318
Chapter 7 Sequences, Minor Cycles, and Event Stratigraphy
a
PRINCIPAL TYPES OF SILICICLASTIC RAMP MARGIN SEDIMENTS
INCREASING SS (SAND) AND SUBSIDENCE
- - - - - - - - - - - - - - - - . - . . .
BASINWARD
'· · 1
REDEPOSITED
RA~_
-=- - - --::.:::.~
b RAMP MARGIN SEOUENCE (3rd order)
FLUVIAI
C PROGRADING PARASEOUENCES (HST) WITH COAL
COASl'AL SANPS
"- .... ....
ALLUVIAL PLAIN
COAL
Fig. 7.14. a Idealized end members of ramp margin
sequences controlled by sediment supply, SS (in particular sand), relative sea-Ievel change, and differential subsidence. With increasing sand supply and accommodation space, lag-dominated shaley systems
pass into systems with prograding coastal sands
capped by transgressive shelf muds and finally systems accumulating sand during both regression and
transgression. b Moderately sand-rich system tracts
of 3rd order sequence on ramp margin; backstepping
trend. c Parasequences consisting of prograding
coastal sands, aggrading alluvial plain deposits including coal, anj thin transgressive muds with carbonate layers. The coastline jumps landward when
relative sea-Ievel rise exceeds sediment buildup.
Thereafter, coastal sands again prograde. (b,c Based
on Van Wagoner et al. 1990; Emery and Myers 1996;
and other sources )