1 Introduction

Kutch is an important Indian sedimentary basin of Mesozoic Era. Located on the western end of the Indian landmass, it is a remarkable site exposing good marine Mesozoic strata which are potential source of natural gas, oil and minerals. Of these, Jurassic rocks are famous all over the world for their varied and exceptionally preserved macrofossils particularly ammonites and subjected to extensive geological and palaeontological studies for quite a long time. The disastrous earthquake of 2001 in this region drew the attention of global geo-science community with renewed interest. Jurassic sediments in Kutch range from Bajocian to Tithonian (Biswas, 1993; Fürsich et al., 2001; Rai, 2003; Rai & Jain, 2012; Talib et al., 2016b) which have been the subject of a large number of studies mainly focused on macrofossils but relatively little research has been done on the microfossils of these sediments including foraminifera.

In view of the above, a detailed study of the Jurassic foraminifera of Kutch is undertaken by us to work out the taxonomy of Jurassic foraminifera in India and their application in interpreting depositional environment, biostratigraphy, and palaeogeography. For this purpose, a large exposure of Jurassic rocks exposed in Jhurio Dome (23° 25′ 45.48″ N and 69° 36′ 33.78″ E) is selected, about 35.4 km northwest of Bhuj, the district headquarters of the Kutch region in Gujarat State of India (Fig. 1).

Fig. 1
figure 1

(modified from Patel et al. 2012a)

Simplified geological map of Kutch, India showing study area

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In the present study, a preliminary account of the work done so far, especially the documentation of the species reported for the first time from the Indian region with some interpretations regarding the palaeoecology and age on the basis of recovered foraminiferal assemblages. Detailed study is in progress and a comprehensive account of the systematics of the foraminiferal assemblages and detailed interpretations regarding biostratigraphy and palaeoecology will be communicated in due course of time.

2 Geology and stratigraphy

Simplified geological map of Kutch is depicted in Fig. 1 which shows the distribution of Mesozoic, including Jurassic rocks of Kutch, India. Lying non-conformably over the Precambrian basement, the Jurassic rocks cover nearly half of the Kutch area (Biswas, 1993; Gaur & Talib, 2009). Due to the breakup of Gondwana the western continental-margin basins are formed in the Triassic/Jurassic age, forming horsts and grabens on local as well as regional scale (Biswas, 1991). At the western continental margin of India, the Kutch basin developed in the Early Jurassic (Jain et al., 2019; Rai & Jain, 2013). The horst and graben structure formed three parallel east–west-trending ridges with intervening valleys. The middle ridge is broken into many dome-like structures and the Jhurio Dome is one of the large domes exposed along this ridge. The Jhurio Dome exposes 302 m thick sediments, covers an extensive area, and categorised into Jhurio, Patcham, Jumara and Jhuran formations following the classification of Fürsich et al. (2020) who adapted the classification of Biswas (1993) with some modifications (Fig. 2).

Fig. 2
figure 2

Lithostratigraphic scheme for the Jurassic sedimentary sequence of Kutch (after Fürsich et al., 2020) showing the studied section with sample locations, Jhurio Dome, Kutch, India

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3 Methodology and materials

A total of 67 samples were collected from exposed section belonging to Jhurio, Patcham, Jumara and Jhuran formations of Jhurio Dome, Kutch. However, samples of Jhuran Formation did not yield foraminifera and, therefore, excluded from the present study. Approximately 300–400 gm of field samples were crushed and boiled for three–four hours with washing soda then sieved with 35, 60 and 120 µm mesh and dried. From the dried material the microfauna is picked out followed by the arrangement on microfaunal slides for identification. The genera and species are identified using generic classification by Loeblich and Tappan (1987) and Ellis & Messina catalogues, respectively. The SEM images are captured by JEOL—JSM-6510LV Scanning Electron Microscope at USIF, Aligarh Muslim University, Aligarh, India.

4 Foraminiferal composition

The measured section of Jhurio Dome produced reasonably rich foraminiferal assemblages encompassing 87 species (Fig. 3) including 27 being reported for the first time from Indian Subcontinent (Fig. 4), pertaining to 26 genera and six suborders. Out of these, the Textulariina having six genera and 17 species and comprising 19.54% of total species, Spirillina with one genus, one species constituting 1.15%, Miliolina including one genus, one species constituting 1.15%, Lagenina having 14 genera, 58 species comprising 66.67%, Robertinina including three genera, nine species constituting 10.34% and Rotaliina with one genus and one species constituting 1.15%.

Fig. 3
figure 3

Frequency Distribution of foraminiferal species, Jhurio Dome, Kutch, India

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Fig. 4
figure 4

Foraminiferal species reported for the first time from India, Jhurio Dome, Kutch. 1. Ammodiscus cheradospirus Loeblich and Tappan; 2. A. yonsnabensis Nagy et al.; 3. Miliammina cf. valdensis Bartenstein and Brand; 4. Reophax aff. R. rudis Terquem; 5. Ammobaculites strigosus Gerke and Sosipatrova; 6. Flabellammina longiuscula Alexander and Smith; 7. Pseudomarssonella media Redmond; 8. Falsopalmula antrorsa Loeblich and Tappan; 9. Pseudonodosaria parallela Marsson; 10. Pyramidulina cf. P. crispata Terquem; 11. P. metensis Terquem; 12. P. orbita Lalicker; 13. P. orthostoecha Loeblich and Tappan; 14. Lenticulina collignoni Epistalie and Sigal; 15. L. helios Terquem; 16. L. infravolgensis Furssenko; 17. L. kosyrevi Kuznetsova; 18. L. saxonica Bartenstein and Brand; 19. Saracenaria pravoslavlevi Furssenko and Polenova; 20. Astacolus dubius Franke; 21. A. semiincisus Terquem and Berthelin; 22. Vaginulinopsis excentrica Cornuel; 23. V. scapha Lalicker; 24. Citharina brevis Furssenko and Polenova; 25. Epistomina carpenteri Reuss; 26. E. hechti Bartenstein et al. and 27. Praebulimina prolixa Cushman and Parker

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The present foraminiferal assemblages incorporate 14 families in which Vaginulinidae is dominant with 39 species (44.83%) followed by Nodosariidae having 16 species (18.39%); Epistominidae with eight species (9.20%); Eggerellidae containing six species (6.90%); Hormosinidae and Lituolidae having four species each (4.60%); Ammodiscidae and Robuloididae with two species each (2.30%), and Rzehakinidae, Spirillinidae, Cornuspiridae, Ichthyolariidae, Conorboididae and Turrilinidae having one species each (1.15%). Overall, present assemblages are dominated by calcareous forms at each level, generic (76.92%), species (80.46%), and specimen level (76.60%), rest of the forms are agglutinated. All calcareous species are perforate/hyaline in nature except a solitary imperforate/porcelaneous form.

Bhalla and Talib (1985, 1991) have earlier described and illustrated 53 species of foraminifera from Jhurio hill, Kutch, India including two species of genus Epistomina, an important genus for Jurassic biostratigraphy along with a brief account of paleoecology, age and Callovian–Oxfordian boundary as well as palaeobiogeographic interpretations. However, they assigned a Callovian to Oxfordian age to these sediments whereas current ammonite evidence favours a Bajocian as lower age limit for these sediments. Mandwal and Singh (1989, 1994) reported 95 foraminiferal species from Jhurio Dome without illustrating them and carried out biostratigraphic interpretations. They favoured Bathonian as the Lower age limit for the sediments exposed in Jhurio Dome.

5 Palaeoecological comments

Foraminifera are abundantly found in marine deposits, have excellent fossilisation potential, long geological history, very sensitive to environment and are frequently utilised as valuable and accurate palaeoenvironmental proxy (Jiang et al., 2020; Kaminski et al., 2020; Koho & Piña-Ochoa, 2012; Rita et al., 2016). The foraminiferal assemblages of Jhurio Dome, Kutch are categorised by the dominance of family Vaginulinidae followed by Nodosariidae, included in superfamily Nodosariacea. The dominancy of family Vaginulinidae demonstrates a shallow water, open marine shelf environs and due to near absence of porcelaneous form which indicates proximity to inner shelf, a middle to outer shelf environment is indicated (Bhat et al., 2016; Canales & Henriques, 2008; Farahani et al., 2018; Hjalmarsdottir et al., 2018; Reolid et al., 2019a, 2019b; Sevillano et al., 2020; Silva et al., 2017, 2020; Smoleń, 2012; Talib et al., 2014, 2016b; Talib et al., 2012a, 2012b; Wasim et al., 2021). Preponderance of hyaline species in the assemblages suggests normal salinity under well aerated vicinity (Amao et al., 2018; Bhalla & Abbas, 1984; Bhat et al., 2016; Canales & Henriques, 2008; Chan et al., 2017; Farahani et al., 2018; Gaur & Talib, 2009; Nagy & Johansen, 1991; Silva et al., 2017, 2020; Talib & Gaur, 2005; Talib et al., 2012a, 2016a; Valchev, 2003; Wasim et al., 2021; Zsiborás & Görög, 2020). Dominance of Nodosariidae suggests a distal and well-oxygenated tranquil environment (Bhat et al., 2016; Gaur & Talib, 2009; Silva et al., 2020; Talib et al., 2012a, 2014; Ziouit et al., 2021; Zsiborás & Görög, 2020).

In the present foraminiferal assemblages, Lenticulina is the most abundant genus at species and specimen levels, which shows the relatively deep open oceanic shelf environment with excessive quantity of dissolved O2 (Bhat et al., 2016; Canales & Henriques, 2008; Reolid & Martínez-Ruiz, 2012; Reolid et al., 2008a, 2008b; Silva et al., 2017; Smoleń & Iwańczuk, 2018; Talib et al., 2012b, 2014, 2016a; Wasim et al., 2021). The dominance of shallow to deep infaunal genera like Lenticulina, Nodosaria, Astacolus, Vaginulinopsis and Vaginulina, shows normal O2 values (Reolid & Martínez-Ruiz, 2012; Reolid et al., 2008a, 2008b; Talib et al., 2016b). Elongated flattened genera with active deposit-feeding and grazing omnivores feeding behaviour and belonging to shallow infaunal microhabitat like Falsopalmula, Frondicularia, Saracenaria, Astacolus, Vaginulinopsis, Citharina, Citharinella and Planularia, included in the submorphogroup J2 of the morphogroup scheme of Reolid et al. (2008a), is dominant in the present assemblages which suggests normal O2 level, followed by elongated, subcylindrical uniserial forms characterising herbivores, bacterial scavengers and active deposit-feeders like Prodentalina, Nodosaria, Pseudonodosaria, Pyramidulina, Vaginulina and Praebulimina belong to submorphogroup J1 of Reolid et al. (2008a), shows open oceanic shelf environment (Colpaert et al., 2017; Oloriz et al., 2006; Reolid et al., 2008a, 2010, 2019b).

In this perspective, the foraminiferal assemblages of Jhurio Dome, Kutch emerge to be flourishing in a shallow water, open oceanic, deeper shelf environment ranging from mid to outer shelf with normal to high oxygen level and normal salinity.

6 Foraminiferal biochronology

Some researchers on Jurassic foraminifera have mentioned the scarcity of restricted vertical ranges in Middle to Late Jurassic sequences and according to them foraminifera are not credible for error-free age determination during this time span (Bhalla & Abbas, 1976; Talib & Faisal, 2006, 2007; Talib et al., 2007), whereas others have demonstrated their suitability in this regard (Herrero et al., 1996; Talib et al., 2007).

The Jhurio Dome assemblages are dominated by the species which are mostly long ranging and various authors emphasised the prospects of ammonites for age determination (Bhat et al., 2016; Gradstein et al., 2017; Kaminski et al., 2020; Sevillano et al., 2020; Silva et al., 2017, 2020; Smoleń & Iwańczuk, 2018; Talib & Gaur, 2008; Talib et al., 2012a, 2014, 2016a; Wasim et al., 2020). Therefore, precise age of this strata using foraminifera is not feasible. However, attempt has been made here to determine an equitable near precise age with the help of few short ranging species of the Jhurio, Patcham and Jumara formations exposed at Jhurio Dome, Kutch.

The Foraminiferal assemblages of Jhurio Dome include four species which are globally restricted to Bajocian age, viz., Ammodiscus yonsnabensis, Reophax agglutinans, Pyramidulina opalini and Vaginulinopsis scapha. Out of these, Ammodiscus yonsnabensis is restricted to Middle Bajocian of England (Nagy et al., 1983). Reophax agglutinans is originally reported from the Upper Bajocian of France by Terquem (1870). Pyramidulina opalini and Vaginulinopsis scapha are restricted to Bajocian of Portugal (Canales & Henriques, 2008, 2013).

A total of six species restricted to Bathonian in the Indian region are present in the studies assemblages. They are Pseudomarssonella inflata, P. reflexa, Cornuspira orbicula, Pyramidulina orbita, Citharina sparsicostata and Conorboides nudus. Out of these, Pseudomarssonella inflata, P. reflexa, Cornuspira orbicula, Citharina sparsicostata and Conorboides nudus are restricted to Bathonian of Kutch, India (Mandwal & Singh, 1989; Talib et al., 2016a; Bhalla et al., 2019 and Wasim et al., 2021) and Pyramidulina orbita is restricted to Bathonian of Montana (Lalicker, 1950).

Callovian age is represented by Indian and global occurrence of eight species, viz., Reophax metensis, Falsopalmula jurensis, Pyramidulina dispar, Frondicularia franconica, F. nodosaria, Lenticulina polonica, Astacolus stillus and Epistomina elschankaensis. Whereas, Reophax metensis is restricted to Callovian of Egypt (Said & Barakat, 1958) and Kutch, India (Alhussein, 2014; Bhalla et al., 2019; Bhat et al., 2016; Talib et al., 2016b), Falsopalmula jurensis is restricted to Callovian of Kutch, India (Bhalla et al., 2019). Pyramidulina dispar occurs in Callovian of Rajasthan, India, (Kalia & Chowdhury, 1983) and Kutch, India (Bhalla et al., 2019). Frondicularia franconica and F. nodosaria are restricted to Callovian of Kutch, India (Bhalla et al., 2019), whereas, Frondicularia franconica is restricted to Callovian of Scotland (Gordon, 1967) and England (Hart et al., 2019), Frondicularia nodosaria is restricted to Callovian of Scotland (Gordon, 1967). Lenticulina polonica occurs in Callovian of Kutch, India (Bhalla et al., 2019) and restricted to Upper Callovian of Poland (Wisniowski, 1890). Astacolus stillus is restricted to Callovian of Kutch in India (Bhalla et al., 2019; Bhat et al., 2016). Epistomina elschankaensis occurs in Callovian of Kutch, India (Pandey & Dave, 1993; Talib et al., 2016b and Bhalla et al., 2019) and this species is also restricted to Callovian of erstwhile USSR (Myatlyuk, 1953) and Russia (Colpaert et al., 2017).

Species restricted within Oxfordian age are represented by the following eight species from Jhurio Dome of Kutch, viz., Ammodiscus cheradospirus, Falsopalmula antrorsa, Pyramidulina metensis, Lenticulina toarcense, L. vistulae, Epistomina charlottae, E. paraghoshi and E. volgensis. Out of these, Ammodiscus cheradospirus is restricted to Oxfordian of Canada (Tingley & Sawyer, 2015). Falsopalmula antrorsa is restricted to Oxfordian of South Dakota, United States (Loeblich & Tappan, 1950). Pyramidulina metensis is restricted to Oxfordian of England (Gordon, 1965). Lenticulina toarcense is a globally long ranging species but in India it is restricted to Oxfordian of Kutch (Bhalla et al., 2019), L. vistulae and Epistomina charlottae are restricted to Oxfordian of Kutch, India (Bhalla et al., 2019). E. paraghoshi is restricted to Oxfordian of Kutch, India (Bhalla et al., 2019; Pandey & Dave, 1993) and E. volgensis is restricted to Oxfordian of Kutch, India (Bhalla et al., 2019 and Wasim et al., 2021).

The present six species, viz., Pseudomarssonella media, P. primitiva, Spirillina polygyrata, Pyramidulina fontinensis, Lenticulina helios and Garantella ornata are represent Bajocian to Bathonian globally including India. Out of these, Pseudomarssonella media is restricted to Bajocian to Bathonian of Saudi Arabia (Malik et al., 2020). P. primitiva is globally restricted to Bajocian to Bathonian of Saudi Arabia (Redmond, 1965 and Malik et al., 2020). Spirillina polygyrata is a globally long ranging species but restricted to Bajocian to Bathonian of Saudi Arabia (Malik et al., 2020). Pyramidulina fontinensis is also globally long ranging species but restricted to Bajocian to Bathonian of Saudi Arabia and Iran (Malik et al., 2020 and Farahani et al., 2018). Lenticulina helios occurs in Bajocian to Bathonian of Iran (Farahani et al., 2018). Garantella ornata is restricted to Bajocian to Bathonian of Canada (Gradstein, 1978).

Two foraminiferal species have restricted vertical range from Bathonian to Callovian in the present assemblages, these are Lenticulina bulla and Epistomina ghoshi. Lenticulina bulla is restricted to Bathonian and Callovian of Kutch, India (Wasim et al., 2021) whereas, Epistomina ghoshi is described by Pandey and Dave (1993) from the Bathonian of Kutch, India and later reported by Talib et al. (2016b) from the Callovian of Kutch.

In the present assemblages, 15 species are restricted to vertical range from Callovian to Oxfordian, viz., Flabellammina macfadyeni, Prodentalina gumbeli, Pyramidulina hortensis, P. orthostoecha, Lenticulina ectypa, L. subalata, L. suturifusus, Astacolus anceps, A. aphrastus, A. eritheles, A. pauperatus, Citharina clathrata, C. colliezi, Citharinella rhomboidea and Vaginulina aff. V. barnardi. Out of these, Flabellammina macfadyeni and Lenticulina ectypa are restricted to the Callovian to Oxfordian sequence of Kutch, India (Bhalla et al., 2019), A. pauperatus to Kutch, India (Bhalla & Talib, 1991; Talib et al., 2012b and Bhalla et al., 2019), Citharinella rhomboidea to Kutch, India (Bhalla & Talib, 1991; Gaur & Talib, 2009; Bhat et al., 2016; and Wasim et al., 2021) and Jaisalmer, India (Kalia & Chowdhury, 1983). Prodentalina gumbeli and L. suturifusus to Kutch, India (Bhalla & Abbas, 1978; Talib et al., 2012b) and to Jaisalmer, India (Kalia & Chowdhury, 1983), Pyramidulina hortensis, Astacolus anceps, A. aphrastus, A. eritheles, Citharina clathrata, C. colliezi and Vaginulina aff. V. barnardi to Kutch, India (Bhalla & Abbas, 1978; Bhalla & Talib, 1991; Talib et al., 2016b and Wasim et al., 2020, 2021). L. subalata is a globally long ranging species but in India it ranges from Callovian to Oxfordian (Gaur & Talib, 2009; Talib et al., 2012b; Wasim et al., 2020). Pyramidulina orthostoecha is globally restricted to Callovian to Oxfordian, as this species is originally described from Callovian of Montana by Loeblich and Tappan (1950) and later by Tingley and Sawyer (2015) from Oxfordian of Canada.

Eight foraminiferal species having a restricted vertical range from Bajocian to Callovian of different parts of the world are present in the Jhurio Dome assemblages. These are Pseudomarssonella maxima, P. plicata, Nodosaria simplex, N. sowerbyi, Pseudonodosaria vulgata, Astacolus varians, Planularia aff. P. beierana and Vaginulina suturalis. Out of these, Pseudomarssonella maxima is restricted to the Bajocian to Callovian in Saudi Arabia (Redmond, 1965; Saad, 2008 and Malik et al., 2020). P. plicata is restricted to Bajocian to Callovian of Saudi Arabia (Saad, 2008) and Kutch, India (Talib et al., 2016a). Nodosaria simplex and N. sowerbyi are restricted to Bajocian to Callovian of Middle-East (Saad, 2008). Pseudonodosaria vulgata is a globally long ranging species but restricted to Bajocian to Callovian sequence of India and Saudi Arabia (Bhalla et al., 2019; Malik et al., 2020). Astacolus varians occurs in the Bajocian to Callovian of Saudi Arabia (Kaminski et al., 2020). Planularia aff. P. beierana and Vaginulina suturalis are globally long ranging species but they are restricted to the Bajocian to Callovian of Saudi Arabia (Kaminski et al., 2020).

Seven species ranging from Bathonian to Oxfordian found in the present foraminiferal assemblages are Reophax ismaili, Pyramidulina corallina, Lenticulina audax, L. quenstedti, Astacolus centralis, Vaginulina misrensis and V. woodi. Out of these, Reophax ismaili and Pyramidulina corallina occur in the Bathonian to Oxfordian of Kutch, India (Bhalla et al., 2019; Talib et al., 2016a, 2016b). Lenticulina audax and L. quenstedti are globally long ranging species but range from Bathonian to Oxfordian of Kutch, India (Wasim et al., 2020, 2021). Astacolus centralis was originally described from the Bathonian of France (Terquem, 1870) and later reported by Talib et al. (2016a) and Wasim et al. (2021) from Bathonian of Kutch, India. Bhalla et al. (2019) suggest that this species occurs in Callovian to Oxfordian of Kutch, India, therefore this species is considered as Bathonian to Oxfordian in age. Vaginulina misrensis and V. woodi are described from Bathonian to Oxfordian of Kutch, India (Wasim et al., 2021).

In the view of above discussion, it is evident that a fair number of relatively short ranging foraminiferal species are present in the Jhurio Dome which are used for dating of these sediments. They include species restricted to a single stage, represented by four species of Bajocian, six of Bathonian, eight of Callovian and eight of Oxfordian; species restricted to two stages represented by six species ranging from the Bajocian to Bathonian, two from the Bathonian to Callovian and 15 from the Callovian to Oxfordian; and species restricted to three stages represented by eight ranging from Bajocian to Callovian and seven from Bathonian to Oxfordian (Fig. 5). Therefore, on the basis of these species, a Bajocian to Oxfordian age is assigned to the studied section of the Jhurio to Jumara formations exposed at Jhurio Dome, Kutch. This age is in conformity with the age assigned on the basis of ammonites.

Fig. 5
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Known global and Indian ranges of foraminifera from Jhurio Dome, Kutch, India

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7 Conclusions

  1. 1.

    The Middle to Late Jurassic sequence exposed at Jhurio Dome, Kutch, yielded benthic foraminiferal assemblages comprising 87 species. A total of 27 species are reported for the first time from the Indian Subcontinent. The foraminiferal assemblages are dominated by the family Vaginulinidae. The calcareous and agglutinated forms are present but the calcareous forms are dominant representing 80.46% of the total species. Hyaline forms are dominant in the calcareous constituent except for a single porcelaneous species.

  2. 2.

    To interpret the palaeoecology and palaeoenvironment of the sediments exposed at Jhurio Dome, Kutch, the foraminiferal assemblages are analysed using various contemporary techniques. On the basis of the dominance of suborder Lagenina, family Vaginulinidae, calcareous hyaline forms, genus Lenticulina, submorphogroup J1 and J2, shallow to deep infaunal group, detritivores and bacterial scavengers group, elongated flattened forms, and elongated uniserial group, the present assemblages are regarded to be flourishing in a shallow water, open oceanic, deeper shelf environment ranging from mid to outer shelf with normal to high oxygen level and normal salinity.

  3. 3.

    Most of the species of Jurassic foraminifera investigated are rather long ranging. However, on the basis of a fairly large number of species representing Bajocian, Bathonian, Callovian and Oxfordian either globally or in the Indian Subcontinent, a Bajocian to Oxfordian age has been assigned to the studied section exposed at Jhurio Dome, Kutch.