Subsample Preparation and Analysis

The CSD Facility coordinates analyses at the lab on a fee-for-service basis. Facility technicians can perform the procedures, or Facility visitors can be trained in preparation and analysis. If you are interested in analysis that we do not routinely perform, please contact Jessica Heck at jheck@umn.edu.

To request analytical services, fill out the Analysis Request Form and email the corresponding Analysis Request Spreadsheet (XLS, 29KB) to CSDstaff@umn.edu.

Rows of small glass vials are filled with dark sediment and topped with aluminum foil.

BASIC PREPARATION

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Freeze Drying

The CSD Facility has a Labconco FreeZone 6 Liter -50°C freeze drying system. The drying chamber has three 10-inch diameter adjustable shelves and 6 ports. Freeze drying is the first step in preparation for many analytical procedures of soft sediment lithologies. In contrast to oven- or air-dried samples, which are typically compressed and brick-like, freeze-dried samples are friable, and sedimentary components emerge intact.

The cost to freeze dry depends on the number of samples that fit in the freeze dryer, the amount of water in the samples, and the open surface area of the samples. For faster freeze-drying times, samples should be in containers that provide a large surface area. Samples must first be frozen, then freeze-dried for multiple days until dry.  

To submit samples for freeze-drying please contact Jessica Heck at jheck@umn.edu.  To request sampling and freeze-drying please contact Kristina Brady Shannon at brad0311@umn.edu.

GEOCHEMICAL ANALYSES

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Isotope Preparation

Carbonate Isotope Prep: Soft sediment samples are prepared for analysis of stable isotopes of carbon and oxygen in carbonate minerals by treatment with an oxidizer (typically bleach) to destroy organic matter that may interfere with the isotopic measurement of the mineral fraction. The bleach is rinsed out of the sample by repeated centrifuging and decanting. Samples may be sieved before or after bleaching to remove larger particles, including sand, detrital carbonates, and shell fragments (gastropods and ostracodes may inhabit a different isotopic environment in the lake and/or carry a different seasonal bias than authigenic carbonates, and thus should be analyzed separately or discarded). Sedimentary carbonate grains are typically <30µm, so 63µm sieves or Nitex screen fabric of various sizes (40 or 70µm) may be appropriate to remove unwanted coarse particles. 

Organic Matter Isotope Prep: If necessitated by the presence of carbonate minerals, sediment samples are prepared for analysis of stable isotopes of carbon and nitrogen in organic matter by treatment with an acid to destroy carbonate minerals that will contribute an unwanted source of CO2 to the mass spectrometer. The acid is rinsed out of the sample by repeated centrifuging and decanting until pH is neutral.  

Please contact Jessica Heck at jheck@umn.edu with any questions.

Loss-On-Ignition

Water, organic matter, carbonate mineral, and siliciclastic+diatom content are estimated by sequentially measuring weight loss in soft sediment core subsamples after heating at selected temperatures. A nonprogrammable oven is used for the 100ºC drying step. A programmable muffle Furnace is used for the 550°C and 1000°C steps. A compositional profile can be generated rapidly and at a low cost. This profile is sufficient to develop a general sense of core stratigraphy and correlation between cores.

The results are accurate to 1-2% for organic matter and carbonate in sediment with over 10% organic matter. In clay- or diatom-rich sediment, the water of hydration is lost during the carbonate burn, resulting in errors of up to 5% for carbonate analyses (and “false positive” carbonate content in carbonate-free sediments). If high precision (0.1%) is needed, or if sediment is in short supply, coulometric analysis is recommended.

To submit samples for LOI please contact Jessica Heck at jheck@umn.edu.  To request core processing and LOI please contact Kristina Brady Shannon at brad0311@umn.edu.

SEDIMENTOLOGY AND MINERALOGY

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Benchtop Scanning Electron Microscope

The CSD Facility has a benchtop Hitachi TM-1000 SEM fitted with a Bruker Quantax 50 EDS which provides magnification from 20x to 10,000x and elemental analysis with no need to coat or dehydrate samples. To schedule training please fill out the SEM Request Form

Coarse Fraction Grain Size

The CSD Facility has a Gilson Wet-Vac Sieve Shaker which can be used for both wet and dry sieving. The particle size range is 1.18mm to 20µm (No.16—No.635) and we have an assortment of 8" test sieves available in that range. 

Please contact Jessica Heck at jheck@umn.edu with questions.

Thin Sections

Thin sections allow for the study of virtually undisturbed structures, fabrics, and particles. This technique can be used in hard or soft lithologies, including high-resolution studies of laminated sediments where individual sets of years can be identified. Sediment components studied include charcoal, precipitated components, diatoms, pollen, insects, zooplankton, and in-washed materials.

For sediment thin sections, carefully prepared blocks of sediment core are embedded in epoxy resin. The blocks are then hardened under heat lamps. The hardened blocks can then be treated as "rocks" for thin-sectioning. This includes cutting, mounting to a slide, making a second cut, and finally grinding and polishing the slide to the desired thickness (usually 30 to 50 μm).

Please contact Jessica Heck at jheck@umn.edu with questions.

X-Ray Diffraction

Routine XRD-mineralogy profiles can provide qualitative and semiquantitative data on mineral components. In sedimentary lithologies, XRD primarily displays information on autocthonous and authigenic minerals, but can provide some indication of the abundance of amorphous silica phases. The CSD Facility uses the Department of Earth Sciences Rigaku Mini Flex diffractometer.

Please contact Jessica Heck at jheck@umn.edu with questions.

FLORAL AND FAUNAL

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Botanical Reference Collections

The CSD Facility curates pollen and seed reference collections for use by any researcher to advance the interpretation of sediment core samples. 

The Pollen Reference Collection contains about 22,300 slides made from about 15,700 accessions (samples of pollen or spores from one or more flowers (sporangia) of a single plant). Over 10,000 accessions were prepared at the University of Minnesota since the collection was established in 1958.  About 91% of those have preparations in bulk, stored in glass vials, from which additional slides may be made. Nearly 5,800 reference slides have been obtained by exchange or purchase from other labs. The oldest reference slides are from 1940 and 1945, and the latest slides added to the collection were made in 2015.  About 300 (or more, after reviewing/updating the plant taxonomy) vascular plant families are presented in the pollen collection as follow: fern allies – all, ferns: ~78%, gymnosperms: ~80%, dicotyledons: ~70%, monocotyledons: ~ 54%. The collection emphasizes the flora of the Northern Hemisphere, especially Eastern North America (> 4800 slides), following by SE Asia (> 2500 slides), Western North America (> 2100), and Africa (~ 2000) slides).  Other well-represented floras are from Europe, the Middle East, and Hawaii.  Reference pollen slides of species with distribution in some parts of South America, Australia, and New Zealand are available as well.

Contact Kristina Brady Shannon at brad0311@umn.edu for details.

Charcoal Picking

In lake cores where terrestrial macrofossils are rare or absent (or simply absent at some horizon of interest), microscopic charcoal fragments manually separated from the lake sediment can provide sufficient material for AMS radiocarbon dating with excellent results.  The process can be time-consuming, and a little practice is required to differentiate burned material from that which has been partially carbonized by retention in soil, for instance.  Insect chitin, aquatic plant material, and dark minerals can also be mistaken for charcoal.  

Material for dating must be carefully chosen.  Ideal charcoal fragments are elongate, wispy, fragile, and sharp-cornered – all signs that the fragment was aerially deposited on the lake surface, rather than reworked from the catchment.  These shapes are also typical of (bi)annual growth material (leaves, needles, grasses), which is better for dating than, say, wood, which may have grown at some earlier time during the life of the tree.  It is not always possible to make up an entire sample of these fine fragments, but it is important to keep in mind their characteristics and attempt to choose fragments that do not appear as though they have been reworked.

Contact Kristina Brady Shannon at brad0311@umn.edu with questions.

Diatom Preparation

Diatom sample preparation removes organic material with hydrogen peroxide, and mineral components with hydrochloric acid, to make a clean side for identification and counting. Samples are mounted on slides with ZRAX for return to the requestor. 

Contact Jessica Heck at jheck@umn.edu with questions.

Macrofossil Picking

Macrofossils can be identified to learn more about the surrounding vegetation and suitable macroscopic plant material can be sent for radiocarbon dating. 

Contact Kristina Brady Shannon at brad0311@umn.edu with questions.

Ostracode Picking

Our ostracode procedure uses disaggregation and mechanical separation to deliver as clean a sample as possible.

Please contact Jessica Heck at jheck@umn.edu with questions.

Phytolith Preparation

The goal in preparing sediment samples for phytolith analysis is to remove as much non-phytolith material from the sample as possible. Successful laboratory processing makes analyzing the phytoliths recovered in the sample simpler, more accurate, and less time-consuming. Processed samples are returned to the requester in alcohol for subsequent microscopic analysis.

Please contact Jessica Heck at jheck@umn.edu with questions.

Pollen Preparation

Samples prepared for pollen identification and counting are treated to remove as much non-pollen material from the sample as possible in order to concentrate the chemically-resistant pollen grains. Proper preparation makes counting the pollen simpler, more accurate, and less time-consuming. Processed samples are returned to the requester in vials containing silicone oil or glycerol. Sediment samples (usually 1.0cc for lake sediments, sampled volumetrically or by mass) are placed in 15mL plastic centrifuge tubes and are treated following a modification of Faegri and Iverson (1975). 

For more information see our poster and standard operating procedure. Please contact Jessica Heck at jheck@umn.edu with questions.

 

Pollen Preparation for AMS Dating

Samples are processed differently for AMS 14C dates than samples for counting, as no carbon-containing chemicals can be used. Successful processing removes non-pollen material, especially other organic material, to concentrate pollen grains for dating. Most samples are suitable for dating after processing. In some cases the there may be too much non-pollen organic matter (e.g., soil material, cellulose, algae, fungal spores) remaining that would skew the dates. Smear slides are prepared to check sample quality and sent to the requester, or for a fee, can be evaluated by Facility staff. AMS samples can be sent to a dating facility, such as the Center for Accelerator Mass Spectrometry (CAMS, Lawrence Livermore National Laboratory), or returned to the requester in acidified water.

Sediment samples (usually 4-5cc) are placed in centrifuge tubes and treated sequentially with centrifuging and water rinses between each of the steps to clear the sediment of the treatment solution. Repeated rinses between some steps are used to remove fine clay particles from the sample and sample checks are used to determine if any step needs to be repeated. Our procedure does not remove all siliciclastic material from the sample.

Please contact Jessica Heck at jheck@umn.edu with questions.

DATING AND MAGNETICS

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AMS Radiocarbon Dating

The CSD Facility coordinates with the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Labs for the radiocarbon dating of samples extracted and processed at the Facility. Currently, CAMS capabilities support two options for AMS 14C analyses.
 
For the highest analytical precision and smallest sample sizes, analyses are performed on the premium CAMS 10 MV high-voltage accelerator. 
 
CAMS can (at the researcher’s discretion) analyze somewhat larger sample masses younger than 30,000 years on a lower-voltage accelerator at about 2/3 the per-sample cost, yielding close to 50% more dates for a given chronological budget at a modest cost in reduced analytical precision for each result.
 
Depending on the dating resources available to a project, and the age range being dated, more 14C results at somewhat lower analytical precision may result in an improvement in the overall uncertainty of a radiocarbon age model (Blaauw et al, 2018). Facility staff can assist researchers in evaluating this possibility.


Reference: 

Blaauw, Maarten, J. Andres Christen, K. D. Bennett, and Paula J. Reimer. “Double the Dates and Go for Bayes - Impacts of Model Choice, Dating Density and Quality on Chronologies.” Quaternary Science Reviews 188 (2018): 58–66. https://doi.org/10.1016/j.quascirev.2018.03.032
 

Lead-210 and Cesium-137 Dating

The CSD Facility sends samples to the Science Museum of Minneota's St. Croix Watershed Research Station (SCWRS) for 210Pb and 137Cs dating. We can assist from the project planning through freeze drying samples and mailing them to SCWRS.  

Please contact Kristina Brady Shannon at brad0311@umn.edu with questions.

U-Channel Magnetometry

U-channels are continuous, single-box subsamples of sediment core sections. Their collection is intended for the analysis of magnetic properties of sediments, such as magnetic susceptibility, or natural and laboratory-imparted remanent magnetization (RM). Magnetic susceptibility can be measured at the CSD Facility using two types of multisensor core loggers, while RM can be analyzed at University of Minnesota Institute for Rock Magnetism, which has a 2G Enterprises Long-Core Magnetometer with remanence imparting and measuring capabilities.

Please contact Kristina Brady Shannon at brad0311@umn.edu with questions.