Page 136 - Carbonate Sedimentology and Sequence Stratigraphy

CHAPTER 7: SEQUENCE STRATIGRAPHY OF THE T FACTORY 127

unconformity class
toplap downlap onlap buildup onlapped

interfingering class
top progradation toe progradation toe retreat buildup interfingering

Fig. 7.25.— Depositional geometries of reefs and platforms where genuine unconformities and pseudo-unconformities caused by
facies interfingering may be difficult to separate.

F
A)
H G

100 m
B)
H G F

.650

time(s) .700

.750

100 m

Fig. 7.26.— Triassic slope-to-basin transition of Picco di Vallandro (Dürrenstein) in the Southern Alps . After Rudolph et al. (1989).
A) Interfingering of carbonate slope deposits (upper left) with marly basin sediments (lower right). B) Vertical incidence seismic model
at 25 Hz shows bedding-parallel reflections within the slope and basin domains but also produces a reflection oblique to bedding - a
pseudo-downlap reflection that follows the climbing toe-of-slope. This base-of-slope reflection is discontinuous and shifts upward in the
middle third of the diagram but the continuous segments in the left third and the right third of the diagram still demonstrably cross time
lines.

pseudo-downlap. In most instances, the true nature of the or impossible with real data. Bracco Gartner and Schlager
interfingering pattern is revealed if frequency, and thus reso- (1999) found that the use of a seismic attribute, instanta-
lution, are increased (Fig. 6.10, Fig. 7.28). However a several- neous phase, allowed one to differentiate between onlap
fold increase in frequency may be required to solve the prob- and interfingering at significantly lower frequencies than in
lem. This is easy to accomplish in a model but difficult standard reflectivity displays.