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Marine deposits of late glacial times exposed by tectonic uplift on the east coast of Taiwan

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Marine Geology, 110 (1993) I-6 I Elsevier Science Publishers B.V., Amsterdam

L e t t e r S e c t i o n

Marine deposits of late glacial times exposed by tectonic uplift

on the east coast of Taiwan*

P . A . P i r a z z o l i a, M . A r n o l d b, P. G i r e s s e c, M . L . H s i e h d a n d P . M . L i e w d

a CNRS-URA141, Laboratoire de Gdographie Physique, 1 Place Aristide Briand, 92190 Meudon-Bellevue, France b CNRS-CEA, Centre des Faibles Radioactivitks, Avenue de la Terrasse, 91198 Gif-sur-Yvette. France c Laboratoire de Recherches de Sbdimentologie Marine, Universit~ de Perpignan, 66025 Perpignan, France

a Department o f Geology, National Taiwan University, 245 Choushan Road, Taipei, Taiwan, R O C (Received September 29, 1992; revision accepted November 26, 1992)

ABSTRACT

Pirazzoli, P.A., Arnold, M., Giresse, P., Hsieh, M.L. and Liew, P.M., 1993. Marine deposits of late glacial times exposed by tectonic uplift on the east coast of Taiwan. Mar. Geol., 110: I-6.

Marine sediments deposited some 14,000 years ago, when the sea level was between 80 and 100 m below the present sea level, have been found exposed at about 17 m in altitude near Tu-lan, on the east coast of Taiwan. This implies a minimum average uplift rate of 7.6+0.9 mm/yr; similar values of tectonic uplift are not uncommon on the eastern Coastal Range of Taiwan. Such rates of tectonic uplift, among the highest reported in the literature, are of the same order as present-day maximum glacio-isostatic uplift rates.

Introduction

T h e m o s t spectacular examples o f late Q u a t e r - n a r y regional crustal uplift are usually reported f r o m formerly glaciated areas. I n F e n n o s c a n d i a , for example, the vertical displacement since the last glacial p e a k is estimated to have reached a m a x i m u m o f 8 0 0 - 8 5 0 m (M6rner, 1979; i.e. an average rate o f a b o u t 40 mm/yr). Even greater values p r o b a b l y o c c u r r e d in n o r t h e r n C a n a d a . H o w e v e r , uplift rates in these areas have been gradually decreasing since the ice d o m e s melted a n d present-day values deduced f r o m tide-gauge records are usually less t h a n 10 m m / y r .

In areas where glacio-isostatic m o v e m e n t s are p r e d o m i n a n t , the n o r m a l b e h a v i o u r over a long

*Results of this paper were presented at the International Symposium "'Diversity in Coastal Evolution in the Quaternary" (Wellington, New Zealand, 7-9 December 1992).

Correspondence to: P.A. Pirazzoli, CNRS-URA 141, Labora- toire de G6ographie Physique, 1 Place Aristide Briand, 92190 Meudon-Bellevue, France.

term is a cyclic u p - a n d - d o w n oscillatory pattern, with m a i n periodicities o f the order o f 19, 23, 41 a n d 100 kyr, related to the effect o f a s t r o n o m i c periodicities o n climatic changes (Berger et al., 1990). A b s o l u t e vertical displacements between two similar climatic periods m a y , therefore, be quite small in these areas.

In regions r e m o t e f r o m ice sheets, on the other hand, tectonic uplift rates are usually one order o f m a g n i t u d e less t h a n the glacio-isostatic rates. A r o u n d the Pacific a n d I n d i a n Oceans, for exam- ple, last Interglacial shorelines (dated 125 + 10 kyr) are reported everywhere at elevations less t h a n 400 m (Yonekura, 1983; Y o s h i k a w a , 1987), corre- s p o n d i n g to uplift rates less t h a n 3.2 m m / y r , and m o s t often m u c h lower t h a n this value.

In this p a p e r we provide further evidence o f tectonic uplift rates o f the order o f 6 - 1 0 m m / y r which have been active t h r o u g h o u t the H o l o c e n e a n d in one case, since at least 14,000 years on the east coast o f Taiwan. F o r Chinese names, the English transcription has been used.

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2 P.A. PIRAZZOLI ET AL.

EURASI'

I ii I I l l

Fig. 1. Lithospheric plate structure in and around Taiwan (schematic). Main thrusts as thick lines, barbs on overriding side. In sections: oceanic crust hachured, continental crust with pattern of crosses, island-arc crust with pattern of overturned "v", lithospheric mantle left white (from Angelier et al., 1986).

The geodynamic context

The Taiwan region forms a transition between two opposite movements o f the Philippine Sea plate (Fig. 1): underthrusting along the Ryukyu Islands, and overthrusting along the volcanic islands extending from the Batan Islands to central Luzon (Hsu, 1971; Angelier et al., 1986; Angelier, 1990). The eastern Coastal Range o f Taiwan is an accreted prism of the Luzon arc, belonging to the Philippine Sea plate, which collided with the Eura- sian plate margin. As shown by paleontologic (Chi et al., 1985; Huang and Lin, 1991), volcanologic (Yang et al., 1992) and paleomagnetic studies (Yang et al., 1983; Lee, 1989), intensive collision has occurred since the late Pliocene and has spread southwards.

Field data

Tu-lan (22°52'N, 121°13'E)

Fifteen kilometres northeast of T'ai-tung, above a pebble beach, a 35-m-high cliff consists of marine and river mouth deposits capping a Pliocene sedi- mentary basement (Fig. 2). Intercalated between a basal conglomerate and a layer of river mouth

deposits with cobbles, a well stratified layer of fossiliferous sand deposits appears in situ (Fig. 3). In the sand, the plagioclase/quartz rate is about 0.66, i.e. near that of the most feldspathic near- shore sands (Biq et al., 1985). The clay fraction is low and consists of several heterogeneous minerals: smectite, kaolinite (and/or chlorite) and traces of illite similar to that of marine clays. The shell fraction includes, in addition to undetermined oyster fragments, thin Lamellibranch and Gastro- poda debris, some of which have been identified:

Anodontia edentula, generally living on the

shallow muddy sea floor;

Paphia undulata, usually found in sheltered

muddy bays:

- Gafrarium tumidum, very frequent on a sandy

shallow sea floor;

Clypeomorus purpurascea, living in the inter-

tidal zone of rocky shores; and

Diodora suprapunicea, which are shallow-

dwelling epiphytal limpets.

The above sediments may have been transported in a water environment calm enough, and/or accu- mulated at a depositional rate rapid enough, to make the sedimentation of thin shell debris and mica grains possible (the average spring tidal range is 1.25 m in this area). As microfauna is totally

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TECTONIC UPLIFT OF LATE GLACIAL MARINE DEPOSITS: E TAIWAN 3

O, 50

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Fig. 2. Location map and simplified profile of the Tu-lan section (from Hsieh, 1990, modified); A = Pliocene sedimentary basement; B = offshore to beach sandy deposits; C = river mouth deposits, nearshore to fluvial environment; S = position of dated samples.

Fig. 3. Detail of the Tu-lan outcrop. The samples dated at about 14,000 years were collected at the level of the observer's eye, at about + 17 m. Above: river mouth deposits with cobbles. Below: the present-day pebble beach. (Photo P.A. Pirazzoli.)

a b s e n t , this c o u l d be the case o f a b e a c h sheltered f r o m swells, or o f a 10-15 m deep sea floor in a n area affected b y significant fluvial influx. These deposits p r o b a b l y d o n o t b e l o n g to s u b m e r g e d

coastal bars, o w i n g t o : (1) the g r a i n size (fine sands, m e d i a n = 110 pm), (2) a limited sorting, (3) the a b s e n c e o f ripple structures, (4) the thickness o f the deposits ( a b o u t 10 m), a n d (5) the o c c u r r e n c e

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4 P A PIRAZZOLI ET AL.

on some quartz grains of a silicic film, which would have been dissolved by prolonged submersion; the last two arguments strongly support the beach interpretation. However, very few beaches in east- ern Taiwan consist of such a fine sand; in the Tu- lan area, in particular, pebble beaches predominate and sandy beds similar to the studied one, exposed above the Pliocene basement in nearby outcrops, have been interpreted as shoreface deposits (Hsieh, 1990).

Two samples consisting of Lamellibranch debris

(Anodontia edentula and Paphia undulata), col- lected from the cliff at about + 17 m, were dated by AMS 14C at 12,250_+ 130 yr B.P. (GilA-90218) and 12,170_+ 160 yr B.P. (GifA-91094) (assuming a reservoir age of 400+ 140 years). A sample of

Gastropoda shell debris (Diodora suprapunicea)

collected from the same place gave 12,480 -+ 160 yr B.P (GifA-91087). These converging dates suggest that the ages of the shell debris samples are fairly representative of the age of the sands in which they are found. The ages fall beyond the calibration curves for marine samples proposed by Stuiver et al. (1986). According to the calibration of the 14C time scale proposed by Bard et al. (1990a, 1992), using mass spectrometric U - T h ages from Barbados corals, the preceding 14C dates corre- spond to the period between 13,800 and 14,400 years ago.

In the absence of a local relative sea-level curve, the sea-level position at that time can be estimated at about - 1 0 0 m using planktonic and benthic 180 data (Shackleton, 1987, fig. 5), or between

- 8 0 and - 8 5 m using calibrated dates of corals from Barbados after correction for the local tec- tonic trend (Bard et al., 1990a,b); these are of course only first order estimations, since glacial- isostatic contributions have a significant spatial dependence on the geometry of the coastline even over distances of less than 100 km (Nakada et al., 1991). A tentative average uplift rate between 6.7 and 8.5mm/yr (i.e. of 7.6-+0.9mm/yr) can be deduced for the last 14,100-+300 years from the above data if the samples studied belong to a beach: this of course would only be a minimum rate in the case of submarine deposits.

According to Bard et al. (1990b), around 14,000 years ago the sea level was rising at a rate of about 37 mm/yr, Though this is probably an average

value, possibly including acceleration and decelera- tion periods, it is much faster than the local tectonic rate (Fig. 4). The sand deposits studied were, therefore, in any case submerged and may have been capped by further nearshore/offshore deposits, most of which seem, however, to have been eroded. The coastal environment changed from sheltered to moderately exposed near the mouth of a torrent, as shown by the colluvium with cobble layers which can be observed a few metres higher in the same section (Fig. 3). Concern- ing the depositional environment of these undated deposits, it should be noted that steep slopes, poorly consolidated rock, heavy rainfall, recurrent great earthquakes and strong uplift and erosion rates have caused frequent landslides in this coastal area and offshore slumpings, bringing from time to time huge masses of land sediments to the narrow coastal, nearshore and offshore zones.

Assuming that the uplift rate remained constant in time, the 14,100_+300 year old sediments were submerged at a maximum depth of about 30 m below the rising sea level, reaching the sea level again only in the Late Holocene (Fig. 4), since when they have emerged, whereas a steep pebble beach has developed on the present-day exposed shore (Fig. 3).

The Ch'eng-kung-Feng-pin area

As shown in a recent study which will be pub- lished elsewhere (Liew et al., 1993), the 65-km- long coastal sector between Ch'eng-kung and Feng-pin exhibits irregular average uplift rates, varying from 2.5 to over 8.0 mm/yr. The highest rates have been reported near Shih-yii-san (6 to 9 mm/yr during the last 9000 years) and between Ta-wan and Feng-pin (over 6 mm/yr during the last 2000 years).

Hua-lien

The occurrence of rapid late-Holocene uplift at Mei-lun near Hua-lien, at the northern end of the eastern Coastal Range, is known to have existed since the late 1960s, when Lin (1969) obtained

dates of 3870_+260 yr B.P. (NTU-4) and

3100 _ 290 yr B.P. (NTU- 13) from corals collected at unspecified elevations from raised reefs over-

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T E C T O N I C U P L I F T O F L A T E G L A C I A L M A R I N E D E P O S I T S : E T A I W A N 5 it 4a -,-I 4a ,--I a~ + 2 0 -20 -40 - 6 0 -80 -100 - -120 0 P r e s e n t - d a y a l t i t u d e q ' ~ o f d a t e d samples \ \ \ P r e s e n t M S L \ \ \

<%

\¢e

\ ~ 25 m m / y r -\ % k \ k k \ 8 m m / y r \ \ \ l d d e p o s i t i o n of d a t e d s a m p l e s 7 ~ 3 7 m m / y r ! I I I I I I I I I I I I I 2 4 6 8 ' 10 12 14 R g e (yr x 103 BP) 5 mm/yr I I ! | I 16 18 20

Fig. 4. Estimated average uplift rate at Tu-lan, versus rates and levels o f the post-glacial eustatic rise according to Bard et al. (1990a,b). After deposition some 14,000 years ago and submergence by the eustatic sea-level rise, the samples studied may have emerged only between 2000 and 3000 years ago.

lying a Pleistocene tableland surface reaching 46 m in altitude. Younger ages (1512+45 yr B.P., NTU-159; 1052+32 yr B.P., NTU-166) were obtained from coral and shell samples collected twenty years earlier by C.C. Lin from reef outcrops overlying the same tableland at elevations lower than + 3 m (Hsu et al., 1973). Aware of these findings, Konishi et al. (1968) collected from an outcrop of reef-wall limestone, 25 m above sea level (for a photograph of these raised reefs, see Pirazzoli, 1991, p. f42), an aragonitic coral sample which was dated 2800+ 115 yr B.P. by 14C (N- 407), and 4200___ 370 yr B.P. by 23°Th. This corres- ponds to an average uplift rate since 4000-3000 yr B.P. estimated between 6.0 and 9.7 mm/yr (Konishi

et al., 1968). Repeated levellings between 1984 and 1987 (Liu and Yu, 1990) have shown uneven uplifts in the Hua-lien area ranging from 20 to 100 mm. Most of the vertical displacements have taken place in 1986, probably related to two large earth- quakes which occurred in this region.

Conclusions

Though uplift trends can be quite variable along the east coast of Taiwan, rates of the order of 6 to 9 mm/yr are not uncommon. These values are among the highest rates, over the time scale of several thousand years, reported in the literature from tectonically active areas and appear to be of

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6 P.A PIRAZZOLI E'F AL t h e s a m e o r d e r as t h e m a x i m u m p r e s e n t - d a y u p l i f t r a t e s i n f o r m e r i c e - s h e e t a r e a s . A t s u c h r a t e s , r e m n a n t s o f l a s t I n t e r g l a c i a l s h o r e l i n e s w o u l d h a v e o c c u r r e d , i f p r e s e r v e d , a t a l t i t u d e s b e t w e e n 750 a n d 1100 m . A t T u - l a n , m a r i n e s e d i m e n t s a b o u t 14,000 y e a r s o l d a r e n o w e x p o s e d well a b o v e t h e p r e s e n t sea level. I t is t h e first t i m e , t o o u r k n o w l e d g e , t h a t s e a d e p o s i t s o f l a t e g l a c i a l t i m e s a r e f o u n d e m e r g e d o u t s i d e a r e a s o f g l a c i o - i s o s t a t i c u p l i f t .

Acknowledgments

T h i s is a c o n t r i b u t i o n t o t h e IGCP P r o j e c t 2 7 4 " ' C o a s t a l e v o l u t i o n i n t h e Q u a t e r n a r y " a n d t o t h e a c t i v i t i e s o f t h e INQUA C o m m i s s i o n s o n N e o t e c t o n - ics a n d o n Q u a t e r n a r y S h o r e l i n e s . T h e p a r t i c i p a - t i o n o f P . A . P . t o t h e field w o r k h a s b e e n m a d e p o s s i b l e b y P r o f . J. A n g e l i e r , i n t h e f r a m e w o r k o f t h e C o o p e r a t i o n p r o g r a m m e i n E a r t h S c i e n c e s b e t w e e n F r a n c e a n d T a i w a n . W e t h a n k O . v a n d e P l a s s c h e f o r m a n y c o n s t r u c t i v e s u g g e s t i o n s a n d M s M . D e l a h a y e f o r h e r r e v i s i o n o f t h e E n g l i s h t e x t .

References

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Angelier, J., Blanchet, R., Ho, C.S. and Le Pichon, X. (Editors), 1986. Geodynamics of the Eurasia-Philippine Sea Plate Boundary. Tectonophysics, 125: 1-287.

Bard, E., Hamelin, B., Fairbanks, R.G. and Zindler, A., 1990a. Calibration of the 14C timescale over the past 30,000 years using mass spectrometric U - T h ages from Barbados corals. Nature, 345: 405-410.

Bard, E., Hamelin, B. and Fairbanks, R.G., 1990b. U - T h ages obtained by mass spectrometry in corals from Barbados: sea level during the past 130,000 years. Nature, 346:456 458. Bard, E., Arnold, M., Fairbanks, R.G. and Hamelin, B., 1992.

23°Th-23'*U and ~*C ages obtained by mass spectrometry on corals. Radiocarbon, in press.

Berger, A., Fichefet, T., Gall6e, H., Marsiat, I., Tricot, C. and van Ypersele, J.P., 1990. Physical interactions within a coupled climatic model over the last glacial interglacial cycle. Trans. R. Soc. Edinburgh, Earth Sci., 82: 357-369. Biq, C., Shyu, C.T., Chen, J.C. and Boggs, S., 1985. Taiwan:

geology, geophysics, and marine sediments. In: A.E.M. Nairn et al. (Editors), The Pacific Ocean. Plenum, New York, pp. 503 550.

Chi, W., Namson, J. and Suppe, J., 1985. Stratigraphic record of plate interactions in the Coastal Range of eastern Taiwan. Mem. Geol. Soc. China, 4: 155-194.

Hsieh, M.L., 1990. The study of late Quaternary deposits, marine terraces and neotectonism of the coastal area between Hualien and Taitung. M.Sc. Thesis, Natl. Taiwan Univ. (Unpubl.: in Chinese.)

Hsu, M.T., 1971. Seismicity of Taiwan and some related problems. Bull. Int. Inst, Seismol. Earthquake Eng.. 8: 41 160.

Hsu, Yu.C., Chou, M.C., Hsu, Yi.C., Lin, S.Y. and Lu, S.C., 1973. National Taiwan University radiocarbon measure- ments II. Radiocarbon, 15: 345-349.

Huang, C.Y. and Lin, S.B., 1991. The geologic role of the Huatung Ridge, offshore eastern Taiwan. Annu. Meet., Geol. Soc. China, Taipei, R.O.C., Progr. Abstr., p. 72.

Konishi, K., Omura, A. and Kimura, T., 1968. 234U-23°Th dating of some Late Quaternary coralline limestones from southern Taiwan (Formosa). Geol. Palaeontol. Southeast Asia, 5:211-224.

Lee, T.Q., 1989. Evolution technique et g6odynamique nbog6nc et quaternaire de la Chaine c6ti~re de Taiwan: apport du palbomagn6tisme. Th6se Doct. Univ. Paris VI, 328 pp. Liew, P.M., Pirazzoli, P.A., Hsieh, M.L., Arnold, M., Barus-

seau, J.P., Fontugne, M. and Giresse, P., 1993. Holocene tectonic uplift deduced from elevated shorelines, eastern Coastal Range of Taiwan. Tectonophysics, submitted. Lin, C.C., 1969. Holocene geology of Taiwan. Acta Geol.

Taiwanica, 13:83 126.

Liu, C.C. and Yu, S.B., 1990. Vertical crustal movements in eastern Taiwan and their tectonic implications. Tectonophy- sics, 183:110 119.

Nakada, M., Yonekura, N. and Lambeck, K., 1991. Late Pleistocene and Holocene sea-level changes in Japan: implica- tions for tectonic histories and mantle rheology. Palaeo- geogr., Palaeoclimatol., Palaeoecol., 85: 107-122.

M6rner, N.A., 1979. The Fennoscandian uplift and Late Ceno- zoic geodynamics: geological evidence. Geojournal, 3.3: 287 318.

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Stuiver, M., Pearson, G.W. and Braziunas, T.F., 1986. Radio- carbon age calibration of marine samples back to 9000 cal yr BP. Radiocarbon, 28(2B): 980 1021.

Yang, K.M., Wang, Y., Tsai, Y.B. and Hsu, V., 1983. Paleo- magnetic studies of the Coastal Range, Lutao and Lan Hsu in eastern Taiwan. Bull. Inst. Earth Sci., Acad. Sinica, 3:173 [90.

Yang, T.Y., Liu, T.K. and Chen, C.H., 1992. Fission track of Lutao volcanics: implications of partial annealing and erup- tion history. J. Geol. Soc. China, 35: 19-42.

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數據

Fig. 1.  Lithospheric plate structure in  and  around Taiwan (schematic). Main thrusts as  thick lines, barbs on  overriding side
Fig. 2.  Location map and simplified profile of the Tu-lan section (from Hsieh,  1990, modified); A = Pliocene sedimentary basement;
Fig. 4.  Estimated  average  uplift  rate  at  Tu-lan,  versus  rates  and  levels  o f   the  post-glacial  eustatic  rise  according  to  Bard  et  al

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