Table 4.

Nine lithofacies types based on core observations and petrological characteristics in the study area.

Lithofacies type	Code	Description
Massive bedding gravelly fine medium sandstone facies	Gm	The structural maturity is medium and low; Gravel content is relatively low; Scouring and filling structure can be seen in some cored wells; Strong hydrodynamic detention sedimentation at the bottom of the channel
Trough cross-bedding fine to medium sandstone facies	St	Grey, grey–white fine medium sandstone; Origin of sand bottom migration; Bottom or lower part of channel sediment; The development scale is related to the water velocity; Scale decreases upwards; The layer thickness of is small
Wedge cross-bedding fine medium sandstone facies	Sl	Greyish white fine sandstone; Staggered and wedge-shaped interlayer interface; Affected by lake waves in the delta front; Low angle oblique layer; There may be a change in flow direction
Plate cross-bedding fine medium sandstone facies	Sp	Greyish white fine sandstone; High angle and low angle undercut and downward truncation; The scale of strata changes greatly; Downstream accretion of longitudinal sand dam
Parallel bedding fine medium sandstone facies	Sh	Greyish white fine medium sandstone; Upper part of river channel; Wide gentle shallow-water delta environment; Vulnerable to cutting; relatively small thickness of strata; High flow regime; Forms a flat bed sand bottom
Sand bedding silty fine sandstone facies	Fr	Very fine sand and siltstone; Upper part of sedimentary sequence small flowing sand grain; The thickness of single layer is thin; Developed in abandoned channel or embankment deposits
Wavy bedding siltstone/argillaceous siltstone facies	Fsc	Grey/greyish green thin siltstone mudstone interbedding; The laminae are wavy and continuously distributed; Sandstone and mudstone are staggered; Developed in a relatively low energy environment; Fine particle size in overflow sedimentation or underwater natural embankment
Horizontal bedding silty mudstone/mudstone facies	Fl	Dark grey, grey–black siltstone and mudstone; Thin layer interface and distributed in a nearly horizontal manner; In abandoned channels or bank deposits; The energy decreases gradually with the flow across the bank
Massive bedding mudstone/silty mudstone facies	Fm	Dark grey, grey–black and black mudstone; Overbank deposits/abandoned channel deposits; Massive structure; The thickness of single layer is thin; Intercalation in composite channel; Poor stability and easy to be eroded; Irregular spatial form