Page 138 - Carbonate Sedimentology and Sequence Stratigraphy

CHAPTER 7: SEQUENCE STRATIGRAPHY OF THE T FACTORY 129

A)

S N
B) Distance (m)
0 0 250 500 750 1000
1000
750
250
500
2000
height (m) 1900

1800

C)
25 Hz

0.0

time (s)

50 Hz
0.1

100 Hz

Fig. 7.28.— Sigmoidal clinoforms of a prograding Cretaceous carbonate platform in the Vercors Mountains, Western Alps (France).
After Stafleu et al. (1994), modified. A) Outcrop photograph. Clean platform lime grainstones in upper right become gradually muddy and
argillaceous as they extend down the clinoform. At the toe-of-slope, the detrital limestones interfinger with argillaceous lime mudstones
and marls (largely covered by scree). B) Lithologic model used to construct the seismic model. Lines represent bedding surfaces
that bound lithostratigraphic units and cross three different facies: clean lime grainstones – dotted, packstones – wackestones – blank,
argillaceous lime mudstones – gray. As different impedance values were assigned to lithostratigraphic units, the bedding surfaces
acted as potential reflectors. C) Vertical-incidence seismic models of B) at three different frequencies. 100 Hz model shows the
lithostratigraphic patterns in essentially correct form. 25 Hz and 50 Hz models show false lapouts owing to incomplete resolution. 50 Hz
model is particularly misleading because the local flattening of clinoforms creates the illusion of a lowstand systems tract onlapping a
highstand slope.