A Pleistocene Quaternary Petrified Forest From Olduvai Gorge, Tanzania

In situ ∼2.0 Ma trees discovered as fossil rooted stumps, lowermost Bed I, Olduvai Gorge, Tanzania

Authors:

Habermann et al

Abstract:

The discovery of fossil rooted tree stumps in lowermost Lower Bed I from the western Olduvai Basin, Tanzania, age-bracketed by the Naabi Ignimbrite (2.038 ± 0.005 Ma) and Tuff IA (1.88 ± 0.05 Ma), provides the first direct, in situ, and to date oldest evidence of living trees at Olduvai Gorge. The tree relicts occur in an interval dominated by low-viscosity mass flow and braided fluvial sediments, deposited at the toe of a largely Ngorongoro Volcano-sourced volcaniclastic fan apron that comprised a widely spaced network of ephemeral braided streams draining northward into the Olduvai Basin. Preservation of the trees occurred through their engulfment by mass flows, post-mortem mold formation resulting from differential decay of woody tissues, and subsequent fluvially-related sediment infill, calcite precipitation, and cast formation. Rhizolith preservation was triggered by the interaction of root-induced organic and inorganic processes to form rhizocretionary calcareous root casts. Phytolith analyses were carried out to complete the paleoenvironmental reconstruction. They imply a pronounced seasonality and indicate a wooded landscape with grasses, shrubs, and sedges growing nearby, comparable to the low, open riverine woodland (unit 4c) along the Garusi River and tributaries in the Laetoli area. Among the tree stump cluster were found outsized lithic clasts and those consisting of quartzite were identified as Oldowan stone tool artifacts. In the context of hominin activity, the identification of wooded grassland in association with nearby freshwater drainages and Oldowan artifacts significantly extends our paleoenvironmental purview on the basal parts of Lower Bed I, and highlights the hitherto underrated role of the yet poorly explored western Olduvai Gorge area as a potential ecologically attractive setting and habitat for early hominins.

The Frasnian Devonian Tropical Forest Found in Svalbard, Norway

UK researchers have unearthed ancient fossil forests, thought to be partly responsible for one of the most dramatic shifts in the Earth's climate in the past 400 million years.

The fossil forests, with tree stumps preserved in place, were found in Svalbard, a Norwegian archipelago situated in the Arctic Ocean. They were identified and described by Dr Chris Berry of Cardiff University's School of Earth and Ocean Science.

Prof John Marshall, of Southampton University, has accurately dated the forests to 380 million years.

The forests grew near the equator during the late Devonian period, and could provide an insight into the cause of a 15-fold reduction in levels of carbon dioxide (CO2) in the atmosphere around that time.

Current theories suggest that during the Devonian period (420-360 million years ago) there was a huge drop in the level of CO2 in the atmosphere, thought to be largely caused by a change in vegetation from diminutive plants to the first large forest trees.

Forests pulled CO2 out of the air through photosynthesis - the process by which plants create food and tissues - and the formation of soils.

Although initially the appearance of large trees absorbed more of the sun's radiation, eventually temperatures on Earth also dropped dramatically to levels very similar to those experienced today because of the reduction in atmospheric CO2.

Because of the high temperatures and large amount of rainfall on the equator, it is likely that equatorial forests contributed most to the drawdown of CO2. Svalbard was located on the equator around this time, before the tectonic plate drifted north by around 80° to its current position in the Arctic Ocean.

"These fossil forests shows us what the vegetation and landscape were like on the equator 380 million years ago, as the first trees were beginning to appear on the Earth," said Dr Berry.

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Will Drilling Project in Petrified Forst Settle Long Norian "Dispute?"

Tourists flock to Petrified Forest National Park in Arizona to marvel at great glittering logs of petrified wood. But geologists hope to flock there this month in search of something less visible and more scientifically significant: a core obtained by drilling half a kilometre into rock more than 200 million years old.

Drillers will spend several weeks boring through layers of rock that house the fossils of tiny early dinosaurs and giant crocodile-like phytosaurs, as well as the leaves and pollen of an entire fossilized ecosystem. The goal of the US$970,000 drilling project is to stitch together a complete picture of most of the middle and late Triassic period, a turbulent interval that saw both a mass-extinction event and the emergence of dinosaurs. Geoscientists hope to use the decay of radioactive uranium in layers of volcanic ash in the core to precisely date events between about 205 million and 235 million years ago, just before the supercontinent Pangaea began to break apart.

“It’s a unique opportunity to put together a coherent time framework for a critical part of the Triassic,” says John Geissman, a geologist at the University of Texas at Dallas and one of the project’s leaders. “Sure, we have other continental Triassic records, but the Petrified Forest area is pretty darn good when it comes to details.”

The Petrified Forest effort has been years in the making. It is a follow-up to a project in which a Triassic core was drilled from New Jersey’s Newark sediment basin between 1990 and 1993 (ref. 1). That project aimed to tease out changes in the amount of sediment that was deposited as Earth went through cyclical shifts in the shape of its orbital path around the Sun. “If we can show that the Newark timescale is correct, we can empirically calibrate the Solar System’s behaviour,” says Paul Olsen, a geologist at the Lamont–Doherty Earth Observatory in Palisades, New York, and a member of the project team. “That’s probably the most exciting aspect for me.”

The effort, funded by the US National Science Foundation and the International Continental Scientific Drilling Program, might also help to resolve a simmering dispute. Comparisons of the Newark data with data from Triassic rocks in the Mediterranean have led some researchers to suggest radically revising the period’s history. This reworking would lead to one subdivision — the Norian stage — taking up nearly half of the entire Triassic period, drastically changing dates of key evolutionary events, including the emergence of certain dinosaurs.

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