ANDRILL – team 3 – MICROPALEONTOLOGY

Reed Scherer (Northern Illinois University – Dekalb – USA)

Diane Winter (University of Nebraska – Lincoln – USA –)

Percy Strong (Geological and Nuclear Sciences – Lower Hutt – Nuova Zelanda )

Michael Hannah (Victoria University of Wellington – Wellington – Nuova Zelanda)

Charlotte Sjunneskog (Northern Illinois University- Dekalb – USA)

What’s analysed?

The fossils present in both rocks (sedimentary) and ancient sediments.

Which analyses are carried out?

Paleontological analyses, the study of fossils, are carried out. In brief, both qualitative and quantitative analyses are done. The former aims to identify the fossil species found in the sample while the latter determines the composition of the fossil population- the number of specimens belonging to each fossil species type.

How are the analyses carried out? (See photogallery no 14)

The Sedimentologists also do some of these analyses during the very first phase, upon the core’s arrival at the laboratory (see photogallery no 7 – ANDRILL Team no 2). They are fast and easy to conduct, and provide immediate and useful information to assist Sedimentologists, as well as others, with their analyses and interpretation.

Let us have a look at the different steps involved in the preparation of a sample for diatom observation:

  1. The sediment/rock sample is suspended in water.
    Any organic matter and other impurities are washed away if needed, (HCl or hydrogen peroxide is used).
  2. A drop of sample is mounted onto a microscope slide (the covering slip, the small part, is placed uppermost during microscope observation).
  3. Sample is dried- water is evaporated and the sample forms a thin layer of “crust” on the slide.
  4. Sample is sealed- a special resin is spread over the sample and the other, smaller piece of glass is placed on top (the microscope slide, the biggest one, is placed underneath during observation).
  5. Sample is sealed tightly between the two glass slides and may be kept for a very long of time.

What is found out?

Micropaleontological analyses provide answers to two very important questions in scientific research such as the ANDRILL project:

  1. Time dating (that is, the estimation of when the rock layer present in the core was formed);
  2. Paleoclimatic reconstruction (that is, the definition of one or more environmental conditions present during layer formation).

Fossils are evidence of past life; they can therefore provide insights into both the age-period of the rock in which they are found, as well as the original paleoenvironments. Some fossils however exhibit some traits that make them more amenable than others to rock dating purposes. In this case, the fossil is known as a BIOSTRATIGRAPHIC MARKER or GUIDE FOSSIL.

Other fossils are precise indicators of certain characteristics of the ancient environments in which they lived (temperature, water salinity and others), and are therefore called PALEOENVIRONMENTAL MARKERS.

Case study within ANDRILL research

Two types of microfossils are studied in ANDRILL, diatoms and foraminiferans. Diatoms are unicellular photosynthetic organisms and foraminiferans are unicellular heterotrophs. Both types are encased within a cell wall (siliceous in diatoms and calcareous in foraminiferans) which maintains its integrity for millions of years. Both live in the Antarctic waters but use very different adaptation strategies. Some diatoms for example live-out the dark Antarctic winter by developing resistant forms (resistant to months of darkness and water temperatures of -1°C!) which reside on the submerged underside of the winter ice platform.

The two most likely paleoenvironmental scenarios we expect to reconstruct are similar to the ones currently seen: alternating periods of ice-free sea and sea covered with ice (sea ice). Let us examine which are the most common paleoenvironmental indicators for each one of these periods:

Frangilariopsis curta develops very well below the sea ice and its presence in the sediment indicates this kind of environment, i.e. sea covered with seasonal ice.

On the other hand, Thalassiosira antarctica is a species that prefers an open sea environment, with cold water of course, but without ice.

Through the identification of these two indicators in the sediments, their time period and paleoenvironmental reconstruction (cross-referencing all the other data as well), the research group aims to reconstruct the ice expansion and retreat history in Antarctica.

Diatomea specie Thalassiosira Antarctica
Diatomea specie Fragilariopsis Curta
Diatomea specie Fragilariopsis Curta

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