Seismic Sequence Analysis
Exercise Four - Objectives & Data

THE STRATIGRAPHY OF THE NEOGENE OF THE WESTERN BAHAMAS

To gain access to the complete image containing the un-interpreted seismic section of the exercise, click on the appropriate image to download it in a series of images (each divided image can be printed on a regular 11" X 8.5" paper).

Complete seismic section (about 50" wide).This is an Adobe Acrobat ".pdf" file and as such may be the easiest to print from at any scale you need. If you choose the largest size the print out will consist of four landscape mode sheets that over lap and can be taped together.

- - - - These five images are linked to .jpg files. Most will find the full image above in .pdf format is easiest to print from. "Chacun a son goût" or to each their own taste!

However you do it, once the 2D seismic line has been downloaded it will be seen that the line is divided in 5 segments. These segments of the line should be taped together to form a complete seismic line.

The objectives for this exercise are listed below. Start with 1) and work through to 4). Problem 3) may be considered as a dangerous call, but without tight biostratigraphic data the use of the Sea Level chart may be a best first pass as a tool for dating the stratigraphic section!!!

1) Determine the sequence stratigraphy of the line and the clinoformed sequences that form this Neogene sedimentary section by

2) Examine the sedimentary architecture of the clinoforms and infer the origins of these features. For instance do the clinoform geometries show evidence of shelf onlap and does the downlap show evidence of slumping related to the shifting base level? Was there a variable rate of sediment supply to the area of study? Is there evidence of widespread changes in base level? To answer these:

3) As indicated above poor biostratigraphic control means it is difficult to determine the ages of the individual clinoforms, never the less Sen and Kendall(1999) have been able to infer the ages of the progradational Neogene clinoforms using the Haq and others (1987) eustatic chart for the Neogene has some 14 major changes in sea level, at least some of which might be expected to produce major second order type 1 unconformities. There were marked sea level lows, particularly the major type 1 unconformities and associated lows, that suggest these may have been large enough to produce erosional events at the crests of the clinoforms displayed by the seismic sections. Below the exercise proposes examination of the erosional events on the seismic sections to see if these events can be tied to the changes in base level predicted on the Haq and others (1987) chart. If this can be done, is it possible to establish their relative timing? Is there a match between the onlapping and downlapping geometries of the clinoformed section and the Haq et al 1987 sea level curves:

4) The tectonic setting of the Bahamas could be considered to be part of a foreland basin. To the south of the Bahamas the effect of subduction beneath Cuba might be expected to generate movement beside and beneath the Bahamas with resulting local changes in accommodation in the Neogene section displayed on the Western Geophysical Line. To this end the internal geometries of the clinoforms seen on the seismic line should be examined to see if a presence or an absence of small-scale tectonic control on the area can be detected.

Similarly a sediment supply would be expected from the folded and thrust areas of Cuba to the South. A deepening just south of the Bahamas would suggest regional tectonic subsidence and the development of extensive accommodation, while reduced accommodation and thinning over the adjacent cratonic fragment of the Bahamas would suggest more stable tectonic regime. To examine the magnitude of these tectonic effects measure the thickness of the updip carbonate shelf.