The fossil cliffs of Joggins

Monday, May 24, 1993

Laing Ferguson, Mount Allison University, Sackville, N.B.

Introduction

In late May of 1992, the Geological Survey of Canada erected a bronze plaque in the little village of Joggins in north west Nova Scotia on the shores of Chignecto Bay in the Bay of Fundy (see Wat On Earth, Fall 1992 Issue). The plaque commemorated the work of Sir William Logan in the area and the 150th Anniversary of the GSC. Logan was the first Director General of the GSC.

The erection of the monument was one of several manifestations of a growing interest in the "Fossil Cliffs of Joggins," a superbly exposed and easily accessible shore section of the late Carboniferous non-marine strata. Other indications of the burgeo ning interest in the locality are the creation of several new museums to house exhibits of material from the Cliffs and a move to nominate it as a World Heritage Site.

In the cliffs, the remains of numerous fossil forests can be found and ancient in-filled river channels can be seen both in the cliffs and on the foreshore. Inside some of the large fossilized tree trunks, the remains of amphibians and early reptiles have been found and it is the occurrence of these primitive reptiles, predated only by the recently discovered fossil Westlothiana lizziae (popularly knows as "Lizzie") in Scotland, that has made the Joggins locality world famous.

The Joggins locality (Fig. 1) is easily reached from the Trans Canada Highway near Amherst, Nova Scotia vis Nappan, Maccan and River Hebert. Going down the main street of the village you will notice the GSC monument on your left just before the Post Office. Immediately behind the monument is the newly built "Joggins Fossil Centre" run by local fossil collector Don Reid. This is worth a visit to "get your eye in" and see the types of fossils that you are liable to encounter once you are on the beach itself. Mr. Reid or his assistant also conduct guided tours of the cliffs from the Fossil Centre in Joggins.

The schedule of tours is controlled by the tides to a large extent and if you are going to the beach independently you should make sure you know when the tide is to be high. It is best to visit the area in the period three or four hours on each side o f low tide. The tidal range can be as much as forty or fifty feet and it is essential that you get off the beach well before high tide as the only access points are about two miles apart.

Access to the beach and cliffs is best obtained via the wooden staircase near the parking lot at the north west end of the village (follow the signs). Alternatively one can get down to the beach at Lower Cove about two miles to the north (Fig. 2).

If you are heading to Joggins from the west you should endeavour to pay a visit to the Geology Department at Mount Allison University in Sackville, New Brunswick, where an extensive exhibit of Joggins fossils is put on display over the summer months each year. Sackville is just off the Trans Canada Highway about five miles west of the Nova Scotia Border and the Geology building is only a few hundred yards away from the Sackville Tourist Office and ample parking. If you are interested in birds you can also visit the nearby Sackville Waterfowl Park and enjoy the relaxed atmosphere of Mount Allison University’s attractive campus.

Significance of the site

The Joggins section (Fig. 3) has attracted much attention over the last 150 years or so for several reasons. In 1843, the section was the subject of the first geological investigation undertaken by the newly formed Geological Survey of Canada. It was one of the first coal-bearing sequences to be described in detail and one where the cyclic nature of sedimentation first attracted attention (Dawson 1854). The rich bivalve fauna is comparable to that found in the European Coal Measures. The amphibian Order Microsauria was based on material from Joggins. The fauna of primitive terrestrial reptiles and amphibians, which is found in the bases of erect fossil tree stumps, is world famous (Carroll, 1964). Tracks of a giant terrestrial arthropod (Arthropl eura) have been found in recent years (Ferguson, 1966).

The thick sequence of sedimentary rocks exposed in the cliffs at Joggins dips to the south at approximately 20o and is best examined at low tide when about a thousand feet of foreshore is also exposed to view. The sediments were deposited by flooding rivers as they flowed northwards across the top of a pile accumulating in a basin which was subsiding between two upraised fault blocks (the Cobequid block to the south and the Caledonia Mountain to the west) during late Carboniferous or Pennsy lvanian time, approximately 300 million years ago. Subsidence was apparently intermittent but generally relatively rapid. The basin of deposition is known as the Cumberland Basin as it occurs in Cumberland County.

The general picture is thus of levee-bound river channels traversing low-lying marshy areas which were occasionally flooded and received minor amounts of fine sediment. The slow accumulation of fine sediment permitted the establishment and growth of sizeable trees. If sedimentation happened to be very slow, forests could establish and a peat could develop. Eventually flooding, and burial perhaps by a sheet sand from a crevasse splay (a breach in a natural levee of a river which allows the formation of an alluvial fan or layer of sediment), would lead to the creation of coal. The thinness of the coals attest to the fact that such periods of relative stability were reasonably short.

At the first small promontory to the north of the steps and stream at the access point to the section there is a very interesting outcrop which is particularly instructive with regard to the conditions in the "forest primeval." A stand or understory of Calamites plants (similar to present day "Horsetails") with stems up to 10 or 12 cm in diameter has been preserved in situ along with occasionally exposed large and medium sized lycopod trunks (e.g. one about 90 cm in diameter and almost three metres height was discovered in 1972). Modern lycopods are represented by only small "club mosses," but in the Carboniferous they reached a height of about 30 metres. The Calamites plants are spaced approximately 15 to 30 cm apart and, with their leaves and any side branches intact, must have formed an almost impenetrable undergrowth around the larger trees. The plants have the lower metre and a half preserved, and are sometimes found with their needle-like leaves intact and penetrating the surrounding sediment. The preservation attests to very rapid burial, such as expected from a crevasse splay. The bamboo-like segments of Calamites pith casts are among the most abundant fossils to be found on the beach at Joggins.

Upright fossil tree stumps

If the streams burst their banks before a forest could establish properly and a peat layer could develop from its detritus, the bases of the pioneer trees would be surrounded by the sheet sands from the crevasse splays and would be killed (Fig. 5,6). It is interesting to note that the former vertical tree trunks found at Joggins are invariably rooted in fine grained sediment although the base of the trunk is usually surrounded by a sandstone (Fig. 5B). Such trees would no doubt have their tops blown off once they had rotted. Sediment would accumulate around them and eventually spill into the hollowed interior once it had reached the level of the rim of the stump (Fig. 5D).

There are many variants to this general mode of infilling. The interiors of some trunks have a layer of charcoal-like material below the sedimentary infilling. This material is the remains of the vascular bundles of the tree stump which rotted and fell into its base prior to the sediment spilling over the rim and preserving it. Others have siderite (iron carbonate) filling in their bases and adjacent root systems. This was presumably precipitated from standing water in the hollow stump before it was filled in by sediment. Short stumps usually have well preserved root systems (Stigmaria) because they were filled in before the weight of accumulating sediment was sufficient to crush them. Tall stumps on the other hand have root systems which are difficult to see because they caved in under the weight of the overlying sediment long before it had accumulated enough to spill over the rim of the trunk and thereby enter the roots (Ferguson, 1988b).

The infilled stigmarian root systems are often exposed on the foreshore and in the cliffs complete with attached rootlets. These sizable fossils may be several metres long and up to 15 or 20 cm in diameter. Broken segments of Stigmaria are common on the beach.

It should be mentioned that horizontal tree trunks are rare in the Joggins section (but do occur in the base of some of the larger channels). Petrification of woody tissue is also extremely rare in the Joggins trees. Only one example has been found by the writer in the last thirty-one years (Fig. 7).

Animal fossils

When the surface of the accumulating sediment was flush with the rim of a hollow tree stump the stump acted as a very effective trap for any unwary amphibians or reptiles crawling over the forest or jungle floor. The first vertebrate remains found inside the Joggins tree trunks were discovered by Sir Charles Lyell and William Dawson in 1851. It was the discovery of these early reptiles which really put the locality on the map and made it world famous.

Up to thirteen vertebrate skeletons have been found inside one tree trunk (as successive levels of infilling) and it is obvious that the trunks provided an ideal situation for fossilization since the animals’ remains were destined to be "rapidly burried in a protective medium" as the accumulating sediment had already reached the rim of the trunk and was in the process of filling it (Fig. 5D). The trunks of the larger trees are almost a metre in diameter near their base and the reptiles and amphibians found inside them are appreciably less than that in length.

One of the well known early reptiles from Joggins (Hylonomus lyelli) appears on one of Canada Post’s fossil stamps issues in the spring of 1992. Another animal which is known to have been relatively abundant at Joggins is Arthropleura – a very large myriapod which is perhaps best compared to a giant woodlouse or sowbug. These attained a length of about two metres and were obviously able to avoid being trapped in the tree trunks as they would not be so prone to toppling in to them as wou ld be the quadrupeds. Only fragments of their exoskeletons have been found at Joggins, but their abundance is indicated by the frequency of the discovery of their distinctive trackways on the surface of some of the sedimentary layers (see cover picture and Figure 8).

Joggins is a protected site

In 1972, a one mile (1.6 km) stretch of the Joggins "Fossil Cliffs" was designated as a protected site under the provisions of Nova Scotia’s Historical Objects Protection Act. In 1980 this act was repealed and superseded by the "Special Places’ Protection Act" which makes it illegal to collect fossils anywhere in Nova Scotia without a permit. For details of this legislation see Ferguson 1988a. Enquiries about collecting permits should be directed to the Nova Scotia Museum, 1747 Summer St., Halifax, N.S.

References

Carrol, R.L., 1964. The Earliest Reptiles. Journal Linnean Society (Zool.), v. 45, p. 61-83.

Dawson, J.W., 1854. On the coal Measures of the South Joggins, Nova Scotia. Quarterly Journal Geological Society of Canada, v. 10, p. 1-41.

Ferguson, L., 1966. The recovery of some large track-bearing slabs from Joggins, Nova Scotia. Maritime Sedimentsz, 2, 128-130.

Ferguson, L., 1986. The Joggins Section. In Boehner, R.C. et al. Carboniferous-Jurassic sedimentation and tectonics: Minas, Cumberland and Moncton basins, Nova Scotia and New Brunswick. Spec. Publ. Atlantic Geosci. Soc. 4, 73-83.

Ferguson, L., 1988a. The "Fossil Cliffs" at Joggins, Nova Scotia: A Canadian Case-Study. In the use and conservation of palaeontological sites. Palaeontological Assoc. Special Papers in Palaeontology, v. 40, 191-200.

Ferguson, L., 1988b. The Fossil Cliffs of Joggins, Peeper Books, Nova Scotia Museum, Halifax, Nova Scotia. 48 pp.

Gibling, M.R., 1987. A classic Carboniferous section; Joggins, Nova Scotia. In Geological Society of America Centennial Field Guide – Northeastern Section, 5, 88, 409-414.

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