Foraminiferal Micropaleontology for Understanding Earth’s History

By Pratul Kumar Saraswati

Foraminiferal Micropaleontology for Understanding Earth’s History incorporates new findings on taxonomy, classification and biostratigraphy of foraminifera. Foraminifera offer the best geochemical proxies for paleoclimate and paleoenvironment interpretation. The study of foraminifera was promoted by oil exploration due to its exceptional use in subsurface stratigraphy. A rapid technological development in the past 20 years in the field of imaging microfossils and in geochemical microanalysis have added novel information about foraminifera.

Foraminiferal Micropaleontology for Understanding Earth’s History builds an understanding of biology, morphology and classification of foraminifera for its varied applications. In the past two decades, a phenomenal growth has occurred in geochemical proxies in shells of foraminifera, and as a result, crucial information about past climate of the earth is achieved. Foraminifera is the most extensively used marine microfossils in deep-time reconstruction of the earth history. Its key applications are in paleoenvironment and paleoclimate interpretation, paleoceanography, and biostratigraphy to continuously improve the Geologic Time Scale.

• Provides an overview of the Earth history as witnessed and evidenced by foraminifera
• Discusses a variety of geochemical proxies used in reconstruction of environment, climate and paleobiology of foraminifera
• Presents a new insight into the morphology and classification of foraminifera by modern tools of x-ray microscopy, quantitative methods, and molecular research

• Language: English
• Publisher: Elsevier Science
• Release date: Jun 12, 2021
• ISBN: 9780128242308

Pratul Kumar Saraswati

Pratul Saraswati has been a professor at the Indian Institute of Technology Bombay since 1988, teaching Micropaleontology and Petroleum Geology to postgraduate students. His research area is focused on foraminifera for biostratigraphy and paleoenvironmental interpretation of Cenozoic marine sequences. Dr. Saraswati has written more than 90 papers in scientific journals and chapters in edited volumes. He has served or still serves as an expert member and in advisory capacity with several research funding agencies, research institutes, and educational institutions.

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Preface

Pratul Kumar Saraswati, Indian Institute of Technology Bombay, Mumbai, India

The early naturalists admired microfossils for their esthetics. The geologists in the 20th-century recognized their applications, and with industrialization, the science of microfossils was promoted by the oil industry for subsurface stratigraphy. The modern world, staring at the worst climate crisis, is leaning on microfossils to learn how they brave catastrophes in the geologic past. There are possibly no other microfossils than foraminifera, which provides diverse information about Earth's evolutionary history. Foraminifera is the timekeeper of the Earth and witness to its evolving environment and climate. In the past five decades, there has been exponential growth in publications in amazingly different disciplines that experimented with living foraminifera or used their fossils as sources of information. The important findings of these publications have not entered most graduate textbooks. Foraminiferal research's phenomenal growth in the past decades has been possible due to almost uninterrupted deep-sea samples and improvements in imaging and microanalytical techniques. A holistic view of foraminifera is emerging because of culture studies for geochemical proxy development and molecular studies. It has furthered the understanding of paleobiology and evolution of foraminifera, besides the paleoclimate reconstruction and paleoceanography. This book aims to communicate these to graduate students and those embarking on a research career. It is assumed that students consulting this book have a basic understanding of micropaleontology. The book is also addressed to professionals using geochemical proxies in paleoclimate and paleoceanography, where knowing paleobiology and paleoecology of foraminifera is as essential as feeding foraminifera in the machine. The data quality will improve, and interpretations will be purposeful if viewed in the biological and geological context of foraminiferal samples.

This book could be written because of the IIT Bombay support and cooperation of my colleagues in the Department of Earth Sciences. I am especially indebted to Prof. Santanu Banerjee and students of our labs for their support over years of association. Sonal Khanolkar, Anupam Ghosh, Asmita Singh, and Christer Pereira deserve special acknowledgment for their help in various ways in writing the book. I thank Darakhshan Fatima and Tathagata Roy Choudhury for the illustrations in the book. Amy Shapiro, Alice Grant, Sruthi Satheesh, and Mohanraj Rajendran of Elsevier are thanked for their prompt response to my queries in planning the book and bringing it in final form.

Ma, Jaya, Supriya, and Raghu gave me the freedom to plan and complete the book during the unprecedented lockdown forced by the Covid-19 pandemic. Without their support, it would not have been possible to write the book. I owe more than a formal thank to them.

1

Introduction

Abstract

The study of foraminifera was built slowly with the early observations by naturalists and philosophers to a more systematic study beginning with Alcide d'Orbigny, who named the group. The oil industry further nurtured it for its exceptional use in subsurface stratigraphy. The scientific voyages were started in the second half of the 19th century to explore the ocean basins, and they grew to modern deep-sea exploration undertaken since the 1960s. The deep-sea sediments contributed immensely to the science of foraminifera. This chapter gives a historical background of the study of foraminifera and explains the nature of its geological records.

Keywords

HMS Challenger; JOIDES; dissolution of foraminifera; stratigraphic resolution; paleontologic resolution

1.1 Historical background

Foraminifera is a single-celled organism similar to amoebae. The recent genomic information places it in the clade Rhizaria of the protists (Adl et al., 2019). Its name is derived from the Latin words foramen (meaning an opening or a hole) and fer (meaning bearing), referring to the bearer of a hole at the base of the partitions of chambers of the shell (formally called test). It appeared in the geological records about 550 million years ago in the Cambrian Period. Foraminifera generally ranges from ~100 µm to 1 mm, but some species attained the gigantic size of more than 10 cm. Although some noncalcified granuloreticulose protists in freshwater belong to foraminifera due to their molecular affinity, it is a strictly marine organism. Foraminifera is an essential part of marine communities at all ocean depths, living as benthos on the seafloor and as planktons floating in the upper water column. The turnover rate of foraminifera in the oceans is approximately 226×10¹⁹ specimens/year (Table 1.1), which is ultimately contributed to the oceanic sediments. Calcareous ooze covers a sizable part of the deep seafloor. It is made dominantly of the shells of calcareous microorganisms, including foraminifera (Figs. 1.1 and 1.2). Foraminifera also contributes significantly to shallow marine sediments, particularly in coral reefs distributed globally in tropical–subtropical regions (Figs. 1.3 and 1.4). Approximately 1.4 billion tons of CaCO3 is added annually in the present-day oceans by foraminifera (Langer, 2008), contributing to the present-day global carbonate budget. Foraminifera was also overwhelmingly present in the sediments of the geologic past. The Permian fusulinid limestone and Eocene nummulitic limestone are well-known examples (Fig. 1.5). Foraminifera is a brilliant storyteller of the Phanerozoic history of the Earth. The outstanding contribution of foraminifera in the reconstruction of ocean history, climate, sea-level changes, and catastrophes in life’s history is testimony to this statement.

Table 1.1

Source: After Langer, M., 2008. Assessing the contribution of foraminiferan protists to global ocean carbonate production. J. Eukaryot. Microbiol. 55, 163–169, reproduced with permission © John Wiley and Sons.

Figure 1.1 Distribution of neritic and pelagic sediments on the ocean floor. Calcareous ooze comprising foraminifera, pteropods, and calcareous nannoplankton are shown in pink. Source: After Skinner, B.J., Murck, B., 2011. The Blue Planet – An Introduction to Earth System Science, third ed. John Wiley & Sons, Inc. (Skinner and Murck, 2011), reproduced with permission © John Wiley & Sons - Books.

Figure 1.2 Calcareous ooze from the Mediterranean Sea, composed mainly of planktic foraminifera and pteropods. Source: Sample courtesy Michael Knappertsbusch, Natural History Museum, Basel.

Figure 1.3 Map showing the global distribution of coral reefs, the major sites of present-day, shallow water carbonate deposition. Source: Reproduced with permission © National Ocean Services, USA.

Figure 1.4 Shallow marine sediments from coral reefs of Akajima (Japan) composed dominantly of larger benthic foraminifera.

Figure 1.5 Eocene nummulitic limestone: extensive outcrop in Kutch, India (top left), a close-up view of the limestone showing tests of Nummulites (top right), and a petrographic thin section view of the nummulitic limestone (bottom).

The beginning

Greek geographer and philosopher Strabo (64 or 63 BCE–CE 24) made the first observation on foraminifera, although in a completely different sense. He described the abundantly occurring Nummulites in the Eocene limestone, making Egypt’s pyramids, as petrified remains of beans leftover by the laborers who built the pyramids (Heron-Allen, 1915). Robert Hooke (1635–1703), a British naturalist and architect, documented various samples under the microscope and published them in his book titled Micrographia in 1665 (Fig. 1.6). It was possibly the first illustration of foraminifera (Cifelli, 1990). Alcide d'Orbigny (1802–57) (Fig. 1.7), an extraordinary naturalist born in France, began a systematic study on foraminifera. He is regarded as the father of micropaleontology. He developed an interest in foraminifera at an early age by studying the beach sands in his coastal neighborhood. His father, a surgeon in the French Navy, encouraged him in his study by arranging beach sands from around the world. D’Orbigny (1826) treated foraminifera as a distinct group, gave it its name Foraminiféres, in his publication referred shortly as Tableau Méthodique. In addition to foraminifera, many terms are used in literature, including foraminiferid and foraminiferan. All the terms are treated as valid, but it is recommended that the same set of singular–plural terms should be used consistently. The term foraminifera is used both as singular and plural, determined from the context (Lipps et al., 2011).

Figure 1.6 The first foraminifera illustrated by Robert Hook (right) in 1665.

Figure 1.7 Alcide d’Orbigny (1802–57) who coined the name Foraminiféres and presented its first classification.

D'Orbigny described above 600 foraminifera species, adding substantially to about a hundred species known till then. The collections of d'Orbigny are kept in the Muséum National d'Histoire Naturelle (MNHN), Paris. Charles Schlumberger was associated with the MNHN, and he contributed to living foraminifera, especially about their dimorphism. The reproductive processes of foraminifera were not known with certainty by this time; some workers believed the dimorphic forms to be of different sexes, while the others considered the two to belong to different generations. Lister (1895) called them megalospheric (with a large central chamber) and microspheric (with a small central chamber) forms. The early naturalists were men of varied interests and pursued the study of foraminifera as a hobby. Colonel Grant, while serving the British Army, collected foraminifera from Kutch in western India and handed it over to James de Carle Sowerby, one of the founders of the Royal Botanic Society and a well-recognized natural history artist. Sowerby, 1840 was the earliest to describe Nummulites acutus, Nummulites obtusus, and Alveolina elliptica from the Indian subcontinent. Henry John Carter (1813–95), a surgeon in the East India Company’s army, described and sketched nummulitids and alveolinids from Sind and Kutch. The details of the foraminifera’s internal structures illustrated by the early workers were remarkable, considering those days’ moderate microscopes. A notable contribution to architecture and the internal structure of foraminifera was made by William Benjamin Carpenter (1813–85), a pioneer naturalist who became the Vice President of the Royal Society. He made exceptional illustrations of complex structures of larger benthic foraminifera (LBF) (Fig. 1.8) in several of his publications, including the monograph Introduction to the Study of Foraminifera (Carpenter, 1862).

Figure 1.8 Illustration of internal structure of a foraminifer Orbitolite by William Carpenter in 1855.

The scientific voyages

In the second half of the 19th century, scientific voyages were planned to explore oceans and ocean floors across the world. A strong idea existed that there is no life beyond 300 fathoms (~550 m) in the sea. Charles Wyville Thomson, a professor of natural history at the University of Edinburgh, convinced Carpenter, the Vice President of the Royal Society, of the significance of investigating the idea of an azoic deep sea. Wyville Thomson was allowed to use HMS Lightning in the summer of 1868. In this expedition, he established that life existed at 600 fathoms and led two more expeditions in 1869 and 1870. These expeditions’ scientific success encouraged Wyville Thomson and William Carpenter to approach the Royal Society for a major expedition. Due to their efforts, the HMS Challenger (Fig. 1.9) was launched in 1872 that succeeded in producing the scientific results in 500 volumes of published reports. The voyage is regarded as the beginning of marine geology and oceanography. John Murray was an onboard scientist whose interest lay in knowing the nature of the ocean floor sediments. He observed that a vast area of the seafloor is covered with microscopic organisms’ remains, and planktic foraminifera constitutes a significant component of calcareous oozes. Contrary to the view of Wyville Thomson, Murray had enough evidence to conclude that Globigerina and the other organisms constituting the ooze were living at or near the surface water. After death, they settled onto the sea bottom. He also made a significant observation that planktic foraminifera is latitudinally distributed. The maximum species occur in tropical belts and decrease poleward in numbers. H.B. Brady (1835–91) was a pharmaceutics and seller of scientific instruments. He developed an interest in foraminifera in his later life and studied the Challenger expedition’s dredged samples. The Challenger Report of Brady (1884) remains a major reference with the description, illustration, and distribution of nearly a thousand extant foraminifera species. These are housed in the Natural History Museum in London.

Figure 1.9 The working platform of the scientific vessel HMS Challenger. Source: From Alamy Limited, UK.

Subsurface exploration

The exploration of hydrocarbon intensified after World War I (1914–18), with an increase in energy demand. The drilling of subsurface stratigraphic sections commenced on a large scale to assess sedimentary basins for their hydrocarbon potential. The subsurface samples’ age and paleoenvironment were required, and the drilled wells were to be correlated stratigraphically. Foraminifera proved useful due to its small size and abundance in a limited sample size of the boreholes. The oil industry recognized the crucial role of foraminifera in exploration and nurtured its study in later years. Biostratigraphic study of foraminifera gained importance as micropaleontologists became more engaged in establishing the time framework of the stratigraphic successions. It helped in the identification of hiatuses and the stratigraphic correlation between boreholes. Joseph A. Cushman (1881–1949) made a remarkable contribution at this time. He had a long association with the US Geological Survey, and he was also a consultant to the oil industry. It provided him an opportunity to examine foraminifera from a wide range of ages and environments and led him to propose its classification. In 1928 Cushman published his famous book, Foraminifera, Their Classification and Economic Use. He set up Cushman Laboratory for Foraminiferal Research in Massachusetts. The laboratory became the foremost center of research in foraminifera, and in 1925 he initiated a publication entitled Contributions From the Cushman Laboratory for Foraminiferal Research. The Cushman Foundation, founded in 1950 in his honor, is publishing the Journal of Foraminiferal Research. The Cushman Collection comprises several thousand slides, including the holotypes of the species created by Cushman, and it is housed in the Smithsonian’s Natural History Museum. Many conceptual advancements in biostratigraphy, biofacies, and paleoecology of foraminifera were made during this time.

To assist oil exploration in Russia, the newly established All Russia Petroleum Research Exploration Institute (VNIGRI) set up the microfaunal laboratory in 1930. Several well-known foraminiferologists were associated with it. N.N. Subbotina (1904–84) and others at the VNIGRI studied the Cretaceous and Palaeogene foraminifera of Russia. She also contributed to Cenozoic planktic foraminiferal zonation of the Crimean–Caucasian region. The Paleozoic foraminifera of Russia, especially the complex-walled Fusulinida, was first studied by G.A. Dutkevich and later by D.M. Rauser-Chernousova. The Russian specialists also helped establish a micropaleontology laboratory in India when the Oil and Natural Gas Commission was set up in 1956. Before this, exploration was confined to the Assam Basin in northeast India, and Yedatore Nagappa (1907–60) pioneered the study of the foraminifera of this region.

Van der Vlerk and Umbgrove (1927) proposed the Letter-Stage Classification based on LBF that became very useful to oil explorations in determining the age and correlation of the Tertiary successions in Indonesia. The similarity of benthic foraminifera might be due to both similar ages and environments. The similarity of planktic foraminifera is a reliable criterion of similar age. Therefore planktic foraminifera–based biozonation was worked out in the 1950s. The British Petroleum micropaleontologists Hans Bolli and Walter Blow worked out zonal schemes based on planktic foraminifera of the Caribbean and Tanzania. Alphanumeric shorthand was used for the biozones, P1–P22 for the Paleogene, and N4–N23 for the Neogene. The resurgence in the deep-sea studies, with the launch of Glomar Challenger in 1968, marked a new phase in the development of planktic foraminiferal biostratigraphy. It became clear that these zonal schemes were not only of regional but also broadly of global application. The continuous cores allowed the investigation of phyletic lineages in planktic foraminifera and thereby the phylozones. It further improved and refined the planktic foraminiferal biostratigraphy during the 1970s and 1980s. Wade et al. (2011) discussed the present status of planktic foraminiferal zonation of the Cenozoic and calibration of the Zones with magnetostratigraphic polarity chron.

Modern exploration relies on seismic and sequence stratigraphy. The seismic reflections represent timelines, and they are required to be calibrated by biostratigraphy. Foraminifera contributes significantly to recognizing sequence boundary, the systems tract, and the maximum flooding surface. With the depleting resources, proper management of the reservoirs is of critical importance. Directional drilling in penetrating the reservoir saves the cost of exploration. Continuous monitoring of drilling using biostratigraphy, called biosteering, is efficient and cost-saver. The tops and bottoms of the taxa, used in conventional biostratigraphy, are considered too coarse for applications at reservoir scales. The assemblages of taxa, the bloom of specific taxa, and foraminifera’s morphotypes are instead used to characterize the reservoir intervals.

The rise of a new science

The Challenger expedition (1872–76) had established the scientific importance of the sea. It busted the myth that deep sea is devoid of life. It encouraged several expeditions in later years, including the Meteor Expedition (1927–29) by Germany and the Albatross Expedition (1947–48) of Sweden that raised deep-sea cores from the major ocean basins. Wolfgang Schott, a biologist on board the Meteor, studied the short cores raised in South Atlantic. He made a novel observation that the top 25 cm of the core consisted of Globorotalia menardii, and below this, it was devoid of G. menardii and associated species. He intuitively hypothesized that the lower part of the core belongs to the last ice age. G. menardii could not tolerate the low temperatures and retreat to lower, warmer latitudes (Corfield, 2003). With this began the reconstruction of glacial–interglacial history based on foraminifera. The relatively longer cores of 10 m or more recovered by Albatross could provide ocean history further deep in time. Foraminifera proved indispensable in the reconstruction of ocean history and promoted a rising new science of paleoceanography. Several conceptual developments were tested in the Albatross cores, including the ocean’s response to glacial conditions, ocean productivity, and the nature of sediment cycles vis-à-vis Milankovitch forcing (Berger, 2013). Two important innovations of this time were the invention of piston core by Kullenberg in 1947 and Rose Bengal staining to recognize live foraminifera by Walton in 1952. The piston core helped raise longer cores that enabled the study of Quaternary and late Neogene sedimentary records. Staining was an essential step in understanding the environmental distribution of foraminifera as the dead assemblages in the sediments might be transported and give misleading information.

A new dimension to foraminiferal research was added in the following years by Harold Urey, a Nobel Prize winner of 1934. He demonstrated in the early 1950s that the oxygen isotopic composition of calcareous shells holds the key to estimating seawater temperatures. Cesare Emiliani (1922–95) was a doctoral student of Urey, and he pioneered the use of oxygen isotopic composition of foraminifera. He observed a systematic periodic variation in the ratios of ¹⁸O and ¹⁶O in the cores raised by the Albatross and thus interpreted the glacial–interglacial cycles in the oceanic records. At that time, only 4 glacial events were known in the Pleistocene, but Emiliani (1955) found isotopic evidence of 15 glaciations in the Pacific’s cores. He also inferred the depth habitat of planktic foraminifera based on their oxygen isotopic composition. These early works demonstrated that foraminifera is the carrier of geochemical proxies that could reconstruct seawater temperatures and salinity.

The idea of the ocean basins as an ancient feature and stable environment had changed by now. The uninterrupted sedimentary records of the deep sea seemed promising for understanding the climate and the oceans’ history with the newly developed isotopic tools. Emiliani was the key person to form Joint Oceanographic Institution for Deep Earth Sampling (JOIDES) to obtain deeper cores from the ocean to realize this goal. In 1966 JOIDES proposed a program of deep-sea drilling to the National Science Foundation of the United States. It was approved with the Deep-Sea Drilling Project (DSDP) commencement, and its first research vessel Glomar Challenger was launched in 1968. Due to advancements in drilling technology, it was now possible to recover long and undisturbed sediment cores from the sea bottoms. Besides the samples raised by DSDP, the foraminiferal study was aided by another innovation at this time. The commercial version of the scanning electron microscope was just introduced in 1965. It provided new opportunities to examine foraminifera’s surface ultrastructure and image them at higher resolutions and magnifications. Surface ultrastructure improved the understanding of evolution and phylogenetic lineages of planktic foraminifera, and its importance in taxonomy and biostratigraphy was recognized. The planktic foraminifera of tropical and temperate regions have distinct evolutionary lineages; therefore separate zonal schemes were maintained for the two regions. The DSDP cores advanced our knowledge of many microfossils that enabled integrating the various planktic microfossil zonal schemes as different experts simultaneously studied the same cores.

The DSDP successor, Ocean Drilling Program (ODP), commenced in 1985 with the launch of JOIDES Resolution and continued till 2003. The international collaboration and interdisciplinary approach to studying these cores from wide-ranging latitudes have raised the foraminiferal research to higher scientific merits. The Cenozoic high-resolution chronology is developed by integrating the planktic foraminiferal zones with magnetic polarity reversals and stable isotope stratigraphy. The timings of major climatic and biotic events in Earth’s history are established and globally correlated due to better time resolution achieved by integrative stratigraphy. The scientific information about the evolution of oceans expanded. Paleoceanography was well-developed by this time, and a new journal named Paleoceanography was launched in 1986 to encourage research contributions in this field. Presently, there are two major scientific drilling programs with international collaborations—the International Ocean Discovery Program (IODP) and the International Continental Scientific Drilling Program (ICDP). The drillships JOIDES Resolution and Chikyu (Fig. 1.10) are involved in executing IODP’s various science plans.

Figure 1.10 Drill ship Chikyu. Source: Reproduced with permission © JAMSTEC/IODP.

1.2 Foraminifera records the Earth’s history

Foraminifera is both the clock and the recorder of the Earth’s history. It has played a crucial role in developing our understanding of the evolution of life and the environment on Earth. The earliest fossil record of foraminifera is from the Cambrian Period (about 550 million years ago). It diversified slowly in the early Paleozoic but had a rapid growth in Carboniferous and Permian times when large-sized fusulinid foraminifera evolved. Microgranular-walled fusulinid foraminifera was abundant in the shallow marine environment and built fusulinid limestone across the tropical belt stretching from the North American platform to Europe and Southeast Asia in the east. The fusulinids became extinct at the end of the Permian mass extinction. The LBF again appeared in the Cretaceous and became abundant in Eocene and Oligocene epochs. The carbonate platforms with their characteristic nummulitic limestone were widespread along the paleo-Tethys. Some nummulitids attained gigantic size due to accentuated dimorphism in the Eocene (Fig. 1.11). The LBF lives in the present-day shallow marine waters of low latitudes. While evolving to large size was advantageous for some foraminifera, small size appears to have helped survive the stressed environments at end-Cretaceous extinction and in hyperthermal events of the Eocene. A group of foraminifera adapted to planktic lifestyle evolved in the middle Jurassic. Their chambers were inflated and more perforated, and the tests were thinner and lighter to help them float in the water column. They diversified and became widespread in the Cretaceous and Cenozoic oceans.

Figure 1.11 Accentuated dimorphism in the Eocene foraminifera Assilina gigantea. Source: From Schaub Collection, Natural History Museum, Basel.

The biology of foraminifera was poorly known for a large part of its historical development. The biological understanding of the group, even today, is based on a small number of species. The culture and field studies in 1970–80 by Robert Angell and Allan Be provided much-needed information on calcification, chamber formation, and life history of foraminifera. The modern foraminifera occupies all parts of the ocean from the surface to deep sea, cold to warm waters, and oxic to dysoxic conditions. They survive oligotrophic seas by symbiosis with algae. It is challenging, although, to prove symbiosis in fossil foraminifera. The test’s internal complexity, pustules in benthic foraminifera, and spines in planktic foraminifera are the morphological adaptations for the benefit of symbionts.

Stable isotope proxies have contributed significantly to the understanding of paleobiology and evolutionary ecology of foraminifera. It is problematic at times to distinguish between benthic and planktic foraminifera on a morphological basis. The late Cretaceous foraminifer Guembelitria that bloomed after the end-Cretaceous mass extinction was believed as benthic and planktic by different workers. The oxygen and carbon isotopes of the test resolved that it was a planktic foraminifer that calcified in surface waters, unlike the associated deep-water benthic foraminifera. The insight gained through isotopic analysis of living foraminifera has given clear signs of symbiosis. Symbiosis is recognized in extinct species of planktic foraminifera of Cretaceous and Paleocene age. Evolutionary paleoecology combines the evolutionary history of species with ecology. There are many examples of how foraminifera changed their ecology in the course of evolution. The extinct genus Hantkenina evolved in deep-water oxygen minimum zone and migrated to near-surface oxygenated water in response to late Eocene global cooling (Coxall et al., 2000). The prolific growth of geochemical proxies and improved analytical techniques are sure to promote paleobiological research in the future. It should not surprise us that the geological records reveal foraminifera as one of the most diverse organisms in terms of their life history strategies in response to the changing climate and environment of the evolving Earth.

Foraminifera has played a significant role in the reconstruction of the marine environment and climate in the Phanerozoic. The present-day distribution of foraminifera provides a strong basis to use them in paleoclimate reconstruction. The LBF is confined to tropical to the temperate climate. The distribution of planktic foraminifera is controlled by latitude, and therefore by analogy, fossil planktic foraminifera is a good indicator of paleoclimate. Oxygen isotope paleothermometry (δ¹⁸O) of foraminifera is a standard tool in paleoclimate reconstruction. Compilation of oxygen and carbon isotope data of deep-sea benthic foraminifera obtained from DSDP and ODP cores contributed significantly to global climate change in the geologic past. It revealed super greenhouse conditions in the Cretaceous and at the Paleocene-Eocene epoch boundary. The sea surface temperatures during the Cretaceous and early Eocene’s extreme warmth exceeded 30°C and cooled through the early Oligocene when a large ice cap appeared in Antarctica (Zachos et al., 2001). The Phanerozoic climate was regulated by atmospheric CO2. The levels of CO2 in the Eocene greenhouse climate were several orders of magnitude higher than the present level. A negative excursion in carbon isotope ratio also characterized the Paleocene–Eocene boundary. It is attributed to the rapid injection of CO2/methane in the global carbon budget, possibly caused by methane degassing at the seafloor. The hyperthermal event’s catastrophic effect is seen in deep-sea benthic foraminifera, whose diversity dropped by >70%. The planktic foraminifera was mostly unaffected, suggesting a decoupling of the deep and shallow ecosystems (Kennett and Stott, 1991). The LBF experienced a relatively high turnover at the Paleocene–Eocene boundary, marked by a decrease in generic diversity but rapid diversification at the species