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Oliver Lehnert

Publications and source records attributed to Oliver Lehnert.

2 recordsLinked to original sources

Did intense volcanism trigger the first Late Ordovician icehouse? REPLY

We appreciate the Comment by Herrmann et al. (2011) to our paper (Buggisch et al., 2010). When we compiled the data set for our publication, we were aware that we had not enough pre-Deicke conodont oxygen isotope data because Webers’ (1966) conodont collections from the Pecatonica Member did not yield enough specimens for isotope analysis. At that time, the recently published data of Herrmann et al. (2010) were not available for comparison. Therefore, we imported data of Herrmann et al. (2005), who reported δ 18 O values from 18.1‰ to 19.1‰ (VSMOW) for conodont samples from Minnesota and Missouri. According to Herrmann et al. (2005, p. 457), “The samples were all collected from limestone beds immediately below the widespread Deicke K-bentonite.”

Geology

Did intense volcanism trigger the first Late Ordovician icehouse?

Oxygen isotopes measured on Late Ordovician conodonts from Minnesota and Kentucky (United States) were studied to reconstruct the paleotemperature history during late Sandbian to Katian (Mohawkian–Cincinnatian) time. This time interval was characterized by intense volcanism, as shown by the prominent Deicke, Millbrig, and other K-bentonite beds. A prominent carbon isotope excursion (Guttenberg δ 13 C excursion, GICE) postdates the Millbrig volcanic eruptions, and has been interpreted to reflect a drawdown of atmospheric carbon dioxide and climatic cooling. The oxygen isotope record in conodont apatite contradicts this earlier interpretation. An increase in δ 18 O of 1.5‰ (Vienna standard mean ocean water) just above the Deicke K-bentonite suggests an abrupt and short-lived cooling that possibly initiated a first short-term glacial episode well before the major Hirnantian glaciation. The decrease in δ 18 O immediately after the mega-eruptions indicates warming before the GICE, and no cooling is shown in the GICE interval. The coincidence of the Deicke mega-eruption with a cooling event suggests that this major volcanic event had a profound effect on Late Ordovician (late Mohawkian) climate.

Geology