Browsing by Author "Jai Krishna"

Now showing 1 - 20 of 20

A new approach to the correlation of the Upper Kimmeridgian Beckeri Zone across the Tethyan Sea
(E. Schweizerbart'sche Verlagsbuchhandlung, 1996) Günter Schweigert; Jai Krishna; Bindhyachal Pandey; Deo Brat Pathak
Based on a preliminary attempt of high resolution subdivision of the Upper Kimmeridgian Beckeri Zone of Southern Germany into ammonite faunal horizons, and on recently collected ammonites from the Kachchh area (India), the lineage of the ammonite genus Hybonoticeras is outlined. In consequence it is now possible to make much more precise correlations around the Kimmeridgian/Tithonian boundary (Beckeri/Hybonotum Zones) all across the Tethyan realm and its adjacent areas (e. g. Submediterranean of Europe, Indo-East-African province, Mexico).
Applicability of the sequence framework in IEAP and GTM, with brief comments on the hydrocarbon prospects in the Indian basins
(Springer, 2017) Jai Krishna
The validity of the Indian first- and second-order sequence stratigraphic framework is first demonstrated in India and IEAP through the isochronous character of as many sequence surfaces as possible. It is realized through investigation of the formulated sequence surfaces in the relatively better studied time slices in specific basins of the different sectors (Fig. 5.1). Subsequently, detailed comparison of the developed Indian succession of sequence surfaces is made, particularly, with the Arabian Triassic–Jurassic, and Madagascar Jurassic–Cretaceous (Figs. 5.1, 5.2, 5.3, 5.4, 5.5 and 5.6), as also mutually among the Jurassic development in India, Madagascar and Arabia (Fig. 5.4). Comparison of the Indian sequence framework is also made with regions/basins east of India at the first-order level with Dampier (Fig. 5.7), West Irian (Fig. 5.8), Timor/Sula (Fig. 5.9), and Timor Gap (Fig. 5.10), as also at second-order level with Dampier and West Irian basins. The comparisons exhibit substantive concordance of the large number of first- and second-order surfaces on the GTM both east and west of India. Comparison is also made of the Indian framework with the ETM framework, and salient differences are brought out. The comprehensive exercise reaffirms the earlier held view of the author of the need of independent development of the Indian framework. In comparison with ETM, almost all the Indian first-order surfaces (SBs/MFSs) invariably disagree in ages with the corresponding ETM surfaces by several ammonoid zones, and the obvious influence of regional tectonics in GTM is brought home well. The discordance is excellently exampled by the GTM intra-Jurassic first-order MFS in late Middle Oxfordian Orientalis Zone Schilli Subzone and the corresponding ETM first-order MFS in late Late Kimmeridgian Beckeri Zone. In contrast to the corresponding diachronous first- and second-order surfaces, the third order and finer high frequency low magnitude sequences are considered punctuated by synchronous sequence surfaces across the globe, since being governed by the earth’s orbital dynamics which could not be distorted by low-frequency and high-magnitude first- and second-order extensional tectonics. The chapter is concluded with summarized sequence stratigraphy-based evaluation of the hydrocarbon prospects in the mega-sequence geological record of the Indian basins that reflect an over all positive outlook. An elaborate Indian hydrocarbon prospect analysis being outside the scope of the present work is planned separately in near future. © Springer Science+Business Media Singapore 2017.
Calliphylloceras heterophylloides (Oppel, 1856) from the basalmost jurassic succession of Sadhara Dome, Kachchh, India
(Palaeontological Society Of India, 2014) Bindhyachal Pandey; Deo Brat Pathak; Jai Krishna
We record and illustrate a septate (85 mm D) Calliphylloceras heterophylloides (Oppel, 1856) from the basalmost sediments of Sadhara Dome near the eastern end of Goradongar, Patcham 'Island', Kachchh, India. This is the oldest ammonoid-bearing horizon of the exposed Mesozoic sediments in the Kachchh Basin. In view of the correlation of the Late Bajocian Leptosphinctes bed of Kaladongar to the base of bed 32 of our column which is about 164 m younger than the Calliphylloceras-bearing bed 2, the age of present Calliphylloceras-bearing horizon is suggested here as Early Bajocian or older.
Characterization of Dichotomoceras in the Oxfordian of Kachchh
(2009) Jai Krishna; Bindhyachal Pandey; Deo Brat Pathak
We report here the first Dichotomoceras of the Indian subcontinent at Kantkote (Wagad) in the proximal most exposed part of the Kachchh Basin. This is further addition to the significant enlargement of the Oxfordian ammonoid record made earlier (Krishna et al. 1994, 1995, 1998,2000). Near continuous presence of ammonoids has been recorded in ca 55 m thick succession, almost immediately above the Schilli Subzone, that was considered ammonoid devoid earlier. The ammonoid density, diversity and frequency in this just discovered ca 55 m thick column are much scarcer in comparison to the underlying 10 m thick ammonoid abundant Schilli Subzone. Examples of Dichotomoceras are determined almost throughout the said interval which in our preliminary taxonomic evaluation appear identical or close to D. rotoides (Ronch.), D. stenocycloides (Siem.), D. bifurcatus (Quenst.) and D. crassus Enay. It thus suggests the characterization of the Rotoides Subzone of the Transversarium Zone and the superjacent Bifurcatus Zone of the column at least up to the early Late Oxfordian. ©GEOL. SOC. INDIA.
Crucial links among evolution, extensional tectonics, ammonoid provincialism and sequence surfaces
(Springer, 2017) Jai Krishna
The first- and second-order sequence surfaces are considered to mark the origin, extinction, drastic reduction, and sudden expansion of ammonoid subfamilies on GTM in general, and in IEAP in particular, even farther to other regions, as held consistently over the last three decades in context of ammonoid faunal cuts and expansion events in the Jurassic (Figs. 6.3, 6.4, 6.5 and 6.6). During the second-order TSTs (particularly near the MFSs) of the first-order TSTs, the faunal similarity within IEAP, as also with ETM, SE Pacific, and SW Pacific is found distinctly greater than in the second-order RSTs and TSTs of the first-order RST. The spatial distribution within the basin, in IEAP, and even outside is wider during the second-order TSTs and MFSs than during any other interval. The temporal punctuation of the infraspecifc, intra-generic, intra-lineage evolution (Figs. 6.7, 6.8, 6.9 and 6.10) occurred at second-order sequence surfaces, and is well attested by the heterochronic ammonoid evolutionary processes of unidirectional paedomorphism in the Macrocephalitinae chrysoolithicus lineage (Fig. 6.8), and unidirectional peramorphism in Katroliceratinae lineage (Figs. 6.8, 6.9 and 6.10). The temporal replacement of one lineage by another, also, occurred near exclusively at the sequence surfaces. The explicit control above the subfamilial ammonoid evolution in IEAP by extensional tectonics encouraged further investigation at higher (superfamily/suborder/superorder/subclass/class) level, and the same provided strong links of the entire evolution of the subclass Ammonoidea, and also of the class Cephalopoda, seemingly controlled by extensional tectonics (Fig. 6.2). The origin of Cephalopoda appears linked to the first-order intra-Cambrian MFS, and also of Ammonoidea at the first-order intra-Devonian sequence surface. The origin of Ceratitina, and extinction of Goniantitina may have occurred at the Carboniferous/Permian second-order SB. The origin of Ammonitina is held at the first-order intra-Triassic MFS, and extinction of Stephanoceratina at the first-order intra-Jurassic MFS. The graded decline of the subclass Ammonoidea began at the major intra-Turonian MFS, with the follow up final extinction at the K/Tboundary second-order MFS. The interpretations require confirmation through further investigation. On similar lines are also speculatively related the major evolutionary landmarks, and transformations of marine and non-marine animals and plants to first-order sequence surfaces (Fig. 6.1). The fossil fuel/energy resources of the GTM in general and India in particular are also age-constrained to sequence framework. © Springer Science+Business Media Singapore 2017.
Development of Oxfordian (Early upper jurassic) in the most proximally exposed part of the Kachchh basin at Wagad outside the Kachchh Mainland
(1998) Jai Krishna; Deo B. Pathak; Bindhyachal Pandey
Over a century and half the Kachchh Oxfordian ammonoid record has remained restricted to Early and early Middle Oxfordian, that too in extremely condensed/reworked/starved sedimentary facies. In this backdrop we here discuss the Middle and Late Oxfordian ammonoid faunas recently discovered in Wagad (Krishna et al. 1994a, b). Among these the mid Middle Oxfordian stratigraphic interval is found exceptionally rich in ammonoids at Kantkote - the richest ever discovered in the Kachchh basin. It is made up of a 10 m thick succession of 13 ammonoid levels. Farther up after a thick ammonoid-devoid sediment interval appear again a few rather ammonoid scarce levels of late Late Oxfordian age with doubtful extension into early Early Kimmeridgian. The Oxfordian/Kimmeridgian boundary may be included in the latter of the two ammonoid bearing intervals in the Orthosphinctes/Lithacosphinctes levels. The rich mid Middle Oxfordian ammonite fauna inspite of being known for over a century from loose imprecise, unlocalised collections has been stratigraphically precise and dated for the first time in the relatively unexplored, stratigraphic section of Wagad. The ammonoid abundant mid Middle Oxfordian Transversarium Zone succession in addition of the restricted Indo-East African mayaitins and widely distributed perisphinctins includes a few examples of the Mediterranean Gregoryceras gr. fouquei, Euaspidoceras and Taramelliceras and suggests maximum flooding and eustatic rise in the Kachchh Mesozoic in the Middle Oxfordian Schilli Subzone of the Transversarium Zone. Another significant aspect of this fauna is the marked continuous presence of the compressed platyconic densely costate lithacoceratins (Larcheria and Discosphinctes) stocks in parallel with the true perisphinctin and mayaitin lineages almost althrough the Middle Oxfordian (Krishna et al. 1994a, b, 1995, 1996a). The mayaitins are for the first time precisely ranged up to the Transversarium Zone. The basin margin Oxfordian ammonoid succession at Wagad shows recurrence only of small portion in its basal part of the previously known Oxfordian section of the Kachchh Mainland (e.g. the common Perisphinctes-Epimayaites assemblage of bed G Lakhapur). The remainder ca 200 m thick Oxfordian at Wagad is interpreted here to correspond to the non-depositional submarine stratigraphic gap elsewhere in the relatively deeper parts of the basin from the later part of the Middle Oxfordian Plicatilis Zone to the early Early Kimmeridgian Hypselocyclum Zone.
Differentiation of the significant Late Valanginian (Early Cretaceous) transgressive event in the Spiti Himalaya, India
(2011) Deo Brat Pathak; Jai Krishna; Bindhyachal Pandey
Nearly continuous sedimentary succession of Early Cretaceous age has been long known in the Tethyan Himalayan belt without differentiation of the individual stages. We discuss here our just realised differentiation of a relatively thin well bedded sandstone interval with significant presence of the characteristic Late Valanginian-Early Hauterivian ammonoid genus Olcostephanus. It lies within a dominantly sandy succession with shale interbeds of Giumal Sandstone Formation, near Gate in Spiti Himalaya. This is the first stratigraphically precise record of Olcostephanus from the Cretaceous of India. It is here circumstantially age constrained to the Standard Tethyan Verrucosum Subzone Olcostephanus expansion event to the High Himalayan belt. © 2011 Elsevier Ltd.
Gregoryceras in the Oxfordian of Kachchh (India): Diverse eventful implications
(Elsevier Masson SAS, 2009) Jai Krishna; Bindhyachal Pandey; Jai Ram Ojha
The Kachchh Oxfordian ammonoid stratigraphic record for over 150 years remained restricted largely to Early Oxfordian condensed oolitic facies in the relatively distal Mainland Kachchh. Recently, it has been enlarged with the discovery in 1994 of over 200 m-thick uncondensed Middle to Late Oxfordian succession at Kantkote in the proximal part of the basin. Apart from abundant Perisphinctinae and Mayaitinae, a 10 m-thick sediment interval in the lower half of the above succession yielded a few examples of Gregoryceras. The specimens are here identified as G. gr. devauxi Bert and Enay and in view of their association with Larcheria subschilli (Lee) are assigned to the Middle Oxfordian Subschilli Horizon of the Schilli Subzone. Gregoryceras distribution south of the equator in Kachchh, Chile, Mexico and Madagascar, all within 35-40° latitude marks the southern limit of its latitudinal expansion during the first order maximum flooding surface (MFS) of the Schilli Subzone of the Kachchh Toarcian-Hauterivian Sequence. The maximum ammonoid diversity, density and frequency of the Kachchh first order sequence coupled with dominance of mayaitins and perisphinctins suggest over 20 m depth in the Gregoryceras interval. Distinctly greater bathymetry in the 200 km distally away basinal part causes sediment starved situation, and explains the Middle Oxfordian to early Early Kimmeridgian submarine nondepositional hiatus in the Mainland Kachchh. © 2008 Elsevier Masson SAS. All rights reserved.
High-resolution intrabasinal to inter-regional geodynamic chronicle during the span of the intra-permian–intra-paleogene mega-sequence in and around India on the GTM
(Springer, 2017) Jai Krishna
This chapter chronicles the geodynamic evolution of India and associated dismemberment history of the Gondwanaland (Figs. 7.43 and 7.44). The narration is through the succession of geological events and their interdisciplinary manifestations that are uniquely punctuated with the first- and second-order physically feelable and visually observable sequence surfaces. These surfaces are considered products of the causative tectonic/igneous events. In the process, the entire ~540 my long Phanerozoic history in general and the intra-Permian–intra-Paleogene Indian/GTM mega-sequence geological record in particular inclusive of the surface and offshore wells is, intrabasinally to interregionally, correlated, integrated and interwoven at a distinctly improved average resolution of ~3.5 my involving a succession of ~40 odd second-order sequence surfaces. Within the Kachchh basin, the precision tell-tale has been realized at yet finer resolution of ~400 ky or multiples with the help of a series of graphics. The mega-sequence began with Panjal and coeval igneous events that are particularly manifested in the north sector. Its differentiation into three first-order sequences (Spitiian, Kachchhian and Dravidian) is punctuated by major igneous events in the west near the ~183 ma Pliensbachian/Toarcian boundary in the Kachchh and Saurashtra wells (coeval to Karoo volcanism), and later in the east near ~the 126 ma Barremian/Aptian boundary first-order SB Rajmahal and coeval igneous events. Major volcanic events are evidenced in the east near the ~243 ma first-order Middle Triassic MFS in Papua New Guinea, and again at the first-order intra-Jurassic ~159 ma MFS with spreading away of the Argo block from Greater India at the Indo-Australian divergent margin. Madagascar separated from India during the ~94 to ~84 ma span. Both the start and end of the span mark significant sequence surfaces. The initial impingement of the drifting India with the Kohistan–Ladakh oceanic island arc is interpreted around the ~51–50 ma late Early Eocene Late Cuisian planktonic foram P8 Zone sequence surface, well after the intra-Paleocene basal/intra P3 Zone SB ~60–59 ma closure of the mega-sequence. The stratigraphic gaps in the Indian record inclusive of the break-up unconformities are better resolved and differentiated as subaerial and submarine, and also are precisely ranged through the succession of sequence surfaces. The succession of the ~40 highly time-precised sequence surfaces, in a process-response relationship, has, precisely, dated as many rift, igneous, eustatic, anoxic, T/R events and the multifaceted collage of other geological phenomena and expressions. The Mesozoic litho- and biostratigraphic units in outcrops and wells, marine and non-marine, guide fossil bearing or devoid, carbonates or clastics, shallow or deep of the Indian basins across the length and breadth of India have been precisely age-constrained and mutually correlated through the succession of sequence surfaces. Major evolutionary landmarks of organic evolution are also speculatively age-constrained, since conceptually influenced by tectonic and magmatic events with or without igneous expressions. The principal energy resources of India, hydrocarbon, coal, and atomic minerals, are temporally and spatially better constrained, and understood through the succession of the second-order sequence surfaces. © Springer Science+Business Media Singapore 2017.
Implications of new data on Mesozoic rocks of Kachchh, western India
(1983) Jai Krishna; Indra Bir Singh; James D. Howard; Syed Abbas Jafar
A lack of detailed facies studies has resulted in a false impression of the Mesozoic depositional setting in Kachchh, western India (previously, Kachchh has been termed 'Kutch' or 'Cutch'). In addition, designation of part of this sequence as Gondawana implies, by tradition, a predominantly non-marine origin. Recently, we examined these Jurassic-Cretaceous units and found numerous wave-built sedimentary structures that have been previously overlooked or unreported, abundant marine trace fossils, and highly bioturbated and glauconite-rich beds. Thus, we now propose a marine origin for the entire Kachchh succession. This interpretation has important implications regarding similar sequences around the Indian plate margin. © 1983 Nature Publishing Group.
Integration of the micro/macro faunal/floral data into ammonoid stratigraphic framework in the Indian mesozoics
(Springer, 2017) Jai Krishna
An integrative mutually correlative stratigraphic framework of the Mesozoic lithobiostratigraphic successions/units is developed in the Indian sedimentary basins. It is realized on the combined strength of the stratigraphic refinement achieved in Chap. 2, together with the succession of the first- and second-order sequence surfaces formulated in Chap. 3. The exercise obligatorily involved large-scale revision and refinement of the imprecise ages of the Indian Mesozoic lithostratigraphic units which in earlier studies were based on unsubstantiated and inadequate data on different macro/microfossil groups. Also, in the process are provided new alternatives to many inaccurate intra/interbasinal correlations and models. The integration of the entire available outcrop and subsurface guide fossil-based biostratigraphic data in conjunction with sequence formulations is applied to intra and interbasinal correlation of marine with non-marine, guide fossil bearing to guide fossil devoid, along with time correspondence among ammonoid, conodont, foraminfer, coccolith, dinocyst, pollen/spore-based zonal schemes across the Indian sedimentary basins in north, west and east sectors. The chapter concludes with precise ages to the Kachchh Mesozoic units (formal formations of Stoliczka, formal members of Biswas and others, also informal/abandoned members created outside the type sections yet otherwise considered useful). © Springer Science+Business Media Singapore 2017.
Introduction and paleogeographic context, previous work, high-resolution scale, magnetochronologic perspective, radiometric scenario, igneous activities, anoxic events and eustatic fluctuations
(Springer, 2017) Jai Krishna
The chapter outlines the multidisciplinary geodynamic transformations in the Mesozoic with focus on the evolution of India as part of the Gondwana dismemberment. The rationale of approaching the chronicle through the innovative sequence stratigraphic approach is emphasized upon through formulation of depositional sequences in the key basins of Spiti in north, Kachchh in west and Cauvery in southeast, respectively, for the Triassic, Jurassic and Cretaceous intervals between the origin to the closure of the Neotethys. Paramount significant is given to ammonoids in developing and updating the integration towards high-resolution chronicle. Updates are also outlined on important aspects of tectonics, volcanism, tectono-sedimento-stratigraphy, eustatics, anoxicism, geomagnetism, radiometry, organic evolution, and others, along with their interrelationships. © Springer Science+Business Media Singapore 2017.
Late Lower Kimmeridgian-Lower Tithonian Virgatosphinctins of India: Evolutionary succession and biogeographic implications
(1993) Jai Krishna; Deo Brat Pathak
A very significant late Lower Kimmeridgian to Lower Tithonian virgatosphictin ammonoid fauna is examined under the rigorest possible stratigraphic precision at Ler-Katrol (Kachchh), India for evolutionary succession and biogeographic implications. The study allows the recognition of at least 12 successive faunas which have been organised into 8 zones and 12 subzones along with their relative precise correlations with Western Tethys. The principal single lineage worked out is Torquatisphinctes intermedius (Alterneplicatus Zone to Acanthicum Zone)-Pachysphinctes bathyplocus (Bathyplocus Zone)-Katroliceras katrolensis (Katrolensis Zone) (up to close of Kimmeridgian)-K. pottingeri (Pottingeri Zone). K. pottingeri in turn gives origin by cladogenesis to two short lived lineages, which include new species one in each lineage marking the termination of the stock at the close of Lower Tithonian with a probable lineage discontinuity in the basal Tithonian Hybonotum Zone. Among the other salient features are: 1. There is a major stratigraphic break at the base (=Vail's subcycles LZA 4.3-4.4). The start of the fauna corresponds to the eustatic rise of LZA 4.5, while the termination of the lineage is correlated with the termination of LZB 1.1. 2. K. pottingeri, known widely in the Indo-East-African province, is precisely dated for the first time as post-Hybonotum Zone, in association of very significant although also not well dated Himalayan Aulacosphinctoides (A. uhligi, A. willisi, A. tibetanus etc.). Aulacosphinctoides in the section is also found older than Virgatosphinctes. 3. The rare presence of non-virgatosphinctin West Tethyan species indicates expansion events related to eustatic rises, which permits correlation with the Western Tethys of the otherwise near endemic Indian faunas. Nothing is found in common with the SE. Pacific faunas, suggesting continued absence of a direct marine connection via the east and south coastal region of Africa. © 1993.
Mesozoic stratigraphic framework in India with focus on the jurassic geological record in the kachchh basin
(Springer, 2017) Jai Krishna
It updates the biostratigraphic refinement in the Indian Mesozoics with focus on the Triassic in Spiti, Jurassic in Kachchh, and Cretaceous in Kachchh and Cauvery. As an example, the ammonoid stratigraphic zonation in Kachchh basin inclusive of the new Oxfordian zones, as also the origin of the basin are developed at length. Also are touched upon the salient pre-sequence Paleozoic features as back drop, along with the start and termination of the sequence. State of the art is presented on the integrated high resolution scales for the three periods. The Early- amd Middle Triassic update includes integration of ~35 ammonoid zones to ~15 conodont zones in the lithostratigraphically and splendidly resolved Spiti sections. The Indian Late Triassic to Early Jurassic is largely ammonoid devoid but for scanty Early Jurassic presence at Lamayuru in Ladakh. The Jurassic includes ~35 ammonoid zones, over 50 subzones, and yet more number of Horizons in the Middle and Late in well-resolved Kachchh sections. The Cretaceous update is compositely presented of 18 informal ammonoid zones with ammonoid presence almost in all the 12 stages in some or other Indian basin yet lacking the desired level of lithostratigraphic differentiation. © Springer Science+Business Media Singapore 2017.
New Ammonoid evidence for theJurassic/Cretaceous boundary in Kachchh Western India, and long distance correlation with Southern Europe
(1994) Jai Krishna; Deo Brat Pathak; Bindhyachal Pandey
The Jurassic/Cretaceous boundary in the ammonoid rich classic Jurassic region of Kachchh could not be precisedfor well over a century (1871-1991) due to the absence of ammonoids or other guide fossils of the Berriasian. Our present studies now firmly establish the basal Berriasian in Kachchh through close or identical ammonoids Aspidoceras cf. taverai Checa,, Argentiniceras loncochensis (Steur)), Spiticeras cf. ducale (Matheron)) and Berriasella sp. Relatively, among these, A. taverai Checa is considered a good marker of the basal Berriasian Jacobi Zone in the Subbetic Spain. Besides precising the Jurassic/Cretaceous boundary in Kachchh, A. cf. taverai Checa also allows long distance correlation to the precision of a single ammonoid zone across the Tethys between Kachchh (Indo-East-African province) on the south/east margin of the Tethys and Spain (Mediterranean province) on the north/west margin of the Tethys. The episodic presence of the ubiquitous Tethyan Aspidoceras in Kachchh during the Upper Kimmeridgian and basal Berriasian, interestingly, is found to correspond with phases of the eustatic rise of the Vail Cycles LZA 4.6 and LZB 1.4 which in turn suggests significant ammonoid faunal expansion events during the said intervals towards South and East from the Mediterranean to the Indo-East-African province. © 1994.
Outcrop-based sequence stratigraphic studies on GTM with focus on the kachchh mesozoic
(Springer, 2017) Jai Krishna
The history of the relatively new interdisciplinary and highly applicative discipline of sequence stratigraphy is summarized. Basics, terminology used in the present work, as also author’s approach to outcrop-based studies in the Kachchh basin are briefly outlined. The five mega-sequence framework in the Indian Phanerozoic is introduced with focus on the fourth one of intra-Permian–intra-Paleogene span from the origin to the closure of the Neotethys. The said mega-sequence is differentiated into 3 first-order sequences in the Indian record, and 37 second-order sequences in Spiti, Kachchh and Cauvery. The Kachchh record is further exampled with third-, fourth- and fifth-order differentiation. The SBs and MFs are précised at ~400/200 ky subzonal/horizonal resolution or its multiples. The chapter concludes with crude investigation of the sequence periodicity at different orders in which the second-order sequences are found to correspond with cyclicity of ~400 ky or its multiples (Tables 3.1, 3.2 and 3.3). © Springer Science+Business Media Singapore 2017.
Preface
(Springer, 2017) Jai Krishna
[No abstract available]
Preliminary remarks on new ammonoid collection from freshly exposed succession of the Spiti Formation between Lidang and Giumal, Spiti Valley, Himachal Himalaya, India
(2013) Bindhyachal Pandey; Deo Brat Pathak; Jai Krishna
The present contribution embodies the preliminary analysis of ammonoids collected from 19 successive levels of a freshly cut ~ 92 m thick succession of the Spiti Formation exposed along a newly constructed motorable road linking the villages Lidang and Giumal in the Spiti Valley. Ammonoids are found present throughout the succession. The preliminary taxonomic determination of over 125 ammonoid specimens registers the identification of 10 families/subfamilies and 18 genera ranging in age from Late Kimmeridgian to Late Tithonian (Late Jurassic). The generic range chart allows the differentiation of four distinct ammonoid assemblages - Pachysphinctes Assemblage (Late Kimmeridgian), Aulacosphinctoides Assemblage (basal Tithonian), Virgatosphinctes Assemblage (Early Tithonian) and Himalayites Assemblage (Late Tithonian) enabling tentative demarcation of the Kimmeridgian/Tithonian Stage boundary and Early/Late Tithonian Substage boundary. These four ammonoid assemblages are correlated with known areas of the Indian subcontinent as also with the Standard Tethyan Scheme developed in Europe.
Record of Tethyan gastropod genus Astrohelix Szabó, 1984 from late Bajocian (Middle Jurassic) of Kachchh, western India
(2012) Bindhyachal Pandey; Deo Brat Pathak; Anand K. Jaitly; Jai Krishna; M. Venkateshwarlu
We here present the first record and illustrate the planispiral gastropod genus Astrohelix Szabo, 1984 through its species Astrohelix (Bifldobasis) cf. hourcqui (Delpey, 1948) from the Late Bajocian (Middle Jurassic) sediments of Kachchh Mainland, western India.
The Tethyan Macrocephalitinae: Evolutionary environmental and dispersal strategies
(1993) Jai Krishna; Elie Cariou
The macrocephalitin evolution and dispersal are examined in context of the high resolution of Lower Callovian ammonoid successions realized recently in France, Germany, Britain and India. The macrocephalitins evolved in SW Pacific in the Bathonian and entered the Tethys at its eastern portal not earlier than during the late Upper Bathonian eustatic rise (Vail's cycle). There was rapid early expansion from S to N. The early Indo-East-African species M. triangularis and M. madagascariensis, are morphologically close to the European M. jaquoti and M. verus, little understood inflated accessories are also present, and this differentiation may already have been complete before their arrival in the Tethys. After the rapid early spread independent successions developed in different areas, with a maximum of 3 in the Submediterranean province reaching into the Medea Subzone: (1) fine ribbed compressed (Gracilis lineage), (2) fine ribbed inflated (Macrocephalus lineage) and (3) coarse ribbed inflated (Sphaericus lineage). India (chrysoolithicus lineage) and Britain (Kamptus lineage) evidence independent successions of only coarse ribbed inflated forms, which terminated at the close of Diadematus Subzone (≈ Koenigi Zone). This is attributed to the eustatic fall at the close of the subcycle LZA 3.1 under their near similar paleolatitudinal and paleogeographical setting. Two new short-lived compressed lineages M. formosus-M. semilaevis-E. eucyclum and M. formosus-M. opis (Formosus Subzone to early Anceps Zone) developed in India as probable derivation from the Submediterranean province which may also be related to the eustatic rise of the following subcycle Z.A. 3.2. © 1993.