Symposium Program - Precambrian Research Office - McGill ...

Symposium Program
Geobiology Symposium 2012
March 23rd and 24th, 2012
Hosted by the Precambrian Research Group and Publican Society,
Department of Earth and Planetary Sciences, McGill University
props.eps.mcgill.ca

Welcome
Dear colleagues,
We welcome you to the 2012 Geobiology Symposium and hope you will have a pleasant time in
Montréal. This meeting not only offers an opportunity to share and discuss research ideas and results
but also to get in contact with other researchers in the field of geobiology to build new relationships.
Please do not hesitate to approach us if you have any request or question, we will be pleased to help
you.
The 2012 Geobiology Symposium organizing committee,
Grant Cox, Marcus Kunzmann, André Pellerin,
Galen Halverson and Boswell Wing
1

Agenda
Friday, March 23
Redpath Museum, McGill University
5pm - Public keynote lecture by Paul F. Hoffman, Climate science and geology – a tale of three
histories
Saturday, March 24
Redpath Museum, McGill University
9 am – 10.30 am - Talks
Nicholas Swanson-Hysell (Invited Speaker), Burgeoning evidence for the primary origin of Neoproterozoic
carbon isotope excursions
Marcus Kunzmann, Zn isotope evidence for immediate resumption of primary productivity after
snowball Earth
André Pellerin, Evolutionary Response of S Isotope Fractionation by Sulfate Reducing Microorganisms
William Leavitt, The sulfur isotope fractionation of dissimilatory sulfite reductase (Dsr)
10.30 am – 11.00 am - Coffee Break
11 am – 12.30 pm - Talks
Clint Scott (Invited Speaker), A Paleoproterozoic collapse in seawater sulfate and its influence
on the global methane cycle
Tom Laakso, The Stability of Low Atmospheric Oxygen in the Proterozoic
Vincent van Hinsburg, The composition of the Early Earth oceans: Constraints from element
partitioning
Thi Hao Bui, Sulphur and carbon isotope records across the terrestrial Permian-Triassic (P-T)
boundary
3

12.30 pm – 1.30 pm - Lunch Break (Lunch will be provided.)
1.30 pm – 2.30 pm - Talks
John Higgins (Invited Speaker), Authigenic carbonates in marine sediments – their global significance
and isotopic composition over Earth history
Grant Cox, Geochemistry of Cryogenian Ironstones - the link to N-MORB and its implications
Emily Bamforth, Life Before Impact: Biodiversity Patterns Preceding the Cretaceous Mass Extinction
(65 Ma) Evidence from the Latest Maastrichtian of Central Canada
2.30 pm – 3.30 pm - Coffee Break
3.30 pm – 4.15 pm - Talks
Phoebe Cohen (Invited Speaker), The Record of Eukaryotic Diversification in Proterozoic Seas
Thomas Maguire, A new model for a biosiliceous Neoproterozoic taphonomic bias
2nd floor, Department of Earth and Planetary Sciences, McGill University
5 pm – Poster presentations and Wine & Cheese
Danielle Thomson, Refined stratigraphy and regional correlation of the early Neoproterozoic Wynniatt
Formation, Shaler Supergroup, Victoria Island, NWT
John Prince, An early Neoproterozoic dynamic sulphur cycle: evidence from the Shaler Supergroup
Kristyn Rodzinyak, Unexpectedly large S isotope fractionation during natural sulfide oxidation at
cold temperatures
Eric Bellefroid, Iron Isotopes and Rare Earth Element Geochemistry for the Cryogenian Tatonduk
River Ironstones
Lucie Hubert-Theéou, Coupled climate-geochemical modeling of the connections between break-up
of Rodinia, flood basalt volcanism, snowball glaciations and strontium cycle
Felix Waechter, Chemostratigraphy of the Virgin Spring limestone: Implications for stratigraphic
correlations in Death Valley, CA
Dylon Trotzuk, The tectonic context of Neoproterozoic stratiform mineralization on the Western
margin of Laurentia
4

Abstracts – Talks
Burgeoning evidence for the primary origin of Neoproterozoic carbon isotope excursions
Nicholas Swanson-Hysell
Winchell School of Earth Sciences, University of Minnesota, USA
The Neoproterozoic Era was a critical interval of climatic and biological change on Earth. An understanding
of Earth’s carbon cycle through the Era is crucial for evaluating hypotheses related
to the extreme variations in climate and evolving redox conditions. The carbon isotope record of
Neoproterozoic carbonates has long been interpreted as a window into the carbon cycle of the Era.
However, the extreme magnitude of variation in δ 13 C values has led to recent proposals that the
record is not reflective of changes to global carbon cycling, but is rather the result of diagenesis. This
debate within the community has inspired additional work seeking to test the hypothesis that the
carbon isotope record is giving insight into large-scale changes to the isotopic composition of dissolved
inorganic carbon in the world’s ocean. I will present new data from strata deposited in Ethiopia and
Svalbard in the time period leading up to the first Neoproterozoic pan-glacial event that support a
primary origin for high-amplitude changes in carbonate δ 13 C. Together with new data sets from other
Cryogenian and Ediacaran successions, these records strongly suggest that the Neoproterozoic carbon
isotope record reflects changing dynamics of carbon cycling on Earth’s surface. Fully explaining these
changes remains a major challenge as we seek to understand the co-evolution of the surface environment
and life through the Neoproterozoic.
5

Zn isotope evidence for immediate resumption of primary productivity after snowball Earth
Marcus Kunzmann 1 , Galen P. Halverson 1 , Paolo A. Sossi 2 , Timothy D. Raub 3 , Justin L. Payne 4 and
Jason Kirby 5
1 Department of Earth & Planetary Sciences/GEOTOP, McGill University, Canada,
marus.kunzmann@mail.mcgill.ca
2 Research School of Earth Sciences, Australian National University, Australia
3 Department of Earth Sciences, University of St. Andrews, United Kingdom
4 School of Earth & Environmental Sciences, University of Adelaide, Australia
5 CSIRO Land and Water, Centre for Environmental Contaminant Research, Glen Osmond, Australia
Zinc is assimilated in the surface ocean by primary producers and exported to the deep ocean where it
is released by re-mineralization. Previous studies of Zn isotopes in the marine environment indicate
a consistent biological control. Organisms preferentially assimilate the light isotopes, leaving behind
an enriched surface ocean and generating a surface-to-deep isotope gradient akin to that of δ 13 C
of dissolved inorganic carbon. Since Zn is incorporated in carbonate in trace amounts and without
significant isotopic fractionation, Zn isotope ratios in carbonate rocks deposited in the surface ocean
should track fluctuations in primary productivity.
We analyzed Zn, C, and O isotope ratios in a 14 m-thick section of the Nuccaleena Formation, a
∼ 635 Ma old cap dolostone that drapes Marinoan age glacial deposits in the Adelaide Rift Complex in
South Australia. Carbon and oxygen isotope composition and sedimentological features mirror other
Marinoan cap dolostones worldwide. The δ 66 Zn ( 66 Zn/ 64 Zn, versus JMC-Lyon) composition begins
with a decline from 0.47 at the base to a nadir of 0.07 at 5.6 m. Above this level, δ 66 Zn increases
to a maximum of 0.87 at the top of the section. In contrast, the insoluble residue fraction (silt and
clay) yields values comparable to previously reported values for siliciclastic rocks, which cluster around
mean continental crust (0.2–0.3 ).
The effect of diagenesis on the Zn isotope composition in carbonates is as yet unknown. However,
is seems likely that post-depositional Zn exchange would drive the δ 66 Zn composition towards the
composition of the detrital component. Hence, it cannot account for the observed trend of decreasing,
than increasing values. We assume the values are primary seawater signatures and propose a two-stage
model to explain them. During the first stage, the δ 66 Zn composition evolves toward the bulk of the
continental crust as the intense weathering input during the post-glacial super-greenhouse climate
dominates the ocean Zn budget. The trend of increasing δ 66 Zn values can be interpreted by an
invigorated biological pump, driven by a high-nutrient flux coupled to continental weathering, which
depletes 64 Zn in the surface ocean and exports it to the deep ocean. Preservation of the biological
signal in the δ 66 Zn profile is a consequence of the hydrological conditions that prevailed after snowball
Earth. Partly melt-derived, brackish surface waters subject to intense heating would have capped cold,
more saline deep water, suppressing upwelling and homogenization of the marine Zn isotope reservoir.
6

Evolutionary Response of S Isotope Fractionation by Sulfate Reducing Microorganisms
André Pellerin 1 , Nadia Mykyczuk 2 , Rebecca Austin 1 , Grant M. Zane 3 , Lyle Whyte 2 , Judy D. Wall 3 ,
and Boswell Wing 1
1 Department of Earth and Planetary Sciences, McGill University, Montréal, Canada,
andre.pellerin@mail.mcgill.ca
2 Department of Natural Resource Science, McGill University, St-Anne de Bellevue, Canada
3 University of Missouri, Biochemistry Division, Columbia, USA
Microbial sulfur isotope fractionation is controlled by the energy metabolism of sulfate reducing
microorganisms. It represents a well-defined and precisely measurable characteristic of the phenotype
of the microorganism. As such, it is dependent both on the underlying genotype and on the response
of that genotype to variability in the local environment. Since genotype and environment have both
changed throughout Earth’s history, the geological record of biogenic S isotopes must reflect the
influence of both environmental change and molecular evolution. However, the basic interplay between
microbial evolution and S isotope fractionation has not been examined.
We investigated the evolutionary response of S isotope fractionation in the sulfate-reducing bacterium
Desulfovibrio vulgaris Hildenborough (DvH). Two bacteria – the wild type DvH as well as a mutant
derived from that strain in which one copy of a gene putatively encoding lactate dehydrogenase was
deleted and replaced with an antibiotic resistance cassette were used as model organisms. In defined
media (sulfate and lactate limited) at 33℃ ancestral wild type and mutant DvH exhibit fractionation
factors that reproducibly differ by 0.5 . We serially transferred six replicate lines of the wild type
and six replicate lines of the mutant for 600 generations in batch cultures. Over the course of the
experiments, we assayed fitness through direct competition experiments between the ancestral mutant
and descendant wild-type strains (or vice versa). In these competition experiments, we used qPCR to
monitor the relative abundance of the mutant through a unique genetic barcode associated with the
antibiotic resistant cassette. After 300 generations, the descendant strains were markedly more fit than
their ancestors, with relative growth rate increases of nearly 30 %. This means that the descendant
strains have a clear selective advantage in the defined media, illustrating that DvH can undergo
evolutionary adaptation on laboratory timescales.
Despite the clear evidence for evolutionary changes over the course of our experiment, isotopic assays
of the descendant wild-type and mutant strains reveal that the 0.5 difference in their fractionation
factors is conserved. Preservation of such a small isotope effect implies that the sulfate reducing energy
metabolism is remarkably robust to the selective pressures of our experimental setup.
7

The sulfur isotope fractionation of dissimilatory sulfite reductase (Dsr)
William D. Leavitt 1 , Inês C. Pereira 2 , André Santos 2 , Alexander S. Bradley 1 , Renata Cummins 3 , and
David T. Johnston 1
1 Harvard University, Department of Earth & Planetary Sciences, Cambridge, MA, USA,
wleavitt@fas.harvard.edu
2 Instituto De Technologia Quimica E Biologica, Oeiras, Portugal
3 California Institute of Technology, Division of Earth and Planetary Sciences, Pasedena, CA, USA
The sedimentary sulfur isotope record is an integrator of biochemical processes, among the most quantitatively
important of which is microbial sulfate reduction (MSR). Interpretations of the sedimentary
sulfur isotope record rely largely on our understanding of the fractionation associated with MSR.
This has been empirically determined by numerous cellular-scale studies [1, 2]. Still, a mechanistic
understanding of the controls on this fractionation has proven elusive. Moreover, metabolic isotope
models of MSR underpin our interpretations of the modern and ancient sulfur isotope records, yet
such models require a quantitative understanding for the magnitude of fractionation at each node
(i.e. enzymatic step) within the metabolic network [3, 4]. We present data from experimental work
with the purified dissimilatory sulfite reductase (Dsr), from which we can measure and calculate the
enzyme-specific isotope fractionation factors ( 34 α Dsr
, 33 α Dsr
, 36 α Dsr
) [2]. In all cases, elemental and
isotopic mass balance was satisfied, and individual sulfur pools were isolated from the bulk solution by
sequential precipitation. These are the first enzyme level constraints on isotope fractionation during
MSR, and serve as a template for evaluating the other prominent enzymatic reduction steps within this
metabolic process. This work also provides a set of fundamental boundary conditions for the metabolic
fractionation models of MSR [2, 4]. By taking an enzyme-level approach to understanding isotopic
fractionation in MSR, we begin to provide the most fundamental constraints on the biogeochemical
fractionation signatures [3]. Akin to the early carbon isotope work on RuBisCO and its importance to
our understanding of the carbon cycle [5], the work presented herein will help to unlock the secrets
of the sulfur cycle and ultimately allow for the full isotopic interpretation of Earth’s sulfur isotope
records.
[1] Kaplan & Rittenberg (1964) J. Gen. Micrbio. 34, 195–212. [2] Johnston et al. (2007) GCA 71,
3929–47. [3] Hayes (2001) Rev Mineralogy & Geochem 45, 255–77. [4] Bradley et al. (2011) Geobio. 9,
446–57. [5] Park & Epstein (1960) GCA 21, 110–26.
8

A Paleoproterozoic collapse in seawater sulfate and its influence on the global methane cycle
Clint Scott
Department of Earth and Planetary Sciences, McGill University, Canada
The initial accumulation of atmospheric oxygen is referred to as the Great Oxidation Event (GOE)
and is fairly well-constrained to between 2,450 and 2,320 Ma. However, the magnitude and duration of
the GOE are subject to debate and it is not clear how early Paleoproterozoic oxidation relates to the
long-lived intermediate redox state of the mid-Proterozoic. In order to investigate Paleoproterozoic
surface oxidation, we used a combination of pyrite multiple-sulfur ( 32 S, 33 S and 34 S) and organic
carbon isotopes from a suite of early Paleoproteorzoic marine black shales. We analyzed the 2,200 to
2,100 Ma Sengoma Argillite Formation, deposited during the peak of the Lomagundi carbon isotope
excursion, and the Upper Zaonega Formation of the Ludikovian Series, Russian Karelia, deposited in
the immediate aftermath of the Lomagundi carbon isotope excursion. Our results suggest that a large
marine sulfate reservoir was an immediate result of the GOE, however, sulfate concentrations collapsed
rapidly following the Lomagundi carbon isotope excursion resulting in invigoration of the methane
cycle as recorded in the organic C isotope record.
9

The Stability of Low Atmospheric Oxygen in the Proterozoic
Thomas A. Laakso and Daniel P. Schrag
Department of Earth and Planetary Sciences, Harvard University
Most studies suggest that oxygen has remained near modern levels throughout the Proterozoic, but
was much less abundant during the preceding billion years. Several decades’ worth of modeling has
shown that a handful of stabilizing feedbacks can explain modern redox conditions; however, it is not
obvious these dynamics are also consistent with a billion years of low pO2. We present a simplified
model of the critical biogeochemical cycles that control the redox evolution of Earth’s surface, and
use it to explore the feedbacks required to maintain an atmosphere with low O2, i.e. ∼1% present
atmospheric levels (PAL). We find that stable low oxygen is only possible if the flux of phosphorus
to the ocean is great reduced compared to its modern value. Model results show that this limitation
holds even if one assumes large differences in Phanerozoic and Proterozoic carbon and sulfur cycling
processes. Therefore, a reduced flux of phosphorus to the oceans is the most likely explanation for the
Proterozoic redox state. We propose this reduction may have been driven by a larger load of ferrous
iron in rivers, favoring efficient scavenging of phosphate ions during co-precipitation of ferric oxides.
10

The composition of the Early Earth oceans: Constraints from element partitioning
Vincent J. van Hinsberg 1,2 , Kristoffer Szilas 3 and Bernard J. Wood 1
1 Department of Earth Sciences, University of Oxford, United Kingdom
2 Department of Earth and Planetary Sciences, McGill University, Canada
3 Geological Survey of Denmark and Greenland - GEUS, Copenhagen, Denmark
Although it is still debated at what point liquid water became stable on the surface of the Earth, it
is widely accepted that dramatic changes took place over time in the properties and compositions of
the Early Earth hydrosphere. These changes reflect changes in the sources, sinks and reservoirs of
elements in and on the Earth, which are directly linked to the nature of the atmosphere and crust, and
the plate tectonic style of the young Earth. Moreover, an intimate link has been suggested between
changes in element availability in the oceans and the direction of life’s evolution, based on the essential
nature of many trace elements as catalytic constituents in enzymes. An understanding of the evolving
oceans therefore provides a window into both the evolving inorganic Earth and the development of the
organisms that inhabit it.
Direct samples of Early Earth ocean waters are exceedingly rare, and constraining ocean compositions
therefore depends on our ability to accurately read the rock record. Marine sediments, such as Banded
Iron Formations, cherts and black shales, are an obvious focus in this research, because of their
direct interaction with ocean water. However, translating marine sediment compositions to actual
water concentrations is complicated, especially owing to possible involvement of organisms that can
preferentially sequester elements.
In this contribution, we focus on the high-temperature, inorganic interaction between ocean water
and basalt, which takes place at the mid-ocean ridges and is a dominant source of trace elements to the
present-day oceans. Combining trace element analysis of minerals taken from well-preserved Archaean
altered oceanic crust with experimentally characterised mineral-fluid element partitioning allows us to
put quantitative constraints on the composition of the oceans at 3.2 Ga, and shows that these were
remarkably similar in trace element composition compared to the modern day.
11

Sulphur and carbon isotope records across the terrestrial Permian-Triassic (P-T) boundary
Thi Hao Bui 1 , Jean-Francois Helie 2 , and Boswell Wing 1
1 Earth and Planetary Sciences, McGill University, Montreal, thi.h.bui@mail.mcgill.ca
2 Département des sciences de la Terre et de l’atmosphère, UQAM, PK-7720, Montreal
The end Permian mass extinction (∼ 252 Ma) is known as the greatest biotic crisis in earth history with
the disappearance of more than 90% of marine species and 70% of terrestrial vertebrate families. To
better understand the interaction of the carbon and sulphur cycles across the terrestrial P-T boundary,
we collected 27 sedimentary rock samples at average resolution of 35 cm and 9 carbonate nodules along
a section of ∼ 10 meters in Karoo Basin, South Africa. We determined carbon and sulphur contents as
well as carbon and sulphur isotope records of above samples.
The organic carbon contents of sedimentary rocks are quite low, less than 0.04 wt %. The average
δ 13 C value of organic carbon is around -25 throughout the section, but at 59 cm before the P-T
boundary, this value increases to -23.8 and drops sharply to -26.5 over a distance of 110 cm. The
background value of -25 is recovered within 19 cm. The δ 13 C values of carbonate nodules in the
≈ 3 m preceding the boundary are around -8.5, while those found in the ≈5 m after the boundary
are around -11.5. Total sulphur contents of sedimentary rocks are generally less than 0.01 wt%, with
the exception of a sharp peak of ≈0.45 wt % at 5 cm above the boundary. Although their full pattern
is noisier than that seen in the δ 13 C record, the δ 34 S values of Cr(II)-reducible sulphides and different
sulphate species (water-soluble, acid-soluble, and acid-insoluble sulphates) all decrease by at least 8
within the 100 cm after the boundary.
The negative shifts of both δ 13 C carbonate and δ 13 C organic (∼-3) at the boundary indicate a decrease
in the 13 C content of carbon input into the P-T terrestrial system. Likewise, the sharp peak of total
sulphur content coinciding with the boundary suggests a rapid addition of sulphur into the terrestrial
environment. The shared initial decreases in δ 34 S values suggest that this sulphur was depleted in 34 S.
Multiple sulphur isotope compositions (δ 34 S and ∆ 33 S) of the different sulphate species are generally
equivalent, indicating a shared sulphate source throughout the section. While the δ 34 S values of the
Cr(II)-reducible sulphides are compatible with bacterial sulphate reduction, the associated ∆ 33 S values
are more negative than those typically associated with this process. Although the δ 13 C and δ 34 S records
imply the coherent transfer of 13 C- and 34 S-depleted material to the PT terrestrial environment, the
∆ 33 S values complicate a straightforward identification of the source of this material.
12

Authigenic carbonates in marine sediments – their global significance and isotopic composition over
Earth history
John Higgins
Department of Geosciences, Princeton University, USA
We propose new framework for interpreting the C isotopic composition of carbonates which focuses
on changes in the abundance and isotopic composition of authigenic carbonate in marine sediments.
The framework is based on the model developed by Higgins et al. (2009) for the global alkalinity and
carbonate cycles which considered the possibility of two sites of carbonate precipitation in the ocean;
well-mixed seawater in the surface ocean and sediment pore-fluids in the near subsurface. The model
predicts that changes in organic carbon cycling and the identity of the dominant electron acceptors
(Fe 3+ , SO 2−
4 , O 2) and a decline in the size of the global inorganic carbon pool had a first-order effect
on the abundance of authigenic carbonates in marine sediments over Earth history. In particular,
increasing oxidation of the ocean and sediments should be accompanied by a decline in the global
importance of authigenic carbonate precipitation in marine sediments. Here, we expand our analyses to
consider the C isotopic composition of the authigenic carbonates, how it has likely varied over Earth
history, and what this means for interpreting the C isotopic composition of sedimentary carbonates
through time. Our model can explain many of the extreme C isotope excursions observed during the
Proterozoic and parts of the Phanerozoic without calling on large changes global redox budgets.
13

Geochemistry of Cryogenian Ironstones – the link to N-MORB and its implications
Grant Cox 1 , Galen Halverson 1 , William Minarik 1 , Ross Stevenson 2 , Daniel Le Heron 3 , Francis
Macdonald 4 , Justin Strauss 4 , Paolo Sossi 5 , Eric Bellefroid 1
1 McGill University, Montreal, Canada, grant.cox@mail.mcgill.ca
2 GEOTOP/UQAM, Montreal, Canada
3 Royal Holloway University of London, Surrey, U.K.
4 Harvard University, Cambridge, U.S.A.
5 Australian National University, Canberra, Australia
The reappearance in the geological record of sedimentary iron formations after a ∼ 1 Ga hiatus [1,2] is
a geologically unique feature of the Cryogenian (∼,850 Ma to 635 Ma). Whereas their close association
with globally distributed glacial deposits invites interpretation that they are the product of snowball
glaciation, they have also been interpreted to be a local product of rifting, similar to modern Red Sea
metalliferous sediments. Based on major element, REE, and 143Nd/144Nd data from stratigraphicallyconstrained
samples from South Australia (Holowilena), NW Canada (Tindir and Rapitan) and
southern Namibia (Numees), Cryogenian iron formations can be characterized as a mixture between a
hydrothermal source and mid ocean ridge basalt (N-MORB), with very little contribution from the
continental crust. Similar positive-upward iron isotope profile in each of these basins suggest a common
depositional process for the iron formation. These data indicate that both snowball glaciation and local
rifting are prerequisites to Cryogenian iron formation. Notably, the Cryogenian IF patterns are distinct
from both Archean-Paleoproterozoic banded iron formation and Phanerozoic ironstones.
[1] Isley, A. E. & Abbott, D. H. (1999) Journal of Geophysical Research, 104, 461-477. [2] Klein, C.
(2005) American Mineralogist, 90, 1473-1499.
14

Life Before Impact: Biodiversity Patterns Preceding the Cretaceous Mass Extinction (65 Ma) Evidence
from the Latest Maastrichtian of Central Canada
Emily Bamforth and Hans C.E. Larsson
Redpath Museum, McGill University, 859 Sherbrooke Street W., Montreal, QC, Canada H3A 1B1
emily.bamforth@mail.mcgill.ca
The timing and cause of the Cretaceous mass extinction has been the topic of much debate in
paleontology for the last several decades. The question as to whether or not diversity was declining
prior to the bolide impact event is hindered by the fact that diversity patterns are not consistent across
different taxonomic groups. In this study, we apply a holistic, multidisciplinary approach to studying
vertebrate biodiversity during the last half-million years leading up the extinction event.
Vertebrate microsites are an invaluable tool in the study of paleoecology. These accumulations of small
vertebrate fossils allow for the quantification of temporal and spatial paleobiodiversity trends. When
coupled with paleoclimate indictors such as oxygen-18 stable isotope analyses and plant macrofossil
data, insight may be gained as to how climatic factors influenced biodiversity in both time and space.
Here, we examine the relationships between climate, area and biodiversity during the last four to six
thousand years of the Cretaceous period in central Canada. Data from thirty-six vertebrate microsites,
together containing some 9000 vertebrate microfossils, were collected from the base of the latest
Maastrichtian (65 Ma) Frenchman Formation to the K-Pg boundary clay in Grasslands National Park,
SK. Stratigraphic level surveys were performed to assess the relative stratigraphic position of each
microsite, and the depositional environment of each was documented.
Diversity appears to peak in at least three stratigraphic horizons, with horizons of lower diversity
situated between them. Both the number of sites and the diversity within the sites decreases dramatically
in the last 10 m below the K-Pg boundary. Alpha (within site) diversity fluctuations may be associated
with the large-scale, repetitive depositional cycles of ironstone, mudstone and sandstone observed
throughout the study area. This study demonstrates that local vertebrate diversity may have been
fluctuating with local environmental conditions until just prior to the K-Pg extinction.
15

The Record of Eukaryotic Diversification in Proterozoic Seas
Phoebe A. Cohen
Department of Earth, Atmospheric and Planetary Sciences, MIT, USA
Proterozoic strata record evidence of dramatic changes to the Earth system, including an increasingly
robust record of eukaryotic diversification. In this talk I will discuss the most recent assessments of
eukaryotic biodiversity in Proterozoic strata, discuss biases in this record, and focus in on new key
components of Neoproterozoic diversity. While the Phanerozoic fossil record of diversity has been
thoroughly analyzed for biases relating to rock volume, taphonomy, and sampling, the Proterozoic
fossil record has not been subjected to the same analyses – in part because of the huge difference
in raw fossil abundance between the two. We can, however, make a start at trying to grasp at the
role of biases on the Proterozoic fossil record, which can in turn help us make better correlations
between environmental and biotic events. I will briefly discuss these issues and then focus in on two
new records of complex eukaryotic life in the Neoproterozoic: diverse biomineralized scale microfossils
from early- to mid-Neoproterozoic strata of the Yukon and macroscopic fossils tentatively assigned to
the red algae from Cryogenian strata of Mongolia. Both of these fossil assemblages shed light on the
evolution of eukaryotic life in Neoproterozoic seas and highlight the changing ecological landscapes
that accompanied major climactic shifts on the Neoproterozoic Earth.
16

A new model for a biosiliceous Neoproterozoic taphonomic bias
Thomas Maguire
School of Earth and Ocean Sciences, University of Victoria, Canada
Citing biomarker, molecular-clock and micro-RNA evidence, Sperling et al. (2010) postulate a Cryogenian
origin for silica-biomineralizing demosponges, >100 Myr before the first documented spicules in
the rock record. They suggest that a secular increase in marine Pedogenic Clay Mineral (PCM) delivery
during the Neoproterozoic supplied more Al(III) to sediment porewaters, thereby stabilizing biogenic
silica (BSi). Subsequent work shows that the secular increase was in micaceous not pedogenic clays,
implying no increase in the spicule-preserving Al(III) flux to the sediment. A new model is proposed in
which a redox-dependent microbial mechanism provides a taphonomic bias against the preservation of
siliceous sponge spicules before the late Ediacaran.
Under reducing conditions, a variety of microbes exhibit the ability to rapidly (days timescale) respire
organic matter (OM) using structural Fe(III) in smectite clays as a terminal electron acceptor. This
promotes illitization of clays at early diagenetic temperatures and pressures, and releases significant
aqueous Fe(II), Al(III) and Si(IV) through clay dissolution. Under oxic conditions, these reactions are
energetically favourable during diagenesis, resulting in intact delivery of clay minerals to sediments.
During the Precambrian, such reactions would have occurred during flocculant settling through the
water column, releasing Fe(II) and Al(III) to seawater rather than to porewaters. Precambrian BSi
was thereby unprotected by Al(III) absorption, and its early diagenetic dissolution was kinetically and
thermodynamically favoured, causing the observed taphonomic bias. This scenario is supported by
changes in clay mineralogy across the Cambrian boundary, Neoproterozoic early-diagenetic mineral
trends, and secular change in chert petrology.
Important corollaries are that in the Neoproterozoic, marine Si may have been significantly lower
than previously suspected, standard models of chert formation may need revision, clays could have
significantly contributed to ferruginous conditions, and a feedback to the Neoproterozoic oxygenation
event is implied by increasing floc-associated sequestration of OM under progressively more oxic
conditions.
17

Abstracts – Posters
Refined stratigraphy and regional correlation of the early Neoproterozoic Wynniatt Formation, Shaler
Supergroup, Victoria Island, NWT
Danielle Thomson 1 and Robert Rainbird 2
1 Department of Earth Science, Carleton University, Canada, dthomso2@connect.carleton.ca
2 Geological Survey of Canada, Ottawa, Canada
The early Neoproterozoic (late Tonian-Cryogenian) Shaler Supergroup of the Amundsen Basin is well
exposed in the Minto Inlier, Victoria Island, NWT. It is correlated with the Mackenzie Mountains
Supergroup (Mackenzie Mountains) and Fifteenmile Group (Ogilvie Mountains).
The Wynniatt Formation (middle Shaler Supergroup) is composed of >900 meters of sediment
deposited on a broad, distally steepened carbonate ramp within a shallow intracontinental basin
that was periodically restricted from an exterior ocean. Study of the Wynniatt Formation supports
division into: 1) lower-carbonate member, an upward-deepening succession of supra- to sub-tidal
carbonates; 2) black-shale member, a recessive interval of dark-grey siltstone and silty shale deposited
on a pro-delta; 3) stromatolitic-carbonate member, comprising stacked upward-shallowing cycles of
sub- to supratidal carbonates and, 4) upper-carbonate member, an upward-shallowing succession
from sub-tidal black calcareous shale to resistant benches of peritidal, cross-bedded grainstone and
stromatolitic limestone. Facies stacking patterns reveal cyclical, upward-shallowing parasequences that
define at least six third-order sequences. Harmonious sets of third-order base-level rise and fall define
three, second-order sequences (supersequences). Correlative strata in the northern Cordillera start
to record northwest-facing rift basins during this time, however our work in the Amundsen Basin
suggests relatively stable tectonics, supporting multi-stage, non-correlative breakup of Rodinia along
the northwestern margin of Laurentia.
A negative δ 13 C excursion was recognized in a Wynniatt section from the northeastern Minto Inlier
and has been correlated with similar excursions in the Mackenzie and Ogilvie mountains, as well as the
global Bitter Springs isotopic stage. The Wynniatt anomaly was recorded in rocks collected adjacent to
a thick diabase intrusion. We re-sampled this stratigraphic interval from a locality in southwestern
Minto Inlier, away from any intrusions, to test its validity. Our data confirms the presence of a negative
anomaly over the same stratigraphic interval, supporting the validity of the excursion and intrabasinal
and extrabasinal correlations.
19

An early Neoproterozoic dynamic sulphur cycle: evidence from the Shaler Supergroup
John K. G. Prince 1 , Boswell A. Wing 2 , Robert H. Rainbird 3 , Galen P. Halverson 2
1 Carleton University, Ottawa, Canada, jkgprince@gmail.com
2 McGill University, Montreal, Canada,
3 Geological Survey of Canada, Ottawa, Canada
The Neoproterozoic (1000-542 Ma) is a dynamic era of Earth history, punctuated by super continental
break-up, global glaciations, and the evolution of metazoan life. During the early to mid-Neoproterozoic,
Earth’s redox budget was in a state of flux, the evidence for which is preserved in the isotopic records
of sulphur and carbon. In order to constrain the initiation of this dynamic behaviour, we described
and sampled 3 outcrop stratigraphic sections and a drill core at ∼ 3 m intervals through the Minto
Inlet Formation of the Shaler Supergroup, which is exposed in the Minto Inlier of NW Victoria Island,
NWT.
The Minto Inlet Formation is >250m thick and hosts well-preserved Neoproterozoic sulphate-rich
evaporites deposited in a periodically restricted intra-continental marine basin. The Minto Inlet
Formation was deposited between ∼900Ma and ∼800Ma based on detrital zircon geochronology and
stratigraphic correlation with well-calibrated sections in the northern Cordillera. We measured multiple
sulphur isotopes (δ 34 S, |Delta 33 S) of the sulphate fraction in all of the stratigraphically controlled
dataset of 67 samples.
Current understanding of the sulphur isotope record suggests that the fraction of S buried as pyrite
relative to sulphate evaporites was high, approaching 1 for most of the Proterozoic, through the
Ediacaran, and into the early Phanerozoic. We used multiple sulphur isotope measurements of Minto
Inlet Formation evaporites to constrain models of S fluxes into and out of the ocean prior to the onset
of the Cryogenian (720-635Ma). This approach suggests that the relative burial fraction of S as pyrite
was extremely low (≈0.2) during the earliest stages of the deposition of the Minto Inlet Formation.
Previously, pyrite burial fractions this low had been recorded only at Permian-Triassic time, more than
≈600 Ma after the deposition of the Minto Inlet Formation. Our results indicate large scale variations
in ocean redox conditions and a dynamic sulphur-cycle were initiated during the early-Neoproterozoic.
20

Unexpectedly large S isotope fractionation during natural sulfide oxidation at cold temperatures
K.J. Rodzinyak 1,2 , B.A. Wing 1 , and R.J. Léveillé 2
1 Earth and Planetary Sciences, McGill University, Montréal, Québec.
(kristyn.rodzinyak@mail.mcgill.ca)
2 Canadian Space Agency
The Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) Curiosity
rover will be able to measure sulfur isotope ratios of Martian samples in-situ [1]. Microbial sulfate
reduction leaves a characteristic ‘biosignature’ behind in the isotopic composition of its metabolic
reactants and products. The measurement capabilities of SAM should be able to address questions of
past Martian habitability for sulfate-reducing microbes.
One issue with this approach is that the strongest isotopic signals are often preserved in sulfide
minerals, which may not be long-lived in the oxidizing surface environment of Mars. However, previous
research suggests that the S isotope composition of the parent sulfides should be indistinguishable
from their oxidative products [2]. This sulfur isotope consistency implies that potential S isotope
biosignatures may be preserved in Martian sulfates despite the intense oxidation on the surface of
Mars.
In order to constrain the sulfur isotope characteristics of oxidative processes in cold dry environments,
we studied the sulfur isotope systematics of mineralized sulfate-bearing crusts on sedimentary pyrite
nodules from Devon Island, Canadian Arctic. These crusts display similarities to rocks studied by the
Mars Exploration Rovers, including the coexistence of Ca-Mg-Fe sulfates with Fe-oxides and nanophase
ferric oxides [3].
While we do not yet have a full understanding of the oxidative mechanism behind these unique
fractionations, their existence has clear implications for investigating potential biosignatures on the
surface of Mars. If an isotopic enrichment of 10–20 can be produced by low-temperature sulfide
oxidation, preservation of potential records of microbial sulfate reduction may be incompatible with
the present Martian surface environment, or for that matter, much of its climatic history.
[1] Franz, H.B., et al. (2011) LPS XL11, 2800-2801. [2] Seal II, R.R. (2006) Reviews in Min. and
Geochem., 633-677. [3] Léveillé, R. (2007) GSA
21

Iron Isotopes and Rare Earth Element Geochemistry for the Cryogenian Tatonduk River Ironstones
Eric J. Bellefroid 1 , Grant M. Cox 1 , Galen P. Halverson 1 , Justin V. Strauss 2
1 Department of Earth & Planetary Sciences/GEOTOP, McGill University, Canada,
eric.bellefroid@mail.mcgill.ca
2 Department of Earth & Planetray sciences, Harvard University, Cambridge, U.S.A.
Cryogenian iron formations, present on nine different continents, are of particular interest in determining
paleo-ocean chemistry as Fe is sensitive to the oceans redox state. While Rare earth element
(REE) and yttrium patterns are broadly understood, iron isotope patterns, which show extraordinary
variability, are controversial. Recently Halverson et al. (2011) argued that the up-section increase in
δ 57 Fe within the Rapitan ironstones is a reflection of a steep iron chemocline in combination with marine
transgression. We present Fe isotope data along with REE + Y data for the Tatonduk River ironstones
which show a similar δ 57 Fe trend. Fe/Ti ratios point to a significant but diluted hydrothermal input
while La-Yb ratios, a good redox indicator, show a positive trend with respect to δ 57 Fe. Therefore, we
suggest that the Tatonduk river ironstones where deposited in a similar fashion to the iron formation of
the Rapitan group. This implies that the depositional mechanism proposed by Halverson et al. (2011)
for Cryogenian ironstones is not restricted solely to the Rapitan group.
Halverson, G., Poitasson, F., Hoffman, P., Nédélec, A., Montel, J. Kirby, J. 2011. Fe isotope and trace
element geochemistry of the Neoproterozoic Rapitan iron formation. Earth and Planetary Letters. 309
(1-2), 100-112.
22

Coupled climate-geochemical modeling of the connections between break-up of Rodinia, flood basalt
volcanism, snowball glaciations and strontium cycle
Lucie Hubert-Théou 1 , Galen Halverson 1 , Yves Goddéris 2
1 Department of Earth & Planetary Sciences, McGill University, Canada
2 Géoscience Environnement Toulouse, CNRS-Université Toulouse III-IRD, Toulouse, France
The Neoproterozoic Era (1000-542 million years ago) constitutes a turning point in Earth’s history. A
series of tectonic (formation and breakup of the supercontinent Rodinia), magmatic (emplacement
of larges igneous provinces (LIP)), climatic (total glaciation of the planet) and evolutionary (faunal
explosion at the Neoproterozoic–Cambrian transition) events characterize this time period. Many
multi-disciplinary studies attempt to better identify and understand the magnitude, number, causes,
and consequences of these events. These studies address questions that regard the conditions of
occurrence and the extent of the Cryogenian glacial episodes, or the correlation between mantle plume
and dislocation of Rodinia. Several hypotheses emerge from these studies, including the contested
Snowball Earth theory and the controversial True Polar Wander phenomenon. However few studies
constrain the global evolution of the Earth-system within the 1000–542 Ma period. A multitude of
geochemical proxies show strong perturbations during the Neoproterozoic. Among these proxies, the
carbon isotope ratio in marine carbonates records an overall high composition (δ 13 C ≥ 5 ), punctuated
by several sharp declines of amplitudes of 10–15 . Strontium isotopes ( 87 Sr/ 86 Sr) are also sensitive to
perturbations of the Earth-system, revealing an increase in marine compositions (from 0.7055 to 0.7090),
that mirrors the record of declining values in the Paleozoic, with superimposed finer-scale structure
that appears to be closely linked to major climatic and tectonic events. I plan to use GEOCLIM, a
powerful coupled climate-carbon model in combination with up-to-date paleogeographies (including a
spatio-temporal distribution of Neoproterozoic large igneous provinces and orogens) and geochemical
analyses of Cryogenian mafic and carbonate rocks, to explore the 850–630 Ma time period. This will
elucidate the relationships between the magmatic, tectonic, and climatic events occurring at the end of
the Precambrian.
23

Chemostratigraphy of the Virgin Spring limestone: Implications for stratigraphic correlations in Death
Valley, CA
Felix Waechter
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
The glaciogenic Kingston Peak Formation of the Neoproterozoic Pahrump Group in Death Valley, CA,
has been assumed to be internally conformable (e.g. Troxel et al., 1987). However, geologic mapping
in the Saddle Peak Hills has revealed a new, pronounced angular unconformity of million-year scale
duration within the Kingston Peak Formation. The unconformity occurs at the base of the Virgin
Spring limestone, and truncates underlying beds of the lowest Kingston Peak member (KP1), the
Beck Spring Dolomite, and the Crystal Spring Formation. Thus, KP1 does not represent the onset of
glaciation but is rather genetically related to the Beck Spring Dolomite (Prave, 1994).
The top contact of the Virgin Spring limestone is a sharp erosional surface leading into hundreds of
meters of glaciogenic strata. These Cryogenian glacial diamictites are highly variable, but uninterrupted
until the overlying Sentinel Peak member of the Noonday Dolomite, a characteristic Marinoan cap
carbonate (Allen & Hoffman, 2007; Peterson et al., 2011) with an inferred 635 Ma age. Whether the
glaciogenic Kingston Peak units represent the Sturtian glaciation, the Marinoan glaciation, or both, is
an unresolved issue, and has prevented conclusive correlation of the glaciogenic stratigraphy across
Death Valley to the Panamint Range, where both glacials, and interglacial strata, are preserved (Prave,
1999). A clue for the interpretation of this glacial sequence was discovered in the Saddle Peak Hills,
where the uppermost member of the Kingston Peak Formation (KP4) is absent in certain locations, and
the Sentinel Peak member rests unconformably on KP3 instead. Further evidence for a disconformable
relationship between KP3 and KP4 is the occurrence of KP3 diamictite clasts within KP4 strata.
The formerly aragonitic, and therefore Sr-rich (1000–3500 ppm) Virgin Spring limestone (Tucker,
1986) yielded 87 Sr/ 86 Sr values as low as 0.7067. Fitting these values to the highest resolution 87 Sr/ 86 Sr
seawater curve available for the Neoproterozoic (Macdonald, in prep), confidently dates the Virgin
Spring limestone as pre-Sturtian. This precludes a previously viable correlation of the Virgin Spring
limestone to the interglacial “un-named limestone” in the Panamint Range. The pre-Sturtian age of
the Virgin Spring limestone, coupled with the disconformable relationship between Kingston Peak
members KP3 and KP4, suggests that members KP2 and KP3 represent the Sturtian glaciation, and
member KP4 represents the Marinoan glaciation.
24

The tectonic context of Neoproterozoic stratiform mineralization on the Western margin of Laurentia
Dylan Trotzuk
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
The Redstone stratiform copper deposit, located in the arcuate Mackenzie Mountains of the NWT,
Canada, contains drill-indicated reserves of 37 million tones averaging 3.92% Cu and 11.3 g/t Ag. The
mineralization occurs within Cryogenian strata which represent a tumultuous period in Earth’s history
and globally host many of the world’s richest stratiform copper deposits. Previous mineralization
models have called for a single expulsion of copper rich fluid or the development of an evaporitic pump
as the means to mobilize and eventually deposit Cu.
This thesis takes a multifaceted approach to constraining the method of mineralization and the unique
terrestrial conditions that caused such vast and rich mineralization. Volumetric analyses suggest that
the single dewatering scenario as explained previously is an insufficient mechanism for mineralization.
Chemical analyses, subsidence models, observations of local igneous intrusions and a more refined
understanding of the major igneous events of the Cryogenian suggest that exhalation from a nearby
mantle large igneous province (LIP) is the only satisfactory mineralizing mechanism that satisfies the
unique set of attributes identified.
The presence of a major mantle LIP proximal to the Redstone deposit could explain the unique
features of the mineral system and stratigraphic assemblage. The surfacing of this LIP could have
dramatically changed the chemistry of the seawater, resulting in the unique chemistry observed.
Additionally, through exhalation of extrusive diatremes, the LIP could have supplied the fluid to
the system and provided the impetus to that fluid to force it through the evaporite rich Redstone
Formation. Thus providing the necessary volume of fluid able leach a satisfactory mass of copper from
the Redbeds to result in the present mineralization.
The recognition of the presence of this major LIP has immense ramifications for the tectonic model
of Rodinia and the possible environmental conditions that led into the Sturtian Glaciation.
25

Maps
How to get from the airport to downtown Montreal
Taxis:
Taxis are situated at the exit of the arrivals and will take you to downtown Montreal for a fixed fare of
$40.
Payment methods include cash, Visa, MasterCard and American Express credit cards; some drivers
accept US currency but provincial regulations require customers to pay in Canadian currency.
City buses:
The 747 city buses going downtown are situated at the exit of the arrivals. It runs 24 hours a day, 7 days
a week. The trip between Montréal-Trudeau Airport and the Montréal bus terminal at Berri-UQAM
metro station takes approximately 35 minutes outside of rush hour. The service stops at Lionel-Groulx
metro station, and along Boulevard René-Lévesque at Guy, Drummond, Peel, Mansfield, Union, Jeanne-
Mance, de l’Hôtel-de-ville, and Saint-Laurent. A map of the downtown stops is shown below. The 747
is free for holders of CAM and TRAM monthly passes, and for holders of 1 or 3-day tourist passes.
Individual tickets valid for 24 hours across the entire STM network are also available, priced at $8 for
a one-way trip. At the airport, tickets are sold at the International Currency Exchange (ICE) counter
on the international arrivals level.
27