Erosion of the Geodetic Hills Fossil Forest, Axel Heiberg Island, Northwest Territories
Summary (2 min read)
INTRODUCTION
- The discovery in August 1985 of the fossil forest at Geodetic Hills on Axel Heiberg Island, 79˚55'N, 89˚02'W, (Fig. 1) sparked much academic and popular interest not only because of its large size, but also because of the remarkable nature of the fossils preserved there.
- Fossil forests have been defined as “groups of preserved tree stumps found generally in growth Many of the initial specimens recovered for the museum— which included a tree stump, cones, and sections of leaf mat—were very fragile, and some tended to disintegrate after removal from their arctic environment to the laboratory.
- For these reasons, the Canadian Conservation Institute, (CCI) was invited to become involved in the project.
- For six years, the authors have studied the effect of the natural environment, as well as the impact of people.
- This includes photography and mapping of stumps and logs, aerial photography, and monitoring of erosion markers placed in sensitive locations.
THE FOSSIL FOREST SITE
- Many large tree stumps project from the ground, and several periods of forest growth are evident in forest litter containing strata interspersed with sands and silt deposits (Francis and McMillan, 1987; Francis, 1991; Ricketts, 1991).
- The site is remarkable for the unusual condition of the specimens that are commonly described as “mummified”: the majority of the fossil leaves, trees, cones, etc. are not mineralized (i.e., there has been negligible mineral replacement of the vegetable tissue) and coalification has occurred only to a limited extent.
- The site, which is the only one of its type in Canada, can be regarded in many ways.
- Much of the cellulose fraction (the main component of fresh wood) is missing, and the molecular weight of what remains is less than one-tenth that of fresh wood (Grattan, 1991).
EROSION
- The sedimentary deposits in which the forest is found are very poorly consolidated when unfrozen, a situation that favours rapid erosion in the harsh northern environment, “a terrain in which disintegration is at a maximum and decomposition at a minimum” (Ray, 1951:200).
- Wind causes direct erosion or ablation of the site as is seen in Fig. 2, which shows dust being lifted hundreds of meters into the air (and also the scalloped shape of the west end of the Hill) during a severe windstorm in 1988.
- This much-studied phenomenon is caused by the formation of cracks, which are evident at the edges of polygons.
- At ground level, moisture content changed very abruptly from ca. 37% to 8% in partially buried wood.
- These observations explain why buried fossil wood remains intact and does not fragment, but exposed wood fragments, delaminates and warps.
Erosion Markers
- Two types of markers were placed in July 1988: these were termed “floating” and “permanent” (Fig. 6).
- Usually this left about 0.3 m projecting above ground.
- Placed at known distances from the fixed markers, these floating markers consist of 15 cm2 marine plywood sections with 0.3 m × 10 mm dowels driven through the centre at right angles.
- Four sets of markers in arrays were placed in different areas of the hill (Fig. 7).
- All distances between markers were measured by steel tape held parallel to the ground surface.
Ground Survey
- Several reference points (also known as “trig. points”) were established on the high spots overlooking stump exposures on Fossil Forest Hill and on the hills to the south and east.
- For charting stumps and logs, a theodolite (1989, 1992 surveys) or alidade and plane table (1988 survey) was established at each reference point overlooking exposures.
- The software allows maps of any scale to be drawn, and also permits the selection of any specific area for enlargement.
- In 1988 a plane table/alidade survey of the upper exposure at the east end of Fossil Forest Hill was completed.
Erosion
- None of the permanent markers, which are spaced at 10 m intervals, moved in relation to one another (within ca. 0.01 m).
- At certain locations, particularly in flatter regions, accretion (i.e., accumulation of wind-blown sand) also occurs.
- This proved very unreliable, as the data had to be corrected because of errors in the readings from the device.
- In the A range at the east end of the Hill, where an extended array of floating markers goes into a steeply declining and totally unconsolidated slope, average total movement was 33 cm by 1992.
CONCLUSIONS
- The site is eroding, at least 3 mm per year on average, with erosion of slopes occurring more rapidly, particularly on the north side of the Hill, and much less erosion in the flatter regions.
- The authors believe that scientists must continue to investigate the site, and that visitors ought to have access to see it.
- While there may be some validity in these arguments, their observations show that exposed stumps deteriorate faster than those which are covered up.
- It is worth emphasising that wood shrinks regardless of the method of drying, and it is their observation that the fossil wood, having lost its elasticity, has very limited tolerance for dimensional change.
- The authors have tried to record the site and changes in it by both ground survey and aerial photography.
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Citations
82 citations
Cites background from "Erosion of the Geodetic Hills Fossi..."
...The modern rate of surface erosion from these unconsolidated sediments is high, averaging a minimum of 3 mm per year (Bigras et al. 1995)....
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39 citations
22 citations
Cites background from "Erosion of the Geodetic Hills Fossi..."
...Although long-term climatic data are not available at these sites specifically, Bigras et al. (1995) report a mean annual temperature for the Expedition Fjord region of approximately 15 C and total annual precipitation of< 100 mm. Site TL1 (75 21’26.8"N 88 40’47.2"W) is located near Thomas Lee…...
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2 citations
Cites background from "Erosion of the Geodetic Hills Fossi..."
...Dunarobba is one of the few sites in the world yielding mummified and upright fossil forests, including (regardless to age) Axel Heiberg Island, in the Arctic region of Canada (45-40 Ma: Bigras et al., 1995; Williams et al., 2008), the Bukkabrany swamp cypress forest in Hungary (7.7-6.3 Ma: Kàzmér, 2008; Csaszar et al., 2009; Erdei et al., 2009; Gryc & Sakala, 2010; Erdei & Magyari, 2011), and the Stura di Lanzo Fossil Forest, in NW Italy (~3.0 Ma: Martinetto et al., 2007; Vassio et al., 2008)....
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...…world yielding mummified and upright fossil forests, including (regardless to age) Axel Heiberg Island, in the Arctic region of Canada (45-40 Ma: Bigras et al., 1995; Williams et al., 2008), the Bukkabrany swamp cypress forest in Hungary (7.7-6.3 Ma: Kàzmér, 2008; Csaszar et al., 2009; Erdei et…...
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...On the bases of ostracofauna, Spadi (2018) and Spadi et al. (2018b) proposed deposits of the Fossil Forest area are almost coeval to the Ponte Naja Unit (2.2-2.0 Ma: Abbazzi et al., 1997; Pontini et al., 2002)....
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1 citations
Cites background from "Erosion of the Geodetic Hills Fossi..."
...Erosion by wind and mass wasting has been measured at 0.3 cm yr 1 in flat areas and up to 11 cm yr 1 in steeper areas (Bigras et al., 1995)....
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References
123 citations
103 citations
"Erosion of the Geodetic Hills Fossi..." refers background in this paper
...Since 1987, work has continued on the identification and analysis of fossil specimens (Basinger, 1991; Lepage, 1993)....
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...From the species distribution, it is possible to reconstruct the forests which grew on this site (Francis and McMillan, 1987; Basinger, 1991; Francis, 1991; McIntyre, 1991; Lepage, 1993)....
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61 citations
"Erosion of the Geodetic Hills Fossi..." refers background in this paper
...From the species distribution, it is possible to reconstruct the forests which grew on this site (Francis and McMillan, 1987; Basinger, 1991; Francis, 1991; McIntyre, 1991; Lepage, 1993)....
[...]
60 citations
55 citations
"Erosion of the Geodetic Hills Fossi..." refers background in this paper
...Many large tree stumps project from the ground, and several periods of forest growth are evident in forest litter containing strata interspersed with sands and silt deposits (Francis and McMillan, 1987; Francis, 1991; Ricketts, 1991)....
[...]
...From the species distribution, it is possible to reconstruct the forests which grew on this site (Francis and McMillan, 1987; Basinger, 1991; Francis, 1991; McIntyre, 1991; Lepage, 1993)....
[...]