Applications of Palynology in Stratigraphy and Climate Studies

Precambrian biota, which primarily includes bacteria, prokaryotes, protists, algal-stromatolites, organic- walled microfossils (micro and macrofossils) and trace fossils, plays a significant role in understanding early life as well as their diversification on the Earth. In addition, they are also used in biostratigraphy, to understand the depositional environment, early biosphere, and atmosphere. A review of Precambrian biota, recovered from the Archean, and Proterozoic sedimentary rocks of India, reveals the presence of diverse assemblages of organic remains. These remains play a significant role in understanding Indian Precambrian biostratigraphy and early life.

The Gondwana sedimentary deposits are spread across the Indian Peninsula. The Gondwana sequences in Peninsular India are mostly non-marine. Based on morphological features of palynoflora and megaflora, palynomorphs from different biostratigraphic sediments (Talchir to Supra Panchet) of Gondwana show a high degree of variation. Based on the microstructures of exine among spores, the primitive and younger states of the sediments are confirmed with time. The morphological characteristics of pollen spores help in their evolutionary sequence through different time scales, hence playing a vital role in biohorizon stratigraphy. Apart from this, palynomorphs also help in delineating the biostratigraphic age, First Appearance Datum (FAD), LAD (Last Appearance Datum), DOD (Dominance of Datum), assemblage zones, and palaeoclimate. The current paper provides an overview of the role of palynology in determining the biostratigraphic ages, palaeoclimatic conditions, and correlation of Indian Gondwana sediments. The data presented here is the basic framework for further refinement of chronology based on palynology. It is a compilation of published data from peninsular India.

The flora of the Rajmahal Formation is typically known as ‘Rajmahal Flora’. It is Early Cretaceous (Barremian to Aptian) in age and is one of the most interesting Mesozoic floral succession characterized by prolific and diversified floral entities. Distinctive amalgamation of volcanic and sedimentary sequences (intercalations of basaltic lava flows and intertrappean sediments) is a unique feature of this formation which had led to the excellent preservation of plant body remains along with anatomical details and it is one of the national geological monuments of India. A number of floral elements of Rajmahal Flora have been under continuous taxanomic reassessment, particularly enigmatic macroremains of angiosperms, though definite pollen records of angiospermid affinity are known from this formation. The present paper provides an updated synthesis and analysis of the palaeofloritics of the Rajmahal Formation and underlying Dubrajpur Formation and its relevance in tracing the angiosperm evolution.

The Upper Cretaceous (Maastrichtian) infratrappean (Lameta Formation) and the Upper Cretaceous-early Paleocene intertrappean sedimentary beds associated with Deccan volcanic flows are windows to understand floral biodiversity, age, and paleoclimate during Deccan volcanic activity. Palynological studies of these geographically separated sedimentary beds at different stratigraphic levels show that the initiation of Deccan volcanism in the area brought climatic changes that consequently affected the biota and the depositional environments. The fluvio-lacustrine infratrappean (Lameta Formation) sediments which were deposited in a semiarid-arid climate, were having a mixture of gymnosperm and angiosperm plants. The onset of Deccan volcanic activity changed the climate and depositional environments. During the repose in Deccan volcanic activity, many small closed lakes were formed over the lava surface between the two volcanic flows. The sediments associated with these ponds have a pteridophyte-angiosperm rich flora. This vegetation is distinctly different from that of Lameta sediments. The Late Cretaceous intertrappean sediments shows dominance of palynotaxa such as Azolla cretacea, Gabonisporis vigourouxii, Aquilapollenites bengalensis, Ariadnaesporites, Farabeipollis spp. Jiangsupollis spp., Scollardia conferta, and Triporoletes reticulatus. The presence of epiphyllous fungi, algal remains (Ovoidites), pteridophytes (Azolla, Crybelosporites, Gabonisporis) and mega-plant fossils, collectively suggest the prevalence of warm, humid tropical climatic conditions. Intermittent dry spells are also indicated at many places. In the Deccan volcanic province, the Paleocene is marked by disappearance/scarcity of Maastrichtian taxa. The Paleocene vegetation is distinctly different and it shows some similarity with the Paleocene-Eocene palynoflora of western India.

At the dawn of the Paleogene that was the beginning of the Cenozoic era, the continents drifted farther apart, heading toward their modern positions. After India separated from Gondwana, it took 160million years to travel 9000 km northward from the Southern Hemisphere to Northern Hemisphere and to its modern geographical position coupled with Eurasia. During that voyage as an isolated Island continent, India experienced various climatic conditions due to latitudinal changes as well as extreme climate variations. Documentation of India's climate during its journey across the paleoequatorial region allows us to assess biotic as well as climatic changes across the low latitudes, at a time when global climate was exceptionally warm. It is also postulated that the similar situation might be experience in the future. The palynological studies of the Paleogene deposits of Indian subcontinent can provide substantial information of past vegetation and climate, and can serve as a natural laboratory to understand the relationship between biota and climate.

Palynology (and pollen analysis) has proven to be a reliable tool in reconstructing the past vegetation (dynamics) and contemporary climatic changes. The chapter reviews the role of pollen in reconstructing the palaeoclimate in India over the pre-industrial Common Era (CE; past ca. 2000 years [2 ka]; past 2 millennia; Late Holocene), comprising the global climatic events, such as the Roman Warm Period (RWP), Dark Ages Cold Period (DACP), Medieval Climate Anomaly (MCA), Little Ice Age (LIA) and the Current Warm Period (CWP). In addition, the hydro-climatic variability, which influences the socio-economic welfare of one-third of the human population through the agricultural output and Gross Domestic Product (GDP) of this densely-populated country, are also analyzed. This chapter also discusses the solar forcing and the other forcing factors behind the hydroclimatic variability during the past 2 millennia in India.

The applications of palynology to understand palaeo-environment and palaeo-vegetation changes have been well established from deposits ranging from the Palaeozoic to the Quaternary. The Holocene epoch has best witnessed the impact of anthropogenic activities lead by a quantum jump in human population. Vegetation distribution and its variations due to exogenous influences are evident in the fossil and modern pollen records globally. Palynology has proved to be a tested tool to decipher these changes in the environmental dynamics and changing floral compositions, as a consequence of anthropogenic activities. We have made an attempt to understand the pattern of preservation of these anthropogenic marker taxa in the pollen records across the different physiographic regions of India. The spatio-temporal distribution patterns of the occurrence of anthropogenic marker taxa have been discussed and their use in deciphering related human activities. We provide an overview of the palynological records which evidently state the presence of the marker taxa with a clear reporting of anthropogenic influence in the different regions. Here we review the Holocene pollen records across India to specify the presence of anthropogenic pollen in the vastly populated and agriculture dominated regions of the country.

The present study was intended to establish a modern pollen analogue from the open-land areas of the Lucknow district as well as to investigate pollen morphological attributes from the same region to resolve and refine the taxonomic categorization and pollen identification. The flowers of 29 plant taxa belonging to 18 different families have been procured from the premises of BSIP and BBAU including the forest edge and open land localities of Lucknow district. Detailed pollen micro-morphological investigation of twenty nine plant taxa has been carried out under the Light Microscopy (LM). The pollen morphological characteristics like aperture number, position and character (NPC), pollen shape, size, exine sculpturing and thickness play a vital role in assigning different pollen taxa to genera, species and families. The palynological studies in the surface soil samples aids in tracing the marker pollen taxa which reflects the current vegetation pattern and climatic condition and hence have a plausible role in the palaeoclimatic interpretation. The pollen assemblage in the surface soil sample reflects the complete dominance of non-arboreal taxa (78.07%) over the arboreal taxa (9.99%). The prominent non-arboreal taxa are represented by Caryophyllaceae, Acanthaceae, Amaranthaceae, Celosia argentea, Lamiaceae, Brassicaceae and Asteroideae, followed by Kydia sp. The arboreal taxa are mainly represented by Butea monosperma, Emblica officinalis, Alstonia scholaris, Holoptelea integrifolia, Lagerstroemia parviflora, Terminalia bellirica, Meliaceae and Syzygium cumini. The distribution of marshy and aquatic taxa is less prominent. Thus, the overall palynological study would help in the precise identification of the pollen in the surface soil and the sedimentary sections for the formulation of the modern pollen-vegetation relationship as well as palaeoecological reconstruction, respectively.

Archaeobotany deals with the interpretation of preserved plant remains from the archaeological sites in order to reconstruct the past vegetation and climate change and past human-plant relationship. The archaeobotanical remains found in the archaeological sites are classified into two groups; macro and microbotanical remains. Usually, the microbotanical investigations includes the extraction of spores/pollen, phytoliths, diatoms, fungal spores and starch grains from the soils/sediments of the archaeological sites. But sometimes archaeological artefacts including potsherds may also provide us with valuable information. Palaeobotanical investigations and palaeoclimate reconstruction from the archaeological potsherds are rare especially from the coastal regions of the globe. In the present study two earthen vessels associated potsherds collected from the Tilpi region of Sundarbans, deltaic West Bengal were studied in a multi-proxy approach. The age of the earthen pots and potsherds found to be 2630 ± 25 years BP. The pollen, phytolith and non-pollen palynomorph data of the potsherds revealed that a non-littoral forest was present in the area under tropical warm and humid climate condition. However, occurrence of pollen grains and phytoliths of palms, and Concentricystes sp. indicate that the coast line was not far away from the area of deposition (Rao 1990, Ramanujam et al. 1998).

A detailed biomarker characterisation has been carried out from the Early Palaeogene samples from the Cambay Basin. The present study examines the biomarker applications in interpreting organic matter sources and palaeodepositional environment from the Palaeogene shales of the Cambay Basin, India. The detailed saturated and aromatic biomarkers identified from the mass chromatograms of GC-MS and GC × GC-TOF-MS, such as sesquiterpanes, tricyclic, tetracyclic, and pentacyclic triterpanes including hopanoids and methylhopanes, oleananes, bicadinanes, secobicadinanes, C₃₀ tetrapolyprenoid, C₂₉ 28-nor-spergulane, aromatic sesquiterpanes, diaromatic tricyclic terpane, aromatic non-hopanoid triterpenoids, aromatic diterpenoids, diaryl isoprenoids, and acyclic isoprenoids efficiently discriminate between the organic matter sources, compositions, and palaeodepositional environment in north and south blocks of the Cambay Basin. Low values of pristane/phytane, along with the extended series of tricyclic terpanes, 3β-methylated hopanes, diaryl isoprenoids, C₃₀ tetrapolyprenoid and C₂₉ 28-norspergulane in the northern block samples, indicate that the organic matter was deposited in the photic zone under sub-oxic to anoxic settings, most likely in a restricted marine/lacustrine environment. Similarly, the occurrence of oleanane, bicadinanes, secobicadinanes and higher plant aromatic triterpenoids in the southern block samples suggests dominant angiospermous organic matter input deposited in an oxic fluvio-deltaic environment. Moreover, the presence of bicadinanes and secobicadinanes clearly indicates the advent of evergreen tropical rainforests in the Early Eocene.

Palynology includes a wide range of organic walled microfossils, including spores, pollen, dinoflagellates, chitinozoa, fungal spores, acritarchs, etc. In this chapter, we discuss the use of palynological studies in the fields of petroleum and coal exploration. As palynomorphs are well known for being extremely resilient to the forces of nature (and also the effects of harsh chemical laboratory processing), in favorable conditions, they are abundantly well retained in litho-units and provide an important tool in stratigraphic correlation and paleo-environmental interpretation. Palynology is also used to infer thermal maturity, as well as to understand the production capabilities of basins and inferring the quality of coal deposits. In the past few decades, with the advent of cutting-edge processing and analyzing scientific tools, more and more uses of palynology in newer frontiers have emerged.