Although
he may not agree with my conclusions, John Calder is
(perhaps) better acquainted with the Joggins strata than anyone. A few of his comments
regarding this strata are cited below:
"Apart from the marine fauna of the Visean, virtually all other aquatic fauna of the Carboniferous in Nova Scotia historically have
been described as
nonmarine, which... is a too restrictive generalization.
The term 'nonmarine'
fails to describe the spectrum from marine to inland aquatic communities.
Aquatic invertebrate taxa of equivocal affinity are found among the
agglutinated foraminifera, spirorbids, limulids, ostracods, eocarid crustaceans and
pelecypods. The crustacean fauna, including the eocarid Pseudotealliocaris- Anthracophausia and ostracod Shemonaella- Beyrichiopsis communities of the lower Mabou Group, belie the consistency of 'non-marine' conditions..."
1
Emphasis Added
"Similar comments apply to the 'nonmarine' bivalve taxa, wherein an
ecological gradient from near marine to inland freshwater is likely.
Apart from
Carbonicola of the Windsor and Mabou Groups,
however, the taxa found in Nova Scotia historically have been designated respectively as
'nonmarine.' The apparent contradiction that certain of these are associated with near-marine environments in western Europe has been accommodated by invoking ecological
adaptation to the lower-salinity waters inferred for Nova Scotia...
An exception is the study of the Joggins section by Duff & Walton (1973), who concluded
that 'in the light of European studies curvirimula and Naiadites could suggest a salinity nearer the "marine" rather than the "fresh" end
of the spectrum." 1 Emphasis Added
"The section contains 49 recorded horizons containing erect
trees,... and new finds are constantly being made as the cliffs
recede and the thin sediment cover on the wave-cut platform shifts. The most spectacular preserved trees
are up to 3 m tall and nearly 1 m in diameter near the base, but
many are also visible truncated shortly above the base of the trunk. (Fallen logs up to
13 m long have been found in former coal mines in the area).
Virtually
all lepidodendrid trees (lycopsids bearing the rootstock Stigmaria) are rooted in coal beds,
however thin. The trees are easily visible in the cliff faces, and numerous occurrences with
tens of trunks in a single layer can be examined in resistant sandstone 'reefs' that
run across the wave-cut platform."
2 Emphasis Added
"How the trees were entombed
before they decayed has always been a
vexing question. Our sedimentological studies show that the tallest trees were
entombed in 'bayfills' of shallow, standing-water bodies as a result of floods that brought in
large amounts of sand from adjacent distributary channels.
The correlation of entombing heterolithic sandstone beds with channel fills can be demonstrated by walking out the layers across the wave-cut platform at this locality.
The heterolithic sandstones that entombed the Lepidodendrid forests invariably are
characterized by the ubiquitous presence of erect calamites... that appear to have persisted by adventitious
propagation. The taphonomy of the calamites and sedimentology
of the enclosing sediments indicate that the heterolithic beds were
emplaced at intervals, presumably from successive, closely spaced flood events... Most erect
trees are sediment-filled, although a few are permineralized, including rare specimens
of possible medullosan (seed fern) affinity." 2 Emphasis Added
"As with all fossil lepidodendrid forests,
the identification of the trees even to
the generic level is a challenge due to their decortication..."
2
Additional Comments from the Nova Scotia Dept. of Natural Resources Web Site:
"In spite of its fame, advances in our understanding
of the Joggins section have been painfully elusive..."
3
"The classic Joggins section lies within the Cumberland Basin...
It comprises the Joggins and Springhill Mines formations... of the Cumberland Group (Ryan et al., 1992), exposed between Lower Cove and McCarron's Creek in a near-continuous section nearly 2 km
thick." 3 Emphasis Added
"Shallow nearshore facies... are largely wave-dominated shales
and sandstones, with hummocky cross-stratification (HCS) and wave ripples. Large-scale (50-100
m across) domal forms can be observed in the cliff and
wave-cut platform exposures. They include stacked HCS
units and delicate exposure features (planed -
off ripples, back-wash drainage structures), and are interpreted as
the deposits of nearshore bars. Dark, organic-rich limestones up to 1 m thick contain an abundant shelled fauna. Brackish marine (?estuarine)
conditions are indicated by the trace fossil suite,
foraminifera, and recent Sr isotope
data on fish fragments (see Calder, 1998)." 3 Emphasis Added
"The coal beds of this famous section have received surprisingly little study, and the bulk of what has been done is largely unpublished
as yet. Coal beds of the Joggins Formation typically are thin... Typically the coals
are bright, clarain-rich and pyritic ..." 3 Emphasis Added
"Analysis of the hydrocarbon -
generating potential of basin wide organic-rich limestones and 'clam coal' beds from the Joggins section reveals that they contain 1.41 to 13.10% TOC...Hydrogen indices
in the range of 316-978 suggest derivation from algal and vascular plant sources, with kerogen types 1, 2 and 2 to 3 represented. These data are consistent with widespread flooding
events, possibly from a marine source, of lowland plant communities." 3
Emphasis Added
"The Joggins section is a coastal to alluvial succession, and should be a good candidate for recognition of high-resolution Exxon sequences, sequence boundaries and
systems tracts. However, our detailed analysis has failed to identify sequence boundaries in the section, despite the very complete exposure.
Paleosols are apparently immature throughout, and channel bodies are meandering or anastomosing in style, in accord with the associated floodplain facies.
There are no indications of major basinward shifts of facies... Instead, the section is dominated by a hierarchy of flooding surfaces, and these define parasequences that are
stacked in progradational and retrogradational sets. The flooding surfaces are marked by
bivalve-ostracod limestones, coals and carbonaceous shales, grey mudstones in predominantly red successions, and ostracod (freshwater) limestones in some redbeds. The parasequence sets form large-scale cycles (˜50-200 m thick) that... vary from near-symmetric to strongly asymmetric in their facies organization.
The sharp-based nature of most subtidal sandstone sheets suggests that many progradational events
were associated with base-level fall... although the falling levels were apparently insufficient to cause incision and valley formation at this locality." 3 Emphasis Added
"It is probable that rapid subsidence in the Cumberland Basin,
with an abundant sediment supply, allowed sedimentation to be virtually continuous.
Under these conditions, major hiatuses that would be represented by valley fills or mature
paleosols would not be generated. Such a style of basinal filling through a thick succession is unusual, and forms an interesting contrast
to the better known Exxon model." 3 Emphasis Added