Glacial-Interglacial 13C Variations of Sedimentary Organic
Carbon in Lan-Yang Plain, Northeastern Taiwan
魏國彥、 陳于高、陳文山 (台灣大學地質科學系)
賴慈華、陳利貞、費立沅 (中央地質調查所)
This paper presents records of 13C of bulk sedimentary organic matter from two
cores retrieved from Lan-Yang Plain of the northeastern Taiwan. The two cores, each 250
meters in length, drilled at Chu-An （竹安）and Wu-Chieh （五結）, yielded very similar
carbon isotope profiles. Both cores exhibit quite stable depleted  C values of –23 /oo ~
13
o
-26 o/oo throughout the upper 4/5 sections, indicative of the dominance of C3 plants under
warm and humid conditions. As confirmed by calibrated radiocarbon dates, these intervals
were deposited over the past 15 kyrs. The lowermost parts of both cores show spiky
pattern of 13C values (–14o/oo ~ -25 o/oo) of the last glacial interval, implying an alternation
of dominance of the C4 and C3 plants.
The boundary that marks the dramatic change in 13C profile coincides exactly with
the regional disconformity that separates the postglacial-aged sediments from the
glacial-aged deposits. This disconfomity marks a shift of the depositional facies from
estuary/flood plain to shore face and offshore environments. The age of the bottom of the
shore face/offshore sequence is 15 ka (calendar age), a time coinciding with the end of a
major sea level rise during the last deglaciation. On the other hand, although the upper
sections of these two cores (top 80 meters of Chu-An Core, 60 m of Wu-Chieh Core)
shifted again to deposits of flood plain sedimentation, the 13C values of bulk sedimentary
organic matter remained the same. This suggests that the 13C of bulk sediments is
governed mainly by climate instead of depositional environment.