Precambrian Research, 18 (1982) 367--396 367 Elsevier Scientific Publishing Company, A m s t e r d a m - Printed in The Netherlands
AN OUTLINE OF STUDIES ON THE PRECAMBRIAN STROMATOLITES OF CHINA*
ZHU SHIXING
Tianjin Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences, Tianjin 300 1 70 (People's Republic of China)
(Received September 30, 1981; revision accepted February 18, 1982)
ABSTRACT
Zhu Shixing, 1982. An outline of studies on the Precambrian stromatolites of China. Precambrian Res., 18: 367--396.
This paper outlines studies of Chinese Precambrian stromatolites, which may be sub- divided preliminarily into two 'stromatoli te successions' and seven assemblages.
Secondly, based on Chinese data, stromatolites have undoubted stratigraphic signif- icance for intrabasinal correlation, but it is necessary to depend on some of the 'bridging elements' and the 'related assemblages', as well as on other methods for interbasinal correlation.
Finally, the paper discusses some problems of fossil stromatolites, i.e. the principal classification and the stromatolite cycles.
INTRODUCTION
In China, Precambrian stromatolites occur abundantly both in mid- to late Proterozoic rocks (Sinian Suberathem) and in the early Proterozoic rocks represented by the Hutuo Group or Supergroup.
The Sinian Suberathem is widely distributed and developed in China. According to the current subdivision, it is subdivided into four Systems, the Changchen, Jixian (Chihsien), Qingbaikou and Sinian Systems with a time range from ca. 1950 +50 to 615 +20 Ma (Table I). It is overlain by the Lower Cambrian, rich in small shelly fossils (Wang Yuelun et al., 1980; Zhao Ziqiang et al., 1980). Among the four Systems, the type section of the Changchen, Jixian and Qingbaikou Systems are in Jixian County, northern China, but the type section of the Sinian System is in the eastern Yangtze Gorges, Hubei, southern China. The author agrees with Chung Fu- tao's and Chen Jinbiao's opinion and subdivides the Changchen System into two Groups or Systems: the Changchen and the Nankou Systems (Chen
*This paper was presented at the International Geological Congress, Paris, 1980.
The scheme of division for the Sinian Subera them (mid- to late Proterozoic rocks) in China
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369
Jinbiao et al., 1980; Zhu Shixing et al., 1978). In addition, based on available data, a reference section in the Liaodong peninsula may partly occupy the interval between the Jixian and Yangtze Gorges sections (Cao Ruiji and Zhao Wenjie, 1977; Chang Shaoquan, 1980). Thus, it is possible to refer this stratum and its equivalents to a new Group or System, as suggested by the Laboratory of Isotope Geology, Kweyang Institute of Geochemistry (1977).
The Hutuo Group and its equivalents are developed mainly in northern China (Fig. 1). These early Proterozoic (pre-Sinian Suberathem) rocks are commonly metamorphosed to low or medium grade. They are covered u~l- conformably by the various formations (including the Changchen System) of the Sinian Suberathem and unconformably overlie the upper Archean repre- sented by the Wutai and Anshan Groups. The maximum K--Ar isotopic ages on amphibole are 1924 Ma in the Hutuo Group and 2302 Ma in the Wutai Group (Wang Qichao et al., 1980). On the basis of the geological and biological data, the author considers that deposit ion of the Hutuo Group and its equi- valents may have taken place between 2400 +-50 Ma.
STROMATOLITE ASSEMBLAGES
In China, the s tudy of the individual characteristics of different stromatol- ite assemblages and their correlations has already become one of the im- portant methods for correlating Proterozoic strata, especially for the Sinian Suberathem. On the basis of the available data from Jixian County, the Liaodong peninsula, the Wutai range and other localities, the Precambrian stromatolites of China may be subdivided into two stromatolite successions and seven assemblages, which are described below in ascending order.
The pre-Sinian Suberathem stromatolite succession
Pre-Sinian Suberathem stromatolites occur mainly in carbonates of the Hutuo Group of the Wutai Range, the Gantaohe Group of the Taihang range, the Zhongtiao Group of the Zhongtiao range, and the Liaohe Group of the southern regions of Liaoning Province (Fig. 1). The early Proterozoic stromatolites of China represented by those in the Hutuo Group are prelim- inarily subdivided into two assemblages (Fig. 2).
Assemblage 1 (Fig. 3) is represented by Kussiella cf. tuanshanziensis Liang et Cao, K. plana (f. nov.), Segosia (?) mini]a Dolnik and Kussoidella cf. limata Semikh. In addition, there are a few Zhongtiaoshania hamagouensis (gr. et f. nov.), Svetliella hebiancunensis (f. nov.), cf. Gymnosolen, cf. Eucapsiphora, cf. Jurusania and Conophyton f. The stromatolites of this assemblage are commonly characterized by a great quanti ty of small convex to fiat types and simple convex types of stromatol- ite of small size, with parallel branching, unwalled margin surfaces and rib- boned microstructure that appear in the impure carbonates as small bio-
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Fig. 2. Generalised biostratigraphy of the Hutuo Group (early Proterozoie), northern China: (1) metamorphosed conglomerate, and sandstone; (2) quartzite and: shale; (3) crystalline carbonate and stromatolite carbonate; (4) metamorphosed volcanic rocks; (5) schist and gneiss.
herms (see below for explanation of new terminology). This assemblage oc- curs in the lower part of the Hutuo Group and the Zhongtiao Group.
Assemblage 2 is represented by Minjaria f., Paraboxonia connexa (gr. et f. nov.), Pilbaria cf. perplexa Walter, Hutuoella ministolona (gr. et f. nov.), Discorsia wutaishanensis (f. nov.), Jacutophyton microstylum (f. nov.), Lenia f., Mistassinia cf. wabassinon Hofmann, M. niushanensis (f. nov.) and cf. LineUa (see Figs. 4--6). (The new taxa mentioned here are described in the appendix to this paper.) This assemblage occurs mainly in the upper part of the Hutuo and Zhongtiao Groups, and in most of the Gantaohe and the Liaohe Groups. On the whole, it consists commonly of large- to medium-sized, although sometimes very small, walled st~omatolites with parallel to markedly divergent branching and some projections, and rib- boned or striated microstructures. Most stromatolites from this assemblage generally appear in cherty carbonates as various biostromes. In the lower part of this assemblage there is a number of convex-fiat types and simple convex types of stromatolites, unwalled and a to/3 branching, such as Dashiqiaoella dashiqiaoensis Cao et Zhao, cf. Eueapsiphora, and cf. Jurusania etc., but these are not predominant.
371
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Fig. 3. (a) Segosia (?) minija Dolnik; (b) Kussiella plana (f. nov.); (c) K. cf. tuanshanziensis Liang et Cao; (d) Kussoidella cf. limata Semikh. (e) Zhongtiaoshania hamagouensis (gr. et f. nov.). (f) Svetliella hebiancunensis (f. nov.). (a--d) from lower part of Huoto Group, (e) middle part of the Zhongtiao Group and lower part of the Hutuo Group.)
372
Fig. 4. (a)Pi lbar ia cf. perplexa Walter; (b)Mistassinia niushanensis (f. nov.); (c) Hutuoella ministolona (gr. et f. nov.); (d) Discorsia wutaishanensis (f. nov.); (e) cf~ Jurusania; (f) Omachtenia f. (a, c--e) occur in the upper part of the Hutuo Group, (b) and (f) in the upper part of the Gantache Group.
373
d
Fig. 5. (a) CoUumnaefacta f.; (b) and (f) Conophyton f. (b is transverse section); (c) Jacutophyton microstylum (f. nov.); (d) Lenia f., (e) Minjaria f. (a--d) occur in the upper part of the Hutuo Group, (e) in the upper part, and (f) in the lower part of the Zhongtiao Group.
374
Fig. 6. (a) Minjaria f.; (b) cf. Gymnosolen; (c) Dashiqiaoella dashiqiaoensis Cao et Zhao; (d,e) Conophyton f. (c is transverse section); (f) Paraboxonia connexa (gr. et f. nov.); (g) cf. Linella. (a, c, f) occur in the upper part of the Hutuo Group, (b) in the lower part of the Hutuo Group, (d, e) in the lower part of the Zhongtiao Group and (g) in the upper part of the Gantaohe Group.
TABLE II
The subdivision of the Sinian Suberathem stromatolites
375
Stratigraphic units
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Stromatolites
Subassemblage C Baicalia f., *Boxonia xifengensis (f. nov.),
*Linella cf; simica, Patomia multigemmia (f. nov.), Gymnosolen f., Stratifera f., etc.
Subassemblage B *Katavia dalijiaensis, K. karatavia, *Linella jia- xanensis, *Gymnosolen cf. furcatus, *G. cf. levis, Clavaphyton (Inzeria) bellum, *Jurusania cylindrica,
*Conophyton ocularoides, *C. lijiadunensis, Baica- lia cf. rata, Tungussia nodosa, *Minjaria nimbi- fera, Anabaria cf. juvensis, etc.
Subassemblage A *Linella avis, *Tsingbaihounia vaginata (gr. et f. nov.), *Inzeria tjomusi, Gymnosolen cf. confrago- sus, Katavia f. etc.
*Chihsienella chihsienensis, Conicodomenia longo- tenuia, *Tielingella tielingensis, Pseudotieling- ella ehihsienensis, *Baicalia of. baicalica, Bai- calla f., *Anabaria chihsienensis, Conophy ton luo- tuolingensis, etc.
*Conophyton cylindricum, C. garganicum, Confucoso- conophyton multiangulum, *Tabulocor~igera paraepi- phyta, *Gaoyuzhuanla gaoyuzhuangensis, C. crassib- revis, G. bulbosa, Kussiella cf. kussiensis etc.
*Gruneria sinensis, *Xiavingella xiavingensis, *Kus- sieUa tuanshanziensis, Yanshania simplex, Crypto- zoon haplum, Eucapsiphora multiramis, Panjiapu- ella palmata, *Nordia cf. laplandica, etc.
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The Sinian Suberathem stromatoli te succession
Mid- to late-Proterozoic stromatolites are widely distributed in the Sinian Suberathem of China. Based on data from the Jixian type section, the refer- ence sections from the Liaodong peninsula, the Sinian System of the central part of Guizhou Province, amongst others, the Sinian Suberathem stromatol- ites have been subdivided into five assemblages (Cao Ruiji (Tsao Rui-chi) and Liang Yuizuo (Liang Yu-zhou) 1974; Zhu Shixing et al., 1978; Tianjin
Fig. 7. Phosphatic stromatolites occurring in the Doushantuo Formation, Sinian System, Sinian Suberathem, Guizhou Province: (a)Boxonia xifengensis (f. nov.) (MS); (b) Linella cf. simica Kryl; (c) Patomia multigemmia (f. nov.) (MS); (d) Gymnosolen sp.
377
Institute of Geology and Mineral Resources et al., 1979; Cao Ruiji et al., 1980; Zhu Shixing and Du Rulin, 1980; Zhu Shixing, 1980). They are syn- thesized in Table II.
Boxonia xifengensis (f. nov.), Linella cf. simica Kryl., Patomia multigemrnia (f. nov.), Gymnosolen f. and Baicalia f. are all phosphatic stromatolites (Fig. 7). They occur in the Doushantuo Formation of the Sinian System in central Guizhou Province, and are characterized by abundant and well- preserved algal micro-fossils. In addition, Eucapsiphora rnultiramis Zhu and Pan]iapuella palmata Zhu are iron stromatolites, which consist mainly of hematite with some quartz, and occur in the lower part of the Changchen System (Zhu Shixing, 1980).
STRATIGRAPHIC SIGNIFICANCE AND USE OF STROMATOLITES
Based on studies of the numerous Proterozoic sections in China, the author tends to the conclusion that respective morphologic features of stromatolites, such as morphology and size of column, branching pattern, marginal features and laminae shape, may be repeated in the Proterozoic, but the different assemblages possess various groups and forms and some predominant characteristics. Thus, stromatolite assemblages may be an im- portant basis for subdivision and correlation of Proterozoic strata under certain conditions. For example, according to the current subdivision, the Changchen System of the Sinian Suberathem contains two assemblages, thus it is necessary to subdivide the current Changchen System into two systems, the Chengchen and Nankou. In the same sedimentary basin, the basic characters and the representative groups and forms in different stromatolite assemblages are more stable in stratigraphically-equivalent horizons, except in the marginal part of the basin. For example, because the Sinian Suberathem rocks in the Yanshan, Taihang and Wutai ranges were deposited in the same basin, the intrabasinal correlations are good not only at the level of the systems, but also at the level of formations, subformations and members.
Between the different basins, there are marked differences in vertical range of stromatolites, even with different assemblages and their representa- tive groups and forms. However, a number of common or similar as- semblages can be found in certain horizons deposited more or less simultane- ously. These groups, forms and assemblages may be termed 'bridging ele- ments ' and 'related assemblages'. For example, a number of groups and forms in assemblage 2 of the Sinian Suberathem stromatolites such as Tabuloconigera paraepiphyta Zhu et al., Confusoconophyton multiangulum Zhu et al. and Conophyton cylindricum (Grabau) Masl., have been found in equivalent rocks of the Yangtze Gorges (Shennongjia Group) and in the north of Yinshan Range (Shinagan Group), so they can be taken as characteristic of the Nankou System. A number of groups and forms in as- semblage 3 of the Sinian Suberathem stromatolites, especially some small- sized stromatolites, such as Microstylus, Scyphus and Pseudogymnosolen,
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distributed extensively in equivalent rocks, become an important clue for correlation of the lower Jixian System in different-basins. Experience in China confirms that interbasinal correlation is possible so long as the stromatolite succession is determined correctly, and that the 'bridging ele- ments ' and 'related assemblages', as well as any other data such as isotopic ages and other fossils, are fully considered. Preliminary correlation of the Proterozoic rocks in China, based on present data, is outlined in Table III.
In analysing the Precambrian stromatoli te data from other parts of the world, it seems that many of them may be roughly correlated to different stromatolite assemblages in China. For example, the Riphean and Vendian stromatolites appear to correlate well with stromatolite assemblages 2--5 of the Sinian Suberathem, and the Aphebian stromatolites of northern North America, Eastern Europe, Australia and South Africa seem similar to as- semblage 1 of the Sinian Suberathem and the assemblages 1 and 2 of the early Proterozoic stromatolites in China, respectively. Of course, there are many problems yet to be solved.
DISCUSSION
At present, more and more data have shown that stromatolites were abun- dant not only in the mid- to late Proterozoic strata, but also in the early Proterozoic. Some of the elements of mid- to late Proterozoic stromatolites can also occur in the early Proterozoic (Hofmann, 1969a, b, 1977; Walter, 1972; Donaldson, 1976}. In addition, many investigators have already ob- served that stromatolites, such as Kussiella, Baicalia and Tungussia can ex- tend up or downward. All these examples have aroused serious discussion on the stratigraphic significance of stromatolites and the factors controlling their morphology. Here, the author puts forward some problems en- countered during his s tudy of stromatolites and preliminarily discusses them below.
Principal classification of stromatolite morphology
Stromatoli te is defined in this paper as a biogenetically-laminated sedi- mentary structure with certain geometrical morphology. All stromatoli tes are characterized by the form of their laminations, which may be sul> divided into three basic types according to their geometrical characters, i.e. flat, convex and conical, and they consist of various types of laminae either alone or alternating.
Different stromatoli tes consisting of one kind of laminae no t only occur in different positions of stratigraphic sections, but are possibly formed by different stromatolite-building communities of organisms. Thus, the author considers that it is necessary to initially subdivide all stromatolites into three principal types and three transitional types, on the basis of laminae morphology, then further to subdivide them into different supergroups, groups and forms, following Rabeen's (1969) recommendations, according
381
to branching patterns, column shapes, marginal features and microstructures or fabric. This is suitable from either biostratigraphic or from sedimentolog- ical points of view. These principal classifications are:
(1) Flat type (F-type). Stratiform type or LIH type, with flattened laminae predominantly, such as Stratifera Korolyuk.
(2) Convex type (V-type). A part of the columnar stromatolites, consisting predominantly of convex laminae, i.e. the SH type of Logan et al. (1964), such as Colonnella Komar and Gymnosolen Steinmann.
(3) Conical type (C-type). A part of columnar stromatolites, consisting pre- dominantly of conical laminae, such as Conophyton Maslov and other branching types.
(4) Flat-convex type (FV-type). Columnar-layered stromatoli tes or a com- pound form (e.g. LLH--SH--LLH), both with flat laminae and convex, such as Omachtenia Nuzhnov and Gruneria Cloud et Semikhatov.
(5) Convex-conical type (VC-type). Both with convex and conical laminae, such as Jacutophyton Schapovalova and Conicodomenia Liang et al.
(6) Flat-conical type (FC-type). Both with flat and conical laminae, such as Straticonophyton Hofmann.
Cyclic characteristics of the stromatolites
Through the s tudy of vertical variation of Proterozoic stromatolites and comparison between the early and the mid- to late-Proterozoic stromatolites, we come to the preliminary conclusion that basic morphologic changes of stromatolites in different bioherms and stratigraphic units exhibit a certain cyclical recurrence at different scales. The basic pattern of stromatolite cycles with different scales is "F- -V- -C- -V--F ' , in ascending order, and ac- cording to the new terms above mentioned. Of course, the different stromatolite cycles may appear to vary owing to repetit ion or absence of certain factors.
The stromatolite cycles at a small scale appear in stromatolite bioherms. In this case, all the three or only two types of stromatoli te constructions oc- cur regularly. For example, when a bioherm is characterized by FV-type of stromatolites, the cyclic pattern is "F - -V- -F" in ascending order (Fig. 8A). When the V-type of stromatoli te predominates in a bioherm, the cyclic pat- tern is also " F - - V - - F ' , but is simplified (Fig. 8B). However, when a bio- herm is composed predominantly of Conophyton, sometimes the flat and convex types may appear firstly at the base of the bioherm, fol lowed by a large number of conical types, the cyclic pattern becoming "F--V--C"
382
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Fig. 8. The emerging sequence of various types of s tromatoli te in different bioherms: (A) KussieUa tuanshanziensis Lang et Cao; (B) Chihsienella chihsienensis Liang et Cao; (C) Conophyton cylindricum (Grabau) Maslov; (D) Tabuloconigera paraepiphyta Zhu et al.
(Fig. 8C). In general, the complete cycle is unique, and is also more complex in some bioherms (Fig. 8D). In this case, the cyclic pattern of stromatolite is "F--V--C--V--F".
The medium-scale stromatolite cycles appear generally in stratigraphic units such as members and formations, and even systems. They are re- flected by a number of bioherms with different characteristics. In general, the bioherms consisting of flat or flat, convex types tend to predominate in the lower parts of these units, and the bioherms of convex type predom- inate in the upper part. When the bioherms consist mainly of a conical type of stromatolite, such as Conophyton, they usually occur in the upper part, or at the top of these units. These phenomena can be clearly seen both in the Jixian section of the Sinian Suberathem and in the early Proterozoic sec. tions represented by the Hutuo Group (Fig. 9). In certain cases, above the bioherm with a predominance of the conical type of stromatolite, other bio- herms mainly with convex or even flat types may again develop, so that the stromatoli te cycle becomes complete. The term 'bioherm rank' is used here 'to designate those bioherms which consist respectively of different s t romatol i tes (with respect to lamina shape) predominating in a b ioherm and occurring regularly in various stratigraphic units. It is obvious tha t the
383
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Fig. 9. Diagram showing the morphologic changes of stromatoli tes in different strati- graphical units. F, V, and C represent : the flat, convex and conical type of stromatolites, respectively; (a) sandstone; (b) sandy and argillaceous dolostone; (c) dolostone; (d) dolomite-bearing limestone; (e) stromatolite-bearing dolostone. (A) Wumishan Format ion with four subformations; (B) Tuanshanzi Format ion; (C) Dahongyu Format ion; (D) Tieling Formation, Jixian County.
term 'bioherm rank' is similar to, but not identical with, the terms 'bioherm series' used by Krylov (1967) and 'set' used by Serebryakov (1976). Different bioherms in every rank differ in their degree of development, so that the repetition or absence of a certain type of bioherm is a widespread phenomenon. For example, the bioherm ranks of the Tuanshanzi, Dahongyu and Gaoyuzhuang Formations in the Jixian section are character-
384
ized, respectively, by the cyclic patterns "F - -V" and "F--V--C", i.e. the stromatolite cycles identified by bioherm ranks are not complete in these formations. The repeated phenomena of different bioherms often appear in the Wumishan Formation of the Jixian System. Of course, the stromatolite cycle identified by bioherm rank is more complete in this formation.
The large-scale stromatolite cycles may be observed in a stratigraphic mega-unit, such as the Sinian Suberathem or the Hutuo Group. The prelim- inary data show that the stromatolite assemblage or the bioherm rank of the lower part of the Changchen System is mainly characterized by F--V type of stromatolites; those of the upper part of the Changchen (or the Nankou) System and the Qingbaikou System are mainly composed of vari- ous V-type stromatolites, and the C-type stromatolite mainly occurs in the upper part of the "Nankou" System to the Jixian System. The stromatolite sub-assemblage or the bioherm rank of the Sinian System is generally characterized by the F and F--V types of stromatolite except some local- ities, such as Guizhou Province. Thus, the stromatolites of the entire Sinian Suberathem seem to show a large-scale cycle and the pattern "F--V--C--V--F" forms the characteristic of every assemblage, or every bioherm rank (Fig. 10A). The preliminary data on the stromatolites of the Hutuo Group show similar cyclic characteristics (Fig. 10B). These large-scale stromatolite cycles are named 'stromatolite succession' in this paper.
With regard to other morphologic factors of stromatolites, such as the column size, branching, marginal structure etc., it seems that they also man- ifest a certain regularity in different bioherms, bioherm ranks and succes- sions. In general, the stromatolites are smaller and more-simply branching in the lower and upper parts of different stromatolite units, but they are larger and more-complexly branched near the middle part. It seems that stromatolites wi thout walls are generally found in the lower part of the cor- responding unit, the walled types occurring in the upper part, especially above the level where conical stromatolites are well developed. Because of the intermixing of these morphological factors, all cycles and units of stromatolite often show complex features in different stratigraphic sections.
To summarize, the external morphological characteristics of stromatolites show a certain cyclic recurrence at different scales. Therefore, various stromatolite groups determined primarily by these external characteristics may appear repeatedly in corresponding locations in different cycles. It is possible that a certain similarity in the stromatolites in the late Sinian Suberathem or late Riphean and those from the upper part of the Hutuo Group reflects this stromatolite cycle at a very large scale.
However, the stromatolite cycles are by no means a simple mechanical repetition. They have also manifested certain orientational changes, especial- ly in combinat ion with analysis of the microstructure and fabrics (Bertrand- Sarfati, 1976; Serebryakov, 1976; Zhu Shixing et al., 1978). Thus, the cyclic characteristics of s t romatohtes not only gives them stratigraphic significance, but can help in a bet ter understanding of these morphologic changes for stratigraphic correlations.
385
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I 0 23~00 2000 ( M a )
B
Fig. 10. Schematic diagram showing the distribution of the principal types of stromatolite: (A) Sinian Suberathem stromatolites; (B) early Proterozoic stromatolites. F, V and C represent flat, convex and conical types of stromatolites, respectively.
CONCLUSION
The Precambrian stromatolites of China occur in abundance in mid- to late-Proterozoic rocks, represented by the Sinian Suberathem, and in early Proterozoic rocks, represented by the Hutuo Group. They may therefore preliminarily be subdivided into two stromatolite successions, i.e. the early Proterozoic succession which is further subdivided into two assemblages, and the mid- to late-Proterozoic succession which is further subdivided into five assemblages and a number of sub-assemblages in a vertical sense.
On the basis of practical experience, the author believes that the strati- graphical significance of the Precambrian stromatolites is doubtless for intra- basinal correlation, and that interbasinal correlation is possible depending upon the 'bridged elements' and the 'related assemblages' among other data.
On the grounds of the data available, the author considers preliminarily that basic morphological changes in stromatolites in the vertical direction ex-
386
hibit a certain cyclic recurrence and the phenomena of repeated and ex- tended stromatolite groups in different horizons are just ~. reflection of these stromatolite cycles. The author still considers that it is unwise to de- pend only upon the stromatolite group, and it is essential to study their forms carefully for Precambrian correlations.
ACKNOWLEDGMENTS
I thank Mr. Chen Jinbiao, Mr. Zhang Huimin for guidance and help in writing this paper, and Mr. Cao Ruiji, Mr. Liang Yuzuo and Mr. Zhang Luyi for discussion on the Precambrian stromatolites of China. I thank Mr. Xu Chaolei, Mr. Wang Qichao and Mr. Wang Yengen for providing many of the specimens. I also thank Mr. Liu Mingquan, Mr. Lu Xianshan, and Lu Songnian for revision of my manuscript. I am greatly indebted to Dr. S.M. Awramik and Dr. J. Bertrand-Sarfati for their detailed review of the manuscript. I am greatly indebted to the Tianjin Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences, for supporting this study.
APPENDIX: SYSTEMATIC DESCRIPTION OF SOME NEW TAXA FROM THE EARLY PROTEROZOIC OF CHINA
Type: Flat-Convex Stromatoli te Group: Svetliella Schapovalova (1968) Svetliella hebiancunensis f. nov. (see Figs. 3c, l l A , E and Fig. 13g). Material: Two specimens from the Hebiancun Format ion of the Hu tuo
Group, Wutai Range. Holotype: TD77010h. Name: After the Hebiancun Formation. Diagnosis; Svetliella with branching tubular and tussock fabrics. Description: The stromatolite occurs in domed bioherms 2--3 m long and 40--80 cm thick. Its basal part is characterized by a stratlform morphology with small wavy relief. Below the top few centimetres, the columns become columnar-layered, grade rapidly into developed columns, and then to dis- crete characteristic columns, ca. 20 cm thick. In the upper few centimetres of the columnar part, the columns start to coalesce and grow stratiform again.
Columns are subcylindrical, 1--2 cm in diameter and 5--10 cm in height. Branching is ~-, H-parallel, sometimes slightly divergent (Preiss, 1976) with one column branching into two or three daughter columns which usually have pointed ends. Lateral surface of columns is delicately ragged with peaks and bridges or locally smooth, where the wall structure appears. Laminae are convex with high inheritance.
The microstructure is r ibboned but uneven. Dark laminae (0.4--0.7 mm thick) consist predominantly of fine grained dolomite, and light laminae
387
(0.1--0.3 mm thick) consist of coarse-grained dolomite. The boundary be- tween dark and light laminae is undulate. There are few organisms remain- ing in both dark and light laminae. They form branching tubular fabric or tussock fabrics (Fig. l l E ) . Comparisons: Based on the columnar-layered type with convex and flat laminae, branching pattern, and developed peaks, bridges and coalescences, the stromatoli te described here is referred to as Svetliella Schapovalova. Because there are two types of fabrics in laminae and there is sometimes a wall on column margin, this stromatoli te differs from previously described forms of Svetliella. Age and distribution: Early Proterozoic: Hebiancun Formation, Hutuo Group, Wutai Range.
Type: Convex Stromatoli te Group: Discorsia Semikhatov (1978)
Discorsia wutaishanensis f. nov. (see Figs. 4d, l l B and 13f) Material: Three specimens from the Yaochi Formation of the Hutuo Group,
Wutai Range. Holotype: TD77028y. Name: After Wutai Range. Diagnosis: Discorsia with pointed projections and wrinkled laminae. Description: The stromatoli te consists of slender subcylindrical columns, 1--3.5 cm in diameter, 15--20 cm in height. Branching is ~-parallel or slight- ly divergent with one column branching into two or three daughter columns or pointed projections. However, the columns are not obviously widening before branching and constricted after branching. The interspace is small. Lateral surface is smooth where the wall is present and delicately ragged where the wall structure is not developed, bridges appear between columns and short peaks on the column margins. Laminae are usually deep- ly convex and even subconical. They are markedly wrinkled in polished sections.
Microstructure and fabric are obscure owing to secondary recrystallization. Comparisons: Some important features of this stromatoli te described here, such as shape of columns, branching pattern, discontinuous wall structure and pointed projections, make it identical to Discorsia Semikhatov. Its dif- ference from Discorsia discorsia Semikhatov is the wrinkled laminae and lack of typical niches. Age and distribution: Early Proterozoic; Yaochicun Formation, Hutuo Group, Wutai Range.
Group: Hutuoella gr. nov. Type form: HutuoeUa ministolona gr. et f. nov. Name: After the Hutuo Group. Content: H. ministolona (gr. et f. nov.) only.
Hutuoella ministolona f. nov. (see Figs. 4c, l l C and 13a) Material: Three specimens.
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, 2cm J . . . .
A 2cm B
1£m D
-'i"i " ".., ~. "~
N 50~m ,
2Cm ' E
Fig. 11. Recons t ruc t ions and drawings of s t romatol i tes : (A) $vetlieUa hebiancunensi~ f, nov. (Holo type , T D 7 7 0 1 0 h ) ; (B) Discorsia wutaishanensis :f. nov. (Holo type , TD77028y) ; (C) Hutuoella ministolona gr. et f. nov. (Holo type , T D 7 7 0 2 7 y ) ; (D) Kussiella planaf. nov. (TD77005h) ; (E) drawings show the tussock and branching tubular fabrics of Svetliella hebiancunensis f. nov. (in thin section).
389
Holotype: TD77027y. Name: After the presence of projections like buds on the column margin. Diagnosis: Nearly Straight, parallelly arranged, subcylindrical columns with typical a-parallel branching. On column margins there are numerous bumps and some small bud-like projections. Lateral surface of columns is generally smooth with discontinuous wall. Description: The stromatolite consists of nearly-straight subcylindrical columns, 0.5--3 cm in diameter, 30--40 cm in height. Columns are closely spaced and parallelly arranged. Branching is a-parallel with one column branching into two daughter columns with smaller diameter. On column margins there are numerous low bumps and few bud-like projections which start out in oblique or horizontal direction. Lateral surface of columns is generally smooth with discontinuous wall. However there are some peaks and bridges sometimes when the wall is interrupted. Laminae are generally convex, but sometimes flattened and rectangular.
The microstructure of columns is generally unevenly ribboned, but it con- sists of three kinds of laminae:
(1) light laminae, which are composed of pure, coarse-grained dolomite, generally 0.2--0.5 mm thick, but they may be replaced by discontinuous and irregular patches (0.4--0.8 thick, 0.6--1.5 wide);
(2) dark laminae, A, composed of impure fine-grained dolomite, 0.4--1.3 mm thick;
(3) dark laminae, B, composed of fine-grained dolomite rich in organic re- mains, 0.1--0.3 mm thick. The dark laminae A intergrade with the light laminae which they overlie, but the boundary of their upper part is sharp_ because of the presence of the dark laminae B. Comparisons: Some features of this stromatolite, such as shape of columns, branching pattern, existence of wall structure and the high degree of in- heritance are common with Boxonia Korolyuk and Collumnaefacta Korolyuk. However the discontinuous wall, especially the existence of the small projection-like buds on column margins, separate this stromatolite from Boxonia. The stromatolite is convex (columnar) type of stromatolite, but the Collumnaefacta was referred to as flat-convex (columnar-layered) type of stromatolite (Krylov and Perttunen, 1978). Thus, the difference between them is great. Age and distribution: Early Proterozoic; the Yaochi Formation of the Hutuo Group, Wutai Range.
Group: Kussiella Krylov (1963) Kussiella plana f. nov. (see Figs. 3b and 11D)
Material: Three specimens from the Wutai Range. Holotype: TD77005h. Name: After the shape of platy columns. Diagnosis: Kussiella with small platy columns. Description: The stromatolite, which occurs in small-domed bioherms
390
(1--2 m long, 0.3--0.6 m thick), consists of small platy columns, 0.3--1.5 cm in width, 1--5 cm long, 20--30 cm in height. Columns are closely spaced and parallel. Their cross sections are oblong. Branching is frequently a- to H-parallel (passive) with one column branching into two or three generally smaller daughter columns and do no t widen upwards, except some of them. Lateral surface of columns is uneven with rugged ornamentation (i.e. cornices). Bridges link several columns. Laminae are gently convex, some- times flattened. Inheritance of laminae is high. The microstructure of this stromatolite is commonly diffuse due to metamorphic effect and appears to be r ibboned where it remains. Comparisons: The shape of columns and the type of branching of this stromatolite make it resemble Kussiella Krylov, Microstylus Komar and Platella Korolyuk (or Scopulimorpha Liang). The size of this stromatolite is almost identical with Microstylus, and its platy columns are almost similar to Platella or Scopulimorpha. However, the uneven lateral surface with rugged ornamentat ion may separate this stromatolite from Microstylus and PlateUa or Scopulimorpha. Thus this stromatoli te must be referred to as Kussiella Krylov, and must be regarded as a new form on the basis of its small dimension and oblong plan outline. Age and distribution: Early Proterozoic; the Dashiling Formation of the Hutuo Group, Wutai Range.
Group: Mistassinia Hofmann (1978) Mistassinia niushanensis f. nov. (see Figs. 3b and 12A)
Material: Five specimens from the Niushan Formation of the Gantaohe Group, Taihang Range. Holotype: TD76005 Name: After the Niushan Formation. Diagnosis: A Mistassinia with slightly divergent branching and discontinuous wall structure. Description: The stromatoli te consists of slender, constr icted and discrete columns with a tuberculate surface, when present, branching is slightly divergent (or dendroid). The organization of column is commonly bipartite, i.e. an axial region and a peripheral portion. The axial region consists of convex laminae of moderate to high relief, more or less symmetrical. The peripheral port ion is composed of steeply-inclined laminae and encrusted generally on the axial portion. Some peaks and cornices on column margins may appear where the peripheral port ion is absent.
Both axial and peripheral laminae are even or slightly crinkled. The micro- structure may be both r ibboned and striated, but they are masked because of the metamorphism. Comparisons: Columns of this stromatoli te are characterized by a special organization in axial and peripheral portion, and a slender shape, therefore the stromatoli te described here must be referred ~o as Mistassinia Hofmann. However its slightly divergent branching, discontinuous wall structure and
391
2era C A
Fig.12. Reconstructions and drawing of stromatoli tes: (A)Mistassinia niushanensis f. nov. (Holotype, TD76005); (B) longitudinal section of Jacutophyton microstylum f. nov. (Holotype, TD77002b); (C)Paraboxonia connexa gr. et f. nov. (Holotype, TD77034y).
existence of two kinds of microstructure differentiated it from M. wabassinon Hofmann. Age and distribution: Early Proterozoic; the Niushan Formation of the Gantaohe Group, Taihang Range.
Group: Paraboxonia gr. nov. Type form: Paraboxonia connexa gr. et f. nov. Content: P. connexa only.
Paraboxonia connexa f. nov. (see Figs. 6f, 12C and 13b) Material: Three specimens. Holotype: TD77034y. Name: After column connect ion by massive bridge. Descriptions: The stromatolite, which occurs in tabular biostromes, consists of almost straight, branching and walled subcylindrical columns (2--8 cm in diameter, 25--40 cm in height). When present, branching is predominantly a- parallel and occasionally/3-parallel with one column branching into two daughter columns. Lateral surface is generally smooth, straight or wavy, with enveloping laminae forming a multiple wall. However, there are mas- sive bridges, several millimetres to 2 cm thick, between columns. Laminae of parent columns are generally rectangular, but laminae of daughter columns are predominantly convex. All laminae commonly show a rhythmic outline in polished section.
Microstructure is r ibboned, dark laminae are 1.4--1.7 mm thick with even
392
Fig. 13. Photographs i l lustrat ing the micros t ruc tures of the early Pro te rozoic s t romato l i tes ; ( a ) H u t u o e l l a rninistolona (gr. et f. nov.); ( b ) P a r a b o x o n i a connexa (gr. et f. nov.); (c, e) Collumnaefacta sp.; (d) Jacutophyton microstylum (f. nov.}; (f) Discorsi~ wutaishanensis (f. nov.); (g)Svet l ie l la hebiancunensis (f. nov.); (h) Zhongtiaoshania hamagouensis (gr. et f. nov.), Scale bars: 0,5 cm.
393
upper boundary and wavy lower boundary; light laminae are thicker than dark laminae, 2--3 mm thick. Fabric is no t clear. Comparisons: Some features of this stromatolite, such as shape of columns, type of branching, existence of wall structure generally, are common with Boxonia Korolyuk and Min]aria Krylov. Min]aria is dominated by/3-parallel branching and lacks massive bridges. Although Boxonia is characterized by a-parallel branching, it lacks massive bridges and has special microstructure. Thus this stromatoli te described here differs from either Minjaria, Boxonia or other groups described previously. Age and distribution: Early Proterozoic; the Yaochi Formation, Hutuo Group, Wutai Range.
Group: Zhongtiaoshania gr. nov. Type form: Zhongtiaoshania hamagouensis gr. et f. nov. Name: After the Zhongtiao Range. Content: Z. hamagouensis only.
Zhongtiaoshania hamagouensis f. nov. (see Figs: 3e and 13h) Material: Five specimens. Holo type: TD 72249z. Name: After Hamagou valley in Zhongtiao Range, where the type form was found. Diagnosis: The stromatolite consists of long, nearly straight, parallel un- walled, subcylindrical columns with very small interspaces and parabolic laminae. Branching is a-parallel, column margin is generally smooth, with oc- casional bridges. Description: The stromatolite occurs in a tabular biostrome, 2--3 m thick, several km long. It is composed of regularly subcylindrical columns 6--20 cm in diameter and more than 100 cm in height. Cross-section of columns is circular or ovate, branching is a-parallel (passive) with one column branching into two daughter columns of similar diameter. Some columns can coalesce at the upper part. Lateral surface of column is general- ly smooth, but unwalled. Interspaces are very small, 1--3 mm wide, and separated by siliceous carbonate. Laminae are usually parabolic, sometimes subconical or strongly convex. Inheritance of laminae is high.
Microstructure is obscured by secondary recrystallization, but can occa- sionally exhibit r ibboned features. Comparisons: Some features of this stromatolite, such as shape of columns, type of branching, lack of wall structure and high degree of inheritance are similar to Kussiella Krylov and Jurusania Krylov. However they differ by its parabolic laminae and the lack of cornices and mantle. Age and distribution: Early Proterozoic; the Yujiashan Formation of the Zhongtiao Group, Zhongtiao Range.
Type: Convex-Conical Stromatolite. Group: Jacu tophy ton Schapovalova (1968)
Jacutophyton microstylum f. nov. (see Figs. 5c, 12B and 13d).
394
Material: Three specimens from Wutai Range. Holotype: TD77002b. Name: With respect to the numerous very small columns starting out from a conical stromatolite. Diagnosis: A Jacutophyton with unwalled and radially-arranged columns of small size. Description: The stromatolite consists of a basic column and numerous daughter columns. The basic column composed of conical laminae with a crestal angle of 45--55 ° and a linear crestal zone is subcylindrical (2--4 cm in diameter and 10--15 cm in height). Column margin is ragged and devel- ops peaks and rhythmic bridges. The daughter columns are radially arranged on upper part of a basic column and are composed of convex laminae. They are unwalled and of small size (0.3--0.5 cm in diameter and 1--2 cm in height). Their margins are slightly ragged with short peaks.
Microstructure is of striated type. Dark laminae (0.1--0.2 mm thick) con- sist of impure and fine grained carbonate. Light laminae (0.05--0.15 mm thick) are composed of pure carbonate. Comparisons: The stromatolite consist of a basic column with conical laminae and a crestal zone and numerous daughter columns with convex laminae. Thus this stromatolite may undoubtedly be referred to as Jacutophyton Schapovalova. However the shape and size of daughter columns differentiate it from other forms previously described. Age and distribution: Early Proterozoic; the Beidaxing Formation of the Hutuo Group, Wutai Range.
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