Page 133 - Carbonate Sedimentology and Sequence Stratigraphy

124 WOLFGANG SCHLAGER

A)

1 km

10 km

increase of phosphorite and
B)
ooids with quartz nuclei.
last lime mud in turbidites

δ 13 C car δ 13 C org

Site 535 δ 13 C org
Site 416

Fig. 7.21.— Jurassic – Cretaceous Mazagan platform off Morocco. Platform (in bold, dented lines) was drowned in the Early Creta-
ceous (Valanginian) and onlapped by siliciclastics (dotted lines) that prograded from right to left over the platform and also piled up on
the seaward side, burying the platform flank from bottom up. This marine onlap is caused by the high declivity of the carbonate slope
◦
(about 20 ); the geometry resembles that of a lowstand turbidite wedge. B) Deepwater record seaward of the platform belt links platform
drowning to paleoceanography. Platform termination is recorded by change in calciturbidite composition of DSDP site 416. Timing
of drowning coincides with a shift towards heavier carbon isotopes in carbonates and organic matter, indicating a global anoxic event
recorded in site 416 as well as 534 in the western Atlantic. Based on Schlager (1980; 1989) and Wortmann and Weissert (2001).

exposure cannot occur and type-3 unconformities may be boreholes and outcrops of carbonates. The characteristic
the only record of this eustatic cycle at a particular location pattern consists of a highstand tract overlain by a trans-
(Fig. 7.24). gressive tract without an exposure surface in between (e.g.
Drowning events or pronounced flooding (=incipient Bosellini et al., 1999; Van Buchem et al., 2000).
downing) events have been used as sequence boundaries in