Lower Ordovician Potsdam Group in the Ottawa Embayment

470 Pages·2016·31.4 MB·English

Sedimentology, Stratigraphic Evolution
and Provenance of the Cambrian – Lower
Ordovician Potsdam Group in the Ottawa
Embayment and Quebec Basin

David G. Lowe

Thesis submitted to the
Faculty of Graduate and Postdoctoral Studies
in partial fulfillment of the requirements
for the Ph.D. degree in Earth Sciences

Ottawa-Carleton Geoscience Centre
Faculty of Science
University of Ottawa

©David G. Lowe, Ottawa, Canada, 2016
Abstract
The Cambrian – Lower Ordovician Potsdam Group is a mostly siliciclastic unit that provides
important insight into the paleoenvironmental, geologic and tectonic history of Early
Paleozoic Laurentia. Nevertheless, in spite of 178 years of study the Potsdam in the Ottawa
Embayment and Quebec Basin remains poorly understood. Also poorly understood is how
the Potsdam relates with coeval strata regionally.
In this work six siliciclastic paleoenvironments are recognized: (a) braided fluvial, (b)
ephemeral fluvial, (c) aeolian, (d) coastal sabkha, (e) tide-dominated marine and (f) open-
coast tidal flat. Fluvial strata were examined in particular detail and interpreted to consist of
two end-member kinds. Braided fluvial deposits are dominated by low-relief bars formed in
wide, shallow channels; however where basement structures limited the lateral growth of
channels, flows were deeper and bar deposits thicker and higher angle. In contrast, ephemeral
fluvial strata are dominated by sheetflood splay sedimentation with rare preservation of
scour-filling supercritical bedform strata – all later subjected to aeolian reworking. In the
upper Potsdam, alternating ephemeral and braided fluvial strata provide a record of climate
change, which, respectively, correlate with documented global cool (arid) and warm (humid)
periods during the Late Cambrian and Early Ordovician.
Three allounits are recognized in Potsdam strata, recording regional episodes of
sedimentation and facilitating correlation with coeval strata throughout eastern North
America. These correlations, aided with provenance data from detrital zircons, show that
changes in the areal distribution of sediment supply, accommodation and deposition/erosion
were principally controlled by episodic reactivation of the Neoproterozoic Ottawa graben,
which then periodically modified the stratigraphic expression of the ongoing Sauk
transgression. Specifically, episodes of tectonic reactivation occurred during late Early to
Middle Cambrian (allounit 1), late Middle to early Late Cambrian (allounits 2 – 3
unconformity), and Earliest Ordovician (allounits 3 – 4 unconformity). The earliest episode
is correlated to regional extension of southern Laurentia, whereas the latter two are linked to
peri-Laurentian accretion events that triggered reactivation of the Ottawa graben via the
Missisquoi oceanic fracture zone.
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Résumé
Le Cambrien - Ordovicien précoce Groupe de Potsdam est une unité silicoclastique qui
fournit des informations importantes sur le paléo-environnement, l'histoire géologique et
tectonique du Paléozoïque Laurentia. Néanmoins, malgré 178 années d’études, le Potsdam
dans la baie d’Ottawa et le bassin du Québec demeure mal comprise. La réaction régionale
du Potsdam avec les strates contemporaines est aussi peu comprise. Dans ce travail six paléo-
environnements sont reconnus: (a) fluviatiles entrecroisés, (b) éphémère fluviatile, (c) éolien,
(d) de sebkha côtière, (e) marine marémotrice et (f) ouvert de marée de la côte. Les strates
fluviatiles ont été examinées en détails et interprétées comme étant constituées en deux types.
Les dépôts fluviatiles entrecroisés sont dominées par des barres en bas-relief formées dans de
larges canaux peu profonds. Cependant, ou les structures préexistantes ont limité la
croissance latérale des canaux, les courants étaient plus profonds et les dépôts de bar plus
épais, avec un angle plus raide. En contraste, les strates fluviatiles éphémères sont dominées
par la sédimentation des épanouissements des inondations peu profondes, avec la
préservation des couches rares surcritique – tous ensuite sujettes au remaniement éolien.
Dans la partie supérieure du Potsdam, dépôts des fluviatiles entrecroisés et éphémères
fluviatiles dépôts sont inter-stratifiées et fournissent un historique du changement climatique,
qui correspondent respectivement à froid globalement (sec) et les périodes chaudes
(humides) documentée au cours du Cambrien tardif et Ordovicien précoce.

Trois allounits sont reconnus à Potsdam strates qui donnent des preuves d'épisodes de
sédimentation régionaux et à permettre la corrélation à contemporain roches stratifiées dans
l'Est l'Amérique du Nord. Ces corrélations, aidées des données provenant de zircons
détritiques, montrent que des changements dans la distribution locale des réserves de
sédiments, accommodements et dépôts/érosions étaient contrôlés principalement par la
réactivation périodique du graben d’Ottawa Néoprotérozoïque, qui, alors, modifiait
périodiquement l’expression stratigraphique de la constante transgression du Sauk. Épisodes
de réactivation tectoniques survenus au cours de la fin précoce à Cambrien moyen (allounit
1), fin du Cambrien moyen au début du Cambrien tardif (la discordance qui sépare allounits
1 et 2), et début du Ordovicien précoce (la discordance qui sépare allounits 2 et 3). Le
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premier épisode est corrélée à l'extension régionale du sud de Laurentia, et les deux derniers
sont est corrélée à des péri-laurentiennes événements d'accrétion qui ont déclenché la
réactivation du graben Ottawa via le zone de fracture océanique Missisquoi.

iv
Dedication
This thesis is dedicated to Al and Dan. Granted, it’s not much in the grand scheme of things
but it means a lot to me. I just wish I could have shared the excitement of finishing this piece
of work with both of you.

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Acknowledgements
I first and foremost wish to thank my thesis supervisor Bill Arnott for giving me the
opportunity to pursue this project and for generously supporting me throughout my PhD
tenure, particulalruy for supporting myself and my field assistants during my field seasons.
Rental car and fuel costs add up – on a montly basis they are more expensive than graduate
students (yet, with the added cost you get greater efficiency). I’d also like to thank Bill for
his patience, encouragement and motivation using both carrot and stick and for his
uncommon attention to detail. Finally, Bill has been and continues to be a worthy role model
for me and for others, given his integrity, honesty and positivity. I’d also like to thank all of
my thesis reviewers, Quentin Gall, George Dix, Denis Lavoie and Rob Rainbird, for
enduring this long-winded account of observations of sandstone and providing very fair
criticism which have improved this thesis. Bruce Sanford is also worth of great thanks and
praise for laying the foundation for this and more work to come in the future. Bruce also
visited many outcrops with me and shared with me his passion and positivity. Bruce is
always willing to chat, and we remain friendly in spite of some minor differences in our
interpretation of the same rocks. Like Bill, he is a worthy role model.
I’d also like to thank everyone who assisted me with my field work and other data
collection including Gurvir Khosa, Chris Barnes, Ed Desantis, Lindsay Coffin, Mike Lowe,
Megan Reardon and Jason Duff. Yes, even Chris Barnes managed to be helpful, in spite of
losing his field notes twice, drawing cartoons in the margins of the notebooks and
relentlessly beating be at Tock night after night. I am especially grateful to Lindsay and
Gurvir whose French-speaking skills without which major parts of the thesis would be
lacking data. I’d also like to acknowledge that the contributions of Lindsay, Mike, Megan
and Jason were voluntary, so thank you for your time. Chris McFarlane and Crystal
Laflamme deserve thanks for their help with the detrital zircon analyses in New Brunswick.
James Conliffe read parts of this thesis to help me revise them for publication. From the
Earth Sciences Department at U Ottawa I was greatly helped by Dave Schneider, George
Mrazek and Helene De Gouffe. I’d also like to thank the members of the Windermere Group
at U Ottawa for their thoughts and contributions, including Viktor Terlaky, Lillian Navaro,
Mike Tilston, Shann Khan, Derrick Midwinter, Natasha Popovik, Katrina Angus and Gerry
Dumachel. Special thanks also too to the many property owners that permitted us to look at
rocks on their land and who took interest in my studies. There are too many people to list but
the few names that come to mind include Brian Sloan, Mark Wilson, Tim Bresset and Bill
Atwood.
I was very lucky early on (in 2010) to join a “Potsdam Sandstone” field trip and meet
the “New York crowd”, including Bruce Selleck, Dave Franzi, Jeff Chiarenzelli and Mike
Rygel, among others. I’d like to thank these individuals and also Lisa Amati for attending
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field trips that I’ve led on the Potsdam and for maintaining interest in my ongoing research
and providing feedback. Special thanks to Dave Franzi who made me feel at home in Chazy,
NY during the summers of 2011 and 2012, and helped me out with some of my field logistics
and ideas. Thanks also to Al Donaldson for attending field trips with us, pointing out unusual
features, and getting me involved in Lanark Country geoheritage. Al also introduced me to
Chris Brett, a Lanark Country geological enthusiast who continues to update us with his
discoveries in that area. In Quebec I was helped out and made feel at home by Mario Lacelle
and Pierre Groulx. Both were more than accommodating and gave up their weekends to take
us to various locations in the field. Pierre is especially deserving of thanks as he opened his
home in Valleyfield to Chris Barnes and me. In Vermont I am grateful to Char Mehrtens for
working with me on one of my field trips and inviting me to come to Vermont to present my
research, meet their Department and to go look at rocks. Part way through my PhD I was
forced to move to Nova Scotia, and so I’m grateful to Martin Gibling for introducing me to
ideas about pre- vs. post-vegetated fluvial systems, giving me space to work at Dalhousie
University and for connecting me with many great people at the Dalhousie University Earth
Sciences Department.
I would like to thank my family for encouraging me (or, at least not discouraging me)
on this quest for esoteric knowledge that none of them really understand. Special thanks to
my wife Megan (also unpaid field assistant) for putting up with the last .. How many years?
My choice to do this PhD required you to make many sacrifices. At many points I felt as
though this PhD process was too trivial a thing to have such an effect on our lives.
Nevertheless, you unwaveringly encouraged me to continue. I assume Bill Arnott was paying
you under the table, which might be why we have such a nice car – I wasn’t getting enough
over the table to afford that fancy Mazda. Seriously though, you recognized my convictions
and long-term commitment to research and understanding the Earth, even when the short-
term circumstances made me forget. Thanks for your commitment to me; you’re the best
partner anyone could have. I’m very lucky.
Finally, thank you (and good luck) to those who endeavor to read this thesis in its entirety. I
am sure that there will realistically be no one to thank on that account. But if that’s you, I
truly appreciate it.

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Table of Contents
Abstract ii
Résumé iii
Dedication v
Acknowledgements ...................................................................................................................... vi
Table of Figures .......................................................................................................................... xv
List of Tables ........................................................................................................................... xxxv
Chapter 1: Thesis Introduction ................................................................................................. 1
1.1 Thesis Rationale ......................................................................................................... 1
1.2 Geologic Setting ......................................................................................................... 4
1.3 Study Area and Previous Work .................................................................................. 7
1.3.1 Previous stratigraphic investigations of the Potsdam Group .............................. 7
1.3.2 Previous facies analyses and interpretations of depositional environments of the
Potsdam Group ................................................................................................................ 14
1.3.3 Previous studies of sediment provenance in the Potsdam Group ..................... 17
1.3.4 Previous studies of tectonics and sedimentation in the Potsdam Group ........... 19
1.3.5 Previous studies of pre-Devonian fluvial sedimentary processes ..................... 20
1.3.6 Previous studies of climate change and its manifestation in the terrestrial
sedimentary rock record .................................................................................................. 22
1.4 Thesis Objectives and Structure ............................................................................... 23
1.5 Statement of Contributions ...................................................................................... 24
Chapter 2: Lithofacies Descriptions and Interpretations ..................................................... 28
2.1 F1: Cross-stratified sandstone .................................................................................. 28
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2.1.1 F1a: Unidirectionally cross-laminated sandstone sets and associated
asymmetric formsets ........................................................................................................ 28
2.1.2 F1a: Interpretation: Subaqueous current ripple stratification ........................... 33
2.1.3 F1b: Bidirectionally cross-laminated sandstone sets with symmetric formsets 34
2.1.4 F1b: Interpretation: Depth-limited wave ripple stratification ........................... 34
2.1.5 F1c: Unidirectional, high-angle cross-stratified sandstone sets ........................ 35
2.1.6 F1c: Interpretation: Subaqueous dune stratification ......................................... 35
2.1.7 F1d:Large-scale unidirectional planar cross-stratified sandstone sets .............. 36
2.1.8 F1d: Interpretation: Unit bar stratification ........................................................ 37
2.1.9 F1e: Low-angle trough cross-stratified sandstone sets with convex-upwards
formsets 38
......................................................................................................................................... 39
2.1.10 F1e: interpretation: Antidune stratification ....................................................... 40
2.1.11 F1f: Scour-filling sigmoidal cross-stratified sandstone sets ............................ 40
2.1.12 F1f: Interpretation: Chute-and-pool stratification ............................................. 41
2.1.13 F1g: Unidirectional low – high angle trough cross-stratified sandstone sets with
opposing paleoflow ......................................................................................................... 43
2.1.14 F1g: Interpretation: Cyclic step stratification ................................................... 44
2.1.15 F1h: Large-scale low angle concavo-convex cross-stratified sandstone .......... 46
2.1.16 Subfacies F1h: Interpretation: Hummocky and Swaley cross-stratification .... 48
2.1.17 F1i: Laterally discontinuous reversely-graded sandstone cross-strata ............. 49
2.1.18 F1i: Interpretation: Aeolian grain flow cross-strata .......................................... 50
2.2 F2: Planar-stratified sandstone ................................................................................. 50
2.2.1 F2a: Planar-laminated sandstone with thin normal or ungraded laminations ... 50
2.2.2 F2a: Interpretation: Upper-stage plane bed stratification ................................. 52
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2.2.3 F2b: Planar-laminated sandstone with thin to thick reversely-graded
laminations ...................................................................................................................... 52
2.2.4 F2b: Interpretation: Climbing translatent wind ripple stratification ................. 53
2.2.5 F2c: Indistinct, diffuse planar laminations and beds and associated surface
crenulations and bumps ................................................................................................... 53
2.2.6 F2c: Interpretation: Adhesion stratification and associated structures ............. 55
......................................................................................................................................... 56
2.2.7 F2d: Coarse-grained, massive and inversely-graded planar strata .................... 56
2.2.8 F2d: Interpretation: Deflation lags .................................................................... 57
2.3 Facies 3: graded sandstone beds .............................................................................. 57
2.3.1 F3a: Very thin to thinly bedded matrix-rich fine- to very fine-grained sandstone
57
2.3.2 F3a: Interpretation: waning flow suspended-load deposits .............................. 58
2.3.3 F3b: Coarse-grained thin- to medium-bedded normally-graded sandstone ...... 59
2.3.4 F3b: Interpretation: Rapid deposition from high concentration, high-energy
waning flows ................................................................................................................... 60
2.4 Facies 4: Conglomerate ............................................................................................ 61
2.4.1 F4a: Clast- and matrix-supported sheet-like conglomerate beds ...................... 61
2.4.2 F4a: Interpretation: Tractional conglomerate: bedload sheets .......................... 63
2.4.3 F4b: Poorly-sorted, lenticular conglomerate .................................................... 63
2.4.4 F4b: Interpretation: Talus Deposits .................................................................. 64
2.5 Facies 5: Fine-grained siliciclastics (siltstone and mudstone) ................................. 64
2.5.1 F5a: silty mudstone, massive and rare laminated ............................................. 64
2.5.2 F5a: Interpretation: Hemipelagic and/or fluid mud deposition of suspended-
load fines ......................................................................................................................... 67
2.5.3 F5b and F5c: Current- and wave-rippled siltstone ............................................ 67
x