Cosmogenic Nuclide Dating

The new cosmogenic nuclide dating Laboratory is under development in 2020 at CENIEH. The method is capable measuring surface exposure ages, rock/soil/basin erosion rates, and deposition ages of sediments. The lab will offer full sample preparation of quartz-bearing geological/archaeological materials for the measurements of 10Be and 26Al via via an accelerator mass spectometry (AMS). The first call for user access will be open in early 2021.

The cosmogenic sample preparation laboratory is located adjacent to GEOLOGY labs on the floor -1. The room is equipped with two large fume hoods with a scrubber unit which has capacity to operate HF evaporation of a few litres at once. Two orbital shakers and ultrasonic bath are equipped for quartz extraction/purification processes via a series of acid cleaning.  
 

Laboratorio de Nuclidos Cosmogéncos

 

Methods

Cosmogenic nuclides are the products of nuclear reactions between cosmic rays and elements in atmosphere and lithosphere on earth. Their production is the function of geomagnetic field intensity, surface exposure times and erosion rates. Exposure ages of rock and sediment/soil surfaces can be determined at timescales of ~1000 years to several million years. Erosion rates in a range of ~0.1 mm/k.y. up to 10,000 mm/k.y. are measurable on quartz-bearing geological materials.

The measurements of multiple cosmogenic isotopes in sediment, such as fluvial terraces and cave sediments, also allow us to calculate deposition ages of the sediment. As such cosmogenic nuclide dating has become indispensable in earth sciences, particularly, in the field of geomorphology and landscape evolution over the last few decades.

The most widely used nuclides include beryllium-10 (10Be) and aluminium-26 (26Al). Both isotopes are produced within quartz lattice from oxygen and silicon, respectively. Quartz is widely available on the globe, chemically resistant, and its simple crystal structure means that production rates for 10Be and 26Al are well constrained.   

The sample preparation therefore requires extraction of pure quartz. The process include isolation of quartz via physical and chemical mineral separation techniques, such as magnetic separation, heavy density liquid separation, acid leaching. The extracted quartz needs to be purified via etching with dilute HF. Pure quartz is then dissolved in concentrated HF. Beryllium and aluminium are isolated from unwanted cations (e.g., Fe, Ti) via anion and cation exchange chromatography. Be- and Al-hydroxides are precipitated by pH control and finally calcined to oxides at 1000°C.

The resulting some milligrams of Be and Al oxides are mixed with pure niobium and silver powder, respectively, packed into AMS sample holder. The measurements of 10Be and 26Al isotopes are carried out in our collaborating AMS facilities.

Facilities and equipment

We are developing facilities and equipment for the following processes:

- Heavy liquid density separation using SPT

- Quartz isolation via H2SiF6-HCl etching on orbital shaker

- Quartz purification via diluted (<5%) HF etching on orbital shaker/ultrasonic bath

- Quartz digestion using concentrated (40-48%) HF on orbital shaker at room temperature

- Fuming of quartz dissolved solution under scrubber fume hoods

- Anion and cation exchange chromatography to isolate Be and Al

- Precipitation of Be(OH)2 and Al(OH)3 via pH control

- Oxidisation to BeO and Al2O3 in a maffle furnace at 1000°C

Applications and Services

Applications of cosmogenic nuclide dating include:

- Surface exposure dating on quartz-bearing rock/sediment samples at timescales from ~1000 years to ~4 million years (e.g., moraine, fault scarp, landslide, flood deposit)

- Erosion rate measurement on rock/soil surfaces or entire basins

- Burial dating on quartz-bearing deposits (e.g., in caves, fluvial/marine terraces) at timescales from ~400,000 years to ~4 million years

Our services include:

- Consultation on the design of research program, sampling strategy

- Joint field sampling

- Target preparation for AMS 10Be and 26Al measurements

- AMS data reduction

- Calculation of exposure ages, erosion rates, or burial ages as required

- Modelling for geomorphological parameter derivation as required (e.g., incision rates, fault scarp slip rates, sedimentation rates, etc.)