Dhirendra K. Pandey

Sequence stratigraphic significance of sedimentary cycles and shell concentrations in the Upper Jurassic–Lower Cretaceous of Kachchh, western India

Abstract Upper Jurassic and Lower Cretaceous siliciclastic shallow water sediments of the Kachchh Basin, western India, form strongly asymmetric coarsening-upward cycles, which are interpreted as recording changes in relative sea level (deepening–shallowing cycles). These cycles correspond to depositional sequences, in which deposits of the lowstand systems tract are not present, the sequence boundary coinciding with the transgressive surface. Shell concentrations are found in the transgressive lags at the base of the transgressive systems tract (TST), in the maximum flooding zone (MFZ), and at or close to the top of the highstand systems tract. They belong to six assemblages, five of them dominated by large bivalves such as Seebachia, Herzogina, Gryphaea, Gervillella, Megacucullaea, Pisotrigonia and Indotrigonia, the sixth by the coral Amphiastraea. Three types of shell concentrations can be distinguished that differ from each other in a number of ecological and taphonomic features, such as species diversity, preservation quality, orientation in cross-section, percentage of disarticulation, and degree of biogenic alteration. Characteristic features of concentrations at the base of the TSTs are moderate time-averaging, sorting, a preferred convex-up orientation, and nearly total disarticulation of shells. They are suggestive of an environment in which reworking and local transport were frequent events. Similar features are shown by concentrations near the tops of the HSTs, except that there shells were largely concentrated in lenses and in pavements rather than in beds as in the transgressive lags. Associated sedimentary structures indicate deposition above fair weather wave base in a high-energy environment. Concentrations occurring in the MFZ, in contrast, are autochthonous and highly time-averaged, having accumulated during times of low rates of sedimentation below storm wave base. This is supported by their high preservation quality (comparatively high percentage of articulated shells, shells of infaunal organisms commonly preserved in life position), biogenic alteration being the most important taphonomic agent. The dominant elements of these shell concentrations, i.e. Seebachia, Megacuccullaea, and Indotrigonia in the Upper Jurassic, and Pisotrigonia in the Lower Cretaceous, are endemic to the Ethiopean faunal province and belong to lineages that rapidly evolved during this time period.

Genesis and environmental significance of Upper Cretaceous shell concentrations from the Cauvery Basin, southern India

Abstract Upper Cretaceous shallow marine calcarenites of the Upper Campanian–Maastrichtian Kallankurichchi Formation from the Cauvery Basin of southeastern India are rich in shell concentrations dominated by large bivalves with minor admixtures of brachiopods, bryozoans, and larger foraminifera. Rarely, these concentrations occur as lenses or pavements, but usually as beds 10 to 200 cm thick. Depending on the dominant skeletal elements, five types of shell concentrations can be distinguished: Isognomon, Pycnodonte, Ceratostreon, inoceramid (?Platyceramus, Cataceramus), and polyspecific concentrations. These shell concentrations occur in various preservational states which reflect the gradual mixing and mechanical destruction of former communities. Analysis of the taphonomic signatures of their components and of the biofabric suggests that storm-induced waves and currents, reduced sediment input, the settling behaviour of taxa, and a high rate of production of biogenic hardparts were responsible, in varying degrees, for the formation of the various shell concentrations. Accordingly they can be classified as storm wave, proximal tempestite, and primary biogenic concentrations. The shell concentrations formed below fair weather wave base in shallow, subtropical, low-stress environments.

Stable isotope analyses of belemnites from the Kachchh Basin, western India: paleoclimatic implications for the Middle to Late Jurassic transition

Stable isotope analyses of 61 diagenetically unaltered belemnite rostra from the Middle to Late Jurassic of the Kachchh Basin of western India suggest stable paleotemperatures across the Callovian-Oxfordian boundary (~14°C). Only at the end of the Middle Oxfordian water temperatures drop for more than 3°C before reaching again higher values during the Kimmeridgian (~12.3°C). The data do not support polar glaciations proposed for the Middle to Late Jurassic transition, which necessarily would have led to a global temperature and sea-level minimum at the boundary. Callovian to Oxfordian rocks in the Kachchh Basin point to a gradual shallowing corresponding to a slight fall in relative sea level. However, the magnitude of this regression is comparatively small, and the sea-level minimum is reached in the late Early Oxfordian and not close to the boundary. Results from the Kachchh Basin therefore, imply almost stable climatic conditions during the Middle to Late Jurassic transition and do not show any evidence for polar glaciations.

Ammonites of the genus Peltoceratoides Spath, 1924 from the Oxfordian of Kachchh, western India

Forty-three ammonites from the Kachchh Basin in western India have been assigned to seven taxa belonging to the genus Peltoceratoides sPAth, 1924. The two most abundant morphospe- cies Peltoceratoides (Peltoceratoides) constantii and Peltoceratoides (Parawedekindia) arduennen- sis are commonly considered as the macro- and microconch, respectively of a single biospecies. The taxa are important for intrabasinal as well as intercontinental correlation due to their wide geographic range during the Early Oxfordian. The specimens occur in beds, which had been assigned to the Cor- datum Zone, but also reworked in the so-called Dhosa Conglomerate Bed, which contains an array of ammonites from different ammonite zones.

On the earliest known occurrence of the Middle Jurassic ammonite genusReineckeia in the Upper Bathonian of Jumara, Kachchh, western India

Two specimens of the Middle Jurassic ammonite genusReineckeia (sensu lato) have been found in the lowest beds of the Pachchham (Patcham) Limestones exposed in the core of the Jumara Dome, Kachchh (Kutch), Gujarat, western India. The stratigraphy is described in detail and the age bracketed to lie between latest Late Bathonian and Middle Bathonian, older than any previously described examples of this genus, either in India or in Europe (middle Early Callovian). The new finds are compared with other known pre-Callovian Reineckeiidae, notably those of the eastern borders of the Pacific, but the relationships are not close. The phylogenetic consequences are briefly discussed. The roots of the Reineckeiidae continue to lie hidden.KurzfassungZwei Exemplare der mitteljurassischen AmmonitengattungReineckeia (sensu lato) wurden aus den untersten Schichten der Pachchham (Patcham) Limestones geborgen, die im Kern des Jumara Dome von Kachchh (Kutch), Gujarat, westliches Indien, aufgeschlossen sind. Die Stratigraphie dieser Schichten wird im Detail beschrieben. Das Alter der beiden Exemplare kann auf den Zeitraum zwischen dem spätesten Ober-Bathon und dem Mittel-Bathon eingegrenzt werden. Damit sind sie älter als alle anderen bekannten Funde der Gattung, ob aus Indien oder Europa (mittleres Unter-Bathon). Die neuen Funde werden mit anderen Reineckeiiden aus dem Prä-Callov verglichen, vor allem mit Formen vom Ostrand des Pazifiks, die jedoch keine engen Beziehungen aufweisen. Die Schlußfolgerungen für die Phylogenie der Gruppe werden kurz diskutiert. Die Wurzeln der Reineckeiidae liegen nach wie vor im Dunkeln.

Oldest camarasauromorph sauropod (Dinosauria) discovered in the Middle Jurassic (Bajocian) of the Khadir Island, Kachchh, western India

Fragmentary isolated remains of large (up to 20 m or more) sauropods from the Middle Jurassic (Bajocian) Khadir Formation of Khadir Island (Kachchh, W India) are described and compared in detail. Three of the bone fragments (a metacarpal, a first pedal claw and a fibula) can be assigned with confidence to the Camarasauromorpha and represent the oldest known record of that derived dinosaur group. The new finds from western India further close a temporal and geographical gap in our knowledge of sauropods and contribute to understanding their early phylogeny.KurzfassungIsolierte Überreste eines großen (bis zu 20 m oder mehr langen) Sauropoden werden aus der mitteljurassischen (Bajocium) Khadir Formation auf Khadir Island (Kachchh, W Indien) beschrieben und detailliert verglichen. Drei der Knochenfragmente (ein Metacarpale, eine erste Fußklaue und eine Fibula) können mit Sicherheit einem Vertreter der Camarasauromorpha zugeordnet werden und repräsentieren damit den ältesten Nachweis dieser abgeleiteten Dinosaurier-Gruppe. Die neuen Funde aus dem westlichen Indien schließen eine zeitliche und geographische Lücke in unserer Kenntnis der Sauropoden und tragen zum Verständnis ihrer frühen Phylogenie bei.

Mining and the environment: a case study from Bijolia quarrying site in Rajasthan, India

Mining is essentially a destructive developmental activity, where ecology suffers at the altar of economy. Unfortunately, in most regions of the Earth, the underground geological resources are superimposed by biological resources (forests). This is particularly evident in India. Hence mining operations necessarily involve deforestation, habitat destruction, biodiversity erosion and destruction of geological records which contain information about past biodiversity. Extraction and the processing of ores and minerals also lead to widespread environmental pollution.However, mankind cannot afford to give up the underground geological resources which are the basic raw materials for development. An unspoiled nature can provide ecological security to people but cannot bring economic prosperity. Scientific mining operations accompanied by ecological restoration and regeneration of mined wastelands and judicious use of geological resources, with search for eco-friendly substitutes and alternatives must provide the answer.A case study from the Bijolia quarrying area in Rajasthan, India, provides some sensational revelations of the impact of mining on the human ecosystem.

Oxfordian (Late Jurassic) gastropods from the Kachchh Basin, western India

A collection of 93 Late Jurassic gastropods from the Kachchh Basin in western India represents 23 species. The material contains new records, such as Purpurina sp., as well as five new species: Bathrotomaria densireticulata, Bathrotomaria depressa, Bathrotomaria gangtaensis, Neritopsis indica, and Eucyclus tramauensis. Additional unnamed species occur, but since they are represented only by single and/or fragmentary specimens in the present collection, they have been left in open nomenclature. The majority of the described gastropods are from the Oxfordian part of the Jurassic succession of the Kachchh Basin. The fauna is strongly dominated by pleurotomariids and resembles that of palaeogeographically neighbouring areas (especially Madagascar) in composition. Most of the occurring genera are wide-ranging and known from localities throughout the Tethyan Ocean, but a strong endemism at the species level seems evident.

Coralline algae from the Aramda Reef Member of the Chaya Formation, Mithapur, Gujarat

The Quaternary sediments of the Aramda Reef Member of the Chaya Formation exposed in the Mojap coast near Mithapur, Gujarat are characterized by well-developed coralline algal build-ups. These algal build-ups are exceptionally rich in coralline algae and corals. In the present paper, thirteen species belonging to eight genera of coralline algae are described. Out of these, seven species (Titanoderma nataliae, Lithophyllum nitorum, Lithophyllum quadratum, Spongites sp. Brandano et al., 2005, Sporolithon lvovicum, Mesophyllum fructiferum and Lithothamnion praefruticulosum) are the new records for India. Four species (Titanoderma pustulatum, Sporolithon intermedium, Mesophyllum commune and Phymatolithon sp.) are first time recorded from the study area. Among the major framework builders of coralline algae of the Aramda Reef Member are Lithophyllum, Titanoderma, Sporolithon, Mesophyllum and Lithothamnion.Two associations of the coralline algal assemblages can be distinguished: one indicating shallow water, high-energy conditions is developed in the upper part, while the other suggesting deposition in low-energy conditions is characteristic of the lower part of the succession. These algal associations, together with their growth-forms (encrusting, warty to fruticose, layered) come from stratigraphically separate beds. They indicate that the temperature, depth and hydrodynamic energy conditions also fluctuated during deposition of the Aramda Reef Member. It is concluded that the lower Hapalidiaceae-Sporolithaceae association dominated during warmer interval, whereas the upper lithophylloids association flourished in relatively low-temperature conditions. The associated corals indicate that minimum winter sea surface temperature remained above 18°–20° C.

Overview on the middle to upper Jurassic sedimentary succession of Gangta Bet in the Kachchh basin, western India, with special emphasis on its lithostratigraphy, biostratigraphy, and palaeoenvironment

The Jurassic succession of Gangta Bet in the Kachchh basin of western India comprises around 130 m of mostly siliciclastic rocks. The strata belong to the Gangta Member of the Gadhada Formation and are herein sub-divided into four units: the Gangta sandstone beds, the lower silty sandstone beds, the upper silty sandstone beds, and the Gangta ammonite beds. These units can be separated by three marker horizons: the Brachiopod bed, the Gangta Conglomerate Bed, and the Gervillella Bed. Ammonites indicate an Oxfordian age for the upper half of the succession, but the scarcity of identifiable fossils in its basal part so far prevented precise biostratigraphic assignments. The shallow-water sediments can be interpreted as parasequences as a result of minor sea-level changes. Deposition took place close to the palaeo-coastline at water depths around the fair-weather wave-base.