Radiolaria are Sarcodine Protozoa, which are single-celled organisms usually much-less than 1 mm in size, that also include other major microfossil groups, such as foraminifera. There are three Orders of Radiolaria but only the Polycystines have a significant fossil record extending back to the Lower Palaeozoic. The secreted tests are composed of opaline silica (a hydrous form of SiO2). They are marine holoplanktonic organisms that inhabit the varying depths in the water column of the World’s oceans. They are useful in stratigraphy and in palaeoenvironmental (palaeoceanographic and palaeoclimate) studies.
Radiolarian Micropalaeontology:Collection and Examination Professor Simon K. Haslett Centre for Excellence in Learning and Teaching Simon.firstname.lastname@example.org 16th March 2010
Introduction Radiolaria are Sarcodine Protozoa (single-celled) that secrete microscopic silica (SiO2) tests (cf. shells). Radiolaria are marine holoplankton that first appear in Palaeozoic rocks. Radiolaria may be extracted for study from marine sediments and rocks.
Collection Techniques Radiolaria may be obtained from: Plankton samples collected using nets, etc. Surface sediments on the sea floor collected using grab samplers, etc. Subsurface deep-sea sediments collected using coring technology. Rocks collected on the seabed or on land where marine rocks have been uplifted.
Collecting Oceanic Sediments Deep-Sea Drilling Project (DSDP) Ocean Drilling Program (ODP) Integrated Ocean Drilling Program (IODP) Other institutional, national and international coring programmes. JOIDES Resolution (ODP vessel), San Diego, 1992.
Sampling Procedures For unconsolidated oceanic cores: Core catchers for preliminary sampling. Interval sampling downcore. Sample size: usually 1 cc is adequate. Label with Site, Core, Section and Interval. Store in plastic vial, bag, or glass tube. Refrigerate samples, but avoid freezing.
Processing Technique For unconsolidated sediments: Wash sediment through nest of 150 and 63µm sieves to concentrate Radiolaria. Wash 150-63µm fraction with dilute (10%) Hydrochloric Acid (HCl) to dissolve calcareous microfossils and particles. Wash with buffered water (H2O) and collect, with water, in a beaker or vial.
Mounting Techniques 1 Pipette the residue and some water onto: Glass coverslip for transmitted light microscopy (TLM), or a stub for scanning electron microscopy (SEM). Allow to dry in a clean atmosphere, usually on a hot plate set at a low temperature.
Mounting Techniques 2 For TLM: pipette a pea-sized amount of mounting medium (e.g. Canada Balsam, Naphrax) onto cover slip and allow to spread (on a warm hot plate) until bubbles are expelled. Then place cover slip on a labeled glass microscope slide and allow to set. For SEM, coat with gold before viewing.
Transmitted Light Microscope Microscope-mounted camera attached to a computer. Eye pieces (optics). Head of the microscope. Objective lenses (various). Microscope stage. Iris diaphragm and condenser. Focusing mechanism. Light source.
Viewing Techniques For TLM: Place slide on microscope stage and view under low magnification to start, adjust iris diaphragm and light intensity controller. Focus through specimens to view internal anatomical structures to aid identification. Photographs may be taken with a microscope mounted camera.
Searching and Counting Search slides systematically for specimens, and count taxa up to pre-defined limit (e.g. 300 specimens). Adopt a consistent search and counting approach from slide to slide. Specimens may be place-referenced on a slide using an England Finder.
Collating Data Tally up counts for each taxa. Tabulate in a database e.g. Excel. Calculate the total assemblage. Convert to percentages: taxa count ÷ total assemblage x 100 Plot downcore graphs of individual taxa.
Analysing Datasets Large datasets often result from radiolarian studies that can be analysed using a range of numerical techniques: Principal Components Analysis Factor Analysis Correspondence Analysis Detrended Correspondence Analysis
Summary Radiolaria can be collected from oceanic sediments through ocean drilling, or extracted from marine rocks. Oceanic sediments may be washed through sieves, and treated with dilute Hydrochloric Acid (HCl). Residues are usually mounted for TLM or SEM. Assemblage data may be collated on spreadsheets. Graphs of individual species variation may be plotted. Entire datasets may be numerically or statistically analysed, using a range of techniques.
Further Reading Armstrong, H. A., Brasier, M. D., 2005. Microfossils (2nd Ed). Blackwell, Oxford. Dale, A. L. and Dale, B., 2002. Application of ecologically based statistical treatments to micropalaeontology. In S. K. Haslett (ed.) Quaternary Environmental Micropalaeontology. Arnold, London, pp. 259-286. Haslett, S. K. and Robinson, P. D., 1991. Detecting radiolaria in the field. Journal of Micropalaeontology, 10, p. 22. Integrated Ocean Drilling Program, 2009. Proceedings of the Integrated Ocean Drilling Program.Available through www.oceandrilling.org (with links to Deep Sea Drilling Program and Ocean Drilling Program publications).
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