Origin and Classification of Coastal Plain Kaolins, Southeastern USA, and the Role of Groundwater and Microbial Action

Abstract

Abstract--Along the inner Coastal Plain, kaolinite-metahalloysite-rich, neritic muds of Cretaceous-Eocene age have undergone intense postdepositional alteration in the recharge area of the regional groundwater system. Weathering processes have had the following profound effects on the original sediments: 1) strong compositional and textural modification of both clay and non-clay minerals; 2) whitening of the originally darker sediments by partial removal of organic matter, Fe and Mn; and 3) recrystallization of kaolinite and metahalloysite, most conspicuous where there are coarse stacks and vermiforms. Where the combination of initial sediment composition and alteration intensity was most favorable, these changes have produced important deposits of commercial quality, which now sustain the world's largest kaolin production district. The earliest change was partial sequestration of iron as sulfide and concurrent destruction of some organic matter, mediated by sulfate-reducing bacteria. Subsequent weathering resulted in gradual leaching of alkalies, alkaline earths, iron and silica, and attendant nucleation and growth of minerals compatible with the compositional changes. The existence of several closely spaced erosional unconformities, separated by neritic sediments, is proof that weathering conditions commonly changed at a given site, in response to changes in thickness or lithology of the overlying rocks. Dsyoxic ---) ~--oxic reversals modified both the rate and kind of alteration. ("Dysoxic" refers to molecular oxygen concentration too low to be toxic to anaerobes or cause abiotic oxidation; less extreme than "anoxic".) Kaolins were produced partly by slower dysoxic weathering in saturated groundwater zones but mainly by more rapid oxic weathering in unsaturated zones, where bauxites also locally formed. Gradual transformation of some sediments to kaolin rarely began and ended in the same epoch. At several places most of the kaolinization (see "Definitions") took place during Recent time, tens of millions of years after deposition of the sediments. Since the kaolins resulted from postdepositional alteration rather than sedimentary processes, they are better referred to as "Coastal Plain" rather than "sedimentary" kaolins.Key Words--Bauxite Origin, Kaolin Classification, Kaolin Origin, Microbial Weathering, Weathering. I N T R O D U C T I O NT h e early interpretation of a s e d i m e n t a r y origin for these kaolins was suggested by their m e g a s c o p i c features and geologic occurrence in sedimentary rocks (Ladd 1898;Veatch 1909;Smith 1929; L e G r a n d and Furcron 1956;Kesler 1963). It drew support from several assumptions n o w k n o w n to be untenable and did not c o n s i d e r i m p o r t a n t factors like the r e g i o n a l groundwater system, the genetic relationship b e t w e e n associated kaolins and bauxites and the key role of microbially mediated reactions. These factors could not be recognized until sufficient petrologic and groundwater i n f o r m a t i o n had accumulated, developm e...

Geobacter pickeringii sp. nov., Geobacter argillaceus sp. nov. and Pelosinus fermentans gen. nov., sp. nov., isolated from subsurface kaolin lenses

“…Kaolinite is a product of the weathering of aluminium silicate minerals, with feldspar being the most common source mineral. When conditions are favourable for weathering, white kaolin without discolouring impurities, such as iron oxides (goethite, hematite), sulfide (pyrite) and organic matter, is formed (Hurst & Pickering, 1997;Elzea Kogel et al, 2002). Depending on their origin, kaolins and kaolin-containing source rocks are either mildly acidic (pH 5-5.5) (Elzea Kogel et al, 2002) or slightly alkaline (pH 7-8.5) (Solodkii, 1995).…”

The roles of pedogenesis and diagenesis in clay mineral assemblages: Lower Cretaceous fluvial mudrocks, Nova Scotia, Canada

“…Flux of meteoric water was favoured by the subaerial intraformational unconformities between the various packets of the Chaswood Formation. A similar process has been proposed for the origin of Cretaceous kaolinitic mudrocks in Georgia, USA, by Hurst and Pickering (1997), with first bacterially-mediated removal of organic matter and later growth of kaolinite taking place below the water table in groundwater recharge zones.…”

Environmental effect and genetic influence: a regional cancer predisposition survey in the Zonguldak region of Northwest Turkey

“…On the other hand, kaolinite was formed in a drained acidic environment due to the removal of mobile alkaline elements by significant pore-water flux in large pores and desiccation cracks, possibly following drought. The formation of organic materials as a result of thick plant growth in the region, and the presence of calcified filaments and knobby microorganisms with alteration products may indicate that the biological processes that produced organic acid and CO 2 might have also led to the dissolution of feldspar and glass shards, as well as the development of kaolinite (Klappa 1979;Curtis 1983;Surdam et al 1984;Anand et al 1985;Wright 1986;Beier 1987;Wright and Tucker 1991;Hurst and Pickering 1997).…”