Abstract:
Although the similarities between depositional processes and products as well as the analogous controls
on basin-filling and evolution appear to have enjoyed great uniformity throughout the sedimentary rock
record, a noticeable distinction exists in the rates and intensities of a broad range of geological processes
in the Precambrian epoch. This paper searches for distinctiveness in the Precambrian sedimentary
record, both siliciclastic and carbonate, through an extensive, though not exhaustive, review of the
relevant literature augmented by new observations. While differences in Precambrian deltaic, aeolian,
glacial and possibly also lacustrine deposits and settings appear to have been small, their large-scale
development was controlled largely by a combination of temporal and geodynamic influences, essentially
of global compass. In this regard the onset of the supercontinent cycle and major perturbations in
palaeo-atmospheric composition appear to have been significant. Marine environments provide a poor
platform for PrecambrianePhanerozoic comparisons of sedimentation patterns, as those from the former
period are preserved almost exclusively in epeiric settings, an environment essentially lacking on
modern Earth. For the shallow marine carbonates, biological mediation of chemical sediment deposition
changed radically from dominance by microbial biota in the Precambrian to a combination of metazons,
protozoans and algae for the skeletal carbonates of the Phanerozoic. Despite it being widely recognized
that Precambrian channel systems were braided in all environments (deltaic, tidal, alluvial, fluvial) as
a consequence of the lack of vegetation and poor development of soils, the fluvial setting has some
enigmatic aspects. Amongst these is evidence for ponding of muddy detritus in apparently sandstone
bed-load dominated braided systems, with effects on local palaeoslopes which have resulted in unusual
palaeohydraulic parameters for Precambrian fluvial systems. This is perhaps a field of research which
holds greater promise when investigating sedimentation patterns prior to the Phanerozoic.
