Siliciclastic facies |
Green to yellowish sandstone |
Lithofacies predominant in the east, in the region of Cedro do Abaeté (Lima et al. 2007). Green to yellowish (when weathered) beds of 5 cm to 2 m-thick, with a fine to medium-grained sandy base and a silt-mud top. Planar, wavy, and truncated lamination. Locally, hummocky cross-stratification with low angle truncated surfaces and wavelengths between 1 to 2 m. |
Deposited by the action of proximal storm waves on a marine shelf. |
Siltstone |
Gray to beige, massive or laminated, coarse- to fine-grained siltstone locally interbedded with calciferous siltstone. |
Fine-grained sediment deposited by weak traction currents or settling in a marine shelf environment. |
Mud-silt-sand rhythmite |
Laminated rhythmites with varying proportions of mud, silt, and fine sand grains. May be intercalated with beds of fine-grained sandstone. It typically weathers to a reddish brown due to the presence of iron oxides and hydroxides. Load casts and flame structures are common. |
Sand-silt-clayey sediment transported and deposited by weak or distal storm waves in marine environment. |
Green and glauconitic siltstones |
Massive or laminated, medium to coarse grained green siltstone, occurring locally with truncated laminations. It shows grains of glauconite, subangular to subrounded grains of quartz and K-feldspar, clay minerals, detritic micas, opaques, and iron hydroxides. When glauconite content is greater than 40%, as predominant in the west, in the region of Matutina and Funchal, it is classified as glauconitic siltstone. |
Deposited by the action of distal storm waves on a marine shelf. |
Phosphatic facies |
Phosphatic rhythmite |
Phosphatic sand-silt-clay rhythmites showing dark gray or brown laminae (with manganese oxides) interbedded with light gray laminae. The light gray laminae are composed of phosphate intraclasts in a microcrystalline grained matrix rich in fluorapatite, colophane, quartz, feldspar, muscovite, chlorite, and calcite (Lima et al. 2007). |
The genesis of the phosphorite likely occurred due to marine transgression and upwelling on the marine shelf. A later regression reworked the primary phosphorite by waves and storm currents on the continental shelf (Lima et al. 2007). |
Carbonate facies |
Reworked carbonate |
Dark gray and fine-grained grainstone and intraformational breccia (rudstone), with angular to subangular intraclasts. |
Formed by the action of waves and currents on a shallow continental shelf. |
Microbial laminite |
Dark gray microbial laminite, occasionally phosphatic, showing typical crenulated and irregular laminations. |
Biogenic carbonate formed by cyanobacteria and other microbial lineages in a shallow marine environment. |
Black organic-matter-rich micritic limestone |
Black organic-matter-rich micritic limestone and light gray ooid grainstone highly fractured. |
Related to high organic matter burial in an inner to outer shelf environmental. |
Volcaniclastic facies |
Volcaniclastic rocks |
Clay-rich, whitish to greenish, 0.5 m-thick layer composed of angular quartz, muscovite, illite, kaolinite, euhedral and rounded zircon grains and a few glauconite aggregates. |
Sedimentation of volcanic ashes and resedimented volcanic material in marine shelf. |
Whitish to greenish, very friable, containing vesicular cavities and a porous matrix. |