Palynological reconstruction of the Antarctic Cretaceous-Paleocene climate.

Artist’s impression of the eastern flank of the Antarctic Peninsula during theMaastrichtian (Artist: James McKay, University of Leeds.)

Artist’s impression of the eastern flank of the Antarctic Peninsula during the Maastrichtian (From Bowman et al, 2014, Artist: James McKay, University of Leeds.)

Past fluctuations in global temperatures are crucial to understand Earth’s climatic evolution. During the Late Cretaceous the global climate change has been associated with episodes of outgassing from major volcanic events, orbital cyclicity and tectonism before ending with the cataclysm caused by a large bolide impact at Chicxulub, on the Yucatán Peninsula, Mexico.
The Antarctic Peninsula is an area of specific interest to modern and past climatic studies, as it seems particularly sensitive to change (Kemp et al., 2014). Most of the studies are focused on Seymour Island which has one of the most expanded Cretaceous–Paleogene successions known. The K-Pg boundary occurs in the uppermost part of the López de Bertodano Formation, where it is marked by a minor iridium anomaly.

The terrestrial palynomorph record at the López de Bertodano Formation was divided into six phases. The first one contains an assemblage dominated by Nothofagidites spp. and Podocarpidites spp., with aquatic fern spores (Azolla spp., Grapnelispora sp.) and rare freshwater algal spores, suggesting a cool and relatively humid period.

 

Two examples of grains pollen from the Lopez de Bertodano Formation: Podocarpidites sp. (left) and Nothofagidites asperus (right)

Two examples of grains pollen from the Lopez de Bertodano Formation: Podocarpidites sp. (left) and Nothofagidites asperus (right). From Bowman et al, 2014.

In the phase two the increased abundance of Phyllocladidites mawsonii implies a gradual increase in humidity. During phase three, bryophytes began to increase. The phase four is characterised by relatively high abundances of Podocarpidites spp. and relatively low levels of Nothofagidites spp.
The phase 5 is characterised by a rapidly changing sequence of abundance peaks of different taxa, which may indicate a successional turnover in forest composition. The phase six suggests a return to a cool climatic conditions with high abundances of Araucariacites australis and Nothofagidites at the top of the section. It seems that Araucariaceae were capable of surviving long periods of adverse climatic conditions during the Early Pleistocene, but most modern araucarians have subtropical to mesothermal climatic preferences.

The nature of vegetational change in the south polar region suggests that terrestrial ecosystems were already responding to relatively rapid climate change prior to the K–Pg catastrophe. The composition of the terrestrial palynoflora indicates that the Maastrichtian climate fluctuated from cool, humid conditions, through a rapid warming about 2 million years prior to the K–Pg event – which is consistent with the evidence from the marine palynomorph record –  followed by cooling conditions in the earliest Danian.

 

Two examples of spores from the  Lopez de Bertodano Formation: Grapnelispora sp. (left) and Azolla sp.(right).

Two examples of spores from the Lopez de Bertodano Formation: Grapnelispora sp. (left) and Azolla sp.(right). From Bowman et al, 2014.

 

Reference:

Vanessa C. Bowman, Jane E. Francis, Rosemary A. Askinb, James B. Riding, Graeme T. Swindles, Latest Cretaceous–earliest Paleogene vegetation and climate change at the high southern latitudes: palynological evidence fromSeymour Island, Antarctic Peninsula, Palaeogeography, Palaeoclimatology, Palaeoecology, 408. 26-47. 10.1016/j.palaeo.2014.04.018
David B. Kemp, Stuart A. Robinson, J. Alistair Crame, Jane E. Francis, Jon Ineson, Rowan J. Whittle, Vanessa Bowman, and Charlotte O’Brien, A cool temperate climate on the Antarctic Peninsula through the latest Cretaceous to early Paleogene, Geology (2014) doi: 10.1130/G35512.1

 

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2 thoughts on “Palynological reconstruction of the Antarctic Cretaceous-Paleocene climate.

  1. Pingback: Palynological reconstruction of the Antarctic C...

  2. Pingback: The palynological record and the extinction events. | Letters from Gondwana.

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