Geology Reference
In-Depth Information
Fig. 9.14.
Fossil record of micro- and macroborers and sub-
strate
excavating grazers destroying carbonate skeletons and
lithified substrates. The fossil record of boring organisms can
be estimated through trace fossils. In many cases a reason-
able delineation of the responsible group or borer is possible,
but often the assignment of the trace fossils remains contro-
versial. The range chart summarizes borings in different set-
tings (reefs, hardgrounds). In addition, the presence of drill
holes in marine invertebrate shells attacked by predators
(mainly gastropods) is indicated. Black columns refer to times
where the group contributed greatly to bioerosional processes;
open columns refer to times with a less significant influence
of borers. Note that the columns also include time intervals
with no or questionable records. Based on Kobluk et al.
(1978), Vogel (1993), Kowalewski et al. (1998), Perry and
Bertling (2000) and other sources.
MICROBORERS MACROBORERS
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
possibly indicating a parallel evolution of Triassic reef-
building corals and macroborers (Perry and Bertling
2000). Norian and Rhaetian reefs were attacked by bi-
valves; sponge boring activity increased in the Rha-
etian. The contribution of macroborers to bioerosion
increased strongly during the Jurassic (Leinfelder et al.
2002). In the Liassic bivalves became the dominant
group. Middle and Late Jurassic reefs suffered from
boring sponges, bivalves and worms. Boring gastro-
organisms, and remained similar during the Mesozoic
and Cenozoic (Schmidt 1992; Balog 1996; Vogel et al.
1999). No macroborers are known from Early Triassic
carbonate platforms. Anisian macroborers are bivalves
and cirripedians. Macroborer diversity and abundance
increased significantly in Norian and Rhaetian reefs,
Fig. 9.15.
Impact of micro- and macroborings on reefs
through time: The graph is based on the Erlangen PaleoReef Database
(see Kiessling and Flügel 2002). Bioerosion was low to moderate in Paleozoic reefs, increased significantly during the
Triassic, and maintained high but fluctuating levels from the Jurassic to the Recent. The Mesozoic increase may be explained
by the coeval diversification of predators. Caution should be exercised when using the graph: The Early Triassic decline is
caused by the single occurrence and rare records of microbial reefs, and the complete lack of metazoan reefs. These microbial
reefs were not attacked by microborers; macroborers were not described. Grazers were abundant, as indicated by common
herbivorous gastropods. The decline of microborers in the Middle Jurassic was probably caused by the low number of reefs
in the database. Similarly, the decline in the Paleogene may be due to bias caused by the lack of sufficient data.
