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The Early Permian floras of Prince Edward Island,
Canada: differentiating global from local effects of
climate change
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Alfred M. Ziegler, Peter McA. Rees, and Serge V. Naugolnykh
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Abstract: New Permian plant specimens are described from Prince Edward Island, Canada. They include attached
specimens of leaf and stem genera Walchia and Tylodendron, enabling reconstruction of this Early Permian conifer. Although poorly preserved, the study of these floras extends our knowledge of diversity and climate conditions in the region. By placing these findings in a broader stratigraphic and geographic framework, we can document the
phytogeographic and climate trends through the Carboniferous and Permian in the Maritimes Basin. Combined data on
temporal trends in climate-sensitive sediments, as well as macrofloral and microfloral diversities, generally match the
independently derived paleolatitudinal estimates. These show the region migrating from the southern subtropics across
the Equator and into the northern subtropics between the Early Carboniferous and Early Permian. Evaporites and
pedogenic carbonates, together with low-diversity floras, match its subtropical position in the Early Carboniferous. In
contrast, coals are present in the Late Carboniferous, accompanied by high-diversity macro- and microfloral remains,
when the region was on or near the Equator. However, the subsequent transition to pedogenic carbonates, eolian sands,
and lower diversity floras is not matched by significant poleward latitudinal motion. We ascribe these changes to a decrease in moisture availability, as transgressions of epeiric seas became less frequent and finally stopped altogether,
causing an increase of continentality in Euramerica.
Résumé : Cet article décrit de nouveaux spécimens de plantes datant du Permien, provenant de l’Île-du-PrinceÉdouard, Canada. Ils comprennent des spécimens de feuilles et de tiges rattachées de genre Walchia et Tylodendron,
permettant la reconstruction de ce conifère du Permien précoce. Bien que ces flores soient mal préservées, leur étude
étend nos connaissances de la diversité et des conditions climatiques de la région. En plaçant ces découvertes dans un
cadre stratigraphique et géographique plus large, nous pouvons documenter les tendances phytogéographiques et climatiques du Carbonifère et du Permien dans le bassin des Maritimes. Des données combinées sur les tendances temporelles dans des sédiments sensibles au climat et des diversités relatives à la macro- et à la microflore concordent
généralement avec les estimations de paléoaltitude dérivées de façon indépendante. Ces données montrent qu’entre le
Carbonifère précoce et le Permien précoce, il y eut une migration des régions subtropicales méridionales, par delà
l’équateur, vers les régions subtropicales septentrionales. Des évaporites et des carbonates pédogénétiques, avec des flores faiblement diversifiées, correspondent à sa position subtropicale au Carbonifère précoce. Par contre, on retrouve des
charbons au Carbonifère tardif, accompagnés de restes de macro- et de microflores grandement diversifiées, lorsque la
région était à ou prés de l’équateur. Toutefois, la transition subséquente à des carbonates pédogénétiques, à des sables
éoliens et à une diversité florale moindre n’est pas corrélée par un mouvement méridien significatif vers le pôle. Nous
attribuons ces changements à une réduction de l’humidité disponible, alors que les transgressions des mers épicontinentales devenaient de moins en moins fréquentes et qu’elles ont finalement cessé tout à fait, causant une augmentation de
la continentalité en Euramérique.
[Traduit par la Rédaction]
Ziegler et al.
238
Introduction
Permian continental strata are well developed on Prince
Edward Island and in the subsurface of the Gulf of St. Law-
rence and have yielded macrofloral and microfloral remains
as well as vertebrate fossils and trackways (van de Poll
1983; Mossman and Place 1989). However, the macrofloras
have not been the subject of modern study and their
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Received 1 April 2001. Accepted 18 September 2001. Published on the NRC Research Press Web site at http://cjes.nrc.ca on
22 February 2002.
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Paper handled by Associate Editor B. Chatterton.
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A.M. Ziegler 1 and P.M. Rees. Department of the Geophysical Sciences, The University of Chicago, 5734 S. Ellis Avenue,
Chicago, IL 60637, U.S.A.
S.V. Naugolnykh. Laboratory of Paleofloristics, Geological Institute of the Russian Academy of Sciences, Moscow, 109017,
Russia.
1
Corresponding author (email: amz1@midway.uchicago.edu).
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preservation is generally insufficient for fine-scale taxonomic
work. These fossils do assume considerable biogeographic
importance because the Maritimes Basin is one of the few
places in North America where Permian floras occur (A.M.
Ziegler 1990; Rees et al. 2002).
We provide a review of the stratigraphy and fossil occurrences
of Prince Edward Island and describe new plant specimens
that add to our knowledge of the branching pattern of the
early conifer, Walchia, and to the relationship of this foliage
type to its stem, commonly given the name Tylodendron. We
then place these findings in the broader context of changing
climate throughout the late Paleozoic by comparing trends in
floral diversity and climate-sensitive sediments with the
paleolatitudinal migration of eastern North America. Finally,
we examine the worldwide occurrences of Walchia to gain
insight into the biogeographic distribution of this important
element of late Paleozoic vegetation.
The Early Permian of the Maritimes Basin comprises the
top of a thick late Paleozoic section, the Carboniferous portion
being much more thoroughly studied (Calder 1998). In fact,
much can be learned about the Permian by examining the
sediments and floral associations that preceded it. Eastern
North America and adjacent parts of Europe traversed the
equatorial zone in the late Paleozoic so the rocks record a
succession of biomes representing the subtropical through
equatorial and back through the subtropical, as the area
moved from the Southern Hemisphere to the Northern
Hemisphere (Besly 1987; Cecil 1990; Calder 1998). The
Permian represents the latter transition toward more arid
conditions, and this helps to explain the declining diversity
and abundance of plants. Moreover, unfossiliferous eolian
strata on the Îles de la Madeleine, northeast of Prince Edward
Island, fit well as part of this trend toward increasing aridity,
and we regard these as being of probable latest Early Permian
(Kungurian) age. Later in this paper we present data compiled
from the literature showing the diversity changes detected in
the macro- and microfloras, and we match this with changes
in climate-sensitive sediments.
Stratigraphic background
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The geology of Prince Edward Island consists of gently
warped clastic redbeds of latest Carboniferous and Early
Permian age that have been mapped and interpreted as a series
of four fining-upward fluvial “Megacyclic Sequences” (van
de Poll 1983). These units were subsequently given formation
names (van de Poll 1989), providing a useful stratigraphic
framework for comparing the earlier described fossil localities
(Figs. 1, 2). It should be noted that a parallel set of
formational names has been erected for the subsurface of the
adjacent Gulf of St. Lawrence (Giles and Utting 1999), implying
that these fluvial cycles lack continuity throughout the basin.
Nonetheless, the stratigraphic sequence determined from the
surface mapping seems to be confirmed by the relative dates
from the available fossil occurrences, as will be seen below.
Dawson and Harrington (1871) published the first and
only monographic treatment of the macrofloras of Prince
Edward Island. The Miminegash and Governor’s Island floras
were correctly assigned to the “Newer Carboniferous,” but
so was the slightly younger Gallas Point Flora (Fig. 2).
Sparse floral and faunal remains above this were regarded as
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Triassic, and most of the Island was mapped as Triassic.
Subsequently, Bain (in Bain and Dawson 1885) concluded
that Permian rocks were present in the Hillsborough Bay
area, but Dawson in the same paper was dubious and continued
to include a chapter in the final edition of Acadian Geology
entitled “The Permian Blank” (1891). Dawson may have
been misled by the identification of the vertebrate skull
fragment, Bathygnathus, as a dinosaur. This fossil is closely
related, if not identical to, Dimetrodon, a late Early Permian
mammal-like reptile (Langston 1963), and it indicates that
the island is really dominated by Early Permian deposits,
since it came from among the youngest strata. Bain and
Dawson (1885) included just two drawings of fossil plants,
one of the conifer, Walchia imbricata, and one identified as
a branch of Walchia, evidently a specimen of Tylodendron.
The twentieth century work on Prince Edward Island
macrofloras is limited to a few short papers. Holden (1913)
figured some pith casts of Tylodendron and reinforced the
Permian assignment of the strata around Hillsborough Bay,
based on collections from Gallas Point. Darrah (1936) provided
a list of a flora collected from Miminegash and included a
description of a Walchia species. This flora was dated as
Stephanian, that is latest Carboniferous, an assignment that
has been borne out by subsequent investigators. Van de Poll
(1983) summarized much of the above information on Prince
Edward Island and included some photographs of floral
elements from an area on the west coast, to the south of
North Point, which he assigned to the Stephanian.
The vertebrate record helps to constrain the age of the
rocks on Prince Edward Island. Langston (1963) provided a
thorough summary of vertebrate finds on the island and
considered that specimens from the Hillsborough Bay area,
including Gallows (= Gallas) Point, implied an Early Permian
age. He expressed more confidence in the scattered remains
from the north side of the island, at Spring Valley and
French River, which he assigned to the early Leonardian
(Artinskian). These faunas come from beds subsequently
mapped as the Hillsborough River and Orby Head Formations,
respectively, and represent the youngest beds on the island.
Vertebrate trackways have been studied from Prim Point,
near Gallas Point, and also mapped as the Kildare Capes
Formation (Mossman and Place 1989). These authors matched
the ichnofauna with European equivalents collected from late
Autunian strata (= Sakmarian Stage?).
Palynology has proved especially useful in confirming the
temporal framework of the late Paleozoic of the Maritimes
Basin, although the highest beds have yet to yield pollen.
Stephanian and Sakmarian microfloras have been identified
in the subsurface (Barss et al. 1963, 1979; Barss et al. 1979),
and these have been related to surface units (van de Poll
1983). The subsurface samples are usefully indicated on a
stratigraphic cross section showing the lithostratigraphy and
biostratigraphy of wells drilled on and around Prince Edward
Island (Giles and Utting 1999). This section shows the
Carboniferous to Permian transition as slightly higher than
the earlier work, reinterpreting the Vittatina-bearing samples
identified by Barss as questionably Stephanian; this is because
the range of this pollen genus is now known to begin in the
Stephanian of the type area (Utting, personal communication,
1999). Of course, this does not preclude the possibility of an
earliest Permian age as seems to be indicated by the
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Fig. 1. Geological formations of Prince Edward Island and geographical position of the localities mentioned in the text: 1,
Miminegash; 2, North Point; 3, Governor’s Island; 4, Rice Point; 5, Hillsborough Bay; 6, Gallas or Gallows Point; 7, Prim Point; 8,
Murray Harbour; 9, Indian River; 10, Spring Valley; 11, French River; and 12, Orby Head or Cape Turner.
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macrofloras and vertebrates from superjacent horizons in the
Gallas Point area, for instance. Also, it should be noted that
these earlier studies used the Sakmarian Stage designation as
the base of the Permian, but in the current international
terminology (Jin et al. 1997), this would be equivalent to the
combined Asselian and Sakmarian stages.
In summary, latest Carboniferous strata assigned to the
Stephanian Stage are limited to the Miminegash and Egmont
Bay formations of the western margin and southwestern corner
of Prince Edward Island, as well as the small Governors Island
anticline in the middle of Hillsborough Bay. Most of the island
is Early Permian and probably ranges from the Asselian and
Sakmarian of the Kildare Capes Formation to the Artinskian
of the Hillsborough River and Orby Head formations. Younger
strata almost certainly exist on the Îles de la Madeleine,
85 km north of the northeast corner of Prince Edward Island.
Here the Cap aux Meules Formation is dominated by eolian
sands (Brisebois 1981) and has yielded a “Lower Permian”
paleomagnetic pole (Tanczyk 1988). Fossils are limited to
nonidentifiable moulds of plant fragments (Brisebois 1981),
and palynological sampling has yet to be successful (Utting,
personal communication 1999). We assume that the Cap aux
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Meules Formation is entirely younger than the fluvial strata
on Prince Edward Island because of its distinctive eolian facies.
We would expect some interfingering of lithofacies if the
deposits were coeval.
New fossil plant specimens from Prince
Edward Island
The Early Permian plants described in the following text
were collected during University of Chicago, Chicago, Illinois,
student field courses to the Maritime Provinces in 1993 and
1997. The visits were brief and no attempt was made to collect
thoroughly. Three sites were visited and all yielded fossil
plant specimens. These include Rice Point and Gallas Point
on the south side of the island (localities 4 and 6, Fig. 1),
which are mapped as the Kildare Capes Formation of earliest
Permian age. We also collected from the Orby Head Formation
at Orby Head (locality 12), on the north side, and these beds
are among the youngest on Prince Edward Island, probably
of Artinskian age as mentioned above. Representative fossils
have been deposited in the Field Museum of Natural History
in Chicago and have been catalogued with numbers ranging
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Fig. 2. Stratigraphical position of the fossil-bearing layers relative to the formations as named and mapped by van de Poll (1989). See Fig. 1 for localities associated with the
various faunas and floras. Fm., Formation; MS, megasequence.
Can. J. Earth Sci. Vol. 39, 2002
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from PP45924 to PP45940. Most of the specimens are poorly
preserved and fragmentary, so we have only assigned them
provisionally to the following taxa, pending further detailed
collecting and study: Paracalamites sp., Odontopteris sp.,
Taeniopteris (?) sp., Cordaites cf. principalis Germar, and a
needle-like leaf of unknown affinity. However, some other
specimens, belonging to the conifer foliage genus Walchia,
are more complete, and show details of the branching pattern
and attachment to the stem genus Tylodendron. We therefore
describe these and illustrate some of them with photographs
(Plate 1) and a reconstruction of the Walchia plant (Fig. 3).
Our lists for the Orby Head, Gallas Point, and Rice Point
floras are shown in Fig. 2, together with those compiled
from the efforts of previous workers. Tylodendron and
Walchia occur in all three floras.
Tylodendron speciosum Weiss
Branch or stem casts with very distinctive longitudinal
ribs corresponding to leaves that initially covered the branch
or stem (Pl. 1, figs. C–D). The wider proximal area apparently
represents the site of lateral branch attachment. The scars of
these attachment sites are very well seen in the part and
counterpart of specimen PP45925, which also shows small
scars where the stem leaves were attached (Pl. 1, figs. C–D).
This species is a most typical form for the European
Rotliegend, but has also been reported from the North American
Virgilian (Upper Pennsylvanian; Rothwell et al. 1997) and
Artinskian–Kungurian deposits of the Middle and South
Cis-Urals, Russia (Zalessky 1939; Naugolnykh 1998a,
1998b). Together with the stems of T. speciosum -type, some
leafy shoots of walchian affinity occur. Without any doubt
they belonged to the same plant, which can be proved by
two specimens in our collection, where lateral branches of
Walchia-type are preserved still in natural connection to the
main stems (see below for a description of Walchia sp.).
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Walchia sp.
Remains of this type are represented by both leafy shoots
and branches (Pl. 1, figs. A–B). We have several specimens
showing a unique case of conifer stem preservation, which
may have belonged to just two individual trees, from localities
6 and 12 (see Fig. 1). One of them (Pl. 1, fig. A) has a main
axis (stem) of 2 cm width, which bears five lateral branches,
preserved in natural connection to the stem and forming a
whorl. The width of the lateral branches is up to 5–7 mm,
the length is more than 26 cm. Each lateral branch bears
many (more than 30–40) leafy shoots (= second-order lateral
branches). The leafy shoots are attached to the main lateral
branch in regular opposite order, pinnately arranged and situated
almost in one plane (Pl. 1, fig. A) or at an open angle to
each other (Pl. 1, fig. B). This construction of lateral branches
seems to be very typical for walchian conifers. The length of
leafy shoots increases gradually towards the lateral branch
apex. Unfortunately, the fine structure of the leaves is not
preserved because of a coarse-grained sandy matrix. The
width of leafy shoots is 2–3 mm, the maximum observed
length is 10 cm. A second specimen (Pl. 1, fig. B) is threedimensionally preserved and has well developed lateral
branches that radiate from their point of attachment to the
main stem. Each lateral branch has many (up to 60 and
more) leafy shoots, which are pinnately arranged on the lateral
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branch in regular opposite order. Another specimen (PP45929,
not shown) has features typical of Walchia foliage, having
needle-like curved leaves with relatively broad bases and
acute apices. The leaves are spirally arranged around a leafy
shoot axis, reach 3–4 mm in length and 1 mm in width, and
are subtriangular in cross section.
Most of the leafy shoots are sterile, but at least two of
them are fertile and bear small, pendant, round, and ovoid
structures situated on the apices of several leafy shoots (Pl. 1,
fig. B; arrowed). These structures are probably male
(polliniferous) cones. Fine characteristics are not observed,
but nonetheless a general similarity to male cones of
walchian conifers is considerable (see, for example, Florin
1938–1945; Meyen 1987, fig. 69e; Kerp et al. 1990, pl. VI,
fig. 9).
The main stem of Walchia sp. was certainly leafy, at least
when the plant was relatively young and (or) at its distal
part. In more proximal parts of the stem, only leaf scars are
present. We attribute some fragments of these proximal parts
to Tylodendron speciosum Weiss (see earlier in this section
of text). Sometimes the leaves were detached during deposition
of the plant remains. In this case, the Tylodendron-like structure
can be observed even on lateral branches of Walchia sp.
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Late Paleozoic climatic and latitudinal context
of the Maritimes Basin
Plant diversity appears to decline through the Permian
sequence of Prince Edward Island and the adjacent Îles de la
Madeleine and this is part of a trend begun in the Late
Carboniferous. In this section we examine various changes
observable in the entire late Paleozoic record of the
Maritimes Basin to determine the underlying reasons for this
trend. The Carboniferous rocks have been the subject of
diverse modern studies, especially in Nova Scotia where the
exposures are excellent, and this body of work has been
skillfully summarized by Calder (1998). He relates the climate
changes to the northward passage of eastern North America
(“Laurussia”) across the Equator, but with some modification
of the expected zonal climate patterns by the local orographic
framework. In this scenario, general favorability of the climate
for plant growth increases during the Carboniferous as the
region drifts toward the equatorial rainy zone, represented by
peak coal swamp development by the early Westphalian.
Continued northward motion brings the region into the drier
subtropical zone, accounting for the diversity decline into
the Permian. Calder suggests that rain-shadow effects may
have limited the seasonal moisture supply to the Maritimes
Basin. A question addressed here is whether the observed
lower diversities of the Permian were caused by sampling
failure and taphonomic bias, in addition to environmental
factors.
The climate trends observed in the Maritimes Basin have
parallels in the Appalachian Basin (Cecil 1990) and in the
northern European basins (Besly 1987), as these three areas
were aligned within the Laurussian paleocontinent and crossed
the Equator at about the same time. In fact, the regularities
in climate-sensitive sediment distribution throughout Laurussia
stimulated Witzke (1990) to use these to trace the orientation
changes of the paleocontinent throughout the Paleozoic. His
work provides a useful check on the paleomagnetic data,
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Plate 1. figs. A, B. Walchia sp. Field Museum of Natural History (A) No. PP45937 (×1/3) and (B) No. PP45940 (×1/3). Specimens
from Orby Head Formation at Orby Head. figs. C, D. Tylodendron speciosum Weiss. (C) No. PP45925, counterpart (×1) and (D) No.
PP45925, part (×1). Specimens from Kildares Cape Formation at Gallas Point.
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Fig. 3. General aspect of the Walchia sp. conifer, as reconstructed from the Prince Edward Island material.
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which for some time intervals are sparse or ambiguous. Witzke
used the distribution of coals across arctic Canada and Europe
to trace the Equator in the Late Devonian and Early Carboniferous, while the subtropical dry zone is indicated by
evaporites, which extended from the western North American
basins across the Maritimes Basin to Europe and the Russian
Platform. He demonstrated that these zones were remarkably
continuous and appear to move south with time, but this, he
assumed, was in response to the northward drift of the
paleocontinent and that the climate zones in fact remained in
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relatively constant paleolatitudinal bands. It should be pointed
out that latitudinal consistency of these is better observed in
the Carboniferous than the Permian (A.M. Ziegler 1990),
presumably because of diminished shallow seaways and the
change to a more continental world. In this scenario, moisture
sources and their influence on vegetation zones became
progressively limited to the perimeter of the accreting
supercontinental landmass of Pangea.
This wider-scale perspective provides a well-established
and consistent framework, in which to examine the fine-scale
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changes observable in the Maritimes Basin. We have compiled
data on the late Paleozoic trends in macrofloral and microfloral
diversity, and we relate these to climate-sensitive sediment
changes and to the paleolatitudinal estimates based on
paleomagnetic and lithofacies data. All of these are compared
on a correlation diagram (Fig. 4) and related to a series of
informal zones, A through J. The absolute time scale is
based on Young and Laurie (1996), which incorporates
some recent radiometric data. This time scale allows less
time for the Carboniferous at the expense of both the Devonian
and Permian periods. For formational names in the Maritimes
Basin, and their correlations with the European Stages, we
generally follow Calder (1998). However, we show the base
of the Cumberland Group as Namurian B, slightly older than
previously thought, based on unpublished palynological
work (Utting, personal communication, 1999). It should be
noted that the formal Group designations in the Maritimes
Basin are known to vary somewhat in age in different parts
of the basin. The term “Prince Edward Island Group” has
been proposed for Late Carboniferous and Early Permian
rocks on that island (van de Poll 1989), but since there is
overlap with the similar Nova Scotian sequence, which includes
Permian rocks (Calder et al. in press), we retain the older
term Pictou Group. The distinctive, and apparently still younger,
rocks of the Îles de la Madeleine have not been given a
group name and so the term “Cap aux Meules Formation”
(Brisebois 1981) is used herein.
Macrofloral diversity trends
The last comprehensive monographs on the macrofloras
of Nova Scotia were by Bell on the Upper Carboniferous
(1943) and the Lower Carboniferous (1960). In the former,
he provided a table containing the vertical ranges of plant
species, which shows an increase of species to a peak in the
Cumberland Group and then a decline through the remainder
of the period. In the latter paper, summary lists from the two
main Lower Carboniferous stratigraphic subdivisions show
rather low diversities. Calder (1998) has updated the taxonomy
and incorporated data from more recent papers on the Nova
Scotian portions of the basin. The net result has been to
increase the apparent diversity of the Cumberland Group and
to shift the peak to the upper portion of this span. The latest
Carboniferous and Permian are not well developed in Nova
Scotia, at least in the basinal facies that yield the most diverse
macrofloras, so we incorporate our own lists from Prince
Edward Island to complete the sequence (Fig. 2; Appendix
A, Table A1). The floral lists reported in the literature are
subject to duplication due to the fact that plant taxonomists
apply different names to separate organs of the same plant.
To achieve consistency, we base our tallies on foliar genera
only, with the exception of stem and trunk genera of the
lycopsids and sphenopsids, which are generally more
consistently preserved than the leaves of the same plants.
The resulting macrofloral diversity plot shows both species
and generic tallies ranging through the Carboniferous and
Early Permian (Fig. 4). The strong peak in the Westphalian
clearly indicates optimal conditions for plant productivity at
that time. By contrast, the Early Carboniferous and Early
Permian must have been stressful times. Of course, a number
of factors in addition to climate might have influenced the
shape of the curve and these include sampling failure,
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taphonomic bias, and the range of communities contributing to the diversity of each time interval. Sampling failure
is suspected in the case of the latest Carboniferous and
Permian levels simply because the Prince Edward Island
strata have not been subjected to thorough collecting and
modern taxonomic study or revision. During our brief trips
to the island, we found plenty of fossil plants at the horizons
we examined. Taphonomic bias probably operates to accentuate
the peak distribution because plant preservation is most
effective in areas of high plant productivity. Organic productivity is greatest today in the high-diversity tropical rain
forests (Lieth and Whittaker 1975) and contributes toward a
reducing environment in the soils, the ultimate example being
peat. There may also be variations through time in the range
of communities sampled in the Maritimes Basin. The highest
diversities seem to be related to communities along the basin
axis, which varies in position through time, and most of the
Permian rocks are in the subsurface. The microfloras are not
necessarily subject to the same biases, and they are examined
next since they represent a somewhat independent measure
of plant diversity.
Microfloral diversity trends
The Carboniferous succession of the Maritime Provinces
has been the subject of numerous recent palynological studies,
whereas only older reports are available for the latest
Carboniferous and Permian (see Appendix A, Table A2 for
references). The identifications in all the published newer
studies were made by John Utting, and he has been very
helpful in providing advice and unpublished tables for our
use (personal communications, 1999). Barss made the identifications in the papers he co-authored (1963, 1979). With
this literature, varying levels of information are provided, so
it is not possible to specify total numbers of samples or relative
abundances of species involved in every tally. Accordingly,
we are limited to raw diversity counts of genera and species,
as was the case with the macrofloras. Compared with the
macrofloral data, a finer level of stratigraphic subdivision is
available for a number of the geological stages, but we have
grouped these spore zone lists together into the same “bins”
as the leaf data to ensure comparability.
The peaks and troughs of the two floral diversity curves
(Fig. 4) generally coincide in time, but the microfloral diversity
is considerably greater in the troughs. We assume that the
spore and pollen record represents the surrounding upland
areas as well as the basin floor and that during more stressful
intervals moisture was limited to upland sites as is typical of
orographic rainfall patterns in tropical drier zones today. The
region was active tectonically, and there is abundant evidence
for river systems entering the basin from the southwest from
the Westphalian into the Permian (Gibling et al. 1992). The
spore samples therefore probably include additions from the
Appalachians, as well as the more local uplifts associated
with this transtensional basin. The Early Carboniferous samples
are dominated by one or two species and these occur in all
available sediment types, including evaporites, and have
been characterized as representing an arid climate (Utting
1987). Even so, some 30–40 pollen genera have been recovered
from zones A through D, but most of these are found in just
a few of the sampling horizons, so moderately diverse plant
communities must have characterized the hinterlands. At the
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Fig. 4. Stratigraphy, plant diversity (black, genus totals; grey plus black, species totals) and climate-sensitive sediment patterns for the Carboniferous and Permian of the
Maritimes Basin. Also shown are independent estimates of paleolatitude (circles, Southern Hemisphere; squares, Northern Hemisphere). Fm., Formation. The Carboniferous–
Permian boundary is the Gzhelian–Asselian.
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other end of the climate spectrum, there are palynological
studies that are limited to transects through individual coal
beds (Calder 1993; Marchioni et al. 1994). These have
diversities of 30–35 species with about eight occurring
consistently through each coal bed but this is far fewer than
in the sequences that enclose them. Again, extra-basinal
contributions are implicated, as well as elements from other
communities within the basin.
There are of course taphonomic and sampling limitations
to the palynological data. The microfossils are generally limited
to the darker, unoxidized strata while red beds dominate the
Early Carboniferous and Permian portions of the sequence.
Palynomorphs do get preserved in evaporites, so the Early
Carboniferous samples are perhaps more trustworthy than
the Permian ones. Also, the Permian has not been the subject
of a modern study so diversity, especially specific diversity,
is under-represented on Fig. 4. Even so, the microfloral diversity
curve is probably a better reflection of climate change than
the macrofloral curve if one is considering the region as a
whole.
Climate-sensitive sediment patterns
The sediment indicators of climate parallel closely the floral
diversity patterns. The peak of coal deposition in the Late
Carboniferous coincides with the high-diversity floral
assemblages and, combined, these effects indicate an excess
of precipitation over evaporation throughout the annual cycle
(Lottes and Ziegler 1994). By contrast, the evaporites of the
Lower Carboniferous and the eolian deposits of the late
Early (?) Permian of the Îles de la Madeleine indicate the
opposite. The pedogenic carbonates and associated redbeds
are intermediate stratigraphically and probably represent a
climate with a prominent dry season (Goudie and Pye 1983).
Our outcrop data come from Calder (1998) and Calder et al.
(1998) and our subsurface data come from Grant (1994) and
Giles and Utting (1999). The focus here is on basinal sediments,
as the margins of the basins are characterized by well-drained
soils and are generally well oxidized (Ryan et al. 1991). An
important point is that the coal-bearing formations typically
include red beds, demonstrating the ephemeral and cyclic
nature of the wetter intervals (Calder 1998).
We argue here that the availability of moisture sources
was a critical influence on the climate of the Maritimes Basin.
The marine nature of the Windsor Group of the middle Early
Carboniferous has always been understood, but the proximity
of marine conditions has only recently been appreciated for
the Horton (Tibert and Scott 1999), Cumberland (Archer et
al. 1995), and Morien Groups (= late Cumberland Gp. of the
Sydney Basin; Wightman et al. 1994). The evidence is tenuous
and is based mainly on the occurrence at points in the
succession of agglutinated foraminifera, but is corroborated
by the observation that individual Late Carboniferous coals
of the subsurface can be traced across the basin, and this has
been taken to imply eustatic control (Grant 1994). The
importance of a local moisture source is evident in the
Sydney Basin, adjacent to the main Maritimes Basin, where
there is a “systematic alternation of coals and other
hydromorphic paleosols with calcretes and calcic vertisols”
(Tandon and Gibling 1994). These authors argued that the
moisture was diminished during sea-level lowstands, and
0
that a seasonal drought was augmented by the rain-shadow
effect of the Appalachian Mountains.
Paleolatitudinal migration of Laurussia
It is clear from paleomagnetic evidence that eastern North
America moved across the Equator in the late Paleozoic, so
this is of fundamental importance in accounting for the changes
evident in the floras and sediments. We have derived a
paleolatitudinal curve for Prince Edward Island (Fig. 4) using
the data compilation of Van der Voo (1993) who applied
strict criteria in selecting the most reliable determinations. In
addition, we have updated the age information for all the
stratigraphic units from which the samples were originally
obtained, and we were able to refine the dating of many of
the rock units. The resultant paleolatitude curve places the
Maritimes Basin on the South Tropic at the beginning of the
Carboniferous and shows it making a transition to the equatorial
zone by the Late Carboniferous. From these estimates, it
remained at very low latitudes through the Early Permian,
crossing the Equator in the late Artinskian. Thus the precipitation shift implied by the change from evaporite to coal
deposition at the beginning of the Late Carboniferous is
paralleled by a latitudinal motion, but the return to arid
conditions at the transition to the Permian is not.
The climate-sensitive sediment approach to orienting
Laurussia (Witzke 1990) yields generally similar results, but
indicates a greater latitudinal excursion of eastern Canada,
with the crossing of the Equator about the end of the Carboniferous. For much of the time interval, the two methods
agree within five degrees, but the Early Carboniferous
estimates of Witzke are significantly different and in our
opinion provide a decidedly better fit of the data for the
paleocontinent as a unit. Specifically, the paleomagnetic data
would place the Early Carboniferous coal occurrences of
both Arctic Canada and the Appalachian Basin in latitudes
that are normally arid and the evaporites of western Canada
and the Russian Platform over the Equator, which is normally
wet. The paleomagnetic data could be giving an underestimate
of the paleolatitude because of sediment compaction, which
would tend to flatten the inclination, or a diagenetic delay in
establishing the magnetic signal. As for the Permian portion
of the two paleolatitude curves, the Maritimes Basin is
shown remaining close to the Equator during the return to
arid conditions, so we conclude that this change could not
have been the result of latitudinal migration beneath climate
belts.
Late Paleozoic climate controls within Euramerica
As has been seen, the floral diversity curves and climatesensitive trends appear to be symmetrical about the middle
Upper Carboniferous when peak diversities and coal swamp
development occurred. The climates of the Early Carboniferous
and the Early Permian were obviously drier, but for different
reasons, and all this is true for Eastern Canada, as well as
the Appalachian Basin and northern Europe. Moreover, there
were a number of drier intervals even within the coal-bearing
sequences, at least in the Maritimes Basin and the Appalachian
Basin (DiMichele and Aronson 1992). The key to the aridity
question seems to be moisture supply—a seaway transgressed
into the Maritimes Basin during the Early Carboniferous but
not during the Early Permian, while alternating marine and
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terrestrial conditions characterize the Late Carboniferous.
Marine conditions were best developed during the Early
Carboniferous, but conditions were dry because the region
lay within the influence of the descending limb of the Hadley
Cell (Parrish 1998). Most authors have explained the drying
trends of the late Paleozoic by appealing to the orographic
blockage of the rising Variscan and Appalachian mountains
to the south and east (Besly 1987; Cecil 1990; Calder 1998).
However important this might have been, we feel that
fluctuations of a local moisture source, in the form of a
transgressive–regressive shallow seaway to the north of
these mountains, were critical in defining the climate of this
broad region.
The transgression of the sea into eastern Canada must
have come from northern Europe. This is indicated by local
paleogeography which shows major river systems entering
the basin from the Appalachian side (Gibling et al. 1992)
and by the general biogeographic similarities of the floras
and faunas with northern Europe (Zodrow and Cleal 1985;
Mossman and Place 1989: Calder et al. in press). The timing
of tectonic and eustatic events in Europe then becomes critical
as so much of the late Paleozoic sequence of this well-studied
region is dominated by continental sediments. The advance
of the Variscan fold and thrust belt dominated the entire
Carboniferous of central Europe and this imposed a tectonic
load on the southern margin of the platform, allowing for an
extensive foreland trench to develop (P.A. Ziegler 1990,
p. 41). Deep-marine conditions persisted along this trench
into the Westphalian when it became filled with sediments
from the orogenic front. It is interesting to note that the
connection with the deep ocean was in the vicinity of the
southern Urals, and the distance from there to the Maritimes
Basin must have been at least 5000 km in the Pangean
configuration.
In Europe, there are at least 49 “marine bands” within the
coal measures of the Namurian through Westphalian C, and
many of these can be traced from Poland to Ireland (Cleal
and Thomas 1996), testifying to the glacio-eustatic sea-level
controls at the time. The marine bands are best developed in
Britain, where they contain the distinctive goniatites of the
northern European basins. The closest known occurrence of
these ammonoids to Nova Scotia is in the Westphalian of
southern Portugal (Oliveira 1983). These goniatites are
mainly restricted to the northern European basins and are
apparently among the few marine groups that could tolerate
these conditions. The agglutinated foraminifera of the
Maritimes Basin (Archer et al. 1995; Wightman et al. 1994)
represent the westernmost extent of this province that must
have been subject to low-salinity conditions. The main point
is that the sea-level fluctuated during the Westphalian, and
the effect on western parts of the seaway was to withdraw
the moisture source from the region many times. This
explains the alternation of soil types noticed by a number of
researchers in the Maritimes Basin (Tandon and Gibling 1994;
Calder 1998). The explanation is related to Milankovitch
cycles, but indirectly through the effect of glacial advances on
sea-level. It is interesting to note that the latest record of a
marine transgression is early Stephanian in the Sydney Basin
(Tandon and Gibling 1994), while the last known marine
beds in Europe are Westphalian C–D (P.A. Ziegler 1990).
This could be a correlation problem, or a lack of preservation
0
of a full range of Stephanian facies in Europe. We favor the
latter because coals do extend into the Stephanian of the
Maritimes Basin (Giles and Utting 1999) and, by our argument,
must have had a moisture source.
25
The phytogeography of Walchia
5
A more complete characterization of the ecotope represented
by the floras of Prince Edward Island may be gleaned from
the worldwide distribution of walchian conifers (Fig. 5) and
from a comparison of this pattern with the results of a climate
model study (Rees et al. 2002). Walchian conifers first
appear in the fossil record in the Late Carboniferous
(Westphalian B) of Europe. They are present in Westphalian
C–D marine shales of the North American midcontinental
cyclothems, but are absent from interbedded coals. Rothwell
et al. (1997) analyzed these occurrences and assumed that
these arborescent plants lived in “drier terrestrial environments”
that were “moisture stressed.” Either these durable remains
were transported past the coal-forming swamps to the sea or
the plants lived during stages of the cyclothems when
swamps were not present, perhaps during low sea-level
phases when the potential moisture source was restricted to
the area between the ancestral Rockies and western Kansas
(Heckel 1980). A more remote possibility is that the conifers
were transported from the paleo-north where conditions
were more arid.
It seems clear that two distinct floras coexisted, and the
question that arises is whether they occupied the same climate
zone and constituted adjacent communities or whether the
climate alternated with the cyclothems. The community-level
distinction could result from the contrast between swampy
water-logged soils and better-drained interfluves. There has
been a tendency to apply the term “xeromorphic” to
Walchia, and this would imply the wider-scale influence of
climate in the form of a dry season (DiMichele and Aronson
1992). These authors performed a discriminant function
statistical analysis on Late Carboniferous and Permian floras
of this broad region and found two distinct associations in
the latest Carboniferous (Stephanian), one collected from
wetland facies and grouping with earlier Pennsylvanian floras,
and the other from red beds and grouping with Permian floras.
So, by the latest Pennsylvanian, walchian conifers appear for
the first time in untransported assemblages, but again they
alternate on a fine stratigraphic scale with the coal-forming
environment, leaving the question of the climate versus environment control in doubt.
Walchia belongs to an extinct group of conifers, so it is
not possible to use the “nearest living relative” approach in
assessing the physiognomic adaptations of this group. However
the Norfolk Island Pine, a species of Araucaria and a house
plant familiar to many, bears a striking resemblance to
Walchia in its small needle-like leaves and in the form and
regularity of its branching pattern. Norfolk Island actually
has abundant rainfall year-round as do most of the sites
around the Tasman Sea and in South America inhabited by
araucarian species (Enright and Hill 1995). In fact, most of
the 18 extant species of Araucaria seem to prefer mountainous
rain forests although a coastal species in eastern Queensland
does live in an area of seasonal drought and an Andean species
does well in the temperate zone. Enright (1995, p. 207)
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Fig. 5. Earliest Permian (Asselian–Sakmarian stages) phytogeography of Walchia (closed circles) relative to floral localities lacking this
genus (open circles). Prince Edward Island is represented by the star. Data are from Rees et al. (2002) and LePage (personal communication, 2000) in the case of the Canadian Arctic site. Paleogeography from Ziegler et al. (1997).
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speculates as follows: “While the emergent habit of araucarias
exposes foliage to high radiation and low humidity conditions
(which might explain their leaf sclerophylly), cloud interception
may be an important source of moisture in addition to rainfall
both for araucarians and for associated species.” This shows
that general assumptions on fossil plant adaptations must be
applied with caution.
We know for sure that Walchia did well in basinal settings,
to judge by the one in situ forest known (Calder et al. in
press) and from its widespread occurrence in the Appalachian
and midcontinent basins of the United States. This is notwithstanding the common assignment of Walchia to “upland”
settings, where really what is meant is “relief that is high
relative to the swamp level.” These basins could have been
0
100 m above sea level during glacio-eustatic lowstands, but
this still should be considered a “lowland” environment. Of
course, this does not preclude the possibility that Walchia
thrived on mountain sides.
By the Early Permian, walchian conifers are common to
most low-latitude sites in Pangea, to judge by our worldwide
compilation (Fig. 5; and Rees et al. 2002). Most of the
occurrences are throughout the paleoequatorial belt from the
southwestern United States through eastern Canada to Europe.
Other sites occur up to 35° from the Equator, including a
new locality in Arctic Canada (LePage, personal communication, 2000) and one in southern Angara, and similarly in
the southern hemisphere in both Niger and Thailand (although
the latter is on the Sibumasu Terrane, which has an uncertain
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position). The main low-latitude areas that possess a good
fossil record and lack Walchia in the earliest Permian are
North China and Mongolia, but the genus does appear in
Chinese lists from later intervals.
We have recently completed a climate model study for the
Early Permian (Gibbs et al. 2002; Rees et al. 2002), and
most Walchia localities plot in the Tropical Summerwet (i.e.,
seasonally dry) Biome with some overlap into adjacent Tropical
Everwet and Subtropical Desert biomes. The modeled climate
for Prince Edward Island is in fact desert, but we feel that a
seasonally dry climate in the tropics and subtropics is a good
compromise for the Walchia habitat. The desert did overwhelm
eastern Canada eventually, to judge by the eolian sands of
the Îles de la Madeleine mentioned above. On the other
hand, everwet conditions can be excluded for Walchia, because
by the Permian, we can demonstrate very limited geographical
overlap of Walchia occurrences with the coal swamp environments (Rees et al. 2002), and modern lowland swamps in
the tropics are indicative of everwet climates (Lottes and
Ziegler 1994).
The genera most consistently associated with Walchia can
be determined from our Permian floral data base (Rees et al.
2002; Table 1; see also DiMichele and Aronson 1992), and
these can help with the climate interpretation. There are four
genera, Callipteris, Odontopteris, Ernestiodendron, and
Gomphostrobus, that ordinate with Walchia in our worldwide
multivariate analysis (Rees et al. 2002), so these were often
restricted to the Walchia habitat. The last two are conifers
and like Walchia have reduced leaves, while the first two are
pteridosperms and superficially resemble many other late
Paleozoic taxa. More significant perhaps is the fact that the
other ten taxa commonly associated with Walchia are otherwise
distributed across many biomes, and this suggests to us that
the precipitation limitation was not that severe, perhaps three
or four dry months during the annual cycle at the most. We
can expect that the 15 taxa listed in Table 1 would be typically
found together and this is a level of diversity that is moderate,
especially when it is considered that these are mostly “form
genera” and any one could represent a number of species.
Interestingly, the in situ walchian forest of Nova Scotia has
yielded just two foliar genera, both conifers, Walchia and
Dicranophyllum (Calder et al. in press). This may represent
patchiness or incomplete preservation, because just 50 km
north in Prince Edward Island, many of the forms in Table 1
are evident from our collecting (Fig. 2). Taking the broader
perspective, the level of generic and morphological diversity
suggests that the Walchia ecotope was fully forested and at
the lusher and better-watered end of the spectrum between
desert and rain forest.
Conclusions
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The Maritimes Basin of eastern Canada contains a continuous
record of climate change from the earliest Carboniferous
through the end of the Early Permian, and we have reconstructed
this from sedimentary evidence and macro- and microfloral
remains. We then compared this record with independent
paleolatitudinal determinations and the results of a climate
modeling study. Given that this portion of Euramerica transited
the subtropical and equatorial zones, the main climate influence
must have been precipitation, especially the way this parameter
0
Table 1. Genera most commonly associated with Walchia in the
Early Permian.
Genus name
%
Walchia*
Callipteris*
Odontopteris*
Pecopteris
Annularia
Neuropteris
Ernestiodendron*
Taeniopteris
Calamites
Cordaites
Asterophyllites
Sphenophyllum
Gomphostrobus*
Sphenopteris
Callipteridium
All others
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69
67
62
50
50
48
48
45
40
31
31
29
29
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19 or less
Morphological category
(adapted from Meyen 1987)
Pinales
Pteridosperm
Pteridosperm
Fern
Sphenophyte
Pteridosperm
Pinales
Cycadophyte
Sphenophyte
Cordaite
Sphenophyte
Sphenophyte
Pinales
Fern or pteridosperm
Pteridosperm
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5
0
Note: These data are taken from our worldwide database of Permian
floras, specifically from the Asselian and Sakmarian stages of the Early
Permian (available on request at https://pgap.uchicago.edu/db/). Of the 144
localities in this database, 42 contained Walchia and (or) Lebachia, a
synonym, and the percentages in this table were calculated from these 42
to show the genera most commonly associated with Walchia. However,
many on the list are widely distributed across Permian floras and the
asterisks (*) indicate forms that group with Walchia in our global
ordination study (Rees et al. 2002), so these can be expected to be
restricted more narrowly to the floras containing Walchia.
was distributed through the annual cycle. This late Paleozoic
sequence displays the driest conditions near the top and bottom
with the evaporites of the Windsor Group (Viséan Stage)
and the eolian sands of the Cap aux Meules Formation
(Kungurian Stage ?). The wettest conditions are seen in the
coal measures of the Cumberland Group (late Namurian and
Westphalian) although the coal swamp environment alternates
with red beds containing pedogenic carbonates. Gradations
between these extremes are found in the Mabou Group (late
Viséan – early Namurian) and the Pictou Group (Stephanian
through Artinskian), so these must represent a seasonal
alternation of wet and dry conditions. The macroflora of the
Pictou Group on Prince Edward Island is the main focus of
this paper as it has, in the past, received the least scientific
attention. The flora, dominated by the conifer Walchia, is
reasonably diverse, implying that there was adequate precipitation for forest growth (8–9 months annually). The lack of
coals and the presence of pedogenic carbonates constitute
the chief evidence for this level of seasonality. This walchian
ecotope is widespread in low-latitude areas during the Permian,
where it supplanted the rain forests best developed during
the mid-Late Carboniferous.
The paleolatitude of the Maritimes Basin must have been
about 30°S in the Early Carboniferous, to judge by the local
and continent-scale climate-sensitive sediment patterns.
Subsequently, however, the area moved into the equatorial
zone, where it remained during the cyclothemically alternating
wet and dry intervals of the Late Carboniferous and the annually
alternating wet and dry seasons of the Early Permian. So the
Carboniferous climate transitions are dominated by the
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equatorward motion of the basin, but the subsequent changes
are a function of the availability of moisture in the form of
the epeiric seas, which advanced across Europe from the east
and across the United States from the west. In the mid-Late
Carboniferous, the transgressions were numerous, but by the
latest Carboniferous, they had become less frequent and finally
by the Permian had stopped altogether. So we ascribe this
variability in precipitation to the fluctuations in sea level and
eventual continentality in Euramerica, but point out that the
Permian equatorial coal swamp environment was well developed
elsewhere, especially in China, where moisture sources
remained.
Acknowledgments
This study was supported by grants from the U.S. National
Science Foundation (EAR-9632286 and ATM 00-00545) and
from the Russian Foundation for Basic Research (00–05–
65257). Merrilee Guenther discovered the unique specimen of Walchia, with branches attached to the stem, while
on a University of Chicago field trip in 1997. Also on this
trip, John Calder of the Nova Scotia Department of Natural
Resources conducted the group around the in situ walchian
forest and trackway site at Brule, Nova Scotia, and provided
many helpful comments during the course of this study. John
Utting, Geological Survey of Canada, provided published
and unpublished data on the palynomorphs of the Maritimes
Basin, and this information provides a critical test of the
conclusions based on macrofloras and sediments. Finally,
Peter Giles of the Bedford Institute and Marcos Zentilli of
Dalhousie University, Halifax, Nova Scotia, pointed out to
us key information on the stratigraphy and geochronology of
eastern Canada.
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Appendix A. Macrofloral and microfloral sources of data
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Table A1. Sources of the macrofloral data on Fig. 4.
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Interval
Stratigraphic unit
Reference
A
B–C
D
E
F
G
H
I
Horton Group
Windsor Group
Mabou Group
Cumberland Group s.s., and Riversdale Series of Cumberland Group
Stellarton Series of Cumberland Group and Morien Series of Pictou Group sica
Miminegash & Egmont Bay formations
Kildare Capes Formation
Orby Head Formation
Calder 1998, appendix
Calder 1998, appendix
Calder 1998, appendix
Calder 1998, appendix
Calder 1998, appendix
This paper, Fig. 2
This paper, Fig. 2
This paper, Fig. 2
B
B
B
B
B
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a
Bell (1943) assigned the Morien Series to the Pictou Group, but most modern authors, including Calder, place it in the
Cumberland Group. S.S., sensu stricto.
Table A2. Sources of the microfloral data on Fig. 4.
Interval
Stratigraphic or temporal unit
Reference
A
Horton Group
Albert Formation
Lower Windsor Group, Zone NS
Upper Windsor Group, Zone AT
Boundary Beds, Zone SM
Rocky Brook Formation, Zone SM
Mabou Group
Cumberland Group
Barachois Group, Westphalian A
Late Namurian
Barachois Group, Westphalian C
Westphalian B–D
Sydney Mines Formation, Westphalian C
Stephanian
Sakmarian
“Permian”
Utting et al. 1989, table 5.1
Utting 1996, pp. 79–80
Utting 1987, table 5
Utting 1987, table 5
Utting 1987, table 5
Hamblin et al. 1997, pp. 50–51
Utting, unpublished data
Utting, unpublished data
Hyde et al. 1991, p. 1912
Barss et al. 1979, p. 7
Hyde et al. 1991, p. 1912
Barss et al. 1979, pp. 5–10
Marchioni et al. 1994, p. 257
Barss et al. 1979, pp. 4–10
Barss et al. 1979, p. 6
Barss et al. 1963, fig. 4
B
C
D
E
F
G
H
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