur higher in the Rodda Beds where carbonate is significantly lighter (σ13CPDB= -1 to + 3%0).

Carbon isotope study of the Permian-Triassic boundary sequences in China

Systematic investigations for carbon isotopes on five stratigraphic sections of the marine carbonate strata from the Upper Permian to the Lower Triassic in the southern China have been conducted. The results obtained in these sections indicate the following characteristics: 1. (1) The δ 13C-values varying from −8.1 to +5.5%o. 2. (2) The δ 13C-values vary periodically from the base to the top in a stratigraphic unit. 3. (3) The δ 13C-values are positive below, but negative above the Permian-Triassic boundary. The δ 13C-values display a sharp drop within a limited stratigraphic interval (0.1 – 0.5 m) across the Permian-Triassic boundary. Our study and carbon isotope investigations of marine carbonate sequences across the Permian-Triassic boundary in other areas suggest that a drastic shift in carbon isotope compositions at the Permian-Triassic boundary probably occurred contemporaneously and globally, at least in the Tethys areas. The variation of carbon isotope compositions in marine stratigraphy sections may be used as a new criterion for stratigraphic correlation.

The Loess-Paleosol Sequence in China and Climatic History

The Loess-Paleosol Sequence in China and Climatic History