Sediment Characterization

Sediment Sampling and Testing

Sediment samples – vibrocores (VC) and grabs – and core penetration tests (CPT) were undertaken during the 2025 Geotechnical Survey by the Armada vessels 8601 and 8603 from Ocean Infinity.

Sediment and geotechnical analyses were conducted by Ocean Infinity for all stations.

Duplicated VCs and grab samples were collected at selected stations, and sent to IPMA for additional sediment analysis, storage and curation.

Additional sediment and geotechnical analyses were conducted by LNEC on a selection of VCs and grabs provided by IPMA.

Number of stations sampled by Ocean Infinity for vibrocores, grabs, and core penetration tests, for Leixões (LEI) and Figueira da Foz (FIG) PAER areas. Of the total stations sampled, duplicate samples were collected at selected stations and provided to IPMA.
Demonstration of vibrocorer operation during mobilization in Porto de Leixões
Vibrocorer tests at Porto de Leixões

Vibrocore analysis @IPMA

IPMA vibrocores were analysed at IPMA-Algés and IPMA-Tavira facilities, by IPMA’s Marine Geology and Georesources Division Sedimentology group, according to the following protocol.

Workflow

Sample and data curation

To preserve sample integrity and ensure future availability, archive core halves and remaining sediment samples are stored at IPMA-Algés cold room archive, at a temperature of 4º C.

Stored samples and their metadata are linked to the analytical results of sediment analysis.

Data and metadata are integrated into IPMA’s SOMOSATLÂNTICO platform.

Vibrocore samples stored @IPMA-Algés cold room archive.
Split VCs – left side; non-split VCs – right side

Computed tomography of cores (MSCL-XCT)

Core CT image

>> FIG: 50 vibrocores from 13 stations

>> LEI: 23 vibrocores from 4 stations

Aims:

  • Computed tomography (CT images) of sediment cores
  • Identification of internal sedimentary structures (stratification/lamination, bioturbation, stratigraphic discordances)
  • Evaluation of the presence of clasts and/or bioclasts (shells)
  • Insightful results for supporting and correlating with other physical property proxies

Method:

  • Two-dimensional (2D) radiographic projections (raw data) are acquired at multiple angles using the Geotek Standard X-ray CT System (MSCL-XCT) at IPMA-Tavira, for full cores
  • CT reconstruction is performed using Geotek’s software, converting raw projection data into tomographic slices and cross-sectional views of the sediment core as TIFF and JPG images
  • CT images are interpreted and correlated with other proxies to distinguish lithologic variations along the sediment cores
Standard X-Ray CT system (MSCL-XCT) @IPMA-Tavira

Image and physical properties (MSCL-S)

>> FIG: 13 vibrocores from 13 stations

>> LEI: 5 vibrocores from 5 stations

Aims:

  • Characterize the lithology of the vibrocores, through imaging and measurement of physical properties
  • Assess variations in density, water content and porosity
  • Evaluate mineral content and variations in detrital inputs
  • Estimate carbonate content and diagenetic/oxidation markers

Methods:

Physical properties are measured using the Geotek’s Standard Multi-Sensor Corer Logger (MSCL-S) at IPMA-Algés with the following sensors:

  • Gamma-ray density,
  • P-wave velocity,
  • Magnetic susceptibility,
  • Colour spectrum

High-resolution imaging of split sediment core surfaces, in the visible wavelength, is acquired with the Geotek Geoscan V Colour Line-Scan Camera and lightbox.

Image and physical properties measured along the vibrocore FIG-038-IPMA
Standard Multi-Sensor Core Logger (MSCL-S) @IPMA-Algés

Vibrocore sub-sampling

>> FIG: 12 vibrocores from 12 stations

>> LEI: 4 vibrocores from 4 stations

Vibrocores were split and working halves were sub-sampled at IPMA-Algés for further sediment analyses:

  • 210Pb << first 30 cm, with syringe for volume determination
  • Elemental analysis and Dry bulk density << every 20 cm, with syringe for volume determination
  • Grain size<< every 20 cm, with spatula
  • AMS 14C << every 20 cm and supplementary levels, with spatula
Sub-sampling the vibrocore FIG34 for elemental, grain size, 210Pb, and AMS 14C analyses

Elemental Analysis

>> FIG: 12 vibrocores from 12 stations

>> LEI: 4 vibrocores from 4 stations

Geochemical characterization of sediments was carried out at IPMA-Algés, for:

  • Total Organic Carbon content – TOC (W%)
  • Total nitrogen content – TN (W%)
  • Calcium Carbonate content – CaCO3 (W%)

Quality control parameters established based on ISO standards (ISO 10694:1995 and ISO 13878:1998) and on methodological studies.

Elemental analyses @IPMA-Algés

Grain Size Analysis

>> FIG: 12 vibrocores from 12 stations

>> LEI: 4 vibrocores from 4 stations

Grain size distribution informs on the origin, transport, depositional processes and controlling environmental conditions of the sediments.

The analysis, undertaken at IPMA-Algés, quantifies the particle size distribution in a sediment sample, in weight %:

  • gravel (> 2 mm)
  • sand (> 63 μm and < 2 mm)
  • silt (4–63 μm)
  • clay (< 4 μm)

The sand fraction is further used for picking of foraminifera for AMS14C.

Grain size analysis @IPMA-Algés

Chronology (210Pb & AMS 14C)

>> FIG: 12 vibrocores from 12 stations

>> LEI: 4 vibrocores from 4 stations

Chronology of marine sediments establishes the ages and timings of the environmental changes recorded in sediment cores.

Two dating methods are applied to the project samples: 210Pb and Accelerator Mass Spectrometry Radiocarbon (AMS14C).

210Pb dating

  • Determines the rate of sediment accumulation using the decay of excess 210Pb activity (half-life = 22.3 years)
  • Recent sediments, generally covering the last ~100–150 years

AMS 14C dating

  • Dating of sediments up to 43 500 years
  • Counts the 14C atoms (half-life of 5 730 years) directly using a particle accelerator
  • Samples: vibrocores were sampled every 20 cm and at supplementary levels
  • Foraminifera and shells were picked (8-12 mg) at IPMA-Algés, and analyzed at SGS – BETA ANALYTIC
Picking foraminifera for AMS 14C dating, @IPMA-Algés

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