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By jeanmichel.theriault - Posted on 27 avril 2011

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Traditionally, the acquisition of solid phase geochemical data is time-consuming and results in loss of sediment. The ITRAX™ core scanner provides the capability of acquiring high-resolution geochemical and radiographic records from marine and lake sediments. This instrument allows relatively rapid, continuous XRF and micro-radiographic scanning of split sediment cores, providing records of down-core geochemical changes. Some examples for marine sediment, lake sediment cores and rocks are decribed below.


MARINE SEDIMENTS


Core from Saanich Inlet, British Columbia, Canada
The marine sediment ITRAX data includes X-Ray radiography, an optical image and elemental XRF analysis (Fe) of a core taken in Saanich Inlet, British Columbia, Canada, as part of the IMAGES VIII (International Marine Past Global Changes Study) program conducted on the western margins of North America.

Saanich Inlet is a silled fjord with a water depth of 250 m, located at the southeastern end of Vancouver Island. The restriction of deep-water renewal by the sill, coupled with high productivity in surface water preserves seasonally laminated sediments. In the ITRAX data, the Mazama ash (7645 yrs), one of the well-known tephra markers , lies at a depth of 139 cm in this section (39.90 m total depth). According to the studies of Ocean Drilling Program (ODP) leg 169S, the sediments over the last 11,000 yrs consist of laminated and homogeneous intervals of olive-grey and grey diatomaceous mud.

(courtesy of Kinuyo Kanamaru, post-doc at the University of Massachusetts, Amherst, Department of Geosciences)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

LAKE SEDIMENTS


Core from Sawtooth Lake, Canada
 Sawtooth Lake (79˚20N, 83˚51W) is an oligotrophic lake containing annually laminations (varves) that are principally formed during the snowmelt season. Mean lamination thickness is about 1 mm but varies between 500µm to 3 cm. Currently, about 2500 years have been measured, providing the opportunity to reconstruct the variations of past climate conditions with an annual resolution (Francus et al, 2002). This example of combined data generated by the ITRAX core scanner shows the radiography, the optical image and the zinc and nickel variations over a small section of the sediment sequence, demonstrates the resolving capabilities of this instrument.

Francus P., Bradley R., Braun C., Abbott M. & Keimig F., 2002. Paleoclimate studies of minerog s. Geophysical Research Letters, 29, 20, 1998, doi:10.1029/2002GL015082.





Core from lake Yoa, Ounianga Kebir, Chad

Lake Yoa (4.3 km2; 26 meter deep) is a permanent hypersaline lake in northeastern Chad (19.03 °N; 20.31 °E), containing annually fine lamination (+/- 1mm). Theses laminations are composed of alternatimg fine-grained aeolian layers, rich organic matter layers and authigenic carbonate layers.

Lake Yoa stratifies during summer but mixes during winter, due to significant temperature seasonality (Tmax 26-42°C; Tmin 13-26°C) and windy conditions from December to March.

This example of combinated data generated by the ITRAX core scanner, over a small section of the sedimentary sequence, shows the radiograph, the optical image and the iron and calcium variations. These profile variations highlight fine laminations and allow their counting.

(P. Francus and J-F Crémer, INRS Centre Eau Terre Environnement)

 

 

 

 

 

 

 

 

 

 

 

ROCK SAMPLE 

This example from analyse on rock samples shows the radiograph, the optical image and chemical variation profiles across hydrothermal alteration zones, veins and mineralisation. A mineralisation zone rich in Ti, V, Mn, Fe and Pb is visible. This zone is denser than the rest of the sample and clearly appears as a dark zone on the radiography.



(Courtesy of Louise Corriveau, Geological Survey of Canada)