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Planktic and Smaller Benthic Foraminifera Are Prepared As Follows: • Crush the Bulk Rock Into Roughly 5-Mm Fragments

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Planktic and Smaller Benthic Foraminifera Are Prepared As Follows: • Crush the Bulk Rock Into Roughly 5-Mm Fragments Foraminifera • Introduction • Foraminifera live in marine, and brackish environments. T • heir mode of life may be planktic or benthic. • The generally accepted classification of the foraminifera is based on that of Loeblich and Tappan (1964). The Order Foraminiferida (informally foraminifera) belongs to the Kingdom Protista, Subkingdom Protozoa, Phylum Sarcomastigophora, Subphylum Sarcodina, Superclass Rhizopoda, Class Granuloreticulosea. • Foraminifera are testate (possessing a shell), protozoa, (single celled organisms characterized by the absence of tissues and organs), which possess granuloreticulose pseudopodia (thread-like extensions of the ectoplasm often including grains or tiny particles of various materials). Bi-directional cytoplasmic flowing along these pseudopodia carries granules which may consist of symbiotic dinoflagellates, digestive vacuoles, mitochondria and vacuoles containing waste products. In the planktic foraminifera, e.g. Globigerinoides sacculifer dinoflagellate symbionts are transported out to the distal parts of rhizopodia in the morning and are returned back into the test at night. Reticulose pseudopodia with granules Aperture Endoplasm Ectoplasm Nucleu s Test Golg i Food body vacuoles Ribosomes Mitochondria A living, single-chambered benthic foraminifer, as seen in cross-section with transmitted light. Test enclosing the endoplasm Radiating spines support pseudopodia Ectoplasm forms bubble capsule A living planktonic foraminifer Globigerinoides sacculifer surrounded by radiating spines and pseudopodia (not all drawn) which support photosymbionts and frothy ectoplasm of the bubble capsule, as seen in transmitted light. Systematic classification • Kingdom: Protista • Subkingdom: Protozoa • Phylum: Sarcomastigophora • Subphylum: Sarcodina • Superclass: Rhizopoda • Class: Granuloreticulosea • Order: Foraminiferida Life Cycle • Of the approximately 4000 living species of foraminifera the life cycles of only 20 are known. There are a great variety of reproductive, growth and feeding strategies, however the alternation of sexual and asexual generations is common throughout the group and this feature differentiates the foraminifera from other members of the Granuloreticulosa. An asexually produced haploid generation commonly forms a large proloculus (initial chamber) and is therefore termed megalosphere. A sexually produced diploid generation tends to produce a smaller proloculus and are therefore termed microsphere. Importantly in terms of the fossil record, many foraminiferal tests are either partially dissolved or partially disintegrate during the reproductive process. The planktonic foraminifera Hastigerina pelagica reproduces by gametogenesis at depth, the spines, septa and apertural region are resorbed leaving a tell-tale test. Globigerinoides sacculifer produces a sac-like final chamber and additional calcification of later chambers before dissolution of spines occurs, this again produces a distinctive test, which once gametogenesis is complete sinks to the sea bed. Diagram showing a generalized foraminiferal life cycle, note alternation between a haploid megalospheric form and a diploid microspheric form. Redraw from Goldstein 1999 The foraminiferal test Composition of test wall 3 basic kinds: - Organic-membrane wall composed of tectin. - Agglutinated, with organic-membrane foundation and, - Calcareous, with organic-membrane inner lining. 1. Organic Test Wall - Organic-walled forms belong to the suborder Allogromiina. These have a thin, non-rigid membrane test of tectin. - The tectin is composed of a proteinaceous or pseudochitinous matter. Similar material is also present as a thin lining to the chambers of most hard tested foraminifera, where it may act as a template for mineralization. 2. Agglutinated Test Wall - Mineral grains from the sea floor are bound together by an organic, calcareous or ferric oxide cement. - Material commonly utilized include quartz grains, heavy minerals, clay or carbonate fragments, and organic debris (e.g., tests of smaller forams, radiolaria, diatoms, coccoliths, fragments of molluscan shells, and sponge spicules). 3. Calcareous Test Wall The major groups of calcareous genera were distinguished as porcelaneous or glassy according to their appearance in reflected light: - Porcelaneous wall may resemble porcelain with a shiny white surface that results from a fine structure that leads to maximum reflection of light. - Glassy wall has a fine structure that readily allows light to pass through, so that some of these genera resemble clear soap bubbles or blown glass. • History of Study The study of foraminifera has a long history, their first recorded "mention" is in Herodotus (fifth century BC) who noted that the limestone of the Egyptian pyramids contained the large benthic foraminifer Nummulites. In 1835 Dujardin recognized foraminifera as protozoa and shortly afterwards d'Orbigny produced the first classification. The famous 1872 HMS Challenger cruise , the first scientific oceanographic research expedition to sample the ocean floor collected so many samples that several scientists, including foraminiferologists such as H.B. Brady were still working on the material well in to the 1880's. Work on foraminifera continued throughout the 20th century, workers such as Cushman in the U.S.A and Subbotina in the Soviet Union developed the use of foraminifera as biostratigraphic tools. Later in the 20th century Loeblich and Tappan and Bolli carried out much pioneering work. • Range • Foraminifera have a geologic range from the earliest Cambrian to present day. The earliest forms which appear in the fossil record (the allogromiine) have organic test walls or are simple agglutinated tubes. • The term "agglutinated" refers to the tests formed from foreign particles "glued" together with a variety of cements. Foraminifera with hard tests are scarce until the Devonian, where the fusulinids began to flourish culminating in the complex fusulinid tests of the late Carboniferous and Permian times; the fusulinids died out at the end of the Paleozoic. • The miliolids first appeared in the early Carboniferous, followed in the Mesozoic by the appearance and radiation of the rotalinids and in the Jurassic the textularinids. The earliest forms are all benthic, planktic forms do not appear in the fossil record until the Mid Jurassic in the strata of the northern margin of Tethys and epicontinental basins of Europe. They were probably meroplanktic (planktic only during late stages of their life cycle). The high sea levels and "greenhouse" conditions of the Cretaceous saw a diversification of the planktic foraminifera, and the major extinctions at the end of the Cretaceous included many planktic foraminiferal taxa. • A rapid evolutionary burst occurred during the Paleocene with the appearance of the planktic globigerinids and globorotalids and also in the Eocene with the large benthic foraminifera of the nummulitids, soritids and orbitoids. The orbitoids died out in the Miocene, since which time the large foraminifera have dwindled. Diversity of planktic forms has also generally declined since the end of the Cretaceous with brief increases during the warm climatic periods of the Eocene and Miocene. • Preparation Techniques • WARNING: Please remember all preparation techniques require the use of hazardous materials and equipment and should only be carried out in properly equipped laboratories, wearing the correct safety clothing and under the supervision of qualified staff. • Foraminifera range in size from a few tens of microns to several millimeters, and are preserved in a variety of rock types. The preparation techniques used depend on the rock type and the "predicted" type of foraminifera one expects to find. Very hard rocks such as many limestones are best thin sectioned as in normal petrological studies. Planktic and smaller benthic foraminifera are prepared as follows: • Crush the bulk rock into roughly 5-mm fragments. The crushed rock is then soaked in water and washing soda or 6% hydrogen peroxide, in a glass beaker for 24 hours (the time depends on the rock type). In case of using hydrogen peroxide, the sample should not be left in the solution for more than about half an hour. Next, the material is washed through a 63 micron sieve untill the liquid coming through the sieve is clean (i.e. the clay fraction has been removed). The sample can then be dried and sieved into fractions (generally 63-125 microns, 125-250 microns, >250 microns) using a "nest" of dry sieves. Clean all sieves and materials used at the preparation of each sample to prevent contamination. Observation Techniques • Thin sections are viewed using transmitted-light petrological type microscopes. • Washed, dried fossil samples can be picked from any remaining sediment using a fine brush and a reflected light, binocular stereo-zoom microscope. The best method is to scatter a fine dusting of sieved residue in a black tray divided into squares, this can then be scanned under the microscope and foraminiferal specimens are picked out with a fine brush (preferably a 000 sable-haired brush). The picked specimens can then be mounted in card slides divided into numbered squares with sliding glass covers. Gum toragacantho was traditionally used to attach the specimens to the slides but modern office-type paper adhesives are now used. Morphology Foraminiferal shells, or tests, are built of hollow chambers separated by partitions, with small openings called foramina that connect the chambers (they get their name from these
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