Page 139 - Carbonate Sedimentology and Sequence Stratigraphy

130 WOLFGANG SCHLAGER

SILICICLASTICS AND EVAPORITES IN Siliciclastics may be found in all systems tracts but they
CARBONATE SEQUENCES are most common in the basinal parts of lowstand tracts and
most exceptional in the shelf margins of highstand tracts.
In chapter 4 it was concluded that siliciclastics and evap- This dichotomy leads to the phenomenon of “reciprocal sed-
orites may occur in all carbonate facies belts but the prob- imentation” in mixed systems such as the Permian of the
ability varies. The situation with regard to sequences and Guadalupe Mts. (Wilson, 1975; Sarg et al., 1999). Reciprocal
systems tracts is similar. sedimentation implies that the zone of maximum sedi-

Marion Plateau Line 20a

20-60 Hz

110-250 Hz

Vertical height: 200 ms twt; Horizontal width: 16 km

Fig. 7.29.— Downlap at the toe-of-slope of a Miocene platform, Marion Plateau, SW Pacific (Isern, Anselmetti, Blum et al., 2002).
Prograding clinoforms are clean calcarenites, flat basin sediments are slightly argillaceous calcarenites. The slight difference in
lithology plus the drastic change in dip suffice to produce a pseudo-unconformity (downlap) at 20 – 60 Hz frequency. At 110–250
Hz, the reflections at the toe-of-slope can be seen to bend rather than terminate at several places. Lines courtesy of A. Isern and F.
Anselmetti.)