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A MICROTEXTURE STUDY OF PALYGORSKITE-RICH SEDIMENTS FROM THE HAWTHORNE FORMATION, SOUTHERN GEORGIA, BY TRANSMISSION ELECTRON MICROSCOPY AND ATOMIC FORCE MICROSCOPY

¹ Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, Illinois 60607, USA
² Department of Geology, Miami University, Oxford, Ohio 45056, USA

^* E-mail address of corresponding author: rhodochrosite{at}email.msn.com

A microtexture analysis by TEM and AFM of palygorskite deposits from the Hawthorne Formation, southern Georgia is given. Palygorskite is the dominant mineral comprising an average of 65–70% of the sample volume with smaller volumes of smectite, illite and kaolinite. Morphologic observations indicate that the palygorskite formed in an unconfined environment, such as in the water column or in open-pore space. Some palygorskite textures appear to be secondary growths filling voids. An unusual texture is observed where smectite or illite-smectite (Reichweite, R = 0) form epitaxially on detrital illite and kaolinite particles. Oxides of Fe and Ti are common, and authigenic cassiterite is present but rare. Apatite is a common trace mineral in these sediments and occurs in a variety of textures. Apatite occurs as clusters which are believed to be small fecal pellets. These clusters have been partially dissolved and recrystallized and the crystals in the clusters are 50–100 µm in diameter. Other apatite crystals occur either as single crystals or in clusters that are not associated with fecal pellets.

The textural data of this study suggest that there was an evolving and complex mineralogical and geochemical system during and after deposition of the palygorskite deposits in the Hawthorne. The epitaxial overgrowths of smectite on detrital illite and kaolinite particles indicate an intermittent stratified water column occurring in the system. Freshwater was introduced into the system from the northeast of the Apalachicola embayment and overrode more saline water in the southwest portion of the embayment. The results of this study are consistent with previous environmental interpretations and provide additional details.

Key Words: AFM • Georgia • Hawthorne Formation • Palygorskite • TEM

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