Precam brian Research, 29 (1985) 93--107 93 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

T I D A L S E D I M E N T A R Y S T R U C T U R E S F R O M U P P E R P R E C A M B R I A N R O C K S OF THE MING TOMBS D I S T R I C T , B E I J I N G (PEKING) , C H I N A

SONG TIANRUI and GAO JIAN

Institu te of Geology, Chinese Academy of Geological Sciences, Belting (People's Republic of China)

(Received May 16, 1984;revision accepted July 6, 1984)

ABSTRACT

Song, T. and Gao, J., 1985. Tidal sedimentary structures from upper Precambrian rocks of the Ming Tombs District, Beijing (Peking), China. Precambrian Res., 29: 93--107.

The Ming Tombs District is a famous historic and scenic site in the vicinity of Beijing. The Proterozoic strata of this region contain many types of tidal sedimentary structures. This paper deals mainly with tidal or shallow water sedimentary structures from carbon- ates but some examples are also described from silicilclastic rocks. The structures include burrow-like tube fillings (from the nearly 2 Ga old Changzhougou Formation), her- ringbone cross stratification, double-crested interference ripple marks, and lenticular and flaser bedding from carbonate rocks of the Gaoyuzhuang Formation.

Well developed sedimentary structures in these upper Precambrian rocks indicate that tidal conditions prevailed throughout deposition of most of a 4500 m thick suc- cession. Supratidal, intertidal and subtidal environments have all been recognised. Wide- spread occurrence of tidal sedimentary structures in carbonate rocks suggests that they were mainly deposited under the influence of physical processes.

INTRODUCTION

The Ming T o m b s are located abou t 50 km f rom the cent re o f Beijing and a b o u t 15 km f rom the Grea t Wall {Fig. 1). A spectacular sect ion of upper Precambr ian rocks is exposed along the new highway tha t runs f rom the Ming T o m b s to the Great Wall (Fig. 2).

The strat igraphic units of the upper Precambrian in the Ming T o m b s Distr ict were established by Tien (1923) , Kao (1934) and by Wang (1980). We have carr ied ou t sedimentologica l investigations of these rocks since 1981 . These studies have revealed the i m p o r t a n t pa r t p layed by tidal proces- ses in the depos i t ion o f the upper P ro te rozo ic succession.

STRATIGRAPHY

The upper Precambr ian succession in the Ming T o m b s District is more than 4 5 0 0 m thick. I t includes sed imenta ry rocks ranging in age f rom 1977 Ma to 884 Ma. These rocks overlie m e t a m o r p h i c Archaean rocks with

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Fig. 2. Typical outcrop of upper Precambrian rocks along the new highway from the Ming Tombs to the Great Wall.

angular unconformity. Twelve formations are recognized (in ascending order): Changzhougou Fm., Chuanlinggou Fm., Tuanshanzi Fm., Dahongyu Fm., and Gaoyuzhuang Fm., which are included in the Changcheng, meaning "Great Wall", System; Yangzhuang Fm., Wumishan Fm., Hongshuizhuang Fm., Tieling Fm., which are included in the Jixian System; Xiamaling Fm., Changlongshan Fm., and Jingeryu Fm., included in the Qingbakuo System (Fig. 3). The following formations include significant amounts of silici- clastic materials: Changzhougou Fm., Chuanlinggou Fm., Hongshuizhuang Fm., Xiamaling Fm. and Changlongsan Fm. These have a total thickness of about 700 m. The remaining formations consist mainly of carbonate rocks (dolostone is dominant) with a total thickness of more than 3800 m. Carbonates constitute more than 80% of the upper Precambrian strata. Tidal sedimentary structures are present both in siliciclastic detrital rocks and in carbonates.

TIDAL SEDIMENTARY STRUCTURES

More than 30 different kinds of shallow water and other sedimentary structures have been identified in the upper Precambrian strata (Fig. 3).

Tidal sedimentary structures in detrital rocks

Detrital tidal sedimentary structures are mainly found in the middle part of the Changzhougou Fm. which is in the lower part of the upper Precambrian succession. The formation is divided into three parts: the bot tom part includes coarse pebbly sandstones with large and small scale trough cross stratification and slump structures. These structures may

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have formed in a distributary mouth bar; the middle part consists of alter- nations of thin bedded light coloured sandstones and dark silty mudstones with many tidal and related shallow water sedimentary structures. These include thick cosets of flaser-lenticular bedding showing distinct foresets (Fig. 4), ripple marks, raindrop impressions, herringbone cross bedding, mud cracks, subaqueous shrinkage cracks, runzel marks, intraformational faulting and folding and water escape structures. This assemblage of sedimentary structures is typical of tidal environments, including supratidal, tidal flat

Fig. 4. Lenticular bedding with foresets (Iqwer part) in the Changzhougou Fm. Coin is 2.0 cm diameter.

___- ---- -.-.- ----

Fig. 3. Stratigraphy and sedimentary structures of the upper Precambrian in the Ming Tombs Dsitrict. Legend of sedimentary structures: (1) Trough cross stratification; (2) Festoon cross stratification; (3) Convolute bedding; (4) Herringbone cross stratification in detrital rocks; (5) Lenticular bedding in detrital rocks; (6) Flaser bedding in detrital rocks; (7) Burrow-like tube filling structures; (8) Ripple mark on detrital rocks; (9) Mud crack on detrital rocks; (10) Sub-aqueous shrinkage crack on detrital rocks; (11) Runzel on detrital rocks; (12) Raindrop impression on detrital rocks; (13) Flaser bedding in carbonate rocks; (14) Slab structure in carbonate rocks; (15) Lenticular bedding in carbonate rocks; (16) Ripple mark with iron-oxide residues in carbonate rocks; (17) Conophyton-like stromatolites; (18) “Birds-eye” structure; (19) Desiccation void struc- ture; (20) Oncolite-like stromatolites; (21) Intraformational folding in dolostones; (22) Herringbone cross stratification in dolostones; (23) Interference ripple mark with double crests in carbonate rocks; (24) Scoured surface with brecciated pebbles; (25) Laminated stromatolites; (26) Mud crack in dolostones; (27) Ripple mark with synaeresis in dolo- stones; (28) Domeshaped stromatolites; (29) Chert intercalation in dolostones; (30) Intraclastic dolomite breccia; (31) Wall-like stromatolites; (32) Small ripple mark in detrital rocks or dolostones; (33) Dark mud drape in dolostones; (34) Wave ripple in marls. Legend of column: 1. Metamorphosed rocks; 2. Coarse sandstone containing small pebbles; 3. Sandstone; 4. Siltstone; 5. Shale; 6. Marl; 7. Limestone; 8. Muddy dolostone; 9. Thin bedded dolostone; 10. Thick bedded dolostone; 11. Dolostone with flaser- lenticular bedding; 12. Dolostone with chert intercalations; 13. Brecciated dolostone; 14. Dolostone with domeshaped or wall-like stromatolites; 15. Dolostone with “birds- eye” or desiccation void structures; 16. Unconformity; 17. Disconformity; 18. Confor- mity.

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and the upper tidal zones (Terwindt and Breusers, 1972; Ginsburg, 1975; Klein, 1977; Reineck and Singh, 1980; Hiscott, 1982).

The upper par t is composed of thick bedded fine -medium grained well sorted and rounded quartz sandstones (Leatherman, 1979) including some white orthoquartzi tes which are typical of the littoral-barrier island environ- ment. Small linguoid ripple marks are present on the surface of some of these beds.

Abundant burrow-like tube-filling structures are present in the middle part of the Changzhougou Fm. These are considered to be typical of tidal flat sediments (Fig. 5). They mostly occur in dark silW mudstones. They

98

Fig. 5. Burrow-like tube-filling structures in the Changzhougou Fro.

Fig. 6. Thin section of burrow-like tube-filling structure.

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are typically about 1-.-2 mm in diameter and are commonly bent. The tubes were filled by sands of the overlying light-coloured sediment. Their internal structure is shown in Fig. 6. We compared these structures with folded mud crack fillings (Pettijohn, 1975), ball and pillow structures (Kuenen, 1965), convolute bedding (Reineck and Singh, 1980), water escape structures (Lowe, 1975; Allen, 1982}, but none of these are identical. They are similar to structures reported as metazoan fossils by Kauffmann and Steidtmann (1981) from the Medicine Peak Quartzite in Wyoming. The exact mode of origin, however, of both the Wyoming structures and those described here, remains controversial {Cloud, 1983; Kauffmann and Steidt- mann, 1983}.

Tidal sedimentary structures in carbonates

Upper Precambrian carbonate sequences in the Ming Tombs District are about 3800 m thick. The Gaoyuzhuang Fm. constitutes about 1000 m of this and the Wumishan Fro., 2200 m so that these two formations make up about 90% of the total thickness of carbonate strata. Most of them are dolostones but there are also marls (about 100 m) in the Jingeryu Fm.

Most of the tidal sedimentary structures observed in carbonates are in the Gaoyuzhuang Fm. and the top part of the Wumishan Fm. Structures include herringbone cross bedding, interference ripples with double crests, flaser--lenticular bedding, mud cracks, synaeresis structures, ripple marks with iron-oxide deposits, intraformational slumps, intertidal scoured surfaces with intraclastic breccias, mud drapes on ripples and different kinds of stromatolites (laminated, dome-shaped, wall-like, conophyton-like and oncolite-like types}. The following is a brief description of four of the above mentioned sedimentary structures:

(1) Herringbone cross stratification Herringbone cross stratification occurs in both dolomites and terrigenous

detrital rocks in the top part of the Gaoyuzhuang Fro. Bimodal-bipolar distribution of foreset dips corresponds to flood and ebb tide directions. Silicified herringbone cross bedding occurs in intraclast-rich carbonate beds (Fig. 7).

(2) In terference ripples with double crests On the surface of dolostone beds at the top of the Gaoyuzhuang Fro.

there are rhomboid interference ripples with double crests (Fig. 8a,b). This feature is common in detrital tidal deposits but is seldom seen in carbonate rocks.

(3) Flaser-lenticular bedding in carbonates Flaser-lenticular bedding is present in carbonates in the middle part of

the Gaoyuzhuang Fm. These structures are similar to those in detrital rocks,

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Fig. 7. Herringbone cross-stratification in silicified dolostones in the upper part of the Gaoyuzhuang Fm.

e.g., distinct foresets in lenses, shown by alternation of light coloured laminae rich in micrite intraclasts and laminae composed of reddish~oloured recrystallised dolomite (Fig. 9a,b,c). Dip angle in lenses of lenticular bedding in the carbonates tends to be more gentle (<~ 10 °) than in terrigenous detrital rocks. Carbonate intraclasts in herringbone cross beddings and flaser- lenticular bedding are similar to pseudo-pellets described by Fahraeus et al. (1974).

(4) Stromatolites The influence of topography, climate, currents and other physical~hem-

ical parameters on the morphogenesis of stromatolites has been studied by many researchers (Logan et al., 1964; Monty, 1967; Bathurst, 1971; Walter, 1972; Milliman, 1974; Young, 1974; Schopf, 1975; Brock, 1976; Hoffman, 1976).

The upper Precambrian rocks of the Ming Tombs area includes the fol- lowing morphotypes: laminated, dome-shaped, conophyton-like, oncolite- like and wall shaped stromatolites (similar to columns elongate perpendicular to the shoreline as described by Hoffman (1976)). In general the laminated, conophyton-like and oncolitic stromatolites occur in the lower part of the upper Precambrian succession, mainly in and beneath the Gaoyuzhuang Fro. Dome-shaped or wall-like stromatolites (Fig. 10a, b) are common in the upper part of the succession, mainly in the upper part of the Wumishan Fro. One of the camel statues that line the route to the Ming Tombs is made of dolostone with dome-shaped stromatolites (Fig. 11). The authors have discovered silicified algal filaments with distinct cell wall septa in the Da- hongyu Fro. (Fig. 12a,b,c). These are present in strata about 1600 Ma old, older than the eucaryotic unicellular microfossils and other filamentous algal fossils (Chang, 1978a,b) in the Wumishan Fro. (about 1300 Ma old). Oncolite-like stromatolites are developed in dolostones in the top part of

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Fig. 8. (a) Interference ripple marks in dolostoncs in the Gaoyuzhuang Fro.; (b) double crested ripple marks.

the Gaoyuzhuang Fm. They contain silicified spherical bodies about 1 cm in diameter. In thin section some oncolite-like stromatoli tes contain cell- like bodies with diameters of 0.2---0.3 mm (Fig. 13a,b,c).

It is commonly assumed that laminated stromatoli tes developed in the upper part of the intertidal zone. Such environments were common during deposi t ion of the Chuanlinggou, Tuashanzi, Dahongyu and Gaoyuzhuang Formations, which were deposited in the early part of the late Precambrian. In the Gaoyuzhuang Fm. stromatoli tes of various shapes alternate with dolostones with "birds-eye" structures, scoured surfaces, small symmetrical ripple marks etc., typical of the supratidal environment. These alternations

102

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Fig. 9. (a) Lenticular bedding in dolostones in the lower part of the Gaoyuzhuang Fro. lenses have foresets with gentle dip angles; (b) parallel arrrangement in outcrop; (c)sof t - sediment deformation.

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Fig. 11. Camel statue made of dome-shaped stromatolitic carbonate along the route to the Ming Tombs.

Fig. 12. (a) Thin section of silicified dolostone with conophyton-like stromatolites in the Dahongyu Fro.; (b,c) algal filaments with cell wall septal structures.

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Fig. 13. (a) Oncolite-like stromatolites; (b) silicified oncolite-like grains; (c) oncolitic grains in a clear carbonate cement.

have been a t t r i b u t e d to p u l s a t o r y m o v e m e n t s in the ear ly late P recambr i an (Qiao and Ma, 1982}. Th ick bedded do lo s tones wi th d o m e - s h a p e d s t r o m a t - ol i tes in te rca la ted with che r t -bea r ing do los tones in the Wumishan Fro. m i g h t have f o r m e d in a re la t ively s table , s o m e w h a t res t r ic ted e n v i r o n m e n t in an ep i con t inen t a l sea.

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CONCLUSIONS

(1) Distinctive sedimentary structttlms in upper Precambr ian detri tal and carbonate-rich strata may reflect tidal deposition in a somewhat restricted epicontinental sea.

(2) Burrow-like tube-filling structures in the Changzhougou Fro. are similar to other structures considered to be metazoan traces. They are, however, considered to be enigmatic and deserve further study.

(3) The presence of double~:rested rhomboid interference ripples, herring- bone cross beddings, flaser--lenticular beddings etc. in carbonates indicates that a large portion of these carbonates were formed by physical processes (Folk, 1959; Dunharn, 1962).

ACKNOWLEDGEMENTS

We grateful ly acknowledge the work o f Tang Shukai in improving the English in this paper.

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