Depositional history of the upper Calvert Bluff and lower Carrizo formations, Bastrop, Texas

Fluvial and Marine Depositional Environments Determined From Groundwater Chemistry and Calculated Clay‐Cation Compositions

“…The exception to this is in the southwest portion of the study area, in Bastrop County, where shallow tidal flat and shallow‐marine sediments, instead of fluvial sediments, were found in several outcrops of the Calvert Bluff formation (Denison et al., 2017; Yancey et al., 2012). This area is marked by a red triangle in Figure 1.…”

“…The highest level of transgression is also shown on the plan map (Figure 1). Because this level changed through time occurring further inland with increased depth, the most landward transgression near the top of the aquifers (Texas Water Development Board, 2020) (blue circles for X Na,clay ≤ 8.0% and red circles for X Na,clay > 8.0%, see text), river water samples (black boxes) (United States Geological Survey, 2020), salt domes (white circles) (Beckman & Williamson, 1990), Chicot/Evangeline and Wilcox aquifer outcrops (shaded gray) (Texas Water Science Center, 2014), hydraulic head contours (black lines) for the Chicot/Evangeline aquifer (after Dutton, 1994) and the Simsboro formation of the Wilcox aquifer (after Dutton, 1999), the inland extent of the shore zone in the Wilcox aquifer (after Xue, 1994) (red dashed line), the location of marine sediments in the Wilcox Group found in outcrops in Bastrop County (after Denison et al, 2017;Yancey et al, 2012Yancey et al, , 2013) (red triangle), and the Texas county lines (solid gray lines). For the Chicot/Evangeline aquifer, the inland extent of the marine transgressions at the top of the aquifer is labeled "Max.…”