The Sinian microfossils from Jinning, Yunnan, south west China

Precambrian Research, 23 (1983) 133--175 Elsevmr Science Publishers B.V., Amsterdam -- Printed in The Netherlands

THE SINIAN MICROFOSSILS WEST CHINA

FROM JINNING, YUNNAN,

133

SOUTH

WANG FUXING, ZHANG XUANYANG and GUO RUIHUAN

Chengdu Institute of Geology and Mineral Resources, Chengdu City 610081, Sichuan (People's Republic of China) (Received November 13, 1981 ; revision accepted June 7, 1983)

ABSTRACT

Wang, F., Zhang, X. and Guo, R., 1983. The Sinian microfossils from Jinning, Yunnan, south west China. Precambnan Res., 23. 133--175. A microfossil assemblage has been detected in phosphorite cherts from the Dengying and Meishucun Formations (610Ma) of the Sinian System in Jinning County, Yunnan Province, southwest China. A unique type (mode) of microfossii preservation - - collophanite or apatite, or even in rare cases, chert-replacement -- is reported here for the first time. The size frequency statistics for the assemblage are consistent with the results obtained by Schopf. The assemblage includes 18 genera and 20 species, among which 4 genera and 10 species are new. The assemblage consists of solitary and colonial spheroidal cells and septate or non-septate filaments, mainly Cyanophyta, especially Chroococaceae, Oscillatonaceae and Nostocaceae The mmrofosslls described are Bigeminococcus grandis n. sp., Myxocoecozdes kmg~, Myxococcoides grandis, Palaeoanacystis vulgaris, Arehaeophycus venustus n.g. et s p , Eomycetops~s robusta, Czrculinema lmningense n.g. et sp., Czrculinema muirae n.g. et s p , Cyanonema inflmtum, Obruchevella parva, Oscdlatoriopszs awramikii n. sp., Palaeolyngbya oehlerd n. sp., Palaeolyngbya spiralis n. sp., Palaeotubulus lamellosus n.g. et sp., Veteronostocale sp. 1, Veteronostocale sp. 2, Allantomorphus septatus n.g et s p , Clonophycus vacus n. s p , Archaeotrichion contortum, Rhicnonema ant~quum, Micrhystridium setulerum and Protosphaeridium densum.

INTRODUCTION During the last two decades, many well-preserved microfossil assemblages h a v e b e e n f o u n d in P r e c a m b r i a n c h e r t s . T h i s p a p e r p r e s e n t s a f i n d in t h e S i n i a n S y s t e m ( l a t e P r o t e r o z o i c - - e a r l y P h a n e r o z o i c ) in s o u t h w e s t C h i n a ( Y u n n a n P r o v i n c e , see F i g . 1), w h i c h is r a t h e r i n t e r e s t i n g d u e t o t h e u n i q u e type of fossil preservahon. T h e f o s s i l i f e r o u s c h e r t s a m p l e s w e r e c o l l e c t e d in D e c e m b e r 1 9 7 9 , a n d during 1981, from the Wangjiawan and Meishucun areas of Jinning County, Y u n n a n P r o v i n c e ( F i g . 1). A l l t h e m i c r o f o s s i l s a m p l e s w e r e s t u d i e d u s i n g

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Fig. 1 M a p show,ng the two fossll locahtms m J m n m g County, Y u n n a n Province, south west Chlna. The fossiliferous samples collected from the Wangjiawan and Me,shucun areas are marked by 'X'.

Ampliva and Universal NU2 optical biomicroscopes, and several samples were studied using SEM and an electron mmroprobe. STRATIGRAPHY

The Siman System is the oldest Phanerozolc (or youngest Proterozoic) sequence occurring widely throughout the whole of China, especially in southern China. In Yunnan Provmce it is divided, from b o t t o m to top, into the Doushantuo, Dengying and Meishucun Formations (Wang and Zhai, 1983). It usually overhes the Upper Proterozoic Nantuo Formation or unconformably overhes Jinning Stage (ca. 800Ma) magmatic rocks, and commonly grades upwards into the overlying trilobite bearing sediments of early Cambrian age (Jiang, 1980). Due to its bearing on the Precambrian-Cambrian transition, the two sections of the Siman System have been studied in detail both blostratlgraphically and sedimentologically, with rece~tly published comprehensive summaries by Cao et al. (1980), Jiang {1980) and Wang (1980). The Dengying Formation consists mainly of thick dolomite with abundant stratiform stromatolites and oncohtes m the middle of the formation and lenses or laminae of chert m its upper part. There is a phosphorus-rich bed (the Xlaowaitoushan member) in the uppermost part of the formation, 10 m or more below the top (Fig. 2)

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The Meishucun Formation consists mainly of phosphoritic siltstone, d o l o m i t e and chert laminae. There are abundant small, shelly fossils in the Meishucun Formation as well as in the uppermost part o f the Dengying Formation, suggesting a Cambrian or Eocambrian age to some workers (e.g., Fig. 2, Jiang, 1 9 8 0 ) . A dark carbonaceous slate bed in the upper part of the Meishucun Formation in the Wangjiawan area yielded an age of 6 0 3 + 3 1 M a (Rb--Sr whole-rock m e t h o d ) and the same horizon from the Meishucun area has a Rb--Sr whole-rock age of 6 1 2 -+ 36 Ma (Cao et al., 1980}. The chert microfossil samples are mainly from two horizons, one from the middle part of the Dengying Formation ~ 100 m or more from the top, and another from the lower part of the Meishucun Formation ~ 5 m above the base (see Fig. 2).

PRESERVATION

Almost all of the Precambrian microfossil assemblages reported so far are preserved mainly in a non-lithified form, that is, they are structurally

136 and orgamcally preserved mlcrofossils (SOM). Recently, some p y n t l z e d bacterial fossils have been discovered (Oehler J.H., 1977) and some researchers have noted siliclfmd mmrofossils (Horodyski and Donaldson, 1980; Ym, 1981). The two different types of preservation are observed m the Jmning assemblage, and the mineralized microfossils (fossil in its literal meaning) are so structurally well-preserved that a special term for this preservation seems to be in order. Hence we shall use the term structurally minerahzed microfossils (SMM). The SOM in the Jinning assemblage are mainly from the WangJiawan area, whereas the SMM are exclusively from the Meishucun area. It appears that the different types of preservation are connected with different hthologles, which suggests different sedimentary and diagenetic conditions. In the Wangjiawan area, sample W7965 (Fig. 2) occurs as in thin bands (a few cm thick) of lenses m dolomite. In thin section, the cherts axe generally amber m colour due to disseminated orgamc matter, the different densltles of which give rise to a detectable lamination. Usually the cherts are obviously recrystallized with radiating chalcedony fans occurring here and there. Only in brown remnant chert patches, which survived this recrystallizatmn, can the SOM be found, with low fidehty of structural preservation. Here, minute (0.1 × 0.2 pro) organic particles dot a rather obscure outhne of the supposed microfossils. Sometimes, minute black pyrite particles can be seen growing into these cellular structures (Fig. 3: 17, 18). On the other hand, the W79861 and W79875 fossiliferous cherts occur as stable black beds, 10--20 cm thick, interbedded with phosphorite. In thin section, the cherts are usually light brown with some irregular orgamc-rich patches of dark brown. On the whole, the cherts are very weakly recrystallized. The SOM occur mainly in the hght areas and the fidelity of preservation is usually high with a continuous or roughly continuous outline of the Fig. 3. Thin sections of fossil structures from the Dengying Formation (15--18), the Meishucun Formation in the Wantqiawan area (1--3, 5, 7--14 and 19) and the Meishucun area (4, 6 and 20), photomicrographed in transmitted light using an optical microscope. The linear scale bar represents 10pro. Those without the scale-bar have the same magnificahon as no. 8. The name of taxon is given, followed by the thin section number and ordinal numbers, respectively, for the fossils illustrated. (1--2)Protosphaeridium densum Tim.; W79875B, W79875B49--50. (3) Fossil identity sp. 4; W79875A. W79875A55. (4) Reticulate spheroid sp. 1; K7943A, K7943A51. (5) Large dark spheroid sp. 3; W79875B, W79875B53. (6) Palaeoanacystls vulgar~s Schopf; K7943B, K7943B38. (7--9) Myxococcoides kingi~ Muir, W79875A, W79875A39--41. (10--13) Myxococcoides grandis Horodyski et Donaldson; W79875A, W79875A42--45. (14)Micrhystridium setulerum Wang et Luo, W79875A, W79875A48. (15--16) Spheroidal cell-like units with a long 'flaggellate', W79651A, W79651A47 and 57 (17--18) Clonophycus vacus n. sp., W79651A; 17, W79651A46, (18) type specimen, W79651A56. (19) Large spheroidal cell-like unit with a star-shape folded structure, dark portion (fold) is a lobe with a hollow in the centre part of the star form; identity fossil sp. 2;W79875B, W79875B52. (20) Palaeotubulus lamellosus n.g. et sp. ; K7943B, K7943B07.

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138 microfossils being clearly seen (Fig. 3: 1, 2, 7--14) under a microscope. The mode of preservation is qmte similar to that described for the Bitter Springs microflora (Schopf, 1968; Schopf and Blacic, 1971). In contrast, in the Meishucun area samples K7942 and K7943 of fossfllferous cherts occur as irregular patches embedded in phosphonte. The phosphorite, constituting the economically significant deposits in the Yunnan Province, is made up of collophanite granules of ~ 1--2ram in diameter cemented by dolomite or silica (chalcedony). Sometimes the granules have a margin of apatite and occasionally silica-replaced granules can be seen with the primary collophanite being remnant or missing (Fig. 4: 6, 7). The irregular chert patches, a few to tens of cm in size, are made of chalcedony particles a few microns in diameter with disseminated collophanite (or recrystallized apatite) particles (tens of microns in size). The mmrofossils are preserved mostly in the silica patches, and, rarely, m the silica cements of the phosphorite (Fig. 4: 4, 5). As seen from the photomicrographs, the structural preservation of the microfossils is so intact that their biological affinity is beyond any doubt. Yet, with rare exceptions (Fig. 3: 4), both filaments and coccoids are no longer organically preserved. On the contrary, they are partly (Fig. 5: 6, 12, 14 and 15; Fig. 6: 10, 11) or, as is the usual case, wholly made up of apatite, sometimes with remnant coUophanite (Fig. 4; Fig. 6: 3), i.e., they axe SMM (identification of the phosphorus minerals is based on polarized microscopic and electron microprobe study). The partly replaced microfossils of both filaments and coccoids are witness to the process of fossilization, confirming the biological ongm of these SMM. It is evident that the SMM are directly connected with collophanite deposits (we have detected some more SMM in phosphorite-bearing rocks in Sichuan and Guizhou Provinces). The collophanite replacement of the microorganisms must have taken place very early, perhaps at the very beginning of the diagenetic process, or even contemporaneous with collophanite deposition, so that diagenesis did little harm to the structural Fig. 4. Transmitted light photograph~ of microfoseils in thin section of a chert from the Meishucun Formation in the Meishucun area. The scale-bar represents 10/~m unless indicated otherwise. (1) Microfossils are well preserved in the light coloured chert laminae and almost absent in the dark phosphorus siltstone. The irregular boundary between the two laminae is also shown. (2) An enlarged photograph of the area in (1), indicated by the arrow, showing the irregular contact of the light and dark laminae. (3) Collophanite spherulite. (4) The silica cement of phosphorus siltstone, showing a rare case of well-preserved filamentous microfossils in the cement, b, c and d are three increasingly enlarged photomicrographs of the ares in a, indicated by the arrow, containing microfossils. (5) Phosphorus siltstone, showing another case of well-preserved filaments in the silica cement, b shows a fan-like form of chalcedony in the area of a, indmated by the arrow. The arrow in c shows a filament, the enlarged photomicrograph of which is shown in d. Both are a portion of a (at the arrow). (6--7) Figures showing the remnant grains of phosphorus siltstone replaced by silica

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preservation. Then followed, still at an early dlagenetlc stage, the wellknown silica-permineralization. Perhaps, the process is the phosphorus blomlneralization of Lowenstam and Margulis which took place geologically earlier than the calcic biomineralization of the late Proterozoic--early Phanerozoic (Lowenstam and Margulis, 1980).

S E M and E L E C T R O N

MICROPROBE

STUDIES

Several chert chips from samples K7942 and K7943, containing SMM, were studied under the SEM. A few specimens were found and photographed showing the morphological structures and some detailed textures of the described microfossils. Some questionable microstructures were found that can, in many cases, be morphologically compared to the microfossils previously described. The bmlogical origin of the photographed microstructures is based on their mutual relationship, both in shape and size range, with analogues (microfossils) observed in thin section from cherts of the same samples or in previously described microfossils. The results of some SEM studies are similar to those of Konzalova (1981).

Fig. 5. Photomicrographs of fossils in thin sections of the Meishucun Formation in the Meishucun area, in transmitted light using an optical microscope. The linear scale-bar represents 10/~m, magnification of figures without a scale-bar is identical to 3 or 13. F o r further explanation see Fig. 3. (1--4) ObrueheveUa parva Reitlinger; K7943B, K7943B35--36 and 58--59. (5) Veteronostocale sp. 1; K7943A, K7943A13. (6) CJrculinema finningense n.g. et sp.; type specimen, K7942A, K7942A09. (7) Circulinema muirae n.g. et sp.; K7942A, K7942A10. (8) OsciUatoriopsis sp. 3; K7942A, K7942A01. (9) Oscillatoriopsis sp. 2; K7943B, K7943B02. (10) Archaeophyeus venustus n.g. et sp.; type specimen, K7943A, K7943A20. (11) Spheroidal structures that may be formed by replacement of apatite in cell-like units. ( 1 2 ) C y a n o n e m a infliatum Oehler; K7943B, K7943B12; b is an enlargement of a. (13) Eomycetopsis robusta Schopf, emend. Knoll and Golubic; K7943B, K7943B08. (14) Oscillatoriopsis sp. 1; K7943A, K7943A04. (15) Palaeolyngbya sp. 1; K7942A, K7942A03. Fig. 6. Photomicrographs of fossils in thin section of the Meishucun Formations in the Wangiawan (4, 6 and 7) and the Meishucun areas, in transmitted light using an optical microscope. The linear scale-bar represents 10/~m, magnification of the figures without a scale-bar is identical to 1 F o r further explanation see Fig. 3 (1)Archaeophycus venustus n.g. et sp.; K7943A, K7943A29. (2)Palaeoanacystis vulguris Schopf; K7943A, K7943A60. (3) Eomycetopsis robusta Sehopf, emend. Knoll and Golubic; K7943A, K7943A14. (4) Unnamed sheath-like f'flamentous structures; W79875B, W79875B26. (5 and 9) Palaeotubulus iameIlosus n.g. et sp., larger magnification of part of 20 in Fig. 3. (6--7) Eomycetopsis robusta Schopf, emend. Knoll and Golubic; W79875B, W79875B31--32. (8) Obruchevella parva Reitlinger; K7943A, K7943A37. (10--11) Palaeolyngbya oehlerii n. sp. ; K7943A, K7943A27--28; (10) type specimen; b is a larger magnification of a. (12) Eomycetopsis robusta Schopf, emend. Knoll and Golubic, K7943A, K7943A05. (13--14) Oscillatoriopsis awramik~z n. sp.; K7943A, K7943A30 and 06, (14) type specimen.

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144 Filamentous microstructures in Fig. 7 : 1 show filaments similar to Eomycetopsis robusta Schopf, emend. Knoll and Golubic which can be compared to those in Fig. 5: 13, 4 - - 5 # m in diameter, and those in Fig. 7 : 2 show ones similar to filaments in Fig. 8: 10, whmh are e m p t y sheath-like microstructures 20/~m in diameter (unnamed). Fig. 7 : 3 represents an example similar to the microfossils of Allantomorphus septatus n.g. et sp. which shows th e sausage-hke nature and double sheath characteristic, 4 - - 6 # m in diameter. Fig. 7 : 4 may be a cross section of a filamentous microfossil. Fig. 7 : 5 - - 6 represent smaller ( 4 - - 5 p m in diameter) spheroidal microstructures similar to Palaeoanacystis vulgaris Schopf (Fig. 6: 2). Fig. 7: 5 shows the mineralized cell-wall with granular surface texture. All the p h o tos shown in Fig. 9 represent several mmrostructures whmh are of questionable biological origin, however t h e y are m some respects similar to some of the microfossils described previously. Fig. 9 : 1 may be an e m p t y , wider filamentous form, representing sheath structure ~ 20 pm in diameter. Fig. 9 : 2 is a microstructure which has not been observed in thin section under the optical microscope. The spheroidal structure is 25 #m in diameter, with a granular surface t ext ure and is o r n a m e n t e d with several larger holes in its surface. The holes are 4 ~m or m ore in diameter, and the f o r m is similar to the acritarch Trematosphaeridium Tlmofeev (Timofeev, 1959), although there is no good evidence to assign the form to this t a x o n or any other. Fig. 9 : 3 shows numerous, irregularly grouped, small spheroidal cell-like microstructures f o rm ed in a nearly circular colony, w i t h o u t a c o m m o n m e m br a ne or sheath. In general m orphol ogy, colonial habit and size range, the specimens can be com pared to Palaeoanacystis vulgaris Schopf (Fig. 3: 6). Both are 4--5 pm in diameter, t hough the too uneven dimensions and shape of the forms d~scussed indicate a non-biogenetic origin. Fig. 9 : 4 may represent a col ony composed of numerous small cell-like mmrostructures within a c o m m o n envelope. The cell-like forms are spheroidal, t h e y have a granular surface t e x t u r e (which m ay have been caused by mineralization) and are 4--5/~m in diameter. The col ony is 4 0 - - 5 0 p m in diameter. It is possible t hat the microstructures represent Fig. 8. Thin sections of fossil structures from the Meishucun Formation in the Meishucun (1--3 and 9--11) and Wangjiawan (4--8) areas. The scale-bar represents 1 0 # m except where indicated otherwise, magnification of the figures without a scale-bar is the same as 5 1--8 and 10--11 are photomicrographs in transmitted light using an optical microscope, and 9 by electron microprobe. (1) Palaeotubulus iomeUosus n.g. et sp.; type specimen, K8140A, K8140A02; b, c and d are three enlarged figures of a, with different magnification. (2) Obruchevella sp.; K8140A, K8140A01; b is an enlargement of a. (3) Archaeophycus venustus n.g. et sp.; K7943A, K7943A61. (4--8)Archaeotrichion contortum Schopf; W79878A, W79878A01--02 (9) Backscattering electron and X-ray (P) complex image of the filament shown in 10 (unnamed foul'l). (10) Unnamed mineral~zed filamentous microfouil (SMM) used in the electron microprobe study to determine components of the filament (see 9). (11) Archaeophycus venustus n,g, et sp.; samples used for electron microprobe study, as in 9 and with the same result.

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DISCUSSION OF PALAEONTOLOGY The mmrofosslls of the Jinnmg assemblage are abundant and well preserved; 18 genera and 20 species and several unnamed microfossils have been detected and preliminary descriptions are given here. The assemblage contains solitary and colonial spheroides and filaments which are sheathed or non-sheathed, and septate or non-septate. Most of the forms are assigned to prokaryotic cyanophyta, although there are other forms assigned to eukaryotic green or red algae, bacterial filaments, as well as acritarchs. No name is given to a few peculiar forms whose affinity is unclear. The filamentous Circulinema n.g. and Palaeotubulus n.g. are assigned to Oscillatoriaceae of C y a n o p h y t a on the basis that they are simple, unbranched, umsenate, multicellular, basically unconstricted at septae and sheathed or non-sheathed, with disc-like or short column-like cells. The genus Allantomorphus n.g. is tentatively assigned to Nostocaceae of C y a n o p h y t a because they are composed of chained ellipsoldal cells, almost of the same size and form, and they apparently occur as unbranched filaments. The dark amorphous body or residue in each internal cell is consldered to be degraded cytoplasm. The spheroidal Archaeophycus n.g. is assigned to Chroococaceae of C y a n o p h y t a in terms of its general morphology and size range, as well as the paired cells and planar tetrads. However, it is also assigned to eukaryotic green algae by Lm on the basis of its mode of cell division, size range and being non-sheathed (Zhu and Liu, 1982). The filaments with regular barrel-like cells (as shown in Fig. 5: 12), which might be considered as eukaryotic by some researchers (Lm, 1982), are tentatively assigned here to cyanophytic Cyanonema infliatum Oehler (Oehler, 1977). Although the new type of filament, Palaeotubulus lamellosus n.g. et sp., is assigned to C y a n o p h y t a on the basis of morphology and size range, the internal structure (as shown in Figs. 10 and 11, and Fig. 6 : 5 and 9 consists

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o f a ' d o u b l e cell wall' a n d t w o kinds of lntracellular d e g r a d a t i o n (one as an irregular ring and one as dark granular residue in the cell), w h i c h indicates a s t r u c t u r e m u c h m o r e c o m p l e x t h a n t h o s e o f c o m m o n degraded prok a r y o t i c m i c r o o r g a n i s m s described previously.

CONCLUSION D e n g y i n g ' s microfosslls, such as C l o n o p h y c u s vacus n. sp., are larger t h a n m o s t o f the c y a n o p h y t i c algae. The m e a n size range o f D e n g y i n g ' s microfossils is c o n s i s t e n t with the d a t a o b t a i n e d b y S c h o p f and Oehler ( S c h o p f and Oehler, 1 9 7 6 ; S c h o p f , 1 9 7 7 ) f r o m s y s t e m a t i c analysis o f P r e c a m b r i a n s t r o m a t o l i t o l c spheroidal cells. T h e microfossils in the Meishucun F o r m a t x o n , especially the f i l a m e n t o u s f o r m s f r o m the M e l s h u c u n area, are very diverse, and t h e y are larger t h a n the previously described pre-Melshucun or pre-Siman P r e c a m b r i a n microfossils (Fig. 12). This is also c o n s i s t e n t with S c h o p f ' s d a t a ( S c h o p f , 1977). The J i n n i n g assemblage is interesting in t h a t : (1) The p h o s p h o r u s mineralized microfosslls (SMM) are described here

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SYSTEMATIC PALAEONTOLOGY

Algae Division C y a n o p h y t a Class Cyanophyceae Order Chroococcales Family Chroococcaceae Genus Bigeminococcus Schopf and Blacic, 1971

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Fig. 13. Optical photomicrographs of B~geminococcus grandzs n. sp. from cherts of the lower Meishucun Formation in the Meishucun area, Jinning County, Yunnan Province. Sample K8140b, fossil number K8140B01, (1) is the holotype Scale-bar equals 10 , m from the lower part of Meishucun Formation, Meishucun area, Jinning, Yunnan. Description. Cells are spheroidal or partially spheroidal, flattened by mutual compression when packed in a cluster; cells in pairs, triads and tetrads are surrounded by a thick lamellate or single envelope, whereas solitary cells do not have a distract envelope. Cells axe 1 5 - - 2 4 # m m diameter, averaging 2 0 . 1 7 p m (N = 18 from 5 cluster); clusters range from 35 to 5 0 p m In diameter, with an average of 4 1 . 6 p m (N-- 5). The cell surface t e x t u r e is psllate, and the envelope is regular and of equal thmkness in a single cluster, ranging from 2--6 pm in thickness for the 5 clusters measured; several to tens of clusters loosely aggregate together. Etymology. In latin, grandis = large, with reference to large dimension o f the cells. Comparison. In general m or phol ogy, especially the nature of t he enveloped cluster, the described microfosslls can be compared and assigned to Bzgeminococcus Schopf and Blaclc (1971). However, as many Precambrian mmropalaeontologlsts have noted, Bigemmococcus and Eozygion S c h o p f and Blacic (1971) may only represent the different growth stages of one kind of mmroorganism (Schopf and Blacic, 1971). In the microfossils

151 studied, forms similar to Bigeminococcus and others similar to Eozygion with two cells were seen. We use the name Bigeminococcus here to represent the various kinds of cells (solitary, pairs, triads and tetrads). Genus Myxococcozdes Barghoorn, 1969

Schopf

(1968)

emend.

Schopf

and

Myxococcoides kingii Muir, 1976 (Fig. 3: 7--9) Description. Cell umts are spheroidal to ellipsoidal, occasionally distorted because of mutual compression, c o m m o n l y grouped, and even colonized. Cells are psilate or slightly granular in surface texture, with the cell o u t h n e being defmed by granular organic microparticles. The cell wall is thin (0.8 um in thickness) and only occurs occasionally, as an obscure trace or encrusted by mmropyritic particles near the internal side of the organic wall which gives the appearance of a thick wall. Individual cells are not enveloped by sheaths, t h e y are c o m m o n l y grouped in irregular colonies of few to a few tens of cells and embedded in an organic matrix. The cells range in size from 2 to 6.3/zm in diameter, but are c o m m o n l y 2--5/~m (Fig. 14), with an average of 4.10 #m (N = 26). 15 N =26

~ ~o "6 E i 0

2

4

ii--I 6

i 8

i

i 10

Diameter of c e l l s ( # m )

Fig. 1 4 . H i s t o g r a m o f t h e d i a m e t e r o f

Myxococcoides kmgii.

Comparison. The microfossfls described here are very similar to those of Myxococcozdes kingii Muir (1976) in morphology and size range except that the average cell size is smaller. The specimens are also morphologically similar to Myxococcoides staphylidion Lo (1980) and are distinguished from the latter by the size range. Furthermore, the described specimen is similar to Palaeoanacystis vulgaris Schopf (1968) and is distinguished from the latter by its smaller size, lesser number of grouped cells, lower cell density and less distinct cells, sometimes the cells contain internal dark bodies (Fig. 3: 7) and are less c o m m o n in pairs and planar tetrad form. Occurrence. Lower part of the Meishucun Formation, Wangiawan area, Jinning County, Yunnan.

152

N=33

lC u

E 2 4 Diameter

6 ol

8 10 cells (#m)

12

Fig. 15 Histogram of the diameter of Myxococcozdesgrandis.

Myxococcozdes grand~s Horodysk, et Donaldson, 1980 (Fig. 3: 10--13) Descnptzon. Cells are spheroidal, ranging from 3.5 to 1 2 # m m diameter, commonly 3.5--5 and 8--10/~m (see Fig. 15), with an average of 6 . 8 3 # m (N = 33). Cells are solitary, without ornament and the cell outline only is defmed by brown orgamc microparticles; the cell walls are 0.2--0.5~zm in thickness. Comparison. In general morphology and size range, the specimens described here are very similar to the specimens of Myxococcozdes grandis Horodyski et Donaldson (1980), especially to those fossils shown m Fig. 7-G, H, J, K--N of their paper {Horodyskl and Donaldson, 1980). However, although the average diameter of the specimens is consistent with the latter, the size range of the specimens described here is smaller (3--32 pro). Discussion. The size range of this specms is very wide, 3--32 pm. Horodyskl and Donaldson (1980) noted that in some specimens " t h e rare occurrence of small spheroidal mlcrostructures preserved within Myxococcotdes grandis suggests that M. grandis might represent the preserved outer sheath of a colonial coccoid cyanophyte whose cells typmally were totally degraded prior to fossilization." However, in our opinion, some of them are similar to Huroniospora Barghoorn (1965). The specimens described here can probably be divided into two groups based on size range, larger (8--12 #m in diameter) and smaller (3.5--5 #m in diameter). The smaller spheroides without mternal structures may represent the Huroniospora microreticulata (Awramik and Barghoorn, 1977), and the larger ones Myxococcoides grandzs. Occurrence. Lower part of the Meishucun Format,on, Wangjiawan area Jinning County, Yunnan. Genus Palaeoanacystis Schopf, 1968

Palaeoanacystls vulgaris Schopf, 1968 (Figs. 3 : 6 and 6: 2) Description. Cells are spheroidal to ellipsoidal, occasionally becoming polyhedral and angular through distortion due to mutual compression; cells are solitary or m pairs and are c o m m o n l y m clusters, or in colomes composed of a few or tens or even hundreds of cells. The specimen illus-

153 40

35

N=e,2

3r3

25

u2C "5

10

i

i

J

4

i

[

6

i

i

t

8

i

10

Dlometer of cells ( # m )

Fig. 16. Histogram of the diameter of Palaeoanacystis vulgaris. trated in Fig. 3: 6a and b shows a spheroidal colony 1 0 0 # m in diameter. Cells are psilate or slightly granular in surface texture, 2--7 #m in diameter (commonly 3--6 ~m, Fig. 16) with an average of 4.74 #m (N = 82). The cell wall is dense and distinct (0.5--1 u m in thickness), sheaths of individual cells are absent, and the colony is embedded in an organic matrix. Comparison. The assignment is based on evidence of their distinct cells, hab]t of colonization,nature of cell division and size range. Discussion. The microfossils are abundant in the cherts studmd from the Meishucun Formation m the Meishucun area. Although they are completely mineralized, their biological origin can be determined from their appearance, general morphology, habit of paired cells, colonial form, etc. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jmning County, Yunnan. Genus Archaeophycus Gen. nov.

Type species: Archaeophycus venustus n.g. et sp. Diagnosis. Cell-like units are spheroidal, hemispheroidal after division, polyhedral, angular or irregular due to mutual compression. They occur singularly, in pairs of two hemispheroidal cells, as fan-shape cells forming planar tetrads and they are c o m m o n l y grouped in colonies composed of a few to tens of cells. Sheaths and organic matrix are absent for individual

154 cells and colonies; t h e outline of cells is very distinct, the cell wall is dense, with psllate or slightly granular surface t e x t u r e ; occasionally some cells c o n t a i n smaller degraded internal bodies. Etymology With r e f e r e n c e to the algal n a t u r e of the microfossils and its o c c u r r e n c e in ancient Sinian sediments, G r e e k , archaios = ancient, p h y k o s = algae. Comparison. In general m o r p h o l o g y this genus is similar to Eoentophysalis H o f m a n n {1976), b u t it has no distinct internal bodies and has no sheath or organic m a t r i x for either individual or colonial spheroidal cells. In addition, we have n o t observed distinct algal mats e n c r u s t e d b y the microfossils. T h e genus is also similar t o Sphaerophycus S c h o p f ( 1 9 6 8 ) and is distinguished f r o m the latter b y its larger size and absence o f sheaths. T h e genus is similar to Bigemmococcus and Eozygion, b u t again the latter t w o have sheaths. T h e genus is distinguished f r o m the Palaeoanacystis vulgaris described here b y its larger dimension, cells in pairs and in planar tetrads, and its h a b i t o f f o r m i n g colonies c o m p o s e d o f o n l y a few cells.

Archaeophycus venustus n.g. et sp. {Figs. 5: 10, 6. 1 and 8: 3) Type specimen. T h e fossils in Fig. 5 : 1 0 are assigned to t y p e specimen, fossil n u m b e r K 7 9 4 3 A 2 0 , discovered in c h e r t o f the Meishucun F o r m a t i o n , Melshucun area, J i n n m g C o u n t y , Yunnan. Description. General m o r p h o l o g y as a generic diagnosis. Cell units desc n b e d here range f r o m 7 to 22 # m in d i a m e t e r (Fig. 17), t h e y are c o m m o n l y 1 1 - - 1 6 # m , with an average o f 1 4 . 2 9 # m ( N = 17). Cells f o r m in pairs and planar t e t r a d s {cluster) 1 6 - - 2 2 # m in d i a m e t e r . As s h o w n in Fig. 6 : 1 t h e r e are several internal dark bodies in some spheroides t h a t m i g h t r e p r e s e n t d e g r a d e d internal cell s t r u c t u r e , cell wall, c y t o p l a s m or nuclei (?).

I

N=17

~s 0 ~ 0

I

I 2

I

DLameter

I 4

I

I 6

~

of c e l l s

I 15

I 10

I 12

I ] 14

L 16

I

~ 18

I 20

22

(#m)

Fig. 17. Histogram of the diameter of Archaeophycus venustus.

Discussion. S o m e specimens o f this t a x a possess one to several nucleilike internal dark bodies. T h e y axe r a t h e r large, b u t n o o t h e r evidence has been observed t o assign t h e m to an e u k a r y o t i c organism. Etymology. With r e f e r e n c e to its b e a u t i f u l appearance, Greek, venustus = beautiful. Occurrence. L o w e r p a r t o f the Meishucun F o r m a t i o n f r o m the Melshucun area, Jinning C o u n t y , Y u n n a n .

155 Order Nostocales Family Oscillatoriaceae Genus Eomycetopsis Schopf, 1968

Eomycetopsis robusta Schopf (1968) emend. Knoll et Golubic, 1979 Description. Filaments are non-branched and non-septate; straight, sinuous or curved; solitary or aggregated in groups, and, rarely, entwined; psilate to reticulate surface texture. The diameter of an individual filament is constant along its long axis (0.1--11.1/am), they are c o m m o n l y 2--8/am and may exceed 100/am in length. Cross sections of filaments are rounded or ellipsoidal. Dzscussion. The microfossil occurs In the Melshucun Formation of the two areas studied and hence shows the two different types of preservation. The specimens from the Wangjiawan area are defined by brown organic microparticles, with psilate or slightly granular surface texture, 1.0--5/am wide (Fig. 19), with an average of 3.47/am (N = 25). The specimens from the Meishucun area occur in two forms with the two types of preservation: (1) filaments of non-septate tubular structures, with reticulate surface texture, 1--6/am in width (Fig. 20) with an average of 3.63 um (N = 32); (2) SMM filaments of psilate non-septate tubular structures, 2.6--11.1/am in width (Fig. 21), with an average of 5.40/am (N = 89). Schopf (1968) previously considered these filaments to be fungi-like or algal organisms, but lately some Precambrian micropalaeontologists have noted that the so-called 'septa' in one of Schopf's specimens represents some folds on the filament surface. Hofmann (1976) believes that this genus can be well compared to the iron-bacterium Leptothrix ochracea Kutzing or some sheath of Phormidium.like oscillatoriacean cyanophytes. Based on TEM studies of the specimen in Schopf's collection, Oehler (1973) noted that these filamentous structures are of cell-wall nature, therefore, the filaments are cell fossils and not sheaths. E. siberiensis and M. amplyomitus are considered by Lo (1980) to be two specimens of one taxa, one bemg a trichome and the other its sheath structure. Knoll and Golubic (1979), in an amended description of the taxa, noted that although the two species E. robusta and E. filiformis are distinguished by the difference in their size range, there is, in fact, no difference in size range between the two studied specimens (Knoll and Golubic, 1979). The following size ranges, at the given locality, have been found for the non-septate tubular e m p t y filamentous structures, Eomycetopsis: Bitter Springs, 2--4.5/am; Belcher, 1.0--3.7 /am; Amelia, 2.4--8.0/am; Yudom, 1.6--7.8/am; and here 1.0--11.5/am. It is evident t h a t the size range of the genus gradually increases as the number of discoveries increases. In this study, in some non-branched, non-septate filaments there are several examples of filaments which may have a partly smooth surface texture and partly reticulate surface texture (Fig. 6: 12). Furthermore,

156 30

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Fig. 19. Histogram of the width of Eomycetopsis robusta in cherts of the Meishucun Formation, Wangjiawan area. Fig. 20. Histogram of the width of Eomycetopszs robusta whmh occur as reticulate non-septate tubular forms in the Meishucun Formation of the Meishucun area. Fig. 21. Histogram of the width of SMM Eomycetopsis robusta which occur as psllate non-septate tubular forms in the Meiahucun Formation of the Meishucun area.

in one long smooth non-septate filament, we can see part of a well preserved portion possessing distmct internal cell-like units occurring along the filamentous structures (Fig. 6 : 5 and 9, which are enlarged mlcrographs of the non-septate filaments •ustrated in Fig. 3: 20). It is qmte probable that the present non-septate, non-branched tubular filaments may represent Fig. 18. Fossils m thin section from the Meishucun Formation, Wangjlawan (2--3) and Meishucun areas, photomicrographed in transmitted light using an optical biomicroscope. The linear scale-bars each represent 10/~m, magnification of figures without a scale-bar is indicated by the scale-bar in 8b. See Fig. 3 for further explanation. (1) Spheroidal structure, consisting of collophanite in the centre and apatite at the periphery, may be the result of recrystallization. (2) A larger, dark spheroidal cell-like unit with a dark central part, fossil, sp. 3, W79861A, W79861A54. (3) Unnamed larger cell-like unit; W79861A, W79861A25. (4--5) Circulinema muirae n.g. et sp., K7943B; (4) K7943B33; (5) type specimen, K7943B34. (6--8) Allantomorphus septatus n.g. et sp., K7943B, K7943B16--18; (8) type specimen; h, c and d are enlargements of a. (9) Palaeolyngbya sp. 2; K7943B, K7943B19; h is a larger magnification of a. (10) Unnamed tubular, nonseptate filament, fossil sp. 7; K7943B, K 7 9 4 3 B l l . (11) Unnamed shrinkage filament with barrel-shaped cells indicating strong degradation; K7943B, K7943B21. (12) Eomycetopsis robusta Schopf, emend. Knoll et Golubic, K7943B, K7943B22. (13) Spheroidal cell-like unit may be preserved after replacement of phosphorus mineral, the light coloured periphery is composed of apatite and the dark centre is organic matter, K7943B, K7943B23.

lz

8

159

Circuhnema muirae n.g. et sp. {Figs. 4: 7; 1 8 : 4 and 5) Type speczmen. The fossil in Fig. 1 8 : 5 is assigned as the t y p e specimen, fossil number K7943B34, discovered in the lower part of the Meishucun Formation in the Meishucun area, Jinning County, Yunnan. Description. General morphology as a generm diagnosis. The five specimens described here are non-septate, well-preserved specimens, 19--20, 20, 19--20, 19--20 and 2 3 # m wide, their coiled ring-like structures are 140, 73, 116, 80 and 95 #m in diameter, respectively. Comparison. It can be distmgnished from C. ]inningense n.g. et sp. by the non-septate habit of the specms. _r*.ymology. After Dr. M.D. Muir, B.M.R., Austraha. Discussion. The species may represent the empty sheaths of C. jinningense n.g. et sp. Occurrence. Same as C. finningense n.g. et sp. Genus Cyanonema Schopf, 1968

Cyanonema mfhatum Oehler, 1977 (Fig. 5: 12a and b) Description. Trichomes are non-branched, uniseriate, multicellular, not constricted at septa, solitary, and sheaths are absent. They are straight to curved and c o m m o n l y break into segments at septa. Cells are short, columnlike to barrel-like, 3.0--4.0 /lm wide (N = 6 cells of one trichome) and 3.5--4/am, rarely 5/am, long. Remarks. Only a few well-preserved specimens have been observed in the sedlments studmd. The assignment is based on its distinct appearance and size range. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinning C o u n t y , Yunnan. Genus Obruchevella Reitlinger, 1948

Obruchevella parva Reitlinger, 1959 (Figs. 5: 1--4; 6: 8) Description. Spiral tube-like filaments, loosely coil around an open-centre. The cross section of the tube is round, 7--9/~m in diameter, with an average of 7.78/~m (N = 8). The coiled structure is 32--45 #m in diameter, with an average of 36.63 pm (N = 8). Filaments axe non-septate, psilate or slightly granular in surface texture. The long axis of the ring-like structures are straight or slightly bent. Discussion. The specimens are very similar in general morphology and size range, except for its larger coiled ring-like structure (the diameter of the helix of Cloud et al's specimens is only 19--38/~m), to specimens of this species described by Cloud et al. (1979) from the Arabian Shield. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinning County, Yunnan.

160

Obruchevella sp. (Fig. 8: 2a and b) Description. A tubular, very loosely coiled, ring-hke, unbranched, nonseptate filament, with no cell structures and a surface texture whmh is psllate to slightly granular. The tube is 25 pm and the coil is 1 7 0 # m m diameter, and the distance between two rings of the coil is ~ 160 #m. Discusszon. The size range of the fossil is similar to that found by Cloud et al. (1979) in the lower Cambrian sediments of Alaska (U.S.A.) of 14--43 and 37--252#m diameter for the tubes and coils, respectively. However, it is distinguished from the latter by its very loosely coiled habit. Judging from the illustration (Cloud et al., 1979, fig. 4--4), the distance between two adjacent rings of the coils in Cloud's specimens is only ~ 80 pm. Clo~. 's specimens have a left spiral (rotatmn) and the specimens described here are right spiral. No specms can be identified due to the scarcity of specimens. Occurrence. Lower part of the Meishucun Formatmn m the Melshucun area, Jinning County, Yunnan. Genus Oscillator~opsis Schopf, 1968

Oscillatoriopsls awramikii n. sp. (Fig. 6 : 1 3 and 14) Type specimen. The fossil m Fig. 6 : 1 4 is assigned as the type specimen, fossil number K7943A06, discovered m the lower part of the Meishucun Formation in the Melshucun area, Jinnmg County, Yunnan. Description. Filaments axe uniseriate, non-branched, multmellular, septate and not constricted at septa, but they are c o m m o n l y broken into segments. The filaments rapidly terminate at the end, they are shghtly bent into a 'reversed S' form, with a psilate surface texture, and mdistmct transparent thin sheaths keep close contact with the trichomes xf present. Filaments are 2.6 /~m wide (N = 2), the maximum length observed is ~ 70/~m; cells are rectangular or square in longitudinal section, 2.6 /~m wide and 2.6--3.0 #m in length. In Fig. 6 : 1 4 a larger cell presents part of the filament near the apical. It is elhpsoidal, 3--4 pm in length, and is perhaps a heterocyst; the apical cell is 'bullet' shaped. Etymology. After Dr. S.M. Awramik, Umverslty of California, Santa Barbara (U.S.A.). Comparison. The fossil is very similar m general morphology and size range to Oscillatoriopsis Schopf (1968) but Is distinguished from them by larger cells, the presence of a thin transparent sheath in some parts of the specimens and the 'bullet'-like tip of the specimen described. Occurrence. Lower part of the Meishucun Formation in the Melshucun area, Jinning County, Yunnan.

Oscillatoriopsis sp. 1 (Fig. 5: 14) Description. Only two non-branched, uniseriate, multiceUular septate filaments have been observed, and these are not constricted at septa. Filaments are slightly bent and solitary, with indistinct thin sheaths and granular

161 surface texture. They are 16--18 #m in diameter (N = 2). The cells are disc-like, but indistinct, with the apical cell absent, and they are very poorly preserved. Discussion. The specimens are larger than most of the previously described Precambrian members of this genus. No special identification or assignment can be made due to the poor quality of preservation. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinning County Yunnan.

Oscillatoriopsis sp. 2 (Fig. 5: 9) ~escription. The strongly mineralized filaments axe broad, non-branched, uniseriate, multicellular septate, slightly or strongly constricted at septa, not embedded in sheaths and display a zig-zagged margin. They occur as solitary, straight or slightly bent filaments with a psilate or slightly granular surface texture, and are 40--43/am wide. Medial cells of the filaments are disc-hke and ~ 8/am in length. The apical cell is hemispherical and only 28/am wide. Discussion. In general morphology, the specimens described here axe very similar to the Palaeolyngbya Schopf (1968) from the Bitter Springs assemblage (Palaeolyngbya barghoorniana Schopf, 1968), except for the absence of sheaths and zig-zagging margins. The specimen described in Fig. 5 : 9 is a segment of a filament and seems to be hormogone-like b o d y , tapering at both ends. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinning County, Yunnan.

Oscillatorzopsis sp. 3 (Fig. 5: 8) Description. Filaments are non-branched, uniseriate, multicellular septate and are not, or slightly, constricted at septa, with psilate or slightly granular surface texture. Some incomplete cross-walls partly divide the cells and sheaths are absent. They are 16--17/am in diameter and the length of a segment of the filament, perhaps a hormogone (see Fig. 5: 8), exceeds 54/am. Medial cells of the filaments are disc-like, 16--17/am wide and 3 - - 4 # m in length. The apical cell is hemispherical or blunt 'bullet'-like and only 14/am in diameter. Discussion. In general morphology the specimens are very similar to the hormogone-like b o d y of Palaeolyngbya barghoorniana from the Bitter Springs assemblage (Schopf, 1968), b u t they are distinguished by the absence of a thick sheath. Although only two hormogone-like specimens have been observed, their specific general morphology and larger size suggest a completely different assignment, if further finds justify it. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinmng County, Yunnan.

162

G e n u s Palaeolyngbya S c h o p f , 1968

Palaeolyngbya oehlerii n. sp. {Fig. 6 : 1 0 and 11) Type spectmen. T h e fossil m Fig. 6 : 1 0 is t h e t y p e specimen, fossil n u m b e r K 7 9 4 3 A 2 7 , discovered in the l o w e r part o f t h e Meishucun F o r m a t i o n in the Meishucun area, J i n n m g C o u n t y , Yunnan. Descriptmn. Filaments are u n b r a n c h e d , u n m e n a t e , multicellular septate and slightly c o n s t r i c t e d at septa, with a think, distinct sheath of ~ 1--2/am m thickness. Filaments are solitary, sinuous or curved, and slightly ornam e n t e d b y a fine granular surface t e x t u r e . T h e y axe 6--7/am m diameter. T h e cells axe short, c o l u m n a r m shape, 4--5/am wide and 4--6/am l o . T h e y are c o m p o s e d o f o r g a m c m a t t e r and are dark m colour, with a r o u n d t r a n s p a r e n t internal area in t h e c e n t r e o f the cell ~ 2 - - 2 . 5 / a m in d i a m e t e r . T h e apical p o r t i o n o f t h e filaments are p o o r l y preserved. Etymology. After Dr. J.H. Oehler, C o n t i n e n t a l Oil C o m p a n y , U.S.A. D~scussion. Based on the t h i c k sheath o f the n o n - b r a n c h e d , multicellular septate specimens and m the absence of any o c c u r r e n c e o f e u k a r y o t i c evidence, the specimens are assigned t o the genus Palaeolyngbya S c h o p f ( 1 9 6 8 ) and given a new n a m e Palaeolyngbya oehlerii n. sp. T h e sheath is thinker t h a n the sheath o f m o s t o t h e r m e m b e r s o f the Palaeolyngbya S c h o p f previously described. T h e smaller d i a m e t e r and specific general a p p e a r a n c e o f the cells are also I m p o r t a n t a r g u m e n t s for establishing t h e new t a x o n . Occurrence. L o w e r part o f the Meishucun F o r m a t i o n m the Melshucun area, J i n n m g C o u n t y , Y u n n a n .

Palaeolyngbya spiral~s n. sp. (Fig. 22. 1--3, 7 and 9) Type specimen. Figure 2 2 : 2 is the h o l o t y p e , fossil n u m b e r K 8 1 4 0 B 0 2 , f r o m the lower p a r t o f the Memhucun F o r m a t i o n in the Memhucun area, J i n n m g C o u n t y , Yunnan. Description. Filaments are n o n - b r a n c h e d , umserlal and septate, with thick sheaths, and are c o m p o s e d o f degraded multmellular cells which are m o s t l y dissolved. Several coiled filaments have b e e n discovered. T n c h o m e s are indistinct and c o m p o s e cells,which o c c u r o n l y m some segments, t h a t appear m the f o r m o f s h o r t columns. Cells are ~ 7--8/am wide (in degraded f o r m ) and 6 - - 1 0 / a m long. Apmal cells were n o t observed. T h e filaments are 17.5-25/am wide with a sheath ~ 7/am or less. T h e filaments are coiled m t o sptral Fig. 22. Optical photomicrographs of fossils in thin sections o f chert from the lower part of the Meishucun Formation in the Meishucun area, Jmning County, Yunnan. The scale-bar equals 10/~m. (1--3, 7 and 9) Palaeolyngbya spzralis n. sp , (1) K8140C, K8140C09, others from K8140B; (2) type specimen, K8140B02, (9) K8140B03; (3 and 7) are larger magnifications of 2 (4--6) Veteronostocale sp 2; K8140C, K8140C01; (5) is the same specimen as 4, photographed using a different focal depth; (6) is a larger magnification of 4. (8) cf Rhicnonema antiquum. K8140C, K8140C02

163

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6

164

bodies, 80--170/~m in diameter, and the distance between each coil (rotation 360 °) is ~ 10 #m, some are loosely and some are closely spaced. Etymology. With reference to the spiral habit of the taxon which have not been previously reported m Precambrian sediments, Latin, spirahs = spiral. Comparison. Although the specimens of the taxon are very similar to Obruchevella Reitlinger in their habit of coiling, they are distinguished from the latter by their trichome, cells and thick sheath which are consistent with a diagnosis of Palaeolyngbya Schopf. The microstructures (microfossils) can be compared to the recent algae, Lyngbya contarta Lemmermann, in its coiled form and to Lyngbya majuscula Harv. in its size range (see "Photographs of Algae" by Department of Biology, Nanjing University, p. 74; and Hu et al., 1980). Occurrence Lower part of the Meishucun Formation In the Meishucun area, Jinnmg County, Yunnan.

Palaeolyngbya sp. 1 (fig. 5: 15) Description. The filament is non-branched, uniserlate, multmellular septate, and is not constricted at septa. It has a thick sheath (distinct and transparent) ~ 3 - - 4 p m in thickness, and occurs singularly, slightly bent and sometimes broken into smaller segments, with a granular or psllate surface texture. The filament is 2 6 - - 2 8 # m wide, and the length of the incomplete specimen studied exceeds 1 6 0 p m . Medial cells of the trichome are disc-like, 2 2 - - 2 4 # m wide and 4 - - 5 # m long, with a length/width ratio of 1/5 and the apical cell absent. Discussion. In general morphology, especially the disc-like form of the medial cells of the trichome and the distinct thick sheatb, the specimen can be compared to members of the genus Palaeolyngbya Schopf. It is larger than most of the previously described members of this taxon. However, no further identification can be made due to the poor preservation and scarcity of specimens. Occurrence. Lower part of the Meishucun Formation m the Meishucun area, Jinning County, Yunnan.

Palaeolyngbya sp. 2 (Figs. 18: 9; 23) Descriptmn. The tubular filament is non-branched, with very indistinct septate, and a very thick transparent sheath (see Fig. 23) which is partly presented in the terminal part of the hlament. The filament is solitary, slightly bent, with psilate to very slightly granular surface texture. It is 16--28 um in diameter, with an average o f - 2 2 . 3 microns (N = 9). The sheath in the specimen illustrated in Fig. 1 8 : 9 is 3 - - 4 p m thick (rarely 7--8/~m). Although the cell units of the filament are obscure, some incomplete cross-walls indicate the septate habit of the filament. The apex of the filament is rounded in shape. Dlscusston. The specimens of this taxon c o m m o n l y occur as short segments

165

5

5e

se

t

Fig 23. Drawing of the fossil Palaeolyngbya sp. 2 illustrated in Fig 18: 9b. s = sheath, t = trichome, se = incomplete cross walls.

w h i c h are only a few tens o f m i c r o n s in length, and this m a y indicate t h a t t h e d e s c r i b e d t a x o n was very brittle. T h e r e is s o m e d o u b t regarding the e s t a b l i s h m e n t o f the t a x o n : the socalled ' s h e a t h ' m a y o n l y r e p r e s e n t an inorganic residue if t h e filaments are n o n - s e p t a t e (as a sheath). Occurrence. L o w e r part o f t h e M e i s h u c u n F o r m a t i o n in t h e Meishucun area, Jinning C o u n t y , Y u n n a n . G e n u s Palaeotubulus n.g.

Type species. Palaeotubulus lamellosus n.g. et sp. Diagnosis. F i l a m e n t s are u n b r a n c h e d , uniseriate, multicellular septate, and are n o t c o n s t r i c t e d at septa. T h e y t e r m i n a t e rapidly, are generally p o i n t e d like a 'bullet', and t h e filaments are sinuous or curved and c o m m o n l y ent w i n e d (see Fig. 3: 20). In some p o r t i o n s o f the filaments t h e r e are thick, lamellated and t r a n s p a r e n t sheaths, w i t h a psilate or slightly granular surface t e x t u r e . Cells are c o m m o n l y a b s e n t or indistinct, b u t occasionally s o m e cell units can be observed in the filaments. Medial cells o f the filaments are s h o r t c o l u m n t o barrel shaped, rarely spheroidal, and c o m m o n l y with a ' d o u b l e ' cell wall (see Figs. 6 : 5 and 9; 1 0 ; 11 and 8: 1 ) . T h e cells c o n t a i n a few internal small dark b o d i e s and a r o u n d e d ring-like s t r u c t u r e w h m h m a y r e p r e s e n t t h e residue o f d e g r a d e d cell wall or c y t o p l a s m , respectively. Several larger cells m a y r e p r e s e n t h e t e r o c y s t s (see Fig. 6 : 5 and 9 ) . Etymology. With r e f e r e n c e t o t h e simple f i l a m e n t o u s a p p e a r a n c e o f t h e t u b u l a r filaments d e s c r i b e d and its o c c u r r e n c e in a n c i e n t P r e c a m b r i a n sedim e n t s , G r e e k , palaios = ancient, t u b u l u s = t u b e .

166

D~scusston. Specimens of this genus are abundant m the cherts of the Melshucun F o r m a t i o n in the Melshucun area. The specimens occur as sunple, psilate 'earth worm'-like structures c o m m o n l y w i t hout cells. Without these cell units t h e y are very similar to Eomycetopsis robusta.

Palaeotubulus lamellosus n.g. et sp. (Figs. 3: 20; 6" 5 and 9, 8: 1, 10 and 11)

Type specimen. T he fossil in Fig. 8 : 1

is assigned as the t y p e specimen, fossil n u m b e r K8140A02, discovered in the lower part of the Meishucun F o r m a t i o n in th e Meishucun area, Jinning County, Yunnan. Description. General m o r p h o l o g y as a generic diagnosis. The specimens are generally 3 - - 5 p m in diameter, rarely exceeding 6 p m (Fig. 24). The sheath of the filaments may be lamellated and 1 - - 1 . 5 p m in thickness. Medial cells of the filaments are c o m m o n l y column shaped with a rectangular, or occasionally spheroidal and irregular spheroidal, longitudinal section 3 - - 4 p m wide and 4 - - 6 # m long. Occasionally t h e y are more than 5--6 ~m wide, and have an average of 4.6 #m (N = 17). The cell wall is 0 . 5 - - 1 p m think. Several larger cells, 7 - - 1 0 p m long and 4--6 #m wide are observed in some specimens (Fig. 6 : 5 and 9). These cells may be heterocysts. Medial cells of the filaments contain some condensed masses ~ 3-4 # m in diameter, and small dark bodies ~ l p m m diameter. When the sheath is n o t lamellated, a lamellated structure occurs m the cell wall (see Figs. 10 and 11), indmating that the cell m ay have a double wall structure (?) or may be surrounded by an individual sheath. Etymology. With reference to the lamellated habit of the filament sheaths, Latin, lamellosus = lamellated. Occurrence Lower part of the Melshucun Form at i on m the Melshucun area, Jinnmg County, Yunnan. 15

N =17

2 E 2_ 10

"6

2 Width

4 6 8 of f i l a m e n t s ( p r o

)

Fig. 24. Histogram of the w i d t h of the Palaeotubulus lamellosus. Family Nostocaceae Genus Veteronostocale Schopf et Blacic, 1971 Diagnosis. The trichome is non-branched, unisenate, multmellular septate, and strongly constricted at septa. It is composed of spheroidal or slightly

167

ellipsoldal cells of relatively uniform size and equidimensional shape, and sheaths are apparently absent. The trichome is solitary, straight to curved. Medial cells of the trichome each contain a dark internal body. Veteronostocale sp. 1 (Fig. 5: 5) Description. The trichome is non-branched, multicellular, and curved into a rounded form, with a granular surface texture. Sheaths are absent and several cells occur intermittently along the filamentous 'trace'. Cells are elhpsoidal, 4 - - 5 # m wide and 4 . 5 - 6 . 5 p m long containing a dark internal spheroidal b o d y , 1.7--3.2 #m in diameter. Discussion. The fossil is distinguished b y its larger cells from Veteronostocale amoenum Schopf et Blacic {1971}, which is only 2 . 0 - - 3 . 5 p m in diameter. However, it is not certain whether the filamentous 'trace' represents a trichome, 2 - - 3 p m wide, or whether the 4 - - 5 p m wide cells represent the trichome. If the second possibility can be demonstrated, then the trichome is similar to Veteronostocale amoenum. Alternatively, the first possibility suggests the presence of heterocysts of the trichome. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinning County, Yunnan.

cf. Veteronostocale sp. 2 (Fig. 22: 4--6) Description. A narrow trichome with uniseriate degraded cells, non-branched, and indistinctly septate because of degradation. Cells appear as spheroidal or ellipsoidal forms with dark internal residues. The filament is coiled into a spring-like form, and sheaths are absent. Cells are 4--5 #m wide and 5-6 pm long (post-degradation measurement). The filament coil is 20--21/am in diameter. Discussion. In general cell morphology the microfossil is similar to Veteronostocale Schopf et Blacic (1971), b u t the coiled habit of the trichome is absent in the diagnosis or description of the taxon given by Schopf and Blacm (1971). The cell size-range of the described Jmning's fossil is only slightly larger than that given for the Bitter Springs' specimens (1.8--2.6 mmrons by 2.0--3.5 pm). In addition, the coiled habit and diameter of the coil (20--21 um) of the fossil is similar to Anabaemdium Schopf (1968), with a coil diameter of 20 #m. However, the latter's cells are column to barrel shaped, whereas the Jinning's microfossil is composed of spheroidal and ellipsoidal (after degradation) cells. The microfossil is rare and poorly preserved and, therefore, is tentatively assigned to cf. Veteronostocale. In addition, the fossil is distinguished from Obruchevella Reitlinger which coiled to spring-like form, too, by its cell occurrence that is absent in the latter (Cloud et al., 1979) and from Palaeolyngbya spiralis n. sp. by its absence of a thick sheath, smaller size and cell form. The taxon can be compared to recent algae in morphology and in coiled form, as the Anabaena spiroides Kleb. (Hu et al., 1980).

168 Genus Allantomorphus n.g.

Type species. Allantomorphus septatus n.g. et sp. Diagnosis. T h e filaments are n o n - b r a n c h e d , uniseriate, multicellular septate, and a p p a r e n t l y constructed at septa t o f o r m sausage-like filaments. T h e y are c o m m o n l y sinuous and e n t w i n e d in groups o f a few to tens o f filam e n t s , with t h m and indistinct sheaths ( m a y be lamellated), and psilate t o slightly granular surface t e x t u r e . T h e cross section o f t h e f i l a m e n t is irregularly r o u n d e d (Fig. 18: 7). Medial cells o f t h e filaments are ellipsoidal (see Figs. 18: 8b--d; and 25), and the apical cell is r o u n d and sometimes enlarged as a ' h e a d ' (see Fig. 18: 6). Etymology. With r e f e r e n c e to its sausage-like appearance, Greek, allantos = sausage, m o r p h e = m o r p h o l o g y . Comparison. In general m o r p h o l o g y , especially t h e sausage-hke a p p e a r a n c e o f the new t a x o n , it is distinguished f r o m all previously described Precambrian microfossils. T h e ellipsoidal cells o f t h e filaments are d i f f e r e n t f r o m the r o u n d cells o f previously described m e m b e r s o f Nostocaceae. T h e general m o r p h o l o g y o f t h e new t a x o n is indicated m Fig 7 : 3 b y SEM photomicrograph.

V¢

Fig. 25. Drawing of the fossil Allantomorphus septatus, tllustrated m Fig. 18: 8. s = sheath, w = cell wall, c = cells.

Allantomorphus septatus n.g. et sp. (Figs. 18: 6--8; 7: 3; and 25) Type specimen. T h e fossil in Fig. 1 8 : 8 is assigned as the t y p e specimen, fossil n u m b e r K 7 9 4 3 B 1 7 , discovered in t h e Meishucun F o r m a t i o n m the Meishucun area, J m n i n g C o u n t y , Yunnan. Description. General m o r p h o l o g y as a generm diagnosis. T h e specimens o f the t a x o n range f r o m 4 to 1 2 p m in d i a m e t e r (Fig. 26), c o m m o n l y 5-8 ~m, with an average o f 7.76 u m ( N = 30). Medial cells o f the filaments are 7 - - 1 2 p m in length and t h e sheath is ( 1/~m m thickness. Discussion. T h e specimens o f the t a x o n are a b u n d a n t m the studmd chert o f the Meishucun F o r m a t i o n in t h e Meishucun area, a l t h o u g h m o s t o f t h e specimens are strongly degraded or mineralized. Based o n the specific

169 15 N =30 E 1C o

L_ 5

E 0

I

I

I

i

2 4 Width

I

I

I

I

6 8 of f i l a m e n t s

I

I

I

I

10 12 (#m)

Fig. 26. Histogram of the width of Allantomorphus septatus.

septate nature, apparent cell structures, distinct sheath and general morphology of the solitary and grouped forms, their biological origin is convincing, as is the establishment of a new taxon. Etymology. With reference to its septate nature. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinning County, Yunnan. Division Cyanophyta, Chlorophyta or R h o d o p h y t a Class Cyanophyceae, Chlorophyceae or R h o d o p h y c e a e Genus Clonophycus Oehler (1977) emend. Oehler, 1978

Clonophycus vacus n. sp. (Fig. 3 : 1 7 and 18) Type specimen. The fossil in Fig. 3 : 1 8 (upper) is assigned as the type specimen, fossil number W79651A47, discovered in the middle m e m b e r of the Dengying Formation in the Wangjiawan area, Jinning County, Yunnan. Description. Cell-like units are spheroidal, often polygonal or ellipsoidal due to mutual compression, and c o m m o n l y grouped in grape-shaped colonies composed of a few, tens, or up to a hundred cell-like units. The cell-like units have a slightly granular surface texture and range from 5 to 29 #m in diameter, c o m m o n l y 8 - - 2 2 # m (Fig. 27), with an average of 1 6 . 4 3 # m (N = 171 cells from 5 colonies). Organic microparticles outline the celllike units which sometimes appear to have a c o m m o n wall structure between adjacent cell-like units (see Fig. 3: 17), and occasionally the cell-like units contain internal irregular dark bodies. Etymology. With reference to the e m p t y appearance of the cell-like units when compared to most members of the Clonophycus Oehler (1977), Latin, vacus = empty. Discussion. According to Oehler (1977), the Clonophycus are cells which are "densely packed within a thin walled, smoothly textured, spheroidal, sack-like structure". The larger colonial habit and suggestion of the cells occurring in larger cell-like units indicate that these units might represent the 'sack-like' structure of the Clonophycus. The described fossil is similar to Clonophycus sp. Oehler, 1978 (Oehler, 1978, Figs. 4A--F and 5B--C) and is distinguished from the latter by its

170 20

N = 171

10

O

I

I 2

l

I 4

I 10 Diameter

12

14

16

18

20

22

24

26

28

30

Of cells ( # m )

Fig. 27. Histogram of the diameter of Clonophycus vacus. larger size range ( 1 6 . 4 3 p m compared with 10.6pm), c o m m o n colonial habit and apparent absence of internal cells. It is tentatively assigned as a new member of Clonophycus. Occurrence. The middle member of the Dengylng Formation m the Wangjiawan area, Jinning County, Yunnan. Bac te r~a

Division Schlzomycophyta Class Schizomycetes Order Eubacteriales (?) Genus Archaeotrichion Schopf, 1968 Archaeotrichion c o n t o r t u m Schopf, 1968 (Fig. 8: 4--8) Description. The trichomes are narrow, non-branched, non-septate, and more or less constant in diameter, c o m m o n l y < 0.5 #m or < 1/~m, along the long axis. They are composed of dark brown organic matter, of solitary occurrence, sinuous or curved, but sometimes loosely entwined in groups, and they are c o m m o n l y broken mto short segments tens of microns long. Discussion. In their general morphology the described specimens are assigned to Archaeotrichion cont or t um Schopf (1968), though the specimens described here are smaller in diameter than the type specimen from Bitter Springs (0.5--0.66 pm in diameter) and Belcher's specimens (1.3--1.6 pm). Occurrence. Lower part of the Meishucun Formation in the Wangjiawan area, Jinning County, Yunnan.

Genus R h i c n o n e m a Hofmann, 1976 cf. Rhzcnonema antiquum Hofmann, 1976 (Fig. 22: 8) Description. The filaments are curved, in pairs or loosely grouped. Darkbrown degraded cells of trichome axe found in the thick light-coloured,

171

tubular sheath. The apical part of the trichome was not observed. Medial cells of the trichome are indistinct and ~ 1.5--1.8#m in width (post degradation measurement), and the filaments are ~ 3.5--4.0 pm wide. Discusszon. In general size and morphology, the microfossils described here are similar to Rh~cnonema antiquum Hofmann (1976) except that the helical habit of the trichomes is absent. The size range of the described Jmning's samples is slightly larger than the t y p e species ( 0 . 3 - - 1 . 5 # m in diameter). Although the cell morphology of the specimens described is indistinct, due to degradation, it can be tentatively assigned to cf. Rhic-

nonema antiquum. Occurrence. Lower part of the Meishucun Formation in the Meishucun area, Jinning County, Yunnan.

Acritarcha Genus Micrhystridium Deflandre (1937) emend. Downie et Sarjeant, 1963

Micrhystridium setulerum Wang et Luo (Fig. 3: 14) Description. The cell-like units have distinct radially arranged setaceous spine structures, are spheroidal, sohtary, w i t h o u t sheaths, with a psilate or granular surface texture. They are 6.5--7.0•m in diameter without spines, with an average of 6.9 # m (N = 4). The spine is composed of brown organic microparticles, is ~ 0 . 5 p m in diameter and 2 . 5 - - 5 . 0 p m in length and its base is apparently connected to the spheroidal cell-like unit with a round cross section. Discussion. Some of the spheroidal cell-like units with spines discovered in the Sinian sediments are flattened fossil-envelopes ~ 20 #m in diameter. They are assigned to Micrhystridium Deflandre (1937) emend. Downie et Sarjeant (1963) and distinguished from another Sinian spinaceous acritarch, Baltisphaeridium, which has a flattened envelope more than 2 0 # m diameter in size range (Wang et al., 1983). Occurrence. Lower part of the Meishucun Formation in the Wangjiawan area, Jinning County, Yunnan. Genus Protosphaeridium Timofeev, 1966

Protosphaeridium densum Timofeev, 1966 (Fig. 3 : 1 and 2) Description. The envelopes are slightly compressed, brown in colour, rounded or irregularly rounded in shape, the walls are thick and dense. The envelopes are 4--6.3 # m in diameter. Some portions of the envelopes are irregularly thickened, perhaps due to degradation, and the opaque thicker parts of the envelopes c o m m o n l y occur within a margin ~ 0.5--1 um wide. Comparison. The specimens studied are similar in general morphology, psilate surface texture (Timofeev, 1966) and stoutness of envelope, to Protosphaeridium densum Tlmofeev, 1966.

172

Occurrence. Lower part of the Meishucun Form at i on in the Wangjlawan area, Jlnning County, Yunnan.

INDETERMINATE FOSSILS Species 1 (Fig. 3: 4) This is a reticulate spheroidal microstructure, 1 9 p m in diameter and is similar in m o r p h o l o g y to Myxococcoides grandzs (Horodyskl and Donaldson, 1980, fig. 3-H) from the Dismal Lakes of Canada, but is distinguished from the latter by its larger size. It is evident t hat the reticulate appearance is caused by degradation. The specimen was discovered m the lower part o f the Meishucun For m at i on m the Meishucun area, Jinnmg County, Yunnan. Species 2 (Fig. 3: 19) The cell-like unit is spheroidal, with the cell o u t h n e defined by brown orgamc matter, It has a psllate or shghtly granular surface texture, and is 23--26 p m in diameter. The cell-like unit apparently possesses a star-like open 'lobe' that may be caused by a break of the cell-like wall and subsequent folding, or it m a y be an original structure. The specimen was discovered in the lower part of the Meishucun F o r m a t i o n in the Wangjmwan area, Jinning County, Yunnan. Species 3 (Figs. 3 : 5 and 18: 2) These cell-hke units are opaque, have a r o u n d e d microstructure, are thinker in the centre, l l - - 1 5 / a m in diameter, and have a granular surface texture. The specimens were discovered in the lower part of the Meishucun F o r m a t i o n and in the Xiaowaitoushan m e m b e r of the Dengying F o r m a t i o n in the Wangjiawan area, Jmning County, Yunnan. Species 4 (Fig. 3: 3) The cells are spheroidal or slightly ellipsoldal and are grouped in crosstetrad with dark margins to the connecting walls between adjacent cells. The cells have a granular surface t e x t u r e and exceed 9 # m m diameter, while a cross-tetrad cluster is 1 5 p m in diameter. In general organization, the tetrad cluster may represent the eukaryotic nature of the specimens studied. Th e specimens were discovered in the lower part of the Meishucun F o n n a t m n in the Wangjiawan area, Jinning County, Yunnan.

173 Specms 5 (Fig. 3 : 1 5 and 16) The cell-hke units are spheroidal with a large and long tubular flagellate structure. Organic microparticles define the fossil outline which is 2 3 - - 3 0 # m in diameter, and the cell-walls are 0 . 5 - - 1 . 5 # m thick. Cell-like units are psilate to slightly granular in surface texture and occasionally contain smaller, internal dark bodies. The tubular flagellate structure is closely connected to the spheroidal cell-like unit, it is dark brown in colour (darker than the cell-like units) and has a granular surface texture. In one specnnen (Fig. 3: 16), the base of the tubular flagellate structure is 25-40~zm long and 7/~m in diameter, becoming gradually constricted and pointed (tapering). The biological affinity of the fossils is in no d o u b t on the basis o f : ( 1 ) the nature of the close connection between the spheroidal b o d y and the flagellate structure; (2) the distinct outline of the cell-like units which are similar to the associated Clonophycus vacus n. sp.; (3) its brown organic nature; and (4) its similarity in general morphology to the fossil Phycomyceres Timofeev, 1973 (1976), which has been discovered in the Riphean and Cambrian of Russia (Timofeev, 1973; Aseeva, 1976; Timofeev et al., 1976), and the Meishucun Formation in the Wangjiawan area (Wang and Zhai, 1983). The specimens were discovered in the middle member of the Dengying Formation in the Wangjiawan area, Jinning County, Yunnan. Species 6 (Fig. 6: 4) The filament is tubular, non-branched, non-septate and not constricted. The apex of the filament ends as a 'bullet'. The filament is straight, solitary, 9 #m in diameter, and the length of the observed incomplete filament is 55 #m. The filament outline is defined by organic matter. The specimen was discovered in the lower part of the Meishucun Formation in the Wangjiawan area, Jinning County, Yunnan. Species 7 (Fig. 18: 10) The filament is tubular, non-branched, non-septate, and is n o t constricted. The apical portion of the filament is absent. Filaments are very straight and occur as solitary, rigid tubes, 24--24.5 pm in diameter, with a granular surface texture. The specimen was discovered in the lower part of the Meishucun Formation in the Meishucun area, Jinning County, Yunnan.

ACKNOWLEDGEMENTS W e are grateful to scientists w h o have helped us in our work, including Professors Zhu Haojan, Liu Zhili, Ding Lianfang, Dr. J.H. Oehler, Dr. S.M.

174 A w r a m i k , Dr. M.D. Muir, Dr. J.W. S c h o p f , Dr. B. Nagy and Dr. C.V. Mendelson, w h o gave advice o n fossil s t u d y and c o m p a r i s o n b e t w e e n the fossils and thetr r e c e n t analogues; L m Yanran, X i o n g Taiquan, G u o Fulin, C h o u D i n g m a o and Yang Y m g x u a n for their help in t h e s t u d y o f p e t r o l o g y and m i n e r a l o g y ; Z h a n g Shlshan, Cao R e n g u a n and Z h u a n g Z h o n g h a i for field w o r k and sample c o l l e c t i o n ; Xie Zhenxi, Li F u h a n , Liao G u a n g y u and Z h o u G u o f u o f t h e P r e c a m b r i a n Geologmal Research G r o u p , C h e n g d u I n s t i t u t e o f G e o l o g y and Mineral R e s o u r c e s for their e n c o u r a g e m e n t and help during the study. We are especially grateful t o Miss Susan Sharp f r o m C h e n g d u College o f G e o l o g y w h o revised t h e final version o f this m a n u s c r i p t .

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