CSDCO coordinates analyses at the LacCore and other labs on a fee-for-service basis. Technicians can perform the procedures, or facility visitors can be trained in and preparation and analysis. Please contact Jessica Heck at firstname.lastname@example.org for details.
Subsampling extracts samples from cores for discrete analyses, using tools appropriate for the lithologies. These include spatulas, scoops, knives, microtome, scroll saw or bandsaw, hammer and chisel, drill press with water swivel and mini-coring bit, and specialized devices for volumetric subsampling or other tools.
Volumetric samples from soft sediment lithologies can be used to determine water content, bulk density, and mass accumulation rates.
LacCore 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 fill out our customer setup form (new customers only), analysis request form, and associated spreadsheet. Email Jessica Heck at email@example.com for more information.
The Large Lakes Observatory at the University of Minnesota-Duluth campus hosts the LacCore XRF Core Scanning Facility. This lab provides ITRAX elemental and X-radiographic core scans for the research community. Cores are commonly first processed at the main LacCore lab, then transferred in batches by facility staff to/from the XRF Lab for the much slower scans on the ITRAX instrument. Data services and archiving are integrated with all other data generated at the LacCore Facility. For more information, please contact the XRF Lab Manager, Aaron "Wally" Lingwall, at firstname.lastname@example.org.
The Department of Earth Sciences Stable Isotope Lab has two mass spectrometers, a Finnigan MAT252 Mass Spectrometer and a Thermo Finnigan Delta V Plus Mass Spectrometer plus the following peripherals, Kiel II, Costech 4010 Elemental Analyzer (EA), Thermo Finnigan Thermochemical Elemental Analyzer (TC/EA), and OI Analytical 1030 Total Carbon Analyzer (TIC-TOC).
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 compositional profile can be generated rapidly and at 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.
A nonprogrammable Lab Line L-C oven is used for the 100ºC drying step. A Fisher Scientific Isotemp Programmable Muffle Furnace is used for the 550°C and 1000°C steps. This furnace holds 200 samples at a time. Another furnace, the Lindberg Blue M, is available for use as a backup, but only holds 50 samples.
Carbonate Isotope Preparation
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 mass spectrometer. The bleach is rinsed out of the sample by repeated centrifuging and decanting. Samles may be sieved before or after bleaching to remove larger particles, including sand, detrital carbonates, and ostracode shell fragments (the latter, microscopic crustaceans, usually inhabit a different isotopic environment in the lake than that in which authigenic carbonates are produced and thus should be separated and discarded). Sedimentary carbonate grains are <30µm, so 63µm steel sieves or various sizes (40 or 70µm) of Nitex screen fabric are appropriate to remove unwanted particles.
Organic Matter Isotope Preparation
Sediment samples are prepared for analysis of stable isotopes of carbon (and nitrogen; see below) in organic matter by treatment with an acid to destroy carbonate minerals that may interfere with the mass spectrometer. The acid is rinsed out of the sample by repeated centrifuging and decanting until pH is neutral.
Sedimentology and Mineralogy
CSDCO/LacCore has a Horiba LA-920 laser particle size distribution analyzer for measurement of particle sizes from 0.02 to 2000 microns. Pretreament options include removal of organic matter, carbonate minerals and cements, and diatoms.
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. CSDCO/LacCore uses the Department of Earth Sciences Rigaku Mini Flex diffractometer.
CSDCO/LacCore has a benchtop Hitachi TM-1000 SEM fitted with a Bruker Quantax 50 EDS which provides magnification from 20x to 10,000x with no need to coat or dehydrate samples. To schedule training please fill out the SEM Visitor Request Form. Please email Amy Myrbo, email@example.com, with any questions.
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).
Core linescan images are calibrated to known standards during acquisition for accurate color representation. Cores are imaged together with a Gretag-Macbeth Minichecker color card that contains 18 calibrated color patches and 6 calibrated grayscale patches. Later, images may be adjusted to the known color values of the patches; thus near-perfect color rendition may be obtained.
Floral and Faunal
Sediment samples are treated with hydrogen peroxide to destroy most organic matter, leaving charcoal intact. Samples are passed through a 125 µm sieve and the >125 µm fraction is kept, dried onto a petri dish, and counted. This relatively large charcoal is likely to come from local fires rather than ones farther away, thus recording fire history in the immediate vicinity of the core locality. For a thorough review of procedures and interpretations, see Whitlock and Larsen, 2001.
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.
The goal in preparing sediment samples for pollen analysis is 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 silicone oil or glycerol for counting slides. Sediment samples (usually 1.0cc, sampled volumetrically or by mass) are placed in 15mL plastic centrifuge tubes and are treated sequentially, as shown in the flowchart below, 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 particles from the sample and sample checks are used to determine if any step needs to be repeated.
Pollen Processing for AMS
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 LacCore 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 pre-burned 40 mL glass centrifuge tubes and treated sequentially, as shown in the flow chart below, 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.
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.
Dating and Magnetics
AMS Radiocarbon Dating
CSDCO/LacCore sends samples to the Science Museum of Minneota's St. Croix Watershed Research Station (SCWRS) for 210Pb dating. CSDCO/LacCore can assist from the project planning through freeze drying samples and mailing them to SCWRS.
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 LacCore 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.