Assistant Professor

Department of Geology

Durgapur Government College, Durgapur

 Paschim Bardhaman, West Bengal, India 

Abstract

The new horizon has yielded four species of Reineckeiidae. Lithological comparisons have been made with adjacent sections under the Jhura dome, where stratigraphy is well established. Reineckeia (Loczyceras) reissi and Reineckeia (Loczyceras) smithi were found in the ironstone-shale bed with limestone intercalation. They never co-occurred with Reineckeia (Reineckeia) tyranniformis. In addition, Reineckeia (Loczyceras) reissi is connected with Subgrossouvria abberens (Kayal 2009). Thus, the Reissi Subzone is associated. The underlying sandstone bed only bears R. tyranniformis fossils and is lithologically similar to bed 9 in other Jhura Dome sections. R. tyranniformis and R. anceps fossils are abundant in the oolitic limestone deposit. Thus, the Anceps Subzone and Reissi Subzone divide between beds 9 and 10. Kutch's hecticoceratin subclade also diversifies during the Middle Callovian. The Mediterranean and Submediterranean Province has 82 Hecticoceratinae species in 13 genera. Authors found six genera, 11 biological species, and seven dimorphically paired species after reconsidering Spath's form in light of sexual dimorphism and intraspecific variability. In the Upper Callovian, the subfamily Hecticoceratinae maintains generic diversity but loses species.During Upper Callovian, Sublunuloceras arose and true Hecticoceras disappeared from all faunal provinces. Sublunuloceras, Putealiceras, and Brightia are numerous in Kutch, as are hecticoceratins of Mediterranean and Submediterranean generic composition.

Introduction

Kutch in western India is famous over the world for its rich assemblages of the Middle – Upper Jurassic ammonites. The family Sphaeroceratidae (Jana 2002), Reineckeiidae (Kayal 2009) and Ataxioceratidae especially the subfamily Virgatosphinctinae (Shome 2009) have already been studied in substantial detail and revised; but the family Oppeliidae Bonarelli was not studied and revised since Spath’s work (1928). The centre point of present study will thus be concentrated on the stratigraphy, phylogenetic systematics and evolutionary palaeobiology of the family Oppeliidae of Kutch.

The basin had opened during the Jurassic period which was also the period when the ammonites reached their evolutionary peak. Kutch ammonites were first investigated by Waagen in 1875 and he gave detailed systematic description. Later, Spath (1927-1933) thoroughly investigated the specimens collected by Blake & also revised Waagen’s work. Spath had also provided a detailed systematic discussion accompanied by stratigraphic position of those ammonites. Ammonites being variously ornamented & having very complicated suture line are charaterised by innumerable combination of these elements, and palaeontologists especially of earlier days, erect a handful of species and genera, with slight differences in such morphology, e.g. presence or absence of a particular ornamental element or size of particular sutural element. This practice has been criticized by many and detailed investigation resulted in clubbing of many preexisting species in a single species. The picture, however, changed drastically when sexual dimorphism in ammonites is recognized (Collomon, 1963; Makowski, 1963). Two sexes of same species differ mainly in their size, microconch, the smaller morph being half or even smaller than the macroconch, the larger morph. They also sometimes differ in minor ornamentation features or shape parameters and particularly in some apertural features like lappet in microconch. Recognition of sexual dimorphism in 60’s was perhaps the most important event in ammonite taxonomy. Many ammonite specialists have since being engaged in establishing species and genera to be reckoned as sexually related. This has curtailed a lot of burden of ammonite classification.

After Spath (1927-33) Middle Callovian ammonites of Kutch particularly macrocephalitids, sphaeroceratids and periphinctids have been investigated by several workers (Bardhan et al. 1988, 1994, 2007; Bardhan and Datta 1987; Datta 1992, Datta et al. 1996; Jana et al. 2000, 2002) but reinekeids (Ammonoidea) have been revised by only by Kayal (2009) and oppelids were revisited by Roy (2014) .

The Oppeliidae are the second most diverse ammonite groups after perisphinctids during the Middle-Upper Jurassic. Hecticoceratinae is the most diverse subfamily within oppelids and has wide palaeobiogeographic and temporal distributions. It is taxonomically well studied (Elmi 1967) in the Mediterranean. This subfamily is known mostly by macroconchs only, although dimorphism has long been recognized by Zeiss (1956). Elmi (1967) recognized microconchiate groups within Hecticoceratinae but did not establish dimorphic pair at generic level. In one case, he recognised dimorphism within a genus i.e., Brightia s.st. (microconch) and Brightia (macroconch), and showed separate evolutionary lineages of them.

Hecticoceras Bonarelli is the type genus of the subfamily Hecticoceratinae. It has stratigraphic importance and is widely used to demarcate subzones and horizons. H. (Chanasia) michalski Lewinsky, H. boginense Petitclerc, H. proximum Elmi and H. (Ch.) turgidum (Loczy) are used as zonal indices for the Michalski, Boginense, Proximum and Turgidum horizons respectively in Subtethyan Province of Europe (Cariou, 1984). In Kutch, Hecticoceratinae was represented by eight genera ranging from the Middle Bathonian to Lower Oxfordian (see Spath, 1928 and present study). The genus Hecticoceras is represented by two species H. giganteum Spath and H. aff. turgidum Loczy which are now synonymised under H. giganteum which ranges from the top of the Lower to basal Middle Callovian in Kutch (see Roy and Bardhan 2007). They have also addressed the sexual dimorphism within Hecticoceras giganteum based on additional topotypes and other materials along with the type specimens. The nature of sexual dimorphism appears to be differing from that of Oppelinae and Prohecticoceras. Microconch is less strongly ornamented and lack primaries on the body chamber. Thus, it comes close to Jeanneticeras Zeiss, a microconchiate genus described by Elmi (1967) within Hecticoceratinae. Roy (2014) has described Ten biological species that have been tdescribed under five genera and sexual antidimorphs are paired within the genera Kheraites Spath, Putealiceras Buckman, Sublunuloceras Spath and Brightia Rollier. Kheraites crassefalcatum and K. igobilis have been paired as sexual antidimorphs; Putealiceras bisulcatum a smaller variant with tricarinate venter has now been paired with Putealiceras trilineatum. Sexual dimorphism has also been established within P. intermedium [♀ and ♂] and P. vijaya [♀ and ♂]. Pseudobrightia dhosaensis an exclusive Lower Oxfordian genus earlier described by Spath (1928) has now been redesignated as Putealiceras dhosaense.

This study involves precise chronostratigraphic delineation of strata with the help of reineckeids and oppelids species which were redescribed here in the light of modern taxonomic knowledge especially sexual dimorphism and population dynamics

Geology and Physiography

A very thick succession (nearly 3000 mts) of marine sediments was deposited in Kutch during Bajocian to Aptian time, which is divided into four major lithounits mainly Patcham, Chari, Katrol and Bhuj Formatins in ascending order. These Mesozoic sequence of Kutch (particularly the Middle to Late Jurassic Patcham & Chari) famous for its invertebrate fossils treasure and attracted attention of mainly palaeontalogests since long. Mega invertebrates of Kutch include molluscs, brachiopods, echinoderms, cnidarians, poriferans etc. Among molluscs bivalves and ammonites occurs in thousands and particularly the later have got much attention from the palaeontologists until recently.

The specimens of the present study have been collected from Jara, Jumara, and Keera sections of the Jumara Formation. Detailed lithostratigraphical succession of each section of Kutch, along with the vertical distribution of the major ammonite species is shown in Jana et al. (2005). Callovian sediments are grouped into the Jumara Formation (Mitra et al., 1979).  Significant sedimentological works and detailed facies analyses are now available (Datta, 1992; Fürsich and Oschmann, 1993; Fürsich et al. 1994). The Jumara Formation is represented by a heterolithic facies association consisting of shale, limestone and sandstone deposited in a mid-shelf environment. The Lower part of Jumara Formation is Early Callovian in age and this part is dominated by shale-limestone (packstone/wackestone) alternation. The Middle Callovian beds are dominantly siliciclastics and represent a shoaling upward phase (Datta, 1992; Fürsich and Oschmann, 1993). The Upper Callovian beds are composed of an alternation between greenish grey shale, occasionally gypseous with secondary gypsum and white fossiliferous limestone. Dominantly argillaceous facies in Jumara Formation were deposited in the outer ramp formed in the Kutch embayment (Fürsich et al., 2004). These sediments were deposited below storm wave base in low-energy environment. 

Fig. 1: Geographic Location, present fossil collecting area, west of Bhakri

Stratigraphy

Kutch basin opened up during early Middle Jurassic as the Indian plate rifted from the African plate and transgression occurred. Then a thick pile of sediment was deposited till early Cretaceous and result in nearly 3000 mts. thick sedimentary sequence (Biswas, 1991). This succession was divided into four units early in the history of studies on Kutch rocks and the scheme with modification still retains its applicability; the units are now formally designated as Patcham, Chari, Katrol, Bhuj Formations (Mitra et al., 1979). The units are thought to be deposited in two trangressive-regressive megacycles – the Patcham and Chari having dominantly carbonate and shale deposits, represent the transgressive megacycle, while the latter two clastic formations were deposited during the regressive megacycle (Biswas, 1991). Patcham and Chari Formations are richly fossiliferous. The present study concerns the middle-upper part of Chari Formation.

The earliest geological work in Kutch is of Sykes (1834). Grant (1837) and Blanford (1867) also contributed substantially. An extremely valuable contribution (Memoires of GSI) was that of Wynne and Fedden (1869-72). They carried out detailed mapping and geological investigations, which provided a basis for all subsequent works. Wynne (1875) was first to publish a geological map of Kutch. He divided the Jurassic rocks (included some Cretaceous rocks also) into a Lower and Upper Group and considered the former unit as equivalent to ‘Inferior Ooolite’ of England. Waagen (1873) included Stolickzka’s field data in his memoire and published his four-fold stratigraphic scheme of Jurassic rocks which was followed with modifications by all later workers. The divisions are Patcham, Chari, Katrol and Umia ‘Groups’. Waagen’s units are defined by ammonite assemblages but are not isochronous to those of European Jurassic. Spath (1927) was the first to correlate the stratigraphic units of Kutch with European ammonite zones, taking help of Prof. Blake’s collection. A detailed account of the stratigraphy of Kutch was given by Rajnath (1932). He demonstrated the mappability of Waagen’s units and proposed twenty-six beds and subdivided ‘Umia Group’ into marine Umia and Ukra ‘Beds’ and nonmarine Bhuj ‘stage/series’. Rajnath (1932, 1942) established a chronostratigraphic classification of Kutch Mesozoic. Agarwal (1957) renamed ‘Chari Series’ as ‘Habo Series’. Biswas (1971, 1977, 1981, 1991) highlighted the drawbacks in treating older names as formal units and introduced a new set of terms to designate the lithostratigraphic divisions. His units are Jhurio, Jumara, Jhuran and Bhuj Formation in ascending order. Mitra et al. (1979) opposed Biswas’s (1971) arguments that Waagen’s divisions were not precisely defined and lack mappability or regional applicability. They added the Bhuj unit of Rajnath (1932) and included Umia and Ukra in Katrol as these are only locally exposed and have little extension both laterally and vertically and treated the four units as Formations – name Patcham, Chari, Katrol and Bhuj.

The Patcham Formation is exposed mainly at the core of two domes in the mainland of Kutch, i.e., Jhura and Jumara and in Patcham island within the Rann of Kutch.

In mainland, it is best developed in Jhura where the formation is constituted of four beds adding up to a thickness of 210 mts. The formation is composed mainly of limestone with some cross stratified shale units. At Jumara, which is more offshore part of the sea, exposed part of Patcham Formation is much thinner and lack shale.

The Chari Formation is a deeper water product than the Patcham Formation (Biswas 1991, Fürsich and Oschmann, 1993), deposited in response to the continuing transgression. The Chari Formation is developed well in the mainland in areas like Jumara, Jhura, Keera and Habo domes and partly in several other localities such as Jara, Samatra, Ler etc. Jumara yielded maximum number of change is quite rapid especially vertically and also laterally, within Chari formation. The litho-motif of the Chari formation in Jumara, is the alternation between white wackestone and grey shale or ironstone. This motif is interrupted at three level by sandstone bodies with sharp boundaries and punctuated at the top by a oolitic limestone shale alternation, popularly known as Dhosa Oolite. The Chari Formation of Jhura is mainly similar in look and disposition, except that it is more arenaceous as a whole. The sandstone bodies at Jhura differ slightly from those of Jumara in composion and grain size (see Text-fig. 2). The stratigraphy of the present study area is very similar to Jhura as it comes under the Jhura dome and is shown in Text-fig. 2.

Brief Descriptions Species:

Description of Reineckeid species:

Reineickeia Tyranniformis

It is compressed at best up to last two whorls and the maximum W/H ratio is 0.77; inner whorls appear to have rounded shape with crateriform umbilicus at least up to 20mm diameter. Ornamentation relatively dense in inner whorls with secondaries not exceeding five; the number gradually decreases ontogenetically and becomes 2 to 3. Secondaries are sharp in the inner whorls but gradually become rounded and blunt in the outer whorls. Primaries are short and rise from the umbilical margin, never very prominent. Number of primaries in each half-whorl varies from 7 to 9. Secondaries are forwardly projecting and are interrupted by shallow ventral sulcus although; primaries are also prorsiradiating in nature. Tubercles are noticed from the beginning and are pyramidal in the early whorls and strength gradually increases but in the last whorl become blunt, elongated. Position of tubercles appears to be migrated from the inner flank in the early whorls to umbilical margin in the later whorl. In the last whorl prominent solitaries are present in between two primaries.

Species large but adult size variable, shell is thin, discoidal in shape; largest phragmocone diameter is about 95mm (DGC/BHK/1). Shell evolute with large umbilicus (U/D: 0.45-0.47) and the shape of the whorl varies ontogenetically (W/H: 0.73-0.77). Whorls are semicircular to semielliptical in cross-section. Umbilicus and ventro-lateral margins are gradual and venter relatively narrow and evenly rounded. Mid- ventral sulcus is present, and it is prominent throughout, but on the adult body chamber it becomes feeble. The nucleus whorls are missing in all the specimens but from the degree of coiling and from the whorl section in some of the specimens it seems that the early stage is crateriform in nature. Umbilical wall is steep to overhanging but in body whorl umbilical margin becomes gradual with inclined wall.

Reineckeia (Reineckeia) Anceps

Reineckeia (R.) anceps is a highly variable species and are found mainly in the Lower Callovian beds throughout Tethys. The holotype of Reinecke (1818, pl.vii, fig.61) is now-a-days lost but from the description of Reinecke, Cariou (1984a) indicated the age of the specimen to be approximately as the top of the Lower Callovian or the beginning of the Middle Callovian. But, since the species demarked a traditional Callovian Zone i.e., Anceps Zone created by Oppel (1856-1858; p-504) it became necessary to retain the species. So Cariou (1984a) following the work of ammonitists of yester years have chosen a neo-type (Fig.1 and pl. XXXIV of Cariou, (1984a) collected from the same stratigraphic level as that of Reinecke’s form.

Shell thick, evolute (U/D= 0.42 TO 0.44) , oval, depressed (W/H= 0.75 to 0.85). Shell is large. Fine delicate primaries are first noticed. Protoconch appears to be smooth. Lamellar spines develop at the end of primary ribs. First conical tubercles develop at the third whorl. During early ontogeny a crateriform umbilicus is observed. Lateral very short and strongly curved. Primaries short and rises from umbilical margin are sharp, angular in cross- section. Secondaries are bifurcating, rarely trifurcating and forwardly inclined. Distinct sulcus developed. Umbilical margin is gradual, and wall is vertical. No. of primaries per half whorl is 12 and no. of secondaries per half whorl is 37.

Reineckeia (Loczyceras) Reissi

Type No: 2101 figured and described by Waagen (1875, fig. LIX, fig. 1a-b) was collected from Jhura hills. The end-phragmocone diameter of the specimen is 144mm. It is evolute with large umbilicus (U/D: 0.43) and compressed (W/H: 0.93). Ventral groove prominent and it loses its strength as it reaches adult stage. Whorl section is oblong to sub-elliptical. Aperture is missing.

Inner whorls are covered with matrix. But the whorls which are not covered are with tubercles throughout. The primary ribs are rursiradiating in nature and originate from the umbilical wall. The primaries are divided into secondaries at about 1/3 ^rd height from the umbilical margin and bear on the point of division a pointed tubercle. The secondaries are two to four in number, and it never exceeds four. Though the inner whorls are not visible but branching of four is noticed on the penultimate whorl. The secondaries are slightly prorsiradiating in nature and are interrupted by a deep furrow in the middle of the siphonal side of the shell. The ribs are fine during early ontogeny and become gradually coarser. Solitary ribs which appear haphazardly and more abundant in later stages are never tuberculated.  

Though R. reissi and R. tyranniformis are found in stratigraphically different horizons but they show close resemblance regarding their forms i.e. both are compressed. They can be easily differentiated by their adsult macroconch sizes. R. tyranniformis is a larger form whereas R. reissi is a middle-sized species. Moreover, the secondaries in R. reissi never exceed 4 which are 5 to 6 in R. tyranniformis.

 R. reissi is closely related with the R. anceps, though they are found at different levels. Adult specimens of anceps are slightly largely in size than reissi. Lappets are common in anceps but rarely found in reissi. Both have crateriform stage in initial whorls as identified by Cariou (1984a).  

Reineckeia (Loczyceras) Smithi

Type No 16060, kept at the Repository Section of Geological Survey of India, Kolkata. Mostly internal mould with shell remains, full grown adult specimen, collected from bed no 7 of Spath (1927) of Keera.

Shell is thin, discoidal with nearly parallel sided laterals. Shell evolute with large umbilicus (U/D: 0.47) and compressed. Aperture is oblong to sub-elliptical in shape. Venter is short and rounded; ventro-lateral margin is gradual whereas umbilical margin is sharp. Mid- ventral sulcus present but its strength varies ontogenetically and is almost feeble towards the peristome where the ribs are continuous across the venter. In the early ontogeny a crateriform stage is noticed.

The present species shows very close resemblance with R. (Loczyceras) reissi in having similar size, shape and ribbing pattern.  But macroconch of R. (Loczyceras) reissi is a highly variable form and characterized by the persistence of tubercles almost to the end of growth and absence of any thread like lirae near the peristome.

Cariou and Krishna (1988) included the present species within their R (R.) anceps which is a macroconch. But macroconch of R. smithi is a much smaller form compared to macroconch R.(R) anceps and it never shows the characteristic 6 to 9 secondaries of the macroconch of R. (R) anceps at any growth stage, it shows maximum of 4 secondaries.

Another stratigraphically contemporaneous species is R. arthritica especially the microconchs. But R. arthritica is relatively involute with inflated whorls and rounded flanks.

Description of Oppelid species:

After the revision work made by Roy (2014), 10 biological species have been described under six genera which are ranging from Lower to Upper Callovian. Brief discussions about the oppelid species are given below.             

Hecticoceras Giganteum

The genus Hecticoceras was earlier represented by two species H. giganteum Spath and H. aff. turgidum Loczy. Roy and Bardhan (2007) had synonymised them under H. giganteum which ranges from the top of the Lower to basal Middle Callovian in Kutch. The authors also addressed sexual dimorphism within Hecticoceras giganteum based on additional topotypes and other materials along with the type specimens.

Kheraites Ignobilis

K. Ignobilis and K. smithi of Spath are now designated as K. ignobilis which is larger in size and described as macroconch while K. crassefalcatum, K. varicosus and K. ferrugineus of Spath are now designated by Roy (2014) as microconchiate counter part of K. ignobilis; they are smaller in size and have ornamental modifications in their body chamber.

Putealiceras Trilineatum

Considering Spath’s (1928) intension, with the support of additional specimens, Putealiceras pseudodynastes has been synonymised with P. trilineatum. Another species of Spath (1928) P. bisulcatum with small adult size and tricarinate periphery forming two prominent sulcus along the mid venter, now designated as the microconch of P. trilineatum.

Putealiceras Intermedium

Spath’s (1928) form showing wide intra-specific variation have been re-described by Roy (2014) and with the help of additional topotypes sexual antidimorphs are recognised.

Putealiceras  Vijaya

Redescription of Spath’s (1928) form with additional specimens and sexual dimorphism has been established.Mostly rectiradiate solitaries both in macroconch and microconch, depressed whorls, keel indistinct in body whorl of macroconch but continue in microconch.

Sublunuloceras Discoides

Involute coiling and smooth outer whorls are the two distinguishing features for this species both for macroconch and microconch. Microconchs are smaller in size showing apertural modification – lappet.

Sublunuloceras Dynastes

Unlike S. discoides, the ornamentation in the present species continues up to the body whorl, though somewhat blunt in nature and it has widely fastigate periphery. S. Nodosulcatum of Spath has been synonymised with the present species.

Lunuloceras  Lunula

Waagen’s (1875) Harpoceraslunula and Spath’s (1928) Lunulocerasorientale have been synonymised as Lunuloceraslunula. Comparing additional topotypes the authors have found that all the specimens have certain common features like highly evolute, compressed whorls, smooth inner whorls and indistinct keel, though ribbing pattern varies to some extent which may be accounted for intra-specific variability.

Brightia Callomoni

A new species has been established which includes Spath’s (1928) Brightia sp. ind. – a fragmentary specimen. It is named after the great palaeontologist John H. Callomon. Sexual dimorphism has also been established.

Biostratigraphic implications:

Ammonites, being nektonic and generally having very rapid evolution are extremely useful in bio- and chronostratigraphy. Short temporal range and wide geographic distribution made many ammonites excellent index fossils for correlation of Jurassic and Cretaceous strata. This fact was recognized early in the history of the detailed stratigraphic works and pioneering workers like Arkell (1956) made use of ammonites for world-wide correlation of Jurassic rocks. Afterwards, every bio- or chronostratigraphic works of the Mesozoic rocks remains heavily dependent on ammonite fossils contained in those. Even when time-diagnostic ammonite taxa with short temporal range are not obtained, ammonite assemblages could provide very important clues to the understanding of age of a particular horizon. This is possible because ammonites, besides, having rapid evolutionary history, are quite abundant in almost all Mesozoic marine sequences. A very detailed documentation on the Middle Callovian horizons of Submediterranean France provided by Cariou (1984), any other major work and observation in the present endeavour attest to this fact. The work of Cariou (1984) proves that ammonite biostratigraphy can be made in the precision level of less than one million year.

This attempt, however, was not directed towards working out a detailed biostratigraphic scheme but rather aimed at demarcating the boundary between the Middle Callovian substages for which time-diagnostic ammonite taxa (sensu Ager, 1984) e.g.,  reineckiids  were used. Representative of the family Reineckeiidae and other associated ammonites seem to be of particular interest in this regard. Temporal ranges of the species of these groups especially reineckeiids which are studied here are given in the Table – 1. When this distribution is compared with the Submediterranean France (Cariou, 1984) following facts emerge:

1. Spath (1927-1933) subdivided the Middle Callovian of Kutch into two zones – Rehmanni and Anceps. However, the European Rehmannia rehmanni is very poorly known (Datta, 1992) or altogether absent (Cariou & Krishna 1988) in India. Indeed, the reineckeiin species abundant in this zone is Reineckeia indosabauda which is now synonymized with Reineckeia anceps (Cariou & Krishna, 1988). R. anceps is a zonal index of Submediterranean France and a chronostratigraphic zone marking the base of Middle Callovian has been named after it (Cariou, 1984a). The base of Middle Callovian is thus directly matched with the base of the Anceps Zone of France (see also Krishna & Thierry 1987; Cariou & Krishna 1988; Jana & Das 2002; Mukherjee et al., 2003). In the present studied area not a single ammonite specimen has been found from the sandstone bed that underlying the oolitic limestone bed, though Jana (2002) reported Eucycloceras opis from this bed in other sections (Bed 7 of Jhura) and also marked it as the base of Middle Callovian. On the other hand side by side occurrences of R. anceps and R. tyranniformis have been documented in the oolitic limestone (Bed 8 of Jhura) but in the overlying sandstone body only R. tyranniformis continue (Bed 9 of Jhura; see Jana , 2002).

Kayal (2009) pointed out that R. anceps and R. stuebeli are not only morphologically very close, they have the same biogeographic and biostratigraphic distributions everywhere, and appear to be conspecific (monospecific assemblage of Callomon, 1985). So, the Anceps Subzone of Kutch matches well with Stuebeli Subzone of France. However, R. tyranniformis occurs at a higher chronostratigraphic level in France (ranging from blyensis horizon, Tyranniformis Subzone to baylei horizon, Baylei Subzone of Coronatum Zone) than in Kutch where it first appears in the semilaevis horizon of Lower Callovian and continues up to the top of the Anceps Zone. The semilaevis horizon is included within the Macrocephalites formosus biozone of Jana (2002) which is co-eval with the middle part of the Gracilis Zone including Pictava Subzone of Cariou (1984a). Moreover, Reineckeia tyranniformis in Kutch is also associated with another reineckeiin R. turgida (see Kayal, 2009) which is restricted to only Lower Callovian in France.  Spath (1928) reported the holotype of R. tyranniformis from the Golden Oolite of Keera which also yields Nothocephalites semilaevis ascertaining its definite Lower Callovian age. In Kutch both Reineckeia tyranniformis and R. turgida continue up to the top of Middle Callovian like R. (R.) anceps (see Kayal, 2009). Hence, The Bed 8 and Bed 9 can be matched with the Tyranniformis Sub Zone of the Sub-Mediterranean Province.                                             

2. The lowermost faunal horizon of Coronatum Zone of France, i.e., villanyensis horizon yields Collotia gignatea (Cariou 1984a). Kayal (2009) reported the species from the base of Reissi Zone and, Cariou & Krishna (1988) also reported a single specimen at Jumara from the base of their Coronatum Zone. So the base of the Reissi Zone can be matched with much confidence with the base of the Coronatum Zone of France. The Reissi Zone of Kutch is subdivided into two subzones, i.e. the lower Reissi Subzone and the upper Aberrens Subzone. The Aberrens Subzone is dominated by Subgrossouvria aberrens. However, R. reissi in the present study area has been found to be occurred along with R. smithi in the Bed 10 of Jhura. Cariou (1984a) also recognized R. reissi in the France from the same biostratigraphic level, so base of Bed 10 in the studied area can be depicted as the boundary between Anceps and Reisii Zone.

3. In Kutch, Hecticoceratinae is represented by eight genera ranging from Middle Bathonain to Lower Oxfordian (see Spath 1928, Roy and Bardhan 2007). Hecticoceras giganteum Spath described by Roy and Bardhan (2007) from Kutch ranges from the top of the Lower Callovian to the basal Middle Callovian Hcticoceras gigunteum spans the semilaevis horizon of Formosus Zone to perisphinctoides horizon belonging to Eucyclocerasopis Subzone of Anceps Zone. In semilaevis horizon H. gigunteum cooccurs with Nothocephalites semilaevis (Waagen) the zonal species along with Macrocephalites formosus (J. De. C. Sowerby), Kheraiceras cosmopolitum (Parona and Bonerlli), Kamptokephalite slamellosus (J. De.C. Sowerby), Dolikephalites subcompressus (Waagen), Reineckeia tyranniformis Spath, Reineckeia anceps (Reinecke), Collotia oxyptycha (Neumayr) and others (Spath, 1927-33; Cariou and Krishna, 1988; Datta, 1992; Bardhan et al. 2002 and Jana et al. 2005). In the Anceps Subzone of basal Middle Callovian H. gigunteum is associated with Eucycloceras opis ((J. De. C. Sowerby), Reineckeia tyranniformis, R. anceps and Choffatia spp. This level marks the disappearance of Macrocephalites spp. and Kheraicerasspp. H. gigunteum goes up to the perisphinctoides horizon of Opis Subzone and is found to be associated with Idyocycloceras perisphinctoides Spath, the zonal index, E. opis, Phlycticeras, Kheraites  and Reineckeia spp. continue (Jana et al. 2005).Lunuloceras lunula appeared at the lowest part of the Ressie Zone and continued up to the Upper Callovian Ponderosum Zone (Table 1). It co-occurred with three species of Putealiceras and two species of Sublunuloceras in the R. reissi horizon of Reissie Zone and AberransZone  of Middle Callovian and continued up to the Ponderosum Zone of Upper Callovian. At the Ponderosum Zone L. lunula disappeared but Putealicerasspp. and Sublunulocerasspp. continued into Mayaitesmaya horizon of Mayaites Zone. Brightia callomoni is restricted within the Ponderosum and Maya Zone of Upper Callovian where it co-occurred with Putealiceras spp. and Sublunuloceras spp. (Table 1 and Table 3).

4. Jana et al. (2005) have attempted a correlation of Kutch biozonation with that of Submediterranean Province. The top of the Gracilis Zone of France has been correlated with Semilaevis Subzone of Kutch. They found faunal homogeneity of many horizons between these two regions. Macrocephalites gracilis shows strong resemblance to Nothocephalites semilaevis (see also, Westermann and Callomon, 1988, p.16). The lower stratigraphic level of H. gigunteum therefore corresponds to H. (J.) girodi Bonarelli and H. boginense Petitclerc of boginense horizon of the Gracilis Zone of France. In fact the Kutch species is morphologically very similar to those European species (Roy and Bardhan 2007). The highest occurrence of H. gigunteum is confined in perisphinctoides horizon where one of the associated taxa is R. tyranniformis and Jana et al. (2005) matched this horizon with blyensis horizon of France which belongs to Tyranniformis Subzone. Recently Jain (1997) reported Phlycticeras gr. pustulatum (Reinecke) at the similar level from Jumara in Kutch. It cooccurs with R. tyranniformis, Eucycloceras pilgrim Spath(= E. opis, see Jana et al. 2005).Kheraites ignobilis has also been reported by Roy (2014) from similar horizon of Jara, Jumara and Keera. Hecticoceras s.st. is short ranging in France. It is confined only to the topmost Lower Callovian (boginense to kiliani horizon) (Cariou, 1984). However, in Kutch Hecticoceras appeared simultaneously in the top of lower Callovian but lived longer and continued up to the lower part of Anceps Zone.In Germany Hecticoceras s.st. also continue into higher stratigraphic level and is found from Middle to Upper Callovian (see Schlegelmilch, 1985; Martill and Hudson, 1994).

5. The upper part of the Callovian (lamberti horizon) is characterized by Kosmoceras and Distichoceras and with clear presence of Hecticoceras punctatum Lahusen. H. punctatum is quite similar in appearance with Putealiceras vijaya of Kutch. Presence of P. vijaya strenghthen the correlation between Mayaites maya zone of Kutch with the Lamberti zone of Submediterranean Realm, The European Athleta Zone is equivalent to Ponderosum Zone of Kutch; Peltoceras athleta is quite similar in morphology with Peltoceras ponderosum as depicted by Datta (1992). Trezeense horizon of Athleta Zone in Subtethyan Province is marked by Hecticoceras (Orbinyiceras) trezeense which is associated with H. (Sublunuloceras) aff. dynastes and H.(Putealiceras) trillineatum. In Kutch, H. (Sublunuloceras) dynastes and H. (Put.) trillineatum though appear in the Subgrossouvria aberrans horizon of Reissi Zone, are become prolific in lower part of Ponderosum Zone.  Putealiceras intermedium and Sublunuloceras dynastes occur throughout the Ponderosum Zone in Kutch, though in Subtethyan Province they are co-occurring again in

the Collotia collotiformis horizon of Athleta Zone. So, the zonal assemblage reinforced the stratigraphic correlation between Kutch and Subtethyan Province especially for the Upper Callovian Athleta Zone.

Table 1. Stratigraphic range of species of family Reineckeiidae and Oppeliidae along with other ammonite species from Jhura Dome, Kutch.

Conclusion

After the pioneering works of Waagen (1875) and Spath (1927-33), very little work has been done on ammonite fauna especially reineckeids, though Kayal (2009) has done extensive work on the family Reineckeiidae of Kutch. The present study has attempted to describe reineckeids from a newly discovered section (west of Bhakri) under the Jhura Dome. The work undertook detailed revision of forms in the light of modern taxonomic knowledge. Chrnostratigraphy as well as biostratigraphic scheme have been addressed with the help of the reineckeids found in this horizon.

Altogether four species Reineckeia (Reineckeia) tyranniformis, Reineckeia (Reineckeia) anceps, Reineckeia (Loczyceras) reissi and Reineckeia (Loczyceras) smithi have been identified from this new horizon, lithological comparison has been carried out with the adjacent sections under the Jhura dome where the stratigraphy has already been well established. Reineckeia (Loczyceras) reissi and Reineckeia (Loczyceras) smithi both found to be occurred within the bed having ironstone-shale alternation with some limestone intercalation. They were never found in this section co-occurred with Reineckeia (Reineckeia) tyranniformis. Moreover, in the adjacent section Reineckeia (Loczyceras) reissi has been reported to be associated with Subgrossouvria abberens (Kayal 2009) in the upperpart of the bed 10. So it is correlated with the Reissi Subzone.

The underlying sandstone bed has sparse fossil occurrences which only contain R. tyranniformis and it is lithologically comparable to bed 9 in the other sections of Jhura Dome. The underlying limestone bed is oolitic in nature and shows prolific fossil occurrences especially R. tyranniformis along with some R. anceps. So the boundary between the Anceps Subzone and Reissi Subzone lies in this section between bed 9 and bed 10.

The hecticoceratin subclade shows a great diversification during the Middle Callovian, and Kutch is not an exception. In the Mediterranean and Submediterranean Province the subfamily Hecticoceratinae is represented by 82 species under 13 genera. While revisiting the Spath’s form in the light of sexual dimorphism and intraspecific variability; authors have come out with six genera and 11 biological species of which seven species have been dimorphically paired. In the Upper Callovian the subfamily Hecticoceratinae is consistent with same diversity at generic level, but the genera become species-poor.

True Hecticoceras are totally absent in all faunal provinces during Upper Callovian; at the same time a new genus appeared i.e. Sublunuloceras. In Kutch also the generic compositions of hecticoceratins remain same as in Mediterranean and Submediterranean and Sublunuloceras are abundant along with Putealiceras and Brightia.

Acknowledgements

PR thankful to the Principal, Durgapur Government College for providing the necessary infrastructure and laboratory facility for carrying out the research work.

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