Polystrate Fossils

A polystrate fossil is one crossing several rock layers — most often an upright tree trunk standing through a metre or more of strata. The term was coined by the creationist writer Nathaniel Rupke and is not used in geology, which calls them upright fossil trees or T⁰ assemblages.

The argument is that if a trunk spans multiple layers, those layers must have been deposited quickly, before the wood rotted. Otherwise the exposed portion would decay while waiting for the next layer.

The reasoning is sound. Individual sequences containing upright trunks were deposited rapidly, and geologists say so.

Where they occur#

They occur in a consistent set of environments: river deltas, coastal swamps, and volcanic settings. All are places where a metre or more of sediment can arrive quickly and where subsidence is ongoing.

Why rapid local burial is expected#

The environments in which upright trunks are found are precisely those with high sedimentation rates.

A delta receives sediment continuously and subsides under its own weight, so a tree growing on a delta plain can be buried by a single flood event depositing a metre or two of silt. Modern examples are documented: the Mississippi delta buries standing timber routinely, and volcanic mudflows at Mount St. Helens buried standing trunks in 1980.

Geologists reached this conclusion from the fossils themselves. Charles Lyell and William Dawson examined the Joggins trunks in 1852 and concluded that individual burials were rapid, while the section as a whole represented a long period of repeated cycles.

What the sections actually show#

The distinction that resolves the argument is between one trunk and the whole formation.

At Joggins the cliff section is roughly 915 metres thick and contains many separate horizons with upright trunks, stacked vertically. Each horizon represents a forest that grew, was buried, and was succeeded by another forest growing on top of the new surface.

Between the trunk horizons are:

• Coal seams, formed from accumulated peat requiring in-place plant growth
• Palaeosols with root systems still attached to the trunks above them
• Marine incursions with brackish and marine fossils

The trunks themselves span one to a few metres. None spans the full section, and none crosses a period boundary.

So the sequence is: forest grows, is buried rapidly, subsides, a new surface forms, a new forest grows. Repeated dozens of times. The rapid part is each burial; the slow part is the repetition.

The Joggins trunks are also rooted in place. Their root systems, Stigmaria, extend into the underlying palaeosol, which shows the trees grew where they stand rather than being transported and dropped.

Yellowstone#

The Specimen Ridge deposits were long described as 27 successive forests, each growing on the volcanic debris burying the previous one.

Later work complicated this. Some of the upright trunks were transported rather than in place, and the deposits resemble the Mount St. Helens mudflows, where floating trunks sank and settled upright in Spirit Lake. The number of distinct in-place forests is smaller than 27.

The revision came from mainstream research, and it is a case where a claim in the geological literature was corrected. Several trunk levels do remain rooted in place with soil horizons beneath.

Common objections#

"A tree standing through multiple layers proves rapid deposition"

Correct, and geologists agree. Each individual burial was rapid — a flood or mudflow depositing sediment in days to weeks.

The claim needed for flood geology is different: that the entire formation was deposited in one event.

The sections contain multiple stacked trunk horizons separated by coal seams and soils with roots in place. Each horizon requires a forest to have grown on a stable surface, which cannot happen during a continuous flood.

The trunks demonstrate rapid burial of individual sites, which is what they are cited for in the geological literature.

"The trunks would rot before the next layer arrived"

The premise behind the argument, and it is correct for a trunk left standing in air. Exposed wood decays within years to decades.

This is why the trunks indicate rapid burial, and geologists draw the same conclusion.

It constrains the burial of each trunk, not the interval between forests. Once a trunk is buried and the surface stabilises, the next forest grows on top of it, and the buried wood is protected from decay by waterlogged, oxygen-poor sediment — which is also why it becomes coal rather than disappearing.

The time between horizons is recorded by what lies between them: soil development, peat accumulation, and in places marine deposits.

"Spirit Lake shows floating logs settle upright and mimic forests"

An accurate observation, made by Steve Austin after the 1980 eruption. Logs floating in Spirit Lake became waterlogged at the root end, sank, and settled upright in lake sediment, producing what could later look like a buried forest.

The mechanism is real and it did prompt reinterpretation at Yellowstone, which is a genuine contribution.

It does not transfer to Joggins. Transported trunks lack root systems and are not attached to underlying soils; the Joggins trunks have Stigmaria root systems extending into palaeosols beneath them.

The Spirit Lake logs also settled at a single level, not in dozens of stacked horizons separated by coal seams.

"Coal seams can form rapidly too, so the interruptions are not long"

Rapid coal formation has been argued, including from experiments producing coal-like material from wood under heat and pressure in laboratory timescales.

Coalification — the chemical conversion — can indeed be fast under the right conditions.

The constraint is the peat, not the coalification. A coal seam requires an accumulation of plant material, and the seams at Joggins contain in-place root systems, upright stumps, and the plant structure of a swamp that grew where it lies.

Transported plant debris produces a different deposit, with sorted, fragmented, and abraded material rather than intact rooted stumps.

What the evidence shows#

Upright fossil trunks demonstrate that individual burial events were rapid, which is the standard geological interpretation and has been since the 1850s.

They do not show that whole formations were deposited in one event. The formations containing them have many stacked trunk horizons separated by coal seams, buried soils with attached root systems, and in some cases marine incursions.

The trunks span one to a few metres and do not cross the boundaries the argument would require.