Large-scale shallow-water deltaic sandbodies are the key exploration objects in the continental basins like Chinese Songliao Basin and Ordos Basin, etc. and also the research focus in sedimentary geology.
Based on the analysis of some core, well logging, seismic data from Cretaceous of Songliao basin and Triassic of Erdos basin in central and eastern China, the paper gave a systematic research of the formation condition and sedimentary characteristics of shallow-water deltas in Chinese continental basins. The geological conditions were favorable for the formation of the large-scale shallow delta as follows: stable tectonic setting, palaeotopography was gentle and smooth slope; strong physical weathering and sufficient material supply, dramatic river and the obvious lake level changed cyclically, shallow lake water (＜10 m).
The shallow-water delta has similar sedimentary characteristics with high-constructional river dominated deltas. It lacks the three-layer structure（topset, foreset and bottomset beds）like Gilbert’s traditional deltas and develops distributary channel but few mouth bar. The Chinese shallow deltas in continental lakes have obvious characteristics, that is low compositional maturity and low to medium textural maturity, finer-medium grain size, plenty of cross bedding formed by strong hydropower, wide purple mudstone with lots of bioturbation structure, several non-continuous normal cycles vertically, imbricated progradation seismic facies, large scale sandbody distribution with low percentage of sandstone to mudstone.
The sedimentation of the shallow delta was controlled obviously by the climate change. When climate was dry, the lake shrank, resulting in branched delta and branched distributary channels which were broad and shallow; the length of channels was more than 20 km, the width from 800 to 1800 m, the average thickness of individual sand-layer was 2-3 meters, and the average percent of sandstone in strata was 35%. While climate was wet, the lake expanded, the river branched off diverted frequently due to the lake water obstruction, formed reticular distributary channels with length of less than 15 km, the width from 500 to 1600 m, the average thickness of individual sand-layer was 2-4 m, and the average percent of sandstone in strata was 40%. Therefore, the sandbodies of delta distributary channels are widely distributed, overlapped vertically, and continuous laterally, and form favorable reservoirs in continental lakes.
