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Neoproterozoic sponge spicules and organic walled microfossils

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Neoproterozoic sponge spicules and organic walled microfossils Powered By Docstoc
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pared to those areas where snow/ice is prevailing in these         1. Masoom, R., Satellite Remote Sensing of Polar Regions – Appli-
two months. For example, a marked change in ice accu-                 cations, Limitations and Data Availability, Lewis Publishers, Flor-
mulation could be demarcated near Ross ice shelf and                  ida, USA, 1991, p. 307.
Weddell Sea regions (Figures 2 a, 4 a and b).                      2. Gloersen, P., Campbell, W. J., Cavaliery, D. J., Comiso, J. C., Park-
(iii) The Antarctic region could be depicted along with               inson, C. L. and Zwally, H. J., Arctic and Antarctic Sea Ice: Satel-
                                                                      lite Passive Microwave Observations and Analysis, NASA
the subtle distinction of regional relief and tectonic fea-           Publications, NASA SP-511, Washington DC, 1992, p. 290.
tures (Figures 2 b, 4 a and b). Transantarctic mountains           3. Allan, T. D. (ed.), Satellite Microwave Remote Sensing, John
are clearly depicted in Figure 4 b. Similar features have             Wiley, Chichester, 1983, p. 526.
been reported elsewhere1,2 (also, see Figure 2 b).                 4. Chang, A. T. C., Gloersen, P., Schmugge, T., Wilheit, T. T. and
(iv) In addition to snow/ice cover changes over Antarc-               Zwally, H. J., J. Glaciol., 1976, 16, 23–39.
                                                                   5. Rao, K. S., Murty, Y. V. S., Gopalan, A. K. S., Ramakrisnan, R.
tica, marked changes in the sea surface processes could be            and Majumdar, T. J., Remote Sensing Environ., 1983, 13, 209–233.
observed (Figure 4 a and b) around the Antarctic subcon-           6. Svendsen, E., Kloster, K., Farelly, B., Johannessen, O. M., Johan-
tinent in the surrounding oceans, which need further                  nessen, J. A., Campbell, W. J., Gloersen, P., Cavalieri, D. and
study. Vertical circulation of the ocean and the associated           Matzler, C., J. Geophys. Res., 1983, 88, 2781–2791.
production of Antarctic bottom water is an important               7. Bhattacharya, B. B. and Majumdar, T. J., Scientific Report, Dept. of
                                                                      Ocean Development, New Delhi, 1987, Pub. No. 4, pp. 35–41.
oceanographic phenomenon2. However, there are some                 8. NSIDC Reports, Colorado, 1999 (pers. commun.).
noise patterns occurring over this region in the processed         9. Jensen, J. R., Introductory Digital Image Processing: A Remote Sens-
imagery. Unfortunately, noises are bound to occur in                  ing Perspective, Prentice–Hall Publishers, New Jersey, 1986, p. 379.
any product obtained by image processing techniques9.
                                                                   ACKNOWLEDGEMENTS. The data over Antarctica as observed by
Hence, during interpretation, the pseudo-features which
                                                                   SSM/I have been obtained courtesy NSIDC, Colorado, USA. Critical
are really not existing on the ground may be discarded.            comments by anonymous referees are acknowledged.
Most of these interpretations match well with ground-
based observations.                                                Received 27 March 2000; revised accepted 23 June 2000




Neoproterozoic sponge spicules and                                 calcareous biomineralization in sponges1. Phylogeneti-
                                                                   cally, they constitute the most original group within the
organic-walled microfossils from                                   metazoa. Presence of sponge spicules provides an evi-
the Gangolihat Dolomite, Lesser                                    dence of metazoan silica biomineralization in the Protero-
Himalaya, India                                                    zoic fossil record. Late Proterozoic sponge spicules have
                                                                   been documented from Vosgas Mountain, Mongolia,
                                                                   China and Australia1–4. Recently, Neoproterozoic sponge-
Meera Tiwari*,†, C. C. Pant** and V. C. Tewari*                    like fossils have been reported from the Upper Vindhyan
*Wadia Institute of Himalayan Geology, 33, General Mahadev Singh
Road, Dehradun 248 001, India
                                                                   in India5. Early Cambrian records of sponge spicules
**Geology Department, Kumaun University, Nainital 263 001, India   are also documented worldwide (ref. 6 and references
                                                                   therein).
                                                                      The sponge spicules described in this communication
Isolated hexactinellid and monaxon sponge spicules
                                                                   have been recorded from two different localities of the
with cyanobacterial filaments have been discovered in
the Gangolihat Dolomite. The microfossils described                Gangolihat Dolomite, which is extensively developed in
were recovered in the thin sections of cherty dolomite             the Inner sedimentary belt of the eastern Kumaun Lesser
and phyllite. Comparable sponge spicules are reported              Himalaya (Figure 1). The fossiliferous samples were col-
so far from lower Vendian sediments; therefore an                  lected near the village of Utrora, ~ 3.5 km south-west of
early Vendian age can be suggested for the Gangolihat              Kapkot (29°57′N: 79°56′E) in the Bageshwar–Kapkot
Dolomite. The main purpose of this communication is                road and near the village of Chhera in Chandak–Cherra
to document the presence of sponge spicules and silica             road section in Pithoragarh (29°35′N: 80°15′E) (Figure 1).
biomineralization during the sedimentation of Gangoli-             The discovery of a well-preserved microbiota from the
hat Dolomite in the Kumaun Lesser Himalaya, India.                 Deoban limestone, Great Limestone, Krol belt of Lesser
                                                                   Himalaya6–13, has given encouragement for further search
SPONGES had a largely undocumented history before their            of palaeobiologic records in the eastern part of Kumaun
entry into the skeletal fossil record. It is accepted that         Lesser Himalaya where no authentic microbiota has been
sponges had achieved skeletal diversity by the latest Pro-         reported so far. Well-preserved sponge spicules and
terozoic and that siliceous biomineralization preceded             organic-walled microfossils from the Gangolihat Dolo-
                                                                   mite may certainly provide a nonpareil perception about
†
    For correspondence. (e-mail: bswihg@nde.vsnl.net.in)           the early stages of animal evolution and complexity of
CURRENT SCIENCE, VOL. 79, NO. 5, 10 SEPTEMBER 2000                                                                                     651
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                             Figure 1.   Geological map of the area showing fossil locality (after Valdiya15).



                         Table 1.   The stratigraphic succession of the Kumaun Leser Himalaya (after Valdiya15)

                                            Thalkedar limestone      Blue–grey banded limestone, often with chert
                                                                     laminae and nodules, and argillaceous limestone
                   Mandhali Formation
                                                                     alternating with calcareous grey phyllite.
                   (Sor Formation)
                                            Sor slate                Light green and grey–green sand stone.

                                            Dhari Member             Blue–grey limestone with calc–slate and marlite.
                                            Chandak Member           Dolomitic limestone characterized by spectacular
                                                                     development of stromatolites. Pockets of flat peb-
                                                                     ble intraformational conglomerate. Conspicuous
                   Deoban Formation
                                                                     chain of lentiform deposits of magnesite.
                   (Gangolihat, Dolomite,
                                            Hiunpani Member          Fine-grained cherty dolomite of pink and white
                   Kapkot Formation)
                                                                     colours alternating with chert laminae.
                                            Chhera Member            Pink violet and maroon slate-phyllite interbedded
                                                                     with subordinate pink, green and white marble,
                                                                     often sandy.



Gangolihat Dolomite ecosystem existing at the time of
sedimentation.
    The stratigraphic succession of the area is shown in
Table 1.
   The argillocalcareous sequence of the present area was
described as the Calc Zone of Tejam14. Valdiya15 has
divided it into two formations, the older Deoban Forma-
tion and the younger Mandhali Formation. The carbonate
sequence was named the Gangolihat Dolomite. In the
Bageshwar–Kapkot section, this unit was described as the
Kapkot Formation16. Gangolihat Dolomite constitutes a
total thickness of about 700 m in Pithoragarh17 and con-
sists predominantly of limestone, cherty limestone, stro-
matolitic dolomite and phyllitic units. It has been divided
into four members, Chhera, Hiunpani, Chandak and Dhari,
respectively, in ascending order. The Gangolihat Dolo-
mite is overlain by the Sor Formation (with Sor slate and
Thalkedar limestone Members of Valdiya15). In the Chhera
village of Pithoragarh, grey and purple coloured phyllite                                     a                       b
(Chhera Member of Valdiya17) is exposed. The phyllite is
highly siliceous. In the lower part of the section, thinly-            Figure 2. Stratigraphic column of a, Chhera section and b, Utrora
                                                                       section, showing the position of fossiliferous samples. a, limestone;
bedded pink limestone alternates with purple calcareous                b, phyllite; c, dolomite; d, cherty dolomite; e, cryptalgal laminates;
phyllite sequence (Figure 2 a). The stromatolitic dolomite             f, stromatolitic dolomite; *, fossiliferous samples.

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               Figure 3. a, c, Hexactinellid sponge spicules; Loc. Chhera; b, Monaxon sponge spicules. Loc. Chhera;
               d, e, hexactinellid sponge spicule in different focal depths. Loc. Utrora; f, hexactinellid sponge spicule.
               Loc. Utrora; g, Nostocomorpha sp. Loc. Utrora. Scale bar is 10 µm for a, b, g and e. Scale bar in e is the same
               for d and f.




exposed in the Bageshwar–Kapkot section is siliceous                     Middle Riphean stromatolites (Baicalia bacalica) in the
dolomite which often contains chert nodules and chert                    Middle and Upper Riphean stromatolites (Minjaria ura-
bands (Figure 2 b). The chert nodules range from 1 to                    lica, Masloviella columnaris) in the upper part. The bio-
12 cm in diameter. The cherty bed is approximately 10 m                  zonation based on stromatolites established that the
thick. Dolomite units become thicker upward in the                       Deoban, Shali and Jammu (Great) Limestone belts are
sequence, and are oolitic at places.                                     correlatable and homotaxial with the Gangolihat Dolomite
   The age of the Gangolihat Dolomite was mainly                         and indicate an Early to Middle Riphean age18. The
deduced on the basis of stromatolites in the absence of                  microfossil assemblage comprising cyanobacteria, algae,
radiometric dates. The carbonate belt shows characteristic               fungi, acritarchs and possible nematodes, suggests an
forms of Lower Riphean stromatolites (Kussiella kussi-                   Early Vendian age for the Deoban Formation9. The micro-
ensis, Conophyton garganicus, Conophyton cylindricus,                    bial fossils, including cyanobacteria, sphaeromorphic and
Colonella columnaris, and Plicatina antiqua) at the base,                acanthomorphic acritarchs and vase-shaped microfossils

CURRENT SCIENCE, VOL. 79, NO. 5, 10 SEPTEMBER 2000                                                                               653
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reported from the Great Limestone suggest a Late                10 µm diameter spheres occurs as a single filament. Such
Riphean to Vendian age10. Besides, in the eastern               structures are known to be remains of filamentous micro-
extension of these carbonate rocks in Nepal, Neopro-            organisms whose organic matter has been completely
terozoic to Cambrian Palaeobasidiospores have been              replaced by diagenesis of iron minerals21, and are classed
recorded19.                                                     under Nostocomorpha Sin and Liu21,22. No organic matter
   Neoproterozoic monaxial siliceous sponge spicules            is visible in these fossils. Comparable structures were also
have been earlier reported from quartz phyllite of the          reported from various Proterozoic successions21.
Ville Series from the Vosges Mountain2. Some disk-like
bodies of hexactinellid sponge spicules have been repor-
ted from the Neoproterozoic Ediacara fauna of South
Australia4. Further, Ediacarian (~ 543 Ma) hexactinellid         1. Brasier, M. D., Green, O. and Shields, G., Geology, 1997, 25,
sponge spicules have been reported from south-western               303–306.
                                                                 2. Doubinger Par, J. and Eller, Jean-Paul., Bull. Serv. Carte. Geol.
Mongolia1. Late Proterozoic sponges have been docu-                 Als. Lorr., 1963, 111–123.
mented with soft tissue from phosphorite of Doushantuo,          3. Li, C. -W. and Chen, J. Y. and Hua, T.-E., Science, 1998, 279,
South China. These sponges are older than the Ediacara              879–882.
and are reported to be of Early Vendian age, ca. 580 Ma          4. Gehling, J. G. and Rigby, J. K., J. Palaeontol., 1996, 70, 185–195.
and they contained only monaxon spicules3. Early Cam-            5. Kumar, S. J., Palaeontol. Soc. India, 1999, 44,141–148.
                                                                 6. Tiwari, Meera, Precambrian Res., 1999, 97, 99–113.
brian sponge spicules were mainly hexactinellids and were        7. Shukla, M., Tewari, V. C. and Yadav, V. K., Palaeobotanist,
documented worldwide (ref. 6 and references therein). It            1987, 35, 247–256.
is concluded on the basis of the worldwide presence of           8. Kumar, S. and Srivastava, P., Precambrian Res., 1992, 56, 291–
these sponge spicules, that silica biomineralization started        318.
during Early Vendian. Therefore, a comparison of the             9. Srivastava, P. and Kumar, S., Curr. Sci., 1997, 72,145–149.
                                                                10. Venkatachala, B. S. and Kumar, Ashok, J. Geol. Soc. India, 1998,
recorded Neoproterozoic sponge spicules, especially from            52, 529–536.
Mongolia1 and China3 to those present in the Gangolihat         11. Venkatachala, B. S., Shukla, M., Bansal, R. and Acharyya, S. K.
Dolomite suggests an Early Vendian age for the Gango-               Palaeobotanist, 1990, 38, 29–38.
lihat Dolomite. The present communication mainly deals          12. Tiwari, Meera, Cotrs. XV Indian Colloq. Micropal. Strat. Dehra-
                                                                    dun, 1996, pp. 559–566.
with the discovery of well-preserved sponge spicules and
                                                                13. Kumar, S. and Rai, V. J., Geol. Soc. India, 1992, 39, 229–234.
cyanobacterial filament from the Gangolihat Dolomite. A         14. Heim, A. and Gansser, A., Mem. Soc. Helv. Soc. Nat., 1939, 73,
detailed study of this microbial assemblage will provide            1–245.
new information on early stages of metazoan evolution           15. Valdiya, K. S., Geology of the Kumaun Lesser Himalaya, Hi-
during Neoproterozoic (Gangolihat) sedimentation. A large           machal Times Press, Dehradun, 1980, p. 291.
                                                                16. Misra, R. C. and Bhattacharya, A. R., Himalayan Geol., 1972, 2,
number of thin sections were examined and unques-
                                                                    252–270.
tioned20 simple small monaxial oxeas and hexactinellid          17. Valdiya, K. S., Sedimentology, 1972, 19, 115–128.
sponge spicules occur abundantly in the collection. Long        18. Tewari, V. C., Himalayan Geol., 1981, 11, 119–146.
and thin monaxons are straight or sometimes bent a little,      19. Brunel, M., Chaye, D., Albissin, M. and Locquin, M. J., Geol.
spicules are equidimensional and smooth, ranging in dia-            Soc. India, 1985, 26, 255–260.
meter from 0.5 to 1 µm and 20 to 70 µm long (Figure 3 b).       20. Pers. commun. with Dr Rigby to Meera Tiwari. Rigby regarded
                                                                    these forms as unquestioned hexactinellid sponge spicules.
The presence of monaxon ray is confirmed by the taper-          21. Hofmann, H. J., Geol. Surv. Can., 1984, 84-IB, 285–297.
ing of the ray in both directions. Hexactinellid spicules       22. Hofmann H. J. and Jackson, G. D., J. Palaeontol., 1991, 65, 361–
are 1 to 5 µm in diameter and 10 to 300 µm in length                382.
(Figure 3 a, c, d–f). In a thin section, there is cross-
section of a vertical ray near the intersection of other rays
(Figure 3 a). Some thicker, short spicules with diameters       ACKNOWLEDGEMENTS. M.T. thanks Prof. J. K. Rigby (Utah), and
                                                                Dr Dorte Mehl (Berlin) for their help during identification and interpre-
ranging from 5 to 7 µm are also seen embedded in the
                                                                tation of sponge spicules. The Director, Wadia Institute of Himalayan
matrix. Long and unbranched chain-like aggregates with          Geology, Dehradun is acknowledged for providing necessary facilities.
the length up to 600 µm are seen in thin section of chert
nodule-bearing dolomite (Figure 3 g). A chain of 8 to           Received 20 March 2000; revised accepted 16 June 2000




654                                                                    CURRENT SCIENCE, VOL. 79, NO. 5, 10 SEPTEMBER 2000

				
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