Speleothem Microscopy Laboratory

A Dedicated Speleothem Microscopy Laboratory

University of Newcastle, Australia
SELS, Earth Sciences

Speleothems are, by definition, secondary mineral deposits formed in caves.
In colloquial terms, we call them stalagmites and stalactites.

We use them to reconstruct climate change in the past. This is absolutely important to understand how climate will change in the future.

How…well, because data from the past allow us to play with mathematical models. If the models are able to reproduce the past climate, then models are good (validated). If they fail to reproduce what happened at a specific point in time, then there is something wrong.

Speleothems (stalagmites, stalactites, flowstones) are particularly good because they can be dated with precision with radiometric techniques. This means that ages are not relative, ages are …real.

At UoN, we are specialized in interrogating climate change recorded in speleothems by looking at crystals under microscopes.

We look at the arrangement of crystals, which is called FABRIC.

First with optical microscopes, then with electron microscopes and, finally, with sophisticated techniques available in Australia such as Synchrotron-radiation based micro-XRF mapping and even…neutron scattering!

Since the year 2000, your humble Silvia published the first pioneering work on stalagmite fabrics in the Journal of Sedimentary Research. And the state of the art has remained unchanged…until 2018

Silvia was trained as a Transmission Electron Microscopist. This means that she investigates the internal structure of crystals, at a very fine scale. She starts from a thin section and an optical microscope. There, she observes bizarre forms. Crystals that seem to have strange patterns of extinction. They look like flames…why? When Transmission Electron Microscopy is applied, then one sees things at a scale that is below the micrometer…which is 0,001 millimeters. One sees DEFECTS. And then one can take a Diffraction Pattern, that allows to identify the crystal. The Diffraction Pattern is a series of dots. Each dot a series of crystal planes defined by the crystal structure. One measures the distance between dots and reconstruct the planes in the crystal structure (lattice planes). The distance between planes is unique to a mineral. We index the planes and know the mineral.

In 2015 UoN Silvia published the ULTIMATE table showing relationships between speleotem fabrics and hydro climatological parameters

And this remains, to date, the benchmark for any palaeo-climate reconstruction based on speleothems. All this was achieved at the Speleothem Microscopy Laboratory

But from our Lab we are also reaching researchers working on other important issues, such as the formation of carbonates and, most critically, that of dolomite. What is illustrated below is one of our top achievements: we demonstrated that the mineral dolomite, which is not supposed to form at surface conditions, did form, and is preserved as primary crystals in 240 million year-old rocks:

Transmission electron microscopy (TEM) images of submicrometre euhedral dolomite crystals embedded in clay. (A) Crystal with mosaic microstructure consisting of nanometre-scale domains of ordered dolomite. (B) a nd (C) close-ups of (A) highlighting the small dimensions of individual crystallites. Moire fringes form where crystallites overlap. (D) Crystal without mosaic microstructure. Locally, nanometrescale domains or crystallites with a different orientation with respect to
the host crystal are observed. (E) and (F) close-ups of (D) highlighting the local occurrence of crystallites
with different orientation (arrows).(Preto et al., 2015)

Thus, what is the Lab providing?

1) Unparalleled expertise in carbonate mineral microscopy;
2) Opportunity to link optical microscopy with high-resolution electron microscopy;
3) A non-conventional view of carbonate minerals nucleation and growth based on experience.

What can the Lab do for you?

You can ask for a Skype meeting and set a date. Silvia will be available to answer your questions, and, if you need, to train you. From her Lab in Newcastle to your location.

Right now is all for free, as Silvia wishes to pass onto the new generation of researchers her expertise.

Please, contact her at: silvia.frisia@newcastle.edu.au

Current Research