Transport and deposition of terrestrial organic matter in marine littoral deltas: New evidence from flume experiments and 3D laser scanning

Terrestrial organic matter (TOM) serves as the primary parent material for source rocks in marine-terrestrial transitional environments. The transport and deposition process of TOM affects the development of high-quality source rocks in shallow marine areas. Based on the sequence stratigraphy of the Enping Formation (upper Eocene to lower Oligocene) in the Baiyun Sag and the petrological characteristics of the source rocks, simulation experiments of terrestrial dispersed organic matter deposition constrained by topography, provenance composition, sedimentation period and other conditions were conducted. Comparative experiments of individual constraints such as topographic slope, hydrodynamic conditions, water salinity and particle size of organic matter were also conducted. The results indicate that TOM enrichment in the littoral delta system initially increases with transport distance but subsequently decreases. Four TOM distribution patterns were identified: interrupted, interbedded, lenticular, and banded types. The interrupted, interbedded, and lenticular types predominantly occur in delta plains, whereas the banded type primarily develops in delta fronts and prodeltas. In the early stages of delta formation, gentle slope conditions are more conducive to the forward transport of TOM. As the delta develops, the sediment thickness increases, which reduces the slope gradient and thus weakens the effect on the transport distance of TOM. Higher flow intensity promotes TOM transport, however, wave action can impede forward transport, creating localized TOM enrichment areas on the delta plain. In shallow water, the increase in water salinity enhances the flocculation of TOM, thus reducing the transport distance of TOM. Meanwhile, Smaller TOM particle sizes correspond to greater transport distances and increased heterogeneity in its planar distribution within the delta-shallow sea sedimentary system.