UNIVERSITY OF CINCINNATI
DATE: May 8, 2003
I, Stephanie R. Fuentes , hereby submit this as part of the requirements for the degree of:
Master of Science in:
Geology
It is entitled:
Faunal Distribution across the
Ordovician-Silurian boundary in Ohio and Ontario
Approved by:
Carlton E. Brett
Arnold I. Miller
Thomas Algeo
Steven M. Holland
FAUNAL DISTRIBUTION ACROSS THE ORDOVICIAN-SILURIAN BOUNDARY IN OHIO AND ONTARIO
A thesis submitted to the
Division of Research and Advanced Studies of the University of Cincinnati
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
in the Department of Geology of the College of Arts and Sciences
2003
by
Stephanie R. Fuentes
B.A., SUNY Geneseo, 2001
Committee Chairs: Dr. Carlton E. Brett, Dr. Arnold I. Miller
ABSTRACT
The Late Ordovician mass extinction is one of the most extensive faunal events in earth history. However, there have been few local analyses on the faunal turnover at this boundary. In addition, it has been suggested that this boundary does not exhibit marked ecologic change.
The purpose of this study is to compare faunal distribution from the Upper
Ordovician to the Lower Silurian in terms of faunal turnover, ecologic structure, and genus richness. Samples were collected from strata that represent comparable depositional environments, including the Drakes and Brassfield
Formations of Ohio, and the Georgian Bay and Cabot Head Formations of
Ontario.
Multivariate techniques suggest a change in the composition and abundance ratios of taxa across the boundary in the study region. There is no evidence of significant ecologic restructuring across the Ordovician-Silurian boundary and the distribution of some rarefied samples suggests slightly elevated richness in the Silurian.
ii
iii ACKNOWLEDGEMENTS
I would like to thank my advisors, Carl Brett and Arnie Miller, for their continued encouragement, guidance, and support throughout this project. Their assistance in the field and the lab, as well as their review of this manuscript, provided me with motivation, insight, and ability, without which this research could not have been completed. I would also like to thank committee members
Tom Algeo and Steve Holland for their significant contributions to this project.
I am very grateful to those who assisted me in the field, including Susie
Taha-McLaughlin, Eric Wysong, Alex Bartholomew, Pat McLaughlin, and Mike
DeSantis. I am especially grateful to Brian Nicklen for his hard labor, support, and good company in Ontario. I would also like to thank James Bonelli for his continued assistance with statistical analysis.
Thanks to my fellow grad students for their encouragement and friendship throughout this program, and also to the department as a whole for providing an intellectually stimulating, cordial working environment.
Thanks to my family for their love and guidance throughout my education, particularly during the past two years of my Master’s.
This research was funded by the University of Cincinnati Geology
Department and the American Museum of Natural History Theodore Roosevelt
Memorial Fund.
iv TABLE OF CONTENTS
Page
ABSTRACT………………………………………………………………………………ii
ACKNOWLEDGEMENTS……………………………………………………………...iv
LIST OF FIGURES……………………………………………………………………...2
LIST OF TABLES……………………………………………………………………….5
LIST OF APPENDICES………………………………………………………………...6
INTRODUCTION………………………………………………………………………..7
GLOBAL LATE ORDOVICIAN MASS EXTINCTION………………………………12
STRATIGRAPHIC FRAMEWORK…………………………………………………...17
METHODS……………………………………………………………………………...38
Date collection………………………………………………………………….38
Date analysis…………………………………………………………………...40
RESULTS AND DISCUSSION……………………………………………………….45
Variations in faunal composition through space and time…………………45
Variations in abundance ratios of key taxa through space and time……..54
Variations in ecologic structure through space and time………………….78
Variations in genus richness through time………………………………….83
CONCLUSIONS……………………………………………………………………….86
REFERENCES…………………………………………………………………………88
APPENDIX I……………………………………………………………………………93
APPENDIX II………………………………………………………………………….122
1 LIST OF FIGURES
Figure Page
1. Diagrammatic chart of the four sampled formations……………………….18
2. Map of the study area…………………………………………………………22
3. Stratigraphic column and outcrop photographs of the Drakes
Formation, West Union, Ohio…...……………………………………………24
4. Stratigraphic column and photographs of the TST of the Drakes
Formation, West Union, Ohio………………………………………………...25
5. Stratigraphic column and outcrop photographs of the Brassfield
Formation, West Union, Ohio………………………………………………...27
6. Stratigraphic column and outcrop photographs of the Georgian Bay
Formation, Oakville, Ontario………………………………………………….30
7. Photographs of EHST samples from the Georgian Bay Formation,
Oakville, Ontario……………...………………………………………………..31
8. Photographs of sedimentary structures in the Cabot Head Formation,
Hamilton, Ontario………………………………………………………………33
9. Stratigraphic column and outcrop photographs of the Cabot Head
Formation at Chedoke Creek, Hamilton, Ontario…………………………..34
10. Stratigraphic column and outcrop photographs of the Cabot Head
Formation at Mountain Brow Drive, Hamilton, Ontario…………………….35
11. Stratigraphic column and outcrop photographs of the Cabot Head
Formation at Jolly Cut, Hamilton, Ontario…………………………………..36
12. Cluster analysis dendrogram of presence/absence data per locality……49
2 LIST OF FIGURES (continued)
Figure Page
13. Two-dimensional MDS ordination of presence/absence data per
locality…………………………………………………………………………..50
14. Cluster analysis dendrogram of presence/absence data per sample…...52
15. Two-dimensional MDS ordination of presence/absence data per
sample………………………………………………………………………….53
16. Cluster analysis dendrogram of abundance data per sample with
slab-counted data scaled to point count coverage…………………………56
17. Two-dimensional MDS ordination of abundance data per sample
with slab-counted data scaled to point count coverage……………………57
18. Cluster analysis dendrogram of abundance data per sample based
on equal weight between point and slab counts……………………………59
19. Two-dimensional MDS ordination of abundance data per sample
based on equal weight between point and slab counts……………………60
20. Histograms showing average percent abundance of key families per
cluster…………………………………………………………………………...64
21. Two-dimensional MDS ordination of abundance data from samples
of the Drakes Formation, West Union, Ohio………………………………..66
22. Two-dimensional MDS ordination of abundance data from samples
of the Georgian Bay Formation, Oakville, Ontario…………………………69
23. Two-dimensional MDS ordination of abundance data from samples
of the Brassfield Formation, West Union, Ohio…………………………….70
3 LIST OF FIGURES (continued)
Figure Page
24. Two-dimensional MDS ordination of abundance data from samples
of the Cabot Head Formation, Hamilton, Ontario………………………….72
25. Two-dimensional MDS ordination from Ordovician samples……………75
26. Two-dimensional MDS ordination from Silurian
samples…………………………………………………………………………77
27. Two-dimensional MDS ordination of samples represented by
trophic group…………………………………………………………………...79
28. Histograms showing average percent abundance of key trophic
groups per formation…………………………………………………………..82
29. Graphs showings number of genera versus number of specimens for
rarefied data……………………………………………………………………84
4 LIST OF TABLES
Table Page
1. Common genera categorized by trophic group membership……………..42
2. Number and percent of shared genera between each formation………...46
3. ANOSIM results showing relationships between formations in terms
of faunal composition per sample……………………………………………55
4. ANOSIM results showing relationships between formations based
on abundance data with equal weight between point and slab counts…..61
5. ANOSIM results showing relationships of formations divided into
systems tracts comparing regions within each period……………………..67
6. ANOSIM results showing relationships of formations based on
trophic structure………………………………………………………………..80
7. Comparison of the number of genera versus the number of specimens
for Ordovician samples, Silurian samples, and each sampled
formation………………………………………………………………………..84
5 LIST OF APPENDICES
Appendix Page
I. Raw abundance data……………………………………………………...93
II. Locality register…………………………………………………………..122
6 INTRODUCTION
As one of the “Big Five” Phanerozoic mass extinctions (Sepkoski, 1995), the global nature of the Late Ordovician event has been studied extensively (e.g.
Sheehan, 2001; Sheehan and Coorough, 1990; Sheehan, 1988; Berry, et al.,
1995;Tuckey and Anstey, 1992; Berry and Boucot, 1973; Rong and Harper,
1988; Cocks, 1988; Brenchley, 1988; among others). However, in comparison with other mass extinction boundaries, there is a relative lack of research documenting local faunal transitions across the Ordovician-Silurian boundary.
Based on qualitative assessment, it has been argued that the Late Ordovician extinction did not result in significant ecologic restructuring on a global scale
(Droser et al., 1995, 1997, 2000). However, this concept is difficult to test on a local level, because of the lack of environmentally comparable sections across the boundary. In this context, the purpose of this study is to compare community-level faunal patterns among comparable environments in the pre- extinction versus post-extinction strata across the Ordovician-Silurian boundary.
Various studies (e.g. Jablonski, 1998) have shown that local faunal patterns do not necessarily correspond to global trends, and, therefore, alpha- level studies may be of great importance in appreciating the significance of widespread events. With respect to the Ordovician and Silurian, Adrain et al.
(2000) compared Silurian trilobite diversity at various hierarchical levels and concluded that the local trilobite response to the Late Ordovician mass extinction was in sharp contrast to the global effect on the clade as a whole. The global trilobite diversity curve shows a decline of about 50% at the genus and family levels, and a slow recovery relative to other groups. However, local populations
7 exhibit less of a decline in diversity and little long-term change after the Late
Ordovician extinction.
In some cases, apparent variations in local trends reflect the recognition of
rare assemblages in local refugia. Many shallow benthic groups, particularly
those occupying epicontinental seas, suffered catastrophic decline during the first
phase of the Late Ordovician extinction (Sheehan, 2001). However, in the few
localities that remained submerged, the Late Ashgill eustatic decline had little
apparent effect on benthic faunas. For example, nearly 75% of bryozoan species
that survived this extinction pulse occur on Anticosti Island, Quebec, which
exhibits continuous sedimentation at this time (Petryk, 1981; Tuckey and Anstey,
1992). In contrast, only five of the 19 surviving North American species occupied
the midcontinent (Tuckey and Anstey, 1992).
Moreover, it is clear that our interpretation of fossil data is greatly
influenced by the way in which we interpret the enclosing strata (e.g. Holland,
1995a; Brett, 1995; Brett, 1998; Holland and Patzkowsky, 1999). Careful
stratigraphic analysis must accompany paleontological studies at local and
regional levels because many of the same factors control both the fossil and
stratigraphic records. Most marine organisms exhibit preference for a particular environment based on depth-related variables like salinity, temperature, turbidity, sedimentation rate, and light. As sea-level fluctuates, depositional environments migrate laterally, with corresponding migration of taxa tracking particular habitats
(Brett, 1995; Brett, 1998; Holland, 1995a, b; Goldman et al, 1999; Holland, 1999).
Therefore, if environmental constraints can be predicted through space and time,
8 it is likely that faunal composition, and perhaps even population structure, can
likewise be inferred as organisms track a preferred depth range.
Sequence stratigraphic analysis permits a more meaningful interpretation
of biotic patterns through space and time. Most importantly, delineation of
sequence architecture enables recognition of important vertical and lateral
changes in environments that are certain to affect faunal distribution, and allows
a researcher to recognize instances in which apparent patterns of transition are
overprinted by erosion and other factors that compromise the biological veracity
of spatio-temporal signatures (Holland, 1995a).
For example, Goldman et al. (1999) described a strong association
between sea-level events and graptolite species turnover in upper Middle
Ordovician strata of Mohawk Valley, New York. They attributed these patterns to
graptolites tracking a preferred environment within a depositional system that shifts in response to sea-level fluctuation. The authors note, however, that this pattern is exaggerated because fossil first appearances coincide with bounding
surfaces that effectively shorten fossil ranges (see Holland, 1995a). However,
with detailed sampling, Goldman et al. (1999) showed that the association of
faunal turnover with sea-level events and depositional environments is
nevertheless biologically meaningful.
Furthermore, a study by Abbott and Carter (1997) on the macrofauna of
the Pleistocene Castlecliff region of New Zealand shows a strong correlation
between key taxa and particular systems tracts of depositional sequences. In
fact, the relationship between fossils and systems tracts was so strong that the
authors were able to predict the positions of bounding surfaces based on the
9 fossil assemblage alone when this information was not readily apparent from the lithology.
Three hypotheses provide the specific focus for this research:
1) Given that the strata in this study straddle a mass extinction boundary, it is expected that community-level faunal attributes will differ significantly between Ordovician and Silurian samples, in terms of both faunal composition and abundance ratios of key taxa. Certainly, this is the case across other mass extinction boundaries, and such changes have also been documented for the
Late Ordovician extinction at various scales (Hallam and Wignall, 1997), albeit to a limited extent at the community-level.
2) As noted earlier, it has been suggested that the Late Ordovician mass extinction did not result in a significant ecologic turnover at the global scale, and, therefore, one might expect to find similar consistency in ecologic structure across the Ordovician-Silurian boundary at the local scale of this study.
However, it was also noted that local trends do not always correspond to global patterns, and for this reason, it would not be unexpected for the alpha-level pattern to differ from the global signature of no marked change in ecologic structure. In this study, the change, or lack thereof, in trophic structure is evaluated as a proxy for general ecologic change, both spatially and temporally.
3) The Silurian samples collected in the present study should be from intervals that postdate the extinction and subsequent recovery, in order to describe the stable fauna that existed after the Late Ordovician extinction and compare it to the pre-extinction fauna. In this case, it is expected that these samples would not exhibit depressed taxonomic richnesses relative to the pre-
10 extinction Ordovician fauna. Rather, Lower Silurian assemblages should be diverse, exhibiting richnesses about equal to or greater than that of the Upper
Ordovician samples. However, it has also been suggested that this recovery lasted well into the Llandovery, perhaps into the Lower Wenlock in some regions
(Sheehan and Harris, 1997), with an estimated recovery interval varying from between 2-3 million years (Sheehan, 1974), 3-5 million years (Hansen and
Sheehan, 1989), and 5-7 million years (Sheehan and Watkins, 1995) in North
America. If the Silurian samples represent part of that recovery phase, it would be expected that these samples show decreased genus richnesses.
4) In addition, recovery stage fauna would not likely exhibit significant distinction between regions, i.e. the fauna might be geographically widespread, nor should there be a significant distinction with respect to sequence stratigraphic architecture within a locality, i.e. genera might be eurytopic.
11 THE GLOBAL LATE ORDOVICIAN MASS EXTINCTION
The Late Ordovician extinction was a two-phase event resulting from
regression and later transgression associated with a short-lived (~ 1 my), major
glaciation centered in West Africa (Sheehan, 1973; Berry and Boucot, 1973;
Brenchley et al., 1991; Brenchely et al., 1994; Berry et al., 1995). Biogeography, particularly endemism versus cosmopolitanism of taxa, played a significant role in determining how faunas responded to various factors associated with glaciation, namely cooling and sea-level decline (Sheehan, 1973).
Eustatic decline of nearly 100 m during the first pulse of extinction was most detrimental to endemic faunas in epicontinental seas, which were forced to migrate to the shallow continental margins; most were unsuccessful in competition with incumbent faunas (Sheehan, 2001; Brenchley et al., 1994).
However, for both pelagic and benthic taxa on continental margins and in the open ocean, cooling and increased deep ocean circulation were the more likely causes for their extinction during the first phase (Jablonski and Flessa, 1986;
Sheehan, 2001).
These changes facilitated the spread of the Hirnantia fauna, a widespread, cool-water fauna first recognized by Elles (1922) as the early Llandovery
“Hirnant” brachiopod assemblage, and later modified to include various provinces in the uppermost Ordovician Hirnantian Stage (Rong and Harper, 1988).
Although some Hirnantian taxa persisted into the Llandovery (e.g., Dalmanella and Leptaena), the demise of the Hirnantian fauna is contrary to the expected preferential survival of geographically widespread, generalist faunas at mass extinction boundaries. Much of the cool-water adapted fauna was annihilated in
12 the second pulse of extinction with the return to pre-glacial, warm-water conditions with decreased circulation (Rong and Harper, 1988). Below, details are provided concerning extinctions among the three most abundant phyla encountered in this study: bryozoans, brachiopods, and bivalves.
Bryozoa
For bryozoans, the first extinction phase at the end-Rawtheyan was the more detrimental event. At that time, North American endemic faunas suffered an 86% decline in species and 21% loss of genera (Tuckey and Anstey, 1992;
Anstey, 1986). As noted above, for most marine taxa, the end Rawtheyan event is associated with regression and related effects. Tuckey and Anstey (1992) corroborate this view for bryozoans in that the majority of North American bryozoan survivors are found on Anticosti Island, which remained submerged throughout the regression (Petryk, 1981). At that time, Baltic taxa suffered only an 8% loss of species and corresponding 5% decline of genera.
The end Hirnantian extinction of bryozoans was most severe in Baltica, which lost 83% of species and 22% of genera, compared to the North American loss of only 5% of its genera (Tuckey and Anstey, 1992). The specific cause of the Hirnantian extinction for many marine biotas is debated among scientists, but may involve a rapid sea level rise (Rong and Harper,1988; Brenchley, 1984) that was associated with anoxia (Fortey, 1989).
13 Brachiopoda
The Ordovician-Silurian boundary marks a significant shift in brachiopod
biogeography. Prior to the first phase of extinction, brachiopods inhabiting
epicontinental seas in Laurentia, Siberia, and Baltica were predominantly
endemic taxa, while the continental margins of those regions were characterized
by a more cosmopolitan, though relatively diverse, fauna. In contrast, both the
Uppermost Ordovician Hirnantian Stage and the Lower Silurian Llandovery are
characterized by a generalist fauna in most environments (Sheehan, 1973).
Although Rawtheyan cosmopolitan faunas in the open oceans and on the
continental margins were more successful than endemics in epeiric seaways, the
Hirnantian Stage was characterized by the sudden dominance of new
brachiopods in open marine environments. About 44% of Lower Ashgillian
genera did not survive into the Hirnantian Stage (Sheehan and Coorough, 1990).
These Hirnantian brachiopods can be divided into three provinces: the tropical Edgewood Province, temperate to subtropical Kosov Province, and the high-latitude Bani Province (Rong and Harper, 1988). The typical Hirnantia fauna, characterized by the genera Hirnantia, Dalmanella, Hindella, Kinnella,
Draborthis, Paromalomena, and Plectothyrella, among others, occupied shallow regions of the Kosov Province throughout modern Europe, Asia, South America,
Australia, and eastern North America. The Bani Province, which developed in close proximity to the Gondwana ice sheets, is considered to be an atypical cold- water Hirnantia fauna that shares few key taxa with the Hirnantia fauna sensu stricto, and includes species that are unique to the province. The diverse
Edgewood fauna of central North America and eastern Canada is more
14 comparable to the typical Hirnantia fauna, with additional genera Stegerhynchus,
Rafinesquina, and Dolerorthis, among others.
Following the height of glaciation, transgression and the return to
preglacial conditions decimated the newly developed Hirnantia fauna. It was
replaced by a cosmopolitan assemblage that did not maintain Hirnantian Stage
provinciality. While approximately half of the Hirnantian brachiopod genera
persisted into the Silurian, overall, brachiopods suffered about a 65% decline in
genus richness from the Ashgill to the Llandovery as a result of both Late
Ordovician extinction phases (Sheehan and Coorough, 1990; Berry et al., 1995).
Bivalvia
Relative to other groups, bivalves have typically been very successful
across extinction boundaries. Sedentary bivalves have the ability to store energy
reserves, which may give them an advantage over mobile bivalves during short
intervals of heightened stress (Kriz, 1984; Martin 1966). However, sessile
bivalves are also restricted by ocean circulation conditions because they are
sensitive to the oxygen and nutrient contents of their particular environments, and are therefore at a disadvantage during extended periods of anoxia (Kriz,
1984).
Kriz (1984) evaluated the autecology of bivalves throughout the Silurian, in the context of the bivalve transition across the Ordovician-Silurian boundary. Of
123 Ordovician genera, only 26 survived the Late Ordovician extinction.
Particularly successful families include Pterinidae, Ctenodontidae, Nuculidae, and Modiomorphidae. In terms of life habit, over 30% of surviving genera were
15 endobyssate suspension feeders, a group whose diversity remained relatively constant throughout the Llandovery and Wenlock, expanded during the Ludlow, and contracted again during the Pridoli (Kriz, 1984). Infaunal deposit feeders, free-burrowing suspension feeders, and epibyssate suspension feeders were less successful into the Llandovery, although the latter two forms increased dramatically throughout the Silurian (Kriz, 1984).
16 STRATIGRAPHIC FRAMEWORK
Given the hypotheses delineated earlier, it was important that stratigraphic units used for comparison across the Ordovician-Silurian (O-S) boundary preserve similar environments of deposition to fairly compare faunal compositions. This study is focused primarily on the Ordovician Preachersville
Member of the Drakes Formation (Richmondian) of Ohio and the Silurian Cabot
Head Formation (Rhuddanian) of Ontario (Fig. 1). In terms of facies and geologic setting, they are the two most comparable formations investigated in the present study, and have, therefore, been sampled at higher stratigraphic resolution than the other sampled intervals, the Silurian Brassfield Formation
(Rhuddanian-Aeronian) of Ohio and the Ordovician Georgian Bay Formation
(Maysvillian-Richmondian) of Ontario. Although the two Silurian formations and the two Ordovician formations are not precisely time equivalent, they were chosen for this comparison for their similarity in depositional environment. In addition, it should be emphasized that the purpose of this study is not to assess the decline or recovery of diversity in the immediate vicinity of the O-S boundary, as the actual boundary between Ordovician and Silurian strata is an unconformity throughout most of eastern North America. Rather, I was interested in faunal comparisons between pre-extinction Ordovician faunas and Silurian assemblages following recovery.
At a broad scale, the four sampled formations are environmentally similar because of the positions of Ohio and Ontario at about the same paleolatitude at
17
Series Stage OHIO ONTARIO A. CABOT HEAD BRASSFIELD Manitoulin Whirlpool Rhuddanian Llandovery G. DRAKES
Ashgill
Richmondian GEORGIAN M. BAY
Figure 1. Diagrammatic stratigraphic chart of the four sampled formations. Yellow indicates high sampling intensity; blue indicates relatively low sampling intensity. M = Maysvillian, G = Gammachian, A = Aeronian
18 approximately 30˚S during the Late Ashgill (Fig. 2). Based on general lithology,
sedimentary structures, and ichnofauna, it is clear that these formations were deposited in shallow, storm-dominated environments below fair weather wave base. Some sections commonly display rippled, sandy beds in the uppermost portions, suggesting a slightly shallower depth.
Moreover, the Upper Ordovician Drakes and Georgian Bay Formations and the Silurian Cabot Head and Brassfield Formations represent mixed carbonate-siliciclastic settings on the western fringes of clastic wedges
(Queenston and Medina “deltas”, respectively) produced by erosion of the
Taconic uplands. The Queenston delta prograded following the second
(Vermontian) tectophase of the Taconic orogeny, while the Medina clastics were derived from the third (Tuscarora) tectophase (Ettensohn and Brett, 1998). Both the Ordovician and Silurian samples were derived from single, third order depositional sequences representing about 2-3 million years duration (see Brett,
1998).
Despite similarity with respect to broad characterization of the depositional environments, there are notable differences between sections from Ohio versus those from Ontario. That is, at the time of deposition modern Ontario was positioned closer to the Taconic uplands, resulting in thicker strata consisting of relatively immature sediments, namely, hematitic shales and sandstones in the upper portions of the Georgian Bay and Cabot Head Formations. In addition, the
Brassfield Formation is significantly more carbonate-rich than the other three sampled formations.
19 Depositional sequences in this study refer to the “subsequences” of Brett et al (1990). These are fourth-order depositional sequences of about 1.0 to 1.5 million years duration, typically corresponding to formations or members of formations. Subsequences are intended as intermediate divisions of strata between true third-order sequences and parasequence sets (see Van Wagoner et al., 1988) such that third-order sequences are comprised of about two to four fourth-order subsequences, which are, in turn, divisible into two to three parasequence sets.
Identification and internal division of third- and fourth-order sequences are analogous. That is, fourth-order sequences have been delineated based on sharp, lower bounding surfaces, which may be conformable in deep-water settings, but are typically unconformable, though not extensively erosive, in the shallower settings discussed in this study. Above this surface, fourth-order sequences deepen upwards to a marine flooding surface, which is comparable to the maximum flooding or maximum starvation surface of true third-order sequences. Thus, the lower interval of a fourth-order sequence described by a lower bounding surface and upper marine flooding surface is similar to the transgressive systems tracts of a third-order sequence in settings where the lowstand systems tract is not represented. Similarly, the shallowing-upward interval described by a lower marine flooding surface and an upper bounding surface in a fourth-order sequence is analogous to the highstand systems tract in a third-order sequence.
In this discussion, fourth-order subsequences will simply be referred to as
“sequences” divisible into transgressive systems tracts (TST), early highstand
20 systems tracts (EHST), and late highstand systems tracts (LHST), which are identified by the surfaces described above, as well as sharp facies transitions corresponding to differences in depositional processes. In general, each sampled section in this study consists of a lower, thin- to medium-bedded, greenish-gray packstone sequence of a deepening TST. The midsection becomes increasingly shaley in the EHST, and each section culminates in a series of sharp-based, reddish shales, limestones, and/or sandstones in the
LHST.
21
Figure 2a. Paleogeographic reconstruction of North America during the Late Ashgill. Red circle indicates Ohio; yellow circle indicates Ontario. Modified from vishnu.glg.nau.edu/rcb.
N
Lake Huron
N ONTARIO 100 km IN OH MI ** * 200 km KY L.Erie NY
Figure 2b. Map of the Indiana- Figure 2c, Map of Ontario. Red SectionKentucky-Ohio 1.01 tristate indicating position of West star indicates Oakville; blue star indicates Hamilton. Union, Ohio.
22 The Drakes Formation, Preachersville Member at West Union, Ohio
The upper six meters of the Preachersville Member of the Drakes
Formation (Richmondian) were sampled at West Union, Ohio (Fig. 3). At this
locality, the Preachersville is overlain by the Belfast member of the Brassfield
Formation; the two units are separated by the Cherokee unconformity, clearly
recognizable on the eastern side of the Cincinnati Arch.
The lower two meters of exposed Preachersville have been delineated as
the TST because they are characterized by light-medium gray packstones that
are rich in ramose trepostome bryozoans and brachiopods. In contrast to the
shaley EHST described below. The orthids Hebertella, Dalmanella, Glyptorthis,
and Plaesiomys are dominant among the brachiopods. These TST limestones frequently include green-shale rip-up clasts, which are common in storm- dominated environments (Fig. 4). The next two meters have been interpreted as the EHST because they consist almost entirely of light-medium gray, soft, barren shales, interspersed with a few thin calcisiltites and wackestones, and this facies is distinct from those underlying and overlying the EHST. At about 4.25 m above the base of the measured interval, there is a package of red Helopora limestones and shales interpreted as the beginning of the LHST because the presence of the hematitic material suggests renewed sedimentation, likely linked to the
Vermontian tectophase of the Taconic orogeny and deposition of the massive
Queenston Delta in New York and Ontario (Brett et al, 1990, 1998). The uppermost half meter of the Preachersville consists of mostly barren, though bioturbated, light to medium gray shales and sandy shales. Common ichnofauna in this interval
23 Fm.
d d 7.0 ssfiel ssfiel TST Bra
Bra Cherokee Unconformity
6.0 1m es Fm. 5.0 Drak es LHST Drak 4.0
3.0
2.0
1.0 TST EHST 0.0m
SH CS WS PS Figure 3a. Stratigraphic column of the Preachersville Member of the Drakes Formation, West Union, Ohio. Red circles indicate the positions of sampled beds used in multivariate analysis. Adjacent 2m photograph shows the Cherokee unconformity separating Ordovician and Silurian strata.
TST = transgressive systems tract, Figure 3b. General outcrop photograph EHST = early highstand systems of the Preachersville Member of the tract, LHST = late highstand Drakes Formation, West Union, Ohio. systems tract. SH = shale, CS = Arrows indicated Cherokee calcisiltite, WS = wackestone, PS unconformity. = packstone, SS = sandstone.
24 1 m 2.0
1.0 TST
0.0m SH CS WS PS
Figure 4a. Diagrammatic stratigraphic column and photograph of the TST of the Preachersville Member, Drakes Fm., at West Union Ohio. Red circles indicate sampled beds used in multivariate analyses.
Figure 4b. Photograph of a typical TST limestone in the Preachersville Mbr., Drakes Fm. at West Union, Ohio. Arrow points to green shale rip-up clast, which implies a storm-dominated environment. Sample taken 1.35 m above base of the section.
25 include Planolites, Chondrites, Rusophycus, Cruziana, Diplocraterion, and
Trichophycus.
The overlying Belfast Member of the Brassfield Formation is a 2 m, thin-
bedded, orange-gray dolomite lacking body fossils, but exhibiting abundant
ichnofossils, namely Chondrites and Planolites. Above the Belfast Member, the
Brassfield is a massive, extensively bioturbated, orange-gray dolomite with abundant crinoid debris and few other identifiable fossils. At most localities, the
Brassfield includes several (up to 10) laterally continuous chert beds beginning at about 3-4 m above the Belfast. However, the Cherokee Unconformity is inconsistent in both the extent of erosion of Ordovician strata and elimination of the Lower Brassfield. In general, the Belfast becomes thinner to the north, until it is no longer recognized in central Ohio. The Brassfield was not sampled at this section, which includes only the lower portions of the unit.
The Brassfield Formation at West Union, Ohio
The mid- to upper portion of the Brassfield Formation, which more closely resembles the depositional environment of the other three sampled intervals than does the lower Brassfield, was sampled about 0.8 km south of the Preachersville section (Fig. 5). The section begins about 3 m above the Cherokee unconformity. The lower 3 m of the section were partially covered at the time of sampling, but collectively, the lower 5 m have been interpreted as the EHST because they consist mainly of greenish-gray barren shales and low-diversity, dense dolomitic wackestones overlain by a sharp-based package of distinctly
26 TST 7.0 30 cm
6.0
LHST 5.0
4.0
EHST 3.0
2.0 TST LHST 1.0 EHST 0.0m
SH CS WS PS
Figure 5a. Diagrammatic stratigraphic column of the Brassfield Formation at West Union, Ohio. Base of the section 1 m occurs about 3m above the base of the Brassfield. Adjacent photograph shows hematitic clay layer, which is about 30 cm, at maximum, in this Figure 5b. General outcrop picture. Red circles indicate sampled photograph of the Brassfield Fm beds used in multivariate analyses. at West Union, Ohio.
27 different lithology. The next 1.25 m have been designated as the LHST, which exhibits thick packages of yellowish-gray, high-diversity dolomitic packstones, interbedded with greenish-gray barren shales. The packstones are dominated by bryozoan Helopora and dalmanellid brachiopods. At about 5.75 meters above the base of the section there is a thin (30 cm at maximum), lenticular, hematitic shale with trepostome bryozoans and rugose corals. Above this interval, the next sequence begins with a TST consisting of about 2.5 meters of massive dolomite, including several continuous chert beds.
The Georgian Bay Formation at Oakville, Ontario
In southern Ontario, the Georgian Bay Formation (Richmondian) consists of 127-177 meters of gray shales and calcareous sandstones, with the former dominant in the lower portion and the latter in the upper. Sandstone-shale packages often exhibit a basal lag zone overlain successively by hummocky cross stratification, horizontal laminations, and cross-laminated beds, all overlain with shale, in a typical storm-dominated shelf sequence (Stanley and Pickerill,
1998).
The Georgian Bay Formation was first identified by Foerste (1924) as the
Meaford Formation, including all strata between the upper Queenston Shale and the lower Maysvillian strata. The age of the unit was determined based on shared faunal composition at the genus level with the Cincinnatian Series in
Ohio, including Hebertella, Strophomena, Rafinesquina, Cyclonema, Hallopora,
Homotrypa, Zygospira, Modiolopsis, and Ctenodonta. Stanley and Pickerill’s
(1998) study of the Georgian Bay ichnofauna and comparison with Osgood’s
28 (1965) ichnofaunal work of the Cincinnatian of Ohio confirms the similarity between these two locales. Stanley and Pickerill (1998) counted 47 ichnospecies divided into 26 ichnogenera, including Chondrites, four ichnospecies of Cruziana, three of Diplocraterion, four of Palaeophycus, three of
Planolites, five of Rusophycus, and two of Skolithos. Ichnogenera shared between Stanley and Pickerill (1998) in the Cincinnatian Series of Ontario and
Osgood (1965) in the Cincinnatian of Ohio include: Chondrites, Lockeia,
Palaeophycus, Palaeodictyon, Phycodes, Rusophycus, Skolithos, and
Trichophycus. This composition is typical of subtidal depositional environments between storm and fair weather wave base. The assemblage has been assigned to the Cruziana ichnofacies of Seilacher (1964,1967), except in the case of short- term occupation of opportunistic organisms, producing traces associated with the sandy substrate ichnofauna of the Skolithos ichnofacies in some storm- dominated layers (Stanley and Pickerill, 1998).
The sampled section of the Georgian Bay Formation at Oakville, Ontario along 16 Mile Creek consists of 13.5 m of strata, including a greenish-gray shale- dominated EHST and a red shale- and sandstone-dominated LHST (Fig. 6, 7).
These portions of the sequence are easily delineated based on such distinctions in lithology suggesting a transition from deposition in relatively deeper water to progradation of immature sediments from erosion of the Taconics. The lower 3 m of exposed EHST include sparse wackestones dominated by Zygospira,
Helopora, and Ambonychia. The upper 4.5 m of the section were also sampled,
29 3.0
2.0 Figure 6a.Diagrammatic stratigraphic column of the EHST of the Georgian Bay Fm.
EHST at Oakville, Ontario. Red circles indicate sampled beds 1.0 used in multivariate analyses.
0.0m
SH CS WS PS SS
Figure 6b. General outcrop 3 m photograph of EHST of the Georgian Bay Fm. at Oakville, Ontario. LHST occurs at the uppermost portion of the section, above the tree line.
30 A.
B.
Figure 7. Photographs of common structures in the Georgian Bay Fm. Slightly hummocky beds (A, about 2.5 m above base) and gutter casts (B, 1.76 m above base) suggest a storm-dominated environment. Note Diplocraterion burrows in gutter cast.
31 but yielded only two fossiliferous samples for data analysis. Float material collected from the intermediate 4 meters, however, yields a rich fauna dominated by Zygospira, Helopora, Loxoplocus, and Modiolopsis.
The Cabot Head Formation at Hamilton, Ontario
The Cabot Head Formation of Hamilton, Ontario exhibits shallowing upward strata with transgressive basal limestones, followed by a middle shaley interval and hematitic sandstones in the upper Cabot Head produced by prograding clastics from the last tectophase of the Taconic orogen (Brett et al.,
1990; Brett et al., 1998; Ettensohn and Brett, 1998). Common sedimentary structures, like hummocky beds, shale rip-up clasts in fossiliferous limestones, basal scours, gutter casts, and interference ripples suggest a storm-dominated environment below fair weather wave base (Fig. 8).
The lower Cabot Head Formation and the uppermost Manitoulin
Formation were sampled at Chedoke Creek in Hamilton, Ontario (Fig. 9). The uppermost Manitoulin and lower 2.3 m of the Cabot Head consist of highly glauconitic packstones exhibiting shale rip-up clasts and graded shell beds, dominated by Helopora and Coelospira. The maximum sediment starvation surface occurs in the uppermost bed of the Manitoulin, while the maximum flooding surface occurs later in the Cabot Head, as sea-level continued to rise through this condensed interval. Thus, these limestones have been delineated as the TST based on lithology and position relative to marine flooding surfaces.
The next 10 m of strata have been interpreted as the EHST based on the sharp
32 A.
B.
Figure 8. Photographs of common structures in the Cabot Head Fm. A) mud-filled Diplocraterion burrow from a TST limestone. B) sandy rippled surface covered with thin green mud from the EHST. Preserved on the ripples are the bottoms of Diplocraterion burrows from the overlying bed. Chondrites traces are preserved in the mud.
33 12.0 *
9.0 EHST
6.0
B 3.0 Cabot Head 3 m Manitoulin TST Cabot Head Fm. A Whirlpool 0.0m
SH CS WS PS SS Manitoulin Fm.
Figure 9. Diagrammatic stratigraphic column of the Lower Cabot Head Fm. at Chedoke Creek, in Hamilton, Ontario. Red circles indicate sampled beds used in multivariate analyses. White star is used to indicate the lowermost LHST package; it is used to indicate equivalent strata in other figures. Lower photograph shows the uppermost Manitoulin Fm. and the lowermost Cabot Head Fm., which collectively, make up the TST. Upper photograph shows the EHST in the Cabot Head Fm. A = maximum sediment starvation surface; B = maximum flooding surface.
34 Mountain Brow Dr. LHST
9.0
2m * 6.0 Cabot Head Fm.
3.0 EHST
0.0m
SH CS WS PS SS
Figure 10. Diagrammatic stratigraphic column of the Cabot Head Fm. at Mountain Brow Drive in Hamilton, Ontario. Red circles indicate sampled beds used in multivariate analyses, and the white star identifies the package equivalent to the uppermost measured package at Chedoke Creek. Adjacent photograph shows the LHST at this locality.
35 .
m Jolly Cut Thorold F
6.0 LHST
3.0
Cabot Head Fm. * EHST 0.0m
SH CS WS PS SS
Figure 11. Diagrammatic stratigraphic column of the upper Cabot Head Fm. Overlain by the Thorold Sandstone at Jolly Cut in Hamilton, Ontario. Red circles indicate sampled beds used in multivariate analyses. The white star identifies beds equivalent to the uppermost measured package at Chedoke Creek. Adjacent photograph corresponds to stratigraphic column.
36 facies shift with respect to bounding strata. The EHST consists of greenish-gray and purplish-gray shales interbedded with a few wackestones, packstones, and thin siltstones exhibiting planar and hummocky cross-stratification, small gutter casts on the soles of some siltstones, and rippled sandstones in the upper EHST, suggesting slight shallowing throughout this systems tract. The EHST is dominated by Stegerhynchus, Dalmanella, Helopora, and Modiolopsis, and ichnogenera Planolites, Phycodes, Chondrites, Cruziana, Rusophycus,
Diplocraterion, and Trichophycus.
The upper Cabot Head Formation was sampled at Mountain Brow Drive and Jolly Cut in Hamilton, Ontario (Fig. 10, 11). This 4-6 meter interval has been designated as the LHST because it consists of hematitic shales and sharp, erosive-based sandstones exhibiting large-scale hummocky cross-stratification, large scours and gutter casts, and numerous interference-rippled beds, and this combination of lithology and sedimentary structures suggests significant shallowing and renewed sedimentation of immature sediments relative to the
EHST. Samples from the LHST are dominated by Stegerhynchus, Ctenodonta, and Modiolopsis, as well as ichnogenera Planolites and Skolithos. The traces
Daedalus and Arthrophycus are more common to the east of Hamilton, suggesting a shallower, tidal flat paleoenvironment. The uppermost half meter of the Cabot Head consists of green shale, and is overlain by the Thorold
Sandstone.
37 METHODS
Data collection
As noted earlier, the two formations exhibiting the greatest environmental comparability, the Ordovician Drakes Formation of Ohio and the Silurian Cabot
Head Formation of Ontario, have been sampled most extensively. The
Ordovician Georgian Bay Formation of Ontario and the Silurian Brassfield
Formation of Ohio are also included in this study to examine lateral variation of
Ordovician and Silurian fauna, though they were sampled at lower resolution.
Nearly every bed exposed at sampling localities of both the Drakes and the Cabot Head Formations was measured and collected. Sections were measured to the centimeter-scale, and with few exceptions, the size of bulk samples varied from about 1 to 2 kg. The general sequence stratigraphic architecture of each section was delineated following a preliminary assessment of all collected samples. Specific faunal data were collected from a random sampling of these beds, but always included the lowermost and uppermost beds within each systems tract. In total, 80 samples from 40 collective meters of section of the Drakes and Cabot Head were analyzed.
The Georgian Bay and Brassfield Formations were collected with lesser intensity because of the predominance of poorly preserved, often dolomitized, beds. Thirteen samples were collected from the Georgian Bay and 12 from the
Brassfield. Faunal data were collected from each of these 25 samples for further data analysis.
Two methods of data collection were used to ensure appropriate assessment of the disparate set of organisms encountered in the 105 samples.
38 Point counts were conducted to assess the percent area coverage of colonial organisms, such as ramose and bifoliate bryozoans, as well as microscopic organisms like conodonts and ostracods. For each point count I used a 50 cm2 grid of 100 points. Many bryozoans were subdivided based on colony growth form (e.g., “thick ramose bryozoan”), although some distinct genera were counted individually (e.g., the twiggy bryozoan Helopora). Crinoid columnals could not be assigned to genera, and were thus simply labeled by class. I also noted the point count abundances of brachiopods, trilobites, bivalves, and gastropods for later comparison with slab-counted data (see below). For most samples, the final point-counted data consists of the average of at least two complete grid counts of both the upper and lower surfaces of the sample.
However, in cases where mud drapes obscured the upper surface of a sample, the upper surface was excluded from the count.
The second method of data collection was to count solitary macroscopic organisms on slab surfaces, including brachiopods, bivalves, trilobites, and gastropods, identified to the genus level. The preservation states of brachiopods and trilobites were carefully considered prior to counting any specimen as a true individual, rather than as a fragment. For example, to be counted as an individual, a brachiopod had to be represented by a beak and/or hinge and the majority of an outline, and a trilobite had to be represented by an articulated pygidium. In some cases, brachiopods were identified only to the family level.
For example, I did not distinguish between Dalmanella, Plaesiomys, and
Glyptorthis in poorly preserved Ordovician samples in which the three may have been confused. Rather, these were simply referred to as “orthid” brachiopods.
39 Similar assignments were made for some large strophomenids. For each sample, the abundance of bivalve genera was determined by counting convex or concave shells/molds, depending on which shape was more prevalent.
Data analysis
There is no universally accepted method for incorporating point and slab counts into one analysis, so several data treatments were incorporated here that vary in the amount of relative weight given to each count. The first method gives equal weight to point and slab counts. The slab count samples were percent transformed to represent relative abundances of solitary macrofauna, while point count data are, by definition, recorded as percent abundance on the 100-point grid. Thus, each sample sums to 200.
For the second treatment, slab-counted data were weighted based on their higher taxonomic representation on the point counts. For example, if an average of 25 brachiopod points were recognized in the point count, the total number of slab-counted brachiopods was rescaled to account for 25% of the total data (point and slab counts). In addition, rescaled data for each phylum or class reflects genus ratios recognized within that group in the slab counts.
The third treatment involved recasting all data as simple presence or absence of genera. In this case, the relatively sparse sampling of the Brassfield and Georgian Bay Formations could be supplemented with published presence/absence data collected by other researchers on these strata, including
Bolton (1957), Liberty and Bolton (1971), and Fritz (1926). This treatment allows for a broad comparison of represented fauna within both major regions and on
40 either side of the Ordovician-Silurian boundary. These data were compiled at three scales to represent the compositions of: a) each formation, b) each locality, and c) each sample.
It has been suggested that the Late Ordovician extinction is distinct from the other “Big Five” events in that it exhibits little marked long-term ecologic transformation (Droser et al, 2000). A fourth data treatment tests the local manifestation of this hypothesis, with data parsed by trophic group membership rather than with taxonomic designations. Each genus was assigned a trophic group and the data were represented as the percent abundance of individuals exhibiting each trophic habit per sample (Table 1). Data are based on genus abundance as represented in the first data treatment (see results and discussion).
Multivariate techniques were performed on each of the four matrices to delineate trends in the distribution of taxa using PRIMER version 5 (Clarke and
Gorley, 2001), a multivariate package appropriate for ecological data from
PRIMER-E Ltd. Data analysis began with Cluster Analysis (CA), a common multivariate technique that reduces the dimensionality of a complex data set by assigning samples in the Q-mode or variables in the R-mode into distinct groups, resulting in a two-dimensional dendrogram. CA was performed with UPGMA, the unweighted pair group method with arithmetic averaging. When higher order clusters are formed with UPGMA, component clusters are proportionally
41
Trophic group Genera I. Intermediate to high level 1. crinoids epifaunal passive suspension II. Epifaunal intermediate to 1. Batostomella 7. Pachydyctya high-level filter feeders 2. Clathropora 8. Phaenopora 3. Fenestella 9. Psuedohornera 4. Hallopora 10. Ptilodictya 5. Helopora 11. Semicoscinium 6. Ramose trepostome bryozoans
III. Encrusting low-level 1. Aspidopora 3. Fistulipora epifaunal filter feeders 2. Ceromoporida IV. Free-lying low-level 1. Atrypa 3. Plectatrypa epifaunal filter feeders 2. Coelospira
V. Pedically-attached low-level 1. Cryptothyrella 8. Platystrophia epifaunal filter feeders 2. Dalejina 9. Rhynchonella 3. Dalmanella 10. Rhynchotrema 4. Eospirifer 11. Rhynchotreta 5. Hebertella 12. Stegerhynchus 6. Homeospira 13. Zygospira 7. Plaesiomys VI. Epibyssate low-level 1. Ambonychia 3. Cornellites epifaunal filter feeders 2. Caritodens 4. Leiopteria
VII. Semi-infaunal filter feeders 1. Amphistrophia 5. Rafinesquina 2. Coolinia 6. Strophondonta 3. Eoplectodonta 7. Strophomena 4. Leptaena 8. Strophonella VIII. Endobyssate filter feeders 1. Modiolopsis
IX. Microcarnivores 1. Tabulate and rugose corals X. Infaunal deposit feeders 1.Ctenodonta 2.Cyrtodonta XI. Vagrant scavenger 1. Calymene 3. Isotelus (carnivore) 2. Flexicalymene
XII. Vagrant scavenger 1. Bellerophont 4. Loxoplocus (herbivore) 2. Buchania 5. Murchisonia 3. Hormotoma 6. Pleurotomaria
Table 1. Common genera categorized by trophic groups.
42 weighted by the number of included samples. All Q-mode analyses on
abundance data were performed on percent transformed data. Similarity
between every pair of samples was computed using the Bray-Curtis similarity
coefficient (Bray and Curtis, 1957) and is represented on the similarity matrix.
The equation for this calculation is as follows:
p Sjk = 100 1 – Σ i=1 Yij - Yik
p Σ i=1 (Yij - Yik)
In this equation, Sjk refers to similarity between the jth and kth samples, where Yij
refers to the abundance of the genus in the ith column present in the sample in
the jth row, and similarly, Yik refers to the abundance of the genus in the ith
column present in the sample in the kth row.
Given some of the well-known limitations of CA with respect to representation of possible gradients in the data (Clarke and Gorley, 2001), non- metric multidimensional scaling ordination (MDS) was also used to interpret faunal distributions (see Kruskal and Wish, 1978). MDS ordinates samples based on their rank similarities to one another, such that points that are closer together in ordination space are more similar than those that are farther apart.
Only MDS plots with stress < 2.0 were considered for final interpretations because, by convention, these are the most reliable results (Clarke and Gorley,
2001). Stress measures dissimilarity between the ordinated distribution of points and the original similarity matrix. A stress value of zero implies no difference
43 between ordination results and the original rank similarities. Thus, lower stress values imply that MDS results are more reliable for interpretation.
In some cases, it was desirable to test the statistical significance of apparent separation of samples on the MDS graphs. This was accomplished with ANOSIM, or analysis of similarity, on the computed Bray-Curtis similarity matrix. This technique generates a test statistic called “R” and compares it to a distribution of R-values produced by randomization of the original data set. Here, the randomized distribution was based on 5,000 permutations, and groups of samples were considered statistically distinct if the real R-values exceeded 95% of randomized values (i.e. p<0.05) and the global R-value did not occur within the range of R for randomized data.
Given the aim here to also compare the relative taxonomic richness of
Ordovician and Silurian samples, it was necessary to account for differences in sample sizes as part of this comparison. Rarefaction was used for this purpose
(program provided by Holland at www.uga.edu/~strata/), which permits comparison of richness among samples with variable sample sizes, in this case specimen abundances. That is to say, rarefaction of the data eliminates the sampling bias that may suggest elevated richness in the case of large samples simply based on size.
44 RESULTS AND DISCUSSION
Variations in faunal composition through space and time
Presence/absence data were organized at several scales to include various sources in a comparison of faunal composition through space and time.
Much of the published literature on the Drakes, Georgian Bay, and Cabot Head formations focuses on composition at the formation or outcrop scales (e.g.
Bolton, 1957; Liberty and Bolton, 1971; Fritz, 1926). The largest scale of data collection describes presence/absence per formation. In this case, multivariate techniques are of little use because the four sampled formations would be treated as four samples.
It is interesting to compare the numbers of genera shared between each pair of sampled formations (Table 2). In terms of genera present, the most dissimilar formations are the Ordovician Drakes and Silurian Brassfield
Formations of Ohio, which share only 5.83% of their genera. The Drakes-Cabot
Head and the Georgian Bay-Brassfield pairs also share few genera (7.77%), which is expected given that these pairs represent formations that are distinct through time and space. Compared to the two Ohio formations, the two Ontario formations, the Georgian Bay and the Cabot Head, share a relatively large percentage of their genera (14.56%). The difference between shared genera across the Ordovician-Silurian boundary for Ohio versus Ontario is not likely a result of different extinction processes operating between regions; rather, it is
45
Formations # shared % shared genera genera Georgian Bay, Drakes 19 18.45
Georgian Bay, Cabot Head 15 14.56
Georgian Bay, Brassfield 8 7.77
Drakes, Brassfield 6 5.83
Drakes, Cabot Head 8 7.77
Brassfield, Cabot Head 25 24.27
Table 2. Number and percent of shared genera between each formation. Includes 103 genera documented from Bolton (1957), Liberty ad Bolton (1971), and Fritz (1926) as well as recent collections.
46 probably a result of the greater similarity in facies between the Ontario units
compared to the Ohio formations. Of all the sampled formations, the Brassfield
is the most distinct in the relative lack of clastic material and abundance of
carbonate sediments.
Given this distinction, the next comparison between the Brassfield and the
Cabot Head is especially interesting because the middle and upper Cabot Head
are largely siliciclastic. These two Silurian formations share about 25% of their
genera. As noted previously, it has been suggested that the Early Silurian was a time of cosmopolitanism, relative to the endemic faunas that characterized many brachiopod and bryozoan assemblages in the Ordovician epicontinental seas of
Laurentia (Sheehan, 1973; Tuckey and Anstey, 1992, 1986). This similarity in genus composition between the two Silurian formations from Ohio and Ontario corroborates that suggestion. In comparison to the Silurian formations, the
Ordovician units share almost 19% of their genera.
To summarize, the greatest similarity between pair-wise comparisons of genus composition between the four sampled formations occurs between the two
Silurian formations, followed by the comparison between the two Ordovician formations. This may suggest an increase is cosmopolitanism over endemism in the Silurian, although the percent of shared genera for the Ordovician units is only somewhat smaller than that for the Silurian formations. In addition, the similarity between the Silurian formations from Ohio and Ontario suggests that
Silurian faunas in this region were geographically widespread. (Given that the
Brassfield is dominated by carbonate material, whereas the majority of the Cabot
Head is siliciclastic, it may also seem that this similarity in composition between
47 these formations is suggestive of eurytopy, but further study suggests otherwise
(see below)). Moreover, because the greatest similarities are observed within
each period, as opposed to within each region, it is clear that the distinction in
genus composition between these formations is primarily related to time, perhaps
in association with the Late Ordovician extinction, rather than to spatial factors.
The next scale at which compositional data (i.e. presence/absence) were considered is that of individual localities, again using data from Bolton (1957),
Liberty and Bolton (1971), and Fritz (1926) as well as field collections for this study. The CA dendrogram and two dimensional MDS plots show a clear separation of samples by age, but samples are not separated in terms of sampling region (Fig. 12, 13). Given the small sample size, interpretations must be made with caution. That is, while further sampling at more localities of the
Drakes and Brassfield Formations may yield a spatial distinction on the MDS plots, the current sampling does not suggest spatial variation in faunal composition, with only one locality for the Drakes and Brassfield (Fig. 13). An interpretation of environmental gradients responsible for faunal distribution with respect to these localities is not appropriate given that this analysis includes only one sample for the Brassfield and one for the Drakes Formations. However, analysis of composition is included in this discussion for comparison with analyses based on abundance ratios of genera (see below).
The most useful treatment of presence/absence data includes collections for the present study from West Union, Hamilton, and Oakville. Unlike the
48 Ranks
Figure 12. CA dendrogram of composition data per locality. Purple = Ordovician; yellow = Silurian. OGB = Ordovician Georgian Bay; ODK = Ordovician Drakes; SCH = Silurian Cabot Head; SBF = Silurian Brassfield; WC = Workmans Creek*; 16M = 16 Mile Creek, Oakville; WU = West Union, Ohio; 10t27 = Creek section, lot 27§; MB = Mountain Brow
Drive; JC = Jolly Cut; CC = Chedoke Creek; 28 = Creek lot 28§; CRT = Cataract§; SC = Stoney Creek§; CF = Credit Falls§; MBB = Hamilton
Mountain§; NA = Nottawasaga§; RC = Railway Cut§; HM = Hornings Mills§; BB = Barrow Bay‡; OCV = Oxenden-Colpoys Village‡; DB = Dyer
Bay‡; RB = Rocky Bay‡. * = Fritz (1926); § = Bolton (1957); ‡ = Liberty and Bolton (1971)
49 50
Figure 13. 2D MDS plot of the distribution of localities by faunal composition. Localities are distinct in terms of position relative to the Ordovician-Silurian boundary, but a spatial distinction cannot be seen with so few Drakes and Brassfield localities represented.
case of comparing composition between the four formations as individual entities,
analysis of individual samples yields a large enough data set that the results of
multivariate techniques are not likely to be randomly reproduced. The CA and
MDS plots exhibit a separation of samples through both space and time such that
individual formations are distinct and there is a separation between the lower,
middle, and upper Cabot Head Formation (Fig. 14, 15).
There are two samples from the Cabot Head that cluster with the
Brassfield on the CA dendrogram, one sample from the Brassfield that clusters
with the Cabot Head, four samples from the Cabot Head and three samples from
the Drakes that cluster with the Georgian Bay (Fig. 14). Of those ten samples,
seven group with their respective formations on the MDS distribution (Fig. 15).
The three that at first seem problematic are not easily explained in this fashion.
Rather, these three Cabot Head samples that group with the Georgian Bay are low abundance, low diversity samples that include only ramose bryozoans of moderate thickness and Helopora, an association that is commonly associated with the Ordovician samples in this study. It should be noted that, given the extent of the Late Ordovician extinction, it is remarkable that Ordovician and
Silurian samples cluster together. However, this similarity is perhaps amplified
by the fact that in many cases, genera have been grouped by growth form, e.g.
“ramose bryozoan”, whereas, genuine taxonomic identifications of such fauna
51 Cluster numbers that will be used to identify CA 14. 1, 3, 5, arrows refer to samples represent fo Figure 14. HCA dendrogram showing distributio Ranks 7, 9, 10 = L rmations, with a loose separation of I o that do not g wer to Mid
II 1
d 2 le Cabot Head; 2, 4, 6
r 3 oup with their respective formations, and correspond to samples on Fig. 4 5 6 7 n of samples by faunal clusters on M the lower, middle, and u III = Drakes; 8 D S ordinations in other figures. composition = Brassfield. pper Cabot Head samples. Numbered 8 IV . In general, Roman nu
9 V merals refer to clusters 10
VI
Mixed Drakes and Georgian Bay Lower Cabot Head L. - M. Cabot Head Drakes Middle Cabot Head
Brassfield Upper Cabot Head
52 COMPOSITION PER SAMPLE
Stress: 0.16
III
1 II
2,3 5,6,7 8 IV
4 9 I V
VI 10
Georgian Bay Lower Cabot Head
Drakes Middle Cabot Head
Brassfield Upper Cabot Head
Figure 15. 2D MDS plot showing the distribution of samples by faunal composition with CA clusters designated with roman numerals (See Fig. 13). Numbers correspond to samples that do not cluster with their respective formations on Fig.13.
53 would likely result in a greater distinction between samples that cluster largely on the basis of including morphologically similar bryozoans.
The most significant separation among samples organized by composition on the MDS ordination is with respect to the Ordovician-Silurian boundary, with a secondary distinction apparent with respect to sampling region (Ohio versus
Ontario). These distinctions are supported by ANOSIM results. In the calculation of the test statistic, R, it should be noted that a value of R=0 implies no distinction between groups, R=1 implies that groups are completely dissimilar, and R<0 implies that samples from different groups are more similar than are samples from the same group. In this case (Table 3), the range of R-values for comparisons between pairs of formations based on randomized data is -0.16 to
0.24, while the global R-value equals 0.59. In all cases, the distinction between each pair of groups appears to be statistically significant, as is the global value.
Environmental constraints related to the faunal distribution and resulting clustering of samples will be discussed later in terms of abundance data, which yields more information.
Variations in abundance ratios of key taxa through space and time
As noted previously, abundance data were organized in two ways reflecting either equal weight between point and slab counts, or scaling of slab- counted data based on point counts. Results of CA and MDS of the latter suggest that this is not the best representation of the data for the questions addressed in this study (Fig.16, 17). That is, the data matrix gives heavier weight
54
Groups R-value p-value Georgian Bay, Drakes 0.674 0
Georgian Bay, Cabot Head 0.526 0
Georgian Bay, Brassfield 0.99 0
Drakes, Cabot Head 0.592 0
Drakes, Brassfield 0.982 0
Cabot Head, Brassfield 0.515 0
Table 3. ANOSIM R-values and p-values between the Georgian Bay, Drakes, Brassfield, and Cabot Head distinguished in terms of faunal composition per sample. All values based on 5000 permutations. Range pf R-values for randomized data = -0.16 to 0.24; Global R = 0.59
55 Ranks
Figure 16. HCA dendrogram of abundance data with slab-counted macrofauna scaled to point count coverage. Georgian Bay Drakes Brassfield Cabot Head
56
Stress: 0.2
Georgian Bay Brassfield
Drakes Cabot Head
Figure 17. 2D MDS plot of abundance data with macroscopic slab counts scaled to point count coverage. Ordovician and Silurian samples are vaguely distinct; compare to Fig. 19.
57 to organisms that show little change across the boundary, including many point-
counted bryozoans. These organisms have been designated primarily by
morphology, rather than proper taxonomy, and this scale may be too broad to
adequately describe variations among many bryozoans through space and time.
For these reasons, further analyses and interpretations will be based solely on
data in which equal weight was assigned to point- and slab-counted data.
Figure 18 shows the CA dendrogram resulting from equal weight between
point and slab counts. Clusters reflect each formation and roughly distinguish
the lower, middle, and upper portions of the Cabot Head Formation. These
clusters are clear in the two-dimensional MDS plot (Fig. 19). ANOSIM confirms
that the distinctions between each formation, as well as systems tracts within the
Cabot Head, are statistically significant (Table 4).
There are three samples in the Drakes cluster that came from the lower-
middle Cabot Head Fm, but these are low diversity samples including only
Helopora and moderately thick ramose bryozoans, and are therefore not representative of any formation in particular since this assemblage is found in each of the four sampled formations (Fig. 18). These samples group with the
Drakes because many Drakes samples are dominated by these fossils. One sample from the lower Cabot Head clusters with the Brassfield on the CA dendrogram, but plots adjacent to the lower Cabot Head samples on the two- dimensional MDS distribution. Similarly, one lower Cabot Head sample clusters with the middle Cabot Head on the CA dendrogram, but is adjacent to the lower
Cabot Head samples on the two-dimensional MDS plot (Fig. 17, 18). There is
58 their respective formations (Middle), and LHST (Upper). N Clusters represent individual formati Figure 18. HCA dendrogram based on abundance data of sa Ranks
I
1
2 3 II . Compare to Fig 19. u mbered arrows identify Lower ons, while the Cabot Head is generally div
III mples with equal weight given
to Middle Cabot Head sample IV
V i ded into the TST (Lower), EHST
4 5 VI to point and slab counts. s that do not cluster with 6
Georgian Bay Lower Cabot Head Drakes Middle Cabot Head Brassfield Upper Cabot Head
59
Stress: 0.19 2 I III 3
II 1 4
V IV 5
6
INCREASING SHALLOWING VI SEDIMENT INPUT
Georgian Bay Lower Cabot Head
Drakes Middle Cabot Head
Brassfield Upper Cabot Head
Figure 19. 2D MDS plot of samples based on abundance data with equal weight between point and slab counts. Numbers correspond to Cabot Head samples that don’t cluster with their respective formations on the CA dendrogram (Fig. 18), and clusters are designated with roman numerals corresponding to Fig. 18. The primary factor of separation between samples in the Ordovician-Silurian boundary.
60
Groups R-value p-value
Georgian Bay, Drakes 0.86 0 Georgian Bay, Brassfield 0.997 0
Georgian Bay, L. Cabot Head 0.956 0 Georgian Bay, M. Cabot Head 0.994 0
Georgian Bay, U. Cabot Head 0.949 0 Drakes, Brassfield 0.924 0 Drakes, L. Cabot Head 0.866 0 Drakes, M. Cabot Head 0.885 0
Drakes, U. Cabot Head 0.855 0
Brassfield, L. Cabot Head 0.793 0 Brassfield, M. Cabot Head 0.781 0
Brassfield, U. Cabot Head 0.947 0 L. Cabot Head, M. Cabot Head 0.935 0
L. Cabot Head, U. Cabot Head 0.938 0 M. Cabot Head, U. Cabot Head 0.739 0
Table 4. ANOSIM R-value and p-values for comparisons between
HCA clusters (Fig. 18) based on abundance data with equal weight between point and slab counts.
Range of R distribution for randomized data = -0.16 to 0.22; Global R = 0.57.
61 one sample from the lower Cabot Head that groups with the Brassfield samples on both the CA dendrogram and the two-dimensional MDS plot. When viewed in three dimensions, this sample groups between the lower Cabot Head and the
Brassfield clusters.
Cabot Head clusters delineated as lower, middle, or upper, correspond to sequence architecture. That is, the TST occurs in the lower Cabot Head, the
EHST in the middle, and the LHST in the upper Cabot Head. Unlike the distinction between formations in general, faunal distribution into systems tracts is not absolute; rather, boundaries between systems tracts are gradational with respect to environment as well as corresponding lithology and fauna. Therefore, the lower Cabot Head cluster does not consist solely of TST samples, nor does the middle Cabot Head include only EHST samples or the upper include only
LHST samples (see Fig. 18). The lower Cabot Head cluster includes a total of six samples, five of which occur in the TST (83%), with only one in the EHST
(17%). The middle Cabot Head cluster consists of 15 samples, of which 11 occur in the EHST (73%), three in the LHST (20%), and one in the TST (7%).
The upper Cabot Head cluster includes 17 samples, which are limited to the
LHST (59%) and EHST (41%).
This separation of Cabot Head samples with respect to sequence architecture clarifies two previously mentioned ideas. First, distinction of Cabot
Head systems tracts, namely the TST from both the EHST and the LHST (see below), by faunal abundance ratios does not suggest eurytopy among the fauna.
Rather, a eurytopic assemblage would distribute randomly among the systems tracts. In addition, the relatively stenotopic fauna suggested by this analysis also
62 confirms that the biota in this region was recovered by the Rhuddanian, contrary
to earlier suggestions by other researchers that recovery persisted in North
America for up to 7 million years (Sheehan and Watkins, 1995).
Given that the majority of samples from each formation group together,
with a few explainable exceptions, grouping on both the CA dendrogram and the
MDS plots reflect individual formations, i.e. samples are distinguishable cleanly
with respect to space and time. The most significant factor in the distribution of
all samples on the MDS plot appears to be temporal, as the greatest separation
of samples on the MDS ordination occurs between samples from each respective
period. The Georgian Bay and Drakes Formations are clearly grouped with each
other, and collectively, stand apart from the Silurian samples. In addition, the
Ordovician samples from Ohio versus Ontario are distinct on the MDS plot and
the CA dendrogram. Thus, there is a secondary separation of samples through
space. Similarly, the Brassfield is distinct from the Cabot Head samples on both
analyses. However, it should be noted that of the three Cabot Head groups, the
Brassfield ordinates closest to the lower Cabot Head on the two-dimensional
MDS plot. This may be a result of similar facies between the dominantly carbonate-rich Brassfield and the TST limestones of the Cabot Head, as opposed to the dominantly shale-rich EHST or the sandy, hematitic LHST of the
Cabot Head.
The faunal distinctions among these clusters are evident at various taxonomic levels, including genus and order, but are most effectively demonstrated at the family level (Fig. 20). The Ordovician Georgian Bay
Formation is dominated by the atrypid Zygospira, while orthids like Plaesiomys
63 Georgian L. Cabot Head Bay
Brassfiel M. Cabot d Head
Drakes U. Cabot Head
1 2 3 4 5 6 7 8 9 10 11 1 2 3 4 5 6 7 8 9 10 11
Figure 20. Histograms of average percent abundance of key families per cluster. Photographs show representative genera from diagnostic families per cluster (Holland, www.uga.edu/~strata/). Y-axis shows average percent of individuals within in group. Horizontal numbers designate families: 1 = Anoplothecidae, 2 = Arthrostylidae, 3 = Atrypidae, 4 = Ctenodontidae, 5 = Dalmanellidae, 6 = Modiomorphidae, 7 = Plaesiomidae, 8 = Plectorthidae, 9 = Pterinidae, 10 = Rhipidomellidae, 11 = Rhynchotrematidae. White scale bar = 1 cm; yellow scale bar = 3 mm.
64 and plectorthids like Hebertella are common in the Ordovician Drakes Formation.
The Silurian is characterized by orthids like Dalmanella in the Brassfield
Formation of Ohio, the rhynchonellid Stegerhynchus in the lower Cabot Head, the anoplothecid Coelospira in the middle Cabot Head, and the bivalves
Ctenodonta and Modiolopsis in the upper Cabot Head of Ontario. The twig bryozoan, Helopora (family Arthrostylidae), is common throughout.
The environmental factors controlling this distribution can be estimated roughly based on the general lithology of each sample group (Fig. 19), and, later, with analysis of trophic structure. In general, sediment input increases as depth decreases from the greenish-gray carbonates and shales of the Drakes to the greenish-gray shales and carbonates in the Lower Georgian Bay and the red, hematitic shales and sandstones of the Upper Georgian Bay. A similar pattern emerges from the carbonate-rich Brassfield and the Lower Cabot Head to the increasingly shaley Middle Cabot Head, and finally to the increasingly sandy, hematitic Upper Cabot Head Formation. A more precise understanding of these environmental variations accompanies analyses of individual formations, as well as separate interpretation of Ordovician and Silurian samples.
A two-dimensional MDS plot of the distribution of Drakes samples shows an apparent distinction between upper LHST samples and lower EHST and TST samples (Fig. 21). The global R-value of 0.49 falls within the range of R-values for randomized data (-0.30 to 0.70), suggesting that apparent distinctions of
Drakes systems tracts on the MDS ordination are not statistically significant, although the greatest difference exists between the TST and the LHST (Table 5).
65
Stress: 0.06
Clastic input
TST EHST LHST
Figure 21. 2D MDS of Drakes samples.
66
A.
Groups R-value p-value
Drakes: TST, EHST 0.103 0.22 Drakes: TST, LHST 0.991 0.02 Drakes: EHST, LHST 1.0 0.07
Georgian Bay: EHST, LHST 1.0 0.07 Brassfield: EHST, LHST 0.3 0.11
Cabot Head: TST, EHST 0.297 0.01 Cabot Head: TST, LHST 0.742 0 Cabot Head: EHST, LHST 0.023 0.31 ORDOVICIAN: Georgian Bay, Drakes 0.921 0
SILURIAN: Brassfield, Cabot Head 0.393 0
B.
Groups Range of R-values for Global R-value randomized data DRAKES -0.3 to 0.7 0.49
GEORGIAN BAY -0.5 to 1.0 1.0
BRASSFIELD -0.4 to 0.6 0.33 CABOT HEAD -0.14 to 0.3 0.23
ORDOVICIAN -0.25 to 0.60 0.92 SILURIAN -0.25 to 0.35 0.39
Table 5. ANOSIM results for comparisons of similarity between systems tracts of each formation and between regions of each period. A) Results for each pair-wise comparison. B) Range of R-values corresponding to randomized data and global R-value for all comparisons.
67 Similarly, the separation between LHST and EHST samples of the
Georgian Bay Formation on MDS plots is not statistically significant (Fig. 22;
Table 5). Both MDS plots and ANOSIM results suggest no significant distinction among samples from the Brassfield Formation (Fig. 23; Table 5).
The above three examples of apparent separations between groups of samples on the MDS ordination in contrast with ANOSIM results that do not suggest statistical significance for any such distinction may be explained in terms of sampling. That is, separation of samples on MDS ordinations reflect distinctions in faunal abundance ratios, while analysis of similarity is computed based on comparisons of the real data with a randomized data set. Therefore,
ANOSIM results suggesting statistical distinctions between groups may not be calculated simply because one group includes too few samples, whereas further sampling of such an interval may alter ANOSIM results.
In each case of inconsistent MDS and ANOSIM results, at least one group in the ANOSIM pair-wise comparison was sampled at low resolution. For example, there are more TST samples from the Drakes Formation than there are from the EHST and the LHST combined, after rare taxa and sparse samples are removed from the data set. Because fauna from the EHST to the LHST are likely transitional, as noted previously, perhaps such low sampling intensity does not recognize a distinction between these portions of the systems tract.
Unfortunately, these packages are too thin at West Union, Ohio to allow for significantly greater stratigraphic resolution in sampling.
68 Stress: 0.01
Clastic input
EHST LHST
Figure 22. 2D MDS showing distribution of Georgian Bay samples relative to sequence stratigraphic architecture.
69 Stress: 0.05
EHST LHST
Figure 23. 2D MDS plot showing distribution of Brassfield samples in terms of sequence stratigraphic architecture
70 Similarly, there are only a total of six Georgian Bay samples used in analysis, four from the EHST and two from the LHST. Given the significant separation of these samples on the MDS plot, degree of vertical displacement on the outcrop, and great disparity between lithology of the EHST and LHST, it is likely that faunal abundance ratios from these portions of the systems tract are appreciably different. Again, further sampling is required to definitively support this claim, and in the case of the Georgian Bay formation, sampling at a higher resolution is indeed plausible.
Finally, analysis of fauna from the Brassfield Formation includes only eight samples, three from the EHST and five from the LHST. This sequence architecture was delineated largely by the greater proportion of shale to carbonates of EHST beds relative to LHST beds. As in the case of the Georgian
Bay, the significance of distinctions in faunal distribution within the stratigraphic framework of the Brassfield, cannot adequately be gauged based on so few samples.
The Cabot Head is the only formation in the study that shows an appreciable intraformational distinction among samples with both MDS and
ANOSIM p-values. Given the separation of lower, middle, and upper Cabot
Head samples on the MDS plot of all samples, it would be expected that this relationship would be recognized when the Cabot Head is tested individually (Fig
24; Table 5). The range of R-values for the randomized data is -0.14 to 0.3, and the global R-value clearly falls within that range at 0.23. However, a careful look at the p-values shows that this overlap in global R with the distribution of random
R-values results solely from similarities between the EHST and LHST (p=0.31),
71
Stress: 0.18
Clastic input
TST EHST LHST
Figure 24. 2D MDS plot showing the distribution of Cabot Head samples with respect to sequence stratigraphic architecture.
72 which, as stated previously, are gradational with respect to lithology and included fauna. Given the relatively extensive sampling extent of this interval, the similarity between the EHST and LHST of the Cabot Head is probably not the result of sampling biases.
Original delineation of systems tracts was based on abrupt facies shifts that are likely causing the significant distinction in fauna between the TST and
EHST, and the TST and the LHST of the Cabot Head. That is, sedimentation greatly increases from the carbonates of the TST in the lower Cabot Head to the shale-dominated EHST in the middle Cabot Head to the sandstones of the LHST in the upper Cabot Head. In general, the TST of the Cabot Head is characterized by a variety of brachiopods, while the EHST contains a significantly lower diversity assemblage dominated by a single brachiopod, Coelospira. In contrast, the LHST is dominated by bivalves and also includes a low diversity assemblage of small brachiopods. This change in taxa is further explored below in analysis of trophic structure through space and time.
Understanding the paleoenvironmental factors responsible for the distribution of samples on Figures 19 would be greatly enhanced by interpretation of similar variables within each formation, e.g. sedimentation rate and local sea level. However, while the low sampling intensity of some units hinders confident interpretations of this sort, description of faunal transitions within each formation is not central to the argument of broad changes in space and time between samples from Ohio and Ontario.
Despite attempts to minimize differences in the environments of deposition between Ordovician and Silurian samples, some variation in faunal distribution
73 through time may result from such distinctions, particularly between the Drakes and Brassfield Formations. Despite that fact, it is more likely that much of the temporal distinction among samples is not linked to environmental controls. As suggested by the paleogeographic map (Fig. 2), it is likely that sedimentation differed greatly between Ohio and Ontario for both the Upper Ordovician and the
Lower Silurian. Given that the Upper Ordovician and the Lower Silurian samples correspond to different tectophases (Ettensohn and Brett, 1998) of the Taconic orogeny, the rate of sedimentation into the basin likely had a dramatic effect on fauna. Proximity to the source of sedimentation is probably a key factor in distinguishing between samples from Ohio versus those from Ontario in each period, i.e. sedimentation rate was significantly greater in Ontario. Figure 25 shows the two-dimensional MDS plot of Ordovician samples from both Ohio and
Ontario. The primary axis corresponds to sedimentation as erosion of the
Taconic highlands resulted in a progradation of sediment into the basin.
Localities in Ontario received more sediment than those in Ohio, reflecting the relative distances of these areas to the sediment source (see Fig. 2).
Lithologically, this is represented as a change from limestones in the TST of the
Drakes Formation and mixed carbonates and (dominantly) green-gray siliciclastics in the EHST of the Drakes, to the green-gray, and particularly, the red, hematitic sandstones of the Georgian Bay, especially in the LHST (refer back to Fig. 3 and Fig. 6). This change in environment is reflected in the corresponding change in trophic groups represented by fauna in both regions
(see below). In addition, proximity to the source is also reflected in the relative size of sedimentary packages. The entire measured Drakes interval is a mere 6
74
Stress: 0.09
Clastic input
OHIO ONTARIO
Figure 25. 2D MDS plot showing separation of samples from Ohio (Drakes) versus Ontario (Georgian Bay). Primary axis describes proximity to clastic source.
75 m from the lowermost measured TST samples to the Cherokee unconformity, whereas the Georgian Bay ranges from about 120 m to over 175 m in thickness.
The MDS plot for the Silurian samples is similar to that of Ordovician samples in terms of environmental gradients and corresponding trophic structure
(Fig. 26). Although Silurian samples from Ohio versus Ontario do not overlap in the MDS plot, they do not exhibit quite as distinct a separation as that recognized through time on the MDS plot for Ordovician samples. This observation may, again, confirm the idea that the Silurian in this region includes a more geographically widespread biota, if differential sampling for the Ordovician versus the Silurian is not a factor. As in the case of the Ordovician samples, sedimentation in Ohio and Ontario in the Llandovery reflects relative proximity to the source of sediment from the Taconic highlands. Thus, the Cabot Head is generally more clastic-rich than the Brassfield, which is dominated by dolomitic carbonates, although both formations represent mixed carbonate-siliciclastic deposits. In addition, sedimentation increases from the lower TST to the upper
LHST of the Cabot Head, corresponding to progradation of sediments derived from the erosion of the Taconic uplands, and is recognized as a change from gray shales and limestones to red shales and sandstones. Faunal variations manifested in abundance ratios of trophic groups correspond to these spatial lithologic variations (see below).
76 Stress: 0.18
Clastic input
OHIO ONTARIO
Figure 26. 2D MDS plot showing distribution of samples from the Silurian of Ohio (Brassfield) versus those from Ontario (Cabot Head). Primary axis describes proximity to source of clastic input.
77 Variations in ecologic structure through space and time
Recall the suggestion that the Late Ordovician extinction did not result in marked global ecologic restructuring (Droser et al., 2000). Figure 27 is an MDS plot of the distribution of samples represented by the percent abundance of individuals utilizing each trophic habit (refer to Table 1). Despite the abundance of Silurian samples from Ontario, this plot shows no clear distinction among samples through time. However, when samples from Ohio are considered alone, there does appear to be a temporal distinction among samples.
The statistical significance of apparent similarities and differences in strophic structure can be evaluated between the four sampled formations based on all represented trophic groups using ANOSIM (Table 6). The global R-value of 0.15 lies within the distribution of R-values for randomized data (-0.14 to 0.20), suggesting that there is no statistically significant distinction among samples through space or time with respect to trophic structure, when all data are considered. Attention to p-values corresponding to pair-wise comparisons of the four sampled formations reveals that the position of the global R-value within the distribution of R-values for randomized data is largely influenced by similarities in trophic structure between 4 of the 15 pair of groups in the comparison.
Specifically, there is no statistically significant distinction in trophic structure computed between the Georgian Bay and the TST of the Cabot Head, the
Drakes and the EHST of the Cabot Head, the TST and the EHST of the Cabot
Head, and the Brassfield and the EHST of the Cabot Head. Based on these data, Droser et al.’s (2000) claim that the Late Ordovician extinction did not result in marked ecologic change in confirmed at the local scale of this study.
78
Stress: 0.16
Ordovician Ohio Silurian Ohio
Ordovician Canada Silurian Canada
Figure 27. 2D MDS plot showing distribution of samples based on trophic group.
79
Groups R-values P-values
Georgian Bay, Drakes 0.333 0.02 Georgian Bay, Cabot Head TST 0.587 0.01 Georgian Bay, Cabot Head EHST -0.092 0.74 Georgian Bay, Cabot Head LHST 0.345 0.07
Georgian Bay, Brassfield 0.282 0.07
Drakes, Cabot Head TST 0.634 0.03 Drakes, Cabot Head EHST -0.054 0.78
Drakes, Cabot Head LHST 0.551 0 Drakes, Brassfield 0.345 0
Cabot Head TST, Cabot Head EHST 0.242 0.08 Cabot Head TST, Cabot Head LHST 0.701 0 Cabot Head TST, Brassfield 0.686 0.02 Cabot Head EHST, Cabot Head LHST 0.113 0.049
Cabot Head EHST, Brassfield -0.032 0.56
Cabot Head LHST, Brassfield 0.565 0
Table 6. R-values and p-values for pair-wise comparisons between each formation, with the Cabot Head divided into its respective systems tracts, based on trophic structure. Range of R-values for randomized data = -0.14 to 0.2; Global R = 0.15.
80 Figure 28 show the average percent abundance of key trophic groups in the analysis per formation, with the Cabot Head divided into its respective systems tracts. It confirms the general lack of change in trophic structure across the Ordovician-Silurian boundary. However, according to these histograms of the most abundant trophic groups, distinctions can be seen among the systems tracts of the Cabot Head Formation. In particular, free-lying low level epifaunal filter feeders become less significant from the TST to the EHST until they disappear in the LHST, while epibyssate and endobyssate filter feeders and infaunal deposit feeders become increasingly common.
While it is difficult to directly compare the collective Brassfield with the collective Cabot Head based on these histograms, it is clear that, of the three
Cabot Head systems tracts, the Brassfield is most similar to the lower Cabot
Head (TST). Recall, this correlation for the Silurian units when abundance data were compared for these groups. The Ordovician units appear more similar in trophic structure than the Silurian formations, but the Drakes includes endobyssate filter feeders, which are absent in the Georgian Bay samples. (This group was noted among float material for the Georgian Bay). In summary, these histograms of key trophic groups corroborate the implications of the MDS ordination and ANOSIM results, and all three lines of evidence suggest local agreement with the recognized global pattern.
81 Georgian Lower Cabot Bay Head
Brassfield Middle Cabot Head AVERGAE PERCENT ABUNDANCE
Drakes Upper Cabot Head
TROPHIC GROUPS
Figure 28. Histograms of average percent abundance of individuals exhibiting key trophic habits. Roman numerals correspond to trophic groups listed on Table 1.
82 Variations in genus richness through time
Table 7 compares the number of genera to the number of specimens counted in each formation and for the collective Ordovician and Silurian samples in the study. It is clear from this comparison that there are more genera represented in the Silurian samples, but also, far more specimens. As a result of this discrepancy, a simple genus count is not a reliable way to compare genus richness in these samples.
The data were rarefied to fairly compare genus richness between samples given these differences in sample size. Rarefaction of the data indicates that at the broad scale, some samples from the Silurian of Ohio (the Brassfield
Formation) show elevated genus richnesses relative to the Drakes and Cabot
Head Formations (Fig. 39a). However, Figure 39b zooms into the lower left corner of that figure to show genus richness at small sample sizes for all samples. At this scale, there is no obvious distribution in richness through space or time, as Ordovician and Silurian samples are not clearly separated on this plot.
Thus, the data do not support a significant change in genus richness across the
Ordovician-Silurian boundary. In addition, rarefied data for the Silurian samples imply, once again, that the Rhuddanian fauna of Ontario represent a recovered biota.
83
ORD SIL GB DR CH BF
# GENERA 24 68 7 17 37 31
# SPECIMENS 910 3381 103 807 2270 1111
Table 7. Comparison of the number of genera versus the number of specimens for Ordovician samples, Silurian samples, and each sampled
25
20
15
10
5 # genera
0 0 20 40 60 80 100 120 140 160 180
# specimens
Figure 29a. Distribution of rarefied data at broad scale. White = Brassfield, purple = Cabot Head, Red = Drakes.
7
6
5
4
3
2
# genera
1
0 0123456789
# specimens
Figure 29b. Distribution of rarefied data, accounting for differences in sample size.
84 25
20
15 g enera 10 g #
5
0 0 20 40 60 80 100 120 140 160 180 # specimens Figure 29c. Distribution of rarefied data with error bars at broad scale.
10
9
8
7
6
5 enera 4 g # 3
2
1
0 0 2 4 6 8 10 12 14 16 18 20 # specimens Figure 29d. Distribution of rarefied data with error bars at
85 CONCLUSIONS
The majority of published literature on the Late Ordovician mass extinction considers the global nature of this event, while few alpha-level studies have been conducted across the Ordovician-Silurian boundary relative to other mass extinctions. In addition, it has been difficult to test the concept of ecologic change within this interval because there are few environmentally comparable sections on either side on the boundary in which to make a fair quantitative assessment. The purpose of this study was to compare faunal distribution on either side of the Late Ordovician mass extinction in comparable environments within the context of third-order sequence stratigraphic architecture. Specifically,
I investigated community-level trends in Ohio and Ontario from the pre-extinction
Ordovician to the post-recovery Silurian, with respect to faunal composition, ecologic structure, and genus richness. The analysis presented herein supports the following conclusions:
1. The four formations sampled in this study, the Drakes
(Richmondian), Brassfield (Rhuddanian-Aeronian), Georgian Bay
(Maysvillian-Richmondian), and Cabot Head (Rhuddanian),
represent comparable depositional environments on either side
of the Late Ordovician extinction in terms of both facies and
sequence stratigraphic architecture. In general, the Brassfield is
more carbonate-rich than are the other three formations, but it is
lithologically and faunally similar to the TST of the Cabot Head
Formation. Spatial distinctions within the Ordovician and Silurian
86 both reflect distance from the sediment source of the Taconic
highlands, the effects of which are seen in lithology as well as
trophic organization.
2. Biotic compositions among samples are distinct primarily through
time and secondarily through space, depending on the sampling
scale (formation, locality, or bed). Comparisons of shared
genera between each locality suggest a relatively widespread
fauna in the Silurian, compared to the more endemic faunas of
the Ordovician.
3. Faunal abundance is statistically distinct through both space and
time, with the Ordovician-Silurian boundary serving as the
primary factor in the separation of samples on MDS ordinations.
Distinction among samples in terms of sequence stratigraphic
architecture supports the fact that the Rhuddanian faunas were
fully recovered in this region.
4. In terms of trophic structure, there was no significant ecologic
restructuring in Ohio and Ontario across the Ordovician-SiIurian
boundary.
5. Rarefaction analysis does not suggest an obvious change in
richness in the lower Silurian, although some Silurian samples
may indicate elevated genus richness. This also suggests that
Rhuddanian samples represent a recovered fauna.
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92 APPENDIX I
This appendix includes raw abundance data of genera within samples of the four sampled formations. Transformations were performed on this matrix to obtain the data treatments described in the methods section of this text.
Samples are listed along the left column of each page such that: OGB =
Ordovician Georgian Bay Formation, Oakville, Ontario; OWU = Ordovician
Drakes Formation, West Union, Ohio; SWU = Silurian Brassfield Formation, West
Union, Ohio; SCC = Silurian Cabot Head Formation, Chedoke Creek, Hamilton,
Ontario; SMB = Silurian Cabot Head Formation, Mountain Brow Drive, Hamilton,
Ontario; SJC = Silurian Cabot Head Formation, Jolly Cut, Hamilton, Ontario.
Numbers following letter codes describe the position of the sample within respect to the base of the section in cm, such that positive numbers imply samples above the base, and negative numbers imply sampling below the base.
The SCC section includes negative sample numbers corresponding to samples taken below the base of the Cabot Head in the Manitoulin Formation, such that the base of the section, sample SCC0, is the uppermost bed of the
Manitoulin, the maximum sediment starvation surface in the TST. Samples SCC-
23 to SCC30 occur in the TST, and all remaining samples occur in the EHST.
SJC samples are all negative, such that the uppermost sample, SJC-31, occurs 31cm below the base of the Thorold Sandstone. Samples SJC-445 to
SJC-411 occur in the EHST, and all other samples occur in the LHST.
In order upsection, SMB samples occur as follows: EHST - SMBm13, 39,
83, 124, SMB377, 336b, 336t, 254,-90, 9, SMBu76; LHST – SMBu101, 145, 181,
221, SMBuu124, 112, 107, 96, 75, 0.
93 All Drakes and Brassfield samples are positive, occurring above the base of the sections. Georgian Bay EHST samples are noted with positive numbers, while LHST samples are noted with letters such that sample A occurs stratigraphically above sample B, etc. The exact positions of these samples relative to stratigraphic horizons are unknown.
Genera or morphologic groups are listed in the top row of each page. O
“orthid” = Ordovician Dalmanella, Glyptorthis, and Plaesiomys. S “orthid” = unidentifiable orthids. “ram” = ramose bryozoan, with modification specifying thickness (thin, moderate, or thick). “ptct” implies a point-count, whereas all other genera/morphologic groups are slab-counted. “p” implies the presence of a microscopic or colonial taxon on a slab count.
94
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C W W W W W W G G G G G G G W W W W W W W W W W W W C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 7 5 3 1 0 - - 1 9 2 1 1 9 7 C B 7 2 1 1 1 9 7 7 5 5 4 4 4 3 2 2 1 1 1 1 7 8 3 0 8 2 2 2 0 0 5 2 2 9 8 3 6
3 5 5 3 2 4 0 7 9 9 9 7 5 9 0 8 7 0 5 3 8 0 1 7 9 8 8 4 6
0 0 5 0 4 5 5 1 7 6 3 1 1 9 0
a
b
0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0
Ambonychia 0 0 0 0 0 0 0 p p 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 p 0 0 0 0 0
Aspidopora 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Amphistrophia 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0
0
Atrypa 0 0 0 0 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Batostomella 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bellerophont 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0
.
.
7 2 5 5
ptct-bifoliate 8 1 2 1 4 1 0 0 2 1 0 0 0 0 2 5 6 1 0 8 1 0 0 0 0 1 5 1 4 1 2 8 1 2 3 1 2 2 0 1 . 5 1 7 . 2
. 3 ...... 1 . 0 . .
3 3 5 5 2 5 5 2 4 7 5 5 5 . .
. .
.
5 8
6 5
5 5
5
95 ptct-brachiopod 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Buchania
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C W W W W W W W W W W W W W W W W W W G G G G G G G C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 1 9 7 5 3 1 0 - - 2 1 1 9 7 C B 7 2 5 5 4 4 4 3 2 2 1 1 1 1 1 1 1 9 7 7 7 8 3 0 8 5 2 2 2 2 0 0 2 9 8 3 6
3
9 0 8 7 0 7 9 9 9 7 5 5 5 5 3 2 4 0 3 8 0 1 7 8 9 8 4 6
0 4 5 5 1 7 6 3 1 1 9 0 0 0 5
b a
0 1 0 0 0 4 0 0 0 0 7 2 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Calymene 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0
ptct-Clathropora 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0 0 0 0 0 0 p 3 2 0 0 1 p 3 0 0 0 0 3 0 0 0 0 0 0
Caritodens 0 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0 0 0 0 0
Ceromoporid bryozoans 0 0 0 0 0 0 0 0 0 0 3 1 2 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0
2 8 4
Coelospira 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Cornellites 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ctenodonta 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
96 Cyrtodonta 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 2 0 0 0 0 0
ptct-crinoid
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C W W W W W W W W W W W W W W W W W W G G G G G G G C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 1 9 7 5 3 1 0 - - 2 1 1 9 7 C B 7 2 5 5 4 4 4 3 2 2 1 1 1 1 1 1 1 9 7 7 7 8 3 0 8 5 2 2 2 2 0 0 2 9 8 3 6
3
9 0 8 7 0 7 9 9 9 7 5 5 5 5 3 2 4 0 3 8 0 1 7 8 9 8 4 6
0 4 5 5 1 7 6 3 1 1 9 0 0 0 5
b a
0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Coolinia 0 2 0 0 0 6 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Dalmanella 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Enterolasma 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Eoplectodonta 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Eospirifer 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Favosites 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
fenestrates 0 0 0 0 0 1 0 0 0 0 1 1 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0
97 fistuliporid 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Flexicalymene
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C W W W W G G G G G G G W W W W W W W W W W W W W W C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 1 9 7 5 3 1 0 - - 2 1 1 9 7 C B 7 2 1 9 7 7 5 5 4 4 4 3 2 1 1 1 1 1 2 1 7 8 3 0 8 5 2 2 2 2 0 0 2 9 8 3 6
3 3 2 4 0 7 9 9 7 5 5 5 9 0 8 7 0 9 5 3 8 0 1 7 8 9 8 4 6
5 0 4 5 5 1 7 3 1 1 9 0 0 6 0
b a
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ptct-gastropod 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Grewinkia 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Hallopora 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ptct-Hallopora 1 0 0 0 0 0 0 0 0 1 3 2 0 1 4 0 0 0 0 0 0 0 0 0 0 0 0 3 5 1 0 1 0 0 0 0 2 1 0 0 6
8 2 0
0
4 4
4
Hebertella 6 2 2 1 0 1 1 5 1 1 6 2 8 2 0 2 9 9 0 1 9 2 9 1 2 4 2 0 1 2 2 3 1 1 3 1 1 1 1 3 . 0 8 0
4 . 3
2 1 . . . 1 . . 9 9 7 3 2 3 5
7
3 5 5 5 5 7 3 7 . .
......
5 5
5 5 5 5 5 5 5 7
5 Helopora 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Homeospira 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
98 Hormotoma 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Hyolith
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C W W W W W W W W W W W W W W W G G G G G G G W W W C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 9 7 5 3 1 0 - - 1 2 1 1 9 7 C B 7 2 5 5 4 4 4 3 2 1 1 1 1 1 9 7 7 2 1 1 7 8 3 0 8 2 2 2 2 0 0 5 2 9 8 3 6
3 7 9 9 7 5 5 3 2 4 0 9 0 8 7 0 9 5 5 3 8 0 1 7 9 8 8 4 6
0 4 5 5 1 7 3 1 1 9 0 5 6 0 0
b a
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 1 0 0 0 2 0 0 0 0 0 0 0 0 0 0
.
.
.
5 5 2
5
ptct-Isotelus 0 0 1 0 0 0 0 0 0 0 2 1 1 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Leptaena 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Leiopteria 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Lingula 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
ptct-Loxoplocus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0
Loxoplocus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 1 0 0 0
Modiolopsis 5 0 0 1 0 0 0 1 0 2 1 0 0 0 0 1 0 7 1 0 0 8 3 3 9 0 4 0 1 9 3 5 0 1 1 2 3 0 0 0
.
9 . . .
. . . . .
. .
. . 5 . 2
5 7 5 5 5 6 2 5 5 5 5 5 2 5
. .
5
5 3
1
5
99 ptct-modram 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ptct-Murchisonid snails
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C W W W W W W W W W W W W W W W W W W G G G G G G G C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 1 9 7 5 3 1 0 - - 2 1 1 9 7 C B 7 2 5 5 4 4 4 3 2 2 1 1 1 1 1 1 1 9 7 7 7 8 3 0 8 5 2 2 2 2 0 0 2 9 8 3 6
3
9 0 8 7 0 7 9 9 9 7 5 5 5 5 3 2 4 0 3 8 0 1 7 8 9 8 4 6
0 4 5 5 1 7 6 3 1 1 9 0 0 0 5
b a
0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Neozaphrentis 0 0 0 0 0 0 0 0 5 1 0 0 0 0 0 0 0 0 0 0 3 2 1 1 8 1 9 1 2 0 0 4 2 4 0 0 0 0 0 0
0
0 5 6
5 0 0
O "orthid" 0 0 2 0 0 0 7 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
S "orthid" 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 p p 0 0 0 0 0 0 0 p 0 0 0
ptct-ostracods 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ptct-Pachydictya 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 1 0 0 0 0
. .
5
5 6 .
5
ptct pelecypod 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Phaenopora 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
100 Platyceras 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0
Platystrophia
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C W W W W W W W W W W W W W W W W W W G G G G G G G C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 1 9 7 5 3 1 0 - - 2 1 1 9 7 C B 7 2 5 5 4 4 4 3 2 2 1 1 1 1 1 1 1 9 7 7 7 8 3 0 8 5 2 2 2 2 0 0 2 9 8 3 6
3
9 0 8 7 0 7 9 9 9 7 5 5 5 5 3 2 4 0 3 8 0 1 7 8 9 8 4 6
0 4 5 5 1 7 6 3 1 1 9 0 0 0 5
b a
0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Plectatrypa 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Pleurotumerid 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Psuedohornera 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ptilodictya 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 2 0 0 9 1 0 2 0 0 0 0 0 0
3
Rafinesquina 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3
Dalejina 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Rhynchonella 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
101 Rhynchotrema 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Rhynchotreta
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O O O C C C C C C C C C C C C C C C G G G G G G G W W W W W W W W W W W W W W W W W W C C C C C C C C C C C C C C C B B B B B B B U U U U U U U U U U U U U U U U U U 4 2 2 2 1 1 9 7 5 3 1 0 - - 1 2 1 1 9 7 C B 7 2 5 5 4 4 4 2 2 1 1 1 1 1 9 7 3 1 1 7 7 8 3 0 8 2 2 2 2 0 0 5 2 9 8 3 6
3 9 9 9 7 5 5 5 2 4 9 0 8 7 0 7 5 3 0 3 8 0 1 7 9 8 8 4 6
0 4 5 5 1 6 3 1 1 9 0 0 7 0 5
b a
0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
.
1
ptct rugose 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0
Semicoscinium 0 0 1 0 0 0 0 0 0 0 0 0 2 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0
1
Stegerhynchus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Strophodonta 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 2 1 2 0 0 0 1 0 0
Strophomena 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 2 0 0 0 0 0 0 0 0 0
Strophonella 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 3 0 9 0 0 1 0 0 7 0 2 8 1 1 1 2 1 2 0 0
3
. . 7
. 8 . . 3
. 5 5 7 5 2 5
5
ptct-thickram 0 1 7 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 8 1 4 1 0 5 0 0 0 0 0
. . .
.
5
. . .
.
5 5 7 5 5 8 5 2 .
5
5
5
102 ptct-trilobite 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 2 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
8
Cryptothyrella
S S S S S S S S S S S S S S S O O O O O O O O O O O O O O O O O O O O O O O OGB OGB C C C C C C C C C C C C C C C G G W W W G G G W W W W W W W W W W W W W W W C C C C C C C C C C C C C C C B B B B B U U U U U U U U U U U U U U U U U U 0 2 2 1 1 1 9 7 5 3 1 - - 4 2 9 7 2 1 1 C B 7 2 9 7 7 5 5 4 4 4 3 2 2 1 1 1 1 1 1 1
7 8 3 0 8 5 2 2 2 2 0 0 3 6 2 9 8
3 2 4 0 9 0 8 7 0 7 9 9 9 7 5 5 5 5 3
3 8 0 1 7 8 9
8 4 6
0 4 5 5 1 7 6 3 1 1 9 0 0 0 5
b a
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 1 1 1 1 2 5 2 0
4 3
Zygospira 103
S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S M M M M M M M M M M M M M M M C C C C C C C C C M M C W W J J J J J J J J J J J C C C C C C C C C C C C C C C C C C C C C B B B B B B B B B B B B B B B B B U U ------1 1 9 8 8 5 5 5 4 1 u u u u u u ------m m m m u 3 5 5 6 2 2 3 4 4 4 4 3 3 9 9 2 3 3 3 1 8 1 0 7 6 0 9 3 0 u u u u u 1 2 1 1 4 1 0 8 7 1 3 4 6 7 3
1 8 1 3 0 5 3 3 7 3 1 1 6 8 6 9 0 1 4 1 1 0 - - 8 . 5 3 6 1 4 1 4 1 7 . 3 3 9 2 7 9 4 6 6 7 4 2 9 2 2 0 1
1 5 6 t b
4 4 7
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ambonychia 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Aspidopora 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Amphistrophia 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Atrypa 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Batostomella 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bellerophont 0 0 0 0 4 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 0 1 0 0 0 0 0 0 4 8 0 0 6 0 2 4 . .
.
9
0
. 5 5 5 5 . .
5
5
ptct-bifoliate 0 2 1 0 0 0 0 0 0 1 2 0 0 1 0 2 0 0 6 2 5 1 4 4 0 0 0 0 1 0 2 0 1 0 0 1 4 1 0 0
. 2
. 7
. . . . .
. .
. . . . 5 5 3 5 5 5 5 5 5 7 5 5 2 .
5
5
5
104 ptct-brachiopod 0 0 0 3 0 0 0 0 0 0 2 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0
Buchania
S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S M M M M M M M M M M M M M M M M M C C C C C C C C C C W W J J J J J J J J J J J C C C C C C C C C C C C C C C C C C C C C B B B B B B B B B B B B B B B B B U U ------1 1 1 9 8 8 5 5 5 4 u u u u u u u ------m m m m 3 5 5 6 2 2 3 4 4 4 4 3 3 9 9 2 3 3 3 1 8 1 0 0 7 6 0 9 3 u u u u u 1 2 1 1 4 1 0 8 7 1 3 4 6 7 3
1 8 3 1 0 5 3 3 7 3 4 1 1 6 8 6 9 0 1 1 1 0 - - 8 . 5 3 6 1 4 1 4 1 7 2 . 3 9 3 7 9 4 6 6 7 4 9 2 2 2 0 1
1
5 6 t b
4 4 7
0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Calymene 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ptct-Clathropora 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Caritodens 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ceromoporid bryozoans 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Coelospira 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 3 0 0 0 0 1 p 0 0 0 0 0
Cornellites 5 2 0 2 0 2 0 0 2 7 8 0 0 0 0 0 0 0 0 1 0 0 0 0 4 2 3 5 0 0 0 2 1 0 2 3 0 1 2 4 7 2 5
9 0 7
3 5
Ctenodonta 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0
105 Cyrtodonta 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
.
5
ptct-crinoid
SWU371 SWU337 SJC-31 SJC-51 SJC-54 SJC-61 SJC-206 SJC-281 SJC-374 SJC-411 SJC-434 SJC-445 SJC-463 SMBuu124 SMBuu107 SMBuu0 SMBuu-75 SMBuu-96 SMBu181 SMBu2.21 SMB-9 SMB-90 SMB-254 SMB-336t SMB-336b SMB-377 SMBm1.24 SMBm83 SMBm39 SMBm13 SCC1134 SCC1049 S S S S S S S S C C C C C C C C C C C C C C C C 1 9 8 8 5 5 5 4 1 8 0 7 6 0 9 3
1 1 6 8 6 9 0 1 2
0 0 0 0 0 0 0 0 0 1? 0 0 6 0 9 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 1 0 0 0 0 0 0 0 p 0 0 0 0
Coolinia 2 0 0 0 0 1 0 2 0
Dalmanella 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Enterolasma 0 0 0 0 0 0 0
Eoplectodonta 0 0 0 0 4 1 0
Eospirifer 0 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 p 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 p 0 0 0 0 0 0 0 0 0 0 0
Favosites 0 0 0 0 0 0 0
fenestrates 0 0 0 2 1 0 0
106 fistuliporid 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Flexicalymene ra od a om t o m r o ptct-gastrop Grewinkia Hallopora ptct-Hallopo Hebertella Helopora Homeospira H Hyolith SCC481 0 0 0 0 0 6 0 0 0 SCC510 0 0 0 0 0 25.5 0 0 0 SCC539 0 0 0 4.5 0 25.5 0 0 0 SCC596 0 0 0 0 0 34 0 0 0 SCC808 0 0 0 0 0 62 0 0 0 SCC866 0 0 0 0 0 42 0 0 0 SCC971 0 0 0 0 0 22.5 0 0 0 SCC1012 0 0 0 0 0 0.5 0 0 0 SCC1049 0 0 0 0 0 7.24 0 0 0 SCC1134 0 0 0 0 0 37 0 0 0 SMBm13 0 0 p 0 0 33 0 0 0 SMBm39 0.5 0 0 0 0 28 0 0 0 SMBm83 0 0 0 0 0 14.5 0 0 0 SMBm1.24 0 0 0 0 0 2.5 0 0 0 SMB-377 0 0 p 0 0 43 0 0 0 SMB-336b 0 0 0 0 0 48 0 0 0 SMB-336t 0 0 0 0 0 8.5 0 0 0 SMB-254 0 0 0 0 0 1.5 0 0 0 SMB-90 0 0 0 0 0 4.5 0 0 0 SMB-9 0 0 0 0 0 23 0 0 0 SMBu2.21 0 0 0 0 0 34.8 0 0 0 SMBu181 0 0 0 0 0 52.5 0 0 0 SMBuu-96 0 0 0 0 0 11 0 0 0 SMBuu-75 0 0 0 0 0 0 0 0 0 SMBuu0 0 0 0 0 0 24 0 0 0 SMBuu107 0 0 0 0 0 11.5 0 0 0 SMBuu124 0 0 0 0 0 53 0 0 0 SJC-463 0 0 0 0 0 11.5 0 0 0 SJC-445 0 0 0 0 0 5.5 0 0 0 SJC-434 0 0 0 0 0 3.5 0 0 0 SJC-411 0 0 0 0 0 29 0 0 0 SJC-374 0 0 0 0 0 4 0 0 0 SJC-281 0 0 0 0 0 7 0 0 0 SJC-206 0 0 0 0 0 6 0 0 0 SJC-61 0 0 0 0 0 p 0 0 0 SJC-54 0 0 0 0 0 7.5 0 0 0 SJC-51 0 0 0 0 0 0 0 0 0 SJC-31 0 0 0 0 0 2.5 0 0 0 SWU337 0 0 0 0 0 0 0 0 0 SWU371 0 0 p 0 0 0 0 0 0
107 us c
s s ptct-Isotelu Leptaena Leiopteria Lingula ptct-Loxoplo Loxoplocu Modiolopsis ptct-modram ptct-Murchisonid snails SCC481 0 0 0 0 0 0 0 0 0 SCC510 0 0 0 0 0 0 0 0 0 SCC539 0 0 0 0 0 0 1 0 0 SCC596 0 21 0 0 0 0 0 0.25 0 SCC808 0 0 0 0 0 0 0 0 0 SCC866 0 0 0 0 0 0 27 0 0 SCC971 0 0 0 0 0 0 0 0 0 SCC1012 0 0 0 0 0 0 0 0 0 SCC1049 0 0 0 0 0 0 0 0 0 SCC1134 0 0 0 0 0 0 2 0 0 SMBm13 0 0 0 0 0 0 3 0 0 SMBm39 0 0 0 0 0 0 0 0 0 SMBm83 0 0 0 0 0 0 0 0 0 SMBm1.24 0 1 0 0 0 0 1 0 0 SMB-377 0 0 0 0 0 0 1 0 0 SMB-336b 0 0 0 0 0 0 0 0 0 SMB-336t 0 0 0 0 0 0 1 0 0 SMB-254 0 0 1 0 0 0 0 0 0 SMB-90 0 0 1 0 0 0 1 0 0 SMB-9 0 0 3 0 0 0 0 0 0 SMBu2.21 0 0 10 0 0 0 35 0 0 SMBu181 0 0 2 0 0 0 7 0 0 SMBuu-96 0 0 1 0 0 0 2 0 0 SMBuu-75 0 0 0 0 0 0 2 0 0 SMBuu0 0 0 1 0 0 0 0 0 0 SMBuu107 0 0 1 0 0 0 11 0 0 SMBuu124 0 0 0 0 0 0 1 0 0 SJC-463 0 0 0 0 0 0 0 0 0 SJC-445 0 0 0 0 0 0 1 0 0 SJC-434 0 0 0 0 0 0 0 0 0 SJC-411 0 0 0 0 0 0 0 0 0 SJC-374 0 0 0 0 0 0 0 0 0 SJC-281 0 0 0 0 0 0 8 0 0 SJC-206 0 0 0 0 0 0 25 0 0 SJC-61 0 0 0 0 0 0 2 0 0 SJC-54 0 0 0 0 0 0 0 0 0 SJC-51 0 1 1 0 0 0 1 0 0 SJC-31 0 0 0 0 0 0 0 0 0 SWU337 0 0 0 0 0 0 0 0 0 SWU371 0 0 0 0 0 0 0 0 0
108 od ds Neozaphrentis O "orthid" S "orthid" ptct-ostraco ptct-Pachydictya ptct pelecyp Phaenopora Platyceras Platystrophia SCC481 0 0 0 0 0 0 0 0 0 SCC510 0 0 2 0 0 0 0 0 0 SCC539 0 0 0 0 0 0 1 0 0 SCC596 2 0 1 0 0 0 0 0 0 SCC808 0 0 0 0 0 0 0 0 0 SCC866 0 0 0 0 0 21.3 0 0 0 SCC971 0 0 0 0 0 0 0 0 0 SCC1012 0 0 0 0 0 0 0 0 0 SCC1049 0 0 0 0 0 0 1 0 0 SCC1134 0 0 0 0 0 0.5 0 0 0 SMBm13 0 0 0 0 18 8.5 p 0 0 SMBm39 0 0 0 0 2.5 0 p 0 0 SMBm83 0 0 0 0 0 0 0 0 0 SMBm1.24 0 0 0 0 0 4.5 0 0 0 SMB-377 0 0 0 0 0 4.5 p 0 0 SMB-336b 0 0 0 0 0 0 0 0 0 SMB-336t 0 0 0 0 0 6.5 0 0 0 SMB-254 0 0 0 0 0 0 0 0 0 SMB-90 0 0 0 0 0 2.5 p 0 0 SMB-9 0 0 0 0 0 7.5 p 0 0 SMBu2.21 0 0 0 0 0 11 p 0 0 SMBu181 0 0 0 0 0 4.5 0 0 0 SMBuu-96 0 0 0 0 0 4 p 0 0 SMBuu-75 0 0 0 0 0 5.5 0 0 0 SMBuu0 0 0 0 0 0 0 p 0 0 SMBuu107 0 0 0 0 0 12 0 0 0 SMBuu124 0 0 0 0 0 5 p 0 0 SJC-463 0 0 0 0 0 0 0 0 0 SJC-445 0 0 0 p 0 1.5 0 0 0 SJC-434 0 0 0 0 0 0 p 0 0 SJC-411 0 0 0 0 0 0 0 0 0 SJC-374 0 0 0 0 0 0 0 0 0 SJC-281 0 0 0 0 0 5.5 0 0 0 SJC-206 0 0 0 0 0 16 0 0 0 SJC-61 0 0 0 0 0 3 p 0 0 SJC-54 0 0 0 p 0 4 p 0 0 SJC-51 0 0 0 0 0 0 0 0 0 SJC-31 0 0 0 0 0 0 0 0 0 SWU337 0 0 0 0 0 0 0 0 0 SWU371 0 0 0 0 1 0 p 0 0
109
a
a a m Plectatrypa Pleurotumerid Psuedohornera Ptilodictya Rafinesquin Dalejina Rhynchonella Rhynchotre Rhynchotret SCC481 0 0 0 0 0 0 0 0 0 SCC510 0 0 0 0 0 3 0 0 0 SCC539 0 0 0 0 0 0 0 0 0 SCC596 0 0 0 0 0 0 0 0 0 SCC808 0 0 0 0 0 0 0 0 0 SCC866 0 0 0 0 0 0 0 0 0 SCC971 0 0 0 0 0 1 0 0 0 SCC1012 0 0 0 0 0 0 0 0 0 SCC1049 0 0 0 0 0 0 0 0 0 SCC1134 0 0 0 0 0 0 0 0 0 SMBm13 0 0 p 0 0 2 0 0 0 SMBm39 0 0 0 0 0 3 0 0 0 SMBm83 0 0 0 0 0 1 0 0 0 SMBm1.24 0 0 0 p 0 0 0 0 0 SMB-377 0 0 p 0 0 0 0 0 0 SMB-336b 0 0 0 0 0 0 0 0 0 SMB-336t 0 0 0 0 0 0 0 0 0 SMB-254 0 0 0 0 0 0 0 0 0 SMB-90 0 0 0 0 0 0 0 0 1 SMB-9 0 0 0 0 0 0 0 0 0 SMBu2.21 0 0 0 0 0 1 0 0 0 SMBu181 0 0 0 0 0 0 0 0 0 SMBuu-96 0 0 0 0 0 0 0 0 0 SMBuu-75 0 0 0 0 0 0 0 0 0 SMBuu0 0 0 0 0 0 0 0 0 0 SMBuu107 0 0 0 0 0 0 0 0 0 SMBuu124 0 0 0 0 0 0 0 0 0 SJC-463 0 0 0 0 0 0 0 0 0 SJC-445 0 0 0 0 0 0 0 0 0 SJC-434 0 0 0 0 0 0 0 0 1 SJC-411 0 0 0 0 0 0 0 0 1 SJC-374 0 0 0 0 0 0 0 0 0 SJC-281 0 0 0 0 0 0 0 0 0 SJC-206 0 0 0 0 0 0 0 0 0 SJC-61 0 0 0 0 0 0 0 0 0 SJC-54 0 0 0 0 0 0 0 0 4 SJC-51 0 0 0 0 0 0 0 0 1 SJC-31 0 0 0 0 0 0 0 0 0 SWU337 0 0 0 0 0 0 0 0 0 SWU371 0 0 0 0 0 1 0 0 0
110
a um
m coscini i ptct rugose Sem Stegerhynchus Strophodonta Strophomen Strophonella ptct-thickra ptct-trilobite Cryptothyrella SCC481 0 0 0 0 0 0 0 0 0 SCC510 0.1 0 0 0 0 1 1 0 8 SCC539 1.5 0 16 0 0 0 0 0 1 SCC596 0.5 0 6 0 0 1 0 0 0 SCC808 0 0 0 0 0 0 0 0 0 SCC866 0 0 1 0 0 0 0 0 0 SCC971 0 0 5 0 0 0 0 0 0 SCC1012 0 0 0 0 0 0 0 0 0 SCC1049 0 0 43 0 0 0 0 0 0 SCC1134 0 0 2 0 0 0 0 0 1 SMBm13 0 0 3 0 0 0 0 0 0 SMBm39 0 0 4 0 0 0 0 0 1 SMBm83 0 0 2 0 0 0 0 0 0 SMBm1.24 0 0 7 0 0 0 0 0 0 SMB-377 0 0 0 0 0 0 0 0 0 SMB-336b 0 0 3 0 0 0 0 0 0 SMB-336t 0 0 8 0 0 0 0 0 0 SMB-254 0 0 0 0 0 0 0 0 0 SMB-90 0 0 9 0 0 0 0 0 0 SMB-9 0 0 0 0 0 0 0 0 0 SMBu2.21 0 0 15 0 0 0 0 0 0 SMBu181 0 0 18 0 0 0 0 0 0 SMBuu-96 0 0 8 0 0 0 0 0 0 SMBuu-75 0 0 0 0 0 0 0 0 0 SMBuu0 0 0 0 0 0 0 0 0 0 SMBuu107 0 0 4 0 0 0 0 0 0 SMBuu124 0 0 1 0 0 0 0 0 0 SJC-463 0 0 0 0 0 0 0 0 0 SJC-445 0 0 0 0 0 0 0 0 0 SJC-434 0 0 4 0 0 0 0 0 0 SJC-411 0 0 0 0 0 0 0 0 0 SJC-374 0 0 0 0 0 0 0 0 0 SJC-281 0 0 0 0 0 0 0 0 0 SJC-206 0 0 0 0 0 0 0 0 0 SJC-61 0 0 0 0 0 0 0 0 0 SJC-54 0 0 57 0 0 0 0 0 0 SJC-51 0 0 95 0 0 0 0 0 0 SJC-31 0 0 9 0 0 0 0 0 0 SWU337 0 0 1 0 0 0 0 0 4 SWU371 0 0 0 0 0 0 0 0 0
111 Zygospira SCC481 0 SCC510 0 SCC539 0 SCC596 0 SCC808 0 SCC866 0 SCC971 0 SCC1012 0 SCC1049 0 SCC1134 0 SMBm13 0 SMBm39 0 SMBm83 0 SMBm1.24 0 SMB-377 0 SMB-336b 0 SMB-336t 0 SMB-254 0 SMB-90 0 SMB-9 0 SMBu2.21 0 SMBu181 0 SMBuu-96 0 SMBuu-75 0 SMBuu0 0 SMBuu107 0 SMBuu124 0 SJC-463 0 SJC-445 0 SJC-434 0 SJC-411 0 SJC-374 0 SJC-281 0 SJC-206 0 SJC-61 0 SJC-54 0 SJC-51 0 SJC-31 0 SWU337 0 SWU371 0
112
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 0 0 0 0 0 0 0
Ambonychia
Aspidopora 0 0 0 3 10 1 0 0 0 3 10 0
Amphistrophia
Atrypa
Batostomella 0 28.5 0 27 0 0 0 15.5 0 27.75 0 10 0 118.5 0 20.5
Bellerophont
ptct-bifoliate
113 ptct-brachiopod 0 0 0 1 0 0 0 0 0
Buchania
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 0 8 0 11 4 0 1 0 4 0 4 0
Calymene 0
ptct-Clathropora 0 p 0 0 0 0 0 p 0 p 0 0
Caritodens
Ceromoporid bryozoans
Coelospira 0 0 0 0 0 0 0 0 1 0
Cornellites
Ctenodonta
114 Cyrtodonta 6 0 28 2 12 0 6 5.5 0
ptct-crinoid
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 2 4 10 0 108 0 55 1 36 1 13 0 98 0 10
Coolinia
Dalmanella 7 0 1 0 0 2 0 0 0 0 4 0 3 0
Enterolasma
Eoplectodonta
Eospirifer 1 0 0 1 0 0 p 0 p 0 p 0 1 0 0
Favosites
fenestrates
115 fistuliporid 0 0 0 0 0 0 0 0 0
Flexicalymene
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 0 4.5 0 3.5 0 3 0 6 0
ptct-gastropod 0 0
Grewinkia 0 p 0 0 p 0 0 0 0 4.5 0 0
Hallopora
ptct-Hallopora 0
Hebertella 9.5 17.5 0 3 2 0 17 0 11 0 23
Helopora 0 5 0 0 0 4 0
Homeospira
116 Hormotoma 0 0 0 0 0 0 3 0 0
Hyolith
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 0 0 2 0 0 1 0 6 0 0 2
ptct-Isotelus
Leptaena 0 0 0 0 2 0 3 0 0 0 0 2
Leiopteria
Lingula
ptct-Loxoplocus 0 0 0 0 0 0 0 0 1.5 0
Loxoplocus
Modiolopsis
117 ptct-modram 0 3 6 0 0 0 4.5 3 0
ptct-Murchisonid snails
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 0 0 0 0 0 0 0
Neozaphrentis
O "orthid" 0 2 0 0 3 p0 11 1 01.5 0 3 p0 0
S "orthid" p 0
ptct-ostracods
ptct-Pachydictya 0 p1 0 0 0 0 0 0 0 0
ptct pelecypod
Phaenopora
118 Platyceras 1 0 0 1 0 0 0 0 10
Platystrophia
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 0 0 p 0 p 0 0 0 p 0
Plectatrypa
Pleurotumerid 0 0 0 0 0 0 0 0 0
Psuedohornera
Ptilodictya
Rafinesquina 13 5 0 0 1 0 1 0 18 13 12 1 0
Dalejina 0 0 0 0
Rhynchonella
119 Rhynchotrema 1 0 1 3 5 0 0 1 3
Rhynchotreta
SWU630 SWU557 SWU522 SWU502B SWU502A SWU502 SWU475 SWU471 SWU385
0 0 0.5 0 0 0 0 0 0
ptct rugose 0
Semicoscinium 0 1 0 0 1 0 13 6 0 1 0 0 22
Stegerhynchus 1 0 c.f.7
Strophodonta 0
Strophomena 0 0.5 0 0 0 0 0 0 0 0
Strophonella
ptct-thickram
120 ptct-trilobite 2 3 1 1 3 0 0 2 1
Cryptothyrella
SWU630 0 SWU557 0 SWU522 0 SWU502B 0 SWU502A 0 SWU502 0 SWU475 0 SWU471 0 SWU385 0
Zygospira 121 APPENDIX II.
Locality register
122 Ordovician Drakes Formation, West Union, Ohio (OWU) – Adams County, Ohio, south side of Ohio State Route 41, west of intersection with Ohio State Route 32.
Section is just west of Lick Run Road, 1.2 miles west of entrance to Adams Lake
State Park.
Silurian Brassfield Formation, West Union, Ohio (SWU) – Adams County, Ohio, south side of Ohio State Route 41, west of intersection with Ohio State Route 32.
Section is about 0.5 miles south of OWU at Lick Run Road.
Ordovician Georgian Bay Formation, Oakville, Ontario (OGB) – 16 mile Creek, at intersection with Cross Avenue, Oakville, Ontario.
Silurian Cabot Head Formation (SCC) – Chedoke Creek on Highway 403, at
Mohawk Road Exit, Hamilton, Ontario.
Silurian Cabot Head Formation (SJC) – Jolly Cut, Hamilton, Ontario. Wellington
Road at top of hill, Arkldin Road at bottom of hill.
Silurian Cabot Head Formation (SMB) – Mountain Brow Drive, at intersection with Concession Street, on Niagara Escarpment, Hamilton, Ontario.
123