38
INCREASING FAULTING
AND UPLIFT
I
I
I
~
a PROGRAD ING
SAND GRAVEL
~
I
I
100'5
to
1000's
01
\
meIers
\
\
I
\
I
\
PROGRADING
ALLUVIAL FANS
c
~~~ -I
I
I
I
10'5
01
meIers
I
\
I
\
I
\
I
\
I
\
I
\
I
\
I
\
I
\ I
I
'J __
I
SAND
I
~
Fig. 2.12. Idealized vertical sequences in alluvial fan
deposits and their possible causes. a Large-scale
coarsening-upward sequence due to continuous faulting and fan progradation (Stages 1-3). b Large-scale
fining-upward sequence caused by retreat of scarp
front and lowering of relief in source area (Stages 4,
Chapter 2 Continental Sediments
RETREAT OF SCARP FRONT
AND LOWERING
DECREASING OR
CEASING FAULTING
AI
I
I
I
100'5
to
1000's
01
meters
b BACKSTEPPING
d
AL TERNA Tl NG
PROGRADING AND
BACKSTEPPING
r-f;
I
I
I
I
I
I
I
I
/
I
/
1-10
/
I
/
I
I
I
I
I
I
I
--'1e
/ /
I
/
I
/
I
1--"-(
1- 10
5), or lateral shifting and abandonment of fan (not
shown). c,d Small-scale coarsening-upward cycles
due to the prograding of individual fan lobes. e
Small-scale fining-upward cycle with channelized
base generated by bar processes or filling of braided
channel. (After Ethridge 1985)