[meteorite-list] Holocene Start Impacts

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Tue, 13 Oct 2009 13:02:48 -0700 (PDT)
Message-ID: <579527.26280.qm_at_web36905.mail.mud.yahoo.com>

Hi -

I need more money and less cr*p from some people:

2009 FALL AGU San Francisco, CA
Field-Analytical approach of land-sea records for elucidating the Younger Dryas Boundary syndrome
SECTION/FOCUS GROUP: Paleoceanography and Paleoclimatology (PP)
SESSION: Younger Dryas Boundary: Extraterrestrial Impact or Not? (PP15)
AUTHORS (FIRST NAME, LAST NAME): Thierry Ge1, MARIE-AGNES MICHELE COURTY2, Francois Guichard3
INSTITUTIONS (ALL):
1. Geoarcheology, INRAP, Pessac, France.
2. Prehistory -IPHES-ICREA, CNRS-MNHN, Tarragona, Spain.
3. Paleoocenography, CNRS-CEA UVSQ, Gif-sur-Yvette, France.

Linking lonsdaleite crystals, carbon spherules and diamond polymorphs from the North American dark layers at 12.9 cal yr B.P. to a cosmic event has questioned the nature and timing of the related impact processes. A global signal should trace the invoked airshocks and/or surface impacts from a swarm of comets or carbonaceous chondrites.

Here we report on the contextual analytical study of debris fall events from three reference sequences of the Younger Dyras period (11-13 ka cal BP):

(1) sand dune fields along the French Atlantic coast at the Audenge site;
(2) A 10 m record of detrital/bioorganic accumulation in the southern basin of the Caspian Sea with regular sedimentation rate (0.1 to 3 mm per year) from 14 to 2-ka BP cal;
(3) the Paijan sequence (Peruvian coastal desert) offering fossiliferous fluvial layers with the last large mammals and aquatic fauna at 13 ka BP sealed by abiotic sand dunes.

The three sequences display one remarkable layer of exogenous air-transported microdebris that is part of a complex time series of recurrent fine dust/wildfire events. The sharp debris-rich microfacies and its association to ashes derived from calcination of the local vegetation suggest instantaneous deposition synchronous to a high intensity wildfire. The debris assemblage comprises microtektite-like glassy spherules, partly devitrified glass shards, unmelted to partly melted sedimentary and igneous clasts, terrestrial native metals, and carbonaceous components. The later occur as grape-clustered polymers, vitrified graphitic carbon, amorphous carbon spherules with a honeycomb pattern, and green carbon fibres with recrystallized quartz and metal blebs. Evidence for high temperature formation from a heterogeneous melt with solid debris and volatile components derived from carbonaceous precursors supports an impact origin from an ejecta plume. The
 association of debris deposition to total firing would trace a high energy airburst with surface effects of the fireball. In contrast, microfacies and debris composition of the recurrent fine dust/wildfire events would trace a series of a low energy airburst. Their record is expressed in the Audenge sequence by a series of water-laid laminae of charred pine residues formed of carbonaceous spherules wrapped by carbonaceous polymers that includes lonsdaleite crystals as detected by high resolution in situ micro-Raman analysis. This association suggests recurrent flash forest wildfires ignited by hot spray of carbon-rich debris, followed by heavy snow falls. The record from the Peruvian desert suggests a possible linkage between the repeated debris fall/wildfires during the Younger Dryas and the following irreversible aridity along the Peruvian cost. In contrast the Caspian record of the Younger Dryas period indicates more gradual changes, possibly
 buffered by the hydrological functioning of the Caspian sea in a complex region. The Audenge context offers the amplified signal needed to understand at local to global scales the spatio-temporal pattern of impact-airburst events.

KEYWORDS: [4901] PALEOCEANOGRAPHY / Abrupt/rapid climate change, [1029] GEOCHEMISTRY / Composition
of aerosols and dust particles, [4924] PALEOCEANOGRAPHY / Geochemical tracers, [5420] PLANETARY
SCIENCES: SOLID SURFACE PLANETS / Impact phenomena, cratering.
Previously Presented Material: Original results, never presented, never published

E.P. Grondine
Man and Impact in the Americas


      
Received on Tue 13 Oct 2009 04:02:48 PM PDT