2018-03-01

New evidence for the Zanclean flooding of the Mediterranean Sea

[ICTJA-CSIC's Press Note on our own research (see open access article linked at the foot of this page)]

A study conducted by an international team of scientists has found new evidence supporting the hypothesis of a mega-flood occurring during the Zanclean period, in which water from the Atlantic poured back into the Mediterranean sea and ended the Messinian Salinity Crisis (MSC) 5 million years ago. The study, led by Professor Aaron Micallef from the University of Malta, has been published in the Scientific Reports journal.
Recreation of the evolution of the Messinian salinity crisis, between 6 and 5.3 milion years ago. This is one of the scenarios competing among the scientific community studying this period. Time scale (milion years per second) not to scale. [Credit: Univ. of Malta]

Using seismic profiles and borehole data from offshore eastern Sicily, researchers have identified a large body of sediments buried in the subsurface of Sicily Channel which are characterized as being "extensive" and "chaotic." They have named this mass of material Unit 2.

The study says that this huge mass of sediments is composed of materials eroded and transported by the great flow of water that flooded the Ionian Basin through the Strait of Sicily once the western basin of the Mediterranean was refilled with the contribution of water coming from the Atlantic Ocean that had poured in previously through the Strait of Gibraltar. This event is known as Zanclean megaflood.
Location and geometry of the "Unit 2" corresponding to the sediment body originated by the Zanclean megaflood. Source: Aaron Micallef (University of Malta)

The discovered sediments have been located over a layer of salts originated previously during the partial desiccation of the Mediterranean Sea during the MSC and under another layer of common marine sediments that were deposited after the flood and during the restoration of the normal marine conditions.

"The deposits identified in our study have little reflectivity of the seismic waves, they are seismically transparent, and present a disordered internal structure of the layers which is very similar to the sediments typically originated in catastrophic floods," explains Daniel García-Castellanos, co-author of the study and researcher from Barcelona's Institute of Earth Sciences Jaume Almera of the CSIC (ICTJA-CSIC).

The study indicates that the sedimentary body found next to the base of the Malta Escarpment, between the eastern and western Mediterranean Sea, is wedge-shaped, and its estimated thickness is up to 860 meters in some parts. According to the researchers, it would be the largest known megaflood deposit on Earth.

"According to the models of the paper that we published in Nature in 2009, the flood would have lasted only a few years, reaching discharges of up to 100 million cubic meters per second, about a rate thousand times the current flow of the Amazon River," adds García-Castellanos.

Researchers have also identified a spot in the channel of Sicily as the most likely gateway for the eastern Mediterranean Zanclean flood across the Malta escarpment, the submarine canyon of Noto (southeast Sicily). The authors of the study explain that this canyon has a unique morphology—its amphitheatre-shaped head is 6 km wide and is "similar to that of bedrock canyons rapidly eroded by megafloods. "The researchers interpret the Noto submarine canyon as the collector of the cascading flow into the Ionian Basin.

The study points to the abrupt and catastrophic nature of the environmental changes that occurred during the Messinian period, the most important since the dinosaurs' extinction 65 million years ago," says Daniel García-Castellanos.

The Messinian Salinity Crisis: an unrecognizable Mediterranean Sea
About 6 million years ago, the connection between the Atlantic Ocean and the Mediterranean Sea was interrupted. This event led to the partial desiccation of the Mediterranean Sea, which became a giant saline lake, with an estimated sea-level drawdown of 1300-2400 meters. This event is known as Messinian Salinity Crisis (MSC).

A major open question about this period is how normal marine conditions were restored. The hypothesis of the Zanclean megaflood proposes that there was a massive inflow of water through the Strait of Gibraltar that first flooded the western Mediterranean Basin. Then, through the Strait of Sicily, which was once the division between the eastern and western basins, flooded the Ionian Basin. Some studies indicate that this filling process lasted between a few months and two years.

Explore further: Mediterranean Sea filled in less than two years: study

Original article: 
Micallef, A., et al. (2018), Evidence of the Zanclean megaflood in the eastern Mediterranean Basin, Scientific Reports, 8(1), 1078, DOI: 10.1038/s41598-018-19446-3

2018-02-27

Nuevos indicios de la megainundación que puso fin a la Crisis salina del Messiniense en el Mediterráneo


(Basado en la nota de prensa de Jordi Cortés y ICTJA_CSIC)
En un nuevo estudio liderado por Aaron Micallef, de la Universidad de Malta, mostramos nuevas evidencias que apoyan la hipótesis sobre una megainundación que habría ocurrido al final del periodo Zancliense, implicando una entrada masiva de agua atlántica en la cuenca semidesecada del Mediterráneo, hace 5.3 millones de años y que puso fin a lo que se conoce como Crisis de Salinidad del Messiniense (CSM). El trabajo ha sido publicado en la revista Scientific Reports.
Gracias a los perfiles sísmicos y los testigos recuperados del fondo marino, hemos identificado en el subsuelo del canal de Sicilia una gran acumulación de sedimentos de carácter caótico y casi transparentes para las ondas sísmicas (Unidad 2 en la figura más abajo). Estos sedimentos estarían formados por los materiales erosionados y arrastrados por el inmenso flujo de agua que, a través del estrecho de Sicilia, inundó la cuenca Jónica una vez se hubo colmatado la cuenca occidental del Mediterráneo con el aporte de agua proveniente del océano Atlántico y que había entrado primero por el actual estrecho de Gibraltar.
Estos sedimentos se encuentran junto al escarpe submarino de Malta tiene forma de cuña y se le estima un grosor de hasta 860 metros en algunos puntos. Descansan encima de una capa de sales depositada con anterioridad durante la desecación parcial del mar Mediterráneo ocurrida durante la CSM y bajo otra de sedimentos de origen marino común depositados una vez se hubieron restablecido las condiciones oceánicas normales, durante el Plioceno. De confirmarse nuestra interpretación, se trataría de la mayor acumulación conocida de sedimentos originados por una mega inundación.
Hemos identificado también el lugar en el Estrecho de Sicilia por el que las aguas procedentes de la cuenca occidental del mar Mediterráneo podrían haber entrado en la cuenca Jónica durante la Mega Inundación Zancliense: el cañón submarino de Noto. Este cañón tiene una forma característica: su cabecera tiene forma de anfiteatro y una anchura cercana a los 6 kilómetros y “es similar a aquellos cañones erosionados rápidamente por mega inundaciones”. El cañón submarino de Noto podría haber actuado como el colector del inmenso flujo de agua que entró en la cuenca Mediterránea Oriental formando en este punto un salto de casi 1,5 kilómetros de altura.

Localización y estructura del cuerpo de sedimentos arrastrados por el flujo de agua de la mega inundación del periodo Zancliense (Imágen: A. Micallef et al., 2018, Sci. Reports)

Según estimaciones que publicamos en la revista Nature en 2009, la inundación del Mediterráneo habría tenido lugar en tan solo meses o unos pocos años, produciéndose descargas de hasta 100 millones de metros cúbicos por segundo, unas mil veces el caudal medio del Amazonas actual.
Nuestro trabajo vuelve a poner sobre la mesa el carácter abrupto y catastrófico de los cambios medioambientales ocurridos durante el periodo Messiniense, los más importantes ocurridos desde la desaparición de los dinosaurios hace 65 millones de años.
En el estudio, liderado por Aaron Micallef de la Universidad de Malta, han participado también Angelo Camerlengui, del Istituto Nazionale di Oceanografia e di Geofisica Sperimentale de Trieste (OGS), e investigadores del Laboratoire Geosciences Océan de la Universidad de Brest y el CNRS, de la Universidad de Catania, del Institute für Geowissenshaften de la Universidad Christian-Albrechts de Kiel y del GEOMAR Helmholtz Centre for Ocean Research de Kiel, además del ICTJA-CSIC (Barcelona).
La Crisis de Salinidad del Messiniense: un Mediterráneo irreconocible
Según una de las hipótesis más aceptadas, hace unos 5.5 millones de años, se cerró la conexión entre el océano Atlántico y el mar Mediterráneo y se produjo la desecación parcial del Mar Mediterráneo debido a su baja precipitación y alta evaporación. La cuenca mediterránea quedó convertida en una inmensa laguna hipersalina y sufrió un descenso del nivel de las aguas de entre 1300-2400 metros, según parte de la comunidad científica especializada en este fenómeno. Es lo que se conoce como Crisis de Salinidad del Messiniense (CMS).
Una de las grandes cuestiones sobre este periodo para los investigadores es determinar cómo las aguas recuperaron su nivel. La hipótesis de la mega inundación del Zancliense propone que se habría producido una entrada de agua masiva a través del estrecho de Gibraltar que habría inundado primero la cuenca occidental y luego, a través del estrecho de Sicilia, habría rellenado la cuenca oriental. 

Artículo científico original (open access):

Micallef, A., et al. (2018), Evidence of the Zanclean megaflood in the eastern Mediterranean BasinScientific Reports, 8(1), 1078, doi: 10.1038/s41598-018-19446-3.

2017-09-26

Did the evaporation of the Mediterranean trigger widespread volcanism?


Artistic interpretation of the proposed lowstand
of the Mediterranean level during the salinity
crisis. Authors: Pibernat and Garcia-Castellanos
130 years have gone by since the scientific recognition of a hypersaline Mediterranean sea around 6 million years ago;
50 years have passed since documenting widespread submarine and riverine erosional features that suggest a subaerial exposure of parts of the Mediterranean Sea;
We are 40 years after the first abissal drilling reaching the top of a salt layer thicker than 1 kilometer...

And yet, the most intriguing and debated question around the Messinian salinity crisis remains whether there was a large sea level fall during the crisis, more than a few hundreds of meters, perhaps more than a kilometer. Evidence in favor and against is piling up on the desks of geoscientists. 

We now publish a new piece of evidence that supports a Yes answer to this long-standing question. A fall in the level of the Mediterranean Sea about 6 million years ago may have increased volcanic activity over the entire region (Sternai et al., 2017, Nature Geosc.).

Geoscientists inspecting the Realmonte mine in Sicily,
where Messinian salt is commercialized. 
A layer ranging from 1 to 2 km of salt (halite) spreads below much of the Mediterranean seabed, formed when the Mediterranean Sea became isolated from the Atlantic Ocean about 6.0 to 5.3 million years ago, leading to evaporation and sea-level fall in an event known as the Messinian salinity crisis. The rate and amount of sea-level fall in the Mediterranean during this time is strongly debated. However, if the sea-level drop was dramatic and rapid, it could have unloaded the Earth’s surface, decompressing the mantle below. Such mantle decompression can enhance magma production and, in turn, lead to more frequent volcanic eruptions at the surface.

Pietro Sternai and the rest of us test this idea using a combination of geological data and numerical modelling. Dated magma intrusions and volcanic eruptions in the region show that there was a pulse of increased volcanic activity towards the end of the Messinian salinity crisis. By calculating changes in the surface load caused by a kilometre-scale drop in sea level, and taking into account the counter weight of the increased density of the remaining highly saline water and accumulating salt deposits we verify that such changes in sea level are sufficient to unload and decompress the mantle, triggering a significant increase in volcanism over the Mediterranean.
Decompression and vertical rebound of the lithosphere
in response to a sudden evaporation of the sea. 

The results provide independent support for the idea that sea-level fall during the Messinian salinity crisis was rapid and occurred on a dramatic scale, and also highlights the sensitivity of Earth’s solid interior to changes at the surface.

Check also the News & Views article by Jean-Arthur Olive: “This proposed link will motivate the collection of high-resolution field data that better constrain the timing of volcanism in the Mediterranean, along with the development of novel approaches for coupled lithosphere–magma dynamics.”

Original paper:
Sternai et al, 2017, Nature Geosc. http://dx.doi.org/10.1038/ngeo3032








2016-10-04

Tomanowos - the rock that went through cosmic billiard, megafloods, and idiocy

Present display of the meteorite at the at the at the AMNH. My photo.
Last week I faced the rock with the most fascinating story on Earth: 
Tomanowos, meaning the visitor from the sky in the extinct Clackamas language, also known as the Willamette meteorite. 
Supernovas spread throughout space the
iron produced in heavy stars. This ejected iron
ends up in particle nebulas that eventually form
new stars and protoplanets. [Image: NASA] 

After being seen by european americans near Portland, more than a hundred years ago, Tomanowos inevitably went through one of the most hilarious and silly geological stories that I know of, surely driven by the fatal attraction that a weird rock like this irradiates on humans. But before going to that: what do we know about this weirdness?

Tomanowos is a rare 15,500-kg meteorite made of iron and nickel (Fe 91%, Ni 7.6%). As in other metal meteorites, these Fe and Ni atoms formed at the core of stars that shattered the space with the sub-products of nuclear fusion when ending their lives as supernovae. Such space bodies eventually formed the nebula that clumped together as protoplanets in the Solar System, and Tomanowos was part of the core of one of these protoplanets, where the heavier metals accumulate. 


Vesta, a surviving protoplanet of the 
early Solar System. Due to their large
 size, protoplanets develop a differenciated 
density distribution with heavier elements like 
iron concentrated in the core. Tomanowos is an 
ejected piece of a protoplanet core like this. 
[EPFL/Jamani Caillet, Harold Clenet]
Then, a collision 4 billion years ago between two of those protoplanets sent our museum piece back to space solitude. Subsequent impacts over billions of years made the orbit of the meteorite eventually go across that of the Earth. As a result of this cosmic billiard, about 20,000 years ago, the meteorite entered our atmosphere at a speed of ~60,000 km per hour and landed on an ice cap in Canada.

Over the following decades, the ice flow slowly brought Tomanowos southwards, towards a glacier lobe that was at the time blocking the Fork River in Montana. The glacial tongue piled ice across the river valley forming a 600-m barrier that impounded the enormous Lake Missoula behind. Tomanowos happened to reach the ice dam on the precise year when it collapsed, releasing one of the largest floods ever documented: the #MissoulaFloods that shaped the Scablands in Washington. This process is known as glacial outburst flooding and it still happens every few years in the Perito Moreno glaciar, for example. Except that the water discharge during the Missoula Floods reached the equivalent to a few thousand Niagara Falls. The research of the Missoula floods by Bretz and Pardee in the early 20th century led to one of the most significant paradigm shifts in recent geoscience: the recognition that catastrophic events can significantly contribute to landscape evolution.
Map of the Missoula Floods path, showing Lake Missoula 
(blue), the ice cap where Tomanowos landed (north of the 
lake outlet), and the inundated areas of Washington and 
Oregon (grey).
Source: Washington Univ.

Trapped in ice and rafted down by the flood, Tomanowos crossed Idaho, Washington and Oregon along the overflown Columbia River at speeds sometimes faster than 20 meters per second. While floating up on the flood waters near today's Portland, the ice case broke apart and the meteorite sunk in the flooding waters. Hundreds of other ice-rafted erratics (rocks that do not match the local geology, nor could be transported by rivers or glaciers) have been found along the Columbia River. All are souvenirs from the Missoula floods.

As the flood ceased, the sunk meteorite became exposed to the atmosphere. Over thousands of years, rain mixed with the iron sulfide inclusions producing sulfuric acid that gradually dissolved the iron of the exposed side of the rock:
These cavities were produced by acid dissolution of iron at the exposed side.
A few thousand years after the flood, the Clackamas arrived to Oregon and named the meteorite as the Visitor of the Sky, a heaven's representative that unified earth, water & sky. Did they know that nickel rocks come from heaven? Were they intrigued by the absence of a crater at the Meteorite site? In any case, the name reminds us that pre-scientific cultures were not idiotic, or not more than us today anyway.

To confirm this latter hypothesis, in 1902 a colonist named Ellis Hughes decided to literally move the iron rock to his own land and claim property. Millennia of peaceful rest in the Willamette had to come to an end. But since moving a 15-ton rock a distance of 1,200 m without being noticed is not easy, not even in Oregon, Hughes and his son labored for three back-breaking months in secrecy: 

As D. J. Preston hilariously explains, after finally
succeeding with the moving, Hughes built a shack around
the meteorite, announced he had found it on his property
and started charging twenty-five cents admission to view
the heavenly visitor.
It was during this transport that the rock sadly underwent severe mutilations.
Unimpressed by this deployment of idiocy, Hughes' neighbor fabricated a lawsuit contending that the meteorite had, in fact, landed on HIS property. And to buttress his case he showed investigators a huge crater on his land. The case was dismissed when a third neighbor reported a great deal of blasting only the week before.

Ironically, the legitimate owner of the original land of the iron meteorite turned out to be the Oregon Iron and Steel Company, which was unaware of the meteorite but soon hired a twenty-four-hour guard who sat on top with a loaded gun while the case was being appealed. They won in 1905 and sold Tomanowos to the AMNH museum in New York, a year later.
Tomanowos in the early 1900s, before being transported to the AMNH.

Today, amazingly enough, the @AMNH exhibition does not even mention the Missoula Floods as a key part of Tomanowos' story, in spite of the wide scientific consensus. But the descendants of the Clackamas still keep the right to visit the meteorite and talk to the visitor who brought the Sky, the Water, and the Earth together. 

2016-04-27

Glacier retreat in southern Iceland

Looking at old pictures, I realise that I had a first-hand glance at the retreat of the Jökulsárlón glacier (S. Iceland) back in 2013. I took these two pictures from the same spot with an 18-years time lag. Although the first one is taken in August and accordingly shows less snow in the background mountains than the more recent one, the latter does show the glacier front retreated by about 3 km. I pasted the Landsat images for comparison.


Not that this is a surprise, really: 
But i had to share.
In the meanwhile, I found this other JAXA (Japan) link as well. 

2016-02-24

Extreme Geodynamics at the Tsangpo Gorge

If you aim at understanding what shapes the surface of the Earth, the Tsangpo Gorge (Eastern syntax of the Himalayas) will inevitably become one of your favorite places.

This is the place where bedrock is
being eroded at the fastest
measured rate of nearly 1 mm/yr.
The uncommonly vertical valley
walls adopt this high angle to cope
by landsliding with the incision rates
produced by water. 
This is the place on Earth where one of the the highest bedrock erosion rates, the fastest tectonic uplift, and some of the highest topographic gradients have been measured. Every year, nearly 1 cm of very hard metamorphic rock is dig by the Tsangpo River, which descends from an elevation of >3000 m near the Tibetan plateau, to a mere 1000 m in less than 100 km. An average water discharge above 1400 m3/s, together with the pronounced slope, implies a huge erosion power.
Upstream from this gorge, there are widespread terraces and shore sediments of a lake that used to cover a few hundred kilometers of the river valley and impounded up to 800 km3 of water in a lake. What caused this impoundment is a matter of discussion: Only the tectonic uplift along the gorge? Or also an increase in landsliding from the valley flanks during the Pleistocene? Or glacial moraine accumulations?
The long duration of this competition between uplift and erosion (at least 10 Myr) implies that the region must be approximately in equilibrium, so uplift rates are presumably in the range of a cm per year, only comparable to the post-glacial isostatic rebound of Scandinavia.


A recent study of the infill of those lake sediments concludes that the steepening of the Tsangpo Gorge started about 2 to 2.5 million years ago as a consequence of a faster rock uplift: 
(A) Longitudinal river profile of the Tsangpo River, location of drill cores with observed depth to bedrock (vertical black bars), estimated depth to bedrock (yellow area), and reconstructed valley bottom before uplift of Tsangpo Gorge (dashed line). (B) Hillslope angles at the river flanks, specific stream power, and landslide erosion rates. (C) Erosion rates of close to 10 mm/yr are reflected in the age at which the minerals cooled down while being exhumed towards the surface. From Wang et al., 2014, Science. 
The extreme uplift and exhumation rates have been linked to a feedback effect of erosion on channelizing crustal rock towards the surface (the so called tectonic aneurysm; Montgomery & Stolar, 2006).

In contrast, other studies favor the role of glacial transport from the high surrounding mountains near the gorge in blocking the river with glacial moraines. This may have triggered megafloods sourced at impoundments formed by glacial dams (Lang et al., 2013, Geology), since some of the largest known outburst floods in the world have also been reported here.

Tsangpo Gorge
Hence, the competition between tectonic uplift and erosion at the Tsangpo encompasses many of the big conundrums in present geomorphology and geodynamics: the importance of episodicity in landscape evolution, the implications of the glacial ages on erosion rates, the possible effects of climate on tectonic deformation...