Significance of calcareous algae across the Cretaceous­ Tertiary sequence of Cauvery Basin in Tiruchirapalli District, Tamil Nadu

Arnit K. Ghosh, B.N. lana & P.K. Maithy

Ghosh AK, Jana BN & Maithy PK 1997. Significance of calcareous algae across the Cretaceous-Tertiary sequence of Cauvery Basin in Tiruchirapalli District, Tamil Nadu. Palaeobolanisl46 0,2) : 161-167.

Calcareous skeletal algae belonging to Cyanophyta (Cyanobacteria), Chlorophyta and Rhodophyta are known from Uttatur, Trichinopoly, Ariyalur and Niniyur groups of Tiruchirapalli District, Tamil Nadu. An artempt has been made to analyse the algal assemblages across the Cretaceous-Tertiary sequence in Tiruchirapalli District, Tamil Nadu. The distribution partern of algal taxa indicales that there is a gradual change in algal nora from Cretaceous to Tertiary.

Key-words--calcareous algae, Distribution pattern, Cretaceous -Tertiary sequence, India.

Am il K. Ghosh, BN Jana & P.K. Mailhy, Birbal Sahni InslilUle of Palaeobolany, 53 Universiry Road, LucJmow 226007, India. ~ ~ ~ ~ ~ ..R''''5';» ~ R1~f..HtqR'f) ~ it ~ sUuit~ all?;~(l~-~it CliT

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SINCE 1931, calcareous algae have been reported Group and reported 31 species of fossil algae from the Cretaceous-Tertiary sediments of belonging to 17 genera of Cyanophyta (Cyanobacte­ Tiruchirapalli District, Tamil Nadu. Rama Rao and ria), Chlorophyta and Rhodophyta. From the Ariyalur Prasannakumar (932) described Lithothamnium Group, Mamgain et at. (968) have reported from the Kallakkudi (Dalmiapuram) limestone mines Sporoltthon (Archaeoltthothamntum) sp., (Dalmiapuram Formation) belonging to Unatur Lithothamntum sp. and Mesophyllum sp. from south­ Group. Narayan Rao 0944, 1946) reported two new west of Ariyalur town. Porostromata algae consisting species, namely, Solenopora coromandelensisand S. of Rivularta li.~avtensts,R. ptae, R. theodort, Rtvularta jurassica and Rama Rao and Gowda (954) described sp. d. R. dianae and Garwoodta toomeyt have been Solenopora sahnii and Sporolithon described by Ghosh and Maithy (995) from the (Archaeolithothamnium) lugeontt (sensu Ghosh & Cretaceous sediments of Sendurai, Tiruchirapalli Maithy, 1996) from the same beds. Gowda (978) District. Rama Rao (931) reported Sporoltthon recorded Solenopora sp. and Amphtroasp. from the (Archaeoltthothamntum) torulosum from Niniyur Varagapaudy Limestone of Unatur Group. Varma beds. In the classical contribution on fossil algae (952), for the first time, reported the occurrence of from Niniyur Group, Rama Rao and Pia (936) Clypenia sahntt from the Trichinopoly Group of described 11 taxa belonging to Dasycladaceae, rocks. In recent times, Misra and Kumar (988) Chaetophoraceae, Solenoporaceaeand Corallinaceae. investigated the Varagur limestones ofTrichinopolly Rama Rao 0938,1956,1958) described few dasyclads 162 THE PALAEOBOTANIST from the Niniyur Group and reviewed the previous argillaceous limestone and limestone is overlain work done on fossil algae from this group. Varma unconformably by the Garudamangalam Formation 0952, 1954) reported Clypenia, Neomeris and which consists of ferruginous sandstone, grey shale, Acicularia (Dasycladaceae) and Gowda 0953, 1959) limestone and, in turn, is followed by current bedded described Holosporella and Piania niniyurenstsfrom sandstone. TheTrichinopoly Groupis unconformably the Niniyur beds. From the Palaeocene (Danian) of overlain by Ariyalur Group, consisting two sandstone Niniyur Group, Rama Rao and Gowda (1954) reponed bodiesseparated by a limestone. The basal Sillakkudi Solenopora tiruchiensis, and Pal (972) reported Formation of Ariyalur Group comprises ferruginous Sporolithon (A rchaeolithothamnium) arkosicsandstone and limestone bands. The overlying pondicherriensis, S. zonatum and DiStichoplax raoi. Kallankurichi Formation consists of grainstone to In the present paper an attempt has been made to wackestone with LepidorbitOidesbryozoans, echinoid analyse the algal assemblages from different outcrop and molluscan shells. The lower part of the upper areas ofCretaceous-Teniarysequence in Tiruchirapalli sandstone body, composed of megafaunal rich buff District and to ascertain the significance ofcalcareous coloured calcareous sandstone is well developed in algae in biostratigraphy. the central part which is designated as Ottakovil Formation (Sastry et al., 1972). The upper part GEOLOGICAL SETTING comprising argillaceous sandstone and ferruginous claystone ofcontinental origin is known as Kallamedu Cretaceous-Tertiary sediments in the Cauvery Sandstone. The topmost lithohorizon of the Basin,' classified into four groups, viz., Unatur, Cretaceous-Tertiary Sequence, conformably overly­ Trichinopoly, Ariyalur and Niniyur, occur as isolated ing the Ariyalur Group is represented by Niniyur patches outcropping in the western margin fringing Group of Danian age and is characterised by fossil­ the Archaean (charnokite/gneiss) basement. The iferous, white to cream coloured marls and calcareous first geological mapping of the area was carried out clays. by Blanford (862). Later, significant contributions on micropalaeontology and sedimentology (Rama A gem.,

Table 1 Solenoporaceae

OUTCROP AREA SOlenoporafiliformis, S. tiruchiensis, cf. Solenopora AGE GROUP A., P. FORMATION sp. Solenoporasp., Parachaetetessp., asvapatii, Thaumatoporella incrustrata. DANIAN NINIYUR NINIYUR Squamariaceae KALLAMEDU A Sandstone Ethelta sp., E. alba. R I OTTAKOVIL Corallinaceae (Melobesoideae, Crustose J\1AASTRI- Y Corallines) CHTIAJ'l A KALLANKURICHI L Limestone Sporolithon (Archaeoltthothamnium) lugeontt, U S. nonsteinensis, S. pm'tsiense, S. rude, cf. Sporoltthon R SILLAKKUDI ------sp., Mesophyllum sp. cf. M. daviesi, M. varians, cf. CA.l\1PANIAN ------Archaeoltthophyllum sp., Lithophyllum sp. A., GARUDAJ\'IANGALAM Lithophyllumsp. S., cf. Lithophyllumsp., Distichoplax TRICHI- ~------SANTONIAN PARAVAY biseriales. NOPOLY ~------Corallinoideae, articulated coral-lines CONIACIAN MARAVATTUR ------Clay Amphiroa elliotii, A. guatemalense, A. varagurense. TURONIAN ------K C. Algal Assemblage from the Ariyalur group U A CENOMANIAN T R From the Ariyalur Group Rama Rao (931) and T A KALLAKUDDI Mamgain et al. (968) reported the occurrence of ALBIAN A I Limestone T Shale Lithothalnnium. Sporolithon (Archaeolith­ U Grey Shale othamniwn) and Mesophyllum belonging to R APTIAN Conglomerate Corallinaceae (Melobesoideae, Crustose Corallines) of Rhodophyta. Recently Porostromata algae have EARLY been recorded by Ghosh and Maithy (995) from the CRETACEOUS THERANI PLANT Cretaceous sediments (equivalent to Ariyalur Group) LATE BEDS JURASSIC of Sendurai, Tiruchirapalli District. The assemblage ~------consists of the following taxa: ARCHAEAN CRYSTALLINES Cyanophyceae (Cyanobacteria)

Red algae Solenopora belonging to Solenoporaceae Rivularia ltssaviensis, R.piae, R. theodori, Rivularia and Amphiroa belonging to Corallinaceae sp. cf. R. dianae. (Corallinoideae, articulated corallines). Codiaceae B. AlgalAssemblagefrom the Tricrunopoly group Garwoodia toomeyi. Cyanophyceae (Cyanobacteria) D. Algal Assemblage from the Niniyur Group RilJularia sp. cr. R. kurdistanensis, Dasycladaceae Palaeomastigocladus indicus. Acicularia sp., A. dyumatsenae, A. indica, Siphonoc1adaceae Acttabularia sp., Clypenia sahnii, Disocladella sp., PycnopOridium lobatum. D. undulata, D. savttriae, lndopolia satyavanti, Neomeria sp., Orioporella malaviae and Piania Dasycladaceae niniyurensis. Clypeniasahnii, Cylindroporellasp. cf. C. sugdenii, Cheatophoraceae lndopolia sp. cf. l. satyavanti, cf. Larvaria sp., NeomeriS cretaceae. Palaeochlya sp. 164 TIlE PALAEOBOTANIST

Solenoporaceae Rama Rao and Pia (936) expressed their view that Parachaetetes asvapattt, Solenopora ttrucht"ensts. presence of Sporoltthon (Archaeoltthothamntum) lugeonttin the Niniyur Group is indicative ofTertiary Corallinaceae (Melobesoideae, Crustose age, but the taxon is now known to occur· in Unatur Corallines) and Trichinoploygroups (Rama Rao & Gowda, 1954; Sporoltthon (Archaeoltthothamnium) lugeonii, S. Misra & Kumar, 1988). The genus COralltna which is torulosum, Sporoltthon sp. ef. S. lycoperdiotdes, known to be restricted to Tertiary everywhere is Sporoltthon aff. provtnciale, Dtsttchoplax raot. found in the Dalmiapuram Formation of Unatur Group (Gowda, 1978). Eventually, it appears that no Corallinoideae, Articulated coral-lines marker algal taxa in true sense is available to date the Corallina raot. Cretaceous-Tertiary rocks of Tiruchirapalli District. However, from the distribution panern (Table 2) it is DISCUSSION evident that there are certain algal taxa which are signifjcanrIy absent, or present or rich in any particular It is evident from the distribution panern (Table horizon. These are enumerated below. 2) that in the marine rocks of Tiruchirapalli District, many Cretaceous algal taxa extend up to the Tertiary The reefoidallimestone of Kallakkudi Limestone (Danian) time, though apparent extinction of many (Dalmiapuram Formation) and Varagapaudy Lime­ algal forms is also visualised during the Cretaceous, stone belonging to Unatur Group contains algae. accompanied by the appearance of new algal species The algal assemblage from the Dalmiapuram Forma­ in the Niniyur Group (Danian). In view of this tion is significantly devoid of Corallinoideae (Artic­ situation it is difficult to recognise the biostratigraphic ulated Corallines). But the Varagapaudy Limestone zonation on the basis of algal assemblages. Earlier it which occurs at the base of Unatur Group (Gowda, has been implied by Rama Rao and Pia (936) that 1978) contains the articulated coralline red alga algae are most helpful in stratigraphic correlation Amphtroa in association with Solenopora (Sole­ based on index fossils. But recent analysis indicates noporaceae). The laner genus ranges beyondjurassic that it is indeed very problematical to use algae as (Rama Rao & Gowda, 1954; Gowda, 1976) up to biostratigraphic marker mainly because of following Danian (Keijzer, 1945; Rama Rao & Gowda, 1954). two reasons : Majority of the algal taxa described from the 1. the algal taxa which were used earlier as index Varagur Limestone of Trichinopoly Group (Misra & fossils are now proved to be long ranging; and Kumar, 1988) are Upper Cretaceous forms, but some of them are also known from the deposits older than 2. many of the forms which were regarded earlier jurassic, jurassic to Middle Cretaceous and Pala­ as index algal fossils are doubtful as well as eocene to Miocene. controversial and in some cases are considered as animal remains. Rama Rao (931) and Mamgain et al. (968) reported the occurrence of crustose coralline red It may not be out of context to mention here that algae from the Ariyalur Group of rocks. Recently Dtsttchoplax bisertales, which is still considered as Ghosh and Maithy (995) described Porostromata an index fossil for the rocks having Palaeocene­ algae from the Cretaceousrocks ofSendurai belonging Lower Eocene age, is present in the Trichinopoly to Ariyalur Group. According to Rama Rao and Pia Group (Misra & Kumar, 1988). Pal (972) reported (936) the Niniyur algal flora indicates a transitional Disttchoplax from the Niniyur Group (Danian) and position between the Cretaceous and Tertiary. The it is stratigraphically quite justified. However, it Niniyur algal assemblage (Rama Rao & Pia, 1936) is should be mentioned here that validity ofDtsttchoplax rich in well calcified Chlorophyra and coralline as an alga had been questioned by Lemoine (958) Rhodophyra. Majority of the algal species in the and Lemoine 0961-62). They have shown analogies Niniyur Group are new and the preliminary indications between chitinous parts ofliving and fossil Pterobran­ given by their affinities are contradictory. The Niniyur chia belonging to Rhabdopleura, and suggested that Group may be included in the Mesozoic due [0 the Dtsttchoplax should not be considered as an alga. presence of Parachaetetesand absence ofspecialised GHOSH et al.-SIGNIFICANCE OF CALCAREOUS ALGAE ACROSS TIlE CRETACEOUS-TERTIARY SEQUENCE 165

Table 2--Distrlbutlon pattern of calcareous algae

DISTRIBUTION IN DIFFERENT GROUPS TAXA UTTATUR TRICHINOPOLY ARIYALUR NlNIYUR

Clypenia sahnii Neomeris sp. Sporolilhon lugeonii Sporolilhon nonsleinensis Acicularia anriqua Halimeda sp. Laroaria occidenlalis RlVularia frnliculosa Rivularia sp. Solenopora jurassica Solenopora coromandelensis Solenopora sahnii Amphiroa sp. Solenopora sp. A Solenopora sp. B Ampbiroa elliollii Amphiroa gualemalense Am;:,hiroa varagurense Cy indroporella sp. ef. C. sugdeni Rlvularia sp. ef. kurdislanensis Elhelia alba Elhelia sp. lndopolia sp. d. l. saryavanri ef. Laroaria sp. Lilhophyllum sp. A Lilhophyllum sp. B ef. Lilbophyllum sp. Neomeris crelaceae Mesopbyllum sp. ef. M. daviesi Mesophyllum varians Palaeomasligocladus indicus Pycnoporidlum lobalum Solenopora fitiform is Solenopora sp. ef. Solenopora sp. A Sporolilhon parisiense Sporolilhon rnde Tbaumaroporella incrnslala Parachaeleles sp. Dislichoplax biseriales Parachaeleles asvapalii Lilholhamnium sp. Lilhophyllum sp. Mesophyllum sp. Sporolilbon sp. Rivularia sp. ef. Rivularia dianae Rivularia lissaviensis Rivularia piae Rivularia Iheodori Garwoodia loomeyi Acicularia dyumalsenae Acicularia indica Acicularia sp. Acilabularia sp. Corallina raoi Disocladella savilriae Disocladella sp. Disocladella undulala DisliChtfc,lax raoi lndopo ia saryavanri Orioporella malaviae Piania niniyurensis Solenopora lirnchiensis Sporolilhon arf. provinciale Sporolirhon pondicherriensis Sporolilbon sp. ef. lycoperdioides Sporolirhon lornlosum Sporolirhon zonarum Palaeochlya sp.

Melobesoideae in the Niniyu!' assemblage. On the (Archaeoltthothamnium) lugeonii and Ortoporella other hand, presence of Sporoltthon would point to a Tertiary age of the Niniyur Group. 166 THE PALAEOBOTANIST

Therefore, Rama Rao and Pia (936) expressed that Ltthothamntum sp., Mesophyllum sp., Larvarta algae can not play any significant role in the occtdentalts, Rtvularta spp. and Amphtroaspp.) stratigraphi::: zonation in south India. However, the is also noticed from Cretaceous to Tertiary. These authors while discussing the age of Niniyur Group are indicative of the fact that there is a gradual based on fossil algal assemblage stated that the change in algal flora from Cretaceous to Tertiary, Niniyur rocks must be given an age towards the close due to which preponderance of new species is of Upper Cretaceous, for they overlie the Ariyalur visualised in the algal assemblage of Niniyur Group. Group (Danian). A perusal ofthe foregoing discussion reveals that algae can not be used as an important tool to REFERENCES demarcate the KIT boundary. However, a critical Banerji RK 1966. 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