Earth-logs
Annual logs
Geohazards
Human evolution and migrations
Magmatism
Miscellaneous Commentary
Sedimentology and stratigraphy
About Earth-logs
Tag: Palaeocene mammals
What followed the K-Pg extinction event?
Published on October 25, 2019 by zooks777Leave a comment
A study of boron isotopes in the tests of foraminifera that lived deep in the oceans and near their surface just after the K-Pg boundary event has revealed that ocean water suddenly became more acidic (Henehan, M.J. and 13 others 2019. Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact. Proceedings of the National Academy of Sciences. Online; DOI: 10.1073/pnas.1905989116). Because the data came from marine sediment sequences exposed in Europe and North America and from ocean-floor cores beneath the Atlantic and Pacific Oceans, the acidification was global in scope. The sharp fall in pH, almost certainly due to massive release of sulphuric and carbonic acids from thick anhydrite and limestone beds beneath the Chicxulub impact site was instrumental in the collapse of marine ecosystems. A rebound to higher, more alkaline pH values (overshooting those of the preceding Late Cretaceous) was equally rapid. That is ascribed to the post-extinction dearth of marine organisms that take up calcium in their shells so that dissolved Ca became more abundant. Within less than 100 ka of the Chicxulub impact ocean pH had returned to its pre-impact levels. Since Deccan flood-basalt volcanism was active until long after, Henehan et al. consider that its influence on ocean acidification was minimal and that The Chicxulub impact 'was key in driving end-Cretaceous mass extinction'.
Records of marine fossils are both more abundant and continuous than are those of land-based organisms. That animal extinctions on the continents were dramatic has been clear for over a century. Entire classes, notably the dinosaurs (except for birds), as well as orders, families, genera and species disappear from the fossil record. The event more than decimated plant taxa too. How and at what pace the vacated ecological niches were reoccupied during the evolutionary radiation among what became modern fauna and flora remain poorly understood. For the first million years of post-impact time fossils of terrestrial and freshwater organisms are very rare. Well-dated sedimentary sequences are patchily distributed, and fossils preserved in them as rare as proverbial hen's teeth, apart from a few, better endowed strata separated by thick, unproductive sediments. A Lower Palaeocene site near Denver in Colorado, USA extends for 27 km. At first sight it does not impress palaeontologists, but it carries concretions that yield rich hauls of tiny vertebrate fossils. Dating using U-Pb dating of interleaved volcanic ash layers, stratigraphy based on normal and reversed polarity of remanent magnetism, and plant pollen variations. The 250 m thick sedimentary unit can be divided into 150 levels that represent the first million years flowing the Chicxulub impact (Lyson, T.R. and 15 others 2019. Paleogene mass extinction -Exceptional continental record of biotic recovery after the Cretaceous. Science, online first release; DOI: 10.1126/science.aay2268.
Reconstruction of the 35 kg early Palaeocene mammal Taeniolabis (credit: Wikipedia)
The levels contain abundant remains of early Cenozoic mammals, particularly skulls that are vitally important in taxonomy and size estimation. During the last few hundred thousand years of the Cretaceous, mammals about the size of a modern racoon (~8 kg) were abundant. The oldest Palaeocene holds nothing bigger than a 600 g rat, and few of them. Then, remarkably, the numbers, diversity and mean body mass of mammals grow; raccoon-size back within 100 ka then, in a series of steps, beasts around 25, 35 and 45 kg emerged successively during the next 600 ka. Clearly, the local food chain had to support this growth in size as well as numbers. Pollen records reveal a terrain first dominated by ferns – not especially nutritious – then after 200 ka by palms and finally legumes (pulses) appear. The diversification of animals and plants changed in lockstep. Studies of fossil-leaf shapes (toothed = cooler; smooth = warmer) indicated a similarly triple-stepwise amelioration in climate from cool, post-impact to hot by 65 Ma ago. This climatic warming may have been connected to successive pulses of Deccan volcanism that drove up atmospheric CO2 levels. Geologically, that is pretty quick. In the context of a possible, equally rapid mass extinction as a result of anthropogenic factors, such a pace of recovery is hardly reassuring…
Categories Palaeobiology, Sedimentology and stratigraphy•Tags Chicxulub impact, Evolutionary recovery, K-Pg extinction, Palaeocene mammals
Mineral grains far older than the Solar System
Active volcanic processes on Venus
The last known Homo erectus
How marine animal life survived (just) Snowball Earth events
Should you worry about being killed by a meteorite?
Search Earth-logs
Monthly posts back to 2000
Monthly posts back to 2000 Select Month January 2020 December 2019 November 2019 October 2019 September 2019 August 2019 July 2019 June 2019 May 2019 April 2019 March 2019 February 2019 January 2019 December 2018 November 2018 October 2018 September 2018 August 2018 July 2018 June 2018 May 2018 April 2018 March 2018 February 2018 January 2018 December 2017 November 2017 October 2017 September 2017 August 2017 July 2017 June 2017 May 2017 April 2017 March 2017 February 2017 January 2017 December 2016 November 2016 October 2016 September 2016 August 2016 July 2016 June 2016 May 2016 April 2016 March 2016 February 2016 January 2016 December 2015 November 2015 October 2015 September 2015 August 2015 July 2015 June 2015 May 2015 April 2015 March 2015 February 2015 January 2015 December 2014 November 2014 October 2014 September 2014 August 2014 July 2014 June 2014 May 2014 April 2014 March 2014 February 2014 January 2014 December 2013 November 2013 October 2013 September 2013 August 2013 July 2013 June 2013 May 2013 April 2013 March 2013 February 2013 January 2013 December 2012 November 2012 October 2012 September 2012 August 2012 July 2012 June 2012 May 2012 April 2012 March 2012 February 2012 January 2012 December 2011 November 2011 October 2011 September 2011 August 2011 July 2011 June 2011 May 2011 March 2011 February 2011 January 2011 November 2010 September 2010 July 2010 May 2010 March 2010 January 2010 November 2009 September 2009 July 2009 May 2009 March 2009 January 2009 November 2008 September 2008 July 2008 May 2008 March 2008 January 2008 November 2006 October 2006 September 2006 August 2006 June 2006 May 2006 March 2006 February 2006 December 2005 November 2005 October 2005 September 2005 August 2005 June 2005 May 2005 April 2005 March 2005 February 2005 January 2005 December 2004 November 2004 October 2004 September 2004 July 2004 May 2004 April 2004 March 2004 February 2004 January 2004 December 2003 November 2003 September 2003 August 2003 July 2003 June 2003 May 2003 April 2003 March 2003 February 2003 January 2003 December 2002 November 2002 October 2002 September 2002 August 2002 July 2002 May 2002 April 2002 March 2002 February 2002 January 2002 December 2001 November 2001 July 2001 June 2001 May 2001 April 2001 March 2001 February 2001 January 2001 December 2000 October 2000 September 2000 August 2000 July 2000 June 2000 May 2000
Annual Logs by Topic
Follow Earth-logs on WordPress.com