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This Week in Research: Dr. Alessandro Ielpi’s research on geomorphology and sedimentary geology of rivers featured in the journal Nature Communications

This Week in Research: Dr. Alessandro Ielpi's recently published article in Nature Communications examines fluvial dynamics in Precambrian landscapes

Dr. Alessandro Ielpi, Assistant Professor of Sedimentology at the Harquail School of Earth Sciences, recently published a paper in Nature Communications. Nature Communications is part of the prestigious Nature Publishing Group, which aims to distribute impactful and open-access research in biology, physics, chemistry, and earth sciences.  What follows is a description and summary of the research Dr. Ielpi is conducting with regards to the geomorphology and sedimentary geology of rivers. He studies modern rivers through remote sensing, ground-penetrating radar, and of course field observations. He also studies sedimentary rocks originally deposited by ancient rivers, with the aim to reconstruct ancient fluvial dynamics from outcrop.

Dr. Ielpi specializes in Precambrian rivers, those that predated the evolution and expansion of land plants.Vegetation-devoid rivers of Precambrian vintage are currently receiving a wealth of renewed interest because of their potential parallels to barren extra-planetary fluvial landscapes such as those observed on Mars or Saturn’s moon Titan. To explore these potential parallels is at the core of Dr. Ielpi’s research motivation. State of art has been for more than 40 years that pre-vegetation rivers could not developed well-incised channels because of the lack of plant rooting along their banks. The objective of this paper is to test this assumption by collecting geometric data from ancient – yet entirely preserved – channel forms of Precambrian age. The research relies heavily on remote sensing, which proved critical for detecting channel forms too big to be resolved from ground observations only (several km wide, which are, incidentally, sizes comparable to the largest modern channels on Earth). Remotely sensed data was ground-checked at several field sites in Arctic Canada (Nunavut and NWT), and the highlands of Scotland. This research, stemmed from a collaboration with the Geological Survey of Canada and the Universities of Padua and Utrecht, was supported by the following agencies: 
- The Natural Sciences and Engineering Research Council (NSERC)
- The Geological Survey of Canada
- The Canada-Nunavut Geoscience Office (Nunavut's de facto geological survey)
- The Canadian Northern Economic Development Agency

Research Synopsis:
The study of fluvial networks observed on barren extraterrestrial bodies such as Mars and Saturn’s moon Titan recently boosted a great deal of interest regarding the dynamics of ancient fluvial channels active on early Earth, when vegetation had not yet evolved. This research discusses the shape and dynamics of rivers during the early span of Earth’s history, and appeals to geologists, geomorphologists, biologists, and also planetary scientists. Barren landscapes dominated the early Earth prior to 450 million years ago, and their rivers had no proven interaction with any macroscopic organism, including in the specific vegetation. It is a widely held view that, in a world devoid of vegetation, fluvial channels lacking rooted banks featured barely entrenched and shallow channels that promptly widened over floodplains in response to floods. Surprisingly, this hypothesis has never been tested because of an enduring lack of data on the geometry of very ancient fluvial channels (specifically, their depth and lateral extent).

In this article, a novel integration of remote sensing and outcrop sedimentology is employed, with the scope of detailing ancient preserved fluvial channels that are visible from satellite imagery but could not be resolved from ground observations alone. It is demonstrated that large and deeply channelled rivers were developed in the early Earth despite the lack of vegetation. The dataset presented in the study comprises 156 fluvial-channel forms from selected rock units exposed in the Canadian Arctic and the Scottish Highlands. These channel forms are dated from 1.9 to 1.0 billion years ago, and were originally deposited a few tens to thousands of kilometres from their headwaters. Most forms represent large channels, likely the record of fluvial networks that transected entirely ancient continental landmasses. The dimensions of the observed channels call for parallels with the largest rivers currently found on Earth, including the Amazon, Ganges, Brahmaputra, and Nile. The channel forms considered in the study consistently present width and depth ranges fully matching those of younger (post-vegetation) counterparts, and their sedimentology allows to infer patterns of discharge comparable to that of modern large rivers. This evidence suggests that the geometry of fluvial channels belonging to continental-scale networks might have remained within a narrow range over almost 2 billion years. These results allow us to conclude that closer parallels could and should be drawn between fluvial channels active in barren and vegetated landscapes.