Article

Late Miocene siliceous endoskeletal dinoflagellates from the Sawai Bay Formation, Neill Island, Andaman Sea, India

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Abstract

Siliceous spicules of endoskeletal dinoflagellates form a very small part of the siliceous microfossil assemblage from Neill Island, Ritchie's Archipelago, Andaman Island and Nicobar Island. They are represented here by a solitary genus Actiniscus, with two species - Actiniscus pentasterias and Actiniscus elongatus. Light microscopy, supported by scanning electron microscopy, illustrates its remarkable symmetry and geometry. Though biostratigraphically unimportant, this genus has considerable value in deriving palaeoecological interpretations. Their association with age-diagnostic calcareous nannofossil taxa indicates that the glauconitic mudstones of the Sawai Bay Formation of Nipple Hill and East Coast sections are Late Miocene in age, equivalent to the Discoaster berggrenii Subzone (Subzone CN9A) corresponding to the lower part of the Discoaster quinqueramus Zone (Zone NN11).

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... Since then, a large number of outcrops, stratigraphic sections and Deep Sea Drilling Project (DSDP) cores of the Neogene rocks have been studied although the emphasis for stratigraphic dating has been on foraminifera. Other microfossils that have received less attention include calcareous nannoplankton, coccoliths diatoms and dinoflagellates (Jafar & Singh 1996, 1999Rai 2006). Sharma and co-workers studied radiolaria (Sharma & Srinivasan 2007;Sharma et al. 2011). ...
... The formation consists of a lower mudstone member and an upper limestone member. Rai (2006) documented late Miocene siliceous dinoflagellates from the mudstones that support a late Miocene age. On Neill Island (Fig. 11.6), the eastern and northeastern parts of the island have prominent cliffs comprising glauconitic mudstones ( Fig. 11.7) (Srinivasan & Azmi 1976b). ...
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The geology and stratigraphy of the Archipelago Group are reviewed and new data presented to improve understanding. Major lithofacies are bioclastic limestones, bioturbated mottled marlstones, micritic limestones, trace fossil-bearing mudstones, quartzose sandstones and reworked volcanic material of Mio-Pliocene and Pleistocene age. The succession overlies the Pre-Neogene submarine fan turbidites and tectonic mélanges of ophiolite derivation and Mithakhari rocks, and is overlain by Quaternary deposits of late Pleistocene–Holocene age. The Neogene sequences were deposited in wave- and current-agitated shallow-marine intertidal and relatively deeper-water subtidal, nearshore and offshore shelfal environments. The existing stratigraphic framework is examined and suggestions made for improvement.
... Since then, a large number of outcrops, stratigraphic sections and Deep Sea Drilling Project (DSDP) cores of the Neogene rocks have been studied although the emphasis for stratigraphic dating has been on foraminifera. Other microfossils that have received less attention include calcareous nannoplankton, coccoliths diatoms and dinoflagellates (Jafar & Singh 1996, 1999Rai 2006). Sharma and co-workers studied radiolaria (Sharma & Srinivasan 2007;Sharma et al. 2011). ...
... The formation consists of a lower mudstone member and an upper limestone member. Rai (2006) documented late Miocene siliceous dinoflagellates from the mudstones that support a late Miocene age. On Neill Island (Fig. 11.6), the eastern and northeastern parts of the island have prominent cliffs comprising glauconitic mudstones ( Fig. 11.7) (Srinivasan & Azmi 1976b). ...
Article
Full-text available
The geology and stratigraphy of the Archipelago Group are reviewed and new data presented to improve understanding. Major lithofacies are bioclastic limestones, bioturbated mottled marlstones, micritic limestones, trace fossil-bearing mudstones, quartzose sandstones and reworked volcanic material of Mio-Pliocene and Pleistocene age. The succession overlies the Pre-Neogene submarine fan turbidites and tectonic mélanges of ophiolite derivation and Mithakhari rocks, and is overlain by Quaternary deposits of late Pleistocene–Holocene age. The Neogene sequences were deposited in wave- and current-agitated shallow-marine intertidal and relatively deeper-water subtidal, nearshore and offshore shelfal environments. The existing stratigraphic framework is examined and suggestions made for improvement.
... Endoskeletal dinoflagellates represent a neglected component of the upper Miocene circum-Mediterranean and global diatomaceous deposits (e.g., Bonci et al., 1991;Rai, 2006;Gaudant et al., 2015). Moreover, studies concerning their present-day ecology are scarce (Takahashi, 1991;Onodera et al., 2015), thereby limiting the paleoecological interpretations. ...
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Siliceous spicules of endoskeletal dinoflagellates constitute a very small fraction of siliceous microfossil assemblage from Southern Ocean. They are represented by a solitary genus Actiniscus with its type species A. pentasterias. They are bilaterally symmetrical. It is useful in deriving palaeoecological interpretations. Their association with age diagnostic calcareous nannofossil blooms along-with reworked Palaeogene nannofossils suggest transport of older age plankton laden current from close proximity.
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Siliceous dinoflagellates of the species Actiniscus pentasterias (Ehrenberg) are described from more than 20 outcrops and submarine exposures in the northeast Pacific rim area. Trends in the geographic and stratigraphic distribution of this taxon are recorded with respect to the documented abundance of the siliceous marine microflora in the interval from the Middle Miocene to the Lower Pliocene. Scanning electron micrographs of specimens illustrate the remarkable symmetry and geometry of this little-known group of microfossils.
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