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Coupled Transgressive - Regressive Systems

Introduction

Some other day, I thought that I need to post a small blogger note. It should describe the spatial extent of a sequence stratigraphic unit. In my experience, it has been an common misunderstanding in communication and interpretation. If one interprets a systems tract over 100s of kilometers with the same nature (e.g. regression), then other will sub-divide it into several strike oriented systems tracts. Well, I will not go that deep but will simply say, "all sequence stratigraphic units are site-specific just like lithostratigraphic units." Sequence stratigraphy has an advantage because it defines time-based units e.g. base level rise/fall.

The main objective of this post is to show my personal opinions on the present day example taken from Louisiana Holocene continental shelf (N. America). 

See the figure below.


Supply vs. Accommodation vs. Shoreline Trajectories:

In the figure above, what do you learn?
  1. Increasing sedimentation of Holocene Mississippi delta compared to the transgression rate. Sediments progrades on to the shelf and build outwards - a regression (HST).
  2. There was an abandoned delta of Pleistocene epoch as it has been annotated in the figure. Nevertheless, that part of the delta has been transgressed and at present it is under strong wave dominated setting. There are several barrier shoals developed parallel to the coast giving hints of wave-dominated settings. Overall, the St. Bernard Shoals and the back shoal margin (Chandeleur region) are transgressive systems (TST).
  3. These systems occur within 20Km of a distance along the coast.
  4. If you try to compare the rate of aggradation in both (red and yellow circles), you will obviously notice that the delta systems aggrades more compared to the wave dominated settings. Note that the later ones are highly destructive systems.

Open Discussion

Along the basin strike, it is quite common to have coupled or coeval systems tracts. When a delta develops outwards, there are some of its components which will either be tide/wave dominated. In principle, most of the delatic systems could have both components at the same time as highlighted in the above system. I wonder if a delta (at present) has all three components (tide, wave, and river) dominating at the coast/shelf. If you know any example, please post here.

I look forward to your comments on my interpretation. I am open and excited to hear back from you either positive or negative.

Cheers,
Farrukh


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