South Tethyan Margin Research Articles

Radiolarian evidence for the stratigraphy and palaeo-oceanography of the deep-water passive margin of the Indian Plate (Karamba Formation, Indus Suture Zone, Ladakh Himalaya)

New radiolarian biostratigraphical information sheds light on the Mesozoic sedimentary, tectonic and palaeoceanographic evolution of a south-Tethyan margin in northern India. Radiolarian cherts studied here form part of deformed deep-water successions within the Indus Suture Zone (Ladakh Himalaya); these are defined as the Karamba Formation and interpreted as the stratigraphically higher and palaeogeographically more distal parts of a passive margin (Lamayuru Group). This formation includes radiolarites, pelagic carbonates, redeposited limestones, ferruginous shales, sandstones, and abundant mafic extrusive rocks.Radiolarian assemblages of early and late Middle Jurassic, mid-Cretaceous (mid-Albian to Cenomanian) and Late Cretaceous (Santonian) age were obtained from four measured sequences. Results indicate: (i) long, intact Jurassic-Cretaceous successions, rather than disrupted mélange, are present in the Karamba Formation; (ii) extensive basic volcanism took place during the Middle Jurassic and can be correlated with an extensional phase affecting the NW Indian continental margin; (iii) non-calcareous radiolarian-rich sediments accumulated during the Middle Jurassic, reflecting the influence either of a broad Jurassic equatorial upwelling zone, or a more localised coastal upwelling system.After drowning of the Zanskar clastic shelf in the late Albian, sedimentation on the distal shelf and upper slope was restricted by bottom current activity. Late Albian-Cenomanian radiolarites of the Karamba Formation are contemporaneous with stratigraphie gaps and glauconite-phosphorite deposition on the Zanskar shelf. A well-developed eastward boundary current off the northern margin of India may have persisted until near the end of the Late Cretaceous. During the late Albian-Cenomanian, current activity and coastal upwelling were probably strong and radiolarian-rich sediments accumulated on the distal margin beneath the CCD. Pelagic limestones accumulated during the Turanian over the entire margin, possibly related to eustatic sea-level rise and consequent reduction in bottom current activity. Intense oceanic circulation apparently was renewed during the Coniacian-Santonian, as indicated by sedimentary hiatuses in the Zanskar shelf succession and accumulation of carbonate-free radiolarian ooze in the Karamba Formation.

Upper Triassic reefs of the Oman Mountains: Data from the South Tethyan margin

The Upper Triassic reefal limestones of the Oman Mountains were investigated with respect to their microfacies, palaeontology and community structure. The reef fauna described and figured for the first time occurs in parautochthonous slope deposits of the Arabian platform (Sumeini Group) and in allochthonous reefal blocks (‘Oman Exotics’, Hawasina Complex). The ‘Oman Exotics’ are tectonically dislocated blocks, derived from isolated carbonate platforms on seamounts in the Hawasina basin or in the South Tethys Sea.

Late Jurassic Transgressive-Regressive Facies Cycle on the South European Tethyan Margin at the Start of the Thermal Subsidence: ABSTRACT

Late Jurassic Transgressive-Regressive Facies Cycle on the South European Tethyan Margin at the Start of the Thermal Subsidence: ABSTRACT

Découverte de Pseudoclydoniceras (Ammonitina), genre callovien d'origine arabo-malgache, sur la marge nord téthysienne: Signification paléobiogéographique

For the first time, a specimen of Pseudoclydoniceras of arbian-malagasian origin is found in the Early Middle Callovian of the North Tethyan margin. The interpretation of this discovery takes into account the historical context of successive waves of immigrants coming from South-East in the north-western part of the Tethys, during the Middle Jurassic. The late representative of the Thamboceratinae was able to separate away from the arabian-malagasian immigrants, arriving probably via the North African shore of the south Tethyan margin, by the extension of shallow water platforms as a result of the Callovian eustatic transgression.

The geodynamic evolution of the South-Tethyan, margin in Zanskar, NW-Himalaya, as revealed by the Spongtang ophiolitic melanges

— The composite nappe of the Spongtang ophiolite is thrust over Mesozoic and Cenozoic sediments of the North-Indian margin and shelf. The ophiolitic peridotiles tectonic-ally overlie a sedimentary melange, the detailed stratigraphy of which reveals the evolution of the South-Tethyan margin from its opening to its closure. The matrix of the melange is dated as Upper Campanian to Lower Eocene. Volcano-sedimentary olistoliths indicate carbonate platform sedimentation associated with alkaline lavas in the Permian, followed by more pelagic sedimentation of Upper Triassic and mid- Cretaceous age. They derived from external platforms near to the Indian shelf, but separated from it. Composite olistoliths of mid to late Cretaceous age, containing Permian elements, are found in the upper Cretaceous to lower Eocene wildflysch. Primary contacts of melange upon serpentinites indicates that the deeply eroded oceanic crust served partly as a substratum for the melange.

Stratigraphic evidence for crustal thickness changes on the southern Tethyan margin during the Alpine cycle

Passive continental margins must be viewed as tectonically alive; they undergo thinning, subsidence, and possibly extension, and their form influences and is influenced by the pattern of the overlying sedimentary cover. Mesozoic and lower Tertiary carbonates deposited on the South Tethyan continental margin during opening of the central Atlantic and Tethys Oceans carry a useful record of subsidence. Since a very large area subsided for more than 150 m.y. with apparently no tectonic activity other than normal faulting, the subsidence was probably an isostatic response to crustal thinning. Isostatic considerations, using reasonable densities, indicate that crustal thickness t′ c at a particular time is given by t′ c = t c − 4.6 t′ w − 1.8 t′ s , where t′ c is the original crustal thickness, and t′ w and t′ s are the water depth and sedimentary thickness, respectively. Calculations based on Apennine Stratigraphic sequences indicate thinning of the Italian continental crust by approximately 40% beneath pelagic basins and 20% beneath carbonate platforms. We suggest that this thinning may have been due to extension of the crust resulting from a mechanism, proposed by Bott in 1971, which indicates, that unbalanced lateral forces should be present at the contact between crusts of different thickness, even when they are in isostatic equilibrium. Extension and thinning of the South Tethyan margin affected a belt several hundred kilometres wide; we suggest that this was due to the effect of the Triassic intracontinental rifting that preceded Jurassic oceanic rifting. During the earlier, intracontinental rifting, numerous basins of Newark type were formed, and the associated crustal discontinuities would have provided a number of loci where Bolt9s lateral flow mechanism could have acted. The Apennine crust is now of at least normal thickness, indicating that it has been rethickened; this probably occurred during Tertiary collisional orogeny, as was suggested for the Eastern Alps by Helwig in 1976. An important aspect of Helwig9s re-thickening model is that it removes the need for subduction of large volumes of buoyant continental crust during collisional orogeny.