Slide 1

By:Syed AzhaRuddinForaminifera and its applications in Paleoclimatology and Paleoceanography

INTRODUCTION TO PALAEOCLIMATIC AND PALAEOCEANOGRAPHIC STUDIES Useful information for reconstructing ocean history is preserved in the marine sediments in the form of microfossils, isotopic composition of shells and other sediment components.Assessing paleoclimate variability using the geological record necessarily depends on the development and reliability of climate proxies (Wefer et al., 1999).Marine sediments are composed of both biogenic and terrigenous materials which are of great interest for Paleoceanographers.

The biogenic component includes the remains of surface dwelling planktic and bottom dwelling benthic organisms, which provide a record of past climate and oceanic circulation in terms of surface water temperature and salinity, dissolved oxygen in deep water, nutrient or trace element concentrations etc.Terrigenous deposits are detrital material derived from the erosion of the land masses surrounding the ocean basins and their mineral composition in sediments varies and reflects the provenance and weathering process (Bradley, 1999).

FORAMINIFERAForaminifera (in short forams) are unicellular organisms that form calcium carbonate tests (shells) recording physical and chemical properties of the ocean and capable of preserving the records of climate change. The advantages of this archive are the ubiquitous occurrence of the foraminifera in marine environments and at sufficiently high temporal resolution in sediment cores to study late Quaternary climate variability .Among the microfossils, planktic foraminifera are the one of the best and widely studied group.They are very sensitive to environmental variations and their distribution through passive transport, as well as their high relative abundances and good preservation potential make them ideal proxies to interpret marine sediments and oceanic conditions.

There are 40 species of living planktic foraminifera and more than thousands of benthic species.

The size of the foraminiferal test typically ranges from 0.05 mm to 0.5 mm although some forams may be large as several centimetres with a recorded maximum of 20 cm in diameter (Xenophyophorea)

Fig :Changes in specific diversity of planktonic foraminifera through time

Fig : Global pattern of planktic foraminiferal diversity from 1,068 sediment samples.

CHARACTERSTICS OF PLANKTIC FORAMINIFERABenthic foraminifera are restricted to certain environments, whereas planktonic foraminifera are dispersed over a much broader part of the world oceans and often are found in large numbers.Being protists, planktic foraminifera are very sensitive to the ambient changes in the environment.As the soft part get disintegrated after death, the hard part remains intact as fossil in sediments.Considering its size, abundance and diversity, it is very much feasible to use foraminifera as a proxy; small amount of sample contains hundreds and thousands of foraminifera while their ability of adaptation to environment lead the diversity of foraminifera.They are omnipresent thus can be recovered from every marine environment from lowest to the high latitude.Their diversity is a function of changing environment thus different environments are characterized by different and typical assemblages.Any change in the environment is visible in the form of a morphological manifestation such as changes in size, coiling direction and deformation of the test.

Fig : Important Planktic foraminiferal species of the late Quaternary sediments of the Andaman Sea.A.V. Sijinkumar, B. Nagender Nath /GCK Science Letters 1-1 (2012) 22-30

Plate 41. Globoturborotalita rubescens (Hofker 1956)a. Apertural view; b. Dorsal view2. Globigerinoides tenellus (Parker 1958)Apertural view; b. Dorsal view

Plate 51. Globoratalia menardii ( Parker, Jones and Brady 1865)a. Apertural view; b. Dorsal view2. Globigerinella aequilateralis (Brady 1879)Apertural view; b. Dorsal view

Plate 61. Neogloboquadrina deutertrei (dOrbigny 1839)a. Apertural view; b. Dorsal view2. Pulleniatina obliquiloculata (Parker and Jones 1865)b. Apertural view; b. Dorsal viewPlate 1:1. Globigerina bulloides (dOrbigny 1826)a. Apertural view; b. Dorsal view2. Globigerina falconensis (Blow 1959)Apertural view; b. Dorsal view

Plate 21. Globigerinoides sacculifer (Brady 1877)a. Apertural view; b. Dorsal view2. Globigerinoides conglobatus (Brady 1879)Apertural view; b. Dorsal view

Plate 31. Globigerinoides ruber (dOrbigny 1839)a. Apertural view; b. Dorsal view2. Globigerinita glutinata (Egger 1893)a. Apertural view; b. Dorsal view APPLICATIONS OF PLANKTIC FORAMINIFERA1) Past Monsoon Variations Among the planktic foraminifera, G. bulloides is widely used as an upwelling/monsoon proxy.Ishikawa and Oda (2007) have reconstructed Indian monsoon variability over 230 ka BP using summer (Globigerina bulloides, Globigerinita glutinata, Globigerina falconensis, Globorotalia menardii) and winter monsoon proxies (Globigerinoides ruber, Neogloboquadrina dutertrei, Neogloboquadrina compacta and Globigerinoides sacculifer) from the NW Arabian Sea.2) Past Productivity ReconstructionPlanktic foraminiferal abundances are widely used as a proxy for upwelling related productivity changes.Within each group of planktic shelled organisms, some species occur preferentially in high productivity regions while others avoid these.Thus relative abundances of certain species have been identified as indicators of high productivity (Prell and Curry, 1981).Singh et al. (2011) used planktic foraminiferal assemblage known as fertile species (G. bulloides, G. falconensis and G. glutinata) for reconstructing paleoproductivity.Relative abundance of 5 abundant planktonic foram species.The shaded area represents glacial stages

3) Past Seawater Temperature Reconstruction

Planktic foraminifera are widely used for past SST estimation by transfer function and also for oxygen isotope studies of shells of Planktic foraminifera.The difference in species composition contain clues to the temperature of the waters in which they lived (Broecker, 1986).Neogloboquadrina pachyderma , is an excellent recorder of water temperature through geologic time.

Fig: Climatic signals derived from coiling ratios of Neogloboquadrina pachyderma

Fig: Sea Surface Temperature range of some contemporary planktonic foraminifera illustrating their temperature dependence. (Boersma, 1978)

4) Past Salinity Reconstruction

Salinity is the second variable with temperature that controls seawater density and deep ocean circulation (Henderson, 2002).Rostek et al. (1993) calculated temperatures for the Indian Ocean using alkenones and then used the 18O values of G. ruber for determining the salinities.Planktic foraminiferal assemblages (Cullen, 1980) and oxygen isotope records (Kudras et al., 2001) of Bay of Bengal was used for reconstructing palaeosalinity for the late Quaternary.5) In determining chemistry of ocean waters

The chemical composition of the shell is useful because it reflects the chemistry of the water in which it grew.

The ratio of stable oxygen isotopes depends on the water temperature, because warmer water tends to evaporate off more of the lighter isotopes.6) Sea level changes

Foraminifera are widely used for reconstructing sea level changes mainly understanding the bathymetry of the different species.

As ice sheets grow on continents, the 18O of the ocean incresed and global sea level fell. (Raymond S. Bradley)7) Biostratigraphy

There are several reasons that fossil foraminifera are especially valuable for determining the relative ages of marine rock layers.They have been around since the Cambrian, over 500 million years ago (fusulinids spp.)They show fairly continuous evolutionary development; so different species are found at different times.Forams are abundant and widespread, being found in all marine environments, very small and easy to collect, even from deep oil wells hence widely applied in biostratigraphy.8) Petroleum exploration

Forams are often used in determining the particular geological period, when the decay of organic matters occurred under anaerobic conditions in marine rock.Usually formation of petroleum occurs in typical environment especially marine and their assemblages are good indicator of particular environment condition and helpful in determine the oil-bearing horizon.TheForaminiferal Colouration Index(FCI) is a tool for assessing thethermal alterationof organic matter buried insedimentary rock.Fig : Foraminiferal Colouration Index (FCI) - Example of thermal alteration colours (FCI 2 - 6) in agglutinated foraminifera from an oil well.

Thank you