P. Molnar et al., QUATERNARY CLIMATE-CHANGE AND THE FORMATION OF RIVER TERRACES ACROSS GROWING ANTICLINES ON THE NORTH FLANK OF THE TIEN-SHAN, CHINA, The Journal of geology, 102(5), 1994, pp. 583-602
Nested stream terraces, warped upward over actively growing anticlines
along the north flank of the Tien Shan in western China, appear to re
cord alternating phases of valley widening and incision. Differences o
f relative heights between remnants of four separate strath terraces a
long one river and between two such terraces along another reach 100 t
o 120 m over the crests of the anticlines. We infer that this spacing
is due to alternating stages of valley widening and rapid incision ass
ociated with climate changes with a periodicity of 100 kyr. The crests
of the anticlines appear to emerge from the aggrading flanks of the a
nticlines at an average rate of about 1 mm/a. The maximum heights of 2
5 and 35 (+/-10) m for the lowest terraces above their projected initi
al profiles imply ages of roughly 25 kyr and 35 kyr (+/-10 kyr). Hence
, they suggest that flood plains, which were abandoned to form the ter
races, developed adjacent to active stream beds during the last glacia
l period, when climates were relatively cold and dry. We presume that
they were incised during deglacial periods when discharges and stream
power increased. Apparent durations of exposure, obtained from Be-10 i
n quartz cobbles lying on the surface of the lower terrace from one an
ticline, concur with abandonment and deep (similar to 150 m) incision
of the flood plain during the last global deglaciation (ca. 20 to 13 k
yr B.P.). A minimum carbon-14 date of 33.9 kyr B.P. from deposits on t
he lowest terrace sequence from the other anticline, however, implies
that such abandonment and incision of this flood plain occurred before
the most recent global glacial maximum, about 20 kyr B.P. We infer th
at incision of this second anticline's floodplain began during an earl
ier deglacial epoch within the last glacial period (between about 70 a
nd 20 kyr, and perhaps near 35 kyr B.P.).