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Layered limestone deposits give unique insight to Roman aqueducts

Layered limestone deposits give unique insight to Roman aqueducts
A field photograph of the Anio Novus aqueducts of ancient Rome. Credit: Bruce Fouke

Mineral-rich waters from the Apennine Mountains of Italy flowed through ancient Rome’s Anio Novus aqueduct and left out an in depth rock record of past hydraulic conditions, researchers have said. Two studies characterizing layered limestonecalled travertinedeposits within the Anio Novus will be the first to document the occurrence of anti-gravity growth ripples and establish these features lend clues to the annals of ancient water conveyance and storage systems.

These multidisciplinary studies, led by University of Illinois Urbana-Champaign geology professor Bruce Fouke and published in the journals Scientific Reports and GSA Special Papers, apply advanced engineering principles and high-resolution microscopy to determine a controversial new theory about how exactly the rippled travertine formed, Fouke said.

Because the watersourced from the Anio River and an underground lake near Subiaco, Italyflowed, it left out rippled layers of calcium carbonate travertine that accumulated across the inside floors, walls and ceilings of the Anio Novus aqueduct.

In the field, the researchers collected upstream-downstream oriented travertine samples that exhibit two standout features: millimeter-scale light and dark layering patterns, and centimeter-scale wavy ripple shapes persist throughout those layers.

Previous studies have proposed, without evidence, that the layers in the Anio Novus travertine will be the consequence of changes in flow rate initiated by seasonal change or engineering methods set up by the Romans, the researchers said. However, travertine with similar layering forms in ancient aqueduct systems occurs worldwide, no matter regional climate or operation.

Layered limestone deposits give unique insight to Roman aqueducts
A field photograph showing travertine crystal growth ripples on the vertical side wall of the Anio Novus aqueduct at Empiglione Bridge. Credit: Bruce Fouke

Fouke’s specialty is interpreting how microbes thriving in mineral-rich waters influence the crystalline architecture of travertine along with other similar calcium deposits in nature. His group spent some time working extensively to reveal the geologic history of layered mineral formationsyielding inferences alive on Mars via Yellowstone to coral reefs in Australiaand even in the body.

“The Subiaco waters are chemically like the waters of Yellowstone National Park, where waterborne microbes form mats and biofilms that play a crucial role in the form and structure of the famous stepped travertine top features of Mammoth Hot Springs,” Fouke said. “We’ve also identified fossil microbes and plant debris at night layers of the Anio Novus travertine deposits. After we realized the similarity between Subiaco and Yellowstone waters, we knew we’d the data base and experience necessary to start unraveling the annals and mystery of the final flow of the Anio Novus, the longest & most significant of the ancient Roman .”

Fouke and Marcelo Garciaa civil and environmental engineering professor at the U. of I. and study co-authorworked making use of their teams to meticulously gauge the geometry of the rippled layers of the Anio Novus travertines to create a unique interpretation.

“A geologist will let you know that the only path to create ripples is through fluid shear and gravity-dependent sediment transport,” Fouke said. “The idea is that water or wind can move loose sediment into wavelike shapes that slowly advance and so are influenced by gravity to create the familiar asymmetric ripple shapes we see along riverbanks, dunes and in the ancient deposited in these environments.”

However, Fouke’s team posits that the Anio Novus travertine crystals precipitated, grew and accumulated in the flowing water of the aqueductindependent of the forces of gravity and along with the shape and biochemical composition of microbial coloniesto form what they call “travertine crystal growth ripples.”

As the complex processes controlling travertine crystal growth ripples are distinctly not the same as those controlling sediment transport ripples, the researchers said they’re visually similar. The geometries of ripples across the vertical walls of the aqueduct are identical to those across the floorsevidence that the mechanisms that form crystal growth ripples aren’t influenced by gravity.

Convinced that the structures are ripple marks that reflect flow, Garcia and his team measured the ripple geometries to reconstruct the quantity and velocity of water flowing through the aqueduct during ancient Roman times.

“Since few researchers had ever recognized these structures as ripples before, no-one had used the energy of the form of a ripple, as well as fluid mechanics principles, to create this sort of reconstruction,” Garcia said.

Utilizing the travertine deposited in immediate connection with the initial aqueduct mortar, researchers conclude that whenever the aqueducts were first fired up, the water flowed through for a price around one meter per secondfast enough to flood a football field in a hourmuch faster than previously hypothesized.

The truth that rippled travertine exists across the ceilings of the aqueduct channels indicates they operated at capacity, the researchers said. This observation shows that previous studies were incorrect in stating that the layers formed because of seasonal flow change or when Romans used engineering methods to control the flow rate.

“These aqueducts were a lot more robust than ever before realized,” Fouke said. “The flow was higher than envisioned, and that rate of flow was constantly maintained.”

The researchers are actually extracting the ancient fossilized microbes and their biomolecules trapped in the travertine for more information about what sort of microbesand possible pathogensthe Romans were drinking.

“Historians and archeologists are keenly thinking about what resulted in nov the Roman Empire,” Fouke said. “Considering that the aqueducts played a significant role in the Romans’ success, any information gleaned from the aqueducts’ demise can be handy in this endeavor.”



More info: Duncan Keenan-Jones et al, Travertine crystal growth ripples record the hydraulic history of ancient Rome’s Anio Novus aqueduct, Scientific Reports (2022). DOI: 10.1038/s41598-022-05158-2

Mayandi Sivaguru et al, Depositional and diagenetic history of travertine deposited within the Anio Novus aqueduct of ancient Rome, GSA Special Papers (2022). DOI: 10.1130/2022.2557(26) pubs.geoscienceworld.org/gsa/b istory-of-travertine

Citation: Layered limestone deposits give unique insight to Roman aqueducts (2022, August 8) retrieved 9 August 2022 from https://phys.org/news/2022-08-layered-limestone-deposits-unique-insight.html

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