MULTIPLE SEDIMENTARY AXES IMPACT ON THE CHICOT AQUIFER

It has been inferred in previous studies that there are multiple axes of deposition within the Chicot Aquifer, which is a fluvial-deltaic deposit of late Pliocene to Pleistocene in age. These axes appear to influence the hydrostratigraphy, texture and ultimately the hydraulics of this aquifer. From the examination of over 1000 electrical logs it is apparent that there are several major river channels that are present within the Chicot. These channels are a result of variable positions of the ancestral Mississippi River or ancestral Red River. These channels show up as regions of unusual sand thickness within the Chicot and as they near the Gulf of Mexico they account for additional thickening of the Chicot relative to positions on either side of the channel.

It appears that from grain-size analysis of about 1500 sieve samples the sands sourced from the Red River are generally finer than those sourced from the Mississippi River. This is indicated by a smaller median grain size determined from sieve test results. In addition, the Red River sands tend to have excess fines more often than Mississippi River sands as indicated by skewness values determined from analysis of sieve test results.

Lastly due to differences of sand thickness, and texture throughout the Chicot the porosity and hydraulic conductivity differ throughout the Chicot. In terms of porosity the Chicot is slightly more porous in areas that are Red River deposits than Mississippi River deposits. This was determined from analysis of about 50 geophysical logs and 1,000 individual points. In addition, hydraulic conductivity of Red River sediments appears to be lower than Mississippi River deposits as determined from a set of about 600 specific-capacity tests analyzed. However, within the Mississippi River deposits the parishes which appear to have more ancestral river channels yield the largest values of hydraulic conductivity.