Anumeha Shukla

A fruit wing of Shorea Roxb. from the Early Miocene sediments of Kachchh, Gujarat and its bearing on palaeoclimatic interpretation

A new fossil fruit wing of Shorea Roxb. belonging to the family Dipterocarpaceae is described from the Early Miocene sediments of Kachchh, Gujarat. It resembles best the extant species Shorea macroptera Dyer, which is a prominent member of the tropical evergreen forests of the Malayan Peninsula. The present finding, along with the other megafossil records described from the same area, indicates a typical tropical vegetation with a warm and humid climate at the time of deposition in contrast to the present day xeric vegetation in the area. As the family Dipterocarpaceae no longer exists in western India, it is essential to discuss the time of its extinction and possible causes, which may include drastic changes in the climate of the region. The present finding also supports the theory of a Malaysian origin for the family in contrast to the hypothesis of a Gondwanan origin.

Emergence and extinction of Dipterocarpaceae in western India with reference to climate change: Fossil wood evidences

Climate has played a crucial role in assigning a different kind of topography to Rajasthan and Gujarat since the Cenozoic time. Evidently, three genera, namely, Dipterocarpus Gaert. f., Hopea Roxb. and Shorea Roxb. of the Dipterocarpaceae are described from the Neogene sediments of western India (Rajasthan and Gujarat). These taxa are marked by their complete absence in the region today. The presence of Dipterocarpaceae in western India has been noticed from the Early Eocene up to the Plio-Pleistocene in deep time. The family is usually a dominant component of the humid tropical and subtropical flora of the Indo-Malayan region and its discovery, along with earlier described fossils from western India indicates existence of ancient tropical rain forests in western India. A change in the climate affected warm and humid conditions occurring there during the Cenozoic resulting in arid to semi-arid climate at present which is responsible for the ultimate extinction of Dipterocarpaceae in the region. In addition, the palaeobiogeography of Dipterocarpaceae is reviewed.

Cocos sahnii Kaul: a Cocos nucifera L.-like fruit from the Early Eocene rainforest of Rajasthan, western India.

Cocos sahnii Kaul, a fossil palm fruit, is validated and described from the Fuller’s earth deposits of Kapurdi village of Rajasthan considered as Early Eocene in age. The fossil best resembles the genus Cocos, particularly Cocos nucifera L., which is now a common coastal element thriving in highly moist conditions. The recovery of this coconut-like fruit, along with earlier described evergreen taxa from the same formation, suggests the existence of typical tropical, warm and humid coastal conditions during the depositional period. The present arid to semi-arid climatic conditions occurring in Rajasthan indicate drastic climate change in the region during the Cenozoic. The possible time for the onset of aridity in the region which caused the total eradication of semi-evergreen to evergreen forests is discussed, as well as the palaeobiogeography of coconuts.

Paleoequatorial rain forest of western India during the EECO: evidence from Uvaria L. fossil and its geological distribution pattern

During the early Eocene, Rajasthan was positioned near the equator and had a warm and humid tropical climate dominated by tropical rainforests like the present-day equatorial forests of South India. Many of the plants retrieved as fossils from Rajasthan are growing there as refugee. This study further strengthens this view as it reports a new species of Uvaria L. from the early Eocene sediments of Bikaner (Rajasthan) showing its best resemblance with the extant U. zeylanica Deless. ex DC., which is presently growing in the evergreen forests of South India and Sri Lanka. The genus is thought to have originated in Africa, and the present finding gives an idea about its geologic distribution in Asia and Australasia via India relying on ‘stepping stone’ hypothesis during the Early Eocene Climatic Optimum (EECO) when climatic conditions were favourable for the luxuriant growth of tropical vegetation. A general cooling trend after EECO and change in the configuration of land and sea affected the climate on the regional scale causing total devastation of tropical evergreen forests that existed in western India during the depositional time; this change is ultimately responsible for creating dry and desertic conditions prevailing in the area at present.

Holigarna (Anacardiaceae) from the early Eocene of Western India and its palaeogeographical and palaeoclimatological significance

Thick lignite deposits on the western margin of India were preserved on account of thick vegetation which got buried underneath due to tectonic activities that occurred in northwestern part of India during the early Palaeogene. Study of the fossil flora preserved in these beds is important to deduce the palaeoclimate of the region. Therefore, a field work was undertaken to collect plant fossils from the Tarkeshwar lignite mine, Surat district, Gujarat (western India) which is still unexplored as far as the plant mega-remains are concerned. A fossil wood is systematically described from the Cambay Shale Formation of the mine considered to be of early Eocene in age. It shows close affinities with Holigarna (Anacardiaceae), particularly with H. beddomei and H. grahamii. This genus is evergreen in nature and grows in the Indo-Malayan region, while both the modern analogues of the fossil are endemic to semi-evergreen to evergreen forests ofWestern Ghats, south India, located at the equator. This not only confirms the palaeolatitudinal position of the Indian subcontinent at the equator during the early Palaeogene, but also indicates the presence of equatorial rain forest in the Indian subcontinent during the period. Based on the timetree, Sapindales started to diverge in the early Palaeocene (62–57 Ma) as its oldest fossil is from the K-Pg boundary. Discovery of the present anacardiaceous fossil (belonging to Sapindales) from the early Eocene strengthens the above phylogenetic view.

Vegetation Response and Landscape Dynamics of Indian Summer Monsoon Variations during Holocene: An Eco-Geomorphological Appraisal of Tropical Evergreen Forest Subfossil Logs

The high rainfall and low sea level during Early Holocene had a significant impact on the development and sustenance of dense forest and swamp-marsh cover along the southwest coast of India. This heavy rainfall flooded the coastal plains, forest flourishing in the abandoned river channels and other low-lying areas in midland.The coastline and other areas in lowland of southwestern India supply sufficient evidence of tree trunks of wet evergreen forests getting buried during the Holocene period under varying thickness of clay, silty-clay and even in sand sequences. This preserved subfossil log assemblage forms an excellent proxy for eco-geomorphological and palaeoclimate appraisal reported hitherto from Indian subcontinent, and complements the available palynological data. The bulk of the subfossil logs and partially carbonized wood remains have yielded age prior to the Holocene transgression of 6.5 k yrs BP, suggesting therein that flooding due to heavy rainfall drowned the forest cover, even extending to parts of the present shelf. These preserved logs represent a unique palaeoenvironmental database as they contain observable cellular structure. Some of them can even be compared to modern analogues. As these woods belong to the Late Pleistocene and Holocene, they form a valuable source of climate data that alleviates the lack of contemporaneous meteorological records. These palaeoforests along with pollen proxies depict the warmer environment in this region, which is consistent with a Mid Holocene Thermal Maximum often referred to as Holocene Climate Optimum. Thus, the subfossil logs of tropical evergreen forests constitute new indices of Asian palaeomonsoon, while their occurrence and preservation are attributed to eco-geomorphology and hydrological regimes associated with the intensified Asian Summer Monsoon, as recorded elsewhere.

Botryococcus from the early Eocene lignite mines of western India: inferences on morphology, taphonomy and palaeoenvironment

ABSTRACT Botryococcus, an important member of the planktonic algae, occurs in freshwater pools, lakes and occasionally in brackish-water lagoons, with wide distribution in tropical and temperate climate zones throughout the world. It is recognised as an oil-producing alga that is found in rock records from the Precambrian onwards. Here, this alga was retrieved from two different lignite mines of Rajasthan and Gujarat (western India), of early Eocene age. Apart from discussing its structural details, alterations in structures and preservation biases, this alga was used to reconstruct the depositional environment of the region based on its morphological and taphonomical characteristics. The images under transmitted light, fluorescence and scanning electron microscopy display aggregates of the irregular colonies, spherical to oval in shape, with cups arranged in definite patterns. The taphonomic characteristics of a large number of these algae indicate their autochthonous origin and in situ burial conditions. The dissolution of their outer layers suggests early diagenetic processes and loss of integrity due to microbial activity in the later phases of their burial in these sediments. The environment in the early Eocene has been reconstructed on the basis of the present findings, along with earlier recorded palynofacies from the region.

Palaeophytogeography of Eucalyptus L’ H’erit: New fossil evidences

Two new fossil woods resembling Eucalyptus L’ H’erit of the family Myrtaceae are described from the Palaeocene and Eocene successions of Gujarat and Rajasthan, respectively. They are characterized by diffuse-porous wood, heavily tylosed vessels arranged in echelon, vasicentic tracheids, simple perforations, thin rays and non septate fibres with bordered pits. Eucalyptus is considered native to Australia as most of its species are found there. The fossil records of Eucalyptus are hitherto known from the Cenozoic successions of Argentina, New Zealand, Australia and India. The genus is phytogeographically important as it has a wide range of distribution in the geologic past which suggests its long history affiliated with different Gondwanaland continents. A warm and humid coastal environment is inferred in western India during the Palaeogene on the basis of the earlier records of the genus.

A new fossil leaf of Kleinhovia L. from the early Eocene of India and its palaeoclimatic and phytogeographical significance

This study reports a new fossil leaf of Kleinhovia L., Kleinhovia bikanerensis sp. nov., from the Eocene clay mine of the Marh Formation of Bikaner, Rajasthan. The leaf resembling Kleinhovia hospita L. of the family Malvaceae is described for the first time from India. The leaf is characterized by very wide ovate shape, basal actinodromous venation with seven primary veins and cordate base. The presence of this leaf fossil indicates tropical warm and humid climatic conditions prevailing in the area during the Eocene and throws light on its past and present distribution.

A fossil coconut fruit from the early Eocene of Gujarat

A fossil fruit resembling extant Cocos nucifera of the family Arecaceae is reported for the first time from the early Eocene sediments of Gujarat. The fossil was collected from the Tarkeshwar lignite mine of the Surat District which belongs to the Cambay Shale Formation. Its occurrence indicates coastal conditions in the region during the depositional period in contrast to arid to semi-arid climate prevailing there at present. The present fossil, along with the previously published palyno-assemblages from the mine supports the equatorial position of the Indian subcontinent at the time of deposition i.e. during the early Eocene.