Latest Miocene (Kapitean/Messinian) glauconite and the central Chatham Rise greensand: an enigmatic, highly condensed, relict/palimpsest deposit on the modern seafloor - Supplementary File, Tables & Figures

A unique 10-140 cm thick veneer of greensand and
glauconite-rich deposits (10-80 wt% glauconite) presently sits atop central
Chatham Rise (CR) in water depths of 200-500 m. The glauconite is dominated by
chemically mature, polished ovoidal and lobate pellets, with a 10-12 Å
phyllosilicate structure and K-Ar ages of 7-5 Ma, indicating that the
glauconite pellets are predominantly allogenic (i.e. derived/reworked) grains,
and not of in situ authigenic origin. Glauconite possibly evolved from seafloor
alteration of detrital and/or volcanogenic smectitic clays, likely concentrated
within organic-rich faecal pellets under unique paleoceanographic conditions
(nutrient cycling, upwelling, carbon isotope gradients) within the latest Miocene
Subtropical Front. The distribution of glauconite abundance suggests a
‘glauconite factory’ existed at this time about Reserve Bank on western central
CR. The pellets were dispersed eastwards along the crest by intensified bottom
currents within the dynamic Subtropical Frontal zone, perhaps during the numerous
glacial periods of lowered sea level throughout the Plio-Quaternary. The
bioturbated greensand veneer, and its mix of other reworked Neogene and
Quaternary skeletal, phosphatic and siliciclastic components, rest
unconformably on mainly Early Oligocene chalks, forming a highly condensed,
relict/palimpsest deposit that alone embodies the last up to 30 My of
sedimentation history atop central CR.