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Abor Volcanic Formation
Click to display on map of the Ancient World at:
Abor Volcanic Fm base reconstruction

Abor Volcanic Fm

Period: 
Permian

Age Interval: 
Lower Permian


Province: 
Arunachal Pradesh

Type Locality and Naming

Arunachal Pradesh, AborVolcanic Series of Coggin Brown, 1912 is first recorded from the Siang valley and were compared with the Rajmahal Trap of the Indian shield. [Original Publication: Coggin Brown, 1912. A geological reconnaissance through the Dihong Valley, being the geological results of the Abor Expedition (1911-1912). Records Geological Survey of India, v.42(4), pp.231-264.]


Lithology and Thickness

Volcanics. Volcanic rocks comprise basalt, andesite, acidic tuffs, lapillis and conglomerate. Sediment horizons are limestone, olive green phyllite/slate and shale. Its thickness is about 5-10 m.; but Chung & Ali say "up to 1500 m thick".


Lithology Pattern: 
Volcanics


Relationships and Distribution

Lower contact

Conformable contact on the underlying Bhareli Fm. However, Ali et al. (2012) note that as of 2012: " However, at no stage have contact relations of any sort – stratigraphic or tectonic – been demonstrated with Abor Volcanic units"

Upper contact

Unconformably overlain by Yamne Fm. [NOTE by Jim Ogg: Maybe a hiatus spanning at least the Middle Permian, based on ages assigned to Abor Volcanics and to the Yamne Fm.]

Regional extent

Exposure mainly in Siang Valley "window" (ca. 27.9-28.8°N, 94.8-95.5°E) in easternmost Lesser Himalayas bound by Main Central Thrust and Main Boundary Thrust. See Chung and Ali (2012): http://www.largeigneousprovinces.org/12apr for overview.

[Figure 1: Simplified geological map of the Siang “window’’ showing the outcrop of the Abor Volcanics (shown in gray – based on Acharyya, 2007). Circled numbers, 1–8, are the exposures sampled in the paleomagnetic investigation. From Chung and Ali (2012; http://www.largeigneousprovinces.org/12apr)]


GeoJSON

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Fossils

Lower Gondwana sporomorphs viz., Cyclograniporites, Suleatispora, triatopocarpites and Vittantina


Age 

Lower Permian based on paleontology of strata above/below. In contrast, on the basis of benthic larger foraminifera in sedimentary rocks interbedded with the Abor volcanic rocks, and age ranging from upper Paleocene to middle Eocene is determined for the entire pocket (Sengupta et al., 1996).

Age Span: 

    Beginning stage: 
Artinskian

    Fraction up in beginning stage: 
0.6

    Beginning date (Ma): 
286.18

    Ending stage: 
Kungurian

    Fraction up in the ending stage: 
0.3

    Ending date (Ma):  
280.62

Depositional setting


Depositional pattern:  


Additional Information

Coggin Brown (1912) correlated the Abor Volcanics with the Rajmahal Trap Fm and erroneously considered them to be Jurassic in age [HOWEVER -- The Rajmahal Trap volcanics are early-Cretaceous]. Gansser (1964) equated them with the Panjal Traps Fm [now known to be of Permian age]. Jain and Thakur (1978) suggested a vague Pre-Gondwana age. Singh and Kumar (1990) see Surendra Singh (1993) suggested Upper Cretaceous to Early Eocene age. See review in Ali et al. (2012; Jour. Asian Earth Sci., 50: 105-115), whose paleomagnetic data indicate a paleolatitude of 73°S (+/- 6°) implying Early Permian. "A number of workers have proposed that the Abor Volcanics formed part of a discontinuous suite of broadly coeval basaltic provinces in Oman, NW India, Southern Tibet and Nepal following detachment of the Cimmerian block from the supercontinent. However, on the basis of stratigraphic, structural and plate modeling considerations, we suggest that the series more likely relates to the extension that was also taking place between India and its southern and eastern neighbors, Antarctica and Australia." (Ali et al., 2012, Jour. Asian Earth Sci., 50: 105-115)

[Figure 2: Distribution of the Abor Volcanic together with several other northern Indian Permian mafic magmatic suites that are exposed in the Himalayan range (from Ali et al., 2012). Note the structural positions of each formation. From Chung and Ali (2012; http://www.largeigneousprovinces.org/12apr)]


Compiler:  

D.S.N Raju