Identification of Foraminiferal Species

Identification of Foraminiferal Species Kutch is well-known for its rich and diverse megafossils, particularly upper Jurassic Ammonites, bivalves and other benthic invertebrates (Kitchen, 1900; Spath, 1933; Cox, 1940, 1952) which provide good intra- and intercontinental correlation. Several workers from time to time tried to explain the geological history, including stratigraphy of the Kutch region, well known for its potential of mineral oil. Vulnerability to natural disasters like the recent Bhuj earthquake has further attracted the attention of researchers from all over the world. Syke’s (1834) contribution, probably one of the first, in the field of stratigraphy and taxonomy of the fossils biota is incomparable. He was followed by a more detailed account by Wynne (1872) based on mapping surveys. Ammonites have proved worthy throughout as far as the age determination and correlation of the Mesozoic formations is concerned. Recently the unearthing of several assemblages of foraminifers by various workers in Kutch region has proved reasonably promising. It is beyond the scope of this study to record the details of each and every finding of all the earlier investigations in different branches of geology on this region. Therefore, on the basis of priority only the researches on foraminifera have been dealt with some detail while the rest have simply been listed. Tewari (1957) reported several foraminiferal genera for the first time from the Jurassic rocks (Patcham ‘series’) of Habo Hill, Kutch including Aulotortus, Textularia, Bigenerina, Spiroplectammina and Gaudryina. Subbotina et al. (1960) described 34 species of Jurassic foraminifera from the southwest of village Lodai and from the shales of Khawda in Kutch and also from Rajasthan; most of the species were benthic. They have proposed a Callovian- Oxfordian age of the studied rocks. Agrawal and Singh (1961) reported Rhabdammina, Ammodiscus, Ammobaculites, Quinqueloculina, Triloculina, Robulus, Lenticulina, Nodosaria, Saraceneria, Vaginulina, Palmula, Nonion, Elphidium, Rotalia and Anomalina from the Habo beds of Walakhawas and Fakirwari, southwest of Bhuj. They also reported some post- Jurassic elements like Elphidium but were unable to offer any explanation for this abnormal mixing. It was only established later on that the post-Jurassic elements are not indigenous but by some means leaked into these rocks. Bhalla and Abbas (1975a, b, c; 1976a, b; 1978, 1984) carried out detailed work on the Jurassic Foraminifera of Kutch. These authors (Bhalla and Abbas 1975a, 1976a) recovered sixty-five species of foraminifera, dominated by the family Nodosariidae. Out of these, ten were new, forty six were reported for the first time from this region, and the rest has been those already described by earlier investigators. Bhalla and Abbas (1975 a) observed variation in Lenticulina subalata (Reuss) and recommended proper caution while dealing with the taxonomy of Jurassic nodosariids. They too found some post-Jurassic elements in the studied rocks (1975 b, c). Shringarpure and Desai (1975) recovered a foraminiferal assemblage of nineteen species representing family Nodosariidae. Shringarpure et al. (1976) observed stratigraphic leakage, a problem with foraminiferal assemblages of Wagad Mesozoic sediments of eastern Kutch. They observed that foraminiferal assemblages occur in association with few ostracoda, brayozoa and echinoderm spines. They also came across some microscopic plant tissues and insect skeleton of Tertiary, sub-recent and Recent age mixed with older Mesozoic sediments of Jurassic and Cretaceous periods. The reason for this highly mixed fauna has been assigned to the natural agencies of erosion and transportation. Bhalla and Abbas (1976b) worked on the age resolution and paleogeographic significance of Jurassic foraminifera from Kutch. They recommended a Callovian-Oxfordian age of the rocks exposed in a section near Habo Hills and proposed that foraminifera from the Jurassic of Kutch can be compared effectively with those of adjoining regions of the world, viz., Rajasthan, Afghanistan, Iran, Egypt, Somalia and Malagasy, which indicates that Kutch was joined with these landmasses during the Middle and Upper Jurassic times. Singh (1977) proposed two biostratigraphic assemblage zones, Epistomina stellicostata- E. alveolata assemblage-zone and E. ventriosa- E. mosquences assemblage-zone (late Jurassic of Banni area, Kutch). Singh (1979) proposed seven Biostratigraphic zones for the subsurface Jurassic sediments of Banni, Rann of Kutch, on the basis of foraminifera, Charites sp., and Ostracoda. He proposed a late Jurassic age for the subsurface rocks in the above mentioned locality and a brackish to marine environment for the beds of the Charites- Otocethere Assemblage Zone; whereas the rest of the sequence was regarded to have been deposited in an inner neritic environment. Singh (1977a) recovered five species of Epistomina from the subsurface rocks intersected by the Banni well on the basis of which an Upper Jurassic age was assigned to this sequence. Subsequently, Singh (1977b) assigned an Oxfordian age to the same strata and suggested an inner neritic environment of deposition on the basis of nannoplanktons from this well. Bhalla and Abbas (1978) carried out a comprehensive study of a section cutting across Patcham, Chari and Katrol â€Å"series† from the Jurassic rocks of Habo Hills, Kutch. Of these, the first two units were highly fossiliferous but the last one was unfossiliferous. The obtained assemblage includes ten new species and many were reported for the first time from the Indian region. Family Nodosariidae dominates the assemblage and it was assigned a Callovian- Oxfordian age. The whole sequence of Habo dome was divided into three part, first two suggested fluctuating environmental conditions, In Patcham series, overall rarity of faunal and the presence of arenaceous form having a simple interior and of glauconite, a shallow, near-shore, slightly reducing marine environment with restricted connection to the open sea such as that in a lagoon, but above the patcham foramtion, it is therefore, evident that through nodosariids migrated from shallow water sediments and through time, they a lways preferred open marine environments of normal salinity. (? Palaeoecology and Palaeogeography) Bhalla and Abbas (1984) continued their studies on Jurassic rocks of Habo Hills and divided them into several palaeoecological units. The study revealed that the overall deposition of the sediments took place in shallow marine water, tectonically unstable marine basin with a frequently changing shore-line. Abbas (1988) on the basis of foraminiferal information tried to demarcate the Jurassic/Cretaceous boundary within the Mesozoic rocks of Kutch. Bhalla and Talib (1978, 1980) carried out a detailed investigation of the Jurassic rocks of Badi in central Kutch. They suggested a Callovian-Oxfordian age for the Chari ‘series’ exposed in the area on the basis of a few short ranging species. On the basic of foraminifera the Chari sequence near badi was accumulated in a near shore, shallow water, marine environment which fluctuated between littoral to infraneritic conditions. It was also suggested that Jurassic rocks of Kutch have close affinity with that of neighboring areas, viz., Iran, Rajasthan, Egypt, Somalia and Afghanistan. (? Palaeoecology, Palaeobiogeography) Bhalla and Talib (1985a, b, c) Published a series on foraminifera from the Jurassic sediments of Jhurio hills, Kutch, western India. These authors (1985a) discussed variation in the population of Lenticulina quenstedti recovered from Jhurio hill, Kutch. They identified four morpho-variants of this species which showed continuous inter-gradation into one another. In a subsequent paper, (1985b) two new species were recovered belonging to family Nodosariidae from Jurassic sediments of Jhurio hill, Kutch, viz., Marginulina sastryi and Vaginulina bhatiai. In another publication these investigators (1985c) reported fifty-three foraminiferal species from Jhurio hill, Kutch. Of these, twenty six species were recorded for the first time from the Indian region. They (Bhalla and Talib, 1985c) also briefly discussed the age and depositional environment of these sediments as well as palaeogeography of the Kutch region prevailed during the Middle and Upper Jurassic times. A Callovian-Oxfordian age was assigned to the enclosing rocks. An attempt was also made to demarcate the boundary between Callovian and Oxfordian of the sequence in the Jhurio Hill. (? Palaeoecology, Palaeobiogeography) (? 1985 a, b, c) Bhalla and Lal (1985) found a foraminiferal assemblage of seventeen species in the Jurassic sediments exposed at northern flanks of Kaiya Hills, Kutch mainly from Chari â€Å"series†. This study pointed to a near shore, shallow water, marine environment and an age of Callovian-Oxfordian was favoured on the basis of a few short ranging species such as Citharina hetropleura, Dentalina guembeli and Patellinetlla poddari. Govindan et al. (1988) studied samples collected across the Jurassic-Cretaceous boundary from wells drilled in Kutch Mainland and recovered a rich calcareous benthic foraminiferal assemblage including epistominids, lenticulinids and agglutinated species belonging to genus Dorothia. The whole sequence was divided into several assemblage zones on the basis of the recovered fauna. Bhalla and Gaur (1989) described Marginulina jumarensis, a new species of Vaginulinidae family and commented that this species is tolerant of highly variable environmental conditions between that of shallow open marine to paralic environment such as a marsh or lagoon. Mandwal and Singh (1989) described sixteen foraminiferal species from the Patcham and lower part of the Chari Formation, Jhurio Hill, Kutch. Their study has shown that these rocks belonged to Bathonian age. Boundary between Bathonian and Callovian was demarcated by these authors. In a subsequent study by Mandwal and Singh (1994) ninety five foraminiferal species were recovered from the Patcham-Chari formations in the same area. A Bathonian-Oxfordian age was supported for the studied sequence and also demarcation of the Bathonian/Callovian and Callovian/Oxfordian boundaries were carried out. Bhalla and Talib (1991) presented a detailed version of their earlier study by describing and illustrating fifty three species of foraminifera from Jhurio Hill. The assemblage is dominated by family Nodosariidae, which suggested deposition of the studied sequence in near shore, tectonically unstable marine basin. A Callovian-Oxfordian age was proposed on the basis of some short ranging species. The foraminiferal assemblage from Chari formation exposed in the section was dominated by nodosariids. Based on the foraminiferal assemblage exposed at Jhurion hills deposition took place in a near- shore, shallow marine basin, which was rather tectonically unstable as suggested by occasional shifting of the shoreline. The evidence furnished by the present foraminiferal assemblage supports the earlier Middle to Late Jurassic time, a gulf of thethys extended from near Afghanistan to Madagascar covering Iran, Arabia and East coast of Africa which also engulfed the Kutch region. The Jhurio hill f oraminiferal assemblage and those recorded from another region of the Tethyan realm has been observed. (? Palaeobiogeography) Pandey and Dave (1993) worked simultaneously on six sections from western Kutch, viz., Jhurio Dome, Jumara Dome, Habo Dome (Kalajar Nala), Mundhan Anticline, Umia River and Patcham Island (Khavda Nala) and described in detail their geology, stratigraphy, and foraminifera. They reported seventy seven benthic foraminiferal species and worked out biozonation along with chronostratigaphy and correlation of different stages and zones. Eleven biostratigraphic zones were delineated within the Jurassic sequence on the basis of the recovered foraminifera. Bhalla et al. (1998) while carrying out studies on foraminifera from the sediments of Jhurio Hill, Kutch, also investigated carbonate micro-facies and foraminiferal paleoecology of the Jurassic sediments of Chari Formation. They grouped the sequence into five ecological units based on foraminiferal assemblages and four microfacies in the limestones of the Chari sequence, suggesting a near shore, shallow marine environment of deposition in a tectonically unstable basin. Bhalla et al. (2000) carried out foraminiferal and sedimentological analysis of a section exposed at Jhurio Hill, Kutch. The foraminiferal assemblage from Chari formation exposed in the section was dominated by nodosariids. Based on the foraminiferal assemblage and the petrographic study of the samples, they inferred a shallow, near shore environment of deposition and with various phases of transgressions and regressions. Gaur and Singh (2000) reported forty-four foraminiferal species from Nara Hill, Kutch. Four biozones, viz., Spirillina polygyrataLenticulinaCitharina clathrata Assemblage Zone, Epistomina mosquensis Assemblage Zone, Flabellammina sp.– Triplasia emsalandensis Assemblage Zone, and Astacolus anceps–Epistomina alveolata Assemblage Zone, were identified within the Callovian-Oxfordian succession on the basis of the foraminiferal assemblage. Gaur and Sisodia (2000) obtained forty-one foraminiferal species from Keera Dome, Kutch. These authors established four benthic foraminiferal biozones, viz., Dentalina guembeliCitharina clathrata Assemblage Zone, Epistomina mosquensis Assemblage Zone, Ammobaculites gowdai Triplasia emslandensis Assemblage Zone, Spirillina Lenticulina Assemblage Zone, and Barren Zone Talib and Gaur (2005) studied the Middle-Upper Jurassic sequence of Jumara Hills, Western Kutch. The foraminiferal evidence supplemented with petrographic, mega faunal and field observations suggested that the overall deposition of the Patcham-Chari sequence at Jumara Hills, Kutch, took place in a shelf zone which was tectonically unstable as is evident from the periodic fluctuations in the environmental conditions. Talib and Bhalla (2006a) favored a Callovian to Oxfordian age for the Chari Formation exposed at Jhurio Hill, Kutch on the basis of foraminifera. The Boundary between Callovian Oxfordian within this sequence was also discussed in detail. In another study of the Chari Formation exposed at Jhurio Hill, Kutch, these authors (Talib and Bhalla, 2006b) correlated some of the recovered Callovian- Oxfordian species with that of Rajasthan and neighboring regions of the world including Afghanistan, Iran, Egypt, Somalia, and Malagasy. They concluded that during Middle-Upper Jurassic time, foraminiferal fauna of these regions were flourishing in a separate provenance of the Tethyan Realm, the Indo-East African provenance, which occupied a southwestern arm of the Tethys covering these regions. Talib and Faisal (2006) recovered a rich foraminiferal assemblage comprising fifty three species from Callovian Oxfordian sediments of the Fakirwari Dome in the Kutch Mainland. Among these twenty five species were reported for the first time from the Indian region. The foraminiferal assemblage helped in assigning a Callovian-Oxfordian age to the sequence. The overall dominance of Vaginulinidae along with nodasariids and Epistomina are indicative of shallow open marine, shelf environment for the studied sequence. The foraminiferal assemblages exhibits affinity with the other Jurassic foraminiferal assemblages of the neighboring countries of the Tethyan Realm, viz, Afghanistan, Iran, Egypt, Somalia and Malagasy is indicating a sea connection between these regions and the Kutch during Middle and Late Jurassic times. Talib and Faisal (2007) studied a section from the Jurassic rocks of Ler Dome situated southeast of Bhuj. A rich foraminiferal assemblage of forty species, dominated by fami ly Vaginulinidae was recovered in the section. On the basis of some foraminiferal species, they assigned a Callovian-Oxfordian age to the studied sequence. The dominance of vaginulinids along with nodasariids in the recovered foraminiferal assemblage of Ler Dome suggested the overall deposition of these sediments in shallow water, near shore, normal marine conditions, most probably shelf environment. Talib et al. (2007) identified some marker foraminiferal species in the Jumara and Jhurio domes, Kutch Mainland, which facilitated in assigning a Callovian-Oxfrodian age of these rocks and marking of Callovian–Oxfordian boundary in the two domes. Talib and Gaur (2008) discussed the affinity of the foraminiferal assemblage from the Jurassic rocks of Jumara Dome and concluded that the foraminiferal assemblage of Jumara Dome compares well with those of neighboring regions and exhibits a distinct Tethyan affinity. On this basis, these authors inferred that during Middle and Late Jurassic times, the Kutch region was having sea connections with these neighbouring regions which were covered by a southeastern arm of the Tethys, the Indo-East African Gulf. Gaur and Talib (2009) reported a fairly rich foraminiferal assemblage from the Callovian-Oxfordian sequence exposed at Jumara Hill, western Kutch, India. He employed the foraminiferal assemblage to assign a Callovian-Oxfordian age to the studied rocks and inferred shallow water near shore environment for the deposition of the Jumara Dome sequence. They further correlated the reported foraminiferal species with those of Rajasthan in India as well as with the neighboring countries. The comparative study revealed their distinct affinity with the aforesaid regions, including Rajasthan, Afghanistan, Iran, Egypt, Somalia and Malagasy which were occupying the Indo-East African Province of the Tethyan Realm during the Middle and Late Jurassic times. Talib et al. (2012a) recovered a foraminiferal assemblage comprising fifty one species from Callovian Oxfordian sediments of the Kaiya Dome Kutch Mainland. Among these eleven species were reported for the first time from the Indian subcontinent. The foraminiferal assemblage was employed for preliminary interpretations regarding age, palaeoecology, and palaeobiogeography. The assemblage suggested a Callovian to Oxfordian age for the exposed sequence at Kaiya Dome. A near shore, open marine environment ranging from mid to outer shelf with fluctuating strandline was interpreted on the basis of the recovered foraminiferal assemblage. The Kaiya Dome foraminiferal assemblage exhibited a Tethyan affinity and suggested that the Kutch region was engulfed by a shallow southwestern arm of the Tethys during the Middle to Late Jurassic times. Talib et al. (2012b) worked on the age resolution and palaeoenvironmental significance of Jurassic foraminifera from Keera Dome, Kutch. The paper presented a systematic account of eight species, reported for the first time from the Indian region. They recommended a Callovian-Oxfordian age for the studied rocks and proposed that foraminifera from the Jurassic of Keera Dome, Kutch were deposited in a near shore, open marine environment ranging from mid to outer shelf.