Abstract Detail

Plants at the Cretaceous-Paleogene boundary

Wilf, Peter [1], Bralower, Timothy J. [2].

Geographic Variation in Marine and Terrestrial Primary-Producer Response to the Terminal Cretaceous Event.

Atmospheric modeling indicates that the 66.0 Ma end-Cretaceous (K-Pg) impact at Chicxulub, Mexico, caused nearly uniform, globally devastating effects on life. However, K-Pg event strata show decreasing sediment disturbance with distance from ground zero, and first principles suggest that environmental destruction would decrease as well. We review published evidence in light of hypothesized geographic variation in extinction and recovery among calcareous nannoplankton (haptophyte algae) and land plants. Testing this hypothesis is critical for understanding the extinction legacy seen in evolutionary patterns reaching to the present day. Nannoplankton consist of globally distributed species that occur in deep-sea cores at massive abundances and fine stratigraphic resolution. Nannofossil data demonstrate significantly higher extinction and slower recovery in the northern vs. southern hemispheres; recovery was eventually led by novel lineages in the northern hemisphere, whereas southern hemisphere recovery stemmed from diversification of incumbent survivors. Interpretation of the land-plant record is restricted by the general lack of well-dated, well-sampled stratigraphic sections that contain latest Maastrichtian and early Danian floras outside of Western Interior North America (WINA). However, the emerging pattern seems to align with the nannofossils in favoring greater survivorship and faster recovery for primary producers at southern latitudes far from Chicxulub. The Hell Creek-Fort Union formation floras of southwestern North Dakota remain the best understood in WINA (and the world) for the K-Pg interval, providing a benchmark of ca. 60% macrofloral and 30% microfloral extinction. Low-diversity floras continued to dominate in WINA throughout the Paleocene, although the unusually rich ca. 64 Ma Castle Rock flora of Colorado reveals a potentially widespread, rainforest-like biome. In contrast, palynological data from New Zealand, Antarctic Peninsula, and Patagonia show a muted extinction and rapid rebound; Patagonian data also record a striking, Danian final pulse of pollen from the extinct conifer family Cheirolepidiaceae, otherwise confined to the Mesozoic. Early Danian leaf floras from Patagonia are notably diverse compared to WINA, and terminal Maastrichtian macrofloras of Patagonia include earliest occurrences of extant conifer genera, showing distinctive lineages that survived the K-Pg. The Australian record includes noteworthy examples of ‘Mesozoic’ plants surviving into the Cenozoic such as corystosperms and bennettitaleans. It appears that biotic effects of the K-Pg event were not globally uniform for primary producers and that Gondwanan land plants, like southern phytoplankton, fared better than their northern counterparts closer to ground zero. Incumbent survivors appear to have seeded a ‘Mesozoic legacy’ with significant evolutionary influence on living southern biotas.

Related Links:
Patagonia Paleofloras Project on Google Scholar
Bralower lab home page

1 - Pennsylvania State University, Geosciences, 537 Deike Bldg., University Park, PA, 16802, United States
2 - Pennsylvania State University, Geosciences, 535 Deike Bldg., University Park, PA, 16802, USA

Cretaceous-Paleogene extinction
calcareous nannofossils
extinction legacy
extinction recovery

Presentation Type: Colloquium Presentations
Number: 0002
Abstract ID:226
Candidate for Awards:None

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