IGCP 653 2020 Virtual Annual Meeting: Zooming in on the GOBE Abstracts & Programme

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Zooming in on the GOBE
Christian Mac Ørum Rasmussen, Alycia L. Stigall, Arne Thorshøj Nielsen,
Svend Stouge & Niels H. Schovsbo (Eds)
DANMARKS OG GRØNLANDS GEOLOGISKE UNDERSØGELSE
GEOLOGICAL SURVEY OF DENMARK AND GREENLAND
DANISH MINISTRY OF CLIMATE, ENERGY AND UTILITIES

Zooming in on the GOBE
The onset of the Great Ordovician Biodiversification Event
Christian Mac Ørum Rasmussen, Alycia L. Stigall, Arne Thorshøj Nielsen,
Svend Stouge & Niels H. Schovsbo (Eds)
DANMARKS OG GRØNLANDS GEOLOGISKE UNDERSØGELSE
GEOLOGICAL SURVEY OF DENMARK AND GREENLAND
DANISH MINISTRY OF CLIMATE, ENERGY AND UTILITIES

Zooming in on the GOBE
The onset of the Great Ordovician Biodiversification Event
Christian Mac Ørum Rasmussen, Alycia L. Stigall, Arne Thorshøj Nielsen,
Svend Stouge & Niels H. Schovsbo (Eds)
DANMARKS OG GRØNLANDS GEOLOGISKE UNDERSØGELSE
GEOLOGICAL SURVEY OF DENMARK AND GREENLAND
DANISH MINISTRY OF CLIMATE, ENERGY AND UTILITIES

GEUS Report 2020 vol 21
Virtual Conference Organizing Committee
Christian M.Ø. Rasmussen
GLOBE Institute and Natural History Museum of Denmark
University of Copenhagen
Copenhagen, Denmark
Alycia L. Stigall
Department of Geological Sciences and
OHIO Center for Ecology and Evolutionary Studies
Ohio University
Athens, Ohio, USA
Niels H. Schovsbo
Geological Survey of Denmark and Greenland (GEUS)
Copenhagen, Denmark
Svend Stouge
Natural History Museum of Denmark
University of Copenhagen
Copenhagen, Denmark
Arne T. Nielsen
Dep. of Geosciences and Natural Resource Management
University of Copenhagen
Copenhagen, Denmark
IGCP 653 Co-leaders
Thomas Servais (Chair)
Lille, France
David A.T. Harper
Durham, UK
Olga T. Obut
Novosibirsk, Russia
Christian M.Ø. Rasmussen
Copenhagen, Denmark
Alycia L. Stigall
Athens, Ohio, USA
Zhang Yuandong
Nanjing, China

GEUS Report 2020 vol 21
Table of Contents
1. INTRODUCTION ................................................................................................. 5
2. CONFERENCE SCHEDULE ............................................................................... 6
3. ABSTRACTS .................................................................................................... 10

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1. Introduction
Welcome online!
So, things did not really work out the way we had hoped they would. We were
supposed to have held the official Closing Meeting of IGCP project 653: the onset of
the Great Ordovician Biodiversification Event, planned as a ‘physical event’ in the
same manner the network has done the preceding four years, only this time it should
have been in Copenhagen. And we were looking forward to welcoming you all here.
However, ‘something happened’ and we were suddenly in the unthinkable situation
that schools, universities and even national borders were closing. And kept being so
for months. In other words, an impossible situation to go ahead with the planning of a
normal conference. We were therefore forced to postpone the official closing meeting
entitled GOBEnhagen: a Baltic perspective on the role of the GOBE. First, we
postponed it to September. Now, it is provisionally postponed until May 2021,
pending the global development of the COVID-19 pandemic.
Instead of an official closing meeting, an additional, virtual meeting named Zooming
in on the GOBE were quickly organized and scheduled to take place on the same
September dates as the GOBEnhagen meeting. The 2020 Closing Meeting therefore
turned into a Virtual Annual meeting in the hopes that we may still close this
successful IGCP-network as a physical meeting in Copenhagen in 2021.
From the first discussions among the IGCP Co-PI’s in early June about a virtual
event to now, things have moved quickly forward. A ‘conference-hungry’ network has
jumped on to this idea with an overwhelmingly positive response: 45 presentations
from all over the world and nearly 150 participants have registered, making this the
largest meeting held within the IGCP Project 653 community so far.
We are excited to offer this virtual conference. The online environment provides a
framework to develop an inclusive conference. The removal of the barrier imposed by
travel and registration fees has allowed participants from many countries that have
not been able to participate in IGCP 653 meetings previously. Presenters span over
some 17 time zones and several continents and the topics reveal a vibrant
community that may have been forced to stay at home during the greater part of
2020, but certainly have continued to produce excellent, exciting research.
We hope that you all will enjoy four days of technical sessions, presenting the latest
GOBE-research.
GO BE ONLINE!

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2. Conference Schedule
Speakers are noted with *. Keynote presentations are in bold and orange. Times are
provided at UTC+). For conversion to your local time, visit https://timeanddate.com.
Monday, September 7th: Diversity, evolution, and stratigraphy
Session 1. Moderator: Christian M.Ø. Rasmussen
Time (UTC)
Speaker
Title
1
12:00
Welcome and official opening of meeting
2
12:20
Rebecca L. Freeman*
Late Cambrian BIMEs, Vicariance, and Extinction:
Patterns in Laurentian Lingulform Brachiopods
3
12:40 Keynote
Adriane R. Lam*, Sarah L. Sheffield and
Nicholas J. Matzke
Estimating dispersal and evolutionary dynamics in
diploporan blastozoans (Echinodermata) across the
Great Ordovician Biodiversification Event
4
13:10
Alycia L. Stigall*
How did invasion events promote evolutionary and
ecological change during the Great Ordovician
Biodiversification Event?
5
13:30
Fernando J. Lavié* and Juan Luis Benedetto
New contributions on the paleobiogeography of
linguliform brachiopods from Ordovician of the
Precordillera Argentina
6
13:50
Olev Vinn*, Mark A. Wilson, Michał Zatoń
and Mikołaj K. Zapalski
GOBE and escalation in symbiosis between large
colonial animals and their endobionts
14:10
COFFEE BREAK
Session 2. Moderator: Alycia L. Stigall
Time (UTC)
Speaker
Title
1
14:30
Arnaud Bignon*, N. Emilio Vaccari, Beatriz
G. Waisfeld and Brian D.E. Chatterton
Reassessment of the Order Trinucleida and its
phylogeny and systematics at familial level
2
14:50
Aske Sørensen*, Arne T. Nielsen, Nicolas
Thibault, Zhengfu Zhao, Niels H. Schovsbo
and Tais W. Dahl
A cyclostratigraphic analysis of the Late Cambrian Alum
Shale
3
15:10
Birger Schmitz*
The breakup of the L-chondrite parent body, its
signature in mid-Ordovician sediments in Baltoscandia
and the precise timing relative to the Ordovician
biodiversity expansion
4
15:30
Marcelo G. Carrera*, Gustavo G. Voldman,
Matías J. Mango and Galina P. Nestell
Early–Middle Ordovician Alcyonacean (octocoral)
sclerites from the Argentine Precordillera
5
15:50
Tais W. Dahl* and Susanne K.M. Arens
Five major ecological stages during early
terrestrialization may distinguish the role of life on
Earths atmospheric composition
6
16:10
Christian M. Ø. Rasmussen*, Nicolas R.
Thibault, Jan. A. Rasmussen, Svend Stouge,
Oluwaseun Edward, Marie-Louise Siggaard-
Andersen, Mikael Calner, Arne T. Nielsen
and Niels Schovsbo
An astrochronological timescale through the GOBE
provides Baltic intra-basinal insights on climate and
richness

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Tuesday, September 8th: Paleontology, oxygenation, and climate
Session 1.
Moderator: Arne T. Nielsen
Time (UTC)
Speaker
Title
1
6:00
Yan Liang*, Olle Hints, Joseph Bernardo,
Daniel Goldman, Jaak Nõlvak, Peng Tang
and Wenhui Wang
Re-explore the biological affinity of chitinozoans:
evidence from morphological variation and exceptional
specimens
2
6:20
Juwan Jeon*, Kun Liang, Stephen Kershaw
and Yuandong Zhang
Two ‘Silurian-type’ stromatoporoid genera from the
Upper Ordovician Beiguoshan Formation of North
China, and their tectonic and faunal implications
3
6:40
Francesc Pérez-Peris, Lukáš Laibl*, Lorenzo
Lustri, Pierre Gueriau, Jonathan B. Antcliffe,
Orla G. Bath Enright and Allison C. Daley
A new Lower Ordovician nektaspid euarthropod from
Morocco
4
7:00
Sofia Pereira*, Isabel Rábano, and Juan
Carlos Gutiérrez-Marco
The trilobite assemblage of the “Declivolithus Fauna”
(Katian) of Morocco: a review with new data
5
7:20
Andrej Ernst* and Hans Arne Nakrem
Early Katian bryozoan faunas of Baltoscandia
6
7:40 Keynote
Joseph P. Botting*, Lucy A. Muir, Stephen
Pates, Luke A. Parry and Lucy McCobb
A new, open marine Middle Ordovician Lagerstätte
from Wales
8:10
COFFEE BREAK
Session 2.
Moderator: Tais W. Dahl
Time (UTC)
Speaker
Title
1
8:30
Qijian Li*, Oliver Lehnert, Rongchang Wu, J.
Park, Kun Liang, S. Yu, Y. Mao and Lin Na
The palaeokarst in the Xiazhen Formation (Late
Ordovician): a record of the mid-Katian glaciation in
South China
2
8:50
Susanne K.M. Arens* and Tais W. Dahl
No consensus on timing and cause of Paleozoic oxygen
rise – a case for the significance of respiration.
3
9:10
Álvaro del Rey*, Mikael Calner, Christian M.
Ø. Rasmussen and Tais W. Dahl
Understanding the relationship between the global
oxygenation state of the oceans and the Great
Ordovician Biodiversification Event
4
9:30
Duy Pham* and Jeong-Hyun Lee
Keratose sponge–microbial carbonate consortium in
the columnar “stromatolites” and “thrombolite”
mounds from the Lower Ordovician Mungok
Formation, Yeongwol, Korea
5
9:50
Yuefeng Shen*, Fritz Neuweiler and Le
Zhang
Ordovician diversification of calcimicrobes and
calcareous algae
6
10:10
Sigitas Radzevičius*, Wieslaw Trela, Andrius
Garbaras, Donatas Kudžma and Marius
Užomeckas
Integrated bio and chemostratigraphy of the upper
Homerian (Silurian) from the Kleczanów PIG - 1 well
(Holy Cross Mountains, Poland)

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Wednesday, September 9th: Paleoecology and geochemistry
Session 1. Moderator: Cole T. Edwards
Time (UTC)
Speaker
Title
1
14:00
Jana Bruthansová* and Heyo Van Iten
Ordovician conulariids as host organisms for epibionts
(Prague Basin, Czech Republic)
2
14:20
Benjamin F. Dattilo*, Roy E. Plotnick and
Dale Springer
Tracking the water depth habitat range of
Megalograptus through the Katian from the
Appalachian Basin to the Cincinnati Region
3
14:40
Sarah R. Losso* and Javier Ortega-
Hernández
Recent developments in the paleobiology and
taphonomy of trilobites from the Walcott-Rust Quarry
(Upper Ordovician)
4
15:00
Ceara K.Q. Purcell* and Alycia L. Stigall
How do ecological niches evolve during Ordovician
environmental change? A test using Laurentian
brachiopods
5
15:20
Alejandro Corrales-García, Jorge Esteve and
Matheo Lopez-Pachon
Burrowing assessment of Illaenus sarsi Jaanusson, 1957
and Megistaspis extenuata (Wahlenberg, 1821) from
the Middle Ordovician of Sweden
6
15:40 Keynote
Jorge Esteve* and Matheo López-Pachón
Swimming and enrolment in a mesopelagic trilobite:
new ecomorphological advantages in the Middle
Ordovician Ocean
16:10
COFFEE BREAK
Session 2. Moderator: Sarah R. Losso
Time (UTC)
Speaker
Title
1
16:30
Joshua B. Zimmt*, Steven M. Holland, Seth
Finnegan and Charles R. Marshall
Recognizing pulses of extinction from clusters of last
occurrences: A Late Ordovician case study
2
16:50
Cole T. Edwards*, Clive M. Jones, Page C.
Quinton and David A. Fike
Oxygen isotope (δ 18 O) trends measured from
conodont apatite using Secondary Ion Mass
Spectrometry (SIMS): implications for paleo-
thermometry studies
3
17:10
Richard M. Robinet*, John T. Haynes,
Steven A. Leslie and Achim D. Herrmann
Examining the Climate/Tectonic Implications of
Sandbian-Katian Environmental Change in the Southern
Appalachians Utilizing K-bentonite Apatite Phenocryst
Geochemical Correlations
4
17:30
Richard G. Stockey*, Feifei Zhang, Noah J.
Planavsky, Junxuan Fan, Lin Na, Seth
Finnegan, Cole Edwards, Sam Goldberg,
Matthew Saltzman, Tais W. Dahl, Kristin
Bergmann, Erik A. Sperling, Hua Zhang, Ying
Cui, Xiangdong Wang and Shu-zhong Shen
On ocean anoxia and the onset of the Great Ordovician
Biodiversification Event
5
17:50
Erik A. Sperling*, Michael J. Melchin, Tiffani
Fraser, Richard G. Stockey, Una C. Farrell,
Liam Bhajan, Tessa N. Browne, Devon B.
Cole, Benjamin C. Gill, Alfred Lenz, David K.
Loydell, Joseph Malinowski, Austin J. Miller,
Stephanie Plaza-Torres, Beatrice Rodewald,
Alan D. Rooney, Sabrina A. Tecklenburg,
Jacqueline M. Vogel, Noah J. Planavsky and
Justin V. Strauss
An exceptional record of early Paleozoic redox change
from the Road River Group, Yukon, Canada
6
18:10
Gustavo Voldman* and Aldo L. Banchig
Conodonts from siliciclastic rocks: a case study from
the Portezuelo del Tontal Formation, Ordovician of the
Western Argentine Precordillera

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Thursday, September 10th: Diversity, paleoecology, and isotopes
Session 1. Moderator: Björn Kröger
Time (UTC)
Speaker
Title
1
10:00
Tomas Želvys*, Antanas Brazauskas,
Aandrej Spiridonov, Donatas Kudžma,
Andrius Garbaras and Sigitas Radzevičius
Preliminary report on δ13Ccarb isotope excursion through
the Silurian of Jočionys-299 borehole, Eastern Lithuania
2
10:20
David A.T. Harper*, Jiayu Rong, Bing Huang
and Rongyu Li
Hirnantian brachiopods in time and space: New insights
on an old fauna
3
10:40
Richard Hofmann*
Why was there no GOBE in Western Laurentia?
4
11:00
Bertrand Lefebvre*, Elise Nardin and
Martina Nohejlová
The great Ordovician diversification of echinoderms:
deciphering a complex global signal
5
11:20
Thomas Servais*, Borja Cascales-Miñana
and David A.T. Harper
Early Palaeozoic diversifications: ‘explosions’ and ‘events’
or a continuum of change?
6
11:40
Ursula Toom*, Olev Vinn and Olle Hints
Ordovician Bioerosion Revolution on Baltica
12:00
Session 2. Moderator: Richard Hofmann
Time (UTC)
Speaker
Title
1
12:20 Keynote
Amelia M. Penny*, Olle Hints, André
Desrochers and Björn Kröger
Marine substrate change and biodiversity in the
Ordovician
2
12:50
Farid Saleh*, Orla G. Bath-Enright, Allison
C. Daley, Bertrand Lefebvre, Bernard Pittet
and Jonathan B. Antcliffe
Untangling the ecology and fossil preservation knot for
Paleozoic biotas
3
13:10
Björn Kröger* and Amelia M. Penny
Early – Middle Ordovician seascape-scale aggregation
pattern of sponge-rich reefs across the Laurentia
Paleocontinent
4
13:30
Olle Hints*, Aivo Lepland, Merlin Liiv, Tõnu
Meidla and Leho Ainsaar
Paired carbonate and organic carbon isotope records
from the Ordovician of Estonia: local, regional or global
drivers?
5
13:50
Bertrand Lefebvre* and Yves Candela*
Introducing the next IGCP-proposal
6
14:00
Closing ceremonies
COFFEE BREAK – Astrogeobiology Laboratory tour and Ordovician fossil meteorites with Birger Schmitz

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3. Abstracts
No consensus on timing and cause of Paleozoic oxygen rise –
a case for the significance of respiration
Arens, Susanne K.M.1* and Dahl, Tais W.1
1Globe Institute, University of Copenhagen, Øster Voldgade 5–7, Denmark
*Corresponding author: susanne.arens@sund.ku.dk
Geochemical proxies and models suggest O2 levels began a rise to near modern
levels in the Ordovician. Earth system models suggest the O2 increase was driven
by the long-term O2 source, represented by organic carbon burial in marine
sediments. This would have demanded an increase in the riverine P flux to the
oceans. Arguably, non-vascular plants could have preferentially weathered P
relative to bulk rock weathering and caused the oxygenation. We propose an
alternative solution in which the emergence of land plants put a brake on a major
O2 sink by promoting respiration in soils. To test this, we developed a 1D reactive
transport model to quantify the effect of respiration in soils on the oxidative
weathering sink on land. The solution depends on uplift rate, porosity and
distribution of labile soil organic matter. Yet, our model shows that respiration
indeed does stave off oxidative weathering, causing a rise in atmospheric O2 until it
reaches a level, where oxidative weathering again balances the O2 source. Our
results suggest that land plants played a significant role in bringing up atmospheric
O2 levels – not only by sourcing O2, but also by reducing its major long-term sink.

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Reassessment of the Order Trinucleida and its phylogeny and
systematics at familial level
Bignon, A.1,2*, Vaccari, N.E.1,2,3, Waisfeld, B.G.1,2 and Chatterton, B.D.E.4
1Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Córdoba,
Argentina
2Centro de investigaciones en Ciencias de la Tierra (CICTERRA), Consejo Nacional de
Investigaciones Científicas y Tecnológicas (CONICET), Córdoba, Argentina
3Universidad Nacional de la Rioja, La Rioja, Argentina
4Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada
*Corresponding author: arnaud.bignon@unc.edu.ar
The Superfamily Trinucleoidea is an iconic trilobite group of the GOBE, but its
evolutionary history has received little attention. In recent decades, this group has
been included in the Order Asaphida. In a recent phylogenetic analysis, we have
shown that this group is more closely related to Ptychopariida. As Ptychopariida is
paraphyletic, we suggested that trinucleoids should be raised to ordinal status, the
Trinucleida, with the aim to define a higher-level taxon based only upon
synapomorphies. A preliminary phylogenetic study raised several unexpected issues
with regard to definition of some of the families within Trinucleida. Most important
among these was that the Family Alsataspidae, as currently defined, is paraphyletic.
Hence, we performed another phylogenetic analysis, focussed on this family. Two
suborders appeared, Trinucleina encompassing the families Orometopidae,
Raphiophoridae and Trinucleidae; and the other one being Dionidina, including the
families Dionididae, Heterocaryonidae, Myindidae, and Alsataspididae. Interestingly,
because of some similarities to trinucleids, we included several Harpetida in the
analysis. As might be expected, most of the harpetids stay close to the outgroup
taxa, but the basal family of harpetids, the Heterocaryonidae is included in the
analysis as a basal member of the Dionidina. The family Liostracinidae is more
closely related to Ptychopariida, so we have excluded them from the Trinucleida,
making it easier to posit the characters of a hypothetical ancestor of the Order
Trinucleida. These analyses offer new views of the evolutionary history of trinucleid
trilobites. Indeed two lineages (suborders of Trinucleida) evolved rapidly during the
Late Cambrian/Early Ordovician generating several families that are less diverse
when compared to earlier views of Alsataspididae (that included all of these families,
excepted Heterocaryonidae). Moreover, our analysis suggests that the bilaminar
perforated fringe evolved separately (more than once) in distinct taxa (Trinucleidae,
Dionididae and Myindidae). These taxa, despite having similar cephalic
morphological innovations did not share equal evolutionary success. Indeed, only
Trinucleidae and Raphiophoridae (the latter does not have a perforated fringe but
does have a marginal suture) are characteristic of the GOBE (Whiterock fauna). Most
derived Dionididae were not as successful (Ibex 2 fauna). However, the systematics
of this family need to be examined in more depth and detail to understand better its
evolutionary history. Myindidae bearing these features (perforated bilaminar fringe
with marginal suture) are restricted to only two genera (Ibex 1 fauna).

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A new, open marine Middle Ordovician Lagerstätte from Wales
Botting, Joseph P.1,2*, Muir, Lucy A.1, Pates, Stephen3, Parry, Luke A4. and McCobb,
Lucy1
1Department of Natural Sciences, Amgueddfa Cymru – National Museum Wales, Cathays Park,
Cardiff CF10 3NP, UK
2Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 East Beijing
Road, Nanjing 210008, China
3Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard
University, Oxford Street, Boston, MA 02138, USA
4Department of Earth Sciences, University of Oxford, 3 South Parks Rd, Oxford OX1 3AN, UK
*Corresponding author: acutipuerilis@yahoo.co.uk
Ordovician Konservat-Lagerstätten are extremely diverse in palaeoenvironment,
taphonomy and palaeoecology, ranging from modified Burgess Shale-type faunas in
the Early Ordovician to a suite of shallow-marine marginal deposits, unique lagoonal
facies, and deep-water assemblages. There are, however, no Middle or Late
Ordovician examples of diverse soft-bodied faunas representing an offshore, open
marine environment that can be compared with the Burgess Shale-type faunas or
illustrate ecological development in this habitat during the main phase of the GOBE.
The closest we have is the diverse suite of deposits in the Darriwilian to basal
Sandbian Builth Inlier of Wales (Llanfawr Lagerstätte, Holothurian Bed and
Llandegley Rocks), each of which is limited in either diversity or preservational
quality. These faunas were preserved in a volcanic island setting, and together with
numerous other localities in the area, provide a uniquely broad palaeoecological
picture, but preserve only part of the total diversity.
A new Builth Inlier locality, Castle Bank, yields a rich exceptionally preserved
fauna from the Darriwilian Didymograptus murchisoni Biozone. It is stratigraphically
and environmentally intermediate between Llandegley Rocks and the Holothurian
Bed, and represents an open marine environment near storm wave base. The small
quarry exposes siltstones and substantial volcanic ash layers, the sediments
composed of laminated, densely graptolitic background beds and (in a two-metre-
thick interval) slightly coarser event beds. Numerous exceptionally preserved
sponges occur through this interval, in both background and event layers. Most of the
other exceptionally preserved organisms are limited to thin event layers in a
particular interval that is 30 cm thick.
The fauna is very diverse, including dozens of sponge species (often with soft
tissue remains as well as full articulation of skeletons), exceptional preservation of
other biomineralised animals such as fully articulated trilobites (with limited soft tissue
mineralisation), palaeoscolecids, asterozoans and a conodont bedding-plane
assemblage, but also diverse non-biomineralised worms, arthropods, cnidarian-like
and lophophorate-like animals, and problematica. Soft tissues such as cuticle and
labile tissues (e.g. tentacles) appear to be preserved as Burgess Shale-type carbon
films and/or pyrite, but taphonomy is yet to be investigated in detail. The
brachiopods, trilobites and graptolites are typical of the time interval, and suggest a
normal marine community. Castle Bank therefore offers a unique opportunity to study
an open marine Ordovician community that lived during the the peak of the
biodiversification interval.

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Ordovician conulariids as host organisms for epibionts (Prague
Basin, Czech Republic)
Bruthansová, J.1* and Van Iten, H.2
1Department of Palaeontology, National Museum, Cirkusová 1740, 193 00, Prague 9, Czech Republic
2Department of Geology, Hanover College, Hanover, Indiana 47243, USA
*Corresponding author: jana.bruthansova@nm.cz
Approximately 4% of just over 5000 examined conulariids from Ordovician formations
in the Prague Basin (Czech Republic) exhibit invertebrate epibionts and/or
attachment scars. The commonest epibionts are craniid brachiopods followed by
bryozoans and edrioasteroids. Less abundant are monoplacophorans and diverse
holdfasts. Epibionts occur on Anaconularia anomala, Archaeoconularia, Conulariella
sp., and Pseudoconularia grandissima, though predominantly on A. anomala and
Archaeoconularia from open shelf deposits in certain Upper Ordovician formations, in
which conulariids are substantially more abundant than in other formations. Except
for monoplacophorans, epibionts occur on the external surface of the conulariids, in
some cases with brachiopods, bryozoans, or edrioasteroids present on all four faces.
Edrioasteroids and brachiopods on some specimens are preferentially centered on or
near the facial midline. These results highlight the importance of Ordovician
conulariids as biological substrates, especially in Perunica and South Polar
Gondwana, and indicate that encrustation occurred both on live individuals and on
dead ones. The corners and midlines influenced the settlement and subsequent
growth of brachiopods and edrioasteroids, and conulariids bearing these epibionts
were buried catastrophically. The record of conulariid epibionts indicates that the
increase in their diversity during the initial stages of the GOBE was very low.
Figure 1: A - Craniid brachiopods and edrioasteroid on the faces of Anaconularia anomala, Sandbian,
NML 52061. B - Trepostome colony encrusting Archaeoconularia fecunda, Sandbian, NML 51780, C -
Cystoporate bryozoans fully covering a schott-bearing specimen of A. anomala, Sandbian, NML
37814. D - Edrioasteroids encrusting Archaeoconularia munita, Sandbian, NML 21971.

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Early–Middle Ordovician Alcyonacean (octocoral) sclerites from the
Argentine Precordillera
Carrera, Marcelo G. 1*, Voldman, Gustavo G.1, Mango, Matías1 J. and
Nestell, Galina P.2
1 CICTERRA-CONICET, CIGEA, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad
Nacional de Córdoba, X5000JJC, Córdoba, Argentina.
2 Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, Texas,
76019, USA.
*Corresponding author: mcarrera@unc.edu.ar
Alcyonacean octocoral sclerites present a highly incomplete stratigraphic distribution,
probably reflecting biases in the fossil record related to the difficulties of finding and
extracting these tiny calcareous fossils. Its oldest established record is the form
genus Atractosella Hinde, present in the Llandovery-Wenlock (Silurian) of Gotland
(Sweden), England, Scotland, and from an erratic boulder in Germany. In the present
contribution, we analyse the occurrence of silicified Early and Middle Ordovician
alcyonacean sclerites in the San Juan Formation of the Argentine Precordillera. The
sclerite assemblage consists of spindle morphotypes, ranging from slightly fusiform
elongated, rod-like forms to oval or strongly ellipsoidal. They are ornamented with
small regular granules or tubercles, and some sclerites are linearly connected by
their tips. The recovered sclerites occur in different stratigraphic levels and localities
of the Argentine Precordillera and therefore could represent associations of different
species or genera. Notwithstanding that, they provide clear evidence on the Floian
(Early Ordovician) occurrence of Alcyonacean sclerites in the fossil record. The
variable morphologic characteristics of these fused and unfused Alcyonacean
sclerites are present in the suborders Alcyoniina (soft corals) and the Scleraxonia
(horny octocorals). Although any of these groups assignment is still speculative at
this state of knowledge, it may imply that these basal forms could be elements of a
possible Alcyoniina-Scleraxonia stem-group.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
15
Burrowing assessment of Illaenus sarsi Jaanusson, 1957 and
Megistaspis extenuata (Wahlenberg, 1821) from the Middle
Ordovician of Sweden
Corrales-García, Alejandro.1*, Esteve, Jorge1 and Lopez-Pachon, Matheo1,2
1Department of Geosciences, Universidad de los Andes, Cra 1 Nº 18A – 12, Bogotá, Colombia
2Department of Mechanical engineering, Universidad de los Andes, Cra 1 Nº 18A – 12, Bogotá,
Colombia
*Corresponding author: a.corrales10@uniandes.edu.co
During the GOBE there was a change from a general Cambrian morphology towards
a greater variety of morphological novelties. A good example of this is the variety of
cephalic forms found in various groups of trilobites, seemingly allowing them to
occupy different levels within the sediment and, therefore, different lifestyles.
Nevertheless, the form-function-environment linkage has rarely been tested despite
being widely known in the field of paleontology. To elucidate if these adaptations
confer a functional advantage we have to mechanically assess such morphological
differences.
Here we evaluate the capacity of burrowing and compare the biomechanical
properties of two contemporary trilobites from the Middle Ordovician of
Sweden: Illaenus sarsi Jaanusson, 1957 and Megistaspis extenuata (Wahlenberg,
1821), which diverge enormously in their body architecture and likely in their lifestyle.
While I. sarsi is an iconic example of an infaunal organism due to its round frontal
shape, M. extenuata bears dagger-shaped anterior border which may be adapted to
infaunal lifestyle. However, given that biomechanical assessment by means of Finite
Element Analysis (FEA) of these organisms has not been carried out yet, so far, we
can only hypothesise the real function of these forms. Therefore, we have carried out
a 3D FEA in order to understand the function behind these morphological designs.
FEA shows that the design of I. sarsi was very effective to withstand greater stresses
than M. extenuata. In fact, M. extenuata shows a very poor design for burrowing and
seems likely that the dagger-shaped anterior border had other functions rather than
burrowing.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
16
Five major ecological stages during early terrestrialization may
distinguish the role of life on Earth's atmospheric composition
Dahl, Tais W.1* and Arens, Susanne K.M.1
1GLOBE institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark
*Corresponding author: tais.dahl@sund.ku.dk
On geological time scales the atmosphere is constantly recycled through the
biosphere and Earth’s interior. Yet, the atmosphere has supported life for more than
3.5 billion years demanding regulatory feedbacks at play within the Earth system.
Both biological and geological processes influence the atmospheric composition and
thereby the climate and oxygenation state of our planet. The colonization of land by
plants, fungi and animals took place in several stages that each may have increased
Earth's O2 levels and acted to cool the Earth's climate by drawing down atmospheric
CO2. Here, we call attention to five distinct ecological stages associated with the
emergence of new traits in land plants:
1) non-vascular plants, 2) vascular plants with lignified tissue, 3) plants with shallow
roots, 4) arborescent vegetation with deep and complex root systems, and 5) seed
plants. A review of the existing paleoenvironmental records is consistent with a
profound transition from a hot and poorly oxygenated atmosphere to a world more
similar to the modern Earth. Further scrutiny of the available records and relative
timing of O2 rise and CO2 drawdown during these ecological shifts will constrain the
processes that have governed Earth's atmospheric composition.
Figure 1: Atmospheric CO2 and O2 constraints from models and proxies during the five major
ecological stages of early terrestrialization.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
17
Tracking the water depth habitat range of Megalograptus through
the Katian from the Appalachian Basin to the Cincinnati Region
Dattilo, Benjamin F.1*, Plotnick, Roy E.2, and Springer, Dale3
1Department of Biology, Purdue University Fort Wayne, 2101 East Coliseum Boulevard, Fort Wayne,
Indiana 46805, USA
2Earth and Environmental Sciences, University of Illinois at Chicago, 845 W. Taylor St., Chicago,
Illinois 60607, USA
3Dept. Environmental, Geographical, and Geological Sciences, Bloomsburg University, Bloomsburg,
Pennsylvania 17815
*Corresponding author: dattilob@pfw.edu
Megalograptus from the Cincinnati region and Appalachian Basin is the best-known
Ordovician eurypterid and thus key to understanding the environmental history of the
clade. Previous discussions of the habitat of eurypterids have focused on the
question of whether they lived in open marine, restricted-marine, or even non-marine
environments. Given that they are consistently associated with normal marine
faunas, it is uncontroversial that megalograptids generally occupied open marine
environments sensu lato.
Since the 1960s more effort has been made to differentiate these Ordovician open
marine environments into finer subdivisions. Using sedimentological and
paleontological criteria the Ordovician ramp can be divided into peritidal, lagoonal,
barrier/biohermal, shoreface, shallow subtidal, and deep subtidal. Recent sequence
stratigraphic work has resulted in multiple thin time slices throughout the Cincinnati
Ordovician. This allows finer environmental and temporal placement of
Megalograptus occurrences.
Original localities and stratigraphic descriptions are precise and most occurrences in
the Cincinnatian can thus be located to the nearest few meters stratigraphically.
Megalograptid occurrences projected onto this high-resolution sequence stratigraphy
show a consistent association between megalograptids and the lagoon-barrier-to-
shoreface facies. Appalachian Basin occurrences in the Martinsburg Formation
appear to be of comparably shallow depths based on fossil evidence.
The megalograptid lineage apparently invaded the Cincinnati region from the
Appalachian region. Martinsburg occurrences are dated Edenian or Maysvillian,
whereas the earliest Cincinnatian occurrence is in the later part of the Maysvillian.
Both the Cincinnati Region and the Appalachian basin received sediments from the
Taconic Orogen and in that way they are the same sedimentary system. During the
Edenian the Cincinnatian sea was far too deep for megalograptids, but the
Appalachian Basin region was shallow. These suitably shallow water habitats
prograded from the Appalachians to the Cincinnati basin –and occurrences of
megalograptids track the facies northward and westward through the Cincinnati
region, with the older being further SE, and the younger being further NW.
Megalograptus is often reconstructed as a fierce predator. The thin and fragile spines
of their grasping appendages make it unlikely, however, that they fed on robust prey.
Instead, they are well-suited for trapping gelatinous organisms, such as jellyfish,
which should have been abundant in the near-shore waters of the Ordovician.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
18
Understanding the relationship between the global oxygenation
state of the oceans and the Great Ordovician Biodiversification
Event
del Rey, Álvaro1*, Calner, Mikael2, Rasmussen, Christian M. Ø.1,3 and Dahl, Tais W.1
1GLOBE Institute, University of Copenhagen, Copenhagen, Denmark
2Department of Geology, Lund University, Lund, Sweden
3Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, DK-1350
Copenhagen K, Denmark
*Corresponding author: alvarodelrey@science.ku.dk
The Middle Ordovician witnessed the most rapid and sustained increase in marine
family- and genus-level diversity in Earth’s history: the Great Ordovician
Biodiversification Event or GOBE. And with such an event, the question is simple:
what caused this dramatic increase in marine diversity? And although a very
straightforward question, it is fundamental in the understanding of the relationship
between life and the environment. How does life relate to the environment? What
causes life to suddenly change so much that the face of Earth was never the same
anymore? Several hypotheses have been proposed to explain why during this
particular time interval life unfolded; including one, planetary cooling leading
temperatures in the oceans more favorable for life to thrive. And two, an increase in
atmospheric oxygen because animal life requires oxygen to survive; thus, more
oxygen would have allowed more life. In this project we assess how the oxygenation
state of the oceans could have been related to the diversification event by analyzing
the uranium (U) isotope composition of a marine carbonate sequence across the
Middle Ordovician within the Baltoscandian paleobasin. A shift towards heavier U
isotopes would indicate a more oxygenated state of the oceans and vice versa. Our
results show that the recorded U isotope signatures remained stable (no observable
important swings) the time interval leading to the maximum diversification rate. An
increase in global oxygenation was not related to the rapid increase in diversification.
A relative stable redox landscape accompanied the ecological change that led to the
highest diversification rates of the GOBE.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
19
Oxygen isotope (δ 18O) trends measured from conodont apatite
using Secondary Ion Mass Spectrometry (SIMS): implications for
paleo-thermometry studies
Edwards, Cole T.1,2*, Jones, Clive M.2, Quinton, Page, C.3, and Fike, David A.2
1Department of Geological and Environmental Sciences, Appalachian State University, Boone, North
Carolina 28608 USA
2Department of Earth and Planetary Sciences, Washington University in Saint Louis, St. Louis,
Missouri 63130 USA
3Department of Geology, The State University of New York at Potsdam, Potsdam, New York 13676
USA
*Corresponding author: edwardsct4@appstate.edu
The oxygen isotopic compositions (δ18O) of minimally altered phosphate
minerals and fossils, such as conodont elements, are used as a proxy for past ocean
temperature. Phosphate is thermally stable under low to moderate burial conditions
and is ideal for reconstructing seawater temperatures because the P-O bonds are
highly resistant to isotopic exchange during diagenesis. Traditional bulk methods
used to measure conodont δ18O include multiple conodont elements, which can
reflect different environments and potentially yield an aggregate δ18O value derived
from a mixture of different water masses. In-situ spot analyses of individual elements
using micro-analytical techniques, such as secondary ion mass spectrometry (SIMS),
can address these issues.
Here we present 108 new δ18O values using SIMS from conodont apatite
collected from four Lower to Upper Ordovician stratigraphic successions from North
America (Nevada, Oklahoma, and the Cincinnati Arch region). The available
elements measured had a range of thermal alteration regimes that are categorized
based on their conodont alteration index (CAI) as either low (CAI = 1–2) or high (CAI
= 3–4). Though individual spot analyses of the same element yield δ18O values that
vary, most form a normal distribution around a mean value when spot locations are
optimized. Variability of individual spots can be minimized by avoiding surficial
heterogeneities like cracks, pits, or the near the edge of the element, and the
uncertainty can be improved with multiple (≥4) spot analyses of the element.
Samples from closely spaced beds or multiple conodonts from the same bed also
have variable mean δ18O values of individual elements (0.0 to 4.3‰, median 1.0‰),
regardless of low or high CAI values. Oxygen isotopic values measured using SIMS
in this study reproduce values similar to published trends, namely, δ18O values that
increase during the Early–Middle Ordovician and plateau by the mid Darriwilian (late
Middle Ordovician). Twenty-two of the measured conodonts were from ten sampled
beds that had been previously measured using bulk analysis. SIMS-based δ18O
values from these samples are more positive by an average of 1.7‰ compared to
bulk, consistent with observations by others, who attribute the shift to carbonate- and
hydroxyl-related SIMS matrix effects. This offset has implications for paleo-
temperature model estimates, which indicate a 4ºC per δ18O (‰) ocean water
temperature correlation. Although this uncertainty precludes precise paleo-
temperature measurements, it is valuable for identifying spatial and stratigraphic
trends in temperature that might not have been previously possible with bulk
approaches.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
20
Early Katian bryozoan faunas of Baltoscandia
Ernst, Andrej1*, Nakrem, Hans A.2
1Institute for Geology, University of Hamburg, Bundesstr. 55, D-20146 Hamburg, Germany.
2 Natural History Museum (Geology), University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo,
Norway.
*Corresponding author: Andrej.Ernst@uni-hamburg.de
Bryozoan diversity increased during the Ordovician and peaked in the late Sandbian.
The early Katian bryozoan communities prospered on the shelf of Baltica, but
suffered heavy losses at the end of this time interval. Studied localities of the early
Katian age in Estonia, Sweden, and Norway exhibit high diversity and abundance of
bryozoans represented by various stenolaemate groups. Bryozoans occupied various
biotopes including reefs. The taxonomic composition of the studied bryozoan
communities shows low level of endemism. Among other factors, the low level of
geographical isolation seems to be responsible for the mass extinction at the end of
the early Katian.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
21
Swimming and enrolment in a mesopelagic trilobite: new
ecomorphological advantages in the Middle Ordovician Ocean
Esteve J.1* and López-Pachón M.1, 2
1Departamento de Geociencias, Facultad de Ciencias, Universidad de los Andes, Bogotá, Colombia
2Departamento de Ingeniería Mecánica, Facultad de Ingeniería, Universidad de los Andes, Bogotá,
Colombia
*Corresponding author: jv.esteve@uniandes.edu.co
Trilobites were marine arthropods with an extraordinary capacity to adapt to their
environment. They occupied most ecological niches as early as the Cambrian,
including benthic and pelagic environments. Despite a few redlichiids and
ptychopariid examples, pelagic environments were not widely occupied by active
trilobite swimmers until the Ordovician. Trilobites reached their maximum
ecomorphological compass among pelagic trilobites during the Ordovician, where we
have found a high number of pelagic and mesopelapelagic trilobites with non-
streamlined and well-streamlined morphology. We focused our work on a well-
streamlined trilobite, the Ordovician cyclopygid Microparia. In contrast to the
nektobenthic Hypodicranotus, which displayed a secondary loss of enrolment
capacity, this little trilobite retained the capacity to encapsulate its body perfectly (i.e.
enroll) like many benthic trilobites. However, most of the living free-swimming
arthropods are unable to enroll, with the exception in some larvae, such as those of
the mantis shrimp, or in some copepods which show an incomplete enrolment style
(i.e. no encapsulation). We examine whether enrolment represented an advantage
for a mesopelagic trilobite like Microparia, and how it did so. A numerical simulation
based on computational fluid dynamics (CFD) was used to explore the hydrodynamic
behavior of Microparia and give a new framework for understanding the
ecomorphological evolution of well-streamlined trilobites. The results show very low
drag coefficients in all simulations in a prone position suggesting that this trilobite
was a good swimmer. In enrolled position drag coefficients are still lower, because
when the trilobite is enrolled the shape becomes markedly oval, a form that is very
efficient to reduce drag. On the other hand, the oval shape of Microparia generates
no lift (CL~0), therefore currents neither push Microparia towards the sea surface nor
to the seafloor; its wakes are symmetric. These results show high stability in the
horizontal plane (parallel to the flow currents) and suggest that Microparia could be
almost stable in the water column when it was enrolled. This represents a new way to
use enrollment in trilobites, not only for protection against predators or environment
but also as a hydrodynamic tool to maintain stability within the water column.
Microparia, as well as several other cyclopygids, shows important
morphological novelties (e.g. stream-lined body, eyes do not project and presence of
“snout”) but also takes advantage of a “plesiomorphic” behavior (i.e. enrolment) to
occupy a special ecological niche in the mesopelagic habitat.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
22
Late Cambrian BIMEs, Vicariance, and Extinction: Patterns in
Laurentian Lingulform Brachiopods
Freeman, Rebecca L.1*
1Department of Earth and Environmental Sciences, University of Kentucky, Lexington, KY, 40506,
USA
*Corresponding author: Rebecca.freeman@uky.edu
Global biodiversity plateaued in the wake of the Cambrian Explosion before
dramatically increasing during the Great Ordovician Biodiversification Event (GOBE).
Recent studies (e.g., Stigall et al., 2017) have demonstrated that accumulation of
species was enhanced through an alternating regime of speciation through dispersal
(biotic immigration events; BIMEs) and vicariance, speciation occurring as ranges are
subdivided.
In Laurentia, this interval is characterized by alternating periods of extinction and
immigration and periods of regional-scale diversification among trilobites, the so-
called “biomeres”. The same pattern is seen in the linguliform brachiopods of this
interval. Ongoing studies examine two of these biomere boundaries, the
Steptoean/Sunwaptan, and the Sunwaptan/Skullrockian. The study areas contrast
paleoenvironments in Laurentia, including the deep outer shelf environment of Utah
and Nevada, and the higher-energy shallow shelf environment of Texas and
Oklahoma.
In all study areas, and at both boundaries, the biomere boundaries involve complete
turnover of linguliform species. At the lower Steptoean/Sunwaptan boundary, globally
distributed species then temporarily replaced the now-extinct endemic fauna in the
outer shelf environment, while new endemic species appeared in the cratonic
environment, potentially demonstrating the role of both BIME’s and vicariance in
rebuilding biodiversity after this extinction event. The second Sunwaptan/Skullrockian
biomere extinction event again produced complete turnover of the linguliform
brachiopods at apparently the same time as trilobite extinction, but during this interval
the replacement faunas were cosmopolitan in all study areas. These repeating
patterns of BIMEs and vicariance are essentially identical to patterns seen in many
clades later during the Middle Ordovician. This pattern suggests that at least some
critical factors for producing biodiversity were in place earlier than the GOBE, even
though repeated extinction events that depleted alpha and beta diversity contributed
to lower gamma diversity.
References:
Stigall, A.L., Bauer, J.E., Lam, A.L., & Wright, D.A. 2017. Biotic immigration
events, speciation, and the accumulation of biodiversity in deep time. Global
and Planetary Change 148, 242–257. doi:10.1016/jgloplacha.2016.12.008

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
23
Hirnantian brachiopods in time and space: New insights on an old
fauna
Harper, David A.T.1*, Rong Jiayu2, Huang Bing2 and Li Rongyu3
1Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham DH1 3LE, UK
2State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and
Palaeontology, and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of
Sciences, Nanjing 210008, China
3Department of Geology, Brandon University, MB R7A 6A9, Canada
*Corresponding author: david.harper@durham.ac.uk
Distributional analysis of Hirnantian brachiopod faunas, based on a new,
comprehensive dataset from over 20 palaeoplates and terranes, confirms that within
the Hirnantian Stage there were two successive faunas: 1. The widespread and
diachronous Hirnantia Fauna related to a glacial acme in the early−mid Hirnantian;
shallow, deeper and deep-water communities diversified in much more complicated
environmental conditions than hitherto envisaged; and 2. The Edgewood−Cathay
Fauna thrived during post-glacial, warmer, shallow-water regimes with both
carbonate and siliciclastic facies in low latitudes during the late Hirnantian−early
Rhuddanian. This faunal succession tracks two climatic perturbations, one with a
glaciation, associated with climatic cooling and a global low-stand, during which the
Hirnantia Fauna flourished, almost globally, and a second characterized by melting
ice, global warming, and sea-level rise (with global anoxia), aligned to the
development of the Edgewood–Cathay Fauna and the repopulation of the seas by
animals adapted to warmer water. Intense climate changes, sea-level fluctuations,
and oceanographic ventilation and anoxia, had important roles in brachiopod
evolution through the Hirnantian extinctions; higher originations of new taxa may be
linked to intervals of accelerated speciation due to extreme climatic conditions.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
24
Paired carbonate and organic carbon isotope records from the
Ordovician of Estonia: Local, regional or global drivers?
Hints, Olle1*, Lepland, Aivo1,2, Liiv, Merlin1, Meidla, Tõnu2 and Ainsaar, Leho2
1Department of Geology, Tallinn University of Technology, Ehitajate 5, 19086, Tallinn, Estonia
2Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia
*Corresponding author: olle.hints@taltech.ee
Carbon stable isotope excursions are widely used as correlation tool in Ordovician
stratigraphy as well as for reconstructing climatic and environmental history. The
mechanisms behind individual carbon isotopic excursions are, however, not fully
understood and their geographic scope, facies dependence and synchroneity need
further assessing. The Baltic region has been a reference area for studying
Ordovician carbon isotope records for several decades. Most previous works in the
region are based on data from bulk carbonate rocks (δ13Ccarb), whereas the
stratigraphic variability of the isotopic composition of organic matter (δ13Corg) has
remained poorly studied.
Here we document paired carbonate and organic carbon isotope records from the
Middle Ordovician to basal Silurian from Estonia. The primary aims of this work were
to: (1) assess the variability and stratigraphic usefulness of the δ13Corg curves, in
comparison with δ13Ccarb data from the same sections and records from other
regions; (2) examine the offset between the carbonate and organic matter isotope
curves (Δ13C) in order to reveal any temporal trends; (3) test the spatial variation of
paired isotope data within the Baltoscandian basin. For this 470 samples at c. 1 m
resolution were analysed from the Lelle, Viki and Tartu cores, each characterising
somewhat different facies within the Baltoscandian basin.
The δ13Ccarb curves from the three sections reveal the isotopic excursions well-known
globally and/or from the region: MDICE, LSNICE (Kukruse low), GICE, Rakvere,
Saunja, Moe and the prominent HICE. The δ13Corg data show more varying patterns
than δ13Ccarb, ranging between c. -33‰ and -26‰. Compared to data from other
regions, however, the new Estonian δ13Corg data sets stand out by relatively small
scatter. The main δ13Ccarb events can usually be identified in the δ13Corg curves; the
agreement between the two curves is particularly good in the Darriwilian and
Sandbian. Starting from the Katian, the paired curves tend to show different
magnitudes, and occasionally slightly diachronous nature or even opposite trends.
Few δ13Corg anomalies observed in one section only are likely related to specific
facies conditions, restricted biota, or early diagenetic effects. On a basinal scale, the
average δ13Corg (as well as δ13Ccarb) values increase towards deeper-water settings.
The Δ13C curves show an overall increasing trend by 1–2‰ in the Viki and Lelle
sections, which agrees with the global data compilation and may suggest a global
driver, such as change in pCO2 and pO2. However, a more pronounced Δ13C
increase occurs in the early Katian post-dating GOBE, and in places the broader
trend is masked by stratigraphically constrained local/regional shifts of up to 5‰.
In summary, the new paired carbon isotope records reveal mixed signatures from
global changes in carbon sequestration and environments, as well as basinal trends
and locally induced shifts. The latter two have limited value for stratigraphy, but may
aid understanding facies changes and diagenetic environments.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
25
Why was there no GOBE in Western Laurentia?
Hofmann, Richard1*
1Evolution and Geoprocesses, Leibniz Institute for Evolution and Biodiversity Science, Museum für
Naturkunde Berlin, Germany
*Corresponding author: richard.hofmann@mfn.berlin.de, fossilrich@gmail.com
Most recent studies have shown that, on a global scale, the main phase of the Great
Ordovician Biodiversification Event (GOBE) can be tied to the Dapingian and early
Darriwilian substages. The Upper Cambrian to Middle Ordovician Pogonip Group of
the Basin and Range Province (western U.S.) represents one of the most
fossiliferous shallow marine successions that straddle this critical time interval.
Superb outcrop conditions in the Ibex Area in western Utah allow for almost
continuous sampling of benthic communities throughout much of Lower and Middle
Ordovician strata. It thus holds great potential to shed light on early phases of the
GOBE. Quantitative palaeoecological analysis of mainly benthic communities was
used to reconstruct diversity patterns on the local community level.
First of all, the late Dapingian to Darriwilian Kanosh Formation fails to record a
notable within-clade diversification among benthic groups (i.e. brachiopods, trilobites,
gastropods), which is seen elsewhere in Laurentia and worldwide.
Palaeocommunities are fairly uniform and low in alpha (within community) diversity
and beta (differential diversity between communities) diversity. These patterns are
most readily explained by comparable harsh local environmental conditions that are
prevalent in the Kanosh system including high siliciclastic input (accompanied by
possible salinity fluctuations), and intertidal to supratidal habitats.
The stratigraphically older Wah Wah (late Floian) and Juab (early Dapingian)
Formations show that this low diversity (and hence the delayed radiation) may be
deeper rooted in larger scale environmental controls. The communities of the Wah
Wah Formation are the most diverse of the Pogonip Group but decline towards the
upper part of the unit. The transition to the overlying Juab Formation, which straddles
the Floian–Dapingian boundary, is marked by a notable drop in species richness and
a complete turnover in both trilobite and brachiopod faunas. The fact that much of the
brachiopod diversity before this boundary “event” was aggregated at low systematic
levels (genera and families) provides evidence for an early stage of the GOBE
already taking place in the late Floian in western Laurentia. The hypothesized
Floian–Dapingian boundary event could have reset the nascent emergence of fairly
diverse, typically Palaeozoic-type communities. Data from Baltica show a similar
pattern suggesting that the Floian–Dapingian transition could be of interregional
significance.
However, the diversity loss may not be perceived as “extinction” because the
diversity has been low throughout the Early Ordovician anyway. The analysis of local
communities reveals that such events, in fact, reset the clock for intra-clade
diversification which, in sum, could explain the damping of diversity dynamics before
the sudden radiation of clades since the middle Ordovician. Probable environmental
controls that would explain this pattern are recurrent anoxic phases and generally
high sea surface temperatures in Early Ordovician shallow marine waters.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
26
Two ‘Silurian-type’ stromatoporoid genera from the Upper
Ordovician Beiguoshan Formation of North China, and their
tectonic and faunal implications
Jeon J.1,2, Liang K.1, Kershaw, S.3, and Zhang Y.1,2*
1State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and
Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of
Sciences, 39 East Beijing Road, Nanjing 210008, China
2University of Chinese Academy of Science (UCAS), Beijing 100049, China
3Department of Life Sciences, Brunel University, Kingston Lane, Uxbridge, UB83PH, United Kingdom
*Corresponding author: ydzhang@nigpas.ac.cn
Stromatoporellid Simplexodictyon and clathrodictyid Plexodictyon are widely
distributed in Silurian and Devonian strata. They are considered to be typical
‘Silurian-type’ stromatoporoids, and thought to have originated in the Wenlock and
Ludlow epochs, respectively. In this study, we report these two genera from the
Upper Ordovician Beiguoshan Formation at Tiewadian, on the southern margin of the
Ordos Basin, Shaanxi Province of North China. The age of the formation is estimated
to be middle Katian, judging from the presence of conodont Taoqupognathus
beiguoshanensis, as well as fossil assemblages including corals, brachiopods, and
graptolites. This finding represents the earliest known record of these genera, and
extends significantly their stratigraphic ranges to earlier times. Their incomplete fossil
records in North China, i.e. the missing of Silurian and Devonian occurrences, are
here interpreted as largely due to the regional sea-level fall in response to the
tectonic uplift of North China during the Late Ordovician, known as the Huaiyuan
Epeirogeny, which led to the absence or erosion of the contemporary stratigraphic
records. In addition, our taxonomic restudies show some of the previously described
Ordovician-Silurian ‘Clathrodictyon’ from peri-Gondwana might not be true
‘Clathrodictyon’ and require further taxonomic investigations. The discovery of
Simplexodictyon and Plexodictyon from the Upper Ordovician adds to our knowledge
on the early diversification of clathrodictyids and clathrodictyid-stock (i.e.
stromatoporellids) taxa, and is crucial for a better understanding of the early
evolutionary history and paleobiogeography of stromatoporoids.

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Early–Middle Ordovician seascape-scale aggregation pattern of
sponge-rich reefs across the Laurentia Paleocontinent
Kröger, Björn1* and Penny, Amelia M.1
1Finnish Museum of Natural History, University of Helsinki, P.O. Box 44, 00560 Helsinki, Finland,
*Corresponding author: bjorn.kroger@helsinki.fi
During the late Cambrian – Early Ordovician the predominant non-microbial reef
builders were sponges or sponge-like metazoans. During the Early – Middle
Ordovician interval metazoans became dominant reef builders. A comparison of
sponge-rich reefs from eight sites of the Laurentia paleocontinent demonstrates that
reef deposition pattern changed across reef – seascape scales in this time interval.
The oldest reefs in this study were deposited during the earliest Tremadocian and
contain abundant microbialites. They grew directly on hard substrate and formed
meter-thick coalescent banks and sheets. Younger reefs are commonly bioturbated
with less microbial textures. These late Tremadocian – Middle Ordovician reefs form
discrete patches and clusters and their growth is not exclusively associated with
underlying hard substrate. Three different seascape level reef growth patterns can be
distinguished: (1) mosaic mode of reef growth, where reefs form a complex spatial
mosaic dependent on hard substrate; (2) episodic mode, where patch reefs grew
exclusively in distinct unconformity bounded horizons within non-reefal lithological
units that have a much larger thickness; and (3) belt-and-bank mode, where reefs
and reef complexes grew vertically and laterally as dispersed patches largely
independent from truncation surfaces. We speculate that the early – Middle
Ordovician trend from mosaic to belt-and-bank mode of reef growth was partly driven
by intensified bioturbation.

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A new Lower Ordovician nektaspid euarthropod from Morocco
Pérez-Peris, Francesc1, Laibl, Lukáš1,2*, Lustri, Lorenzo1, Gueriau, Pierre1, Antcliffe,
Jonathan B.1, Bath Enright, Orla G.1, and Daley, Allison C.1
1Institute of Earth Sciences, University of Lausanne, Géopolis, CH-1015 Lausanne, Switzerland
2Czech Academy of Sciences, Institute of Geology, Rozvojová 269, 165 00 Prague 6, Czech Republic
*Corresponding author: lukaslaibl@gmail.com
Nektaspids are non-biomineralized euarthropods that were at the peak of their
diversity during the Cambrian Period. Post-Cambrian nektaspids are a low-diversity
group with only a few species described so far. Tariccoia tazagurtensis is a new
species of small-bodied nektaspid (of the family Liwiidae) from the Lower Ordovician
Fezouata Shale of Morocco. This species is characterized by a sub-circular cephalon
with pointed genal angles and with a marginal rim; a thorax consisting of four tergites,
the 1st and 2nd of which are overlapped by the cephalic shield; and by a pygidium
with its anterior margin curved forwards, a rounded posterior margin and a long
medial keel that does not reach the posterior pygidial border. T. tazagurtensis differs
from the type (and only other known) species from the Ordovician strata of Sardinia
(Italy), Tariccoia arrusensis, mainly in its cephalon and pygidial morphologies. The
two specimens of T. tazagurtensis preserve remains of the anterior part of the
digestive tract, which are comparable to the ramified digestive glands seen in the
Cambrian nektaspids Naraoia and Misszhouia canadiensis. The rare occurrence of
T. tazagurtensis in the Fezouata Shale and the distribution of other liwiids suggest
that these liwiids were originally minor members of open-marine communities during
the Cambrian, and migrated into colder brackish or restricted seas during the
Ordovician.

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Estimating dispersal and evolutionary dynamics in diploporan
blastozoans (Echinodermata) across the Great Ordovician
Biodiversification Event
Lam, Adriane R.1*, Sheffield, Sarah L.2, and Matzke, Nicholas J.3
1Department of Geological Sciences and Environmental Studies, Binghamton University, 4400 Vestal
Parkway East Binghamton NY, U.S.A.
2School of Geosciences, University of South Florida, 4202 E Fowler Ave, NES 107, Tampa, FL 33620,
U.S.A.
3School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New
Zealand
*Corresponding author: alam@binghamton.edu
Robust statistical inference of early Paleozoic macroevolutionary patterns of
invertebrate taxa have been primarily focused on brachiopods and trilobites. These
taxa, along with other clades, have been used to infer the drivers and impacts of
Ordovician diversification events, namely the Great Ordovician Biodiversification
Event (GOBE). To date, echinoderm paleobiogeographic patterns have been
excluded from these statistical analyses. In this study, we use a phylogenetic
hypothesis of early Paleozoic diplopore-bearing blastozoan echinoderms to estimate
ancestral biogeographic histories and dispersal pathways across the GOBE to infer
their drivers of evolution and dispersal. The number and type of dispersal events for
three Ordovician time slices that encompass the time before, during, and after the
GOBE was estimated using Biogeographic Stochastic Mapping (BSM) within
BioGeoBEARS. The best-fit model incorporated jump dispersal, and indicated
several source regions for blastozoans, with deep nodes within the tree indicating a
Gondwana or Baltic origin. From the BSM analysis, the most dispersal occurs in the
Early to Middle Ordovician, with several events occurring between Gondwana and
Laurentia, and Laurentia and Baltica. There are reduced dispersal events within the
Middle Ordovician GOBE interval, but it is clear that Baltica and Laurentia exchanged
taxa during this time. During the Late Ordovician, there is again an increase in
dispersal events between Baltica, Laurentia, and Gondwana. These reconstructed
dispersal events indicate that oceanic gyre systems, currents, and upwelling regions
were likely important factors to facilitate species movement on a global scale.
Speciation events plotted against δ18O and other geochemical data indicate the
blastozoan speciation events are not clustered during times of global cooling, unlike
speciation events for brachiopods and trilobites. Additional phylogenetic hypotheses
of this group will further reveal drivers of echinoderm speciation through the early
Paleozoic.

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New contributions on the paleobiogeography of linguliform
brachiopods from Ordovician of the Precordillera Argentina
Lavié, Fernando Julián1* and Benedetto, Juan Luis1
1CICTERRA, CONICET-Universidad Nacional de Córdoba. Vélez Sarsfield 1611, X5016GCA
Córdoba, Argentina
*Corresponding author: fernandolavie@gmail.com
In the last decade, several analyzes on the biogeographic distribution of Ordovician
linguliform brachiopods have been carried out (e.g. Popov et al., 2013; Holmer et al.,
2016). In the present study, we reassess the biogeographic affinities of the Middle
and Upper Ordovician linguliform genera recorded globally, including new data from
the Precordillera of western Argentina (Cuyania terrane). Clustering analyzes and
PCoA (Principal Coordinate Analysis) were performed using the Dice and Raup-Crick
indices in two sets of taxa, one including the genera present in the Middle Ordovician
and the other those present in the Upper Ordovician (both excluding endemic
genera). Results obtained in this paper based on linguliform brachiopods mostly
match with the patterns observed in other benthic groups from Cuyania (mainly
rhynchonelliformean brachiopods). During the Darriwilian, many of the genera from
the Precordillera show clear Laurentian and Baltic affinities, sharing with these
regions at least 13 genera (excluding cosmopolitan and widely distributed taxa).
Additionally, there are several genera in common with the Kazakhstanian terranes.
Another remarkable feature is the appearance in the Precordillera of some endemic
taxa, which also have been recorded in the Famatina Range, on the western margin
of Gondwana. By the Late Ordovician, however, despite the scarcity of data at the
global scale (Popov et al., 2013), many genera become restricted to Laurentia and
are absent in the Argentine Precordillera. This pattern may be due to the fact that at
this time the Cuyania terrane was already close to the western margin of Gondwana
(the so-called “pre-accretion stage”, Benedetto et al., 1999).
References:
Benedetto, J.L., Sánchez, T.M., Carrera, M.G., Brussa, E.D., & Salas, M.J. 1999.
Paleontological constraints on successive paleogeographic positions of
Precordillera terrane during the early Paleozoic. In: Ramos, A., and Keppie, J.
D., (eds.) Laurentia-Gondwana connections before Pangea. Geological
Society of America Special Paper 336: 21–42.
Holmer L.E., Popov L.E., Lehnert O. y Ghobadi Pour M. 2016. Ordovician
(Darriwilian-Sandbian) linguliform brachiopods from the southern Cuyania
Terrane of west-central Argentina. Memoirs of the Association of Australasian
Palaeontologists 49, 31–50.
Popov, L.E., Holmer, L.E., Bassett, M.G., Ghobadi Pour, M. y Percival, I.G. 2013.
Biogeography of Ordovician linguliform and craniiform brachiopods. In: D.A.T.
Harper and T. Servais (Eds.) Early Palaeozoic Biogeography and
Palaeogeography. Geological Society London, Memoirs 38: 117–126.

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The great Ordovician diversification of echinoderms: deciphering a
complex global signal
Lefebvre, Bertrand1*, Nardin, Elise2 and Nohejlová, Martina3
1UMR CNRS 5276 LGLTPE, Université Claude Bernard-Lyon 1, 69622 Villeurbanne, France
2UMR CNRS-IRD-UPS 5563, Géosciences Environnement Toulouse, Observatoire Midi-Pyrénées,
31400 Toulouse, France
3Czech Geological Survey, Klárov 3, 118 21 Praha 1, Czech Republic
*Corresponding author: bertrand.lefebvre@univ-lyon1.fr
The most dramatic increase in echinoderm diversity and disparity took place during
the Ordovician, with a peak of about 15 classes instead of e.g. only 5 in the latest
Cambrian (Furongian) and in post-Palaeozoic seas. The global analysis of about
2,000 Ordovician echinoderm taxa recovered from over 300 areas worldwide
suggests that their diversity remained relatively low from the Tremadocian to the
Dapingian, before rising from the Darriwilian to the Katian, and finally collapsing in
the Hirnantian. Taxonomically, this pattern largely depicts the major diversification of
crinoids, which represent from 30 to 70 percent of the whole echinoderm diversity,
and become, during the Ordovician, one of the major components of marine
ecosystems. However, the analysis of the geographic origin of included taxa
indicates a strong historical and/or sampling bias towards Laurentian faunas (e.g.
North America, Scotland; 20 to 50 percent of the data), themselves largely dominated
– faunistically – by crinoids. Zooming in on the situation in other well-represented
areas in the database (e.g. Avalonia, Baltica, high-latitude Mediterranean Province)
provides distinct regional temporal patterns of biodiversity, and especially on non-
crinoid-dominated faunal compositions. However, Ordovician echinoderm faunas
remain very poorly known in many other areas in the world (e.g. Australia, Central
and Southeastern Asia, China, South America, Siberia). In recent years, significant
sampling efforts in some areas (e.g. Morocco) have significantly modified our
knowledge of some regional faunal assemblages and contributed to fill in databases,
which, however, still remain largely dominated by data from a single palaeocontinent.

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The palaeokarst in the Xiazhen Formation (Late Ordovician): a
record of the mid-Katian glaciation in South China
Li, Q.1-3*, Lehnert, O.1-4, Wu, R.1,2, Park, J.5, Liang, K.1,2, Yu, S.1,2, Mao, Y.1,2 and
Na, L.1,2
1State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and
Palaeontology, East Beijing Road 39, Nanjing 210008, China
2Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, East Beijing
Road 39, Nanjing 210008, China 3GeoZentrum Nordbayern, Friedrich-Alexander University
Erlangen Nürnberg, 91054 Erlangen, Germany
4Faculty of Environmental Sciences, Department of Environmental Geosciences, Czech University
of Life Sciences, Prague 16500, Czech Republic
5Institute of Construction and Environmental Research, Handong Global University, Pohang 37554,
Republic of Korea
*Corresponding author: qjli@nigpas.ac.cn
Sedimentary record and oxygen isotope data from different palaeocontinents
display multiple episodes of moderate glaciation and deglaciation during Katian
(Late Ordovician) times with a glacial peak in the middle Katian. In South China,
the Katian palaeokarst in the Xiazhen Formation at Zhuzhai, briefly reported
several years ago, was recently investigated in detail. There, the Xiazhen
Formation has been re-studied and divided into four informal members: a lower
limestone member, a lower shale member, a middle mixed-lithology member, and
an upper shale member. The palaeokarst occurs in the top part of the middle
mixed-lithology member, where karstified limestones are capped by greenish to
brownish shales of the upper shale member displaying a significant sea level rise.
The palaeokarstic surfaces show an irregular topography, with shale fillings in
potholes and cracks descending down at least 7.5 metres. Based on new
conodonts collections, the Yaoxianognathus yaoxianensis Zone has been
confirmed in the limestones below the palaeokarst surface, corresponding in age to
stage slices Ka2 and top of Ka1. This biostratigraphic result coincides with
published conodont data from the type section at Tashan (Waicun), implying that
the lower part of the Xiazhen Formation should be correlated to the early Katian
rather than late Katian as previously assumed. High resolution δ13Ccarb data record
the Kope and Fairview excursions in the middle mixed-lithology member. These
chemostratigraphic data show stratigraphical overlaps between the sub- sections at
Zhuzhai. Published graptolite data suggest a late Katian (Ka4) age for the upper
shale member infilling the cracks and cavities cutting down from the karst surface
into the underlaying limestones and overlaying this surface. Thus, the time of
subaerial exposure falls into the mid-Katian when the corresponding, dramatic and
globally recognized glacio-eustatic sea-level fall affected and widely karstified
tropical and subtropical carbonate platforms (e.g., Baltica, Laurentia).

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Re-explore the biological affinity of chitinozoans: Evidence from
morphological variation and exceptional specimens
Liang, Y.1*, Hints, O.2, Bernardo, J.3, Goldman, D.4, Nõlvak, J.2, Tang, P.1 and Wang,
W.5
1State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and
Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
2Department of Geology, Tallinn University of Technology, Tallinn 19086, Estonia
3Department of Biology, Texas A & M University, Texas 77843, USA
4Department of Geology, University of Dayton, Ohio 45469, USA
5School of Geosciences and Info-Physics, Central South University, 410083 Changsha, China
*Corresponding author: liangyan@nigpas.ac.cn
As an extinct group of cryptic organic-walled microfossils, chitinozoans widely
distributed in Ordovician to Devonian marine sedimentary rocks, however, with a
hitherto debated biological affinity. Since the first description in the 1930s, they have
been classified as multiple groups of protists, metazoans or egg capsules of
metazoans. A fungi hypothesis, possible polyphyletic origin, vegetative reproduction,
and ontogenetic development have also been hypothesized, however, with less
general acceptance. Over the last three decades, chitinozoans have almost
exclusively been interpreted as eggs of unknown marine metazoans, possibly some
wormlike animals. Nevertheless, no further discussions related to their affinity have
been advanced.
In our recent study, three-dimensionally preserved specimens of Hercochitina violana
show a highly variable morphological variation. A compiled size variation dataset of
chitinozoan species and a dataset of coefficients of variation (CV) in eggs of extant
aquatic metazoan have been carried out. The result shows that the magnitude of the
size variation within chitinozoan species is larger than observed in fossil and modern
eggs, which indicates, more plausibly, chitinozoans are not eggs. Furthermore, the
previously reported abnormal specimens which preserved as “vesicle-in-vesicle” turn
out to be the key specimens during the life history of chitinozoans. All of those
specimens are distinguished by occupying regularity and repeatability, i.e., a
complete vesicle carrying one or several “less-complete” but highly similar one(s) at
the base. With more details decoded by the Field Emission Scanning Electron
Microscope and X-ray micro-computed tomography, the “less-complete” specimens
are verified to be or to have the potential to develop into a complete specimen, which
points to a reproduction stage. Herein, chitinozoans should not be eggs, instead, they
are an independent group of microorganisms.

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Recent developments in the paleobiology and taphonomy of
trilobites from the Walcott-Rust Quarry (Upper Ordovician)
Losso, Sarah R.1*, Ortega-Hernández, Javier1
1Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street Cambridge
USA 02138, United States of America
*Corresponding author: sarahlosso@g.harvard.edu
Trilobites are the dominant group of macroscopic euarthropods throughout the
Paleozoic, and are known primarily from their biomineralized dorsal exoskeletons.
Despite their impressive diversity (ca. over 20,000 described species) the
appendicular ventral anatomy of trilobites is only known from 31 taxa, most of which
consist of highly compressed macrofossils. In 1879, Charles Doolittle Walcott
reported the preservation of trilobite appendages preserved in 3D from the Upper
Ordovician Spillway Member (Rust Formation; Trenton Group) in Herkimer County,
New York. Over 280 thin-sections from this site are housed at the Museum of
Comparative Zoology at Harvard, most of which belong to the phacopids Cerausus
pleurexanthemus and Flexicalymene senaria. Walcott-Rust trilobites show that non-
biomineralized tissues are exceptionally preserved by an isopachous rim of fibrous
calcite perpendicular to the exoskeleton, and sparry calcite crystals that completely
fill the void formed by the body. The occurrence of calcite had previously been
attributed to a microenvironment created during decay (Brett et al., 1999). This
peculiar mode of calcite preservation captures exceptional detail, including delicate
structures such as exopod lamellae and endopod endites. However, the precise
appendicular morphology of C. pleurexanthemus and F. senaria has been
controversial given the difficulty of interpreting the preserved anatomy from obliquely-
cut thin sections. Here, we provide an updated account of the work on this iconic
locality, focusing on the taphonomy of soft tissue preservation, distribution of calcite
preservation within the Rust Formation, and trilobite limb morphology.
Extensive restudy of the thin-sections shows that calcite occurs in veins and nodules
throughout the matrix, and are not isolated within the fossil specimens. Whereas all
previous findings of calcite preservation were from Layer 3 in Spillway Member, new
discoveries demonstrate a stratigraphically wider distribution. Comparisons of thin-
sections with computed tomographic scans of partially enrolled trilobite specimens
allow to better understand the orientation of the thin sections, and facilitate precise
morphological interpretations. Future work will characterize the taphonomic pathway
through use of elemental and isotopic analysis, compare the calcite preservation of
Walcott Rust with that of the Silurian Herefordshire Biota in England, and reconstruct
the 3D limb morphology of C. pleurexanthemus and F. senaria. The Walcott-Rust
specimens provide a unique opportunity to study exceptional Ordovician 3D
preservation of animal soft tissues.
References:
Brett, C.E. Whiteley, T.E., Allison, P.A. & Yochelson, E. 1999. The Walcott-Rust
Quarry: Middle Ordovician Trilobite Konservat-Lagerstätten. The
Paleontological Society, 73, 288-305.doi.org/10.1017/S0022336000027773

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Marine substrate change and biodiversity in the Ordovician
Penny, Amelia M.1*, Hints, Olle2, Desrochers, André3 and Kröger, Björn1
1Finnish Museum of Natural History, P.O. Box 44 (Jyrängöntie 2), FI-00014, University of Helsinki,
Finland
2Department of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia
3University of Ottawa, STEM Complex, 150 Louis-Pasteur Private, Ottawa, Ontario, Canada
*Corresponding author: amelia.penny@helsinki.fi
The Ordovician was a time of tremendous evolutionary and environmental upheaval,
incorporating both the unprecedented marine diversification of the GOBE, and
substantial changes in shallow marine environments at both local and global scales,
mediated by a complex interplay between biotic and abiotic processes.
Understanding how early Palaeozoic environments constrained biotic evolution is a
major topic of palaeoenvironmental research, though knowledge of the magnitude
and nature of the feedbacks between proliferating macroscopic life and global
environments is less completely developed.
Among the regional-scale environmental changes of the Ordovician were the
development of extensive shallow marine carbonate shelf environments, together
with the expansion of novel habitats generated by metazoan ecosystem engineers.
Drawing on data from both Baltica and Laurentia palaeocontinents, we evaluate the
impact of regional substrate changes on diversity at a variety of spatial and temporal
scales.
We used the Ordovician-Silurian record of the Baltic palaeobasin as a case study,
using hierarchical diversity partitioning to evaluate the impacts of environmental
heterogeneity and temporal turnover on brachiopod diversity patterns, using data
from the Paleobiology Database and the database of the Geoscience Collections of
Estonia. We find that the development of an extensive carbonate shelf in the Baltic
palaeobasin during the Sandbian-Katian had a major influence over regional diversity
patterns because of the relatively high heterogeneity (beta diversity) of assemblages
in these carbonate-dominated environments.
The development of widespread metazoan reefs in the Baltic paleobasin occurred
alongside this diversification, and imposed small-scale habitat heterogeneity on
marine seascapes. The Middle Ordovician rise of metazoan reefs enhanced
complexity in shallow marine environments, which can be investigated in areas of
exceptional exposure. With reference to metazoan reefs of the Mingan Archipelago,
Quebec, we explore the forms of seascape heterogeneity generated by this change
in carbonate deposition at community scale.
Developing understanding of the interactions between environmental and faunal
heterogeneity is required for a mechanistic picture the long-term development of
marine ecosystems. The early Palaeozoic marks the inception of major metazoan
impacts on marine environments, and developing knowledge of these links could
have general implications for our understanding of the feedbacks between
macroscopic life and global environmental change.

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The trilobite assemblage of the “Declivolithus Fauna” (Katian) of
Morocco: a review with new data
Pereira, Sofia1*, Rábano, Isabel2 and Gutiérrez-Marco, Juan Carlos3
1Centro de Geociências, Universidade de Coimbra, Rua Sílvio Lima, 3030-790 Coimbra, Portugal
2Instituto Geológico y Minero de España, Ríos Rosas 23, 28003 Madrid, Spain
3Instituto de Geociencias (CSIC, UCM), and Área de Paleontología GEODESPAL, Facultad de
Ciencias Geológicas, José Antonio Novais 12, 28040 Madrid, Spain
*Corresponding author: ardi_eu@hotmail.com
The very peculiar Upper Ordovician trilobite Declivolithus Přibyl & Vaněk
(Trinucleinae) was defined in the Voltuš Fm (Rožmitál trough) of the Czech Republic
and later recognized in the High Atlas and the Anti-Atlas of Morocco. Within the
Prague Basin, it occurs in the Bohdalec Fm (upper Berounian), and, putatively, in the
underlying Zahořany Fm (middle Berounian). Previous records of Declivolithus-
bearing assemblages from Morocco (Destombes 1971; Fortey & Edgecombe, 2017)
were assigned to the middle Katian based on trilobite biostratigraphical correlation
with the Bohdalec Fm. This unusually large trinucleid is the most conspicuous
element of an assemblage occurring in the Bofloss locality, a local biofacies
development of pelagic mudstones and sandstones cropping out in a small anticline,
isolated by faults, in the Tizi n’Oufite area. Its stratigraphical correlation remains
problematic due to the structural setting, but it probably corresponds to the upper part
of the Lower Ktaoua Fm, although a correlation with the lower half of the Upper
Tiouririne Fm cannot be excluded.
The assemblage is composed almost exclusively of trilobites preserved either in grey
fine mudstones or in coarse-grained sandstones, with scattered representatives of
graptolites, machaeridians, echinoderms and brachiopods. The “Declivolithus fauna”
trilobite assemblage is herein revised, being dominated by Declivolithus and
abundant cyclopygids (Cyclopyge, Symphysops and Heterocyclopyge), with fewer
representatives of Dionide, Eudolatites, Nobiliasaphus, Phacopidina, Prionocheilus,
Selenopeltis and a new species of Ulugtella? The preservation allows a systematic
revision of some species previously known from Bohemia, but the biostratigraphical
data are not definite. Although some support the previous assignment of the
Moroccan assemblage to the upper Berounian, a middle Berounian age cannot be
excluded. The type-locality of Declivolithus is also of difficult correlation, due to its
location within a faulted block (Rožmitál) and has been mostly assigned to the middle
Berounian due to the presence of the brachiopod Aegiromena aquila. Its trilobite
assemblage has seven of ten species in common with the Bofloss assemblage. The
recent revisions on the Upper Ordovician trilobites of Morocco suggest that this
region and the Czech Republic are within the same cluster of high Gondwanan
latitude. At least from Sandbian until mid Katian, the fossil assemblages of Bohemia
are greatly correlated at species level with those from Morocco.
References:
Destombes, J. 1971. L’Ordovicien au Maroc –essai de synthèse stratigraphique.
Mém. Bureau de Recherches Géologiques et Minières 73, 237–263.
Fortey, R. A. & Edgecombe, G. D. 2017. An Upper Ordovician (Katian) trilobite fauna
from the Lower Ktaoua Formation, Morocco. Bulletin of Geosciences 92, 311‒
322. doi: 10.3140/bull.geosci.1649

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Keratose sponge–microbial carbonate consortium in the columnar
“stromatolites” and “thrombolite” mounds from the Lower
Ordovician Mungok Formation, Yeongwol, Korea
Pham, Duy1 and Lee, Jeong-Hyun1,2*
1Department of Astronomy, Space Science, and Geology, Chungnam National University, 99 Daehak-
ro, Yuseong-gu, Daejeon 34134, Republic of Korea
2Department of Geological Sciences, Chungnam National University, 99 Daehak-ro, Yuseong-gu,
Daejeon 34134, Republic of Korea
*Corresponding author: jeonghyunlee@cnu.ac.kr
Lower Ordovician “stromatolites” and “thrombolites”, composed of keratose sponges
and microbial carbonates, are reported from the Mungok Formation (Tremadocian),
Yeongwol, Korea. The columnar “stromatolites” are up to 10 cm in width and height,
and consist of the inner core with lower-angled (10–45º) layers that are covered by
higher-angled (>45°) layers. The inner core is made up of keratose sponges
alternating with microbial carbonates, whereas microbial carbonates dominantly
consist of the outer cover. The “thrombolite” mounds are up to 100 cm high and 40–
60 cm wide domes embedded within ribbon rocks. These thrombolite mounds
comprise the keratose sponge-microbial carbonate “clots” and minor lithistid sponge-
microbial carbonate “clots”. The columnar “stromatolites” formed under high-energy
subtidal setting, where laminoid keratose sponges alternate with microbial carbonate
and form the columns. On the other hand, “thrombolite” mounds developed under
low-energy environments possibly below normal wave base, where bulbous to
globular keratose sponges formed the “clots”, and microbial carbonates developed
within the sponges by soft-tissue degradation, probably by sulfate-reducing bacteria.
Lithistid sponges and microstromatolites developed small “clots” in between the
keratosan-microbial clots.
The current study demonstrates the importance of hydrodynamic controls on
overall reef morphology and configurations during the Early Ordovician. Columnar
“stromatolites” represent tight laminar frame reefs, formed under high-energy
environments, whereas “thrombolite” mounds are similar to cluster reefs developed in
low-energy environments. Coeval lithistid-microbial reefs mainly developed under
intermediate-energy conditions. The keratose and lithistid sponges rarely occur
together in the reefs, suggesting that there could have been ecological or
environmental factors affecting the distribution of these sponges in reef habitats. The
increasing reports of keratosan-microbial consortium from the early Paleozoic
successions worldwide suggest that these may be an integral component of the
Great Ordovician Biodiversification Event, together with the coeval lithistid sponge-
microbial consortium.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
38
How do ecological niches evolve during Ordovician environmental
change? A test using Laurentian brachiopods
Purcell, Ceara, K.Q.1* and Stigall, Alycia L.1,2
1Department of Geological Sciences, Ohio University, 139 University Terrace, Athens OH, USA
2OHIO Center for Ecology and Evolutionary Studies, Ohio University, 139 University Terrace, Athens
OH, USA
*Corresponding author: cp698919@ohio.edu
The Ordovician was a complex interval of Earth history, characterized by dramatic
environmental changes including climatic shifts, sea level fluctuations, and explosive
biotic diversification. In order to understand the impact these changes had on ancient
ecosystems, it is necessary to investigate the temporal correlation between species
ecological responses and changing environmental factors. This project addresses
this complex relationship by using ecological niche modelling (ENM) to quantify
patterns in Laurentian brachiopod niche occupation over the course of multiple
environmental changes in the Ordovician.
ENM analysis requires taxon occurrence and environmental layer data. Brachiopod
occurrence data were downloaded from the Paleobiology and iDIGBio Databases
(Fig. 1). Major gaps in the records were supplemented with field investigation of
under- sampled Ordovician strata. Environmental layers were created using detailed
stratigraphic records published in relevant literature or collected in the field. Niche
models were generated for stage-level time slices over the entire Ordovician Period
using Maxent. For genera that could be modelled in multiple time slices, niches were
compared among distinct intervals. The degree of similarity between models of
adjacent time slices was analysed, and patterns of niche stability versus evolution
were compared with contemporaneous local and global environmental change.
Patterns in niche occupation reveal that rates of niche stability differed during
intervals of abiotic versus biotic environmental change. Similarly, trends in niche
evolution differ between generalist and specialist taxa, particularly in response to
rapid competitive pressures. The results of this study indicate that species respond
differently based on different types and rates of environmental change, and suggest
that major environmental changes in the modern can have similar long-term
ecological results.
Figure 1: Occurrence data for Ordovician
brachiopods downloaded from the PBDB and
iDIGBio Databases. This initial dataset
comprises over 33,000 discrete occurrence
points.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
39
Integrated bio- and chemostratigraphy of the upper Homerian
(Silurian) from the Kleczanów PIG - 1 well (Holy Cross Mountains,
Poland)
Radzevičius Sigitas1*, Trela, Wieslaw2, Garbaras Andrius3, Kudžma, Donatas1 and
Užomeckas, Marius1
1Department of Geology and Mineralogy, Institute of Geosciences, Vilnius University, M. K. Čiurlionio
21/27, LT-03101, Vilnius, Lithuania
2Polish Geological Institute–National Research Institute, Zgoda 21, 25-953 Kielce, Poland
3Center for Physical Sciences and Technology, Nuclear Research Department, Vilnius University,
Saulėtekio av. 3, 10257 Vilnius, Lithuania
*Corresponding author: sigitas.radzevicius@gf.vu.lt
A distinctive biotic crisis (including graptolite and conodonts) referred to as the Mulde
Event was recognized worldwide in the upper Homerian of Silurian period. It has a
conspicuous carbon isotopic signature referred to the middle-late Homerian
glaciation and climate aridity.
New carbon isotope data have been obtained from Silurian dark shales of the
Prągowiec Beds in the Kleczanów PIG – 1 borehole (depth 206 – 178 m), which is
located in the southern Holy Cross Mountains (Poland). Samples for δ13Corg analysis
were collected approximately every 1 m. They were grinded and dissolved using 5 N
of HCl acid to remove carbonate material, and then washed with distilled water and
dried. The stable carbon isotope values from organic material were measured using
Thermo Gasbench II coupled with a Thermo Delta V isotope ratio mass
spectrometer.
The stratigraphy of studied well was established based on graptolites, which
indicates the presence of the lundgreni, parvus - nassa, praedeubeli, deubeli,
ludensis and nilssoni biozones.
The δ13Corg values are stable in the lower part of investigated interval of the
Kleczanów PIG – 1 borehole and rise from -31.7 ‰ (lundgreni Biozone) to maximum
of -29.22 ‰. The maximum value of δ13Corg is reached at the lundgreni/parvus
biozonal boundary and falls to -30.81 ‰ near the boundary of the nassa/praedeubeli
biozones. The δ13Corg values rise again to -29.78 ‰ in the deubeli Biozone and
decrease to -31.36 ‰ in the upper part of the ludensis biozone. There are stable
values of δ13Corg in the upper part of ludensis and lower part of nilssoni biozone,
varying from -31.21 to -31 ‰.
According to these findings, the lundgreni, parvus, nassa, praedeubeli, deubeli,
ludensis and nilssoni biozones are distinguished in the studied interval of Kleczanów
PIG – 1 borehole. The thickness of the graptolite biozones are very narrow compared
with those in carbonate facies (e.g. the East Baltic Basin). Both positive δ13Corg value
peaks of the Mulde Event are identified in the investigated interval of Kleczanów PIG
– 1 borehole.

GEUS Report 2020 vol 21
40
Zooming in on the GOBE – Abstract Volume
An astrochronological timescale through the GOBE provides Baltic
intra-basinal insights on climate and richness
Rasmussen, Christian M.Ø.1,2*, Thibault, Nicolas R.3, Rasmussen, Jan. A4., Stouge,
Svend2, Edward, Oluwaseun5, Siggaard-Andersen, Marie-Louise1, Calner, Mikael6,
Nielsen, Arne T.3 and Schovsbo, Niels7
1GLOBE Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark
2Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, DK-1350
Copenhagen K, Denmark
3Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster
Voldgade 10, DK-1350 Copenhagen K, Denmark
4Museum Mors, Fossil and Moclay Museum, Skarrehagevej 8, DK-7900 Nykøbing Mors, Denmark
5Institute of Earth Surface Dynamics, University of Lausanne, Géopolis, 1015 Lausanne, Switzerland
6Department of Geology, Lund University, Sölvegatan 12, SE-223 62, Lund, Sweden
6Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K,
Denmark
*Corresponding author: c.macourm@sund.ku.dk
Recent studies have pinpointed the onset of the Great Ordovician Biodiversification
Event (GOBE) to occur within a narrow timespan of a few million years during the
early–mid Darriwillian. This onset is, as such, well-constrained with climatic changes
suggesting that cooling climate facilitated an Earth-state shift that again led to the
radiations. The Ordovician Baltic Palaeobasin is likely one of the best studied regions
with respect to the GOBE interval. Still, little is known about intra-basinal differences
across clades and ecological niches, as well as temperature proxies at this time. This
is fundamental data that needs to be obtained if one is to understand
macroevolutionary trends and ecosystem evolution.
To address this issue, we have built an astrochronological time scale allowing for
high-precision correlation across the basin. New 18O-brachiopod data, collected bed
by bed from Öland, further enable direct comparison on a bed-by-bed scale across
facies belts and, geographically, across the East Baltic. In addition, new conodont
richness data through the Dapingian–Middle Darriwilian from the Steinsodden area,
southern Norway, permit a similar scale temporal correlation between the deep-water
Norwegian section and that of already published shallow-water brachiopod data from
the St. Petersburg Region, Russia. Thus, enabling direct comparison between the
sessile benthos and the nektobenthos across facies belts in absolute time.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
41
Examining the Climate/Tectonic Implications of Sandbian–Katian
Environmental Change in the Southern Appalachians Utilizing K-
bentonite Apatite Phenocryst Geochemical Correlations
Robinet, Richard M.1*, Haynes, John T.2, Leslie, Steven A.2, and
Herrmann, Achim D.1,3
1Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA, U.S.A
2Department of Geology & Environmental Science, James Madison University, Harrisonburg, VA
22807, U.S.A
3Coastal Studies Institute, Louisiana State University, Baton Rouge, LA, U.S.A.
*Corresponding author: rrobi65@lsu.edu
The stratigraphic record of the late Sandbian to early Katian interval along the
southeastern margin of Laurentia contains evidence of significant environmental
change. However, opposing interpretations exist regarding environmental conditions
during the Late Ordovician. Paramount to developing a clearer understanding of the
relative importance of climate or tectonic drivers for these depositional changes is
correlation between sections with sufficient resolution to distinguish among
alternative explanations for environmentally significant events. To correlate and to
test the interregional synchronicity of important events in the Sandbian-Katian
interval (which includes the GICE, the M4/M5 sequence boundary, conodont
speciation, and changes in carbonate lithologies) we established a K-bentonite
framework based on apatite geochemistry. These isochronous tie-points for K-
bentonite beds, including the Deicke and Millbrig, were established in four spatially
distant sections across the southern Appalachians allowing us to determine the
precise stratigraphic position of these events and their stratigraphic relationships in
time and space.
Results show that magmatic apatite from beds identified as the Deicke and
Millbrig K-bentonites at Fort Payne, AL, Gladeville, TN, Hagan, VA, and Dolly Ridge,
WV display similar elemental concentrations to previous analyses of Deicke and
Millbrig beds, while beds in the upper Stones River and lower Dolly Ridge formations
at Fort Payne and Dolly Ridge display trends similar to previous analyses of the
Elkport K-bentonite. The start of the GICE at Fort Payne begins in the upper Stones
River Fm. and predates the proposed M4/M5 boundary, while both events are
younger than the Elkport K-bentonite. The GICE, M4/M5, and the base of the
Plectodina tenuis zone at Gladeville are coeval, but predate the Millbrig K-bentonite.
The M4/M5 at Hagan and Dolly Ridge is slightly younger than the Millbrig, while
tentative first appearance of Plectodina tenuis and the base of the GICE are slightly
younger than the M4/M5. Additionally, all sections show a shift from peritidal
depositional conditions to shallow ramp or deeper ramp conditions across the M4/M5
boundary. The timing of events and their positioning relative to one another suggests
a causal relationship between the events. However, the order of events and their
positioning relative to K-bentonite stratigraphy differ between sections. This suggests
that the stratigraphic positions of the M4/M5 and the initiation of the GICE do not
always appear as synchronous events in the stratigraphic record, and that their
stratigraphic positions may be influenced by local tectonic forces that can override
climate driven eustatic changes.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
42
Untangling the ecology and fossil preservation knot for Paleozoic
biotas
Saleh, Farid1*, Bath-Enright, O.2, Daley, A.C.2, Lefebvre, B.1, Pittet, B.1 and Antcliffe,
J.B.2
1Université de Lyon, Université Claude Bernard Lyon1, École Normale Supérieure de Lyon, CNRS,
UMR5276, LGL-TPE, Villeurbanne, France
2Institute of Earth Sciences, University of Lausanne, Géopolis, CH-1015 Lausanne, Switzerland
*Corresponding author: farid.nassim.saleh@gmail.com
Fossil deposits are a tangle of multiple signals that make understanding the
functioning of past ecosystems a complicated and fraught process. The main
difficulty is whether differences between fossil sites show an evolutionary or
ecological signal or are influenced by fossil preservation. These processes are not
independent as anatomical or behavioral differences can alter preservational
pathways. It is particularly important to untangle these interacting processes when
examining the animal communities of the Cambrian Explosion and Ordovician
Radiation, where exceptional preservation of soft tissues provides relatively complete
assemblage data. A novel method of data partitioning based on probabilistic
modelling is used to examine these factors with respect to the Walcott Quarry,
Burgess Shale, Canada (510Ma) and the Fezouata Shale, Morocco (c. 475Ma). As
the prototypical Burgess Shale-type locality, the Walcott Quarry, is usually used as a
basis for understanding Cambrian community structure and early ecosystem
evolution. The result of probabilistic modelling shows that the Walcott Quarry biota
best preserves the endobenthic community whilst systematically under-representing
the nekton/plankton. The reverse is true for the Fezouata biota, with under-
representation of the endobenthos. Taken in concert with data from a bioturbation
index for these sites, a new model of comparative taphonomy is developed based on
sedimentary flow timing with respect to organism mortality. These results suggest
that during the Cambrian Explosion and Ordovician Radiation the most exceptional
fossils sites must still be calibrated against each other to understand the unfolding
evolutionary events and ecosystem structures at the transition between the Cambrian
Explosion and the Ordovician Radiation.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
43
The breakup of the L-chondrite parent body, its signature in mid-
Ordovician sediments in Baltoscandia and the precise timing
relative to the Ordovician biodiversity expansion
Schmitz, Birger1*
1Astrogeobiology Laboratory, Department of Physics, Lund University, Sweden
*Corresponding author: birger.schmitz@nuclear.lu.se
The breakup of the L-chondrite parent body (LCPB) in the asteroid belt 465.8 ±0.3
Ma is a unique event in the late history of the solar system. We know of no other
breakup event during the past 3 Gyr of the same magnitude with similar
consequences. Even today the most common type of meteorite falling on Earth, the
L-chondrites, originate from this event. The majority of these L-chondrites have K-
Ar degassing ages of ~470 Myr linking them to the breakup of a ~150 km parent
body in the asteroid belt at that time. There is also ample evidence in Earth's
geological record for this event, such as:
• A one-order-of magnitude increase in the flux of asteroids 0.1–2 km large that
impacted Earth in the 30 Myr period after the breakup. This is the only confirmed
asteroid shower on Earth the past 3 Gyr.
• An extreme abundance of macroscopic (1–21 cm large) fossil L-chondritic
meteorites recovered from Baltic Orthoceratite limestone during quarrying.
• A two to three orders of magnitude increase in extraterrestrial 3He, representing
the most fine-grained dust from the breakup, accompanied by a similar increase in
relict spinel grains from L-chondritic micrometeorites.
Judging from the distribution of extraterrestrial 3He in the Hällekis quarry section at
Kinnekulle the LCPB breakup took place when sea level began to fall in
Baltoscandia, leading to the formation of the prominent Täljsten lowstand deposit.
The Occam's razor explanation to this coincidence is that the enormous amounts of
dust ejected into the inner solar system by the LCPB event shaded Earth from
sunlight. This may have triggered an ice age or accelerated an ice-age trend
already underway; water was transferred from the oceans to continental ice. It
cannot be ruled out, as an alternative explanation, that the LCPB event and a long-
term gradual cooling of the Earth during the Ordovician are both effects of a large-
scale astronomical process that disturbed the inner solar system. One argument in
favour of this scenario is the anomalous character of the micro-meteorite
assemblages of the mid-Ordovician sediments that formed just before the LCPB
event, but more research is needed.
There appears to be different views to what extent the great Ordovician biodiversity
"expansion" (GOBE) is represented by a step-wise series of events or a more-or-
less gradual increase in biodiversity over ~30 Myr. This complicates any attempts
to relate the effects of the LCPB breakup to the GOBE.

Zooming in on the GOBE – Abstract Volume
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Early Palaeozoic diversifications: ‘explosions’ and ‘events’ or a
continuum of change?
Servais, Thomas1*, Cascales-Miñana, Borja1 and Harper, David, A.T.2
1UMR 8198 Evo-Eco-Paleo, CNRS-Université de Lille, 59000 Lille, France
2Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham DH1 3LE, UK
*Corresponding author: Thomas.servais@univ-lille.fr
Based on several ‘high impact’ publications and (text-) books aimed at a general and,
wider audience, it is currently generally considered that the diversification of early
Palaeozoic marine life was established through a number of relatively radical
‘events,’ such as the Cambrian ‘Explosion’ and the Great Ordovician
Biodiversification ‘Event’ (GOBE). In particular the first ‘event’, the Cambrian
‘Explosion,’ is the focus for many research projects, because it is considered, by
many, a truly spectacular moment in the history of life. In the last four decades, the
Ordovician Radiation has also been the subject of numerous studies, and more
recently some authors have considered that the Ordovician biodiversification was a
relatively brief ‘event.’
Here we present a somewhat different scenario. Our review of biodiversity curves of
marine organisms indicates that, despite fluctuations in amplitude (some substantial),
a large-scale, long-term radiation of life took place during the early Palaeozoic Era; it
was aggregated by a succession of more discrete and regionalized radiations across
geographies and within phylogenies. This major biodiversification within the marine
biosphere started during the late Precambrian time and was only finally interrupted in
the Devonian Period. It includes both the Cambrian ‘Explosion’ and the GOBE.
There are sufficient grounds to indicate that the establishment of modern marine
ecosystems took place during a continuous chronology of the successive
establishment of organisms and their ecological communities, developed during the
‘Cambrian substrate revolution’, the ‘Ordovician plankton revolution’, the ‘Ordovician
substrate revolution’, the ‘Ordovician bioerosion revolution’ and the ‘Devonian nekton
revolution’. At smaller scales, different regional but important radiations can be
recognized geographically and some have been identified and named (e.g. those
associated with the ‘Richmondian Invasion’ during the Late Ordovician in Laurentia
and the contemporaneous ‘Boda event’ in parts of Europe and North Africa), in
particular from areas that were in or moved towards lower latitudes, allowing high
levels of speciation on epicontintental seas.
Most available datasets remain incomplete for many geographical areas, but also for
particular time intervals (e.g. the late Cambrian ‘Furongian Gap’).
The early Palaeozoic biodiversification therefore appears to be a long-term process,
modulated by bursts of significant diversity and intervals of inadequate data ; its
progressive character will become increasingly clearer with the availability of more
complete datasets, better global coverage and more advanced analytical techniques.

Zooming in on the GOBE – Abstract Volume
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45
Ordovician Diversification of calcimicrobes and calcareous algae
Shen, Yuefeng1*, Neuweiler, Fritz2 and Zhang, Le1
1Department of Resource Science and Engineering, School of Resources and Environmental
Engineering, Hefei University of Technology, 193 Tunxi Road, Hefei, China
2Department of Geology and Geological Engineering, Laval University, 2325, rue de l'Université,
Québec, Canada
*Corresponding author: yuefengshen@hfut.edu.cn; yuefeng.shen.1@ulaval.ca
Despite the crucial role of epibenthic primary producers (cyanobacteria, green and
red algae), no diversity curves for calcimicrobes and calcareous algae are available
to assess the pyramiding paleoecology characterizing the Ordovician
biodiversification episode. A total of 24 taxa of calcimicrobes and calcareous algae
are identified from a Dapingian to lower Katian succession of carbonate sedimentary
rocks exposed at the Leyayilitag ridge, Bachu Uplift, Tarim Basin, northwest China.
These are 14 taxa of calcimicrobes, seven taxa of Dasycladales, one taxon of
Bryopsidales and two taxa of Cyclocrinales. Within the lower Katian Belodina
confluens Zone, the diversity increases substantially from around five to more than
20 taxa per 2 Ma. This increase in diversity is based on new calcimicrobes (Bija,
Ortonella, Garwoodia, Hedstroemia, Rothpletzella, Phacelophyton, Rauserina) and
the diversification of Dasycladales and Cyclocrinales. By comparison, the global
diversity of calcimicrobes and calcareous algae (derived from literature data) started
to increase earlier, namely within the late Darriwilian Pygodus serra Zone (offset of
about 4 Ma). This offset might be due to the peculiar lithology of the Sandbian
Tumuxiuke Formation (condensed section of red nodular limestones bounded by
disconformities). However, a similar temporal offset is recorded for calathid sponge
mounds. Therefore, the Tarim tectonic microplate (Tarim Block) might display an
endemic–anachronistic character. The diversity curves of Ordovician benthic primary
producers (calcimicrobes, calcareous algae) are similar to those recorded by some
fossil groups, in particular eleutherozoan echinoderms. Global diversification of
calcimicrobs, calcareous algae, non-calcified marine microalgae, phytoplankton in
association with the landing of plants together cooled and oxygenized the Ordovician
and might co-evolve or trigger the Great Ordovician Biodiversification Event.
References:
Shen, Y., & Neuweiler, F. 2016. Taphocoenoses and diversification patterns of
calcimicrobes and calcareous algae, Ordovician, Tarim Basin, China. Canadian
Journal of Earth Sciences 53, 702-711. doi: 10.1139/cjes-2015-0173

Zooming in on the GOBE – Abstract Volume
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46
An exceptional record of early Paleozoic redox change from the
Road River Group, Yukon, Canada
Sperling, Erik A.1*, Melchin, Michael J.2, Fraser, Tiffani3, Stockey, Richard G.1,
Farrell, Una C. 1,4, Bhajan, Liam1, Browne, Tessa N.1, Cole, Devon B.5, Gill, Benjamin
C.6, Lenz, Alfred7, Loydell, David K.8, Malinowski, Joseph9, Miller, Austin J.1, Plaza-
Torres, Stephanie10, Rodewald, Beatrice11, Rooney, Alan D.5, Tecklenburg, Sabrina
A.1, Vogel, Jacqueline M.1, Planavsky, Noah J.5 and Strauss, Justin V.1,9.
1Dept. of Geological Sciences, Stanford University, Stanford, CA, USA
2Dept. of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scota, Canada
3Yukon Geological Survey, Whitehorse, Yukon, Canada
4Geology, Trinity College, Dublin, Dublin, Ireland
5Dept. of Earth and Planetary Sciences, Yale University, New Haven, CT, USA
6Dept. of Geosciences, Virginia Polytechnic University and State University, Blacksburg, VA, USA
7Dept. of Earth Sciences, Western University Canada, London, ON, Canada
8School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth, UK
9Dept. of Earth Sciences, Dartmouth College, Hanover, NH
10Dept. of Geological Sciences, University of Colorado, Boulder, USA
11Dept. of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN, USA
*Corresponding author: esper@stanford.edu
Determining the causal relationship (if any) between biological evolution and
changing environmental conditions requires knowledge of the long-term record so
that minor fluctuations can be correctly distinguished from major changes. Here we
report an expansive record of Paleozoic seafloor redox change from the upper
Cambrian to Middle Devonian Road River Group deposited in the Richardson trough
of Yukon, Canada. This represents an ideal sedimentary succession to investigate
long-term redox change, as it provides a nearly continuous record of deep-water
marine sedimentation over ~110 million years of Paleozoic history. More than 1,100
shale samples from the Road River Group and other Paleozoic shale units worldwide
were analyzed for major- and trace-element geochemistry, iron speciation, and total
organic carbon content. Redox geochemical data indicate that bottom waters were
broadly anoxic during the entirety of Road River Group deposition, but independent
evidence from iron speciation and Mo/U ratios suggests that the biogeochemical
nature of anoxia changed through time. Both in Yukon and in a global dataset,
Ordovician through Early Devonian anoxic water columns were broadly ferruginous
(non-sulfidic), with a transition towards more euxinic (sulfidic) water columns in the
mid-Early Devonian (Pragian). Thus, an ~80 million-year interval of the early
Paleozoic was characterized by ferruginous bottom waters, similar to the
Neoproterozoic redox geochemical record. Utilizing this new global shale
compilation, trace metal-based inferences of the global extent of reducing conditions
suggest that dynamic redox conditions characterized the Paleozoic, with relatively
more oxygenated conditions in the late Cambrian-Early Ordovician and Mid-Late
Devonian. Within the context of this long-term redox record, the shale geochemical
record does not provide evidence for oxygenation events temporally associated with
the Great Ordovician Biodiversification Event, either locally in the Richardson trough
or in global trace metal datasets.

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47
How did invasion events promote evolutionary and ecological
change during the Great Ordovician Biodiversification Event?
Stigall, Alycia L.
Department of Geological Sciences and OHIO Center for Ecology and Evolutionary Studies, Ohio
University, 139 University Terrace, Athens OH, USA
*Corresponding author: stigall@ohio.edu
The biotic and ecological changes of the Great Ordovician Biodiversification Event
fundamentally shifted the marine ecosystem. Understanding ecosystem change
across this interval requires detailed consideration of local, regional, and global
processes that combined to produce this dramatic change. During the course of
IGCP 653 and related projects, considerable progress has been made in terms of
quantifying biotic, ecological, and abiotic environmental change during the Ordovician
Period. From the datasets developed, it has become clear that the Middle
Ordovician, particularly the Darriwilian Stage, was a time of coordinated change in
the earth-life system. Abiotic processes, particularly sea level changes and shifting
oceanic circulation, resulted in oscillating intervals of biotic immigration events
(BIMEs) and isolation. The dispersal—or species invasion—phase of BIME events
was critical for facilitating species movement and introduction of clades to new
paleocontinents. The complementary process of geographical isolation—due to
paleogeography, numerous interoceanic islands, tectonism, glacial-interglacial cycles
and newly developed habitat heterogeneity—would have promoted speciation via
vicariance. When considered in the context of Stigall’s (2019) invasion hierarchy, the
GOBE is best categorized as an Interchange Invasion. By explicitly considering the
hierarchical structure and biogeographical aspects of evolutionary processes during
the GOBE, it is possible to more synthetically consider the factors and processes
driving diversity increase during this key interval.
Figure 1. Invasion hierarchy from Stigall (2019).
Characteristics of biotic patterns during the GOBE
correspond to those of an Interchange Invasion.
Reference:
Stigall, A.L. 2019. The invasion hierarchy:
ecological and evolutionary
consequences of invasions in the fossil
record. Annual Review of Ecology and
Evolutionary Systematics 50, 355-380.
doi.org/10.1146/annurev-ecolsys-110617-
062638

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On ocean anoxia and the onset of the Great Ordovician
Biodiversification Event
Stockey, Richard G.1*, Zhang, Feifei2, Planavsky, Noah J.3, Fan, Junxuan2, Li, Na4,
Finnegan, Seth5, Edwards, Cole6, Goldberg, Sam7, Saltzman, Matthew8, Dahl, Tais
W.9, Bergmann, Kristin7, Sperling, Erik A.1, Zhang, Hua10, Cui, Ying11, Wang,
Xiangdong2, Shen, Shu-zhong2
1Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA
2State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering,
Nanjing University, Nanjing, Jiangsu 210093, China
3The Department of Earth & Planetary Sciences, Yale University, New Haven, CT 06511, USA
4State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences,
Wuhan, Hubei 430074, China
5Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley,
Berkeley, California 94720, USA
6Department of Geological and Environmental Sciences, Appalachian State University, Boone, NC,
USA
7Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology,
Cambridge, MA 02139, USA
8School of Earth Sciences, The Ohio State University, Columbus, OH, USA
9GLOBE Institute, University of Copenhagen, DK-1350 København K, Denmark
10LPS, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and
Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
11Department of Earth and Environmental Studies, Montclair State University, Montclair NJ 07470
*Corresponding author: rstockey@stanford.edu
The Great Ordovician Biodiversification Event (GOBE) is one of the most significant
increases in marine biodiversity in Earth’s history. The cause(s) of the GOBE remain
poorly understood and may include profound changes in external environmental
conditions. Marine dissolved O2 levels specifically could have played a critical role in
controlling the physiological viability of marine habitat. Reconstructing Ordovician
marine redox conditions is therefore key to evaluating whether environmental factors
could have facilitated the expansion of metazoan ecosystems across the GOBE.
Here, we provide the first quantitative analyses of the extent of global marine redox
chemistry changes in the Early-Middle Ordovician oceans using δ238U of marine
carbonates. The δ238U trends from three widely spaced carbonate sections are
remarkably similar, yielding a mean value of −0.49‰. The nearly invariant and low
δ238U values over ~15 Myr indicate persistent anoxia in the Early-Middle Ordovician
oceans. A U isotope mass balance model combined with a Monte Carlo framework
suggests >3% of the global seafloor was overlain by euxinic bottom waters. Using an
intermediate complexity Earth system model (cGENIE), we suggest that increases in
nutrient supply and primary productivity were likely necessary to maintain persistent
oceanic anoxia through the Early-Middle Ordovician in the context of other inferred
changes in surface temperature and atmospheric O2. We present two endmember
scenarios for environmental change across the GOBE: 1) a stable marine system
with dominantly anoxic deep-waters in which environmental change is unlikely to
have driven early increases in biodiversity, 2) a model compatible with existing
reconstructions of cooling and atmospheric oxygenation, requiring increased primary
productivity to balance the marine redox landscape – potentially playing a key role in
the onset of the GOBE.

Zooming in on the GOBE – Abstract Volume
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A cyclostratigraphic analysis of the Late Cambrian Alum Shale
Sørensen, Aske L.1*, Nielsen, Arne T. 2, Thibault, Nicolas2, Zhao, Zhengfu2,
Schovsbo, Niels H.3, Dahl, Tais W.1
1GLOBE Institute, University of Copenhagen, Denmark
2Department of Geosciences and Natural Resource Management, University of Copenhagen,
Denmark
3Geological Survey of Denmark and Greenland (GEUS), Denmark
*Corresponding author: kcr644@ku.dk
We report evidence for Milankovitch cycles in two drill cores from the Cambro–
Ordovician Alum Shale Formation of Scandinavia. The signal is preserved in
elemental abundances recorded at high stratigraphic resolution by core scanning
XRF analysis (0.2 mm resolution). The new data enable us to establish a floating
timeline calibrated to the stable 405-kyr eccentricity cycle for a ∼8.7 Myr interval
across the Miaolingian–Furongian boundary. This interval spans the Steptoean
Positive Carbon Isotope Excursion (SPICE), which is recorded in the δ13Corg in the
studied drill cores. We calculate the durations of the Olenus Superzone to 3.4 ± 0.2
Myr, the Parabolina Superzone to 1.9 ± 0.3 Myr, the Leptoplastus Superzone to 0.33
± 0.18 Myr, the Protopeltura Superzone to 0.51 ± 0.20 Myr, and the SPICE event
straddling the Paibian and lower main part of the Jiangshanian Stage to 3.0 ± 0.2
Myr. The sedimentation rate shows similar trends at both drilling locations and is
inversely correlated to eustatic sea level changes in certain time intervals, opening
tantalizing new prospects of using cyclostratigraphic analyses of shales to track
eustatic sea level variations. The identification of obliquity cycles enables us to
calculate the Cambrian Earth–Moon distance as well as the day length at ∼493 Ma to
368.9 ± 2.3 · 106 m and 21.78 ± 0.29 hr, respectively.

Zooming in on the GOBE – Abstract Volume
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Ordovician Bioerosion Revolution on Baltica
Toom, Ursula1*, Vinn, Olev2 and Hints, Olle1
1Department of Geology, Tallinn University of Technology, Ehitajate 5, 19086, Tallinn, Estonia
2Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia
*Corresponding author: ursula.toom@taltech.ee
Macroboring organisms have evolved and changed through the Phanerozoic. The
major rise in the diversity of macroboring ichnofossils took place during the Middle
and Late Ordovician. When the term "Ordovician Bioerosion Revolution" was coined
by Wilson and Palmer in 2006, seven bioerosional ichnogenera were listed from the
Ordovician. A decade later 11 Ordovician bioerosional ichnogenera were reported by
Mángano and co-authors. The Ordovician succession of the Baltic region, however,
hosts no less than 13 macroboring ichnogenera: Trypanites, Oichnus, Tremichnus,
Gastrochaenolites, Sulcolithos, Pinaceocladichnus, Dendrina, Sanctum,
Osprioneides, Petroxestes, Bicrescomanducator, Rogerella, and Entobia. Moreover,
several undescribed macroborings, different bite marks, as well as microborings have
been recovered from the Baltic Ordovician in recent years. It is noteworthy that the
oldest representatives of eight bioerosional ichnogenera come from Baltoscandia.
The earliest bioerosional traces in the Baltic region – Trypanites and Oichnus –
appeared in the Cambrian. Carbonate sedimentation commenced during latest Floian
in the region, and bioerosional traces Trypanites and Gastrochaenolites appear
below the Early/Middle Ordovician boundary. A rich assemblage of
macrobioerosional traces occur on Dapingian hardgrounds, consisting of Trypanites,
Gastrochaenolites and Sulcolithus. Also, the tracemaker of Balanoglossites
demonstrated the ability to bioerode. Only few Dapingian finds, assigned to
Tremichnus and Pinaceocladichnus, are related to biogenic substrates. In the
Darriwilian, three new ichnogenera associated with biogenic substrates appeared:
Sanctum, Bicrescomanducator and Dendrina. From the Sandbian, already eight
ichnogenera are known and six have been recorded from the Katian. The majority of
Upper Ordovician bioerosional ichnogenera in the Baltic region are related to various
shelly fossils. Trypanites is an exception to this occurring in both organic and
inorganic substrates.
Mikuláš and Dronov (2004) expressed the opinion that the Baltic region was the
birthplace of bioerosion. Our data corroborate to this idea and show that the
Ordovician Bioerosion Revolution might have begun in Baltica. The rapid
diversification of bioerosional traces in the region was probably a coincidence of
multiple global and regional factors. The major global factors were the seawater
chemistry and oxygenation, stability of the sea level and increasing phytoplankton
availability. The main regional drivers supporting the diversity of bioerosional
organisms were the unusually long “colonisation window”, a warming climate and a
nutrient-rich, well-oxygenated epeiric sea.
References:
Mikuláš R., Dronov, A. V. 2004. Early Ordovician of the Baltic Region: a birthplace of
modern bioerosion and complex ichnofabrics? Ichnia 2004. Abstract book –
First International Congress on Ichnology, Trelew, 57–58.

Zooming in on the GOBE – Abstract Volume
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GOBE and escalation in symbiosis between large colonial animals
and their endobionts
Vinn, Olev1*, Wilson, Mark A.2 Zatoń, Michał3 and Zapalski, Mikołaj K.4
1Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia
2Department of Earth Sciences, The College of Wooster, Wooster, Ohio 44691, USA
3Institute of Earth Sciences, University of Silesia in Katowice, Będzińska 60, 41-200 Sosnowiec,
Poland
4Faculty of Geology University of Warsaw Żwirki I Wigury 93, 02-089 Warszawa, Poland
*Corresponding author: olev.vinn@ut.ee
Ordovician large colonial animals with calcareous skeletons (i.e. bryozoans, corals,
stromatoporoids) were often inhabited by soft-bodied wormlike organisms,
conulariids, rugose corals, cornulitids, and more rarely by gastropods. One can
speculate that symbiotic relationships may have influenced the diversification of
animals in the Ordovician. However, we did not find any increase in symbiotic
relationships before the increase in diversity of the host group.
It seems that the evolution of symbiotic relationships did not contribute much to the
Great Ordovician Biodiversity Event (GOBE), but the GOBE may have been the
catalyst that started the evolution of symbiotic relationships between large colonial
animals and their endobionts, likely as a result of the increased space competition
among sessile benthic invertebrates. In addition, increased biodiversity resulting from
the GOBE generated more diverse behaviors and physiologies, which in turn made
the appearance of symbiotic relationships more likely than in the less diverse pre-
GOBE biosphere. There was a progressive escalation in symbiotic relationships in
the Ordovician starting from the Darriwilian. Large colonial animals in the Sandbian
were more symbiotic than in the Darriwilian, and the Katian ones were more
symbiotic than during the preceding stage.
This escalation in symbiotic relationships in the Ordovician can be explained by
several hypotheses. Species with mutualistic relationships may have outcompeted
species without mutualistic relationships, leading to an increase in mutualistic
species. Infestation strategies of parasites likely improved with time, possibly at a
faster pace than the anti-parasite strategies of their potential hosts, leading to an
increase in parasite-infested species. Finally, those invertebrates that sought refuge
from predators may have reacted to an increase in predation pressure with a more
intense search for substrates suitable for endobiotic life mode. It is likely that all the
factors listed above operated together and caused the escalation in symbiotic
relationships between large colonial animals and their endobionts in the Ordovician.

Zooming in on the GOBE – Abstract Volume
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Conodonts from siliciclastic rocks: a case study from the
Portezuelo del Tontal Formation, Ordovician of the Western
Argentine Precordillera
Voldman, Gustavo G. 1* and Aldo L. Banchig2
1CICTERRA, CIGEA, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de
Córdoba, Av. Vélez Sarsfield 1699, X5016GCA, Córdoba, Argentina.
2Departamento de Geología, Universidad Nacional de San Juan, c/ Ignacio de La Rosa y Meglioli s/n,
5400, San Juan, Argentina.
*Corresponding author: gvoldman@unc.edu.ar
During the past three decades, conodont investigations in the Ordovician of the
Argentine Precordillera included major developments in taxonomy, biostratigraphy,
palaeoecology, palaeogeography and paleothermometry. Conodont studies
flourished within the fossiliferous limestones of the San Juan Formation and the
overlying calcareous units of the central and eastern Precordilleran domains. In
contrast, conodont reports from the deeper siliciclastic sedimentary successions of
the Western Precordillera, which involve slope to ocean floor sedimentary rocks
including pillow lavas and mafic-ultramafic bodies in its westernmost sections, are
noticeably scarce, and are essentially restricted to the mixed clastic-calcareous
turbidites of the Yerba Loca Formation. Thus, the general absence of appropriate
facies for sampling conodonts, along with the laboratory difficulties in recovering
conodonts from siliciclastic rocks, hinders the assessment of the conodont
biostratigraphic framework of the Precordilleran basin.
In an attempt to precisely date of deposition of the ca. 2 km-thick siliciclastic
Portezuelo del Tontal Formation, we thoroughly searched for rocks samples with
calcareous reaction in the Telégrafo Creek and the Cerro Cóndores stratigraphic
sections, on the western and eastern slopes of the Sierra del Tontal, respectively.
After processing 10 rock samples in total (2-3 kg each) following standard laboratory
procedures, only 2 samples from Cerro Cóndores were productive, yielding merely
50 conodont elements. The recovered assemblage includes Ansella jemtlandica
(Löfgren), Costiconus costatus (Dzik), Drepanodus arcuatus Pander, Parapaltodus
simplicissimus Stouge, Paroistodus originalis (Sergeeva), P. h. horridus (Barnes &
Poplawski), P. h. secundus Albanesi, Periodon macrodentatus (Graves y Ellison),
Protopanderodus graeai (Hamar), and Spinodus spinatus (Hadding), which typically
coexist in the Darriwilian (Middle Ordovician) Yangtzeplacognathus crassus Zone
(Dw1–Dw2), a critical interval in the tectonostratigraphic history of the Precordillera.
This zone has wide geographical distribution, involving most of the transitional
interval from the San Juan Formation to the overlying Las Aguaditas, Las Chacritas,
Los Azules, and Gualcamayo formations at the eastern and central domains of the
Precordillera. Recognition of the Y. crassus Zone in the Portezuelo del Tontal
Formation also allows for a tight intercontinental correlation with South China and
Baltoscandia. In view of our results, the great importance of conducting conodont
investigations in siliciclastic sedimentary deposits is reaffirmed.

Zooming in on the GOBE – Abstract Volume
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Preliminary report on δ13Ccarb isotope excursion through the
Silurian of Jočionys-299 borehole, Eastern Lithuania
Želvys, Tomas1*, Brazauskas, Antanas1, Spiridonov, Aandrej1, Kudžma, Donatas1,
Garbaras, Andrius2, Radzevičius, Sigitas1.
1Department of Geology and Mineralogy, Institute of Geosciences, Vilnius University, M. K. Čiurlionio
21/27, LT-03101, Vilnius, Lithuania
2Center for Physical Sciences and Technology, Nuclear Research Department, Vilnius University,
Saulėtekio av. 3, 10257 Vilnius, Lithuania
*Corresponding author: tomas.zelvys@chgf.vu.lt
Lithuania is located in the eastern part of the Silurian Baltic Basin which was located
near the equator during the Silurian. Jočionys-299 borehole is located in the Eastern
Lithuania. The Silurian geological section of Jočionys-299 borehole is composed of
siliciclastic, carbonate and sulfatic deposits and represents shallow-marine; lagoonal
and sabkha environments.
Samples for δ13Ccarb isotope analysis were collected from the interval between
234.35 – 90.3 m approximately every 1 m. The stable carbon isotope values from
carbonates were measured using Thermo Gasbench II coupled with a Thermo Delta
V isotope ratio mass spectrometer.
According to preliminary δ13Ccarb isotope results, Silurian can be subdivided in five
intervals in the Jočionys-299 borehole. The first interval spans from 234.25 to 211.8
m, here the δ13Ccarb values were close to +1 ‰ with some minor fluctuations and
varied from 0.39 ‰ to 1.44 ‰. In this interval conodont Pterospathodus am.
amorphognathoides which mark the upper part of Llandovery was found. The δ13Ccarb
values rise gradually from 0.44 ‰ (depth 211.8 m) to 6.4 ‰ (depth 188 m) and
gradually fall to –2.29 ‰ (depth 162 m). This positive δ13Ccarb excursion can be linked
to the Ireviken Event of the lower Wenlock. Additionally, Kockelella ranuliformis is
documented in this interval of Jočionys-299 well core. δ13Ccarb values are moderately
stable in 162 m – 146 m depth and vary from – 2.53 ‰ to – 0.39 ‰. Then, δ13Ccarb
values fall rapidly to – 8.1 ‰ at 145 m depth and rise to – 0.9 ‰ at 141 m depth. The
fluctuations of δ13Ccarb values are rapid in 141 m to 90 m interval. Values vary from –
5.41 ‰ to – 0.92 ‰. There are no major excursions of δ13Ccarb in the last interval. In
the upper part of Jočionys-299 borefole section, Ozarkodina crispa (uppermost
Ludlow) and Ozarkodina eosteinhornensis biozones (lower Pridoli) were
distinguished.
In summary, the δ13Ccarb values varied from – 8.1 ‰ up to 6.4 ‰ in the Silurian
section of Jočionys-299 well core. Such a large range of δ13Ccarb values can be
related to shallow marine environments and local peculiarities of sedimentation rates.
A more detailed biostratigraphic and lithological study is needed to better understand
stratigraphy of Silurian geological section in Jočionys-299 borehole in the future.

Zooming in on the GOBE – Abstract Volume
GEUS Report 2020 vol 21
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Recognizing pulses of extinction from clusters of last occurrences:
A Late Ordovician case study
Zimmt, Joshua B.1*, Holland, Steven M.2, Finnegan, Seth1, and Marshall, Charles R.1
1Department of Integrative Biology and Museum of Paleontology, University of California Berkeley,
California, 1101 Valley Life Sciences Building, Berkeley, California 94720, USA
2Department of Geology, University of Georgia, 210 Field Street, Athens, Georgia 30602, USA
*Corresponding author: josh_zimmt@berkeley.edu
The Late Ordovician mass extinction is commonly expressed as two clusters of last
occurrences in the Hirnantian fossil record. These clusters appear to coincide with
sequence-stratigraphic surfaces and facies shifts generated by the glaciation and the
deglaciation of the supercontinent Gondwana. Consequently, glacioeustatic changes
have been proposed as a principal driver of the Late Ordovician mass extinction, with
each cluster of last occurrences interpreted as a pulse of extinction. However,
stratigraphic architecture can produce clusters of last occurrences that can be
misinterpreted as extinction pulses. These clusters typically occur at abrupt changes
in facies or sequence-stratigraphic surfaces. Misinterpreting these clusters of last
occurrences as pulses of extinction can lead to a misunderstanding of the pattern
(number of extinction pulses), timing (age), and tempo (rapidity) of the extinction,
which would result in a misunderstanding of possible causes of the extinction.
It has been proposed that a basin-wide analysis of the fossil record within a
sequence-stratigraphic framework can be used to distinguish between clusters of last
occurrences caused solely by extinction pulses from those generated by sequence-
stratigraphic architecture. A basin-wide approach makes it possible to take into
account lateral facies shifts in response to sea-level change and thus to determine
the extent to which patterns of last occurrences reflect extinction dynamics versus
stratigraphic architecture.
Here, we use a modelling approach to test how glacioeustatic changes would affect
the expression of a variety of possible Late Ordovician mass extinction scenarios.
Using the sedimentary basin model Sedflux 2.1, we simulate stratigraphic columns
based on an inferred Late Ordovician sea-level curve. We combine these with a
branching model of evolution and extinction, as well as water-depth preferences for
each taxon, to simulate several Late Ordovician mass extinction scenarios.
We first show that stratigraphically-generated clusters of last occurrences are
observed even in a basin-wide analysis of the fossil record because for some taxa
there is a basin-wide loss of their preferred facies. However, by coarsening the
stratigraphic resolution to the systems-tract level and removing taxa whose last
occurrences coincide with a basin-wide loss of their preferred facies, we can
consistently and correctly identify the pattern of extinction for a variety of extinction
scenarios. We are undertaking the field work to determine whether this approach will
enable the identification of the extinction pattern across the Ordovician/Silurian
boundary on Anticosti Island, Canada.

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Denmark and Greenland (GEUS)
Denmark
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institution in the Danish Ministry
of Climate, Energy and Utilities