RIGGS, STANLEY R., and SCOTT W. SNYDER
Department of Geology, East Carolina University, Greenville, NC 27858
Abstract: Macrobenthic Bioerosional Processes and Morphological Succession on Continental Shelf Carbonate Hardbottoms
Bioeroders degrade carbonate hardbottoms,
sculpting morphological features that range from millimeters to tens of
meters in scale. These features evolve from flat freshly broken hardbottom
surfaces (young) to more irregular surfaces with increased relief and surface
area that support a greater diversity and abundance of benthic
bioeroders
(mature). Composition of this
benthic
community is determined by lithology
and latitude. Lithology determines rates, scales, and mechanisms of morphological
evolution. Well indurated lithologies on sloped surfaces support a diverse
endolithic infauna and epilithic fauna and flora. Because of high rates
of bioerosion, weakly to moderately indurated lithologies on sloped surfaces
support a less diverse endolithic infauna and only minor epilithic fauna
and flora. Mobil epibenthos and nekton accentuate the rate of degradation.
Well indurated flat hardbottoms, often covered with thin (<5 cm) ephemeral
sands, are colonized largely by epifloral macroalgae which chemically degrade
and pluck carbonate to initiate development of 3-D morphology that increases
surface area and species diversity. Increased relief exposes more sloped
surfaces above the sand and provides habitat for infaunal borers. In temperate
conditions, bioeroders produce 'new' sediment to the modern regime at minimum
rates ranging from 0.03 kg/m2/yr on highly lithified flat hardbottoms
to 0.4 kg/m2/yr on moderately lithified sloped surfaces to 5.5
kg/m2/yr on soft mudstone sloped surfaces with scarp recession
rates of 2-4 cm/yr. Comparison of carbonate hardbottoms in the mid-latitude
North Atlantic with high latitude Kattegat Sea reveals differing
benthic
community compositions but similar morphological successions.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas