Shallow-Marine Carbonates - Trace Fossils as Indicators of Sedimentary Environments - page 684

TABLE 1 Relevant Differences Between Carbonates and Siliciclastics
with Respect to Formation and Preservation of Trace Fossils. Modified
from Curran (1994)

Carbonates Siliciclastics

Infaunal
distribution

1. Favored trace fossils (e.g.,
crustacean burrows, Thalassinoides,
Ophiomorpha, Psilonichnus,
Macanopsis, and Pholeus) due to
preferential occurrence of various
benthic organisms in tropical and
subtropical zones where shallow-
marine carbonate environments
dominate.

A wide range of ichnotaxa
commonly occurs.

2. Carbonate platforms and ramps
comprise broad and very shallow
facies belts, often with restricted
environments that are favorable for
intense bioturbation.

Differentiated depositional
systems with relatively small
facies belts, heterogeneous
bioturbation patterns, and intense
bioturbation in offshore
sediments.

3. Given their very low-gradient,
carbonate platforms are commonly
subject to wide-ranging subaerial
exposure, resulting in the
development of peritidal
ichnofauna and trace fossils formed
by plant roots (rhizomorphs or
rhizoliths) and prostrate stems.

Rhizomorphs (rhizoliths) can
occur, but are not nearly so
common.

Nature of
sediment

4. Bioerosion is common and
related to reefs, bioherms,
biostromes, and reworked skeletal
components.

Bioerosion is subordinate because
organic buildups are much less
dominant, and relatively few
organisms bioerode
non-carbonates.

5. Borings driven by chemical
means dominate (Trypanites,
Entobia).

Borings with a mechanical or
combined mechanical/chemical
method occur.

6. Hardgrounds and firmgrounds
common and form rapidly, both
have significant degrees and
diversity of borer and burrower
forms of the Glossifungites and
Trypanites ichnofacies.

Hardgrounds rare, firmgrounds
less common.

7. Preferential preservation of trace
fossils (including fecal pellets) due
to fine-grained lime mud in
combination with microbial mats,

Delicate traces or parts of them are
rarely well preserved due to the
clastic nature of sediment,
reworking, compaction, and
late-diagenetic cementation.