Fig 1.
Study site located in intertidal zone, East China Sea (A-1, 2); Two typical samples, stratified type (S-type) (B-1, 2) and nodule-cemented type (N-type) (C-1, 2), were found in field.
The photos of B-1 and C-1 were taken during field work, and those samples were cut in laboratory (B-2 and C-2).
Table 1.
Key information for collected sample names, description and analysis techniques.
Fig 2.
Plane polarized light (left), scanned electron (right upper two) and backscattered electron (right lower two) micrographs of epoxy-embedded thin sections of two typical samples.
S-Y and S-B represented the yellowish-red part and the black part of S-type sample, respectively; N-Y and N-B for the yellowish-red part and the black part of N-type sample, respectively.
Fig 3.
Digital mapping of the different precipitates among the sand particles in two typical samples.
S-type samples from the pink squares in Fig. 2 S-Y (2) and S-B (2) were carried on Environmental Scanning Electron Microscopy (ESEM)-X-Ray mapping (top two), and N-type samples from Fig. 2 N-Y (2) and N-B (2) were performed on Electron Microprobe Analyzer (EMPA)-X-Ray mapping (bottom two).
Fig 4.
XRD patterns of different coatings in two typical samples.
Y-Coating: Q-Quartz; R-Rutile; F-Ferrihydrite; G-Goethite. B-Coating: Q-Quartz; R-Rutile; F-Ferrihydrite; B-Birnessite.
Fig 5.
Scanning electron microscopy (SEM) photos of S-type sample and Energy diffraction spectrum (EDS) of selected areas (marked with red star) in SEM images.
The top showed the images/spectrum of S-Y part, and the lower displayed the feature of S-B part.
Fig 6.
Scanning electron microscopy (SEM) photos of N-type sample and Energy diffraction spectrum (EDS) of selected areas (marked with red star) in SEM images.
The top showed the SEM images of N-Y part, the middle displayed the feature of N-B, and the bottom were the spectrum of EDS. The red arrows indicated the biofilm-like object/remnants there.
Table 2.
Summary statistics for REE in the coatings and related materials in the intertidal area, East China Sea.
Fig 7.
REE patterns normalized by PAAS.
BR, RS and WS were characterized by middle REE depletion. However, BIOS, BM and ferromanganese coatings were characterized by a distinct middle REE hump. The normalized pattern of GW was almost flat, and SW with small MREE enrichment.
Fig 8.
Trace metal elements in the coatings and related materials were normalized by BR.
Fig 9.
REE patterns normalized by BIOS. BR, RS, WS and BM were characterized by middle REE depletion.
However, SW and ferromanganese coatings were characterized by a distinct middle REE hump. The normalized patterns of GW were almost flat.