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Estimation of the durations of breaks in deposition – Speleothem case study

Pawlak J., Hercman H., Sierpień P., Pruner P., Gąsiorowski M., Mihevc A., Zupan Hajna N., Bosák P., Błaszczyk M., Wach B.

Geochronometria

2020

Vol. 47, no.1

154--170

Speleothems provide one of the most continuous terrestrial archives. However, due to changing conditions in temperature/humidity or the chemistry of percolating water, sedimentation breaks (hiatuses) and erosional events are possible and are commonly recorded in speleothems. Sedimentation breaks with durations longer than the resolution of the studied record should be considered in potential speleothem age-depth models. The most classic and reliable solution to the problem is the independent construction of age-depth models for the parts of speleothems separated by the hiatuses. However, in some cases, it is not possible to obtain a sufficient number of dating results for reliable age-depth model estimation. In such cases, the problem can be solved by the application of other sources of chronological information. Here, based on a few speleothem examples, an alternative approach – oxygen isotopic stratigraphy – is used to estimate the chronology for the parts of speleothems where there is not enough chronological information for classic age-depth models. As a result, the deposition break duration can be estimated.

230Th-excess and 14C dating of pelagic sediments from the hydrothermal zone of the North Atlantic

Kuznetsov V. Yu., Arslanov K. A., Shilov V. V., Cherkashev G. A., Chernov S. B.

Geochronometria

2002

Vol. 21

33-40

A comprehensive geochronological study of a pelagic sediment core altered by hydrothermal processes from the Mid Atlantic Ridge (14.5°N) was carried out using both the 230Thexcess and the radiocarbon methods. Complementary foraminiferal tests and oxygen-isotope determinations were done. The main task was to check whether 230Thexcess dating of such diagenetically changed sediments yields reliable absolute ages. For this purpose the vertical distribution of the 238U, 234U, 232Th and 230Th activities along the core was measured. The results proved that it was not disturbed during the aging of the sediment. The long-term hydrothermal influence had been constant during at least the last 300 ka and did not change the natural 230Thexcess distribution along the core. Hence, 230Thexcess dating yields reliable ages and allows to calculate sedimentation rate. Between the uppermost and lowermost sublayers of the core we obtained 1.35š0.15 cm/ka which agrees with 1.47š0.03 cm/ka derived from conventional 14C ages. These numerical dates, the results of the foraminiferal tests and the d18O values place the studied sediments to the marine isotope stage 5 (MIS 5). These dates are well correlated with the corresponding sedimentary records from pelagic sediments of the North Atlantic Ocean.