Sedimentologic data and core descriptions from surface samples and sand augers collected in 2023 from the northern Chandeleur Islands, Louisiana

Sample collection- Sand augers were collected using an AMS, Inc. sand/loose sediment soil probe, which can accommodate a 2.54 centimeter (cm) (1 inch) diameter by approximately 96 cm (3 feet) plastic sleeve. After extraction, each core was capped, sealed, and labeled with the core number and orientation. All cores were transported to the SPCMSC sediment laboratory for processing and analysis. Surface samples were collected using (a) a scoop for samples collected on the emergent island or shallow intertidal areas or (b) a WILDCO Petit Ponar grab sampler deployed from a skiff or boat for submerged samples collected from water depths greater than about 1 m. Position and elevation data at each sand auger site and selected surface sample sites were recorded using a Spectra Precision SP80 DGPS receiver and geodetic antenna recording full-carrier-phase positioning signals from satellites at a rate of 1 second (s). Raw data were recorded for a minimum of 5 minutes. DGPS data were recorded concurrently throughout the survey at a nearby base station established at MRK3 using a Spectra Precision SP90M DGPS receiver and Trimble Zephyr-3 Base antenna. Position data at the remaining sample sites were recorded at the time of collection using a Garmin GPSMap 79SC handheld GPS or Garmin Echomap UHD 64cv boat-mounted GPS.

Navigation Processing- Base station data were post-processed through the NGS OPUS and the time-weighted coordinates calculated from all base-station occupations at MRK3 were used for post-processing. The base station coordinates were imported into GrafNav and, for DGPS sites, the data from the rover GPS were post-processed to the concurrent base-station session data. The final, differentially corrected, GPS positions for each rover session were processed and exported in the North American Datum of 1983 (NAD83) (2011) coordinate system and processed orthometric elevations are reported relative to the North American Vertical Datum of 1988 (NAVD88), derived using the GEOID18 geodetic model. For samples locations recorded using a Garmin GPSMap 79SC handheld GPS or Garmin Echomap UHD 64cv boat-mounted GPS, sample elevations were subsequently interpolated from lidar data collected in October 2022 (OCM Partners, 2025) or SBES and MBES data collected in June and August, 2023 (Lyons and others, 2025; Stalk and others, 2025).

Sand auger processing- At the SPCMSC sediment laboratory, each sand auger section was split lengthwise, photographed, x-rayed, described macroscopically using standard sediment-logging methods, and subsampled for grain-size analysis. The split sand augers were photographed in approximately 30-cm overlapping segments with a Nikon D3500 digital camera with an 18- to 55-mm zoom lens using consistent (manually programmed) settings with autofocus from a fixed height. The raw images were white-balanced using GIMP software, cropped to the same extent (to remove areas outside of the core barrel), and "stitched" together using The Panorama Factory software, providing seamless high-resolution whole-core images exported as Joint Photographic Experts Group (JPEG) format. Core x-rays were acquired using an Ecotron EPX-2800 x-ray unit at 85 kilovolts for 16 milliampere-seconds from a height of 79 cm. Each x-radiograph was captured on an 11 × 14-inch phosphor cassette, which was scanned on an iCRco, Inc., iCR3600+ scanner at 254 pixels per inch and exported as a 16-bit Tagged Image File Format (TIF) image. The raw x-radiographs show a slight anode heel effect, which is a variation in x-ray intensity along the anode-cathode axis that results in non-uniform pixel intensity across the image. This effect was corrected by subtracting a background pixel intensity template from each raw image (Bernier and others, 2014). The images were cropped (to the same extent and to remove areas outside of the cassette), background image subtracted, and grayscale color inversion was applied using ImageJ software. Depending on core length, sand augers that did not fit onto the phosphor cassette were x-rayed in "top" and "bottom" or "top," "middle," and "bottom" segments and then merged in Adobe Illustrator. Textural descriptions for the core logs are based on macroscopic observations. Sediment color is based on the Munsell soil color system (https://munsell.com/color-products/color-communications-products/environmental-color-communication/munsell-soil-color-charts/). Descriptive core logs were compiled using Rockware LogPlot software. Samples consisted of 3-cm sections sampled at varying intervals down-core based on observed sedimentologic changes. Two samples from core 23BIM03-20 collected for radiocarbon dating and were sealed, labeled, and shipped to Beta Analytic, Inc. for analysis.

Grain-size PSA analysis- At the SPCMSC sediment laboratory, grain-size analyses were performed using a Coulter LS13 320 (https://www.beckmancoulter.com/) PSA. The LS13 320 uses laser diffraction to measure the size distribution of sediments from 0.4 µm to 2 mm, encompassing clay to very coarse-grained sand. To prevent large shell fragments from damaging the instrument, particles greater than 1 mm in diameter (coarse sand) were separated from all samples prior to analysis using a number 18 (1 mm) U.S. standard sieve, which meets the American Society for Testing and Materials (ASTM) E11 standard specifications for determining particle size using woven-wire test sieves. Prior to processing through the LS13 320, samples with visually observed organic content were digested in 30% hydrogen peroxide (H2O2) to remove excess organic material; six samples were analyzed both undigested and digested for comparison. Following SPCMSC standard procedures, samples were (a) dried at 60 degrees Celsius and dry loaded into the LS13 320 (well-sorted sandy sediment) or (b) homogenized in water and sonicated to suspend in solution prior to transferring to the LS13 320 (sediment with visually observed mud content or samples that were previously digested with H2O2). Two subsamples from each sample were processed through the instrument a minimum of four runs each. Once introduced into the LS13 320, the sediment in the sample well was sonicated with a sonicator wand for 30 to 60 seconds to separate any aggregates before starting the first run for both subsamples. The LS13 320 measures the particle-size distribution of each sample by passing sediment suspended in solution between two narrow panes of glass in front of a laser. Light is scattered by the particles into characteristic refraction patterns measured by an array of photodetectors as intensity per unit area and recorded as relative volume for 92 size-related channels (bins).

Grain-size processing- For samples that were dry loaded into the LS13 320, sediment >1 mm in diameter was reported as a percent fraction of the total bulk dry weight of each sample (bulk dry weights were not measured for samples loaded in solution). The raw PSA grain-size data were run through the free software GRADISTAT version 9, (Blott and Pye, 2001; kpal.co.uk/gradistat), which calculates the mean, sorting, skewness and kurtosis of each sample geometrically, in metric units, and logarithmically, in phi (Φ) units (Krumbein, 1934), using the Folk and Ward (1957) scale. GRADISTAT also reports the descriptive sediment texture after Folk (1954) and calculates the fraction of sediment from each sample by size category (for example, clay, coarse silt, fine sand) based on a modified Wentworth (1922) size scale. A macro function in Microsoft Excel, developed by the USGS SPCMSC, was applied to the data to calculate average and standard deviation for each sample set (8 runs per sample), and highlight runs that varied from the set average by more than ±1.5 standard deviations. The highlighted runs were removed from the results and the sample average was recalculated using the remaining runs. The averaged results for all samples and the number of averaged runs are included in an Excel workbook, organized by subFAN, and comma-separated values (.csv) data files, organized by sample type (core or surface sample). The raw LS13 320 output files, which list the class weight retained in each aperture bin as a percent of the total sample weight for each sample run, were compiled by GRADISTAT, imported into Matlab, and averaged for each sample (8 runs per sample except for samples with runs flagged and removed as described above); those grain-size distribution data are also included in this data release for advanced users.

Grain-size plots- The down-core grain-size distributions (>1 mm fraction, coarse sand, medium sand, fine sand, very fine sand, and mud classes) for each sand auger were plotted in Matlab and exported as a JPEG image; cores are arranged from north (top) to south (bottom) of image. The sediment texture for all samples were also plotted in Matlab on a ternary diagram using the Folk (1954) fine sediment classification and exported as a JPEG image.

Radiocarbon dating- Both the organic sediment fraction and plant material from two organic-rich subsamples from core 23BIM03-20 were analyzed using accelerated mass spectrometry (AMS) radiocarbon (14C) dating at Beta Analytic, Inc. (Miami, Florida). For each sample, the conventional 14C radiocarbon age as well as calibrated age ranges are reported. Calibrated ages are based on terrestrial calibration curves from INTCAL20 (Reimer and others, 2020) using the High Probability Density (HPD) Range Method (Bronk Ramsey, 2009). For additional information on understanding calibrated radiocarbon ages, refer to the Beta Analytic, Inc. (https://www.radiocarbon.com/calendar-calibration-carbon-dating.htm) or University of Oxford Radiocarbon Accelerator Unit (https://c14.arch.ox.ac.uk/calibration.html, https://c14.arch.ox.ac.uk/explanation.php) websites.

Populating image headers- Credit, contact information, copyright, usage terms, image descriptions, attribution url, metadata link, and georeferencing information were added to the exchangeable image file format (EXIF) header of each image using Phil Harvey’s ExifTool. The images were grouped by image type (core logs, photographs, and x-rays) into separate folders: 2023-307-FA_CoreLogs, 2023-307-FA_CorePhotos, and 2023-307-FA_CoreXRays. All information in the scripts were the same among all images, aside from the EXIF:ImageDescription, EXIF:DateTimeOriginal, EXIF:GPSLatitude and EXIF:GPSLongtitude information, as that information varies for each core. A separate script containing the core-specific header information was run on each image individually to populate those headers. The core logs and photographs are published as JPGs, whereas the core x-rays are published as TIFs. Therefore, all mentions of the file extension in the example scripts below used ".TIF" rather than ".JPG" for the x-ray images. Image header information was also populated for the files 2023-307-FA_Cores_GrainSizeDistributions.jpg and 2023-307-FA_GrainSize_TernaryPlot.jpg in 2023-307-FA_GrainSizeData.zip. However, since these image details grain-size data for all samples, the EXIF:GPSMapDatum, EXIF:GPSAreaInformation, and core-specific headers were not added.
First, the following command was run on all images in a folder to preserve filenames: exiftool -P "-XMP:PreservedFileName<Filename" *.jpg
Second, the following command was run on all images in a folder to populate the first set of headers. exiftool -IPTC:Credit="U.S. Geological Survey" -IPTC:Contact="gs-g-spcmsc_data_inquiries@usgs.gov" -EXIF:Copyright="Public Domain" -XMP:UsageTerms="Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty." -XMP:AttributionURL="https://doi.org/10.5066/P13KRKA4" -XMP:Event="2023-307-FA" -EXIF:GPSAreaInformation="Location of core collection site, GPS coordinates are in NAD83" -XMP:ExternalMetadataLink="https://www1.usgs.gov/pir/api/identifiers/USGS:4e67da86-b79a-4666-984b-5fb89ee580c8" -EXIF:GPSMapDatum="NAD83" *.jpg
Third, the following command was run on each image in the folder to populate the unique image headers for each core. This command called on a .csv file “23BIM03_CorePhotos_ExifHeaders.csv") containing the image file name, image description, core collection date, GPS latitude, and GPS longitude of each core. exiftool -csv='23BIM03_CorePhotos_ExifHeaders.csv' *.jpg
Fourth, the following command run on all images in a folder to copy information into duplicate tags: exiftool -P "-XMP-photoshop:Credit<IPTC:Credit" "-XMP-iptcCore:CreatorWorkEmail<IPTC:Contact" "-XMP-dc:Rights<EXIF:Copyright" "-XMP-dc:Description<EXIF:ImageDescription" "-XMP-exif:all<GPS:all" "-XMP-photoshop:DateCreated<EXIF:DateTimeOriginal" "-EXIF:GPSDateStamp<EXIF:DateTimeOriginal" -overwrite_original *.JPG
To extract the information from the image headers using ExifTool, run the following command after connecting to the unzipped folder containing the images: exiftool a.jpg, where 'a' is replaced with the filename (example: 23BIM03-13_Stitched.jpg)