Variation of sediment grain size and relationship to water depth in a tidal environment: An example from a modern flood tidal delta in Texas
Abstract
Sediment grain size and water depth measurements were collected and integrated with water current data in the San Luis Pass tidal delta, a modern deposit on the microtidal Texas coast, located between Galveston and Follets islands. The relationship between grain size and water depth is studied to understand flood tidal delta dynamics and control factors for sediment distribution that can be extrapolated to other modern and paleo- tidal environments. 150 seafloor sediment samples have been collected and analyzed for grain size and lithology along the flood tidal delta. Water depth was measured and corrected to a datum of mean sea level using measurements from the San Luis Pass NOAA station. Sediment statistics and parameter such as mean, median, sorting, and skewness were calculated. The Texas beach and shoreface are characterized by fine sand, in some areas with coarser sediments of medium sand. These fine sands, transported by the longshore drift, are the sediment source for the flood tidal delta. In the San Luis Pass area grain size values vary between clay and fine sand (0.98 to 250 μm), with a mean of fine sand (125-250 μm). Transects of sediment grain size variation along the flood tidal delta show a fining trend in a landward direction as the two main control factors vary: current velocities decrease from 1 to 0.1 m/s and water depths increase from less than 10 to 200 cm. This study compares the sediment grain size distribution of samples taken at the same locations both pre- and post- Hurricane Harvey, the major flood to impact the Texas coast in the fall of 2017. Post-Harvey sediments have a finer grain size distribution, possibly related to the increased rain runoff occurred during the storm which carried finer sediments into the bay. Pre- and post Harvey deposits have a similar lithology, with more than 95% of quartz and less than 5% of heavy minerals. The San Luis Pass flood tidal delta provides a unique setting for the characterization of modern microtidal sediments and provides an important insight into the understanding of control factors for sediment distribution in tidal environments. The resulting sediment distribution model along with sedimentary structures can be used as an interpretation model for paleo-tidal deposits and other modern deposits.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP13D2131R
- Keywords:
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- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSESDE: 4914 Continental climate records;
- PALEOCEANOGRAPHY