The flux of extraterrestrial matter to Earth as recorded in Paleogene and Middle Ordovician marine sediments
(2009) In Litholund theses- Abstract
- This thesis aims at reconstructing events in the solar system, mainly collisional events in the asteroid
belt, by searches for extraterrestrial minerals in Paleogene and Middle Ordovician marine sediments
on Earth. Recent empirical evidence show that Earth has experienced a few brief periods during
the Phanerozoic when the flux of extraterrestrial matter significantly increased. The most prominent of
these occurred at approximately 470 Ma, as a consequence of the massive break-up of the L-chondrite
parent body in the asteroid belt. The finds of more than 87 fossil L chondritic meteorites (Ø = 1-21 cm)
in mid-Ordovician strata at Thorsberg, Kinnekulle, give testimony to the spectacular... (More) - This thesis aims at reconstructing events in the solar system, mainly collisional events in the asteroid
belt, by searches for extraterrestrial minerals in Paleogene and Middle Ordovician marine sediments
on Earth. Recent empirical evidence show that Earth has experienced a few brief periods during
the Phanerozoic when the flux of extraterrestrial matter significantly increased. The most prominent of
these occurred at approximately 470 Ma, as a consequence of the massive break-up of the L-chondrite
parent body in the asteroid belt. The finds of more than 87 fossil L chondritic meteorites (Ø = 1-21 cm)
in mid-Ordovician strata at Thorsberg, Kinnekulle, give testimony to the spectacular flux of meteorites
that followed the break-up event. The fossil meteorites are almost completely pseudomorphed, with
the exception of chromite, an exceptionally resistant accessory mineral (~0.25 wt%) in ordinary chondrites.
Extraterrestrial chromite (EC) is distributed in the immediate surrounding limestones beds of the
fossil L chondrites, indicating that most meteorites that reached the sea floor were dissolved, dispersing
the EC grains in the contiguous sediments. The distribution of EC has previously been studied at mid-
Ordovician sections in Sweden.
The goals of this thesis are threefold: (1) establish the normal background distribution of EC to corroborate
the extraordinary circumstances recorded during the mid-Ordovician; (2) investigate the global
pattern of the EC distribution during the mid-Ordovician, by studying a remote site; (3) study variations
in the marine osmium isotope (187Os/188Os) record across the EC-rich interval at Hällekis, Kinnekulle.
The Paleogene marine sediments at Gubbio and Massignano, Italy, were analysed for EC content,
yielding 7 EC in a total of 377 kg whole-rock (0.019 EC kg-1). This result is very similar to previously
studied mid-Ordovician strata, forming prior to the L-chondritic breaking event, in Sweden and China
(0.009-0.013 EC kg-1). In addition, the low EC content at Massignano contradicts a proposed ordinary
(L) chondritic meteorite shower in the late Eocene.
The general trend in the distribution of sediment-dispersed EC in Swedish strata during the mid-Ordovician
has been reproduced in the coeval stratigraphic interval at Puxi River, central China. At this
time, the Chinese section was positioned at mid-latitudes on the southern hemisphere, a few 1000 km
east of the Swedish sites. The EC-rich interval at Puxi typically has 1-4 EC grains per kg rock, equivalent
to previous results for coeval Swedish limestone. Consequently, a global correlation has been established
for the EC distribution across the Arenig-Llanvirn transition. A close temporal correlation
has also been suggested for the main phase of the Great Ordovician Biodiversification Event and the
disruption of the L-chondrite parent body at ~470 Ma, based on bed-by-bed records of EC, 187Os/188Os
and invertebrate fossils in Middle Ordovician sediments in Baltoscandia and China. The intense species
radiation and level of change in biodiversity of this event changed the biological composition of
the Earth’s oceans forever. The causes of the event remain elusive, although influences of extraterrestrial
origin cannot be excluded, and further studies are warranted. At Hällekis, the first appearance of
common EC grains is marked by a negative 187Os/188Os excursion in the strata, verifying an increased
influence of unradiogenic osmium. This source is most likely extraterrestrial in origin, as corroborated
by stable strontium isotope ratios from late Arenig to early Llanvirn.
In all, 665 kg of Paleogene and Middle Ordovician sediments from Italy and China has been searched
for EC grains in this thesis work. The composite background material from the Italian and Chinese sections
represents 487 kg of rock, and yielded only 8 EC altogether. The EC-rich Ordovician interval, representing
the sequential L. variabilis, Y. crassus and M. hagetiana conodont zones, yielded a total of 290
EC grains in 178 kg of limestone, signifying an average 1.63 EC per kg rock. This clearly shows a two
orders-of-magnitude increase in the flux of L-chondritic matter during the mid-Ordovician. In conclusion,
the largest documented break-up event in the asteroid belt has left a prominent signature in the coeval
sediments on Earth, and this thesis corroborates the significance and global consequences of this event. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/1393615
- author
- Cronholm, Anders LU
- supervisor
- opponent
-
- Professor Alan, Hildebrand, University of Calgary, Canada
- organization
- publishing date
- 2009
- type
- Thesis
- publication status
- published
- subject
- keywords
- L-chondite, sediment-disperesed, chromite, break-up event, Arenig-Llanvirn
- in
- Litholund theses
- issue
- 17
- pages
- 104 pages
- defense location
- Lithosphere and Biosphere Science, Geocentrum II, Pangea (room 229)
- defense date
- 2009-06-03 13:15:00
- ISSN
- 1651-6648
- 1651-6648
- language
- English
- LU publication?
- yes
- id
- 1b8099da-1fd0-4cc0-a005-bb69d6b7e808 (old id 1393615)
- date added to LUP
- 2016-04-04 09:03:42
- date last changed
- 2019-05-21 15:02:37
@phdthesis{1b8099da-1fd0-4cc0-a005-bb69d6b7e808, abstract = {{This thesis aims at reconstructing events in the solar system, mainly collisional events in the asteroid<br/><br> belt, by searches for extraterrestrial minerals in Paleogene and Middle Ordovician marine sediments<br/><br> on Earth. Recent empirical evidence show that Earth has experienced a few brief periods during<br/><br> the Phanerozoic when the flux of extraterrestrial matter significantly increased. The most prominent of<br/><br> these occurred at approximately 470 Ma, as a consequence of the massive break-up of the L-chondrite<br/><br> parent body in the asteroid belt. The finds of more than 87 fossil L chondritic meteorites (Ø = 1-21 cm)<br/><br> in mid-Ordovician strata at Thorsberg, Kinnekulle, give testimony to the spectacular flux of meteorites<br/><br> that followed the break-up event. The fossil meteorites are almost completely pseudomorphed, with<br/><br> the exception of chromite, an exceptionally resistant accessory mineral (~0.25 wt%) in ordinary chondrites.<br/><br> Extraterrestrial chromite (EC) is distributed in the immediate surrounding limestones beds of the<br/><br> fossil L chondrites, indicating that most meteorites that reached the sea floor were dissolved, dispersing<br/><br> the EC grains in the contiguous sediments. The distribution of EC has previously been studied at mid-<br/><br> Ordovician sections in Sweden.<br/><br> The goals of this thesis are threefold: (1) establish the normal background distribution of EC to corroborate<br/><br> the extraordinary circumstances recorded during the mid-Ordovician; (2) investigate the global<br/><br> pattern of the EC distribution during the mid-Ordovician, by studying a remote site; (3) study variations<br/><br> in the marine osmium isotope (187Os/188Os) record across the EC-rich interval at Hällekis, Kinnekulle.<br/><br> The Paleogene marine sediments at Gubbio and Massignano, Italy, were analysed for EC content,<br/><br> yielding 7 EC in a total of 377 kg whole-rock (0.019 EC kg-1). This result is very similar to previously<br/><br> studied mid-Ordovician strata, forming prior to the L-chondritic breaking event, in Sweden and China<br/><br> (0.009-0.013 EC kg-1). In addition, the low EC content at Massignano contradicts a proposed ordinary<br/><br> (L) chondritic meteorite shower in the late Eocene.<br/><br> The general trend in the distribution of sediment-dispersed EC in Swedish strata during the mid-Ordovician<br/><br> has been reproduced in the coeval stratigraphic interval at Puxi River, central China. At this<br/><br> time, the Chinese section was positioned at mid-latitudes on the southern hemisphere, a few 1000 km<br/><br> east of the Swedish sites. The EC-rich interval at Puxi typically has 1-4 EC grains per kg rock, equivalent<br/><br> to previous results for coeval Swedish limestone. Consequently, a global correlation has been established<br/><br> for the EC distribution across the Arenig-Llanvirn transition. A close temporal correlation<br/><br> has also been suggested for the main phase of the Great Ordovician Biodiversification Event and the<br/><br> disruption of the L-chondrite parent body at ~470 Ma, based on bed-by-bed records of EC, 187Os/188Os<br/><br> and invertebrate fossils in Middle Ordovician sediments in Baltoscandia and China. The intense species<br/><br> radiation and level of change in biodiversity of this event changed the biological composition of<br/><br> the Earth’s oceans forever. The causes of the event remain elusive, although influences of extraterrestrial<br/><br> origin cannot be excluded, and further studies are warranted. At Hällekis, the first appearance of<br/><br> common EC grains is marked by a negative 187Os/188Os excursion in the strata, verifying an increased<br/><br> influence of unradiogenic osmium. This source is most likely extraterrestrial in origin, as corroborated<br/><br> by stable strontium isotope ratios from late Arenig to early Llanvirn.<br/><br> In all, 665 kg of Paleogene and Middle Ordovician sediments from Italy and China has been searched<br/><br> for EC grains in this thesis work. The composite background material from the Italian and Chinese sections<br/><br> represents 487 kg of rock, and yielded only 8 EC altogether. The EC-rich Ordovician interval, representing<br/><br> the sequential L. variabilis, Y. crassus and M. hagetiana conodont zones, yielded a total of 290<br/><br> EC grains in 178 kg of limestone, signifying an average 1.63 EC per kg rock. This clearly shows a two<br/><br> orders-of-magnitude increase in the flux of L-chondritic matter during the mid-Ordovician. In conclusion,<br/><br> the largest documented break-up event in the asteroid belt has left a prominent signature in the coeval<br/><br> sediments on Earth, and this thesis corroborates the significance and global consequences of this event.}}, author = {{Cronholm, Anders}}, issn = {{1651-6648}}, keywords = {{L-chondite; sediment-disperesed; chromite; break-up event; Arenig-Llanvirn}}, language = {{eng}}, number = {{17}}, school = {{Lund University}}, series = {{Litholund theses}}, title = {{The flux of extraterrestrial matter to Earth as recorded in Paleogene and Middle Ordovician marine sediments}}, url = {{https://lup.lub.lu.se/search/files/5220737/1393642.pdf}}, year = {{2009}}, }