The Indian Paleogene

The Paleogene stratigraphic record in India left imprint with many clues towards understanding the global and Indian plate events. The KTB and the beginning of the Paleogene is heralded by the Deccan volcanism, which is considered to be the main killer responsible for mass extension. Towards the end of the Paleogene there was a global drop in sea-level and major hiatus which left marks in the Indian basins. Within the limits of the Paleogene a number of major geological events are recognizable. They are: (1) Maximum flooding during zones P4/P5 (Late Paleocene), (2) Paleocene-Eocene Thermal Maxima (PETM), the impacts of which are not fully explored in Indian strata, (3) Late Paleocene-Early Eocene sedimentary succession of India occupies an important position as a major source rocks and to a lesser extent reservoirs of hydrocarbons. Case examples are: (a) Bombay Offshore Panna Formation deposited in several cycles in a marginal marine setup, (b) Facies comparable to the Panna Formation extended up to Kerala-Konkan basin where these are referred to Kasargod Formation. (c) Cambay Basin: Olpad/Cambay Shale deposited in lacustrine to marginal marine environment is the source for the sandstone reservoir in several fields, (d) Tura Formation in NE Region, (4) Zone P13 (Middle Eocene) maximum flooding surface recognizable and valuable in correlation, (5) Himalayan orogenic movement-I (41.3–42 Ma), (6) Late Eocene drop in sea-level left record in several basins except in Cambay Basin and NE Indian basin where there was sea-level rise due to local tectonic subsidence greater than sea-level drop, (7) drop in paleotemperatures during the Early Oligocene documented globally and in the Kutch basin. (8) Extinctions close to the Paleocene-Eocene boundary and top of the Eocene. Further studies by Research scholars require access to deep well samples of the ONGC and other oil companies. Lithostratigraphy of Paleogene strata of India from exposures and subsurfaces, paleoshelfs and bathyal settings is well recognized/established. All the formations are briefly described and further references are being provided for more detailed account. Sedimentary basins covered in this paper include: Himalayan foreland, NE Region, Andaman, West Bengal, Mumbai offshore, Cambay, Kutch and Jaisalmer basins. Preserved record in exposed sections is incomplete-punctuated by hiatuses. Diachronos nature of the limits of the formations on basin scale is not fully appreciated by workers in India.

The Andaman-Nicobar archipelago in the northeastern Indian Ocean is a nonvolcanic outer arc island chain developed by tectonic accretion of sediments and ocean crust along the eastern margin of the subducting Indian lithosphere. The Paleogene stratigraphy of the island chain comprises olistostromes, olistoliths and coarse-grained volcaniclastic turbidite facies, and reefal limestones of late Paleocene-Eocene Mithakhari Melange and finer-grained siliciclastic turbidites (Andaman Flysch) of Oligocene age. The lower Paleogene sedimentary rocks were deposited in shallow-water basins formed on the upper trench slope and growing accretionary wedge and contain material sourced from a local volcanic arc and eroded ophiolite. By contrast, the Oligocene continent-derived siliciclastic sediments were originally deposited outside of the accretionary wedge as part of a large submarine fan system. Subsequent deformation and thrusting juxtaposed these different formations as trench rollback progressed and the accretionary wedge expanded westwards.

High resolution seismic data processed by Pre-Stacking and Depth Migration (PSDM) and Pre-Stacking and Time Migration (PSTM) processing techniques, have made on eloquent exposition of basin forming and modifying tectonics of Paleogene basins in and around peninsular India. These basins are characterized by prolonged extensional tectonics, development of rift and grabens, subsidence along nearly vertical faults, decompression melting and outpouring of enormous lava units during Cretaceous and deposition of uninterrupted Paleogene and Neogene succession. Cretaceous volcano-sedimentary sequence is invariably present in all the basins and is believed by the author to have formed due to down ward progression of faults associated with rift and grabens to critical limits to cause decompression melting. This sequence also forms technical basement for the deposition of Paleogene succession. Processing by PSDM and PSTM techniques have improved the resolution, due to which litho-units of Paleogene sequence could be identified. These litho-units have various proportions of limestone, shale and sandstone and are some of the finest source rocks of hydrocarbons in and around peninsular India. Extensional tectonics has deformed the entire Mesozoic and Tertiary succession; however, the Mesozoic rocks are more severely deformed mainly by nearly vertical faults. The effect of these faults progressively diminishes in over lying younger Paleogene and Neogene rocks. Most of these faults show upward or downward convergence, intersecting each other at the boundary between Paleogene and Neogene, thus forming an hour-glass structure. The prolific growth of coral reef complexes is also observed on volcanic platform, where gradual subsidence of certain blocks is ascertained.

Palaeoenvironmental studies based on organic matter associated with the biostratigraphically continuous Cretaceous-Paleogene transition section of the Langpar Formation, Meghalaya promise to provide crucial evidence of foraminiferal effects close to K/Pg boundary. Present work primarily focuses on the upper Maastrichtian Pseudoguembelina hariaensis Zone (= Zone CF3) that records incidence of ‘regional fire’ to affect paleoenvironment, which facilitated planktonic foraminiferal disappearance. Incidence of coaly matter towards the upper part of the Racemiguembelina fructicosa Zone (= CF4 Zone) endorses that the incidence of ‘fire’ prevailed for a longer period, encompassing the upper Maastrichtian biozones CF4-CF3. The yellowish brown clay layer in biozone CF3 is marked with well established excursions in HMW PAH compounds which coincide with the Ce anomaly layer occurring below the PGE anomaly layer around the contact between Pseudoguembelina palpebra Zone (= CF2 Zone) and Plummerita hantkeninoides Zone (= CF1 Zone) and below the planktonic foraminiferal change at the K/Pg. Significantly, strong (~4 fold increase) peaks were noticed in biozone CF3 (sample JP12) as marked by sudden increase in the total PAHs—4, 5, 6 ring PAH compounds and few 3 (anthracene, fluorine) ring PAH compounds; biozone CF2 (sample JP-13) also shows excursions in 3 ring PAHs—phenanthrene, 3-methylphenanthrene, 2-methylphenanthrene, 9-methylphenanthrene, 1-methylphenanthrene, but the former shows n-alkane and fatty acid (including their CPI values) excursions. Besides, remarkably high amount of combustion marker PAHs [fluoranthene, (10.46 µg/gc), pyrene (7.20 µg/gc), chrysene (8.28 µg/gc), benzo(a)anthracene (9.92 µg/gc)] in the biozone CF3, similar to those of well studied K/Pg boundary sections of Stevns Klint (Denmark), Gubbio (Italy), Woodside Creek (New Zealand), and Arroyo el Mimbral, Tamaulipas, (Mexico) suggesting correspondence in the incidence of ‘fire’ in India where it was triggered presumably by the heat radiating from the epigenic plumes of Abor volcanic and Ninetyeast Ridge, and greenhouse effects of Deccan volcanism. The fire seemingly facilitated step-wise disappearances of planktonic foraminifera during biozones CF4-CF3 and instigated migration of some forms from the warm water environment. A very strong proton peak at δ1.51 ppm in yellowish brown clay layer (JP-12) indicating the presence of CH₂ group of alkane compound in the sample. FTIR spectra shows weak bands in the region of 2304–2370 cm⁻¹ and attributed to the presence of traces of CO₂ and CO, which are related to the combustion incidence. Such environment was possibly created in the interspaces of the sediments by burning of organic matter in the presence of oxygen whereby CO₂ formed and water released in the environment. High abundance of combustion derived PAH in the yellowish brown layer of biozone CF3 of the succession endorses this observation. The study considers ‘regional fire’ as one of the factors for step-wise disappearance of planktonic foraminifera prior to the advent of the K/Pg boundary in the shallow shelf of Meghalaya.

Thar Desert is characterised by arid-semiarid ecologically fragile environment and occupies a unique tectonic-sedimentary domain in north-western (NW) India. It is confined essentially to West Rajasthan Shelf (WRS). The tectonic disposition and basement configuration of intra-cratonic basins and sedimentary formations here range from the Precambrian Delhi Supergroup in the east, Late Proterozoic to Early Palaeozoic Marwar Supergroup of sedimentary rocks in the middle, to Mesozoic and Cainozoic cover sedimentary formations on the western and north-western fringe areas in western parts of Thar desert in Rajasthan and Haryana in north-western India. It is remarkable that successive geological young age of sedimentary formations is mapped from the highly deformed Precambrian rock formations of the Aravalli Hill ranges on the east to the recent sand covered structurally undisturbed rocky plains on the west in the Thar Desert. Distinctive geomorphic expressions and relative lowering of relief are also deciphered and recorded across an east–west transect along northern parts of the Thar Desert. Geological mapping of Palaeogene–Neogene formations in NW India have helped reconstruction of the palaeo-geographic shore-line limits of the Tertiary sea. Such inferred basement disposition ostensibly had a bearing on the source of evaporate minerals and continuing salinity aspects of the present day inland lakes and playas in the region. Successive northward deepening of the Palaeogene–Neogene sedimentation basin is also inferred from the geological strata logs prepared during the drilling probes for the Potash Mineral Investigation by Geological Survey of India in NW India. It has been inferred that the NE–SW trending Aravalli hill ranges were rejuvenated as a horst bound by the Great Boundary Fault (GBF) in the east and well known Sardarshahar Fault (west of Churu) and a series of westerly down-thrown step faults (called Manpia Faults) on the west thus segmenting the Thar Desert in north-western Rajasthan into several Neogene depressions or the depocenters in-filled with Quaternary continental aggradational deposits of fluvio-lacustrine and aeolian origin. Based on geological field surveys, interpretation of sub-surface data and dug-well inventory, it has been feasible to delineate a series of linear stepped grabben structures hosting a succession of Quaternary deposits separated respectively by denudational relief features. Their stratigraphic succession is established and correlated to build-up a model for improved geological understanding. Present contribution attempts to elucidate role of Palaeogene–Neogene tectonics and its implications for the geological evolution of Thar Desert in NW India.

The late Paleocene clastic member of the Matanomadh Formation (MF) is an overall sandstone dominated succession wherein sub-ordinate proportion of thinly-laminated silty-mudstones is found lying between the sandstone beds. Provenance of these late Paleocene Matanomadh Sandstones (MS), Kachchh is not known till date and the same has been determined based on petrography and heavy mineral analysis supported by paleocurrent studies. These sandstones reveal an abundance of sub-angular to rounded monocrystalline non-undulatory quartz; and polycrystalline quartz, feldspar and rock fragments occur as minor constituents. These sandstones are classified as quartzose arenite. The rock fragments in these sandstones are dominated by mica-schist, slate, chert and limestones. Q-F-L and Qm-F-Lt diagrams suggest margin of the craton interior to transitional continental stable craton provenance for these sandstones. The paleocurrent measurements of the cross-bedded sandstones suggest NW-SE-directed bipolar and WNW-directed unimodal paleocurrent patterns and suggest a marine-continental transition zone as depositional site for these sandstones where sediments were contributed from both the shallow-marine and continental sources. The heavy mineral assemblages of these sandstones show sub-angular to rounded grains of magnetite, tourmaline, monazite, rutile, kyanite, staurolite and hematite where magnetite is the dominant component; and hence suggest that the heavy minerals might have been supplied from a basic igneous source, low- to medium-grade metamorphic rocks and reworked sedimentary rocks.

Subtle paleoenvironmental fluctuations are difficult to detect in sedimentologically uniform carbonate rocks, however, study of relative increase and decrease of marine and terrestrial organic matter content provides a useful tool for deciphering the deepening and shallowing cycles in these successions. Lakadong Limestone Member in Khasi and Jaintia hills in South Shillong Plateau is late Paleocene in age and forms part of the carbonate platform. It represents deposition during High Stand Systems Tract. In the present study palynofacies analysis were carried out in two Lakadong Limestone sections i.e., Dohsniang (Kurtinsiang) (KPL) and Laitmowksing (LTL) from Khasi hills for detailed palaeoenvironmental interpretations, for the correlation and for the identification of higher order sea level cycles. Both the sections have been dated as late Paleocene based on the characteristic larger benthic foraminiferal assemblages belonging to the Tethyan Shallow Benthic Zones SBZ 3. For palynofacies analysis various type of organic matter were characterized and counted. The study shows cyclicity pattern in the organic matter types in both the sections which may be linked to the sea level changes of higher order cycles. Based on the variation in the organic matter content both the sections were subdivided into distinct palynofacies units. Each palynofacies unitsstart with high proportion of black oxidized palynomaceral along with dinoflagellate cysts representing a transgressive surface, followed by high quantity of degraded brown and cuticle organic matter from terrestrial source. Each palynofacies unit thus represent progradational deposit of High Stand Systems Tract starting with the deepening facies followed by shallowing facies of more terrestrial origin. Four progradational sequences have been identified in the KPL and three in the LTL section that can be correlated. Palynofacies study thus offers a logical approach for the study of uniform carbonate facies. Based on the present palynofacies criteria it has been possible to identify higher order sea level cycles in the Lakadong Limestone exposed at KPL and LTL section in Khasi Hills.

The transition from super hot Cretaceous to transient Palaeogene climate and therein reasonably fast northward movement of island Indian plate from equatorial tropics to buckling with Tibetan plate after subducting and engulfing the Tethys Sea and giving rise to lofty Himalayas, affected the oceanic current patterns and both fanua and flora drastically. These rapid tectonic processes from 65 to 50 Ma led to eustatic rise and in its response imprints could be seen in several areas of the Indian subcontinent. The calcareous nannoplankton being marine, tiny (2–10 μm), photosynthetic golden brown algae, and its fossil counterpart the calcareous nannofossils having fast turnover rate during Cenozoic are ideal as biostratigraphic markers. The Palaeogene statotypes are demarcated in Europe and biostratigraphy on varied biotic parameters were erected there but these can be well utilized in India also wherever the imprints of Palaeogene transgressions on Indian craton are recorded. After the global catastrophic late Cretaceous mass extinction around 65 Ma in which over ninetynine percent nannofossil species after gigantism died out. With the dawn of Palaeocene, new Lilliputian species evolved which grew exponentially in number and size during early Palaeogene. Massive release of greenhouse gasses at the beginning of the PETM (Paleocene Eocene Thermal Maximum) occurred and the end of PETM was met with a very large sequestration of carbon dioxide in the form of methane clathrate, coal, and crude oil which reduced the atmospheric carbon dioxide. The beginning of the Eocene Epoch indicated increased amount of oxygen in the earth’s atmosphere. At the end of the Middle Eocene Climatic Optimum, cooling and the carbon dioxide drawdown continued through the late Eocene and into the Eocene-Oligocene transition.

Conjoined and aberrant adult tests of Nummulites aff. Nummulites acutus (Sowerby) from the subsurface Middle Eocene sediments south of Pondicherry in Cauvery Basin, India show in situ development of minute biotic bodies as rare and unusual incidence. Since usual test of extinct as well as modern nummulitids hardly shows such development, these bodies are studied to know their nature of relation with the host adults. Being indigenous, intact and regular in shape, these forms have diverse mode of occurrence from cluster of embryo-like tiny featureless globular bodies to discrete lenticular bodies with granulated surface and as minute lenticular juvenile tests. The rudimentary and pre-mature morphologic features in the juveniles appear septal filaments, involute spiral sheets, planispiral whorls, quadrangular to rectangular chambers, narrow alar prolongations, marginal cord and septa, whose mature counterparts typify adult Nummulites; therefore, these are the offspring of the adult Nummulites aff. acutus. Their remarkably small size compared to the size of the host test indicates young age whereas their embedded emplacement at crucial morphologic parts of the host test points for a genetic relationship between adult and ‘baby’. With minute initial chamber (<1 µm) followed by several whorls, the offspring resemble microspheric juveniles. Their persistent development only in the ‘conjoined’ and ‘separated’ adult tests indicate that test abnormality is linked with their origin. An entity of conjoined Nummulites aff. Nummulites acutus comprises two megalospheric adult individuals of the species with fused apertures, and resembles ‘plastogamy’ in modern smaller benthic foraminifera, in which two adult individuals of a species unite for sexual reproduction. As in the latter, the two individuals in conjoined Nummulites are fused using secreted lime deposit as adhesive. Since modern larger foraminifera including nummulitids are not known to develop conjoined entity, taking a cue from plastogamy, sexual reproduction is held responsible for the development of the offspring in Nummulites aff. Nummulites acutus. This is supported by the occurrence of minute bodies inside the cavities, pores, and fused apertures and along the fused contact zone, and resemblance of a studied offspring with the offspring of modern nummulitids. The study indicates that sexual reproduction by adult individuals was prevalent in extinct Nummulites aff. Nummulites acutus to generate microspheric forms. This particular life cycle is supposed to prevail in the species towards the end of the Middle Eocene.

Two distinct foraminiferal assemblages, viz., (a) larger benthic foraminifera viz; Ranikothalia sp., Miscellanea sp., Daviesina sp. and Discocyclina spp. and (b) planktonic foraminifera viz; Globigerina daubjergensis, Globorotalia fringa and Chiloguembelina sp. cf. C. wilcoxiensis represent two prominent Palaeocene faunal events and marks the basal and top part of the Palaeocene sequence in Andaman Islands. Deep water depositional environment beyond the influence of clastic supply prevailed during Lower Palaeocene and shallow marine high energy condition during Upper Palaeocene period. Process of accretion started during later part of Palaeocene as evidenced in the North and Middle Andaman but not witnessed in South Andaman. Non-availability of the Palaeocene sequence in South Andaman maybe due of presence of barrier causing hindrance to sediment supply towards South.

The study of late Middle Eocene-Early Oligocene planktonic foraminifera at the Arabian Sea DSDP Site 219 and the Site 237, western tropical Indian Ocean has led to significant advancement over the sporadic and sketchy Eocene-Oligocene biostratigraphy described earlier. Orbulinoides beckmanni Zone (E12) that serves as the biostratigraphic proxy for climatic warming phase, the middle Eocene climatic optimum (MECO), is recorded at the Site 237. Sudden warming resulted in the extinction of Acarinina bullbrooki and A. topilensis at the begining and decline of large acarininids at the top of the Zone E12 with the extinction of muricate surface dweller species A. praetopilensis and Morozovelloides coronatus and M. lehneri. Contrary to the conventional attribution to cooling for which there is no geochemical evidence, eutrophication of species in the warm interval approximating the biozone E12 best explains the decline and extinction of muricate large acarininids and morozovelloidids close to the MECO warming event. Although the onset of MECO is marked by the appearance of Orbulinoides beckmanni its culmination is coincident with the extinction of, Globigerinatheka kugleri, G. euganea, Morozovelloides coronatus, M. lehneri and O. beckmanni. Thus, there is a distinctive episode of extinction of five species close to the end of MECO with the drop in temperature. The change from the greenhouse to the icehouse world occurred during the latest Eocene–Oligocene Transition (EOT) ~34 Ma is expressed by the composition and pattern of change in the planktonic foraminiferal assemblages of the zones E13 to O2 at the two Sites. Almost complete Eocene-Oligocene stratigraphic record from zones E12 to O2 at the Deep Sea Sites studied in tropical Indian Ocean is consistent with other global reference sections. The late Eocene cooling and continental glaciation on Antarctica effected successive closely spaced events of extinction of cerroazulensis group of species and hantkeninids; only the first pulse of extinction of cerroazulensis group of species is recorded at the two Sites as the hantkeninid extinction at the E/O boundary is not documented in the present work due to the nonrecovery or non-availability of core samples. The significant bioevent documented here at the two Sites is the early origin of Globoquadrina tapuriensis, G. selli and G. venezuelana in the late Eocene. Similar early appearance of these globoquadrines recorded from Tanzania, Spain and Italy extend down their range to Late Eocene.

An analysis of the palaeobiogeographic distribution of the Oligocene corals of the world reveals strong specific endemism whereas large generic pandemism. Four palaeobiogeographic provinces are identified here based on this distribution: the Western Indian Province (WIP) represented by Kutch, the Mediterranean-Iranian Province (MIP) consisting of Greece, Italy and Iran, the Caribbean-Northern South American Province (CNSAP) composed of Antigua, Puerto Rico and Venezuela, and the Northwestern American Province (NAP) represented by the state of Washington, USA. Different basins within a province show some specific similarity whereas specific provincialism is nearly absolute. Genera show wide distribution—the WIP shows 82% similarity with the MIP and 36% with the CNSAP; the CNSAP has 69% similarity with the MIP. However, the NAP shows significant generic endemism. The tropical affinity, and wide and rapid dispersability of the Oligocene corals are evident from this distribution pattern. Dispersal beyond tropics was apparently limited. This explains the relatively higher endemism of the NAP. Generic exchange between the WIP and the MIP, both belonging to the Tethys Realm, has been known for gastropods. Affinity of these provinces with the CNSAP is worth noticing. This similarity reflects the presence of a trans-Atlantic current during the Oligocene. The circumtropical distribution of the coral genera also evinces protracted planktotrophic larval ontogeny. However, endemism in the species level indicates rapid evolution. This distribution pattern having tropical yet wide longitudinal extent of genera and provincialism of species resembles the present day distribution of corals. It reflects that the scleractinian coral biology had already attained modern aspects in the Oligocene.

In the present paper we tried to highlight Paleogene events of the Manipur region on the basis of fossil evidences. The Paleogene succession of the Manipur region is represented by the Disang and Barail groups that are mainly exposed in the Imphal valley. In the present investigation, 108 species (80 bivlaves and 28 gastropods) belonging to 51 genera of bivalves and 26 genera of gastropods have been recovered from the Upper Disang Formation of Changamdabi area of Imphal valley. Based on the faunal assemblage, three biostratigraphic zones namely Zone-I Castocorbula (Parmicorbula) regulbiensis–Flemingostreapharoanum var-abivulina with age ranging from Late Paleocene-Early Eocene (Thanetian-Ypresian), Zone-II Vulsellapakistanica-Corbula (Varicorbula) daltoni with age ranging from Middle Eocene-Late Eocene (Lutetian-Bartonian) and Zone-III Callista (Callista) yawensis-Lucina Yawensis with Late Eocene age (Priabonian) were identified in ascending order of stratigraphy. Two ecological events in the Upper Disang Formation are identified i.e. shallowing of the sea-aerated water corresponding to zones I and open sea conditions with well aerated warm water condition corresponding to zones II and III. The occurrence of dinoflagellates (Eocene), flasher bedding and lenticular bedding in the shale, siltstone and sandstone containing succession of the Upper Disang of Gelmoul quarry (Churachandpur) suggests a shallow marine (tidal flat) depositional environment. The overlying plant fossils containing Barail sequences (Oligocene) of Kaina Hills, Imphal valley indicate coastal/terrestrial environmental condition under warm and humid tropical climate. Thus, there is a shallowing up in the depositional environment from Upper Disang Formation to Barail Group.