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Models of rock varnish formation constrained by high resolution transmission electron microscopy
Author(s) -
KRINSLEY D.
Publication year - 1998
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1046/j.1365-3091.1998.00172.x
Subject(s) - varnish , geology , clay minerals , mineralogy , sedimentary rock , manganese , calcite , transmission electron microscopy , geochemistry , materials science , metallurgy , composite material , nanotechnology , coating
Nanometre‐scale transmission electron microscope imagery of manganiferous rock varnishes from Death Valley, California, Peru, Antarctica, and Hawaii confirms prior infrared mineralogy studies. The building blocks of rock varnish are clay minerals that are cemented to the rock by oxyhydroxides of manganese and iron. Rock varnish is layered on the scale of nanometres, with the basic structure defined by the subparallel alignment of detrital clay minerals. Although only a few examples of bacteria were found, possible cell‐wall encrustations are ubiquitous and aligned with the clay minerals. Mn–Fe oxides appear to be mobilized from bacterial casts and then reprecipitate on clay minerals that weather into monolayers. These observations have implications for varnish dating and palaeoenvironmental techniques: K–Ar and uranium‐series dating of rock‐varnish oxides can only yield minimum ages; however, this small spatial scale of mobilization would not alter the signal from micron‐scale microchemical laminations.