Reconstructing orogens without biostratigraphy: The Saharides and continental growth during the final assembly of Gondwana-Land

A hitherto unknown Neoproterozoic orogenic system, the Saharides, is described in North Africa. It formed during the 900–500-Ma interval. The Saharides involved large subduction accretion complexes occupying almost the entire Arabian Shield and much of Egypt and parts of the small Precambrian inliers in the Sahara including the Ahaggar mountains. These complexes consist of, at least by half, juvenile material forming some 5 million km2new continental crust. Contrary to conventional wisdom in the areas they occupy, evolution of the Saharides involved no continental collisions until the end of their development. They formed by subduction and strike-slip stacking of arc material mostly by precollisional coastwise transport of arc fragments rifted from the Congo/Tanzania cratonic nucleus in a manner very similar to the development of the Nipponides in east Asia, parts of the North American Cordillera and the Altaids. The Sahara appears to be underlain by a double orocline similar to the Hercynian double orocline in western Europe and northwestern Africa and not by an hypothetical “Saharan Metacraton.” The method we develop here may be useful to reconstruct the structure of some of the Precambrian orogenic belts before biostratigraphy became possible.

Checklist of Indian Lebiinae Bonelli, 1810 (Coleoptera: Carabidae)

Distribution patterns and literature details of 263 Lebiinae species reported from India are provided. List includes 14 species missed out by Andrewes (1930a) and the 98 species described thereafter. Distribution patterns revealed among the 263 species, 104 species are exclusively Oriental species and 35 species are exclusively Palaearctic species. Among the 263 Indian speceis, 130 species are exclusively Indian species with reports only from the Indian subcontinent and one species with report only from Andaman & Nicobar Islands. Of the 130 Indian species, 89 species are recorded from the Oriental, 27 species from the Palaearctic and 14 species recorded from both Oriental and Palaearctic regions in India. Among the 129 Indian subcontinent species, 45 species are endemics to the three global hotspots of the biodiversity in India with 31 species endemic to the Western Ghats and Sri Lanka hotspot of biodiversity; six species endemic to the Eastern Himalayas hotspot of biodiversity; eight species endemic to the Indo-Burma hotspot of biodiversity; four species recorded only from Chota Nagpur plateu and 27 species recorded only from Indian Himalayas. Four species (Microlestes parvati, Singilis indicus, S. squalidus and Lebia cardoni) recorded only from Chota Nagpur plateu and the 31 endemic species from the Western Gahts and Sri Lanka are of special interest for their Gondwana relationships. 133 species have wider geographic distribution pattern with 15 species having distribution in Oriental and Indian regions; 8 species having distribution in Palaeractic and Indian regions; 10 species having distribution in Oriental and Indo-Australian regions; 48 species with distribution in Oriental and Palaearctic regions; 29 species with distribution in Oriental, Indo-Australian and Palaearctic regions; 2 species with distribution in Oriental, Australian and Palaearctic regions; 6 species with distribution in Oriental, Palaearctic and Afrotropical regions; 9 species with distribution in Oriental, Indo-Australian, Australian and Palaearctic regions; and 6 species with random distributions in different regions. Distribution records indicate that the arrival/origin of 228 species- 137 species with wider geographic distribution outside India and the 91 species with Indian distribution and not endemics to the Western Ghats and the Chotanagpur Plateau- is likely to have occurred after the joining of Indian subcontinent with Asian continent and during the subsequent faunal exchange between the newly formed Indian subcontinent and the surrounding regions (Indo-Burma and Indo-China on the north east front; Mediterranean and Ethiopian regions on the north-western front; Central Asian elements on the northern front). These 228 species represent the younger Indian Lebiinae species compared to the 35 species representing the older/ancient species with Gondwana land origin. Key words: Carabidae, Lebiinae, Perigonini, Pentagonicini, Odacanthini, Cyclosomini, Lebiini, India

Contributions of the Geological Survey of India, 1851-1890, to the Concept of Gondwána-Land

In 1864, Sclater proposed a Tertiary continent connecting Africa, Madagascar, and the Mascarene Islands, off of the southwest coast of India, to explain the distribution of small mammals. His ‘Lemuria’ was superseded among biogeographers by Wallace's land bridges in 1876. The notion of an ancient continent of Gondwána-Land had a different intellectual lineage. It grew as a paleogeographical idea from the fieldwork and paleontological studies of the Geological Survey of India (GSI) in the 1850s, 1860s, and 1870s and proved to be durable, albeit with different configurations, over the last century and a half. Initially, the Gondwána rocks were termed Raniganj Series, Talchir Series, and so on, after the great coalfields in India, but in the 1870s they were consolidated into the Gondwána Series and then Gondwána System. At the same time, the GSI scientists posited a continent of Gondwána age rocks stretching from Africa across India and on to Australia. In 1885, Suess proposed a more limited Gondwánan-aged Indo-African continent, mostly similar to Sclater's Lemuria, which he named Gondwána-Land. Suess's construct also included a tectonic component that the GSI's landmass did not. But it was not the vast continent in terms of its size that the GSI people had envisioned, which, in time, Suess would also acknowledge. In 1890, William Blanford, a central figure in the GSI part of the Gondwána story, reviewed and expanded the concept of the continent to South America, based on Neumayr's 1887 work, and suggested an Antarctica involvement. Curiously, however, some historians and geologists have overlooked the work that preceded Suess and have credited Suess with the entire idea.

The Chicanery of the Isthmian Links Model

Two papers, ‘Gondwana land bridges’ by Charles Schuchert and ‘Isthmian links’ by Bailey Willis, were published together in 1932. They were apparently motivated by Schuchert's desire to defend his paleogeography of fixed continents against the threat of Alfred Wegener's continental mobilism. Schuchert and Willis both held to land-bridge theory but admitted that they could not accept each other's types of bridges. Schuchert insisted that some bridges had to be wide and of continental material, without explaining why he felt this was so. Willis insisted that wide continental bridges were isostatically and volumetrically impossible; so any ancient bridges that had sunk must have been narrow isthmuses of dense oceanic rocks. They wrote separate papers, but issued together, perhaps to lead readers to the impression that a compromise was possible; but it was not. They avoided alerting readers to fatal flaws in both their models, in part by limiting their discussion to the less familiar southern hemisphere (Gondwana) and never mentioning the continental connection between Europe and North America. Willis went further in his inventions than Schuchert, trying to explain the extremes of Permian climate. Fixed-continent paleogeography required glacial conditions at equatorial latitudes and tropical conditions at arctic latitudes. We now understand that these climate differences can only be explained by ‘continental drift’ (or plate tectonics), but in his valiant effort to support fixism, Willis postulated not only tectonic uplifts of oceanic isthmuses, but also uplifts in continental areas that were known to be stable.

Allochthonous terrane processes in Southeast Asia

Southeast Asia comprises a complex agglomeration of allochthonous terranes located at the zone of convergence between the Eurasian, Indo-Australian and Philippine Sea plates. The older continental ‘core’ comprises four principal terranes, South China, Indochina, Sibumasu and East Malaya, derived from Gondwana-Land and assembled between the Carboniferous and the late Triassic. Other terranes (Mount Victoria Land, Sikuleh, Natal, Semitau and S.W. Borneo) were added to this ‘core’ during the Jurassic and Cretaceous to form ‘Sundaland’. Eastern Southeast Asia (N. and E. Borneo, the Philippines and eastern Indonesia) comprises fragments rifted from the Australian and South China margins during the late Mesozoic and Cenozoic which, together with subduction complexes, island arcs and marginal seas, form a complex heterogeneous basement now largely covered by Cenozoic sediments. Strike-slip motions and complex rotations, due to subduction and rifting processes and the collisions of India with Eurasia and Australia with Southeast Asia, have further complicated the spatial distribution of these Southeast Asian terranes. A series of palinspastic maps showing the interpreted rift-drift-amalgamation-accretion history of Southeast Asia are presented.

PALAEOGEOGRAPHY OF THE AUSTRALIAN PERMIAN IN RELATION TO OIL SEARCH

Aspects of Permian glaciomarine sedimentation in Australia in relation to petroleum generation are treated in the light of the "Gondwana-land" hypothesis and recent studies in palaeolatitudinal distribution of Tertiary oilfields. The Permian segment of the Gondwana (U. Dev. to Trias.) succession is characterised by Glossopteris-Gangamopteris flora, glacial. glaciomarine and glaciofluvial sediments, coal measures and cyclothems.Evolution of the Hunter-Bowen Geosyncline of eastern Australia was accompanied by major volcanic activity along an arc-like archipelago. Sedimentation in this longitudinal ortho-geosynclinal belt linked acrosn the continent via shallow infra-basins and intra-cratonic basins to a series of graben-troughs (Perth, Carnarvon, Fitzroy and Bonaparte) developing about the western margin of Neo-Australia. These latter elongate and generally extremely deep "basins" were early manifestations of, and incipient riftings related to, the embryonic Indian Ocean.The Permian (south) palaeomagnetic pole was located approximately 30 degrees of are west of south from Melbourne, placing Australia in relatively high southern latitudes. Middle to Upper Tertiary oilfields of the Northern Hemisphere on the other hand have been indicated elsewhere to be products of tropical palaeolatitudes from which it has been implied that warm temperatures may be critical in oil formation.Recent investigations indicate that, acre for acre, Antarctic waters are potentially richer in organic life than any other. This is related primarily to abundance of nitrates and phosphates brought into sunlit (20 or more hours per day in summer) waters by upwelling currents. In consequence a high nutrient status of marine waters may be more important than palaeolatitudes in facilitating organic build-up in accumulating sediments. More research into contemporaneous sedimentation in relation to "Antarctic Convergence" in continental shelf settings is undoubtedly desirable.The great variety of Australian palaeo-environments of Permian age includes those of the open sea, continental shelf, hinge-line, barred embayment and alternating marine to fresh water basin. These offer a range of settings favourable to the entombment of organic matter under a variety of conditions presumed favourable to the formation of petroleum source-beds. Encouraging discoveries at Yardarino (W.A.), Gidgealpa (S.A.) and Cabawin (Qld.) justify accelerated exploration for commercial petroleum in the Australian Permian.