『Abstract
Despite recent work, a comprehensive understanding of pre-Devonian
terrestrial ecosystems remains elusive, resulting in frequent
speculation about their composition. Terrestrial microbial mats
are known from the Precambrian paleosol record, and bryophytes
are known from the Middle Ordovician palynological record. The
intervening time, however, remains enigmatic, although recent
studies indicate a progressive “greening” of the Precambrian prior
to the first unambiguous fossil evidence for land plants. In this
study, an older than 503 Ma, heavily weathered, clay-rich soil
was identified and provides a window to a probable Cambrian terrestrial
landscape. The paleosol developed on the ancient continent of
Laurentia in a dry, subtropical climate. Mobilization of Si, Al,
and P indicate the influence of organic acids. Apatite, a recalcitrant
mineral present throughout the majority of the weathered section,
is notably absent from the top 30 cm of the paleosol. Few secondary
phosphates and a complete absence of oxide- or carbonate-bound
P indicate that once biologically weathered, P remained in an
ecosystem-available form during lifetime of this paleosol. The
zone of apatite dissolution coincides with intense argillan development,
indicating clay flocculation in the presence of soil solutions
rich in labile Ca2+. Enhanced P weathering coupled
with high Ca2+ concentrations as a result of in situ
apatite dissolution is a biosignature previously linked to the
activities of mycorrhizal fungi. Biosignatures of mycorrhizal
fungi in a Middle Cambrian paleosol add further evidence to the
notion that there was an important terrestrial fungal presence
prior to the first unequivocal evidence for terrestrial land plants.』
Introduction
Materials and methodology
Results
Discussion
Subtropical weathering
Apatite dissolution and fate of phosphorus
Conclusions
Acknowledgments
References cited