CHAPTER II REVIEW OF PREVIOUS WORK REVIEW OF PREVIOUS WORK A. STRATIGRAPHY The Danish ship *Galathea* during her roxmd the world scientific cruise visited Nicobar Islands in 1840. Based on this visit. Rink, a member of this cruise, published his geological observations in 1847* He classi­ fied the roclcs of Nicobar Islands into three major units in ascending order as follows s 1. The Brown Coal Forma­ tion (found in Katchal and some southern Nicobar Islcinds), 2* Igneous rocks s serpentine and gabbro, and 3. Older Alluviizm (exposed on central and northern Islands of Nicobar)• Though the islands were under the control of British regime, the second scientific expq,dition was undertaken by the Austrian in 1857 in the ship 'Novara*® Hochstetter (1866),‘ the leader of this scientific cruise, ptiblished his observations on the stratigraphy of Nicobar group of islands* Ho opined that the Brovm Coal Formation and the Older Alluvium proposed by Rink (1847) are only the facies variations of one and the same formation* He replaced the term 'Older Alluvium' and introduced the term 'Mari' at its place accortsnodating both the Brown Coal Formation and the Older Alluvium* Ball (1870) studied for the first time rocks of both the Andaman and Nicobar Islands and c"»rrelated the Brovm Coal Pormatlon with sandstone shales alternations near Port Blai.r, Like Hochstetter (1866), he also rejected the term 'Older Alluvium* and preferred to call them as the Nicobar Clay Formation* Mallet (1884) accompanied with captain Hobday visited Barren and Narcondam Islands of Volcanic Origin* Mallet studied the geology of these islands and prepared a large scale geological map# while captain Hobday studied the topography of these volcanic islands®^ Oldham (1885) resurveyed the rocks of Andaman Islands proposing two distinct series for sedimentary formations besides treating separately the intrusives and metamorphics* His basal series was the Port Blair Series having Eocene age while the younger upper sedimentary was named as Archipelago Series assigning the Miocene age to ito He then correlated the Brown Coal Formation with the Port Blair Series and the Nicobar Clay with the Archi­ pelago Series. During the field season 1904-05# Tipper explored the Northern Andaman Islands and visited Nicobar Islands for a brief period* He could not visit Middle Andaman due to ferocious Jarwa tribe inhabiting L.-.sre* As a result. Tipper®s paper (1911) is entirely devoted to the geology of Andaman Islands. He proposed 'six formations in the Andaman as follows i 8 Recent and sub-Recent Raised beaches and coral reefs# etco Miocene Clays of Ritchie* s Archi­ pelago Miocene (Burdigalian) Poramihiferal limestone, shell marls of Paget Island. Eocene (Lower Lutetian) Conglomerates of the Nojrth and Middle Islands#' sand­ stones of the South Islands* Cretaceous Serpentine Series Pre-Tertiary In part Lower Cretaceous* Scattered exposures of quartzites# jaspers and porcellanic limestones* On the basis of fossil contents and lithology he compared these formations with some of the known forma­ tions like Laki# Gaj, etc. Further# he replaced the term 'Archipelago Series* by the ’Archipelago Group*• Besides stratigraphical and geological aspects# Tipper covered other interesting aspects like structure# recent sea level changes and rocks of economic importance* Thus# Tipper* s paper is one of the comprehensive papers on the geology of the Andaman Islands* Gee (1926) accepted the classification proposed by Oldham (1885) and Tipper (1911) with irtinor changes* He subdivided Archipelago Series into a Lower series of grey and greenish clays# argillaceous sandstones vrith shelly limestones and occasional conglomerate# and an upper more recent subdivision of very loosly consolidated saidstones containing fossils* Like Tipper (1911)# Gee also recog­ 9 nised the Older Sedimentaries and considered them to be of Cretaceous aga* On the Wilson Island# Gae noted a Lepido- cyclinO. limestone boulder and assigned a Mid-Tertiary age to it. Narayana Rao (1942) suggested a Late Oligocene or e.n Early Miocene age to the Lepidocyclina limestone# dis­ covered by Gee (1926) on the Wilson Island* Boileau (1950) suggested the Oligocene age for Archipelago Series of Oldham (1885) « He sxibdivided Archi­ pelago Series into three stages# the Lower Arenaceous Stage with some limestones and clays? the Middle Argilla­ ceous Stage with sxibordinate sandstones *Diatomites* and the Upper Interview Island Stage with limestone and sand­ stone* Boileau (op*cit*) first time s3tudied the geology of Baratang Island and named Baratang Formation for the pre-flysch sediments and assigned Juracsic-Cretaceous(?) age for these rocks* Chandra and Guha (1963), geologists from O.N.G.C. subdivided Archipelago Series into four lithostratigra- phic units in ascending order such as j 1* Strait Sandstone Formation, 2* Round Silt and Chalk Formation, 3* Guitar Liniestone and Calcareous Sandstone Formation# and 4* Long Clay Formation* On the basis of forsminifers and ostracodes they assigned a Lower Miecene age (Burdi- galian) to the Strait Sandstone Formation and Pliocene 10 age to the Guitar Limestone and Calcareous Sandstone Forma­ tion*' Pawde and Roy (1964) proposed a ne\j classification for the younger sedimentaries in South Andaman which had been described under Port Blair Series by Oldham (1885). VJithout assigning any specific name, they have preferred dividing the rocks on the basis of lithological diversi­ ties into three divisions assigning them an age ranging from Cretaceous to Recent. They assigned Eocene (Kirthar) age to conglomerates# grit with calc-lutites and calc- arenites and Upper Eocene to Oligocene age to graywacks. Chatterji, A.K* (1964) of the geological survey of India studied the foraminifers of the Tertiary formations of the South Andaman# the Archipelago and the Little Andaman and proposed geological sequence of Andaman Islands as follows : Recent (& Pleistocene ?) Alluvium terraces# raised beaches# wave-cut platform# coral reefs# calcareous tuffa# and shell-limestones of Little Andaman Island. (c) Interview I Stage : sandstone-limestone of Interview I# and Chitamale limestone of Little Andaman I , containing Lepidocyclina sumatrensi s and Operculi- noides niasi with many algae 11 (b) Upper Argillaceous zones with sandstones and clays containing rich assemblages of radiolarians and plank- tonic forarainifera like Orbulina universa# 0. bilobata# Globiqerina spp*# Globigerl- neides spp»» etc. (a) Lower Arenaceous zones Lower^Archipelago with the calcarenite beds of Miocene Series') Little Andaman containing Eulepidina dilatata» Cyclo- clypeus spp»» Miogypsinoides dehaarti/ Orbulina spp./ Giobiqerina spp»# etc. and underlying rich foramini- feral limestones of Havelock Wilson IIs*# western coast of Little Andaman containing Miogypslnoides dehaarti# Mieqypsina irregularis# Cycloclypeus indopaciflcus# S* eidae# C, posteidae# Lepidocycllna martini# L* borneensis# L. dilatataT etc. (?) (c) Graywacke Stage : Unfossiliferous graywackes Formerly reported as sand­ stones and shales* The age may range from upper-Middle Eocene to Oligocene (?) (b) Grit Stage : coarse­ Bocene(Port Blair grained grits; may be termed (S« Oligocene ?) Series) as sub-graywackes; contain Assillna papillata# Nummu- lites atacicus# N* sxjb- atacicus# Discocyclina sp.» arid a few gastropods and lamellibranchsa The assemblage confirms a Kiirthar age for these beds* (a) Conalbmerate Stage : boulder of older rocks v/ith fine to coarse-grained matrix containing A*daveisi# confirms the Laki age for 12 this stage. Among the older boulders, a Palaeocene limestone boulder is also met with. Palaeocene (Ranikot) : This has been noted only as a boulder in Laki Con­ glomerates* This is a hard limestone containing Disti- choplax biserialis and ” Rotalia trochidiformls. Prs-Tertiary formations : Basic and ultrabasic (Cretaceous-Jiirassic 7 ) intrusives with radiolarian cherts and metamorphosed sediments like marble, silicified shales# quartzites# porcellanic limestones, etc* Thus, ha subdivided both the Port Elair Series and Archipelago Series into three subdivisions as shown in the table* Chatterjee, P*K. (1967) of 0*N.G.C* proposed following stratigraphic sequence* Pleistoceno Swampy mud flats, coral £c Recent rags and raised beaches — -— Unconfonrdty---- Archipelago Long Clay Formation 200 ft* Guitar Limestone Formation 1500 ft. Neogene Group U nconf oirraity (Mio-Pliocene) Round Chalk & Silt Formation 2000 ft. Strait Sandstone Formation 1700 ft* unconfortnity--- - 13 U. Eocene-(?) P©rt Blair Formation Oligocene 2500 ft* Unconformity — Palaeocene Igneous Series — — Igneous contact U* Cretaceous- Baratang Formation Palaeocene 4500 fte -- — Unconformity - Mesozoic Older Sedimentaries (extending Lnto M. Cretaceous ?) He suggested a phase of igneous activity between the Baratang Formation and Port Blair Formation* Kairunakaran# Ray and Saha (1968Q,|^the geologists from Geological Survey of India modified the stratigraphy of Andaman Islands in accordance \^»ith the recommendation of the International Commission on Stratigraphic Nomencla­ ture* They proposed following stratigraphic succession for Andaman and Nicobar Islands* Age Group Formation Geotectonic ___ _________ ___________ Units Recent Beach sand# Mangrove swampy clay» Alluvial and Deluvial soil and Gravel Bed (30 m) Unconformity Sub- Skytic or Rutland Conglomeratic Recent Pre-Siwalik Shell-limestone (330 m) to movement Pleisto- -----------------Unconformity------- H Age Group Formation Geotectonic Units___