cycles that deepen upward in the stratigraphic record




shallow upward

shoal upward


Rates of carbonate sediment production respond to photosynthesis and this production rate increases as the water becomes shallower . For this reason carbonate depositional systems commonly fill towards sea level and so "shoal" or "shallow" upward. The result is the depositional cycles of Goldhammer et, 1990), and the "simple" carbonate sequence cycles of the platform carbonate cycles of the Upper Miocene of Mallorca (Pomar, personal communication). However working in the Murray basin Lukasik & James, 2003 have established that varying nutrient levels affected the carbonate fill of this basin. As can be seen in the animated gifs and summary diagrams below the carbonate depositional surface of the Murray basin built towards sea level but did not reach it. The carbonates responded not only to base level change but also the varying nutrient levels in the basin. Thus during sea level "lows" the shallower and more isolated the basin caused nutrient productivity to rise (the setting became eutrophic) while carbonate accumulation slowed. In contrast as the basin deepened during the onset of the following sea level rise, the rate of nutrient productivity fell (the setting became oligotrophic) while the rate of carbonate production increased. Eventually during the greatest rate of base level rise the rate of carbonate production was reduced by the increasing depth of water. Simultaneously as the Murray basin increased in size and deepened upward in response to this sea level rise with the result that the increased fetch enabled storms to scour the sediment surface while it was starved of higher rates of carbonate production. The effect that Lukasik & James, 2003 describe is probably not uncommon in the many deepening upward carbonate cycles of the geological record.

References Cited
Goldhammer, R. K., Dunn, P. A., and Hardie, L. A., 1990, Depositional cycles, composite sea-level changes, cycle stacking patterns, and the hierarchy of stratigraphic forcing: Examples from Alpine Triassic platform carbonates: Geological Society of America Bulletin, v. 102, p. 535–562.
[Landmark paper on the use of the character of cycles to determine their origins?].
Lukasik, Jeff J., and Noel P. James, (2003), Deepening-Upward Subtidal cycles, Murray Basin, South Australia, Journal of Sedimentary Research, Vol. 73, No. 5, P. 653–671
[Mix of ichnology & faunal diversity are used to determine Deepening Upward Cycles, depositional setting & correlate Lithofacies and chronoStratigraphic Surfaces.].