『Abstract
Considerable mobilization of Fe without mobilization of Al in
Precambrian paleosols has been documented and attributed to either
anoxic- or ligand^promoted dissolution. To elucidate these mechanisms,
basalt was dissolved under oxic and anoxic conditions with and
without citrate, and the mobility of several elements was analyzed.
The extent of release of Fe and P was minor (in citrate-free conditions)
or considerable (with citrate) regardless of oxygen pressure.
Release of Al was minor in all cases, whereas release of Cu was
minor (in anoxic conditions) or considerable (in oxic conditions).
Release of Cu was enhanced by citrate. In comparison, in the weathered
surface of two of the oldest-known basalt-derived paleosol−the
Mount Roe (2.76 Ga) and the Hekpoort (2.25 Ga)−Fe and P were considerably
depleted and Al retained, consistent with the presence of organic
ligands. Cu, retained in the Mount Roe paleosol but considerably
mobilized i the Hekpoort paleosol, documents formation under an
anoxic atmosphere and an oxic atmosphere, respectively, as inferred
by others on the basis of Fe mobility. The immobility of Al in
both paleosols is consistent with formation under conditions in
which the annual volume of rain-water was lower than the topsoil
pore volume. Mobilization of P in such paleosols developed under
low-rainfall conditions provides a new proxy for identification
of ligands secreted by terrestrial organisms on early Earth.
Keywords: Precambrian paleosols; organic ligands; basalt; element
mobility; dissolution; early Earth.』
Introduction
Experimental results
Proposed schemes for paleosol interpretations
Paleosol interpretations
Summary
Appendix 1. Materials and methods
Acknowledgments
References cited