Vol. 1 No. I G l: O C H l: M I S T R Y Jam-Mar . 1982

A Preliminary Report on Holocene Geochronology in Southern Liaoning

(Quaternary Geology Laboratory and l~adivearbon Laboratory, Institute of Geochemistry, Acade~nia Sinica)

The Holocene which started about 10,000 yr ago is an entirely new page in the course of the earth's evolution. This short geological span is most closely related to mankind. Therefore, studies on Holoeene geology are helpful to understanding the de- velopment of present natural environments, such as climatic fluctuation, vegetation alternation, shoreline changes, sedimentation rate, and to providing the fundamental geological information for reforming and utilizing the nature, e.g., peat mining, under- ground water exploration and industrial-agricultural construction.

Radiocarbon dating and sporo-poUen analysis are two important routine methods employed in studying Holocenc geology. By sporo-pollen analysis the characteristics of ancient vegetation and climate it manifests can be used to determine the relative ages of sediments, whereas by radiocarbon dating one can measure the absolute ages of sedi- ments, and therefore establish geological time scale of the Holocene.

Investigations have been carried out on some Holocene geologic profiles along the coastal regions of the Yellow China Sea from Dandong to Lfida in southern Liaoning, and radiocarbon dating and sporo-polle~ analysis on peat samples from these profiles performed. From Table 1 it can be seen that they both have well identical results. These results are correlative not only with such Holocene profiles as bearing the seeds of Nelumbo Nucifera at Pulandian m but also roughly with those in the Baltic Sea region, which have been studied in more detail ~J. Accordingly, a preliminary evolu- tionary picture of paleoclimate and paleovegetation has been established and the division and correlation for Holocene stratigraphy in these regions have been proposed for the first time (Table 1).

In the Qianwadun profile at Zhuanghe, sporo-pollen assemblage in the peat layer represents a coniferous and broad-leaf mixed forest, namely, Pinus, Quercus and Alnu~ mixed, corresponding to the Nelumbo Nucifera layer at Pulandian. Radio- carbon dating carried out in our lab. gave an age of 700 ----- 90 yr B.P. for Nelumbo Nucifera and the ages of 2050 ± 95 yr B.P. and 2435 ± 100 yr B.P. for peat and wood from Qianwadun, respectively. These results correspond to the sub-Atlantic Period (0--2500 yr B.P.) of the Blytt-Sernander's climatic periods of North Europe. Pre- sumably, the climate was colder and, humider. In the light of M.I. Neishtadt's sub- division E~, these sediments belong to Late Holocene (Hh or Q4).

The sporo-pollen assemblages in the mud layer under the peat layer in the Qian- waduu profile and in the peat layer in the Lijiagou profile at Zhuanghe represent a broad-leaf forest predominated by Alders with considerable coniferous composition

Tab

le 1

. R

adio

carb

on a

ges

and

spor

e-po

llen

asse

mbl

ages

of

Hol

oeen

e se

dim

ents

in

sou

ther

n L

iaon

lng

Sedi

men

t

Yel

low

-loa

m

Qia

nwad

un p

eat

laye

r

Lij

iago

u pe

at

laye

r

Qia

nwad

un m

ud

laye

r

Dag

usha

n pe

at

laye

r

Pul

andi

an p

eat

laye

r

Loa

m w

ith

grav

el(?

)

Pro

file

(in

thi

s wo

rk)

C" age (

yr)

peat

: 2,

050+

95

woo

d:

2,48

5~10

0

peat

: 2,

750:

t: 1

00

mud

: 3,

7304

-120

peat

: 6,

660+

160

peat

: 7,

3904

-190

top:

8,

0704

-190

bo

ttom

: 9,

950+

300

Spor

e-po

llen

asse

mbl

age

Con

ifer

ous

and

broa

d-le

af m

ixed

fo

rest

P/

nus-

Que

rau~

, A

ln~

Ald

ers

prev

aili

ng

broa

d-le

af f

ores

t X

ln~

, Q

uerm

bs-P

inus

Ald

ers

broa

d.le

af

fore

st

Aln

u~

Bir

eh f

ores

t

~lan

dian

pro

file

Sedi

men

t

Bro

wnl

sh-y

ello

w l

oam

Dar

k.gr

ey m

ud

(bea

ring

ane

lent

I~

tus)

C

:4:7

00+

90 y

r

Top

par

t of

bla

ek

elay

, C

~4 a

ge:

4,31

0+12

5

Bot

tom

par

t of

bl

ae.k

ela

y

Pea

t la

yer

Sand

-gra

vel (7

)

9por

e-po

llen

asse

mbl

age

Con

ifer

ous

and

broa

d-le

af ~

ed

fo

rest

: P

in~.

Que

reua

, B

etul

o

Bro

ad-l

eaf

fore

st:

Que

rm~.

P¢nu

s

Bro

ad-l

eaf:

Q

uer~

Bir

ch f

ores

t,

2~ef

uZa

Cllm

atle

per

iod

Sub

-Atl

anti

e P

erio

d (cold an

d hu

mid)

0-

-2,5

00 y

r

Sub-

Bor

eal

Peri

od

(war

m,

and

dry)

2,

500-

-500

0 yr

Atlanlde Per

iod

(war

m,

hum

id)

5,00

0--7

,500

yr

Bor

eal

Per

iod

(war

m,

dry)

7,

500-

-9,5

00 y

r

Pre

-Bo

rea

l P

erio

d 9

,50

0--

10

,80

0 y

r

Hol

oeen

e su

bdiv

isio

n

Lat

e H

ol~e

ene

Hh

0-

-2,5

00 y

r

Mid

dle

Hol

oeea

e H

h

2,50

0--7

,700

yr

Ear

ly H

oloe

ene

Hh

7,

700-

-9,8

00 y

r

Pale

o-H

oloe

ene

Hh

9,80

0--/

2,00

0 7

r

©

I-! ~o

136 GEOCHEI~ISTRY Vo]. 1

~Pinus. These two layers correspond to the top part of the black mud layer at Pulandian. The radiocarbon age of peat from Lijiagou is 2,750 --+ 100 yr B.P. and that of mud from Qianwadun is 3,73'0 -+ 120 yr B.P. These results correspond to the sub-Boreal Period, the age of which ranges from ca. 2,500 to 5,000 yr B.P. The climate was rather warm and dry during that period. These peat and mud sedi- ments belong to late Middle-Holocene (HI,~ or t~b).

The sporo-pollen assemblages in the sediment layer under the Lijiagou peat layer and in the peat layer at Huangtukan are identical, both being characterized by Alders prevailing broad-leaf forests. These two layers correspond to the bottom of the black mud layer at Pulandian. Radiocarbon ages of Huangtukan peat at Dagushan are 6,660 ± 160 yr B.P. and 7,390 _+ 190 yr B.P. These results can be correlated with the Atlantic Period, the age of which ranges from ca. 5,000 to 7,500 yr B.P. The climate which was most agreeable in the postglaeial epoch was rather warm and humid during that period. These sediments belong to early Middle Holoeene (I-II~, or Q~).

The peat at the bottom of Pulandian profile reflects a birch forest with Betula predominent. The radiocarbon age is 9,950 -- 300 yr B.P., corresponding to the Boreal Period which ranges from 7,500 to 9,500 yr B.P. in age. The climate was rather warm and dry at that time. This layer belongs to Early Holoeene (Hl~ or Q~).

The palco-Holocene (HL or Q~), namely the pre-Boreal Period, is such a period during which glaciers began retreating and the climate turning warm. Its age ranges from ca. 9,500 to 10,300 yr B.P. Presumably, sediments deposited during this period in southern Liaoning mainly consist of sand-gravel layers and loam layers with sand- gravel. Due to little amount of sporo-pollen contained in the sediments, specimens suita- ble for radiocarbon dating ean hardly be found in this region.

From the foregoing discussions, we have come to the conclusion that the so-called "Dagushan peat beds" acturally consist of peat sediments belonging to four different stages of the Holocene. Our study has thrown much light to the history of Holocene geologic development during which the sedimentary stages ~are distinguished, i.e., the sand-gravel layer--paleo-Itolocene (the pre-Boreal Period); the Pulandian peat layer - -Ea r ly Holoeene (the Boreal Period); the Dagushan peat layer early Middle-Holo- cene (the Atlantic Period); the Lijiagou peat layer--late Middle-Holocene (the sub- Boreal Period); the Nelumbo Nucifera layer, Qianwadun peat layer and brownish- yellow loam layer--Late Holocene (the sub-Atlantic Period). Based on this work, a preliminary Holoeene geogieal time scale for southern Liaoning has been establish- ed and a general picture drawn in regard to paleoelimate, paleovegetation and geo- logic evolution of various periods during the Holoeene.

R e f e r e n c e s

[ 1 ] ~ , ~ , )~$~: 1965, i ~ , ~ _ ~ ~ i ~ t ! ~ i E ~ C ~ ) / ~ Y ~ o ¢ ~ ! ~ h 2 ~ ~¢~g[~----]~, 167--173 ~o

[ 2 ] Kalorvo Panka~na edit. : 1965, ' ' Quaternary ", Vol. 1, p. 1--300, Interseienee Publishers, New York- London-~ydney.

[ 3 ] ) ~ : 1965, ~ J ~ $ ~ ] ! ~ ~ ~ } } : ~ o ¢ ¢ p [ ~ g ~ t ~ , ~ [ ~ g - - ~ ] , 118 --134 ~'o