Deltaic Depositional System

As early as 1885–1890, G. K. Gilbert studied the Pleistocene lacustrine delta deposits in Lake Bonneville, America, and first found that the delta deposit body has a three-tier structure. Later, according to Gilbert’s description, J. Barrell (1992 and 1914) studied the characteristics of the sedimentary facies of the Devonian Catskill Delta in the Appalachian Basin, identified the topset, foreset, and bottom set, and respectively depicted the characteristics of the lithology, beddings, and fossils of all formations thus pioneering the study of the sedimentary facies of ancient marine deltas. Although Barrell noted that not all delta deposits have the three-tier architecture of a Gilbert-type delta, the delta depositional models established by Gilbert and Barrell have influenced researchers’ awareness about deltas in the 20th century. Previously, researchers used to consider a megascopic foreset as an important sign for identifying an ancient delta. Moreover, because abundant energy source deposits (including coal, petroleum, and natural gas) having large economic value had not yet been found in delta sedimentary formations, studies on deltas were lacking. As a result, we barely understand the complex and changeable sedimentary characteristics of a deltaic depositional system. Nonetheless, these early research achievements have been of great significance.