BACTRYLLIUM HEER 1853 FROM THE EJECTA OF MUD VOLCANO, NORTH ANDAMAN 109Journal of the Palaeontological Society of IndiaVolume 59(1), June 2014: 109-111

ISSN 0522-9630

A RARE BODY FOSSIL BACTRYLLIUM HEER 1853 FROM THE EJECTA OF SHYAMNAGAR MUD VOLCANO, NORTH ANDAMAN AND ITS STATUS

TARUN KOLEY

PALAEONTOLOGY DIVISION, EASTERN REGION, GEOLOGICAL SURVEY OF INDIA, BHU-BIJNANABHAVAN DK-6, SECT-II, SALT LAKE KOLKATA -700 091

ABSTRACTBactryllium Heer 1853 has been treated by different authors as a fossil community under diatom, pteropods and faunal excreta. The present investigation

recorded Bactryllium cf. B. canaliculatum Heer 8153 as a group of tubular fossil mass trapped on a lump of sandstone ejected through the mud volcano at Shyamnagar, North Andaman, revealing a different history of faunal affinity altogether. Bactrylluim Heer 1853 sensu stricto conforms to body fossil and its age range can be extended up to Cretaceous from the Triassic.

Keywords: Body fossil Bactryllium Heer, Mud volano, North Andaman

INTRODUCTIONBactryllium Heer 1853 is a little known fossil with an

ambiguity on the status of this genus. The genus Bactryllium Heer 1853 has been systemized by Hantzschel (1966) under the “Trace fossils and Problematica” as noticed in the pertinent section of Treatise on Invertebrate Palaeontology Part (W) and has been treated as body fossil among the genera of doubtful affinity or completely uncertain systematic status. This genus was created by Heer (1853) from the Triassic rocks of Switzerland and North Italy and considered to be a diatom. He diagnosed this genus as small bacilliform bodies, with parallel sides, rounded at either end and the surface traversed by one or two longitudinal grooves. Wall is thick and firm and probably composed of siliceous material, with a hollow interior. Seven species have been figured from the beds of Muschelkalk, Keuper and Rhaetic age under this genus and regarded as a Triassic diatom. Othmar (1940) reported Bactryllium schmidii Heer from the Rhaetian of Voralberg and kept under problemetica. However, Stefani (1882) was in favour of placing Bactryllium among the Pteropods instead of diatoms. Allasinaz (1968) in his review placed this genus under ichnofossil and interpreted it as excreta of gastropods. In the present note, the forms collected from North Andaman have been identified as Bactryllium sp. cf. B. canaliculatum and a comment has been made regarding its status and age range with possible justification.

MATERIALThe mound formed by the ejecta of the mud volcanos of

Shyamnagar (Lat. 13°24’34”N, Long. 92° 53’ 35”E), North Andaman is strewn with fragments of fine-grained hard sandstone. The sandstone fragments bear well-preserved ichnfossils viz. Planolites spp. and Thalassinoides spp. One specimen of dark grey, fine-grained, weakly calcareous sandstone collected from mud volcano mound was found to contain the cluster of numerous bacilli-form tube like structures (Fig. 1) identified as Bactryllium Heer 1853. The studied specimen is preserved in the repository of the Palaeontology Division, Eastern Region, Geological Survey of India, Kolkata.

DESCRIPTIONGenus Bactryllium Heer, 1853

Bactryllium sp. cf. B. canaliculatum Heer 1853(Figs. 2-3)

This species occurs as elongated, flattened, straight to slightly curved tubes with haphazard alignment and frequent crossover (Fig. 2). Individual tubes are tapering at one end and often flattened (Fig. 3). Thick wall is made up glossy opaline material. Raman spectroscopy of the wall material confirms that the wall is made up of siliceous material. Structurally, the material is similar to chrysoprase or chalcedony (Fig. 4 a, b, c). Length of individual tube varies from 0.5 cm to 2.5 cm and width from 3mm to 6 mm. Longitudinal furrow is present along the full length of the individual tubes. In cross section, the tubes are elliptical to circular in outline with a narrow central cavity. The wall is thick compared to the width of the central cavity. Faint transverse striations which are widely spaced, are noticed at right angles to the longitudinal axis of the tube.

Fig. 1. Photograph of the specimen showing cluster of bacilliform structures of Bactryllium.

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Fig. 2. Photomicrograph of the cluster of Bactryllium sp. cf. B. canaliculatum; scale bar represents 2mm.

Fig. 3. Photomicrograph of Bactryllium sp. cf. B. canaliculatum showing median furrow and transverse striations; scale bar represents 1mm.

Fig. 4. a, Raman spectroscopy of the wall material with the peak value at 465; b, comparison with chrysoprase ; c, comparison with chalcedony.

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REMARKSThe present species is distinguishable from other six species

in having longer tubes, widely-spaced, faint transverse striations, and single principal medial furrow.

There is only one reported occurrence of this genus from India from the Lower Triassic rocks of Khrew, Kashmir Himalaya. Agarwal (1988) tentatively identified the two species of Bactryllium Heer 1853 and interpreted them as excreta of pelecypods. His description and illustration of the chambered forms does not match with that of the Bactryllium Heer 1853 sensu stricto. Moreover, he did not indicate the nature of wall structure in his description, while Heer clearly described the wall as composed of silica which is also clearly noticed in the present specimens of the species. Examination of the figures given in his paper reveals that the forms reported by him may be excreta of pelecypods but not Bactryllium sensu stricto.

Interestingly, Bactryllium has often been recognized as algae in algal database (Guiry and Guiry, 2014). Many workers have interpreted Bactryllium as coprolite – fecal excreta /pellets of gastropods or crustaceans. Most of the authors have overlooked the nature of the siliceous composition of the wall. Study of the present specimen collected from North Andaman indicates that it is very unlikely that the forms belong to diatoms because the present species does not contain any morphological feature of diatom except the siliceous wall without any pore structure. Considering the specimens in terms of coprolite is also improbable as the wall is purely opaline in nature. Therefore, it is reasonable to consider Bactryllium Heer 1853 as a siliceous body fossil of uncertain affinity.

Bactryllium Heer 1853 is mostly reported from the Triassic and Jurassic rocks. There is an inclination towards using this genus as an index fossil. Somma et al. (2009) assigned Carnian age, based on the presence of this genus. In Andaman Island, the oldest rock reported is Cretaceous. The material spewed out from the mud volcanos of Andaman Island have been reported to contain Cretaceous planktonic foraminifers, such as Globotruncana. Therefore, it may be concluded that the age range of the genus Bactryllium Heer 1853 is not confined to

Triassic. Rather, it may be raised up to Cretaceous.

ACKNOWLEDGEMENTSThe author thanks Dr. Amitava Lahiri, Suptd. Geologist,

Geological Survey of India for his critical review of the manuscript and inspiration during its preparation. The author is grateful to Dy. D. G. and HOD, Geological Survey, Eastern Region, Kolkata for giving opportunity to work in Andaman Island. The author acknowledges the co-operation extended by Dr. K. M. Wanjarwadkar, Associate Professor, Aurangabad Institute of Science during the field work. Thanks are also due to Anindya Bhattacharya, Senior Geologist for providing the Raman Spectroscopy analysis of the samples.

REFERENCESAgarwal, P. N. 1988, A record of Bactryllium Heer from the Triassic rocks

at Khrew, Kashmir Himalaya. Journal of Geological Society of India, 31: 495-498.

Allasinaz, A. 1968, Revisione ed interpretazione del genere Bactryllium, Heer. Rivista Italiana di Paleontologia e Stratigrafia, 74(4): 1065–1114.

Guiry, M.D. and Guiry, G.M. 2014. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org.

Hantzschel, W. 1966. Trace fossils and Problematica. In: Treatise on Invertebrate Palaeontology, Pt. W (Ed. Moore, R. C.), Geological Socoety. America and University of Kanssas Press, pp177-244.

Heer, O. 1853. Beschreibung der angeführten Pflanzen und Insekten, p. 115-135. In: Allgemeine Schweizer Gesellschaft für die gesamten Naturwissenschaften (Ed. Escher Von Der Linth, A.), Neue Denkschriften, 13.

Othmar, K. 1940. Mitteilungen des Alpenländischen geologischen Vereines (Mitteilungen der geologischen Gesellschaft in Wien), 33. Band, pp. 111-157.

Somma, R., Martin-Rojas, I., Delgado, F., Estévez, A., Iannace, A., Perrone, V. and Zamparelli, V. 2009. Facies and facies association distribution on the Triassic carbonate platform of the Alpujarride Complex (Betic Internal Zone, SE Spain). Geogaceta, 47: 81-84.

Stefani, K. de. 1882. Vorlaiufige Mittheilung Uber die rhatischen Fossilen der apuanischen Alpen. Verhand. k. k. Geol. Reichsanst. Wien, pp. 96

Manuscript Accepted April 2014

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