--> Abstract: From Skeletal Needles To Micrite, Part 2: Post-Mortem Recrystallization In Calcareous Green Algae And Porcelaneous Foraminifera In Shallow Marine Sediments, by R. P. Reid and I. G. Macintyre; #90928 (1999).

Datapages, Inc.Print this page

REID, R. PAMELA1 and IAN G. MACINTYRE2
1RSMAS, University of Miami, Miami, FL
2Smithsonian Institution, Washington D.C.

Abstract: From Skeletal Needles to Micrite, Part 2: Post-Mortem Recrystallization in Calcareous Green Algae and Porcelaneous Foraminifera in Shallow Marine Sediments

Skeletal recrystallization in the calcareous green alga Halimeda and the porcelaneous foraminifer Archaias, which begins in live organisms, continues as a post-mortem process on the shallow sea floor. As in live Archaias, skeletal rods in dead foraminifera break down to granular minimicrite (< 1 µm). This minimicrite may, in turn, recrystallize to pseudomicrite, a mosaic of very small equant crystallites (0.02-0.05 µm), which are typically aligned in radial or blocky patterns. Minimicrite and pseudomicrite also recrystallize to blocky micrite (1-4 µm). Processes of postmortem recrystallization in Halimeda are similar to those in Archaias, but also involve the growth of skeletal needles to form blocky micritic textures. Textural alteration of crystals from minimicrite to pseudomicrite or micrite may involve changes in mineralogy from Mg-calcite to aragonite or from aragonite to Mg-calcite.

Progressive recrystallization in Halimeda and Archaias results in gradual micritization. Concomitant with the formation of pseudomicrite and micrite, the golden brown color characteristic of live and recently dead specimens, as seen in plane polarized light, is progressively replaced by gray cryptocrystalline textures. Our detailed studies of this micritization process indicate that the widely held concept that micritization results solely by the infilling of microborings is an oversimplification of a complex process that often involves recrystallization. Our studies further indicate that carbonate recrystallization is not restricted to the realms of vadose and burial diagenesis, but is a widespread early diagenetic process in shallow tropical seas throughout the world. Reasons for early textural and mineralogical crystal alteration are largely unknown, but are clearly not related to mineralogical stabilization to low Mgcalcite, a commonly cited driving force for recrystallization.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas