Micropalaeontological and Geochemical Evidence of the Late Jurassic Radiolarians Cherts of Naga Ophiolite Hill, Nagaland, Northeast-India

We analyzed the radiolarian assemblages (pelagic sediments) and geochemical studies of 15 samples collected from Meluri district Nagaland, Naga Hills Ophiolite belt (NHO) and it consists of the Flysch Naga-Arakan-Yoma trough beyond the Indo-Myanmar border. It reflects one of the many components of the Himalayan Orogenic systems of Tethyan oceanic crust discovered in Nagaland at Meluri district of India and they have very well-preserved studies and can be identified to Upper Jurassic (Kimmeridgian-mid-Tithonian). As well as a continuous sequence of Kimmeridgian-mid-Tithonian, five radiolarian assemblages have been identified in this study. This is so far the first re-covery of pelagic sediment assemblages (Radiolarians) from the Naga field, and only one sample falls into an island arch, suggesting that the tectonic framework of the Naga Hills-Chert samples was deposited in the active continental margin and the diagrams K 2 O/Al 2 O 3 and MgO/Al 2 O 3 illustrated the tectonic setting of the marine environment from Naga Hill Ophiolite Chert. Such findings have been consistent with the current geology of Naga Hills in the province of Nagaland.


Introduction
The NE-SW Naga Hills in the northeastern region of the Indo-Myanmar Ranges (IMR) at Manipur, Nagaland, regions of Arunachal Pradesh, and neighboring Western Myanmar states, Myanmar and central part of the mountainous region have been recognized as a small arcuate area for the formation of ophiolite [1]. Naga Ophiolite is a succession of strongly deformed and tectonized ophiolitic rocks that have formed in the Nagaland and Manipur northeastern provinces. The Naga-Andaman suture passes through West Burma at the northeastern end of such a large collection of authorities, which flows over more than 3000 kilometers from NE India to the Andaman Island in the Ocean [2] [3] [4]. The NHO consisted of serpentinized peridotite dismembered bodies, mafia-ultramafic deposits, volcanic mafic, pyroclastic, oceanic sediments, and high-pressure metamorphoses along with glaucophane bearing meta basics, and cherts [1]. The Naga Hills, in northeastern India, represents the northern segment of the N-S trend in the Indo-Burmese Range (IBR), which is generally recognized as an extension of the Andaman-Indonesian island arc. Further north, the Naga Hills have connected to the eastern end of the Himalayas [4] and a narrow path from the late Mesozoic to early Paleogene.
The ophiolitic rocks are situated at the northern edge of the Himalayas and the east side of the Indo-Burmese range, then proceed to a submarine sub arch of the Indonesian arch system, toward the south, towards the islands of Andaman-Nicobar-Mentawi. In Naga Hills and the Andaman Islands, ophiolitic rocks are in occurring as stacks of thrust. Even at close intervals, the 69 various parts of the dismembered suite are often difficult to correlate. Such parts are exposed and appear around a specific belt that holds a strong tectonic and a typical position in the centre of open Synformal Klippen. The ophiolite belts are approximately 200 kilometers long and relatively broad in its northern Nagaland. A number of deep-sea deposits, such as chert, carbonaceous mudstone, fine-grained sandstone, and the Naga Ophiolite itself, are driven westward by the formation of Disang and it is pressed out over to the super young Paleogene's to the west. Both higher growth areas have been assigned mostly to Upper Eocene [5]. In the appearance of Nummulite sp., the natural gas horizon was moved from Disang formations (Upper Eocene) and this biostratigraphic study was recently verified by Uddin [6]. According to the Disang Formation, other regions of Nagaland are divided into a range of sandy beds with Oligocene fragments for plants [7] [8] [9].
The previous study by [2] [8] [9] [10] [11] [12] results of the biostratigraphy of the Nagaland Ophiolite radiolarian location is summarized in Cretaceous foraminifera, calcareous Nano fossil, and six positions in Nagaland radiolarian assemblages. Unfortunately, photomicrographs are of poor quality and a large proportion of the dinosaur bones have been classified from genus-level inner chapters [10]. The ages allocated to these assemblages indicate that in this section of the Neotethyan Sea there are deep-sea requirements. In every tectonic study, it is necessary to better understand the life of the sea associated with the collapse of Gondwana and enabling the emergence of the Neotethyan Ocean.
The research paper provides an informative characteristic of the deep marine sediments of pelagic red Chert samples from the Naga Hills Ophiolite Belt, to determine their period (era) within the Neotethyan Ocean tectonic approach, based on radiolarian assemblages recorded from the study area. In comparison, earlier kinds of research on the geochemistry of the Naga hill in these regions are not available. To date, the Naga hills geochemistry of cherts samples India Nagaland state was not yet explored in detail to define its rock source characteristics, provenance, paleoclimate, and tectonic setting. The research article aims to present evidence of the oceanic pelagic sediments of NHO Red cherts, their tectonic settings, provenance, paleoclimate of the Naga ophiolite complex, Northeast India.
We carried out the radiolarian species identification and geochemical analysis of radiolarian cherts to obtain an improved understanding of the biota and age determination from the Naga Ophiolite complex.

Study Area
The Naga Ophiolite itself is thrust westwards over the Disang formation, a series of deep-marine deposits including cherts, carbonaceous mudstones, and fine-grained sandstones. The Disang Formation is thrust over younger Paleogene flysch to the west. It has been assigned to the Upper Eocene using foraminifers extracted from the upper portions of the formation. [5] assigned a shale horizon from the Disang Formation to the Upper Eocene, based on the presence of Nummulites sp. Recently, this biostratigraphic work was confirmed by [6]. The present study was performed at the Naga Hills Ophiolite, which is one of Nagaland, Northeast India's four distinct tectonostratigraphic units. Fifteen samples have been collected at Zipu and Mokie Village in the Meluri district, Nagaland ( Figure 1). Various lithologies such as limestones, cherts, spillites, and many other volcanic rocks of ophiolite-derived sediments have been formed. All the samples collected from the Pelagic oceanic sediments of feebly metamorphosed red chert samples containing radiolarian were concentrated for the present study.

Laboratory Procedures
Fifteen samples were taken from the Mokie and Zipu roadside areas and we followed the methods of [13] to perform radiolarian analyses. Red chert samples were collected and evaluated for various geochemical and Micropaleontological studies. A Chert sample fragment is etched with concentrated hydrofluoric acid (52% -55%) for three to five minutes, removed from the acid and washed briefly but carefully with water and then with a stone mill or ground a steel mortar and pestle in fragments of 1 cm up to 5 cm. The crushed chert is placed in beakers with diluted HF acid (nine parts of water to one part of acid) for 24 hours. Radiolarian analyses were identified and extracted from the dried residues under a stereomicroscope and thereafter photograph with an SEM. The identified radiolarian species were later scanned and taken with SEM images from IIT, Chennai. For geochemistry, all the samples were selected from the cherts for preparation of laboratory works and analyzed using XRF instruments at the University of Madras, Chennai. Ten samples of the major and trace geochemical elements have been analyzed. Perhaps every sample collected has been salted into an agate mortar and heavy metal particles have been analyzed of the major elements of the PW 2404 Rhodium X-ray fluorescence spectrometer [13] [14]. Every sample has been analyzed three times and the results were compared. The LOI has been evaluated by a pre-and post-calcination weight of 1 h at 1000˚C. The digested mixture of Hydro Fluoric acid, Sulphuric acid, and HclO 4 reagent is completely dissolved.

Radiolarians Identification, Accumulation, and Age Obligation
Radiolarians, the primary sediment-producing organisms, are abundant in all varieties of cherts exposed in this present study, but they are often affected or destroyed by diagenetic dissolution in the middle part of individual beds and are usually better preserved close to the bedding surfaces of chert layers. Their concentrations accentuate fine lamination, which is disrupted occasionally by bioturbation [2] [5]. We have been identified a total of five radiolarians taxa from the pelagic sediments of the study area and dominated the species of Zhamoidellum ovum dumitrica, Gongylothorax favosus dumitrica, Williriedellum crystallinum dumitrica, Hiscocapsa sp. Verbeeki and Holocryptocanium sp. dumitrica. The preservation of radiolarians was good excellent in all samples (Plates 1-3). It has been identified from the late Jurassic radiolarians of the NHO complex [15] [16]. The present research work on the radiolarian assemblages and their distribution in Naga Hills Ophiolite was carried out on the basis of morphological characteristic features and the previous work published literature carried out by [17] [18]. Radiolarians were often utilized key attributes of deep-sea sediment deposition in suture zones, which are also of crucial importance for limiting the time of major events. They are commonly used during Neotethyan Ocean researches and thus can be discovered in the sedimentary covering of the seafloor or interspersed with basalt pillows [17]. Some of the important constituents of the recorded radiolarian assemblage of the Naga Hills Ophiolites include Zhamoidellum ovum Dumitrica, gongylothorax favosus dumitrica, Williriedellum crystallinum dumitrica, Hiscocapsa sp. Verbeeki and Holocryptocanium sp. dumitrica as indicated in Plates 1, 2, 3. From the analysis of radiolarian assemblages, NHO determines their age from Jurassic to Cretaceous by [18], and it is determined using the standard proceedings and well-preserved taxa of five (5) radiolarians and found its dominance of age ranging from Kimmeridgian to mid-Tithonian. A biostratigraphic site of the Unitary Association (UA) with areas strongly connected to either the geological time of scale (2004) was evaluated using the very well-established Jurassic to Cretaceous Radiolarians Zoning [19]. Samples indicate that the Kimmeridgian to in the Mid-Tithonian period overlaps with large, well-preserved taxa (

Implications on Provenance, Paleoclimate, Tectonic Settings of the Pelagic Sediments
Our results demonstrate the radiolarian cherts samples from the NHO complex provide insight into provenance, paleoclimate, and tectonic settings. First, the provenance of classification in major elements of the analysis of this study is us-ing a geochemical classification diagram and in Sublitharenite, two samples in litharenite, and one sample in the Fe-shale Fe-sand region (Figure 3)

Conclusion
The present study using the pelagic sediments from red chert samples from Naga Hills ophiolite was carried out for geochemical and Micropaleontological studies. This shows that the iron-rich chert samples are rich in pelagic micro-organisms, i.e. Radiolarians. The chert comprises various radiolarian skeletons which are contained in a silica matrix in the form of cryptocrystalline quartz crystals. They are inserted into the silicate clay matrix with iron-rich minerals. The disappearance of pelagic calcite and the very low calcium content of the chert indicate that the chert is lower in the compensatory depth at which more calcite dissolves within the ocean. Five (5) radiolarians were identified and distributed in Naga hills Ophiolite namely Zhamoidellum ovum dumitrica, gongylothorax favosus dumitrica, Williriedellum kristallinum dumitrica, Hiscocapsa sp. Holocryptocanium sp. and Verbeeki sp. dumitrica has age supremacy ranging between Kimmeridgian and mid-Tithonian. Geochemical data of pelagic sediments in the NHO samples showed the provenance of the rocks are sublitharenite, Litharenite, Fe-shale, and Fe-sand field, and the A-CN-K, discrimination plots indicated the deep to moderate weather conditions and quartzose sedimentary provenance in the source region for these sediments. The tectonic settings of chert samples illustrated the marine environment of NHO and the diagram of Log (K 2 O/Na 2 O) vs. SiO 2 , for the determination of various tectonic-adjusting chert samples, only one sample drop in the field of the active margin falls inside this area of the island arc, implying that the tectonic setting of the Naga Hills has been deposited in the active continental margin.