[meteorite-list] burning at 12.9 Ka, Allen West -- also extinctions, Douglas Kennett, poster abstracts 2011 INQUA, Bern, Switzerland: Rich Murray 2011.07.27

From: Rich Murray <rmforall_at_meteoritecentral.com>
Date: Wed, 27 Jul 2011 17:04:51 -0700
Message-ID: <CAHqJ8pbe3KR68DpL84pmr+p=GsMaqk36Dj0O=uJ+wXtN-KH1dw_at_mail.gmail.com>

burning at 12.9 Ka, Allen West -- also extinctions, Douglas Kennett,
poster abstracts 2011 INQUA, Bern, Switzerland: Rich Murray 2011.07.27

http://www.inqua2011.ch/?a=programme&subnavi=abstract&id=1619&sessionid=60

Abstract Details

ID: 1619
Title: Evidence for Widespread Biomass-Burning at the Younger Dryas
Boundary at 12.9 ka

Content:
Abundance peaks in charcoal, grape-cluster soot, and carbon spherules
suggest that a major, cross-continental episode of biomass-burning
occurred at the onset of the Younger Dryas (YD) cooling.
These peaks appear contemporaneous with Greenland ice core spikes in
ammonium, nitrate, formate, and oxalate, which also are interpreted to
represent biomass-burning.
This evidence is consistent with a cosmic impact at 12.9 ka.

Contradicting this, the Marlon group (2009) analyzed 35 lakes cores
from across North America and found no evidence for a biomass-burning
episode within ?50 yrs of 12.9 ka.
We propose that multiple 14C dating errors, along with statistical
issues, may have led the Marlon group to an erroneous conclusion.
Their lake records contain numerous cumulative dating uncertainties:

Average chronological sample resolution was about ?180 yrs;
The 14C dates they used had a mean error of ?132 yrs; and
For the 14C dates closest in age to 12.9 ka, the mean interval was
>1100 yrs younger or older.

Collectively, these errors make it impossible to reach conclusions
about the timing of a burning episode at 12.9 ka with a certainty of
?50 yrs.
After reviewing Marlon's results, we argue that there is sufficient
evidence for widespread wildfires dating to the YD onset.
In addition, we analyzed cores from 35 other lakes broadly distributed
across North America and found that they also exhibit a collective
charcoal peak at 12.9 ka within the limits of 14C uncertainty.
We also detected above-background concentrations of charcoal in 23 of
25 non-lacustrine sedimentary sections that date to about 12.9 ka.
The existence of charcoal that is widespread, but not ubiquitous,
plausibly supports a major continental biomass-burning episode at 12.9
ka.
The K-T impact layer is the only other known horizon that contains
peaks in charcoal, soot, carbon spherules, and nanodiamonds, further
suggesting a cosmic connection for the YDB layer.

Session: 60 The enigmatic Younger Dryas climatic episode
Authors: James Kennett
Ted E. Bunch
Allen West
Presenter: Allen West
Type: poster


http://www.inqua2011.ch/?a=programme&subnavi=abstract&id=3116&sessionid=60

Abstract Details

ID: 3116

Title: Megafaunal Extinction at the Younger Dryas Onset in North America
Content:
At least 35 mammal and 19 bird genera became extinct across North
America near the end of the Pleistocene.
Modern increases in stratigraphic and dating resolution suggest that
this extinction occurred relatively rapidly and perhaps in two stages
near 12.9 ka (11 radiocarbon kyrs).
Within the context of a long-standing debate about its cause,
Firestone et al., (2007) proposed that this extinction resulted from
an extraterrestrial (ET) impact over North America at 12.9 ka.
This hypothesis predicts that the extinction of most of these animals
should have occurred abruptly at 12.9 ka.
To test this hypothesis, we have critically examined radiocarbon ages
and the extinction stratigraphy of these taxa.
>From a large data pool, we selected only radiocarbon dates with low
error margins with a preference for directly dated biological
materials (e.g., bone, dung, etc.) and modern chemical purification
techniques.
The stratigraphic and chronologic data are consistent with megafaunal
extinction being caused by continental-scale ecosystem disruption at
the onset of the Younger Dryas.

Session: 60 The enigmatic Younger Dryas climatic episode
Authors: Douglas Kennett
Douglas Kennett
Presenter: Douglas Kennett
Type: poster
Received on Wed 27 Jul 2011 08:04:51 PM PDT