Stable Isotope Signatures of Middle Palaeozoic Ahermatypic Rugose Corals – Deciphering Secondary Alteration, Vital Fractionation Effects, and Palaeoecological Implications
Fig 3
Micro- and ultrastructure of the studied coral specimens.
A-F: Microcyclus praecox, upper Eifelian, Holy Cross Mountains (Poland), UAM Tc/B/SK/20. A-B. Transmitted-light photomicrographs showing clearly distribution of septa (with 'dark lines' representing former centres of calcification; arrows) and fibrous interseptal stereome (ST). C. Close-up of a former centre of calcification (COC); note the presence of microspar to small-spar crystal mosaic (MS) cutting across the primary structural elements. D. CL view; note clear difference in the luminescence pattern between lower (dully luminescent, DL) and uppermost (red- to orange-luminescent, RL) parts of the corallite. Location of former centres of calcification is underlined by their bright luminescence (arrows). E-F. SEM photomicrographs of former centres of calcification (COC, arrows). G-L: Microcyclus roberti, lower Givetian, Madène el Mrakib (Morocco), UAM Tc/B/MM/01. G-H. Transmitted-light views showing traces of the original skeletal elements mostly preserved as ghosts within the irregular calcite crystal mosaic. Former centres of calcification (cut diagonally) with recognizable thickening deposits of fibrous stereome (ST) are indicated with arrows. I-J. CL patterns with distinct luminescence responses of a central, relatively well-preserved portion of the corallite (non-luminescent, NL), alteration rims surrounding the original skeleton, as well as diagenetic cement encrusting the corallite surface (both red-luminescent, RL; see a lower right part of G for a transmitted-light view of I). K-L. SEM photomicrographs illustrating a well-defined former centre of calcification (COC, arrows) with still recognizable original fibrous texture of interseptal stereome (ST).