Sedimentary facies and architecture of point-provenance fan deltas: A case study of modern lacus fan delta in the Xiligou Lake

Fan delta deposits are important reservoirs for oil and gas. To illustrate the sedimentary facies and architecture of lacustrine fan delta deposits, we have quantitatively characterized the geometric attributes of different architecture units and clarified the regularity of their distribution. Based on detailed outcrop measurements and architecture interpretations using ground penetrating radar, we have recognized 16 sedimentary facies, eight vertical sequences, and eight architecture units, including main channel (MCH), distributary channel (DCH), sheet flood (SF), braided bar (CB), overbank flow (OF), subaqueous distributary (UCH), river mouth bar (RMB), and sheet sand (SS). The thickness of the distributary braided channels varies from 1.5 m to 2.0 m, with a width-to-thickness ratio of 30 to 70. The thickness of the braided bar varies from 2.0 m to 3.0 m, with a width-to-thickness ratio of 50 to 70. During the same sedimentary period, lacustrine fan delta developed five basic architectural unit combinations, namely, SF-MCH-SF, OF-DCH-CB-DCH-OF, SS-UCH-RMB-UCH-SS, SS-RMB-SS, and SS-UCH-SS. The distribution of architecture units in different depositional periods shows lateral repetition of the five basic combinations and vertical superposition.