Cenozoic evolution of sediment accumulation in deltaic and shore-zone depositional systems, Northern Gulf of Mexico Basin

Paleogeographic and volumetric lithofacies mapping of 18 Cenozoic genetic sequences within the Northern Gulf of Mexico Basin quantifies the proportional sequestering of sediment within wave-dominated shore-zone vs. deltaic systems through time. Three long-term depositional phases are revealed by plots, based on paleogeographic and sediment isochore maps, of total shore-zone system area and volume to total delta system area and volume (SZ/D). (1) SZ/D area and volume ratios are highly variable in Paleocene through Eocene sequences. However, typical volume ratios for major genetic sequences (Upper, Middle, and Lower Wilcox; Queen City (QC), and Yegua) range between 0.2 and 0.6. Minor sequences (Sparta (SP), Jackson (JS)), which record very low rates and volumes of sediment accumulation, have the greatest variability in their ratios. (2) Oligocene and Miocene sequences display consistently high proportions of shore-zone sediment. SZ/D area ratios range from 0.6 to 1.0, and volume ratios cluster between 0.4 and 0.8. (3) A substantial late Neogene decrease in SZ/D ratios is presaged in the late Miocene sequence. Pliocene and Pleistocene sequences are uniformly characterized by very low ratios of <0.2. Consistently high Oligocene–Miocene ratios reflect a post-Eocene period of strong E–W climate gradient across the Northern Gulf margin. Shore-zone volume displays no correlation to overall rate of sediment supply. The late Neogene decrease in proportional shore-zone system importance corresponds to development of the West Antarctic and Northern Hemisphere ice sheets and related increase in amplitude and frequency of glacioeustatic sea level cycling.