Origin and Location of the Sparta Sand
The Sparta Sand Formation makes up most of the Middle Claiborne Group, a hydrogeologic unit of the Mississippi Embayment. The sands were laid down as part of the ancient Gulf of Mexico beach system when the Earth was much warmer than it is today, the world ocean was much larger, and the mouth of the ancient Mississippi River was at Cairo, Illinois. The formation extends from southeast Texas, north into Louisiana, Arkansas, and Tennessee, and eastward into Mississippi and Alabama. (1) (Figure 2) An endnote tells more about the Mississippi Embayment. The Middle Claiborne group dates to the Eocene age, which spanned the time period of 55 to 34 million years ago. (2)
Description of the Sparta Sand
‘The Sparta Sand consists of fine to medium sand interbedded with coarse sand, silty clay and lignite. The sands become (thicker) with depth of the aquifer. Laterally, they are discontinuous. The percentage of sand… (depending upon the location within the aquifer) varies from almost completely sand, generally at the base, to fifty percent sand, for example, in an area of Ouachita Parish, where sands are broken with many small clays (layers of clay).’ (3) In north Louisiana and south Arkansas, the Cane River Formation, predominantly marine clay, underlies the aquifer, and the Cook Mountain Formation overlies it. These confining units, of clay, mud, marl, and shale, were depositions of rising seas interrupted by sedimentary rock deposited by streams that emptied into the Gulf of Mexico. (4) (Figure 3)
Description of the Sparta Aquifer in Louisiana
The Sparta aquifer in Louisiana downdips (inclines at an angle downward) from the outcrop area in parts of Bossier, Webster, Claiborne, Bienville, Jackson, and Winn Parishes to the approximate limit of freshwater, which extends from Morehouse south to Caldwell Parish and then southeast to Sabine Parish. (3) (Figure 4)
Average Annual Rainfall and Sparta Recharge
Rainfall arrives in the Sparta aquifer directly in outcrop areas, and by water flowing in overlying terrace and alluvial deposits, and by leakage from the Cockfield and Carrizo-Wilcox aquifers.’ (5) ‘In north Louisiana, average rainfall is 56.19 inches per year (range 40 to 80 inches per year), as derived from 1971-2000 data.’ (6) ‘Most rainfall runs off to streams and rivers, or is returned to the atmosphere from plants and soil by processes of evapotranspiration, or discharges as baseflow to streams.’ (4a) ‘(F)ew, if any, studies have been conducted in the (Mississippi) embayment to determine actual recharge rates.’ (7) In their optimization model, McKee, Clark, and Czarnecki fixed a recharge range from 0.39 to 0.77 inches per year for the Sparta region in the outcrop and suboutcrop area of southern Arkansas and north-central Louisiana. (8) Figure 5 shows the general location of the Sparta primary recharge area.