Microbioerosion - Trace Fossils as Indicators of Sedimentary Environments - page 211

A B C D E

fossil

Vacuum

70 ° C

Ultrasonic bath

recent

F G H I I J

SEM

~1 h

SEM

~30 s

FIGURE 2 Schematic sketch illustrating the vacuum cast-embedding technique. (A) The bored
calcareous substrate, either fossil with partial sediment fill or recent with microendoliths and bio-
films. (B) Removal of sediment or organic material by treatment with tensides and/or hydrogen per-
oxide. (C) Cleaning in an ultrasonic bath. (D) Drying at 70 C. (E) Infill with epoxy resin under
vacuum conditions. (F) Curing for 24 h. (G) Formatting of blocks for surface SEM and cross-section
SEM with a rock saw. (H) Removal of calcareous substrate via treatment with diluted hydrochloric
acid. (I) Rinsing with distilled water. (J) SEM visualization after drying and sputter-coating
with gold.

low-viscosity epoxy resin (e.g., Ciba-Geigy: Araldite BY158 Aradur 21)

while the samples are held under vacuum. In this way, a complete infiltration
of the borings is assured while trapping of air is avoided. After curing, the sam-
ples are formatted with a rock saw, decalcified by a treatment with diluted HCl
(

þ

5%), rinsed in distilled and filtered water, and dried. The samples—now
exhibiting the positive casts of the borings—are then mounted on aluminum
stubs before gold sputter-coating and SEM analysis.
In order to prevent delicate casts from collapsing and to aid the recognition of
the actual penetration depth of the traces, a complemental procedure is to prepare
sample cross sections that are only partially etched (

5% HCl),
allowing a visualization of the traces in context of the shell or rock matrix.

10-30 s with