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Faults offsetting sedimentary strata can record changes in sedimentation driven by tectonic and climatic forcing. Fault kinematic analysis is effective at evaluating changes in sediment volumes at salt/shale-bearing passive margins where sediment loading drives faulting. We explore these processes along the northern Gulf of Mexico. Incremental throw along 146 buried faults studied across onshore Louisiana revealed continual Cenozoic fault reactivation punctuated by inactive periods along a few faults. Fault scarp heights measured from light detection and ranging (LiDAR) data are interpreted to show that Cenozoic fault reactivation continued through the Pleistocene.The areas of highest fault throw and maximum sediment deposition shifted from southwest Louisiana in the early Miocene to southeast Louisiana in the middle--late Miocene. These changes in the locus of maximum fault reactivation and sediment deposition were controlled by changing tectonics and climate in the source areas. Early Miocene fault throw estimates indicate a depocenter farther east than previously mapped and support the idea that early Miocene Appalachian Mountain uplift and erosion routed sediment to southeast Louisiana.By correlating changes in fault throw with changes in sediment deposition, we suggest that (1) fault kinematic analysis can be used to evaluate missing sediment volumes because fault offsets can be preserved despite partial erosion, (2) fault throw estimates can be used to infer changes in past tectonic and climate-related processes driving sedimentation, and (3) these observations are applicable to other passive margins with mobile substrates and faulted strata within overfilled sedimentary basins. [ABSTRACT FROM AUTHOR]

Point bars formed by meandering river systems are an important class of sedimentary deposit and are of significant economic interest as hydrocarbon reservoirs. Standard point‐bar models of how the internal sedimentology varies are based on the structure of small‐scale systems with little information about the largest complexes and how these might differ. Here a very large point bar (>25·0 m thick and 7·5 × 13·0 km across) on the Mississippi River (USA) was examined. The lithology and grain‐size characteristics at different parts of the point bar were determined by using a combination of coring and electrical conductivity logging. The data confirm that there is a general fining up‐section along most parts of the point bar, with a well‐defined transition from massive medium‐grained sands below about 9 to 11 m depth up into interbedded silts and fine–medium sand sediment (inclined heterolithic strata). There is also a poorly defined increase in sorting quality at the transition level. Massive medium sands are especially common in the region of the channel bend apex and regions upstream of that point. Downstream of the meander apex, there is much less evidence for fining up‐section. Finer sediment accumulated more readily after the establishment of a compound bar in the later stages of construction, at the terminal apex and in the bar tail. This work implies that the best reservoir sands are likely to be located in the centre of the point bar, deposited in a simple bar system. Reservoir quality decreases towards the bar edge. The early‐stage channel plug is largely composed of coarsening‐upward cycles of silt to clay and is dominated by clay and clayey silt material with poor reservoir characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Seismic refraction velocity-versus depth models can complement our understanding of natural soils beneath flood protection levees at locations between geotechnical sites. Levee failures in New Orleans in 2005 are attributable in part to poor understanding of sediments between geotechnical sites. To a first order, subsurface fluvial–deltaic facies in the lower Mississippi delta plain correlate with general geotechnical properties of water content and cohesive strength, but are too laterally variable to be easily predicted from geotechnical sites spaced 100m apart. An artificial earthen levee, suitable for seismic investigation, lies ~15km S of the city of New Orleans, Louisiana. Values of shear-wave velocity (VSH ) versus depth (0–20m) are derived by forward-ray-trace models of seismic refraction arrivals which match key boundaries identified at (geotechnical) cone-penetration testing sites, spaced at 300m apart. In particular, a 100-m section along the levee crest shows continuous cracks which are as much as 10cm wide, and 30cm deep at their northern end. Cracking may relate to high strain, induced by variable near-surface subsidence of organic-rich sediments. Topographic cross-sections across the levee show variable differential subsidence of 1–2m. Based on effective medium theory, VP - and VSH -versus-depth profiles indicate unexpectedly greater saturation and lower shear moduli on the unprotected levee side adjacent to the cracks. Integration of geophysical, sedimentary and topographic data, even if only at a few locations can help locate anomalous zones in sub-levee soil between geotechnical boring sites. Future preventive monitoring of flood-protection barriers stands to benefit greatly from integrated data sets “ground truthed” to geotechnical data. [Copyright &y& Elsevier]