1 Departamento de Cristalografía, Mineralogía y Q. Agrícola. Universidad de Seville, Spain.

1. CLAY MINERALOGY OF SEDIMENTS IN FRESHWATER MARSH ENVIRONMENTS OF THE MISSISSIPPI RIVERAparicio, Patricia1 and Ferrell, Ray E.2 1 Departamento de Cristalografía, Mineralogía y Q. Agrícola. Universidad de Seville, Spain. e-mail:patric@cica.es 2 Department of Geology and Geophysics. Louisiana State University, Baton Rouge, LA 70803-4101, USA. e-mail: rferrell@lsu.edu

2. The clay mineral composition of sediments collected from the freshwater marsh in the area of Lake Des Allemands near New Orleans (Louisiana, USA) from a depth of 200 to 300 cm is complex because of the variety of materials derived from the drainage basin and postdepositional alteration.

3. MATERIALS • Samples from the freshwater marsh in the area of Lake Des Allemands near New Orleans (Louisiana, USA) from a depth between 200-206cm and 290-300cm. • The dark gray samples belong to the Kenner-Allemands soil association. They are typical of the moderately alkaline, fluid clays occurring beneath slightly acid mucks in freshwater marsh environments of the Mississippi River Deltaic Plain.

4. Sampling Kenner - Des Allemands Association

5. Kenner - Allemands Association ..moderately alkaline, fluid clays overlain by acid mucks...

6. METHOLOGY Sample normal settling by centrifugation <2µ fraction <0.2µ fraction K-saturation Mg-saturation air-dried glycerol-dried air-dried EG-solvation XRD-patterns EG-solvation Heat-treatment at 300°C and 550°C 2q correction 1st qualitative result Layer type determination

7. METHOLOGY 1st qualitative result Layer type determination profile-fitting of Mg-EG patterns Mixed-layered clay mineral identification according to: Moore & Reynolds (1997), Srodon (1984) 2nd qualitative result Mulcalc simulation pattern Clay++ procedure Mulcalc library Assess concordance of experimental and theoretical pattern Qualitative analysis (QR) and Ideal layer percentage of clay minerals Change calculated parameters Bad R2> 0.01 Good R2 ≤ 0.01

8. 9.98 A 16.86 A 3.32 A 4.98 A K-550 12.2 A K-300 9.91 A MgEG 14.5 A 7.2 A MgAD SAMPLE C9, <0.2 micrometers Des Allemands

9. SAMPLE C9, <2 micrometers Des Allemands 3.34 A 9.98 A 13.9 A 4.99 A Qtz 3.57 A K-550 16.8 A K-300 MgEG 15.34 A MgAD

10. Des Allemands Mg- saturated Fine Clay Residual Smoothed composite Individual peaks 23 28 Two theta (Cu)

11. Des Allemands Coarse Clay Residual Individual peaks Smoothed composite 23 28 Two theta (Cu)

12. actual XRD simulation 9 14 19 24 29 5 Two theta (Cu) “FIT” Mg-saturated Fine Clay (C9)

13. “FIT” K-saturated Fine Clay (C9) actual XRD simulation 5 9 14 19 24 29 Two theta (Cu)

14. RESULTS - Simulated minerals

15. RESULTS - Simulated minerals

16. RESULTS-Ideal layers

17. RESULTS - Simulated minerals

18. RESULTS - Simulated minerals

19. RESULTS - Ideal layers

20. SUMMARY • The reported differences in the clay assemblages call attention to the complex mineralogy of modern sediments and soils. • The various minerals are all potentially present considering the alteration that may be occurring in the present-day environment and the variability of source materials contributed by the Mississippi River and its tributaries. • Differences in the quantities of vermiculite-like materials in the coarse and fine fractions of samples are ones that could be attributed to hydroxy-interlayer formation by diagenesis and crystallite growth.