WHAT NO ONE TELLS YOU ABOUT SEQUENCE STRATIGRAPHY

A strong rooted paradigm in the geological culture is that related to the falling of the base level with the generation of regressive deposits in the basin. Although intuitively this may seem correct, just analyze the relationship between the accommodation space and the sedimentation rate allows to notice that something goes wrong.

For pragmatical purposes we will consider that the sedimentation rate is constant. Under this condition, also is added that when there is a relative rise of the base level, the product will be an increase in the accommodation space. This is the key to understanding not only the mechanics of sequence stratigraphy analysis, but also that eustatic rise generate the greatest sediment accumulation in the basin.

If we analyze at a certain point the evolution of the sedimentary package, different stacking patterns will ocurrs depending on the rate of relative rise of the base level. Thus, under a constant sedimentary supply, it can produce a prograding pattern where the velocity of relative base level rise is low. This pattern will change as the relative rise becomes more faster, until it turns to be aggrading. If the process of increasing rate of base level rise continue, finally it will turn to retrograding stacking pattern exceeding the sedimentary supply. 

As we saw, the developed deposits were always developed on generation of space, associated with a relative base level rise. In this way, the sedimentary wedges that show prograding and aggrading stacking patterns, are called normal regressions. The main feature is that it places continental to coastal facies above marine deep facies. Packages with retrograding patterns produced during the phase of highest acceleration rate of the base level are associated to marine transgressions, where deep facies are deposited on shallower facies. In the case that the rate of sedimentary supply exceeds the rate of relative rise of the base level, a stacking pattern called degradant occurs and the resulting sedimentary wedge is known as forced regression.

Concluding, as it said, it is easily to see the relationship between the relative rise of the base level and the greater development of the sedimentary wedges developed in a basin.

For more details, please read the work of Octavian Catuneanu and others (LINK)

What do you think?