Relationships between Glauconite and Sequence Stratigraphic Units In a Lower Paleocene Passive-Margin Shelf Succession (Clayton Formation, Central Alabama)

摘要

Detailed study of a marine-shelf depositional sequence in the Lower Paleocene Clayton Formation of central Alabama confirms that glauconite abundance and maturity vary predictably through component systems tracts. More importantly, this study demonstrates that glauconite can be an effective tool for delineating parasequences and associated marine flooding surfaces in relatively sediment-starved, passive-margin shelf successions in which traditional criteria for deciphering higher-order relative sealevel variations (e.g., primary textural variations, sedimentary structures, ichnofabrics, etc.) are absent or poorly expressed. Parasequences in the condensed section and high-stand-systems tract are defined by meter-scale, asymmetrical, upward-fining cycles characterized by abrupt increases and gradual decreases in glauconite abundance and maturity. Lithologic variations (i.e., mudstone-limestone alternation) and subtle textural trends observed in the highstand-systems tract do not reflect shifts in marine facies that normally characterize parasequences. Instead, they mainly record diagenetic processes (carbonate concretion growth and glauconite authigenesis) that are more readily understood when viewed in the context of short-term sea-level changes deciphered from glauconite.