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Irrespective of geologic age, Phanerozoic coated phosphate grains deposited beneath productive surface waters in organic-rich paleoenvironments are of only two types. Unconformity-bounded grains contain internal discordances and erosional surfaces, attributable to multiple episodes of phosphogenesis and sedimentary reworking during periods of stratigraphic condensation. Redox-aggraded grains consist of concordant concentric phosphate laminae that are intimately interlayered with circumgranular layers containing pyrite, chamosite, or barite, recording in situ diagenetic mineralization driven by changes in pore-water redox potential. Such changes can be attributed to variations in biological oxygen demand within suboxic pore-water environments resulting from fluctuations in sedimentation rate of organic carbon. Redox-aggraded grains are thus sensitive indicators of variations in organic carbon export and record changes in primary productivity and/or ecological dynamics of the surface ocean. This concept of coated-grain formation necessitates a long residence time just below the sediment-water interface. If sedimentation rate is too high, grains are rapidly buried and so removed from the zone of active phosphate precipitation. Coated phosphate grains can therefore be considered the granular equivalents of condensed beds. These concepts are equally applicable to the interpretation of other types of coated grains and concretions that contain Eh-sensitive minerals, such as iron-bearing ooids and polymineralic concretions.

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Shallowing‐upward, decametre‐scale, Palaeoproterozoic iron formation cycles in northern Wisconsin record the combined effects of tectonism and changing oceanographic conditions on a storm‐dominated shelf. Cycles consist of a lower unit of laminated, Fe‐ and Si‐rich chemical mudstone that is transitional into an upper unit dominated by trough cross‐stratified chert grainstone. Grainstone lenses become progressively thicker upwards in cycles with the largest at cycle tops, where they are sharply overlain by a unit of slumped chemical mudstone. The cycles developed through progradation when offshore‐directed storm currents transported chert sand intraclasts that were formed in nearshore settings into middle and distal shelf environments. Abrupt subsidence events, probably resulting from normal faulting associated with extensional tectonism, repeatedly terminated chert grainstone accumulation and may also have generated the slumped units at cycle boundaries. The episodic storm currents are also interpreted to have transported biologically oxygenated waters from the shallow‐water, inner shelf into otherwise anoxic bottom waters of the strongly stratified distal shelf. The consequence of such transport and mixing was rapid deposition of chemical mud, mainly as precipitated Fe‐oxide. In many cases, the resultant decrease in Fe2+ in the water column, together with pelagic inorganic precipitation of SiO2 and rainout of terrigenous clays, resulted in submillimetre‐ to millimetre‐thick, chemically graded laminae. The concomitant decreasing Fe2+/Mn2+ ratio also led to increasing Mn‐compound precipitation and enrichment in the upper portions of some chemically graded layers.

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________________________________________________________________________The ephemeral nature of most sedimentation processes and the fragmentary character of the sedimentary record are of first-order importance. Despite a basic uniformity of external controls on sedimentation resulting in markedly similar lithologies, facies, facies associations and depositional elements within the rock record across time, there are a number of secular changes, particularly in rates and intensities of processes that resulted in contrasts between preserved Precambrian and Phanerozoic successions. Secular change encompassed (1) variations in mantle heat, rates of plate drift and of continental crustal growth, the gravitational effects of the Moon, and in rates of weathering, erosion, transport, deposition and diagenesis;(2) a decreasing planetary rotation rate over time; (3) no vegetation in the Precambrian, but prolific microbial mats, with the opposite pertaining to the Phanerozoic; (4) the long-term evolution of the hydrosphere-atmosphere-biosphere system. A relatively abrupt and sharp turning point was reached in the Neoarchaean, with spikes in mantle plume flux and tectonothermal activity and possibly concomitant onset of the supercontinent cycle. Substantial and irreversible change occurred subsequently in the Palaeoproterozoic, whereby the dramatic change from reducing to oxidising volcanic gases ushered in change to an oxic environment, to be followed at ca. 2.4-2.3 Ga by the "Great Oxidation Event" (GOE); rise in atmospheric oxygen was accompanied by expansion of oxygenic photosynthesis in the cyanobacteria. A possible global tectono-thermal "slowdown" from ca. 2.45-2.2 Ga may have separated a preceding plate regime which interacted with a higher energy mantle from a ca. 2.2-2.0 Ga Phanerozoicstyle plate tectonic regime; the "slowdown" period also encompassed the first known global-scale glaciation and overlapped with the GOE. While large palaeodeserts emerged from ca. 2.0 -1.8 Ga, possibly associated with the evolution of the supercontinent cycle, widespread euxinia by ca. 1.85 Ga