Academia.eduAcademia.edu

Figure 2 – uploaded by Dominic Papineau

See full PDFdownloadDownload figure
Fig. 2. Field outcrop photographs showing various stromatolite morphologies from the McLeary Formation. The captions in the bottom left corner of each image correspond to the thin sections that are at a similar stratigraphic height. A-B) Dolomite outcrops showing horizontal cross sections of decimetre-size, non-branching domal to turbinate stromatolites; C-D) bed of decimetre-size, non-branching, domal to turbinate stromatolites in dolomitic chert; E-F) tabular bioherms ot centimetre-size multifurcate, anastomosed stromatolites in chert-rich limestone; G-H) turbinate and bulbous stromatolites, sometimes with multifurcate branching and decimetre-size black chert concretions.

Figure 2 Field outcrop photographs showing various stromatolite morphologies from the McLeary Formation. The captions in the bottom left corner of each image correspond to the thin sections that are at a similar stratigraphic height. A-B) Dolomite outcrops showing horizontal cross sections of decimetre-size, non-branching domal to turbinate stromatolites; C-D) bed of decimetre-size, non-branching, domal to turbinate stromatolites in dolomitic chert; E-F) tabular bioherms ot centimetre-size multifurcate, anastomosed stromatolites in chert-rich limestone; G-H) turbinate and bulbous stromatolites, sometimes with multifurcate branching and decimetre-size black chert concretions.

Related Figures (17)

Fig. 1. Geological context for this study. A) Geological map of North America with the cratons labelled and a white ‘X’ showing the location of the Belcher Islands modified from St-Onge et al., 2006; B) stratigraphy and colour-coded formations for the Belcher Group and sample positions within the measured cross section of ths McLeary Formation (see Table 1); C) geological map of the Belcher Islands; D) aerial photo of the field site of the McLeary Formation. “ The Belcher Islands are located on a section of the Trans-Hudson Orogen called the Circum-Superior Belt, which consists of oceanic ba- salts and sedimentary rocks (Arndt and Todt, 1994). Uranium-lead dating on zircons carried out by Hodgskiss et al. (2019) shows that the maximum age of the Belcher Group is 2.0185 + 0.001 Ga (obtained from
Fig. 1. Geological context for this study. A) Geological map of North America with the cratons labelled and a white ‘X’ showing the location of the Belcher Islands modified from St-Onge et al., 2006; B) stratigraphy and colour-coded formations for the Belcher Group and sample positions within the measured cross section of ths McLeary Formation (see Table 1); C) geological map of the Belcher Islands; D) aerial photo of the field site of the McLeary Formation. “ The Belcher Islands are located on a section of the Trans-Hudson Orogen called the Circum-Superior Belt, which consists of oceanic ba- salts and sedimentary rocks (Arndt and Todt, 1994). Uranium-lead dating on zircons carried out by Hodgskiss et al. (2019) shows that the maximum age of the Belcher Group is 2.0185 + 0.001 Ga (obtained from
Stable isotope composition of organic matter and carbonate from the studied samples. * The contact with the top of the Fairweather Formation in this section is at 61 m. One standard deviation variations on standards analysed during these sessions 2 respectively 0.3, 0.1 and 0.1% for 38° Corg, 5 3Ccarp, and 8180 carp. Table 2
Stable isotope composition of organic matter and carbonate from the studied samples. * The contact with the top of the Fairweather Formation in this section is at 61 m. One standard deviation variations on standards analysed during these sessions 2 respectively 0.3, 0.1 and 0.1% for 38° Corg, 5 3Ccarp, and 8180 carp. Table 2
Table 1
Table 1
Fig. 3. Scans of the thin sections used in this study, arranged in stratigraphic order (low to high). The red numbered squares correspond to the subsequent figures in this study. A) Micritic carbonate with numerous outsized quartz crystals (two crystals are indicated) and no laminations; see Figs. 6 and 10; B) micritic carbonate with laminations caused by variations in kerogen content or the amount of pyrite crystals present; see Fig. 9; C) micritic carbonate with stylolites and pyrite crystals (black circles) inside a domal stromatolite; see Figs. 6, 9, and 10; D) micritic carbonate with a pyrite concretion and undulatory wrinkly layers; see Figs. 4 and 9; E) diverse stromatolite morphologies with stylolites between their columns within sparry carbonate; examples of an anastomosed multifurcate column (a) (also shown in higher magnification) and a bifurcate column (b) are highlighted; see Figs. 9 and 10; F) carbonate filled with wrinkly layers of probable microbial origin, and calcite veins; see Figs. 4, 5, and 6; G) smaller stromatolites preserved in chert; see Figs. 4 and 7; H) wrinkly layers of probable microbial origin, and masses of kerogen in chert, carbonate and isopachous quartz; see Figs. 4, 7, and 8; I) cherty stromatolite with filamentous clumps of kerogen and groups of filamentous microfossils (in red circles); see Fig. 5; J) cherty domal stromatolite; see Fig. 5. The dashed arrows in the lower right corner represent the approximate stratigraphic up direction (based on stromatolite morphology) and the scale bar at the bottom is approximately the same for all images.
Fig. 3. Scans of the thin sections used in this study, arranged in stratigraphic order (low to high). The red numbered squares correspond to the subsequent figures in this study. A) Micritic carbonate with numerous outsized quartz crystals (two crystals are indicated) and no laminations; see Figs. 6 and 10; B) micritic carbonate with laminations caused by variations in kerogen content or the amount of pyrite crystals present; see Fig. 9; C) micritic carbonate with stylolites and pyrite crystals (black circles) inside a domal stromatolite; see Figs. 6, 9, and 10; D) micritic carbonate with a pyrite concretion and undulatory wrinkly layers; see Figs. 4 and 9; E) diverse stromatolite morphologies with stylolites between their columns within sparry carbonate; examples of an anastomosed multifurcate column (a) (also shown in higher magnification) and a bifurcate column (b) are highlighted; see Figs. 9 and 10; F) carbonate filled with wrinkly layers of probable microbial origin, and calcite veins; see Figs. 4, 5, and 6; G) smaller stromatolites preserved in chert; see Figs. 4 and 7; H) wrinkly layers of probable microbial origin, and masses of kerogen in chert, carbonate and isopachous quartz; see Figs. 4, 7, and 8; I) cherty stromatolite with filamentous clumps of kerogen and groups of filamentous microfossils (in red circles); see Fig. 5; J) cherty domal stromatolite; see Fig. 5. The dashed arrows in the lower right corner represent the approximate stratigraphic up direction (based on stromatolite morphology) and the scale bar at the bottom is approximately the same for all images.
Fig. 4. Petrographic textures of microbialites in plane polarised (pp) and cross polarised light (cp). A-B) A turbinate stromatolite preserved in chert with outsized quartz grains at its base; C-D) turbinate-multifurcate stromatolite with a millimetre-size bulbous shape, preserved in chert, the surrounding matrix consists of sparry carbonate, chert and isopachous quartz; E-F) chert lenses of a domal stromatolite in a micritic carbonate matrix; GH) sparry carbonate cutting across the micritic matrix and wrinkly layers; I-J) chert matrix with isopachous quartz, coarse-grained carbonate, a chert vein and microscopic coccoid-like structures. The red numbered squares correspond to the relevant figures.
Fig. 4. Petrographic textures of microbialites in plane polarised (pp) and cross polarised light (cp). A-B) A turbinate stromatolite preserved in chert with outsized quartz grains at its base; C-D) turbinate-multifurcate stromatolite with a millimetre-size bulbous shape, preserved in chert, the surrounding matrix consists of sparry carbonate, chert and isopachous quartz; E-F) chert lenses of a domal stromatolite in a micritic carbonate matrix; GH) sparry carbonate cutting across the micritic matrix and wrinkly layers; I-J) chert matrix with isopachous quartz, coarse-grained carbonate, a chert vein and microscopic coccoid-like structures. The red numbered squares correspond to the relevant figures.
Fig. 5. Morphologically distinct filamentous microfossils and fluid inclusions in the McLeary Formation. A) The locations of inclusions in a quartz crystal, the red arrows indicate fluid inclusions, the inset shows the same crystal in cross polarised light and indicates that it is a single crystal; B-D) filamentous microfossils composed of pyrite and kerogen; E) a fluid inclusion containing CO2 and CH; F) Raman spectra for the corresponding structures in the outsized quartz crystal; G) filamentous microfossils in transmitted light; H) Raman image shows that the filaments in G) are composed of kerogen (red) and quartz (blue); I) magnified image of the filaments; J-K) coiled filamentous microfossil composed of dense kerogen nanoscopic particles.
Fig. 5. Morphologically distinct filamentous microfossils and fluid inclusions in the McLeary Formation. A) The locations of inclusions in a quartz crystal, the red arrows indicate fluid inclusions, the inset shows the same crystal in cross polarised light and indicates that it is a single crystal; B-D) filamentous microfossils composed of pyrite and kerogen; E) a fluid inclusion containing CO2 and CH; F) Raman spectra for the corresponding structures in the outsized quartz crystal; G) filamentous microfossils in transmitted light; H) Raman image shows that the filaments in G) are composed of kerogen (red) and quartz (blue); I) magnified image of the filaments; J-K) coiled filamentous microfossil composed of dense kerogen nanoscopic particles.
Table 3
Table 3
Fig. 6. Granules of quartz and carbonate. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A-B) Chert granules with dark rims, one has isopachous quartz at its centre but the others are composed of just chert; C-D) a granule that contains quartz, feldspar, rutile (circled in yellow) and kerogen: E) Raman spectra for this figure; F) dark sub-ellipsoidal to elongate micritic carbonate granules within a lighter-coloured micritic carbonate matrix; G) irregular- shaped micritic carbonate granule in a sparry carbonate matrix; H) Raman image for the square inset in G) showing a mixture of microscopic inclusions of kerogen, feldspar (coloured white) and quartz in dolomite (with variable peak intensity), the orange dashed line shows the boundary between the granule and the matrix.
Fig. 6. Granules of quartz and carbonate. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A-B) Chert granules with dark rims, one has isopachous quartz at its centre but the others are composed of just chert; C-D) a granule that contains quartz, feldspar, rutile (circled in yellow) and kerogen: E) Raman spectra for this figure; F) dark sub-ellipsoidal to elongate micritic carbonate granules within a lighter-coloured micritic carbonate matrix; G) irregular- shaped micritic carbonate granule in a sparry carbonate matrix; H) Raman image for the square inset in G) showing a mixture of microscopic inclusions of kerogen, feldspar (coloured white) and quartz in dolomite (with variable peak intensity), the orange dashed line shows the boundary between the granule and the matrix.
Fig. 7. Photomicrographs and Raman maps showing the petrography of organic matter. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A-B) Kerogen, quartz and carbonate within turbinate stromatolite laminations; C-D) microscopic turbinate-multifurcate stromatolite from Fig. 4C with apatite (circled in blue); E-F) kerogen-rich microscopic coccoid-like structures in chert; G) Raman spectra for this figure.
Fig. 7. Photomicrographs and Raman maps showing the petrography of organic matter. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A-B) Kerogen, quartz and carbonate within turbinate stromatolite laminations; C-D) microscopic turbinate-multifurcate stromatolite from Fig. 4C with apatite (circled in blue); E-F) kerogen-rich microscopic coccoid-like structures in chert; G) Raman spectra for this figure.
Fig. 8. Diagenetic mineral structures in microbial mats. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A-B) Kerogen-ricl coccoid-like structures surrounded by layers of kerogen, quartz, and carbonate; C-E) concentric laminations that contain grains of carbonate (circled in green) anc rutile (circled in yellow), and are surrounded by kerogen-rich coccoid-like structures (circled in red); F) Raman spectra for this figure with the most intense peaks fo carbonate spectra circled in red; G-H) carbonate rhomb in chert with a dark core; I-J) carbonate rosettes with concentric layers of kerogen which become pro gressively denser toward the cores, they contain two different carbonate spectra with variably intense peaks at 301 cm~ (dark green, towards the centre) and 1101 cm! (light green at the edges), respectively.
Fig. 8. Diagenetic mineral structures in microbial mats. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A-B) Kerogen-ricl coccoid-like structures surrounded by layers of kerogen, quartz, and carbonate; C-E) concentric laminations that contain grains of carbonate (circled in green) anc rutile (circled in yellow), and are surrounded by kerogen-rich coccoid-like structures (circled in red); F) Raman spectra for this figure with the most intense peaks fo carbonate spectra circled in red; G-H) carbonate rhomb in chert with a dark core; I-J) carbonate rosettes with concentric layers of kerogen which become pro gressively denser toward the cores, they contain two different carbonate spectra with variably intense peaks at 301 cm~ (dark green, towards the centre) and 1101 cm! (light green at the edges), respectively.
Fig. 9. Pyrite in McLeary Formation stromatolites. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A) A pyrite-rich concretior about 8 mm in length; B) higher magnification of A) shows that the concretion contains several pyrite framboids in micrite as well as disseminated quartz visible a: clear crystals; C) high magnification of a pyrite framboid in reflected light showing that it is composed of several microscopic pyrite euhedral crystals; D) pyrite-ricl layers in micritic carbonate; E) Two pyrite crystals in close proximity to a stylolite; F) a stylolite with several pyrite crystals along its length (a few are highlightec with black circles); G) the inset in F); H) a micro-Raman image of G); I) Raman spectra for this figure.
Fig. 9. Pyrite in McLeary Formation stromatolites. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A) A pyrite-rich concretior about 8 mm in length; B) higher magnification of A) shows that the concretion contains several pyrite framboids in micrite as well as disseminated quartz visible a: clear crystals; C) high magnification of a pyrite framboid in reflected light showing that it is composed of several microscopic pyrite euhedral crystals; D) pyrite-ricl layers in micritic carbonate; E) Two pyrite crystals in close proximity to a stylolite; F) a stylolite with several pyrite crystals along its length (a few are highlightec with black circles); G) the inset in F); H) a micro-Raman image of G); I) Raman spectra for this figure.
Fig. 10. Accessory minerals in carbonate matrix. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A) Backscattered image of SEM showing small grains of rutile and fluorapatite and a larger grain of microcline within micritic dolomite; B) SEM spectra for the map A) (the unlabelled peaks around 2 keV were produced by the gold coating on the thin section); C—D) part of a stylolite that contains various minerals; E) Raman spectra for this figure; F—I) photomicrographs of rutile needles.
Fig. 10. Accessory minerals in carbonate matrix. The colours in the hyperspectral maps correspond to the colours in the Raman spectra. A) Backscattered image of SEM showing small grains of rutile and fluorapatite and a larger grain of microcline within micritic dolomite; B) SEM spectra for the map A) (the unlabelled peaks around 2 keV were produced by the gold coating on the thin section); C—D) part of a stylolite that contains various minerals; E) Raman spectra for this figure; F—I) photomicrographs of rutile needles.
Related topics:
Organic GeochemistryPetrography and DiagenesisMicrobial Carbonates
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved