Seismic clinoforms are the key building blocks for constructing the seismic stratigraphy of progradational depositional sequences. However, not all progradational systems are necessarily represented by seismic clinoforms. We evaluated the definition and interpretation of progradational systems that do not associate with seismic clinoforms. Nonclinoform (or subseismic clinoforms) seismic facies are mainly related to shallow-water deltas where the thickness of a prograding clinoform complex is too thin to be imaged as an offlapping reflection configuration. The clinoform detection limit for clinoform imaging is defined as one wavelength (the thickness of two seismic events) and is related to the predominant frequency of the seismic data and the velocity of the sediments. Three examples from the Songliao Basin of China and Gulf of Mexico illustrated ancient shallow-water deltas with various morphologies in lacustrine and marine environments by integrating the analysis of the core, wireline logs, and amplitude stratal slices made from nonclinoform seismic events. A seismic model of an outcrop carbonate clinoform complex in west Texas further demonstrated the seismic frequency control on clinoform seismic stratigraphy, including transitions between different types of clinoforms and between clinoforms and nonclinoform seismic facies. Ambiguity in interpreting nonclinoform seismic facies can be reduced by high-resolution acquisition, high-frequency enhancement processing, and seismic sedimentology.

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