Syntaxial Overgrowths in Muddy Crinoidal Limestones: Cathodoluminescence Sheds New Light on an Old Problem
- Maurice E. Tucker2 and
- Robin G. C. Bathurst3
Published Online: 29 APR 2009
Copyright © 1990 The International Association of Sedimentologists
How to Cite
Walkden, G. M. and Berry, J. R. (1990) Syntaxial Overgrowths in Muddy Crinoidal Limestones: Cathodoluminescence Sheds New Light on an Old Problem, in Carbonate Diagenesis (eds M. E. Tucker and R. G. C. Bathurst), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304510.ch18
Department of Geological Sciences, University of Durham, UK
Derwen Deg Fawr, Llanfair DC, Ruthin, Clwyd, North Wales, UK
- Published Online: 29 APR 2009
- Published Print: 21 AUG 1990
Print ISBN: 9780632029389
Online ISBN: 9781444304510
- syntaxial overgrowths in muddy crinoidal limestones - cathodoluminescence sheds new light;
- Lower Carboniferous shallow water limestones of Asbian and Brigantian age, containing abundant interparticle micrite;
- high-Mg calcite stabilization;
- neomorphic replacements;
- cyclic subaerial emergence
Lower Carboniferous shallow water limestones of Asbian and Brigantian age in Britain commonly contain abundant interparticle micrite and characteristically display large syntaxial calcite overgrowths on crinoid and echinoid grains. These overgrowths appear to have developed at the expense of the micrite and are widely regarded as neomorphic replacements. However, cathodoluminescence of these has revealed growth features which indicate that they are not neomorphic but originated as passive cement fills of solution voids surrounding echinoderm grains.
We introduce the term solution corona for these grain selective voids and consider that three processes may have contributed to their development, namely: high-Mg calcite stabilization of host grains, crystal ripening, and meteoric dissolution. Cyclic subaerial emergence was a critical factor in these processes, and we contrast the morphology of the overgrowths in question with forms produced in basinal limestones which never experienced comparable early meteoric conditions.
These early-formed solution coronas around echinoderm grains are therefore a useful indicator of meteoric diagenesis and have important implications for porosity evolution. The syntaxial cements which fill the solution coronas show distinct phases of growth in cathodoluminescence which reflect a progression from near-surface meteoric conditions to deep burial with pressure solution.