- Email: [email protected]
Gondwana Lithostratigraphy of Peninsular India: Reply*
Gondwana Research (Gondwana Newsletter Section) I! 7, No. 2, pp. 608-612. 02004 International Association for Gondwana Research, Japan.
SPECIAL CORRESPONDENCE
Gondwana Lithostratigraphy of Peninsular India: Reply“ Prodip Dutta Department of Geography, Geology and Anthropology, Indiana State University, Terre Haute, IN 47809, USA, E-mail: [email protected] (Manuscript received January 1,2004; accepted January 10,2004) Dr. Shah’s comment adds yet another piece to the longstanding stratigraphic controversy on the relation between Tiki-Parsora in the Son Basin (SB). The interpretation he has offered has been known to us for more than a century and therefore needs a rationale for further work on the same problem. However, the interpretation offered by Dr. Shah and many more before him is contradicted by geologists who have mapped the area in detail to bring out the field relation between Tiki and Parsora on a larger, basin-wise scale. Although this controversy is not going to be resolved through my reply to Dr. Shah’s letter, I will try to give a synopsis explaining why and how the problem started and why it continues. Then, in reply to the points raised by Dr. Shah, I will suggest a possible way to resolve the issue. Hughes first mapped the Son Basin (also known as South-Rewa Gondwana Basin) in 1881. In determining the relative age of Parsora (variously known as Mahadevd Upper-levelMaleri) and Tiki (Lower-levelMuleri) he relied more on fossil evidence that, incidentally, was in conflict with the observed physical relationships. This had been the crux of the problem when the most fundamental principle of stratigraphy based on superposition of strata was side-tracked in favor of fossils to determine the relative age of beds. How these fossils dictated the relative age is clear from Hughes’ statement, “...without the fossil I should certainly have shifted the rock in the Johilla .... to a higher horizon.” (Translation: I would have put Parsora above Tiki). With his stratigraphic interpretation it became difficult to make a map where the rocks had contradicting double litho- and bio-identity. Hughes (1881) observed that the Upper Gondwana-looking rocks contained Lower Gondwana fossils. Therefore, on the basis of fossil evidence the Upper Gondwana-looking rocks were relegated to Lower Gondwana status disregarding the field relationship. To circumvent the problem, as he was facing *See Pradip Dutta (2002) Gondwana Research [GNL), v. 5,pp. 540-553.
while making the map, he invoked conjectural faults. He argued, “... the high-level Maleris (e.g., Parsora), are rocks alarmingly like the Mahadevas (e.g., Parsora); and if it were not for the intervening clays (e.g., Tiki), I should make them fall into the Mahadevu (e.g., Parsora) horizon. The likeness suggests afault”. However, these imaginary faults were not enough to assuage even Hughes’ own doubts as he states, “My mind has passed through several stages of doubts.” So he returned to the area but was unable to make up his mind, and created a blanket term, “Supra Barakar” for the sequence between coal-bearing Barakar and Jabalpur formations and deferred the decision until he could return to re-examine the stratal relationship for a final verdict (Hughes, 1884). Hughes could not make the third trip but since then numerous researchers visited the area to resolve the problem. Results of the various findings can be summarized in a simple diagram (Table 1).As the table shows, from 1881 to 2004, a span of 123 years, our contribution regarding the Tiki-Parsora relation has resulted in no further clarification of this issue. Collectively, those of us who have worked to resolve this issue owe an explanation to the scientific community at large for our collective failure to offer a clear picture acceptable to all. Regarding the specific issues raised by Dr. Shah I will only discuss those points that have relevance to the core of the problem. (1) The opening sentence in his introduction reads, “The lithostratigraphy of the Gondwana formations vary from basin to basin.. ..” Dr. Shah makes the statement as he attempts to correlate between his Lower Pali Member, Upper Pali Member, and Parsora Formation in SB respectively with the Barren Measures, Raniganj, and Panchet formations in the DB (Table 2; Shah, 2004). Such lithostratigraphic correlation is untenable as the units
609
could not be more dissimilar. He correlates a coal-bearing Raniganj Formation that has nothing in common with the non coal-bearing Upper Pali Member characterized by sandstone and red, purple and gray/green shale. As it appears in the text, he changes the lithostratigraphic units into chronostratigraphic units by assigning faunal ages. This is exactly the kind of correlation that landed us in this mess in the first place. For example, he assigns Lower Triassic age to rock units as diverse as Parsora in SB and Panchet in DB and makes a correlation. Correlation between chronostratigraphic units having diverse lithological associations is perfectly valid, but such correlation in peninsular Gondwana may be difficult-to establish. It is well known that every lithological response is related to certain processes/controlling factors such as plate tectonic setting, climate, environment of deposition, etc. (Suttner and Dutta, 1986; Dickinson and Suczek, 1979; Suttner, 1974). In order to support his chronostratigraphic correlation between diverse lithological units as mentioned above, Dr. Shah has to explain how the controlling factors, particularly the plate tectonic setting, climate, and environment of deposition were significantly different in adjacent basins that simultaneously deposited sediments of very different and contrasting nature? Contrary to his observation of changing lithostratigraphy from basin to basin, similarities of continental Gondwana lithostratigraphic units, not only across the basins in peninsular India but also across continents, are remarkably similar. This is an observation that was first noted back in the 19” century. If someone were taken blindfolded, from the Tiki outcrop (Facies C) near Tiki village to the Sydney Basin in Australia, Karoo Basin in South Africa, and Parana Basin in South America where Facies C are exposed, the observer might not even realize if there had been intercontinental flights involved in the field trip! (2) Dr. Shah states that I “downplayed the stratigraphic value of biotic elements ...” Indeed, I did! My paper was on lithostratigraphy and established the stratigraphy on physical criteria, first by defining lithostratigraphic units and then by establishing their order of superposition. This is the first and the most fundamental step in any
stratigraphic work. In an undisturbed sequence like the Gondwanas of peninsular India, if one can define lithostratigraphic units and can physically verify that unit A is overlying unit B, no fossil is needed to establish their relative age. If fossil evidence contradicts the physical evidence then that particular fossil evidence should be re-examined. After all, the Last Appearance Datum (LAD) of biota is not sacrosanct. The range of the Glossopetris flora illustrates the point. Glossopteris was considered as a Late Paleozoic flora that later was extended to Early Triassic. Glossopteris or Glossopteris-like leaves, Mexicoglossa have been found in sediments of Middle Jurassic from Mexico (Delevoryas and Person, 1975). Palaeontological arguments in the Son Basin have been used, it seems, in two contrasting ways; in placing the Tiki above the Parsora (ala Hughes, 1881; Fox, 1931, Lele, 1968; Mitra, 1993; Shah, 2004) as well as placing the Tiki below the Parsora (ala Maheshwari, 1978; Kundu et al., 1993; Sinha et al., 1993; Tarafdar et al., 1993). This clearly demonstrates the inconclusive nature of biostratigraphic interpretation in the Son Basin. In this area, as well as in the Pranhita Godavari Basin, the fundamental principle of arranging strata in order of superposition was ignored (Dutta, 1996; Dutta, 1987). I suspect that if Hughes had followed this fundamental principle of stratigraphy back in 1881, we would not be debating the issue in 2004. It must also be stated that biostratigraphy has its role to play. Once the stratigraphy is established on physical criteria the most important role of biostratigraphy is to fine tune the stratigraphy by identifylng biozones; tracing the evolutionary pattern of the biota locally; and use biozones in regional and intercontinental correlation. But when the stratigraphy is still fuzzy as in the case of peninsular Gondwana (Figs. 2 and 3, Dutta, 2002) the question of fine-tuning has no meaning. My objective was to remove that fuzziness through physical criteria and therefore I kept the fossils out of discussion in my paper. (3) It had been difficult to follow how Dr. Shah differentiated the lithostratigraphic units since the sandstone composition from Pali through Hartala Hills are all rich in feldspar and the colors of associated shales
Table 1. Previously suggested stratigraphic superposition. Hughes, 1881
Cotter,
Fox,
1917
1931
Rao and Shukla,
Lele, 1968
1954
B PS B PS B Tiki-Maleri Parsora Tiki Parsora Tiki Tiki Parsora ParsoraTiki Parsora Mahadeva Basis of interpretation: B-Biostratigraphy, PS-Physical Stratigraphy Gondwana Research, V. 7, No. 2,2004
Maheswari et al.,
Dutta and Gosh,
1978
1993
B Parsora Tiki
PS Parsora Pali-Tiki
Mitra,
Kundu et al.,
1993
1993
B Tiki
PS Parsora Tiki
Parsora
Shah 2004 B
Tiki Parsora
610
are predominantly red and shades of purple, pink, and violet. In describing sandstone composition, he uses two classification schemes, one possibly by McBride (1963) as he used terms like arkose, and subarkose to describe the Pali and Tiki sandstones. But in describing the Parsora sandstones he used the term feldsarenite, possibly meaning feldspathic arenite as used by Williams, Turner, and Gilbert (1982). Because of such mixing of terms it is difficult to assess the exact composition of his Parsora sandstones. Dutta and Ghosh (1993) observed a systematic variation in sandstone composition between Pali-Tiki and Parsora. Immature feldspar-richarenites such as arkose and subarkose characterize Pali-Tiki while
Parsora is represented by supermature quartz arenite. However, according to Shah, Parsora and Tiki are both compositionally rich in feldspar. He also finds, ‘TheParsora and Tiki formations exposed near Neosi village are both made up of trough cross-bedded medium to coarse grained multistoried sand bodies’. If both the Parsora and Tiki compositionally and sedimentologically so similar, how does he distinguish them, the two most important lithostratigraphic units in this debate? (4) Dr. Shah questioned if the Parsora sandstones are cornpositionally quartz arenite as claimed by Dutta and Ghosh (1993). He not only finds Parsora to be compositionally immature but also states that the feldspars
Fig. 1. Geological map of the Pali-ParsoraTiki area. Parsora outcrops at higher elevation and Tiki in the valley. An unconformity can be seen a t the convergence of the contact pattern between the Parsora and Tiki and strike-dip trends. Unconformitycan also be seen as the Parsora outlier at higher elevation rests on Tiki at lower elevation (Dutta and Ghosh, 1993). Gondwana Research, V: 7, No. 2,2004
611
in them maintained their freshness (Fig. 3, Shah, 2004). He has an explanation how feldspar-rich sandstones could turn into quartz arenite, diagenetically, either through transformation of feldspar into “kaolinite or underwent near complete dissolution leaving behind atplaces their relict outline or remnants.” There is an internal inconsistency in his arguments on diageneticallygenerated quartz arenite. He needs to explain why feldspars in Parsora sandstones, examined by Dutta and Ghosh (1993) were selectively destroyed during diagenesis while his samples, presumably from the same suite not only escaped diagenetic destruction but retained their freshness as well? Here we are mixing apples (quartz arenite) of Dutta and Ghosh (1993) with oranges (feldspathic arenite) of Dr. Shah (2004). (5) Doubts regarding dip and strike readings of Dutta and Ghosh (1993) at the Parsora-Tiki boundary near Neosi village (Fig. 1, Shah, 2004) have been raised by Dr. Shah. He explains that a domal uplift of a dolerite body might have confused Dutta and Ghosh in finding the younging direction. It is not clear how such a structure would hinder establishing the order of superposition of strata! One does not need the dip direction to determine the order of superposition between units in an undisturbed sequence if a contact between them can be observed. Going beyond a single outcrop, on a much larger scale, the geological map of the area can provide critical information on stratigraphic relationships. The first comprehensive geological map of the area was made by Rao and Shukla (1954). That map demonstrated that the stratigraphic relation between the two units was well established. Any further work on this problem should have been stopped at that point. Dutta and Ghosh (1972) were sent to the Son Basin to map the area by someone in authority to find out the Tiki-Parora relationship that was already established by Rao and Shukla before. What was needed at that time was to invite those biostratigraphers who contradicted the interpretation of Rao and Shukla (1954) to join the field geologists to be a part of the mapping project to bring the controversy to a final conclusion. A geological map of the area is shown in figure 1. In an undulatory hilly terrain the Parsora outcrops on the hills unconformably overlying the Tiki in the valley as indicated by a zigzag contact that abuts against the strike direction. A similar relationship is also established by isolated outlier hills of Parsora surrounded by Tiki at lower elevation. Surprisingly,the biostratigraphers who had put the Tiki above the Parsora did not question this relationship nor have they produced any map of the area to show it otherwise. Earlier, we mixed lithostratigraphy and biostratigraphy and then used biostratigraphy to put Parsora both above and below Tiki. Now with Dr. Shah’s contribution we have Gondwana Research, V. 7, No. 2,2004
a few more elements to confuse the issue further: (a) Mixing of lithostratigraphy and chronostratigraphy; (b) Mixing of petrographic character, quartz arenite with feldspathic arenite; (c) Questioning data on sandstone composition and on the order of superposition observed by Dutta and Ghosh (1993). It seems communication is totally breaking down between scientists by taking an individual approach. Obviously, any further effort by an individual or by any single group would be meaningless, as it had been in the past. How long should we live in watertight compartments, continue to ride the seesaw-Parsora above Tiki, Tiki above Parsora, and waste taxpayer’s money? In science, communication is the key. We must communicate at the outcrop! Collectively,we must decide which is the apple and which is the orange; verify if the apple is above the orange or below it; and most importantly, do not use fossils until we have a stratigraphy based on the fundamental principle of superposition. In order to do all these we need to have a ‘Field Seminar’ where all doubts and questions can be verified and answered right at the outcrop. If this is the way many geological controversies are resolved at the outcrop elsewhere in the world, why not in India? It can be done only if someone in authority takes the initiative to organize a field seminar inviting all interested scientists to participate, work together and then publish their findings jointly and close the chapter once for all. The initiative could come from many institutions, either jointly or individually, like the Birbal Institute of Paleobotany, Geological Survey of India, Indian Statistical Institute, Oil and Natural Gas Commission or other institutions which have taken interest in the study of Gondwana stratigraphy. Alternatively, if we decide to live in our own world as we did during the last quarter and a century and continue our individual approach, we only indulge in meaningless activities in the name of science.
References Cotter, G. de P., 1917, A revised classification of the Gondwana System. Geol. Surv. India, Rec. v. 48, pp. 23-33. Delevoryas, T. and Person, C.P. (1975) Mexiglossa Varia Gen. Nov., a new genus of Glossopteroid leaves from the Jurassic of Oaxaca, Mexico, Paleontographica, Bd. v. 154, pp. 114-120. Dickinson, W.R. and Suczek, C.A. (1979) Plate tectonics and sandstone composition. Amer. Assoc. Petrol. Geol. v. 63, pp. 2164-2182. Dutta, P. (2002), Gondwana lithostratigraphy of peninsular India. Gondwana Research (GNL Section), v. 5, pp. 540-553. Dutta, P.K., (1996) The nineteenth century stratigraphic paradigm and the problem of the Gondwana stratigraphy in peninsular India. Ninth International Gondwana Symposium,
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Hyderabad, India. Oxford & IHB Publishing Co. Pvt. Ltd., New Delhi, pp. 165-178. Dutta, P.K. (1987) Upper Kamthi: A riddle in the Gondwana stratigraphy in peninsular India. In: McKenzie, G.D. (Ed.), Geophysical Monograph 41. Amer. Geophys. Union, pp. 229-238. Dutta, P.K. and Ghosh, S. (1993) The century old problem of the Pali-Parsora-Tiki stratigraphy and its bearing on the Gondwana classification of peninsular India. J. Geol. SOC. India, v. 42, pp. 17-31. Dutta, P.K. a n d Ghosh, S. (1979) Stratigraphy a n d sedimentation in Pali-Tiki-Parsora area, South-Rewa Gondwana Basin, Madhya Pradesh. Report Geol. Surv. India, pp. 1-15. Dutta, P.K. and Ghosh, S.K. (1972) Triassic sedimentation in Pali-Tiki-Parsoraarea, Madhya Pradesh. Proc. 59thIndian Sci. Congress, Calcutta, pt. 3 (Abst.), pp. 232-233. Fox, C.S. (1931) The Gondwana System and the related formations. Geol. Surv. India Mem., v. 58, pp. 1-117. Hughes, T.W.H. (1884) Southern coalfields of Rewa Gondwana Basin. Geol. Surv. India Rec., v. 21, pp. 1-103. Hughes, T.W.H. (1881) Notes on the South-Rewa Gondwana basin Geol. Surv. India Rec., v. 14, pp. 126-138. Kundu, A., Pillai, K.R., and Thanavelu, C. (1993) Elucidation of stratigraphic inter-relationship of Pali-Tiki-Parsora formations of South Rewa Gondwana Basin, MF? In: Dutta, K.K. and Sen, S. (Eds.), Gondwana Geol. Mag. Spec. v. pp. 49-59. Lele, K.M., (1968) The problem of Middle Gondwana in India. Int.Geo1. Congr. 22nd Proc. Pap. Sect. 9, pp. 181-202. Maheshwari, H.K., Kumaran, K.P.N. and Bose, M.N. (1978) The age of Tiki Formation with remarks on the miofloral succession in the Triassic Gondwana of India. The Paleobotanists, v. 25, pp. 254-265.
McBride, E.E (1963) A classification of common sandstones. J. Sediment. Petrol., v. 33, pp. 664-669. Mitra, N.D. (1993) Stratigraphy of Pali-Parsora-Tikiformations of South Rewa Gondwana Basin and Permo-Triassic boundary problem. In: Dutta, K.K. and Sen, S . (Eds.), Gondwana Geol. Mag. Spec. v. pp. 41-48. Rao, C.N. and Shukla, R.N. (1954) Examinations of the Supra-Barakars around Parsora-Tiki tract in Shadol District, Vindhya Pradesh, Progress Report for the Filed Season 1953-54, Geol. Surv. India, pp. 1-54. Shah, B.A. (2004) Gondwana Lithostratigraphy of Peninsular India: Comment, Gondwana Res. (GNL Sec.), v. 7, pp. 600-607. Sinha, P.K., Rajaiya, V., Das, D.P., Tarafdar, P., Agasty, A., Thanavelu, C., Patel, M.C., Datta, D.R., Parui, P.K., Kumar Ashok, Dutta, N.K., and Pillai, K.R. (1993) Contribution of fossil flora and Estheriids in Supra-Barakar stratigraphy in parts of Rewa Basin. In: Dutta, K.K. and Sen, S. (Eds.), Gondwana Geol. Mag. Spec. v., pp. 501-511. Suttner, L.J. (1974) Sedimentary petrographic provinces: an evaluation: SEPM Spec. Pub. No. 21, pp. 75-84. Suttner, L.J. and Dutta, P.K. (1986) Alluvial sandstone composition and Paleoclimate I: Framework mineralogy. J. Sediment. Petrol., v. 56, pp. 329-345. Tarafdar, P., Sinha, P.K., Das, D.P., Kundu, A., Dutta, D.R., Rajaiya, V., Parui, P.K., Patel, M.C., Thanavelu, C., Kumar, M.R.A., Pillai, K.R., Agasty, A. and Dutta, N.K. (1993) Recent advances in post-Barakar stratigraphy in parts of Rewa Gondwana Basin. In: Dutta, K.K. and Sen, S. (Eds.), Gondwana Geol. Mag. Spec. v., pp. 60-69. Williams, H.F., Turner, F.J. a n d Gilbert, C.M. (1982) Petrography, an introduction to the study of rocks in thin section, 2ndEd., W. H. Freeman and Co., San Francisco, p. 327.
Gondwana Research, V. 7 ,No. 2,2004
SPECIAL CORRESPONDENCE
Gondwana Lithostratigraphy of Peninsular India: Reply“ Prodip Dutta Department of Geography, Geology and Anthropology, Indiana State University, Terre Haute, IN 47809, USA, E-mail: [email protected] (Manuscript received January 1,2004; accepted January 10,2004) Dr. Shah’s comment adds yet another piece to the longstanding stratigraphic controversy on the relation between Tiki-Parsora in the Son Basin (SB). The interpretation he has offered has been known to us for more than a century and therefore needs a rationale for further work on the same problem. However, the interpretation offered by Dr. Shah and many more before him is contradicted by geologists who have mapped the area in detail to bring out the field relation between Tiki and Parsora on a larger, basin-wise scale. Although this controversy is not going to be resolved through my reply to Dr. Shah’s letter, I will try to give a synopsis explaining why and how the problem started and why it continues. Then, in reply to the points raised by Dr. Shah, I will suggest a possible way to resolve the issue. Hughes first mapped the Son Basin (also known as South-Rewa Gondwana Basin) in 1881. In determining the relative age of Parsora (variously known as Mahadevd Upper-levelMaleri) and Tiki (Lower-levelMuleri) he relied more on fossil evidence that, incidentally, was in conflict with the observed physical relationships. This had been the crux of the problem when the most fundamental principle of stratigraphy based on superposition of strata was side-tracked in favor of fossils to determine the relative age of beds. How these fossils dictated the relative age is clear from Hughes’ statement, “...without the fossil I should certainly have shifted the rock in the Johilla .... to a higher horizon.” (Translation: I would have put Parsora above Tiki). With his stratigraphic interpretation it became difficult to make a map where the rocks had contradicting double litho- and bio-identity. Hughes (1881) observed that the Upper Gondwana-looking rocks contained Lower Gondwana fossils. Therefore, on the basis of fossil evidence the Upper Gondwana-looking rocks were relegated to Lower Gondwana status disregarding the field relationship. To circumvent the problem, as he was facing *See Pradip Dutta (2002) Gondwana Research [GNL), v. 5,pp. 540-553.
while making the map, he invoked conjectural faults. He argued, “... the high-level Maleris (e.g., Parsora), are rocks alarmingly like the Mahadevas (e.g., Parsora); and if it were not for the intervening clays (e.g., Tiki), I should make them fall into the Mahadevu (e.g., Parsora) horizon. The likeness suggests afault”. However, these imaginary faults were not enough to assuage even Hughes’ own doubts as he states, “My mind has passed through several stages of doubts.” So he returned to the area but was unable to make up his mind, and created a blanket term, “Supra Barakar” for the sequence between coal-bearing Barakar and Jabalpur formations and deferred the decision until he could return to re-examine the stratal relationship for a final verdict (Hughes, 1884). Hughes could not make the third trip but since then numerous researchers visited the area to resolve the problem. Results of the various findings can be summarized in a simple diagram (Table 1).As the table shows, from 1881 to 2004, a span of 123 years, our contribution regarding the Tiki-Parsora relation has resulted in no further clarification of this issue. Collectively, those of us who have worked to resolve this issue owe an explanation to the scientific community at large for our collective failure to offer a clear picture acceptable to all. Regarding the specific issues raised by Dr. Shah I will only discuss those points that have relevance to the core of the problem. (1) The opening sentence in his introduction reads, “The lithostratigraphy of the Gondwana formations vary from basin to basin.. ..” Dr. Shah makes the statement as he attempts to correlate between his Lower Pali Member, Upper Pali Member, and Parsora Formation in SB respectively with the Barren Measures, Raniganj, and Panchet formations in the DB (Table 2; Shah, 2004). Such lithostratigraphic correlation is untenable as the units
609
could not be more dissimilar. He correlates a coal-bearing Raniganj Formation that has nothing in common with the non coal-bearing Upper Pali Member characterized by sandstone and red, purple and gray/green shale. As it appears in the text, he changes the lithostratigraphic units into chronostratigraphic units by assigning faunal ages. This is exactly the kind of correlation that landed us in this mess in the first place. For example, he assigns Lower Triassic age to rock units as diverse as Parsora in SB and Panchet in DB and makes a correlation. Correlation between chronostratigraphic units having diverse lithological associations is perfectly valid, but such correlation in peninsular Gondwana may be difficult-to establish. It is well known that every lithological response is related to certain processes/controlling factors such as plate tectonic setting, climate, environment of deposition, etc. (Suttner and Dutta, 1986; Dickinson and Suczek, 1979; Suttner, 1974). In order to support his chronostratigraphic correlation between diverse lithological units as mentioned above, Dr. Shah has to explain how the controlling factors, particularly the plate tectonic setting, climate, and environment of deposition were significantly different in adjacent basins that simultaneously deposited sediments of very different and contrasting nature? Contrary to his observation of changing lithostratigraphy from basin to basin, similarities of continental Gondwana lithostratigraphic units, not only across the basins in peninsular India but also across continents, are remarkably similar. This is an observation that was first noted back in the 19” century. If someone were taken blindfolded, from the Tiki outcrop (Facies C) near Tiki village to the Sydney Basin in Australia, Karoo Basin in South Africa, and Parana Basin in South America where Facies C are exposed, the observer might not even realize if there had been intercontinental flights involved in the field trip! (2) Dr. Shah states that I “downplayed the stratigraphic value of biotic elements ...” Indeed, I did! My paper was on lithostratigraphy and established the stratigraphy on physical criteria, first by defining lithostratigraphic units and then by establishing their order of superposition. This is the first and the most fundamental step in any
stratigraphic work. In an undisturbed sequence like the Gondwanas of peninsular India, if one can define lithostratigraphic units and can physically verify that unit A is overlying unit B, no fossil is needed to establish their relative age. If fossil evidence contradicts the physical evidence then that particular fossil evidence should be re-examined. After all, the Last Appearance Datum (LAD) of biota is not sacrosanct. The range of the Glossopetris flora illustrates the point. Glossopteris was considered as a Late Paleozoic flora that later was extended to Early Triassic. Glossopteris or Glossopteris-like leaves, Mexicoglossa have been found in sediments of Middle Jurassic from Mexico (Delevoryas and Person, 1975). Palaeontological arguments in the Son Basin have been used, it seems, in two contrasting ways; in placing the Tiki above the Parsora (ala Hughes, 1881; Fox, 1931, Lele, 1968; Mitra, 1993; Shah, 2004) as well as placing the Tiki below the Parsora (ala Maheshwari, 1978; Kundu et al., 1993; Sinha et al., 1993; Tarafdar et al., 1993). This clearly demonstrates the inconclusive nature of biostratigraphic interpretation in the Son Basin. In this area, as well as in the Pranhita Godavari Basin, the fundamental principle of arranging strata in order of superposition was ignored (Dutta, 1996; Dutta, 1987). I suspect that if Hughes had followed this fundamental principle of stratigraphy back in 1881, we would not be debating the issue in 2004. It must also be stated that biostratigraphy has its role to play. Once the stratigraphy is established on physical criteria the most important role of biostratigraphy is to fine tune the stratigraphy by identifylng biozones; tracing the evolutionary pattern of the biota locally; and use biozones in regional and intercontinental correlation. But when the stratigraphy is still fuzzy as in the case of peninsular Gondwana (Figs. 2 and 3, Dutta, 2002) the question of fine-tuning has no meaning. My objective was to remove that fuzziness through physical criteria and therefore I kept the fossils out of discussion in my paper. (3) It had been difficult to follow how Dr. Shah differentiated the lithostratigraphic units since the sandstone composition from Pali through Hartala Hills are all rich in feldspar and the colors of associated shales
Table 1. Previously suggested stratigraphic superposition. Hughes, 1881
Cotter,
Fox,
1917
1931
Rao and Shukla,
Lele, 1968
1954
B PS B PS B Tiki-Maleri Parsora Tiki Parsora Tiki Tiki Parsora ParsoraTiki Parsora Mahadeva Basis of interpretation: B-Biostratigraphy, PS-Physical Stratigraphy Gondwana Research, V. 7, No. 2,2004
Maheswari et al.,
Dutta and Gosh,
1978
1993
B Parsora Tiki
PS Parsora Pali-Tiki
Mitra,
Kundu et al.,
1993
1993
B Tiki
PS Parsora Tiki
Parsora
Shah 2004 B
Tiki Parsora
610
are predominantly red and shades of purple, pink, and violet. In describing sandstone composition, he uses two classification schemes, one possibly by McBride (1963) as he used terms like arkose, and subarkose to describe the Pali and Tiki sandstones. But in describing the Parsora sandstones he used the term feldsarenite, possibly meaning feldspathic arenite as used by Williams, Turner, and Gilbert (1982). Because of such mixing of terms it is difficult to assess the exact composition of his Parsora sandstones. Dutta and Ghosh (1993) observed a systematic variation in sandstone composition between Pali-Tiki and Parsora. Immature feldspar-richarenites such as arkose and subarkose characterize Pali-Tiki while
Parsora is represented by supermature quartz arenite. However, according to Shah, Parsora and Tiki are both compositionally rich in feldspar. He also finds, ‘TheParsora and Tiki formations exposed near Neosi village are both made up of trough cross-bedded medium to coarse grained multistoried sand bodies’. If both the Parsora and Tiki compositionally and sedimentologically so similar, how does he distinguish them, the two most important lithostratigraphic units in this debate? (4) Dr. Shah questioned if the Parsora sandstones are cornpositionally quartz arenite as claimed by Dutta and Ghosh (1993). He not only finds Parsora to be compositionally immature but also states that the feldspars
Fig. 1. Geological map of the Pali-ParsoraTiki area. Parsora outcrops at higher elevation and Tiki in the valley. An unconformity can be seen a t the convergence of the contact pattern between the Parsora and Tiki and strike-dip trends. Unconformitycan also be seen as the Parsora outlier at higher elevation rests on Tiki at lower elevation (Dutta and Ghosh, 1993). Gondwana Research, V: 7, No. 2,2004
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in them maintained their freshness (Fig. 3, Shah, 2004). He has an explanation how feldspar-rich sandstones could turn into quartz arenite, diagenetically, either through transformation of feldspar into “kaolinite or underwent near complete dissolution leaving behind atplaces their relict outline or remnants.” There is an internal inconsistency in his arguments on diageneticallygenerated quartz arenite. He needs to explain why feldspars in Parsora sandstones, examined by Dutta and Ghosh (1993) were selectively destroyed during diagenesis while his samples, presumably from the same suite not only escaped diagenetic destruction but retained their freshness as well? Here we are mixing apples (quartz arenite) of Dutta and Ghosh (1993) with oranges (feldspathic arenite) of Dr. Shah (2004). (5) Doubts regarding dip and strike readings of Dutta and Ghosh (1993) at the Parsora-Tiki boundary near Neosi village (Fig. 1, Shah, 2004) have been raised by Dr. Shah. He explains that a domal uplift of a dolerite body might have confused Dutta and Ghosh in finding the younging direction. It is not clear how such a structure would hinder establishing the order of superposition of strata! One does not need the dip direction to determine the order of superposition between units in an undisturbed sequence if a contact between them can be observed. Going beyond a single outcrop, on a much larger scale, the geological map of the area can provide critical information on stratigraphic relationships. The first comprehensive geological map of the area was made by Rao and Shukla (1954). That map demonstrated that the stratigraphic relation between the two units was well established. Any further work on this problem should have been stopped at that point. Dutta and Ghosh (1972) were sent to the Son Basin to map the area by someone in authority to find out the Tiki-Parora relationship that was already established by Rao and Shukla before. What was needed at that time was to invite those biostratigraphers who contradicted the interpretation of Rao and Shukla (1954) to join the field geologists to be a part of the mapping project to bring the controversy to a final conclusion. A geological map of the area is shown in figure 1. In an undulatory hilly terrain the Parsora outcrops on the hills unconformably overlying the Tiki in the valley as indicated by a zigzag contact that abuts against the strike direction. A similar relationship is also established by isolated outlier hills of Parsora surrounded by Tiki at lower elevation. Surprisingly,the biostratigraphers who had put the Tiki above the Parsora did not question this relationship nor have they produced any map of the area to show it otherwise. Earlier, we mixed lithostratigraphy and biostratigraphy and then used biostratigraphy to put Parsora both above and below Tiki. Now with Dr. Shah’s contribution we have Gondwana Research, V. 7, No. 2,2004
a few more elements to confuse the issue further: (a) Mixing of lithostratigraphy and chronostratigraphy; (b) Mixing of petrographic character, quartz arenite with feldspathic arenite; (c) Questioning data on sandstone composition and on the order of superposition observed by Dutta and Ghosh (1993). It seems communication is totally breaking down between scientists by taking an individual approach. Obviously, any further effort by an individual or by any single group would be meaningless, as it had been in the past. How long should we live in watertight compartments, continue to ride the seesaw-Parsora above Tiki, Tiki above Parsora, and waste taxpayer’s money? In science, communication is the key. We must communicate at the outcrop! Collectively,we must decide which is the apple and which is the orange; verify if the apple is above the orange or below it; and most importantly, do not use fossils until we have a stratigraphy based on the fundamental principle of superposition. In order to do all these we need to have a ‘Field Seminar’ where all doubts and questions can be verified and answered right at the outcrop. If this is the way many geological controversies are resolved at the outcrop elsewhere in the world, why not in India? It can be done only if someone in authority takes the initiative to organize a field seminar inviting all interested scientists to participate, work together and then publish their findings jointly and close the chapter once for all. The initiative could come from many institutions, either jointly or individually, like the Birbal Institute of Paleobotany, Geological Survey of India, Indian Statistical Institute, Oil and Natural Gas Commission or other institutions which have taken interest in the study of Gondwana stratigraphy. Alternatively, if we decide to live in our own world as we did during the last quarter and a century and continue our individual approach, we only indulge in meaningless activities in the name of science.
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