Research ArticlePALEONTOLOGY

UV-B radiation was the Devonian-Carboniferous boundary terrestrial extinction kill mechanism

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Science Advances  27 May 2020:
Vol. 6, no. 22, eaba0768
DOI: 10.1126/sciadv.aba0768
  • Fig. 1 A deep (left) to shallow water (right) lake transect through the D-C boundary in East Greenland.

    As the lower lake flooded (Stensiö Bjerg), spore diversity increased (LN* zone) until recovery was lost in the high-TOC AOM-rich interval. The upper lake contains VI spores of earliest Carboniferous in age. The LN* to VI spore zone correlates the lower lake to the more proximal locations on Celsius Bjerg and Rebild Bakker. At Rebild Bakker, the lower lake contains high numbers of malformed and dark-colored VI zone spores of earliest Carboniferous age. The high Hg content at Stensiö Bjerg is coincident with both a high TOC and AOM content. However, when normalized as Hg/TOC, there is no anomaly characteristic of a large igneous province (LIP) eruption. This level is coincident with the malformed spores at Rebild Bakker, where, in the absence of AOM, Hg content is low again, indicating that there was no LIP. Analytical data are presented in table S1. mdst, mudstone; sndst, sandstone; m, medium sandstone; c, coarse sandstone.

  • Fig. 2 Abundance, distribution, and width of the stems of plant fossils through the D-C boundary on Celsius Bjerg.

    The maximum diameter and number of the stems are plotted against the altitude and section thickness. Large plants completely and abruptly disappear at the D-C boundary in the lower lake and remain absent for the 7 Ma of the Tournaisian. The plant data are in table S2.

  • Fig. 3 Normal and malformed G. cornuta from the lower lake, Rebild Bakker.

    (A) Upward increasing percent of malformed and tetrads. (B) Average translucency of G. cornuta showing increased pigmentation as malformations increase. (C) Dispersed phytoclast reflectivity showing a high charcoal content (>2%) through the boundary interval and hence no reduction in ozone from lower atmospheric PO2. (D and E) Normal specimens of G. cornuta. (F), (H), and (J) show reduced numbers of irregularly distributed spines and increased brown pigmentation. (G) has irregularly developed sinuose processes. (I) has hooked tips. (K) to (M), (P), and (U) have processes that are reduced in number and irregularly fused. (N), (S), and (T) are irregularly distributed, fused in groups, and highly irregular. (O) has irregular sporopollenin masses adhering to inner body. (V) is a tetrad of inner bodies, whereas (Q) is an isolated inner body. (R) and (W) are tetrads, with irregular sculpture, with (W) being pigmented to a dark brown color. Sample and slide numbers plus England Finder coordinates are in table S4. Translucency data are in table S3, and phytoclast reflectivity data are in table S5.

  • Fig. 4 V. nitidus spores from below, in, and above the D-C boundary showing UV-B malformations.

    (A) to (C) are from below the boundary (Stensiö Bjerg) and have the characteristic packed verrucae sculpture of V. nitidus. (D) to (K) are from the lower lake (Rebild Bakker), with (H) to (M) more strongly pigmented and more regular sculpture with a wider range of diameter than normal. (D) to (G) are paler in color and smaller in size and have irregularly developed sculpture. (N) to (P) are normal specimens of V. nitidus from the upper lake bed (Rebild Bakker). Sample and slide numbers plus England Finder coordinates are in table S4.

  • Fig. 5 The D-C boundary correlated between low paleolatitude terrestrial (Stensiö Bjerg, Greenland) and marine shelf [Stockum II, Germany; (11)] sections with high paleolatitude (Chaguaya, Bolivia).

    The LN* to VI spore boundary is the correlation tie and the interval of terrestrial extinctions. The terrestrial arid interval on Stensiö Bjerg correlates to the interval at Stockum II between the Hangenberg Black Shale and the LN* spore zone and equivalent to the glaciation. The Chaguaya composite section (note the reduced scale) includes a channel-filling sandstone of glacigenic origin that terminates immediately below the D-C boundary.

Supplementary Materials

  • Supplementary Materials

    UV-B radiation was the Devonian-Carboniferous boundary terrestrial extinction kill mechanism

    John E. A. Marshall, Jon Lakin, Ian Troth, Sarah M. Wallace-Johnson

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