Tethyan Sequence Research Articles

Geotraverses through Higher and Tethyan zones of Lahaul and Spiti sector of N-W Himachal and adjoining part of Ladakh Himalaya

Systematic geological cross-sections along traverses of Manali-Leh Highway, Satluj River section, Spiti River section and Pin and Parahio River sections have been sketched in course of expeditional work. An attempt has been made to illustrate the real ground picture visible in the field, keeping as far as possible in mind the vertical and horizontal scales and directional orientation. The extrapolation has been avoided. The profile along the Manali-Leh Highway presents the picture of tectonic contact between central crystalline unit of Vaikrita and thick sedimentary sequence of Phanerozoic with Haimanta Group at the base. Unique features of inverted Mesozoic synform and younger granitic intrusion along the deep fracture have been illustrated. Along the profile of Satluj Valley the Rampur antiform with Precambrian volcanics is succeeded by Vaikrita crystalline of high grade metamorphism ending up with tectonic contact with Tethyan sediments at Khab, sense of movement and intrusive granitic rock-types suggest the nature of visible thrust contact. The profiles along Spiti, Pin and Parahio rivers are very illustrative to confirm the missing carboniferous zone - the conjectural flexure of Hercynian orogenic phase. Profuse disharmonic folding with Triassic horizon and thrust structures with limited displacements within the formations have also been noticed. Structural profiles indubitably confirm the tectonic contacts on either side of the Tethyan sedimentary sequence. Low amplitude thrusting and recumbent folds are sometimes indicative of vivid tectonic phenomenon within the thick pile of deformed Tethyan sequence.

Palynological studies on a late Palaeozoic-Mesozoic Tethyan sequence in the Niti area of the Central Himalaya, Uttar Pradesh, India

The results of a palynological study in eight sections from the Tethyan sequence in the Niti area are reported. The output of plant microfossils is generally poor because of adverse preservational factors. Still qualitative determinations could be made for the Late Permian, the Early Triassic and the Late Jurassic sequences. The palynological compositions, thus identified, have been correlated with well-established fauna in this sequence. The palynoflora bears similarity with that of peninsular India, as described from the Damodar, Rajmahal and Kutch basins, with other regions in eastern Gondwana, and to a limited extent with the Middle East. On the basis of comparisons with the Tethyan sequence in the Niti area, the age of the non-marine Permian-Triassic sequence on the Indian Peninsula has been evaluated; thus the Raniganj Formation is ascertained to be of Late Permian age and the Lower Panchet Formation of Induan (earliest Triassic) age.

Multi-stage development of the southern Tibet detachment system near Khula Kangri. New data from Gonto La

Field observations from Gonto La (southern Tibet), a pass through the high Himalaya, reveal a continuous, planar, ∼10°N-dipping detachment horizon (the Gonto La detachment). The detachment juxtaposes Tethyan dark slates over a footwall of extensive leucogranite of the Khula Kangri pluton, intruded into an injection complex layer regarded as an early Southern Tibet Detachment System (STDS) horizon. The leucogranite emplacement is protracted, and overlaps the STDS development. It is observed to intrude the earlier horizon of the STDS, which is deformed, partially cut by the pluton, and, in the southern part, rotated to a present south dip. Evidence for large scale folding and plutonism is also found east of Khula Kangri at Lhozag-La Kang, where the earlier STDS horizon is inferred. Here it excises the entire Palaeozoic Tethyan sedimentary sequence and is similarly folded. The Gonto La detachment, which cuts the Middle-Upper Miocene Khula Kangri pluton is, in turn, cut by the more steeply N-dipping Dzong Chu fault, demonstrating later N-S extension in this area. We interpret known outliers of Tethyan sequences in Bhutan as klippen, underlain by an early STDS horizon, which provide a more regional illustration of early extension on the STDS. In the Khula Kangri area, early extension was followed by plutonism and local relative uplift, and further N-S extension.

Early Cretaceous radiolarians of the Northeast Indian Ocean (Leg 123: Sites 765, 766 and DSDP Site 261): The Antarctic-Tethys connection

During ODP Leg 123, abundant and well-preserved Neocomian radiolarians were recovered at Site 765 (Argo Abyssal Plain) and Site 766 (lower Exmouth Plateau). Assemblages are characterized by the numerical dominance of a small number of non-tethyan forms and by the scarcity of tethyan taxa. Remarkable contrasts exist between radiolarian assemblages extracted from claystones of Site 765 and reexamined DSDP Site 261, and faunas recovered from radiolarian sand layers, only found at Site 765. Clay faunas are unusual in their low diversity of apparently ecologically tolerant (or solution resistant?), ubiquist species, whereas sand faunas are dominated by non-tethyan taxa. Comparisons with Sites 766 and 261, as well as sedimentological observations, lead to the conclusion that this faunal contrast resulted from a difference in provenance, rather than from hydraulic sorting or selective dissolution. The ranges of 27 tethyan taxa from Site 765 were compared to the tethyan radiolarian zonation by Jud (1992) by means of the Unitary Associations Method. This calculation allows to directly date the Site 765 assemblages and to estimate the amount of truncation of ranges for tethyan taxa. Over 70% of the already few tethyan species of Site 765, have truncated ranges during the Valanginian-Hauterivian. Radiolarian assemblages recovered from claystones at Sites 765 and 261 in the Argo Basin apparently reflect restricted oceanic conditions during the latest Jurassic-Barremian. Neither sedimentary facies nor faunal associations bear any resemblance to what we know from typical tethyan sequences. We conclude that the Argo Basin was paleoceanographically separated from the Tethys during the Late Jurassic and part of the Early Cretaceous by its position at higher paleolatitudes and/or by enclosing land masses. Assemblages recovered from radiolarian sand layers are dominated by non-tethyan species that are interpreted as circumantarctic. Their first appearance in the late Berriasian-early Valanginian predates the oceanization of the Indo-Australian breakup (M11, late Valanginian), but coincides with a sharp increase in margin-derived pelagic turbidites. The Indo-Australian rift zone and the adjacent margins must have been submerged deeply enough to allow an intermittent influx of circumantarctic cold water into the Argo Basin, creating increased bottom current activity. Cold-water radiolarians carried into the Argo Basin upwelled along the margin, died, and accumulated in radiolarite layers due to winnowing by bottom currents. High rates of faunal change and the sharp increase of bottom current activity are thought to be synchronous with possible pronounced late Berriasian-early Valanginian lowstands in sea level. Hypothetically, both phenomena might have been caused by a tendency to glaciation on the Antarctic-Australian continent, which was for the first time isolated from the rest of Gondwana by oceanic seaways as a result of Jurassic-Early Cretaceous sea-floor spreading. The absence of most typical tethyan radiolarian species during the Valanginian-Hauterivian is interpreted as reflecting a time of strong influx of circumantarctic cold water following oceanization (M11) and rapid spreading between Southeast India and West Australia. The reappearance and gradual abundance/diversity increase of tethyan taxa, along with the still dominant circumantarctic species are thought to result from overall more equitable climatic conditions during the Barremian-early Aptian and from the establishment of an oceanic connection with the Tethys Ocean during the early Aptian.

Field relations, petrogenesis and emplacement of the Bhagirathi leucogranite, Garhwal Himalaya

Abstract The Bhagirathi leucogranite forms a series of low-angle en echelon, lensoidal intrusions at the top of the High Himalayan slab in the central Himalaya of Garhwal, northern India. The leucogranite comprises the assemblage: K-feldspar + quartz + plagioclase + tourmaline + muscovite ± biotite ± garnet. Compared to other High Himalayan leucogranites it is particularly rich in tourmaline. The granite is generally compositionally homogeneous although it is magmatically banded in both the upper and lower portions. The Bhagirathi leucogranite is situated structurally above the kyanite and sillimanite gneisses of the Vaikrita Group which, in turn, overlie the north-dipping Main Central Thrust zone of inverted metamorphic isograds. A pegmatite — aplite leucogranite sill and dyke swarm is present around the margins of the leucogranite. Vaikrita Group gneisses below the leucogranite contain a pronounced northeasterly component to generally randomly orientated mineral stretching lineations. This reflects localized reorientation of early, coaxially constrained, mineral growth by later, non-coaxial deformation. Various shear criteria in the gneisses immediately below the granite document the existence of a major zone of ductile NNE-SSW-directed extension across a northeastward dipping, low-angle normal fault zone. The top of the 1500–1800 m thick leucogranite sheet exposed on the peaks of Bhagirathi, Shivling and Thalay Sagar are intrusive into Martoli Formation metasediments of the Tethyan sequence which locally contain andalusite and staurolite. The roof complex shows numerous stoped blocks, xenoliths and elongate rafts of host rock in the top 100 m together with an extensive zone of layer-parallel leucogranite veining. The northward-dipping Bhagirathi leucogranite was intruded syn-tectonically during the ductile to brittle transition and has been deformed into linked, en echelon bodies within the extensional shear zone at the interface between the Vaikrita Group gneisses and the Tethyan sedimentary cover. The long axes of the leucogranite lenses lie parallel to the y-z plane of the finite strain ellipsoid for this extensional duplex. During extension, sub-orthogonal dilatational forces exceeded sub-horizontal shear stresses thus facilitating the repeated emplacement of sheeted granite melt, a process analogous to low-angle tension gash development. The final emplacement level in the crust must have been ultimately controlled by the density contrast between melt and country rocks, the thermal blanketing of the Tethyan sedimentary cover, and the extensional stress field along the top of the High Himalayan slab.

Palynological studies of the Tethyan sequence in Malla Johar area, Kumaon Himalaya, India

The sediments ranging from Palaeozoic to Mesozoic in the Tethyan sequence of Malla Johar were palynologically analysed. In spite of ill-preservation, a significant assemblage has been recovered from the Upper Permian to Jurassic comprising 35 genera and 45 species of pollen and spores and a number of fungal as well as other alete forms. The Devonian sediments have also yielded a characteristic assemblage of Chitinozoa. The miospore assemblages show a general resemblance with the constituents of the corresponding miofloras known from Peninsular India. The comparisons with other miofloras indicate a Gondwana affinity rather than the Angarian resemblance.

The Permian faunal succession in New Zealand

Abstract The New Zealand succession spans the full length of the Permian, and unlike that of most areas of the world, is almost entirely marine, with faunas ranging from Sakmarian to topmost (Tatarian) Permian. The Lower Permian is correlated by brachiopods, bivalves and gastropods with faunas of Queensland and New South Wales, and the Upper Permian by brachiopods, an ammonoid, and fusulinids with Tethyan sequences of south and east Asia.