Calcareous Green Algae from the Umlatdoh . Limestone Belonging to Sheila Formation Oaintia Group) of Southjaintia Hills, Meghalaya, India

The Pa/aeoboianisl 56(2007) 2/-28 003/-0/74/2007 $2.00

Calcareous Green Algae from the Umlatdoh . Limestone belonging to SheIla Formation Oaintia Group) of SouthJaintia Hills, Meghalaya, India

AJANTA SARMA! AND .AN1ITK. GHOSH2'·

I Department of Geology, G C. College, Silchar 788 004, India. 2Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226 007, India. *Email.·[email protected]

(Received 30 August, 2006; revised version accepted 10 October, 2007)

ABSTRACT

Sanna A & Ghosh AK 2007. Calcareol)s Green Algae from the Umlatdoh Limestone belonging to Shel1a Fonnation (Jaintia Group) of South Jaintia Hil1s, Meghalaya, India. The Palaeobotanist 56( 1-3) : 21-28.

Thin section analysis ofUmlatdoh Limestone belonging to Shel1a Fonnation exposed in the southern part of Jaintia Hills yielded well preserved calcareous algae. Detailed taxonomical analyses of the algal fonns reveal the existence ofudoteacean and halimedacean green algae that includes three species of the genus Ovulites Lamarck belonging to family Udoteaceae. One species of Halimeda Lamouroux belonging to family Halimedaceae also has been described in the present paper. Based on the algal assemblage along with sedimentological and micropalaentological observations interpretations on palaeoenvironment and palaeobathymetly have been made.

Key-words-Calcareous algae, Udoteaceae, Halimedaceae, Taxonomy, Palaeoenvironment, Umlatdoh Limestone, Sheila Fonnation, Meghalaya, India.

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INTRODUCTION GEOLOGICAL SETTING

ROM the Palaeogene sequence ofEast Khasi Hills The Jaintia Group of South Jaintia Hills, Meghalya Fof Meghalaya shelf some contributions on is subdivided into two broad divisions, i.e. Sheila calcareous algae have been made by Rao (1943), Pal Formation and Kopili Formation (Murthy et al., 1976). and Dutta (1979), Boruah and Dutta (200I), Misra et The Sheila Formation is the lowermost lithounit ofthe al. (2002), Ghosh (2003), Gogoi et al. (2003). Jaintia Group. The Palaeogene carbonates exposed However, till date there is only one record ofcalcareous along the southern fringe ofMeghalaya Plateau belong algae from the Palaeogene carbonates exposed along to the Sheila Formation (Jaintia Group) and represented the southern fringe ofMeghalaya Plateau belonging to by three sandstone units in alternation with tlu'ee Sheila Formation ofJaintia Group (Sarrn

IOW'II (Biswas, 1992). Thin section analysis of the samples collected from the study area (Figs 1-2; PI. 1.1,2) yielded green algal forms, which are systematically Fig. i-Location map of the study area. described as follows. SARMA & GHOSH-CALCAREOUS GREEN ALGAE FROM SOUTH JAINTIA HILLS, MEGHALAYA, INDIA 23

lAUE STAGE -EITHOSTRATI(;RAPHIC L1THOCOLUMN Penicillus in their morphology and ecology. Segments UNIT of Ovulites were compared with the Recent species of I i I NA'RPUH SANDSTONE :::::::.::0::::::::':' :':T:::::::::::::: the genus Penicillus, e.g. P arbuscula Montagne and ..... , ..,, .. ,, ., , . '" ~ some other species of Penicillus (Massieux, 1966). !2~8 1--- -- lj ~ :3>- Dragastan et al. (1997) opined that the species of

53 z -( UML,\TOOII LIMESTONE Ovulites are morphologically velY close and sometimes > «...J identical to those of the recent species ofPenicillus. < ~ '" >- I. ,\ KMJONG SA 1'-I)SI\lNI· ::is:::/:·.;:·····.4::: Ovulites morelletti Elliot, 1955 UJ..J <: )I~~ t: trl z < t-:s ...J ::: .?::::·~~/·~~··~····.:;···LJ:·:(PI. 1.3-5) ~ '--L 8:>Miliolids c::> Nummulitids ~ Algae 1955 Ovulites morelletti Elliot, p. 126-127, pI. - Coal seam.:lifl2 Current bedding 1, figs. 4-6. 1989 Ovulites morelletti Elliot-Kuss & Leppig, Fig. 2-Lithostratigraphy and Lithocolumn of the studied p. 323, figs 10 f, g. section (Figure not to scale). 1993 Ovulites morelletti Elliot-Kuss & Herbig, p. 277, pI. 5, figs 9, 12. SYSTEMATICS Description-Segments ofthallus are club shaped, elongate, measuring 1.18 to 2.0 mm in diameter (D) The systematics ofthe order Bryopsidales followed and 0.65 to 0.72 mm in height (H). The segments are here has been adopted from Silva et al. (1996), Littler crossed by a hollow medullary space/cavity measuring and Littler (2000), Dragastan et al. (1997) and Hillis 0.48 to 0.63 mm in diameter (d). Cortical region finely (1984,1991,2001). perforated with straight and radial pores measuring 15 ~20~m. ' Division-CHLOROPHYTA Remarks-Ovulites morelletti described here are akin to those ofKuss and Herbig (1993) illustrated (pI. Class-BRYOPSIDOPHYCEAE Round 1963 5, figs 9,12) from the Thanetian-I1erdian limestones of NE Egypt. Ovulites morelletti has been frequently Order-BRYOPSIDALES Schaffiner 1922 reported from the Palaeocene ofIraq (Elliot, 1955) and Egypt (Kuss & Leppig, 1989). Suborder-HALIMEDACEAE Hillis-Colinvaux 1984 Ovulites arabica (Pfender, 1938) Massiex, 1966

Family-UDOTEACEAE Endlicher 1843 emend, (PI. 1.6) Agadh 1887 1938 Griphoporella arabica-pfender in Moret, Genus-oVULITES LAMARCK 1816 p. 69-70, figs 5-8. 1966 Ovuliles arabica (Pfender) Massieux, p. Remarks-Morphology of the fossil segments of 240-243, table 1. the genus Ovulites Lamarck is very closely comparable 1968 Ovulites arabica Pfender-Elliot, p. 51, pI. to the Recent genus Penicillus. According to Elliot 12, figs 1,3. (1978) species of Ovulites known from Cretaceous 1989 Ovuliles arabica (Pfender)-Massiux-Kuss to Eocene Period resemble the Recent species of & Leppig, p. 323, fig. lla. 24 THE PALAEOBOTANIST

1991 Ovulites arabica (Pfender)-Herbig, p. 33, Description-Thallus segments are typically oval pI. 8, fig. 5. to pear shaped in outline. Outer diameter (D) of the 1992 Ovulites sp.-Radoicic, pI. 8, fig. 10. segments measure 1.45 to 1.65 mm and height (H) of 1993 Ovulites arabica (Pfender)-Kuss & Herbig, the segments are 0.8 to 1.15 mm. Segments are crossed p. 277, pi. 5, figs 10,13-14. by large medullary hollow measuring 1.25 to 1.35 mm 2002 Ovulites arabica (Pfender)-Dragastan & in diameter (d) and 0.65 to 0.95 mm in height. The Soliman, p. 12, 14, pI. 4, figs 1-6. medullary hollow is infiltrated with a lower layer of 2006 Ovulites sp.-Sanna & Ghosh, p. 1280, fig. micrite that settled down on the cavity floor and the 3k. upper part is filled with sparry calcite resembling geopetal stmcture. The cortical layer is considerably Description-Segments are club shaped to oval thick measuring 85 to 125 ~m in width. The cortex is in outline, measuring 0.84 mm in diameter (D) and pierced by tiny primary canals/siphons having a more crossed by a large hollow medulla measuring 0.68 mm or less unifonn width of20 to 25 ~m. in diameter (d). Medullary hollow spacei.s filled with rrucrocrystalline and sparry calcite. Cortical wall is thinly Comparison--Dwing to somewhat oblique nature calcified measuring 70 to 85 ~min width and perforated of the section, the presently described species is not by perpendicularly crossed tiny primary cylindrical confidently assignable to any known species ofthe genus siphons/canals having more or less constant diameter vulites Lamarck. The taxon described here as of 18 to 20 ~m.The cylindrical siphons/canals have a Ovulites sp. is comparable to three known species of tendency to increase in diameter towards the distal end. the genus Ovulites, viz., 0. arabica, 0. margarilUla Remarks-Pfender (1938) first described and 0. PYriformis. The presently described fonn is Ovulites arabica (=Griphoporella arabica) from the comparable to 0. arabica and 0. margaritula by the Lower Eocene of Morocco. Later on, Pfender (1940) oval shape of thallus segments. However, 0. arabica described the taxon from the Middle Eocene of Egypt is readily distinguishable from the present one in having and Syria. 0. arabica has also been recorded from thin cortical walls that is pierced by primary cylindrical the Palaeocene of Egypt (Kuss & Leppig, 1989) and siphons that possess a tendency to increase in diameter orocco (Herbig, 1991). 0. arabica has been noticed towards the distal end. On the other hand, unlike the by Kuss and Herbig (1993) in the late Paleocene and present species tangential section of the cortical layer early Eocene limestones of Egypt. Our specimens also of 0. margaritula shows a regular Intercalary resemble 0. arabica described by Dragastan and deposition of siphon rows (Dragastan & Soliman, Soliman (2002) from the early Eocene limestones of 2002). Occasionally the pearshaped outline ofthe thallus Dnmka Formation, Egypt. segments of the presently described species is also comparable to 0. pyriformis. But 0. pyriformis differs Ovulites sp. from the other species of the genus Ovulites by its constant pearshape (Kuss & Herbig, 1993). Moreover, (Pi. 1.7-8)

PLATE 1 ) All the figured slides are slored in the Repository of the Department ofGeoiogical Sciences, Gauhati University, Guwahati, Assam, India.

1,2 Wavy bedded limestone in the studied section. 7-8. Ovulites sp., 7. Slide No. AS/L2 5.ld. 8. Slide No. AS/L2 3-5. Ovulites morellelti Elliot. 3. Slide No. AS/L2 5.1 a. 4. 51e Slide No AS/ L2 5.1 b. 5. Slide No.AS/ L2 5 Ie. 9. Halimeda sp. Slide No. AS/L2 5.1 f. 6. Ovu/ires arabico (Pfender) Massiex, Slide No. AS/L2 5.1. SARMA & GHOSH-CALCAREOUS GREEN ALGAE FROM SOUTH JAlNTIA HILLS. MEGHALAYA. INDIA 25

PLATE 1 26 THE PALAEOBOTANIST

in the presently described species the cortical layer is Remarks-Solitary transverse section of the considerably thick in comparison to 0. pyriformis. segment recovered in the present study has been described as Halimeda sp., because based only the Family-HALIMEDACEAE Link 1832 transverse section it can not be safely assigned to any particular species. However, the presently described Genus-HALIMEDA Lamouroux 1812 fonn resembles Halimeda cylindracea Decaisne figured by Dragastan and Soliman (2002, text-fig. 15, Remarks-The most cliversified genus ofthe famjly no. 4). Halimeda segments of similar affinity were Halimedaceae is Halimeda with more than 33 species. reported earlier by Pia (1932) from the Palaeocene of The genus has a wide geological range extending from Morocco and Kuss and Herbig (1993) from the Mesozoic to Recent. In thin section analysis, fossil Thanetian-Ypresian of NE Egypt. Dragastan and Halimeda segments exhibit random cuts through Soliman (2002) included nineteen fossil species (known different regions of the thallus and it is indeed very from late Cretaceous to Pleistocene) ofHalimeda under difficult to distinguish the intraspecific variations. the taxonH. cylindracea Decaisne and considered them Recently, Dragastan et al. (2002) studied the segmental synonymous. morphology of33 Recent species of Halimeda based on the collections of Littler and Littler (housed in SEDIMENTOLOGICAL AND Smithsonian Institution, Washington, D.C.), Hillis MICRO PALAEONTOLOGICAL (housed in Smithsonian, STRI, Panama) and Silva OBSERVATION (housed in University Herbarium, University of California, Berkley). Dragastan et al. (2002) opined Thin section analysis of Umlatdoh Limestone that large number of fossil species of Halimeda shows development of two different lithofacies. The described earlier is based upon insufficient material and lower part of the unit is dominated by grainstone that as a matter offact they re-assessed and re-evaluated grades to packstone and wackestone towards the upper the validity ofnumber ofspecies ofthe genus Halimeda. part. Top part of the limestone is arenaceous at places Study of Dragastan et al. (2002) revealed wide with development ofthin sand beds showing current variations of the segmental morphology of Halimeda bedding. Presence ofcurrent bedding in the intervening species from base to apex. Dragastan and Soliman sandstone, asymmetric ripples in limestone beds imply (2002) recognized three evolutionary lineages arose a shallow water regime during deposition ofUmlatdoh during Mesozoic and early Cenozoic, viz. Halimeda Limestone. The fossil grains occur as framework and cylindracea lineage (Late Triassic-Recent), Halimeda the larger fossi I grains occuras floating grains in a sparry incrassate lineage (Cretaceous-Recent), Halimeda crystalline groundmass towards the lower half and opuntia lineage (Cretaceous/Palaeocene-Recent). towards the upper part the fossils are found to be bounded by microcrystalline calcite. The fossil interiors Halimeda sp. are filled with sparry crystalline as well as microcrystalline calcite. Towards the lower halfgreen (PI. 1.9) algae are dominant. The medullary portion of some Description-Transverse section of the segment Ovulites species is found to be filled in sequential ofthallus more or less circular to spheroidal (measuring episodes with a lower layer of mud (micrite) infiltrated 0.5 mm in diameter) with slight lateral compression. and settled down on the floor ofthe cavity and the upper Possibly the section is fi'om the basal zone ofthe thallus. portion is filled by sparry calcite cement (PI. 1.7,8) Siphons in the medullary region are ill preserved. resembling geopetal structure. The contact between the Filamenis/utricles in the cortical region are well two calcite surfaces marks the bedding surface. The developed, bifurcated, measuring 15 to 25 11m. medullary portions of some Ovulites species are also SARMA & GHOSH-CALCAREOUS GREEN ALGAE FROM SOUTH JAINTIA HILLS, MEGHALAYA, INDIA 27 filled completely by micrite. Replacement by drusy Therefore, it can be concluded that the Umlatdoh sparite through solution and later precipitation is very Limestone Unit was deposited under shallow, tropical common. Both oriented and random thin sections show environment with variable salinity condition. that fossils present as framework grains in Umlatdoh Limestone and is represented by larger foraminifera and Acknowledgements- The authors are thankjitl to Dr N.C. calcareous algae. Two distinct foraminiferal-algal Mehrotra, DirectOi: BS!P, Lucknowfor his permission to cany out this collaborative work. A.K. Ghosh is indebted to associations have been recognized. The lower part is Professor Bruno Granier (Brest Cedex. France) and Professor dominated by larger species of Alveolina, along with Robert Riding (Cardiff U.K.) for their advice and personal few smaller miliolids (Sarma, 2005, 2006) and communications. A. 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