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Fig. 10. Secondary electron images and EDS elemental mapping of spheroids from dark colored laminae. A, SEM image showing copious nano-particles covering spheroids and scattering on rocks. B, One complete spheroid growing in background calcite crystals with coarse calcite crystal sheaths on surface. Note that nano- particle aggregates (arrow). C, Close-up of boxed area in A showing that one broken spheroid possesses coarse calcite crystal nucleus (red arrow) surrounded by thin layer of sparitic calcite envelope (white arrow), and is covered partly with micrite sheaths (nano-particles). D, Close-up of boxed area in A showing that one spheroid is covered by thick micrite sheaths composed of nano-particles. E, EDS elemental mapping of one spheroid in B showing that Si content is limited to the microscopic spheroid and nano-particles. Oxygen content is high in all phases, whereas Mg, Ca and C content (dolomite) is low in the spheroid and nano-particles, but high in the host matrix. F and G, A broken microscopic spheroid in black and white and with features labelled in various colors, respectively showing a nucleus of coarse calcite (light red) surrounded by thin sheath of coarse sparitic calcite (purple), which are coated with micrite (nano-particles) layers (green).

Figure 10 Secondary electron images and EDS elemental mapping of spheroids from dark colored laminae. A, SEM image showing copious nano-particles covering spheroids and scattering on rocks. B, One complete spheroid growing in background calcite crystals with coarse calcite crystal sheaths on surface. Note that nano- particle aggregates (arrow). C, Close-up of boxed area in A showing that one broken spheroid possesses coarse calcite crystal nucleus (red arrow) surrounded by thin layer of sparitic calcite envelope (white arrow), and is covered partly with micrite sheaths (nano-particles). D, Close-up of boxed area in A showing that one spheroid is covered by thick micrite sheaths composed of nano-particles. E, EDS elemental mapping of one spheroid in B showing that Si content is limited to the microscopic spheroid and nano-particles. Oxygen content is high in all phases, whereas Mg, Ca and C content (dolomite) is low in the spheroid and nano-particles, but high in the host matrix. F and G, A broken microscopic spheroid in black and white and with features labelled in various colors, respectively showing a nucleus of coarse calcite (light red) surrounded by thin sheath of coarse sparitic calcite (purple), which are coated with micrite (nano-particles) layers (green).

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Fig. 1. A, Geological map of the Jixian area, Tianjin City, North China showing distributions of Proterozoic rocks and location of the studied Mopanyu section in Jixian County, Tianjin City. B, Integrating lithostratigraphy and chronostratigraphy of the Meosoproterozoic succession exposed in the Jixian area showing the horizon of stromatolite and U-Pb zircon radiometric ages (geological map after Mei et al., 2008). Abbreviations of stratigraphic units: Q = modern loose sediments. FJS = Fujunshan Formation, JEY = Jingeryu Formation, XML = Xiamaling Formation, TL = Tieling Formation, HSZ = Hongshuizhuang Formation, WMS = Wumishan Formation, YZ = Yangzhuang Formation, GYZ = Gaoyuzhuang Formation, DHY = Dahongyu Formation, TSZ = Tuanshanzi Formation, CLG = Chuan. linggou Formation, CZG = Changzhougou Formation, QX = Qianxi Group of the Archean-Paleoproterozoic metamorphic basement.
Fig. 1. A, Geological map of the Jixian area, Tianjin City, North China showing distributions of Proterozoic rocks and location of the studied Mopanyu section in Jixian County, Tianjin City. B, Integrating lithostratigraphy and chronostratigraphy of the Meosoproterozoic succession exposed in the Jixian area showing the horizon of stromatolite and U-Pb zircon radiometric ages (geological map after Mei et al., 2008). Abbreviations of stratigraphic units: Q = modern loose sediments. FJS = Fujunshan Formation, JEY = Jingeryu Formation, XML = Xiamaling Formation, TL = Tieling Formation, HSZ = Hongshuizhuang Formation, WMS = Wumishan Formation, YZ = Yangzhuang Formation, GYZ = Gaoyuzhuang Formation, DHY = Dahongyu Formation, TSZ = Tuanshanzi Formation, CLG = Chuan. linggou Formation, CZG = Changzhougou Formation, QX = Qianxi Group of the Archean-Paleoproterozoic metamorphic basement.
120Q. Fluorescent images were captured under both blue exciting light (wavelength 450-490 nm) and purple exciting light (wavelength 510-560 nm). When these photons interact with organic matter in a specimen, a strong fluorescence is emitted in both green and red colours, respectively for the excitation wavelengths used. In contrast, when organic matter content is low, the rock appears dim and without fluo- reerancre (C1if et al 1000: Reitner and Nenweiler 10Q5: Riuieen et al
120Q. Fluorescent images were captured under both blue exciting light (wavelength 450-490 nm) and purple exciting light (wavelength 510-560 nm). When these photons interact with organic matter in a specimen, a strong fluorescence is emitted in both green and red colours, respectively for the excitation wavelengths used. In contrast, when organic matter content is low, the rock appears dim and without fluo- reerancre (C1if et al 1000: Reitner and Nenweiler 10Q5: Riuieen et al
Fig. 3. Polished slab of the Wumishan stromatolites. A, Polished slab in cross-sectional view showing digitate to microdigitate, low-relief columns of stromatolites, dolomitic wackestone (white arrows). B, Polished slab of a planar view of an MDS bed showing circular, domal outlines of stromatolite columns. C, Polished slab in cross-sectional view showing digitate, branching and non-branching columns of microdigitate stromatolites. On polished slabs, stromatolite columns comprise brown carbonate with distinct alternations of dark and light colored laminated layers in sharp contrast with interspaces between columns, which are typically Fibrous fabrics are also conspicuous under polarized light micro- scopy and are partly recrystallized and replaced by quartz (Fig. 5E, brown area). Single fibers are fine and between 10 and 15 pm in width, straight, and radially-oriented (Fig. 5E, white arrow). These vertically
Fig. 3. Polished slab of the Wumishan stromatolites. A, Polished slab in cross-sectional view showing digitate to microdigitate, low-relief columns of stromatolites, dolomitic wackestone (white arrows). B, Polished slab of a planar view of an MDS bed showing circular, domal outlines of stromatolite columns. C, Polished slab in cross-sectional view showing digitate, branching and non-branching columns of microdigitate stromatolites. On polished slabs, stromatolite columns comprise brown carbonate with distinct alternations of dark and light colored laminated layers in sharp contrast with interspaces between columns, which are typically Fibrous fabrics are also conspicuous under polarized light micro- scopy and are partly recrystallized and replaced by quartz (Fig. 5E, brown area). Single fibers are fine and between 10 and 15 pm in width, straight, and radially-oriented (Fig. 5E, white arrow). These vertically
Fig. 4. Photomicrographs of the Wumishan MDSs. A, B, Digitate columns branching and merging occasionally with laminae being destructed occasionally by cavitie: that are filled with calcite. C, Close-up of B, digitate columns showing distinct alternations of light coloured (white) and dark coloured (yellow) laminae. D, Digitate columns showing distinct alternations of light coloured (white) and dark coloured (yellow) laminae, flanked with dark coloured interspaces between columns (arrows) filled with spheroids or stromatolite fragments. E, showing dark coloured laminae that contain aggregates of spheroids and some small cavities filled witt outsized dolomite crystals (arrows). F, Close-up of E showing dark coloured laminae that contain aggregates of spheroids and a cavity-like structure lined witt botryoidal features near the bottom. G, showing spheroids consortia penetrated by tiny vertically orientated fibrous fabrics.
Fig. 4. Photomicrographs of the Wumishan MDSs. A, B, Digitate columns branching and merging occasionally with laminae being destructed occasionally by cavitie: that are filled with calcite. C, Close-up of B, digitate columns showing distinct alternations of light coloured (white) and dark coloured (yellow) laminae. D, Digitate columns showing distinct alternations of light coloured (white) and dark coloured (yellow) laminae, flanked with dark coloured interspaces between columns (arrows) filled with spheroids or stromatolite fragments. E, showing dark coloured laminae that contain aggregates of spheroids and some small cavities filled witt outsized dolomite crystals (arrows). F, Close-up of E showing dark coloured laminae that contain aggregates of spheroids and a cavity-like structure lined witt botryoidal features near the bottom. G, showing spheroids consortia penetrated by tiny vertically orientated fibrous fabrics.
Fig. 5. Photomicrographs of the Wumishan MDSs. Spheroids consortia in dark coloured laminae. Colour arrows stand for different kinds of spheroids. A, B, spheroic with shell-like annulus, red arrows. C, two kinds of spheroids, spheroids with shell-like annulus, red arrows, and brown solid spheroids, blue arrows. D, four type spheroids, light brown hollow spheroids, yellow arrows, spheroids with shell-like annulus amd black core, white arrow, red and blue arrows as described in C. E brown four light brown hollow spheroids. Fibrous fabrics (brown area) and single fibers (white arrow). F, three concatenated light brown spheroids and, in inset, ar histogram of the diameter sizes frequency distribution of 246 individual spheroids measured.
Fig. 5. Photomicrographs of the Wumishan MDSs. Spheroids consortia in dark coloured laminae. Colour arrows stand for different kinds of spheroids. A, B, spheroic with shell-like annulus, red arrows. C, two kinds of spheroids, spheroids with shell-like annulus, red arrows, and brown solid spheroids, blue arrows. D, four type spheroids, light brown hollow spheroids, yellow arrows, spheroids with shell-like annulus amd black core, white arrow, red and blue arrows as described in C. E brown four light brown hollow spheroids. Fibrous fabrics (brown area) and single fibers (white arrow). F, three concatenated light brown spheroids and, in inset, ar histogram of the diameter sizes frequency distribution of 246 individual spheroids measured.
Fig. 6. Photomicrographs of the Wumishan MDSs. A, Spheroids consortia in dark coloured laminae. B, Interpretive cartoon of microscopic spheroids and associated botryoidal features and dolomite rhombs in A. C-D, Slightly curved filaments between the MDS columns that are mostly parallel-aligned and brown in colour due to their composition of organic matter.
Fig. 6. Photomicrographs of the Wumishan MDSs. A, Spheroids consortia in dark coloured laminae. B, Interpretive cartoon of microscopic spheroids and associated botryoidal features and dolomite rhombs in A. C-D, Slightly curved filaments between the MDS columns that are mostly parallel-aligned and brown in colour due to their composition of organic matter.
Fig. 7. Polarized microscope and fluorescent images showing coccoid-like spheroid consortia. A, D, G, Polarization microscope images. B, E, H, Fluorescence images (purple fluorescent wavelength 450-490 nm). C, F, I, Fluorescence images (green fluorescent wavelength 510-560 nm). Organic-enriched particles (arrows) show strong fluorescence in both green and red colours. Inside laminae rich in organic matter and microscopic spheroids, note the presence of botryoid-like cavity- structures lined with dense organic matter around cores almost free of of organic matter in G-I.
Fig. 7. Polarized microscope and fluorescent images showing coccoid-like spheroid consortia. A, D, G, Polarization microscope images. B, E, H, Fluorescence images (purple fluorescent wavelength 450-490 nm). C, F, I, Fluorescence images (green fluorescent wavelength 510-560 nm). Organic-enriched particles (arrows) show strong fluorescence in both green and red colours. Inside laminae rich in organic matter and microscopic spheroids, note the presence of botryoid-like cavity- structures lined with dense organic matter around cores almost free of of organic matter in G-I.
Fig. 8. Secondary electron images of micro-fabrics and aggregates of microscopic spheroid in dark coloured laminae and EDS analytical results of spheroid surfac« (Natural weathering without acid treatment). A-B, aggregates of spheroids. C, Close-up of boxed area in A showing solitary spheroid having unsmooth surface. D Close-up of boxed area in A showing paired spheroids with irregular outline and unsmooth surfaces. E, EDS peaks of the crossed point in A showing major com ponents of Si and O, and minor contents of C, Ca and Mg, indicating a replacement of silica due to silicification. F-H, Close-up of boxed area in B, showing solitary spheroid having one broken opening (arrows) on surface.
Fig. 8. Secondary electron images of micro-fabrics and aggregates of microscopic spheroid in dark coloured laminae and EDS analytical results of spheroid surfac« (Natural weathering without acid treatment). A-B, aggregates of spheroids. C, Close-up of boxed area in A showing solitary spheroid having unsmooth surface. D Close-up of boxed area in A showing paired spheroids with irregular outline and unsmooth surfaces. E, EDS peaks of the crossed point in A showing major com ponents of Si and O, and minor contents of C, Ca and Mg, indicating a replacement of silica due to silicification. F-H, Close-up of boxed area in B, showing solitary spheroid having one broken opening (arrows) on surface.
Fig. 9. SEM images of spheroids detected in light coloured laminae. A, Spheroids grew on sparry calcites. B, Close-up of boxed area in A showing three spheroids elevated from sparitic calcite crystals. Note the middle spheroid embraces a distinct rounded opening on surface (arrow). C, Close-up of boxed area in A showing a coarse sparitic crystal calcite nucleus (red arrow) surrounded by a thin layer of micrite envelope (white arrow) in one broken spheroid. D, Close-up of boxed area in A showing a micrite framboidal nucleus (red arrow) surrounded by coarse calcite crystal rims (white arrow) in one broken spheroid that is covered partly by back- ground sparry calcite. E, Close-up of boxed area in A showing one spheroid being covered partly by background sparry calcite with nano-particles on surface. F, Colony of three coccoid-like spheroids, with each embracing one pronounced circular opening (arrows) and nano-particles on surface. G, Close-up of one spheroid with a distinct rounded opening (arrow) and nano-particles on surface. H, Close-up of one spheroid that is broken around the opening (arrow). I, Close-up of one opening on spheroid surface in G showing rough margins of opening that comprise nano-particles.
Fig. 9. SEM images of spheroids detected in light coloured laminae. A, Spheroids grew on sparry calcites. B, Close-up of boxed area in A showing three spheroids elevated from sparitic calcite crystals. Note the middle spheroid embraces a distinct rounded opening on surface (arrow). C, Close-up of boxed area in A showing a coarse sparitic crystal calcite nucleus (red arrow) surrounded by a thin layer of micrite envelope (white arrow) in one broken spheroid. D, Close-up of boxed area in A showing a micrite framboidal nucleus (red arrow) surrounded by coarse calcite crystal rims (white arrow) in one broken spheroid that is covered partly by back- ground sparry calcite. E, Close-up of boxed area in A showing one spheroid being covered partly by background sparry calcite with nano-particles on surface. F, Colony of three coccoid-like spheroids, with each embracing one pronounced circular opening (arrows) and nano-particles on surface. G, Close-up of one spheroid with a distinct rounded opening (arrow) and nano-particles on surface. H, Close-up of one spheroid that is broken around the opening (arrow). I, Close-up of one opening on spheroid surface in G showing rough margins of opening that comprise nano-particles.
Fig. 11. SEM images of nano-particles, Po = polyhedrons and Ng = nanoglobules. A, Nano-particle aggregates. B, Close-up of nano-particle aggregates showir abundant polyhedrons (Po) and nanoglobules (Ng). C, Close-up of boxed area in A showing dumbbell-shaped bursts of polyhedrons (Po) and nanoglobules (Ng). | Close-up of boxed area in A showing primitive form of dumbbell-shaped bursts of polyhedrons (Po) and nanoglobules (Ng) with closely arranged bell-like aggregate E, Close-up of boxed area in A showing spherical aggregate of polyhedrons (Po) and nanoglobules (Ng). F, Nano-particle aggregates containing abundant filamen and mucuslike films (purported EPS), polyhedrons (Po) and nanoglobules (Ng). G, Close-up of boxed area in F showing filaments and mucuslike films (purporte EPS), polyhedrons (Po) and nanoglobules (Ng). H—-J, EDS analytical results of crossed points in C, D and G, respectively showing almost same elemental compositic patterns of polyhedrons (Po), nanoglobules (Ng), and mucuslike films, respectively.
Fig. 11. SEM images of nano-particles, Po = polyhedrons and Ng = nanoglobules. A, Nano-particle aggregates. B, Close-up of nano-particle aggregates showir abundant polyhedrons (Po) and nanoglobules (Ng). C, Close-up of boxed area in A showing dumbbell-shaped bursts of polyhedrons (Po) and nanoglobules (Ng). | Close-up of boxed area in A showing primitive form of dumbbell-shaped bursts of polyhedrons (Po) and nanoglobules (Ng) with closely arranged bell-like aggregate E, Close-up of boxed area in A showing spherical aggregate of polyhedrons (Po) and nanoglobules (Ng). F, Nano-particle aggregates containing abundant filamen and mucuslike films (purported EPS), polyhedrons (Po) and nanoglobules (Ng). G, Close-up of boxed area in F showing filaments and mucuslike films (purporte EPS), polyhedrons (Po) and nanoglobules (Ng). H—-J, EDS analytical results of crossed points in C, D and G, respectively showing almost same elemental compositic patterns of polyhedrons (Po), nanoglobules (Ng), and mucuslike films, respectively.
Fig. 12. Optical petrographic images and corresponding Raman maps of areas corresponding to boxed area showing the spatial distribution (recorded by the parameter I-1350 and I-1600) of the organic matter in MDS without spheroids. (A) Transmitted light image of finely laminated domal stromatolite with layers of organic matter (brown) but without microscopic spheroids. (B) Selected Raman images of the laminated dome showing D-band, G-band, calcite, and combined images. Raman spectra for calcite, which shows peaks at 154, 281, 712 and 1086 cm“, and for organic matter, which shows peaks at 1350 cm~' (D-band) and 1600 cm~? (G-band).
Fig. 12. Optical petrographic images and corresponding Raman maps of areas corresponding to boxed area showing the spatial distribution (recorded by the parameter I-1350 and I-1600) of the organic matter in MDS without spheroids. (A) Transmitted light image of finely laminated domal stromatolite with layers of organic matter (brown) but without microscopic spheroids. (B) Selected Raman images of the laminated dome showing D-band, G-band, calcite, and combined images. Raman spectra for calcite, which shows peaks at 154, 281, 712 and 1086 cm“, and for organic matter, which shows peaks at 1350 cm~' (D-band) and 1600 cm~? (G-band).
Fig. 13. Optical petrographic images and corresponding Raman maps of boxed area showing the spatial distribution (recorded by the parameter I-1350 and I-1600) of the organic matter in the spheroids laminated dome. (A) Transmitted light image of light-brown spheroids in organic-rich laminae. (B) The Raman spectra obtained in (A), bands at 176 and 299 cm~ that are assigned to dolomite. The peak at 465 cm~’ represents microcrystalline quartz, while the peaks for organic matter are centered at 1350 and 1600 cm’. Selected Raman images of spheroids in organic-rich laminae for the D-band and G-band of organic matter, for quartz, and for the combined hyperspectral image.
Fig. 13. Optical petrographic images and corresponding Raman maps of boxed area showing the spatial distribution (recorded by the parameter I-1350 and I-1600) of the organic matter in the spheroids laminated dome. (A) Transmitted light image of light-brown spheroids in organic-rich laminae. (B) The Raman spectra obtained in (A), bands at 176 and 299 cm~ that are assigned to dolomite. The peak at 465 cm~’ represents microcrystalline quartz, while the peaks for organic matter are centered at 1350 and 1600 cm’. Selected Raman images of spheroids in organic-rich laminae for the D-band and G-band of organic matter, for quartz, and for the combined hyperspectral image.
References We are grateful to guest editor Zhongwu Lan, and both reviewers Yi- Ni Wang and Dongjie Tang for their critical comments and constructive suggestions that have improved greatly the quality of the paper. This study was supported by a National Key R & D Program of China grant (2017YFC0603103), a NSFC grant (41821001), and the 111 Program of China (BP0820004).
References We are grateful to guest editor Zhongwu Lan, and both reviewers Yi- Ni Wang and Dongjie Tang for their critical comments and constructive suggestions that have improved greatly the quality of the paper. This study was supported by a National Key R & D Program of China grant (2017YFC0603103), a NSFC grant (41821001), and the 111 Program of China (BP0820004).
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Petrography and DiagenesisMicrobial Carbonates
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