Polished stone: thinly laminated limestone - #2
The vertical plane of view shown here is perpendicular to the layering (lamination), providing a cross-sectional view of this sedimentary rock; my fingertips provide scale here. Note the small-scale folding of the layering, and at lower right a vertical crack has been infilled with coarse sediment. (The term "limestone" is used loosely; if this carbonate rock is Mg-rich, it would be classed as dolomite or dolostone.)
Sandy layers and tiny lenses are present, with some alternation of coarser (sandy) and finer (muddy) laminae. The finer-grained laminae (carbonate mud) may have had a biological origin: e.g., as cryptalgal laminites, more recently known as microbial laminites, that formed stromatolitic layering on a tidal flat. The folding, upward arching of the lamination, could be accounted for as desiccation (drying) and slight curling of thin 'bundles' of laminae, with some vertical cracks (desiccation cracks; in plan view, these would be at the margins of desiccation polygons, a.k.a. 'mudcracks') disrupting the lateral continuity of some bundles of laminae (as can be seen at a few sites in the photo).
C. J.R. Devaney
Polished stone: thinly laminated limestone - #2
The vertical plane of view shown here is perpendicular to the layering (lamination), providing a cross-sectional view of this sedimentary rock; my fingertips provide scale here. Note the small-scale folding of the layering, and at lower right a vertical crack has been infilled with coarse sediment. (The term "limestone" is used loosely; if this carbonate rock is Mg-rich, it would be classed as dolomite or dolostone.)
Sandy layers and tiny lenses are present, with some alternation of coarser (sandy) and finer (muddy) laminae. The finer-grained laminae (carbonate mud) may have had a biological origin: e.g., as cryptalgal laminites, more recently known as microbial laminites, that formed stromatolitic layering on a tidal flat. The folding, upward arching of the lamination, could be accounted for as desiccation (drying) and slight curling of thin 'bundles' of laminae, with some vertical cracks (desiccation cracks; in plan view, these would be at the margins of desiccation polygons, a.k.a. 'mudcracks') disrupting the lateral continuity of some bundles of laminae (as can be seen at a few sites in the photo).
C. J.R. Devaney