LARGE-SCALE TABULAR CROSS-BEDDINGS IN LOWER CRETACOUS AEOLIAN SEDIMENTS, NORTHERN ERDOS BASIN, CHINA: FEATURES AND SIGNIFICANGCES

The Zhidan Formation encompasses a lower Cretacous fluvial-eolian-delta-lacustrine succession deposited within a wide northern edge of the Erdos basin, inner Mongulia, China. The Erdos basin is a large scale intracratonic basin with an area of 370.000km². The eolian sandstone in the Zhidan formation, distributed extensively in the northeastern edge of the Erdos basin, was achieved by the detailed outcrop observation and the reconstruction of its depositional history. The large scale wind-induced tabular cross-bedding s are developed in light gray-reddish brown siltfine sandstone, well-sorted, mainly fine-grained. The height of the wind-induced tabular cross-beddings are ranging from tens of centimeters to 7-8m, dominantly 3-4 meters. By measuring the well-exposed and accessible outcrop, it is evident the wind-induced tabular cross-beddings present consistent northerneast– southernwest oriented palaeo-wind trends, between195°to 260°，approximately, 235°. The palaeo-wind trends during their formation period can lend insights into the important information of palaeo climate, potentially palaeo-latitude. The palaeo-wind trends in the early Cretacous epoch is absolutely compatible with the southwestward blowing trade wind that only develops within latitude N30°, which potentially suggests that the temporal position of the study area was at least within latitude N30°and nevertheless, at present, the study area locates in about latitude N40°, which is inconsistent with the location in the early Cretacous epoch. Therefore it is speculated that the study area must should be located within latitude N30°, being likely in latitude N15°in the early Cretacous epoch, when the wind-induced tabular cross-beddings were formed, and from then on, it has continuously moved northwards and till now arrived its present position, moveing northwards for a minimum of 10°(even up to 25°) for a long distance of 1111km(even up to 2775km).