Concerning the advanced nature of the plant and insect microfossils found in the Salt Range Formation, Sahni (1947b, pp. xlv–xlvi) noted: “Quite recently, an alternative explanation has been offered by Mr. Gee. the suggestion is that the angiosperms, gymnosperms and insects of the Saline Series may represent a highly evolved Cambrian or Precambrian flora and fauna! In other words, it is suggested that these plants and animals made their appearance in the Salt Range area several hundred million years earlier than they did anywhere else in the world. One would scarcely have believed that such an idea would be seriously put forward by any geologist today.”
Gee, by questioning basic evolutionary assumptions about the progression of life forms on earth, introduces another possible solution to the Salt Range Formation controversy. Up to this point, the relatively late appearance of the angiosperms, gymnosperms, and certain insects had been taken for granted. Evidence of their presence in the Salt Range Formation had to be resolved by (1) suggesting they were intrusive into the formation, which was of Cambrian age or (2) suggesting that they were native to the formation proving it was Eocene and invoking a massive overthrust to account for the formation’s presence below formations generally accepted as Cambrian. Supporters of the former proposal, including Gee, were troubled, however, by the strength of Sahni’s evidence for the in situ status of his microfossils. So Gee suggested that perhaps the Salt Range Formation is, after all, Cambrian, as the geological evidence strongly suggested, and the microfossils of angiosperms, gymnosperms, and insects were in situ. This could only mean that the angiosperms, gymnosperms, and insects evolved far earlier than allowed by any current evolutionary account. It was a bold proposal, but fell on deaf ears at the time.
Subsequently, evidence for angiosperms and gymnosperms was also found in other beds of Cambrian age overlying the Salt Range Formation. These included microfossils of angiosperms and gymnosperms from the Salt Pseudomorph Beds (Ghosh and Bose, 1947), gymnosperms from the Purple Sandstone (Ghosh, et al., 1948), wood fragments from the Neobolus Shales (Ghosh, et al., 1948), and wood fragments from the Magnesian Sandstone (Ghosh, et al., 1948).
Ghosh and Bose (1950a, p. 76) proposed two possible explanations for this evidence of advanced vascular plants in the above-mentioned formations: “1. The geologically known Cambrian beds are of post-Cambrian age. 2. The vascular plants existed in Cambrian or pre-Cambrian times.” Ghosh and Bose rejected the first proposal because geologists unanimously agreed that the beds in question were in fact Cambrian. Ghosh and Bose found the second proposal more likely, even though it was “inconsistent with the prevailing concepts of plant phylogeny.” They pointed out that there had been discoveries of advanced plant remains in beds of similar age in Sweden (Darrah 1937) and in the USSR (Sahni 1947b, in note following plates).
Ghosh and Bose (1947) reconfirmed the original discoveries by Sahni and his coworkers of advanced plant remains in the Salt Range Formation itself. They also obtained fragments of advanced plants from a sample of shale from the Cambrian or pre-Cambrian beds of the Vindhyans of northern India (Ghosh and Bose 1950b) and from a sample of Cambrian rock from Kashmir (Ghosh and Bose 1951a). In some cases, Ghosh and Bose (1951b, pp. 130–131; 1952) found fragments of advanced plants (conifers) in Cambrian rock samples that also contained trilobites. The samples were from the Salt Pseudomorph beds of the Salt Range and the shales of the Rainwar locality in Kashmir.
Other researchers confirmed the work of Ghosh and his associates (Jacob et al. 1953), finding evidence for advanced vascular plants, including gymnosperms, in Cambrian rock samples from the Salt Range and other sites in India. Jacob and his coworkers also called attention to similar Cambrian paleobotanical discoveries in Sweden, Estonia, and Russia, as reported by S. N. Naumova, A. V. Kopeliovitch, A. Reissinger, and W. C. Darrah (Jacob et al. 1953, p. 35).
German researchers (Schindewolf and Seilacher, 1955) took samples of rock from the Salt Range to Germany, where specialists found no evidence of plant remains. But in his discussion, Schindewolf mentioned that he personally witnessed an Indian scientist obtain plant microfossils from a Cambrian Salt Range rock sample in India. After this, active discussion of the controversy diminished. It is quite possible that this was the result of the partition of India and Pakistan. After partition, members of the Geological Survey of India may not have had such easy access to the Salt Range in the newly independent Islamic state of Pakistan.
In recent years, petroleum geologists have conducted extensive studies of the Salt Range region, with no reference or only slight reference to the debates that took place earlier in the century. Although modern geological reports acknowledge overthrusts in the Salt Range, they unanimously declare the Salt Range Formation to be Eocambrian (Yeats et al. 1984, Butler et al. 1987, Jaumé and Lillie 1988, Baker et al.
1988, Pennock et al. 1989, McDougall and Khan 1990). One paper (Butler et al. 1987, p. 410) mentions discoveries of wood fragments in the salt deep in the mines at Khewra. The authors propose these are intrusive, but neglect to discuss the extensive reporting by Sahni and others ruling out such an explanation for the microfossils discovered in various kinds of rock from the Salt Range Formation.
Discussion
In the early stages of the debates about the nature and age of the Salt Range Formation, fossil evidence did not play a major role. Geological considerations dominated the discussion. With the introduction of paleobotanical evidence by Sahni and others in the 1930s and 1940s, the Salt Range controversy became interesting from a paleontological perspective. Sahni, along with his coworkers and supporters, believed that microfossils of advanced plants and insects, along with a few plant macrofossils (pieces of wood and leaf imprints), indicated an Eocene age for the Salt Range formation. They explained the presence of the Salt Range Formation below undisputed Cambrian beds (the Purple Sandstone, the Neobolus beds, the Magnesian Sandstone, and the Salt Pseudomorph Beds) as the result of a massive overthrust.
Advocates of a Cambrian age for the Salt Range Formation challenged Sahni’s conclusions on two fronts.
First, they argued that the plant and insect fossils must have been intrusive. But even these opponents acknowledged it would be difficult to explain how such fossils could have intruded into resistant rock such as the oil shales found in the Salt Range Formation. Overall, it seems there is fairly good evidence for the presence of microfossils and even some macrofossils in the Salt Range Formation. Sahni and his coworkers presented good arguments against possible contamination of their rock samples, either in situ or in the laboratory.
Second, the advocates of a Cambrian age for the Salt Range Formation argued against Sahni’s hypothesis of a massive overthrust, that covered the Eocene Salt Range Formation with Cambrian formations. Opponents disputed the overthrust hypothesis, citing signs of normal contact between the Salt Range Formation and the overlying beds. Modern geological opinion partly favors Sahni. There is evidence of thrust faulting in the Salt Range. But modern geological opinion is also unanimous in assigning the Salt Range Formation to the Eocambrian.