Details

Autor(en) / Beteiligte

• Friedman, Gerald M.

Titel

Beachrocks record Holocene events, including natural disasters

Ist Teil von

• Carbonates and evaporites, 2011-07, Vol.26 (2), p.97-109

Ort / Verlag

Berlin/Heidelberg: Springer-Verlag

Erscheinungsjahr

2011

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Rocks that form by cementation of sediments in intertidal parts of beaches are known as beachrocks. Modern beachrocks are restricted to warm climatic belts between latitudes 35EN and 35ES. Pottery fragments and debris from humans (including World War II relics such as shell casings) affirm that cementation in the rocks is still occurring today. The rate of cementation of sedimentary particles into beachrocks is very rapid. The cement between the particles may include aragonite, high-magnesian calcite, and/or low-magnesian calcite. All beachrocks sampled worldwide, except samples from Java, Indonesia, and Bardawil (Pelusium, Nile Delta), Egypt, have similar δ 13 C and δ 18 O signatures ranging from +0.1 to +5.2 and from +2.2 to −3.5, respectively. By contrast, beachrock from Java produced δ 13 C‰PDB −18.0 and δ 18 O‰PDB −14.8, and from Bardawil (Pelusium, Nile Delta) δ 13 C‰PDB −39.3 to −3.3 and δ 18 O‰PDB 3.8 to −36.6. The Krakatoa explosion on Java in Indonesia of August 27, 1883 has been designated as “the day the world exploded,” and was involved in its beachrock formation. The carbonate beachrock samples of dolomite from Bardawil yielded anomalous negative δ 13 C values that suggest the carbon was derived from methane, which had formed at the expense of original gypsum and dolomite. Bacteria converted methane to CO 2 , thus making isotopically light bicarbonate available for precipitation. The timing (3,300–3,500  bp ) appears to be related to the Exodus event as described in Jewish tradition.