The Weissert Event, also referred to as the Weissert Thermal Excursion (WTX), was a hyperthermal event that occurred in the

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 137.05 ± 0.2 Ma and 132.6 ± 0.2 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

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of the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

epoch. This thermal excursion occurred amidst the relatively cool Tithonian-early Barremian Cool Interval (TEBCI). Its termination marked an intense cooling event, potentially even an

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

Duration

The start of the WTX has been astrochronologically dated by one study to 134.50 ± 0.19 million years ago (Ma), with its positive δ¹³C excursion being found to last until 133.96 ± 0.19 Ma and the plateau phase of elevated δ¹³C values until 132.44 ± 0.19 Ma. However, astrochronological studies of sediments in the Vocontian Basin have yielded a duration of 2.08 Myr, with the positive δ¹³C excursion being 0.94 Myr in duration and the δ¹³C plateau being 1.14 Myr. A different study concludes the WTX lasted for about 1.4 million years (Myr) based on the chronological length of the high δ¹³C plateau observed over its course in the Bersek Marl Formation of

Hungary Hungary is a landlocked country in Central Europe. Spanning much of the Pannonian Basin, Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia and ...

Causes

An addition of carbon dioxide into the atmosphere via the activity of the Paraná-Etendeka Large Igneous Province (PE-LIP) is generally accepted as the leading candidate for what sparked the WTX, although this is not universally accepted, with some reconstructed geochronologies showing a lack of causality between the emplacement of the PE-LIP and the onset of the WTX. The prolonged, drawn out manner in which the PE-LIP erupted has been brought up as a further argument against its emplacement as the driving perturbation causing the WTX.

Effects

The WTX resulted in a rapid global temperature increase during the otherwise mild TEBCI. The sharp jump in global temperatures during this hyperthermal event was accompanied by oceanic anoxia. However, unlike other oceanic anoxic events, the WTX is not associated with widespread

black shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g., kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...

deposits. Nannoconids experienced a decline at the onset of the WTX resulting from

marine regression A marine regression is a geological process occurring when areas of submerged seafloor are exposed during a drop in sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously-exposed land. Descript ...

, but bloomed in abundance later on in the event as ocean productivity skyrocketed. In the Vocontian Basin, the WTX is associated with an increase in marlstones. At the end of the WTX, temperatures cooled by ~1–2 °C based on the results of palaeothermometry done in southern France, whereas the Boreal Ocean and its surroundings cooled by as much as 4 °C. Geochemical records of ¹⁸⁷Os/¹⁸⁸Os point to an increase in unradiogenic osmium flux into the ocean, suggesting the occurrence of

silicate weathering A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used for ...

of PE-LIP basalts during this slice of time, providing the most likely explanation for the temperature drop. Some studies have suggested that a transient ice age with limited but significant

polar ice caps A polar ice cap or polar cap is a high-latitude region of a planet, dwarf planet, or natural satellite that is covered in ice. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor a ...

occurred in the aftermath of the WTX, although the lack of a positive δ¹⁸O_seawater excursion during the latest Valanginian interval of cooling and the presence instead of a very slightly negative excursion calls into question the existence of any significant polar ice growth.

References

Anoxic events Valanginian Stage {{improve categories, date=November 2023