Abstract
The palaeobiogeography and age of the upper calcareous part of the Nimar Sandstone (NS), Bagh Group is determined based on ostracod fossils. The rocks of the NS directly rest over the Precambrian basement rocks outcropping near Pipaldehla, Gola Chhoti (Sajwani), Dhekal Badi, Ranapur, Udaygarh (Kanas) and multiple locations in Jhabua District. The present paper is the first report on ostracod fauna from Pipaldehla (N 22° 46’ E 74° 39’), Jhabua District, Madhya Pradesh, India. A total of 15 species of ostracods belonging to 11 genera have been identified. The assemblages of ostracods from the western and eastern exposures of the Bagh Group have been compared. The overall ostracod fauna suggests an early Turonian age and shows affinity to the ostracod assemblage of (1) the lower part of the Nodular Limestone of the Bagh-Jeerabad area, Dhar District, Madhya Pradesh (eastern exposures), and (2) also with the westernmost exposures of the Kawant-Rajpipla area of Gujarat.
Introduction
The Upper Cretaceous Bagh Group of rocks is popularly known as Bagh beds. The Bagh Group of rocks, composed of thick siliciclastic and calcareous sediments, were deposited during the late Cretaceous (late Cenomanian-Coniacian) global sea-level rise in a shallow epicontinental sea or an embayment that invaded the western and central parts of India from the west along the Narmada valley (Figure 1) (Bhattacharya et al., 2020; Jaitly & Ajane, 2013; Keller et al., 2021; Kumari et al., 2020; Saha & Shukla, 2022; Saha et al., 2010; Singh, 1981; Singh & Srivastava, 1981). The Bagh Group comprises three formations, which in ascending order are: Nimar Sandstone (NS), Nodular Limestone and Coralline (Bryozoans) Limestone (Jaitly & Ajane, 2013; Tripathi, 2006). Bose (1884) subdivided the NS into the ‘Lower Member’ consisting mainly of conglomerate, sandstone and carbonaceous clay, and the ‘Upper Member’ comprising calcareous sandstone with marine fossils.
(A) Inset map of India showing the distribution of the Deccan Traps and the Precambrian rift system in India; Abbreviations are as follows: NR = Narmada Rift; GR = Godavari Rift; MR = Mahanadi Rift; (B) Distribution of Bagh Group, Lameta Formation, Deccan Traps and Inter-trappean sequences (modified from Kumari et al., 2020).
At Pipaldehla, NS directly overlies the Precambrian basement, while the overlying sediments (Upper Cretaceous) occur as a linear belt of restricted distribution. To enhance our knowledge of the ostracods of the NS of the Bagh Group, samples were collected from different sections of Pipaldehla (N 22° 46’ E 74° 39’), Ranapur, Dhekal Badi, Gola Chhoti and Udaygarh (Kanas) by the authors during fieldwork in Jhabua District. However, in the present work, the authors first reported the presence of ostracods from the northernmost exposure of the NS at Pipaldehla village about 7 km east of Jhabua town (Figure 2). A total of 15 taxa were recorded, out of which six are common with ostracods reported earlier from the late Cenomanian of the Kawant-Rajpipla area (Chaudhary & Nagori, 2019; Keller et al., 2021), while 14 taxa are common with ostracods of the Bagh-Jeerabad area (Chaudhary & Nagori, 2019). Based on the ostracods age and palaeobiogeography are also discussed.
Lithostratigraphy and photo illustrations of key lithologic horizon of the studied Pipaldehla section, Bagh Group, Jhabua District, Madhya Pradesh, India.
Previous Work
The top part of NS is calcareous and full of megafossils, mainly bivalves, gastropods, echinoids and microfossils viz., calcareous algae, rare foraminifers and ostracods. It is worth noting that ostracods from the Bagh Group of eastern and western exposures of different localities were previously described and recorded by Jain (1961, 1975b), Roy Chowdhary and Sastri (1962), and Guha and Ghosh (1970). Recently, ostracods from these beds were described and illustrated (Chaudhary, 2017; Chaudhary & Nagori, 2019; Chaudhary et al., 2017a, 2017b, 2019; Keller et al., 2021). So far studies on calcareous algae are concerned, considerable work has been carried out in the past. Badve and Nayak (1983) first time reported five species of the algal genus
Sanganwar and Kundal (1996) recorded 10 species of the melobesioidean calcareous algae from the same locality. Kundal and Sanganwar (1998), while dealing with calcareous algae from the calcareous top of the NS, recorded 72 species belonging to Cyanophyta, Rhodophyta and Chlorophyta. Based on these algal assemblages they discussed the stratigraphical, palaeogeographical and palaeoenvironmental significance and assigned Cenomanian-Turonian ages to this lithounit of Bagh Group and late Albian for part of NS at the base. Further, they concluded that the calcareous top of the NS might have been deposited in tropical waters at a depth of 10–12 m from below low tide level in moderate energy setting and turbulence with normal salinity of water.
Foraminiferal studies from this locality were carried out by Nayak (1987) and first time recorded following taxa:
Evolution of the Basin
During the late Cretaceous (late Cenomanian-Turonian-Coniacian) marine incursion, which influenced farther inland regions (Rajpipla, Gujarat, up to Barwah near Indore, Madhya Pradesh), several hundreds of kilometres into central India. This transgression is linked with the breakup of Greater India from Madagascar ~90 Ma ago (Kumari et al., 2020). This late Cretaceous dispersal event was due to spreading along the central Indian Ridge, which opened up the Mascarene Basin (Chatterjee et al., 2013). The southward drift of Madagascar concerning the Indian subcontinent exposed the western coast of India. This breakup is associated with Marion plume activity that resulted in the eruption of the Mahajanga Flood Basalt, reactivation of the Narmada fault and subsequently opening of the Narmada Basin and allowed seawater to inundate the pericratonic rifts (Biswas, 1987, 1999, 2003; Jafar, 2016). The Narmada rift had been reactivated and opened due to the extensional tectonics (separation of Madagascar) at that time (~90 Ma) and acted as the pathway for this transgression. The average sea level was higher than the present-day mean sea level throughout the Cretaceous. It reached a maximum of ~250 m at the beginning of Turonian between 93.9 and 91.6 Ma (Gradstein & Ogg, 2020; Haq, 2014). The temporal coincidence of tectonics as a result of the separation of Madagascar from India, and the subsequent global sea-level rise, allowed seawater to transgress onto the Indian subcontinent during the late Cenomanian (Jafar, 2016; Keller et al., 2021). Oyster beds, the calcareous top part of Nimar Sandstone Formation (NSF), Nodular Limestone and Coralline (Bryozoan) Limestone Formations of the Bagh Group are well-preserved evidence of transgression during late Cenomanian-Turonian-Coniacian age (Chaudhary & Nagori, 2019; Keller et al., 2021; Ruidas et al., 2018).
The Bagh Group of rocks rests over Precambrian Basement rocks of Lower Proterozoic to Archean ages. The continental sediments, NSF overlying the Precambrian basement, cover a very large part of the area, while the overlying marine sediments show restricted distribution forming linear belts and were deposited in an intracratonic rift basin (Biswas, 1987; Kumar et al., 2019; Tripathi, 2006) following the Precambrian tectonic grain. Three separate marine basins in a linear belt were identified by Tripathi (1995). The ENE-WSW trending basins are the Bagh-Jeerabad basin (Madhya Pradesh) and Kawant basin (Gujarat) while the third Jobat-Dohad basin follows the NE-SW Aravalli trend.
The distribution and thickness variation of marine strata across the basins suggests that these basins were probably half grabens, where southern or southwestern faults were active (Tripathi & Lahiri, 2000). The reactivation of Pre-Cambrian tectonic grain during the anticlockwise movement of the Indian plate at the Cretaceous Period resulted in the formation of tectonic basins following the Precambrian trends and generated Cretaceous triple point junction (Tripathi, 1995, 2006; Tripathi & Lahiri, 2000).
Material and Methods
A total of five fresh samples, each of approximately 200 g, were collected at an interval of 2 feet from the 7-foot-thick hard calcareous sandstone (NS), which is full of molluscan shells. All the samples were processed for ostracods by standard procedure. About 100 g of each sample was soaked in water overnight, and a spoonful of sodium carbonate was added and boiled for more than two hours. The disaggregated samples were washed under a jet of water using 30, 72 and 150 B.S.S. mesh-size sieves. The ostracods were picked from the washed residue of a 72-mesh sieve under a stereo-zoom binocular microscope. Ostracod species were photographed under SEM (Zeiss-Gemini 300) at IIT Roorkee. All the illustrated specimens are deposited in the Micropaleontology Laboratory, Department of Geology, Mohanlal Sukhadia University, Udaipur, with repository number SUGDMF No. 1458–1472.
Age of the Bagh Group
These beds are very rich in invertebrate fauna, and on this basis, different ages have been assigned. The majority of earlier workers, including Duncan (1865, 1887), Vredenburg (1907, 1908), and Chiplonkar (1939a, b), assigned Cenomanian age based on echinoids, ammonites and lamellibranchs. Based on the above fossil groups (Bose, 1884; Fourtau, 1918; Mukherjee, 1934 in Fermor) assigned Albian to Senonian ages. Taylor and Badve (1995), based on the new bryozoan genus
Rajshekhar (1995) recorded 23 genera belonging to benthic and planktonic foraminifers from the Coralline Limestone Formation. On this basis, he assigned an age ranging from Aptian to Maastrichtian but Turonian was the dominant element. In the Jeerabad area (Man Valley) marl and Coralline Limestone overlies Nodular Limestone, which is very rich in mega as well microfossils (foraminifers and ostracods), suggesting a late Coniacian age (Chaudhary & Nagori, 2019).
On the other hand, Dassarma and Sinha (1975) described rich assemblages of lamellibranches, gastropods, ammonites, echinoids and shark teeth from eastern and western exposures of the Bagh Group. They concluded that different marine patches of the Bagh Group exposed along Narmada Valley are not of the same geologic age. According to them Bagh Group from Barwah to east of Alirajpur ranges in age from Cenomanian to Turonian, while the Group in the west of Alirajpur to Kawant–Rajpipla, which is lithologically different than that of the eastern part, shows younger ages, that is, Coniacian and ranging at least up to uppermost Cretaceous. The arenaceous series designated as NS also has a composite character regarding its origin and age. Badve and Nayak (1984) designated the term
The environment of deposition predicted for the lower part of NS is fresh water (fluvial), whereas the upper calcareous sandstone represents a shallow marine setting (Fluvio-Marine estuarine deposit) (Bhattacharya et al., 2020; Bose & Das, 1986; Singh & Gosh, 1977; Singh & Dayal, 1979; Tripathi, 2006).
Palaeobiogeography
The disintegration of Gondwanaland and their separation into different parts initiated roughly ~180 Ma. During the late Jurassic (about 158 Ma), Madagascar and India rifted away from Africa and the movement was almost directly south and nearly parallel to the African coastline. Such genetic communication was still possible in shallow marine environments until the earliest Cenomanian, that is, about 100 Ma (Puckett et al., 2016).
During the early late Cretaceous, Africa, Madagascar and Indian-Seychelle plate remained as the major tectonic elements of the southern-central Tethys, with Africa having already been separated from a Madagascar-India-Seychelle ‘plate’. A rapid northward drift of India together with the Seychelle block may be due to extensional processes that occurred between 90 and 80 Ma and may have caused changes in the palaeoceanographical currents, which influenced the distribution of the ostracod faunas. Until about 90 Ma, India remained close to Madagascar, but during Campanian, seafloor spreading initiated between India and Madagascar via the Carlsberg Ridge resulted from the rapid movement of India away from Madagascar (Dingle, 1988; Luger, 2003; Puckett et al., 2016).
The Southern Gondwanaland oceans fostered a distinctive ostracod fauna that can be recognised in Bajocian-Cenomanian strata, that is, South Gondwana Fauna (Dingle, 1988). It contains numerous endemic forms, with the most characteristic species belonging to the Progonocytheridae. A major faunal change occurred between the late Cenomanian and early Turonian times, when new taxa migrated from the equatorial South Atlantic, via the Temperate South Atlantic, and ousted the extant South Gondwana Fauna.
Some palaeoceanographical and palaeogeographical changes, such as opening pole change at 105 Ma (early Albian), probably led to the deep-water passages forming along the line of the Falkland Plateau-Southern Africa fracture zone, allowing the dysaerobic temperate South Atlantic to be flushed by oxygenated waters, which favoured the appearance of new taxa and rapid distribution in the Albian, along the Southern margins of Gondwana (Ballent & Whatley, 2006). At the same time, some old or original element of the South Gondwana fauna such as
The genus
According to the available records,
1. Cytherelloidea oudiapurensis Jain, SUGDMF No. 1458. A complete carapace, left valve view, scale bar = 100 µm; 2. Cytherelloidea thuatiensis Jain, SUGDMF No. 1459. A complete carapace, left valve view, scale bar = 100 µm; 3. Bairdoppilata sp., SUGDMF No. 1460. A complete carapace, right valve view, scale bar = 100 µm; 4. Ovocytheridea baghensis Chaudhary and Nagori, SUGDMF No. 1461. A complete carapace, right valve view, scale bar = 100 µm; 5. Perissocytheridea batei (Jain), SUGDMF No. 1462. A complete carapace, right valve view, scale bar = 100 µm; 6. Rostrocytheridea baghensis (Jain), SUGDMF No. 1463. A complete carapace, right valve view, scale bar = 100 µm; 7. Rostrocytheridea sp. cf. R . Cerasmoderma Ballent and Whatley, SUGDMF No. 1464. A complete carapace, left valve view, scale bar = 100 µm; 8. Rostrocytheridea sp., SUGDMF No. 1465. A complete carapace, right valve view, scale bar = 100 µm; 9. Neocytherideis reymenti Jain, SUGDMF No. 1466. A complete carapace, right valve view, scale bar = 100 µm; 10. Curfsina ? hanumapuraensis Chaudhary and Nagori, SUGDMF No. 1467. A complete carapace, left valve view, scale bar = 100 µm; 11. Haughtonileberis thuatiensis (Jain), SUGDMF No. 1468. A complete carapace, right valve view, scale bar = 100 µm; 12. Makatinella punctata Chaudhary, SUGDMF No. 1469. A complete carapace, right valve view, scale bar = 100 µm; 13. Makatinella thuatiensis (Jain), SUGDMF No. 1470. A complete carapace, right valve view, scale bar = 100 µm; 14. Veeniacythereis raoi (Jain), SUGDMF No. 1471. A complete carapace, left valve view, scale bar = 100 µm; 15. Nigeroloxoconcha baghensis Chaudhary and Nagori, SUGDMF No. 1472. A complete carapace, left valve view, scale bar = 100 µm.
The genus
The records of
During the early Turonian, just after the end of the Oceanic Anoxic Event 2 (OAE2), the taxonomic diversity decreases, while the level of oxygenation and the palaeoproductivity increase (along with the supply of nutrients); the water becomes hypoxic in the outer ramp environments that spread over the whole platform. The climate becomes hot and humid (Andreu et al., 2013). At Pipaldehla, ostracods are rare and non-specialised, associated with calcareous algae, benthic foraminifers and lamellibranches.
In the late Cenomanian-early Turonian marine communication is relatively easy between the carbonate platforms of the Kawant–Bilthana area with that of the Jhabua and Bagh–Jeerabad area, with the number of ostracod species in common ranging from 5 to 11, respectively.
Systematics
Subclass OSTRACODA Latreille, 1806
Order PODOCOPIDA Müller, 1894
Suborder OSTRACODA Latreille, 1806
Family CYTHERELLIDAE Sars, 1866
Genus
Suborder PODOCOPA Sars, 1866
Superfamily BAIRDIACEA Sars, 1888
Family BAIRDIIDAE Sars, 1888
Genus
Superfamily CYTHERACEA Baird, 1850
Family CYTHERIDEIDAE Sars, 1925
Subfamily CYTHERIDEINAE Sars, 1925
Genus
Genus
Genus
Family PROGNOCYTHERERIDAE Sylvester-Bradley, 1948
Subfamily PROGNOCYTHERINAE Sylvester-Bradley, 1948
Family NEOCYTHERIDEIDAE Puri, 1957
Genus
Family TRACHYLEBERIDIDAE Sylvester-Bradley, 1948
Genus
Genus
Genus
Genus
Suborder CYTHEROCOPINA Gründel, 1967
Superfamily CYTHEROIDEA Baird, 1950
Family LOXOCONCHIDAE Sars, 1925
Subfamily NIGEROLOXOCONCHINAE Reyment, 1963
Genus
Conclusions
In the present work, 15 species of ostracods belonging to 11 genera are recorded. In general, the average number of specimens of each species is very less but the overall assemblage as a whole is very helpful in determining the precise age of the top part of calcareous sandstone at Pipaldehla. All these ostracod taxa are abundantly found in the Nodular Limestone of the Bagh-Jeerabad region, where they flourished during the whole Turonian period, probably due to the increased depth of the sea and good ecological conditions. During the early Turonian period, which occurred just after the end of the OAE2 era, taxonomic diversity decreased while the level of oxygenation and palaeoproductivity increased. These changes were accompanied by an increase in the supply of nutrients. The climate during this time was hot and humid, as evidenced by the algal assemblage reported by Kundal and Sanganwar (1998). This suggests that the calcareous top of the NSF was deposited in tropical waters at a depth of 10–12 meters below low tide level. The deposition occurred in a moderate energy setting with moderate turbulence and normal salinity of water.
After analysing the ostracods in this bed, we have concluded that they share a close resemblance to the ostracod fauna found in the lower section of the Nodular Limestone in the east, as well as the oyster-bearing limestone in the west of the Bagh Group. Probably these might have been deposited during the same time when the lower part of Nodular Limestone was deposited in the eastern part. It is believed that the first marine transgression occurred from the west during the late Cenomanian Period, resulting in the deposition of Oyster beds and oyster-bearing limestone in the Rajpipla-Kawant area of Gujarat. As the transgression progressed towards the eastern part of the Narmada Valley, these marine sediments were deposited in other linear belts of graben or half-graben. In the Jhabua area, marine incursion took place during the early Turonian period, and the top of the calcareous sandstone exhibited the presence of calcareous algae, ostracods, foraminifers and other mega fossils. Among these, calcareous algae and ostracods are indicative of the early Turonian age.
Footnotes
Acknowledgements
The authors are thankful to the Department of Geology, Faculty of Earth Sciences, Mohanlal Sukhadia University, Udaipur for extending their support in this work by providing laboratory facilities. We thank anonymous reviewers for their critical and constructive suggestions to improve the manuscript.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest concerning the research, authorship and/or publication of this article
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors are thankful to the Ministry of Education, Government of India, New Delhi for the funding through Rajasthan State Higher Education and State Project Directorate Jaipur under RUSA scheme to the Department of Geology, Mohanlal Sukhadia University Udaipur.
