Stratigraphy, Sedimentology and Palaeontology

Imaggeo on Mondays: Escullos

Imaggeo on Mondays: Escullos

This picture shows a Quaternary aeolianite fossil dune at the Escullos beach, in the Nature Reserve of Cabo de Gata (Almeria, Spain). Originally a soft accumulation of sand grains, shaped by the wind into large mounds and ridges, the dunes eventually turn into rock. As the sediments compact under their own pressure and expel any moisture and fluids retained within them, they become lithified and become the structure seen in this week’s Imaggeo image. This particular example is a richly fossilifeorous and contains abundant cidaroid spines. Cidaroids are primitive forms of sea urchins, but unlike the more familiar, well rounded spike covered sea hedgehogs, their spikes are much more separated and sparse.

A present day cidaroid. Note the sparse and relatively flat spines. Credit, Alicia Morugán.

A present day cidaroid. Note the sparse and relatively flat spines. Credit, Alicia Morugán.

Almeria is the eastern most province of Andalucia, located in South East Spain. Almeria province is geologically very interesting as the relationships between tectonics, sedimentary geology and geomorphology are evident throughout the landscape. The province lies within the Baetic Cordillera, an Alpine mountain chain resulting from the collision of the micro-Iberian and African plate from Late Mesozoic to Middle Cenozoic times. This characteristic makes it very tectonically active. Furthermore, Almeria province has the driest climate in Europe, resulting in mean annual precipitation of less than 300 mm. In terms of geomorphology, quaternary alluvial fans are the most common structure in the region. Geologically speaking, aeolianite rocks are the most common rock in the region. A final thanks: thanks Maria Burguet for support editing the picture.

By Alicia Morugán, Universitat de València, València, Spain

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at

Imaggeo on Mondays: Painted Hills after the storm.

The geological record preserved at John Day Fossil beds, in Oregon, USA, is very special. Rarely can you study a continuous succession through changing climates quite like you can at this National Park in the USA. It is a treasure trove of some 60,000 plant and animal fossil specimens that were preserved over a period of 40 million years during the Cenozoic era (which began 66 million years ago).

The geography of Oregon 45 million years ago was significantly different to present. The region received a whopping 1350 mm of annual rainfall (compare this to the approximate annual rainfall in London of 500 mm or 300 mm in Madrid) as the Cascades Mountain range had not yet formed, meaning moisture from the Pacific was not blocked. In addition, the climate was much warmer and Oregon was primarily subtropical, dominated by broad-leaved evergreen subtropical forests.

Then, 12 million years later temperatures began to lower and the climate changed from subtropical to temperate. Deciduous forests became abundant at low altitudes, whilst at higher altitudes coniferous forests dominated the landscape. Imagine a setting not dissimilar to the present day eastern USA. There were a number of active volcanic centres in the area at the time and ash, lava, and volcanic mudflows frequently spread over the region. The volcanicity culminated over a period of 11 million years during which the Columbia River Basalt Group, an extensive large igneous province, was emplaced. The current landscape was shaped during the most recent Ice Age as glaciers from the Cascade Mountains eroded their way towards the low lying terrain in central Oregon.

Painted Hills. (Credit: Daniele Penna, via

Painted Hills. (Credit: Daniele Penna, via

Photographs don’t really come any more dramatic than this one. “The conditions were prefect; I was very lucky”, says Daniele Penna, who photographed the striking Painted Hills Unit within the National Park , “I visited the area right after a storm, when the sky was partially clearing, leaving space for some light that contrasted with the remaining dark clouds in the background. The combination of atmospheric conditions made me enjoy this stunning place even more and gave me the opportunity to capture several striking images.”

During his PhD in hydrology, Daniele spent a few months at the Oregon State University, in 2007. He took the advantage of his time there by exploring the diverse natural beauties that Oregon boasts.

If, like Daniele, you are interested in photography he has some top tips for achieving a photograph as remarkable as this week’s Imaggeo On Mondays image: “Switching from a wide angle to a moderate telephoto lens can give free rein to the photographer’s creativity in playing with the colors, juxtaposed intersecting lines and interlacing forms. An extremely vivid image emerges as a result of the contrast of light and dark, yellow and red colours, and the contrasting curved and straight lines at Painted Hills. The best time for capturing images that make an impact is reserved for the late afternoon in summer and during late spring when the local park ranger service provides information over the telephone on which species are in bloom.”

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

The known unknowns: Climate, Life, and the Solid Earth (Part V)

After four fascinating instalments in the known unknowns series we have (sadly) come to the final post. Since the series began in September we have explored the top questions that still remain unanswered when it comes to understanding the inner workings of the planet as well as how the interplay of a number of systems that occur at the Earth’s surface give rise to its varied landscapes. The series would not be complete without assessing the open questions on how climate and life have contributed to shape the planet and so it seems fitting that we should end the series with this topic. The geological record shows that climate is relatively stable over tectonic time-scales whereas it undergoes abrupt changes in periods ranging from decades to hundreds of thousand years. Past periods when the planet underwent extreme climate conditions may help to understand the mechanisms behind that behaviour and its significance for the evolution of the Solid Earth and for the current climate change challenge. However, we are still a long way from having all the answers…

65 Myr Climate Change (Image Source: Wikimediacommons; Image credit: Robert A. Rohde published as part of the Global Warming Art project)

Image Source: Wikimediacommons; Image credit: Robert A. Rohde published as part of the Global Warming Art project)

  1. What caused the largest carbon isotope changes in Earth? (Grotzinger et al., Nat. Geosc, 2011) How does Earth’s climate respond to elevated levels of atmospheric CO2?
  2. Was there ever a snow-ball Earth during the earliest stages of Life on Earth? 
  3. Were there also rivers and lakes on Mars? (Hand,Nature, 2012) Were there large outburst floods similar to those on Earth?
  4. What were the causes and what shaped the recovery from mass extinctions as those at the K-T boundary, the Permian-Triassic or the Late Triassic? Massive volcanism? Meteorites? Microbes? Some recent papers: (Rampino & Kaiho, Geology, 2012;  Lindström et al., Geology, 2012; Chen & Benton, Nat. GeoSci, 2012; Rothman et al.,PNAS, 2014).
  5. What triggered the extreme climatic variability during the Quaternary and the roughly coeval acceleration in continental erosion and sediment delivery to the margins? [Peizhen, Molnar et al., Nature, 2001; Herman et al., Nature, 2013) Was this related to the tectonic closure of the Central American Seaway? How do these climate events translate quantitatively into sea level changes?
  6. How do climate changes translate quantitatively into sea level changes? How do ice sheets and sea level respond to a warming climate? What controls regional patterns of precipitation, such as those associated with monsoons or El Niño?
  7. What caused the Quaternary extinction(s)? Human expansion? Climate Change? How sensitive are ecosystems and biodiversity to environmental change? Was the large fauna extinction ~13,000 yr ago a result of the Younger Dryas climatic event? Was this caused by an extraterrestrial impact? (see this article and this other article) Or may it be linked to the outburst of Lake Agassiz?
  8. How relevant are subsurface microorganisms to earth dynamics by controlling soil formation and the methane cycle? What are the origin, composition, and global significance of deep subseafloor communities? What are the limits of life in the subseafloor realm?
  9. The atmosphere is shaped by the presence of life, a powerful chemical force. The Earth’s evolution has seems to affect the evolution of life (see the Cambrian explosion of animal life, for instance; plus this recent paper on that). To what extent? And how much control has life on climate? (another recent paper). Is it possible to quantify these links to make reliable predictions that allow filling the data gaps or assessing the chances for extraterrestrial life?
  10. How much of the present climate change is anthropogenic and how much is natural? How will growing emissions from a growing global population with a growing consumption impact on climate? Computer models are in need of well documented extreme scenarios from the geological past to be properly calibrated and make reliable predictions in this field.

The 49 questions covered in this series address very specific problems and unresolved problems but there are broader difficulties that limit our understanding of how the planet works.

Not for the first time, we must acknowledge that technology continues to limit direct observation of process that might clarify the source of complex geological phenomena. For example, many processes including plate tectonics are known to be driven by the nature of the materials that make up the planet interiors, down to the smallest atomic scales, as thought for instance for the trigger of earthquakes. Answers may arrive via new devices and analytical tools working at the high pressures and temperatures of Earth’s interior.

Another issue is that of reconciling time scales. We can only make observations in the present, whilst the phenomena we try to understand occur in time scales with very different orders of magnitude. We are also limited by having to convincingly scale rates of lab experiments (e.g., mineral physics), and/or analogue models to corresponding geological scenarios. Not unreasonably, this approach does not always yield satisfactory/reliable outcomes.

Global Surface Reflectance and Sea Surface Temperature (Credit: MODIS Instrument Team, NASA Goddard Space Flight Cente).

Global Surface Reflectance and Sea Surface Temperature (Credit: MODIS Instrument Team, NASA Goddard Space Flight Cente).

Implementing Episodicity in Gradualism: For historical reasons, geology has generally underestimated the role of episodicity in nature. However, there is a growing interest driven to exceptional events and to the stochasticity of Earth’s subsystems. An example for this is the preeminence of extreme flooding events (larger than average) in erosion and surface sediment transport and during the evolution of landscape, and the importance of upscaling flood stochasticity into sediment transport models (eg., Lague, JGR, 2010). Even plate tectonics may have been episodic (during the Archean at least, (Moyen & van Hunen, Geology, 2011).  4D hyperscale data sets in geomorphology are increasingly showing the limits of smooth-process approaches. Future understanding of the Earth will benefit from incorporating the full frequency spectrum (the episodicity) in modeling natural phenomena, rather than systematically approaching these as gradual processes. 

Finally, whilst computer models help us understand whether the complexity of nature can be explained by the interplay between simple processes, can we further model the Earth as a complex system of complex systems? And when can we expect ‘compact’ explanations? 

With these last broad considerations we close the known inknowns series. Hopefully, it has achieved what it set out to do: provide an overview of what  earth scientists are up to and what the hot topics and questions in Earth sciences are. Understanding these will lead us ever closer to understand phenomena that are fundamental to societal needs such as mineral resources, global change, or waste disposal.

By Laura Roberts Artal, EGU Communications Officer, based on the article previously posted on RetosTerricolas by Daniel Garcia-Castellanos, researcher at ICTJA-CSIC, Barcelona

The known unknowns – the outstanding 49 questions in Earth Sciences (Part IV)

We are coming to the end of the known unknowns series and so far we have explored issues which mainly affect the inner workings of our planet. Today we’ll take a look at the surface expression of the geological processes which shape the Earth. Topography significantly affects our daily life and is formed via an interplay between primarily tectonics and climate, but it also affected by biological, mechanical and chemical processes at the Earth’s surface. We’ve  highlighted how advances in technology mean detailed study of previously inaccessible areas has now become possible, but that doesn’t mean there aren’t still plenty of questions left unanswered!

Earth’s landscape history and present environment

Drainage patterns in Yarlung Tsangpo River, China (Credit: NASA/GSFC/LaRC/JPL, MISR Team)

Drainage patterns in Yarlung Tsangpo River, China (Credit: NASA/GSFC/LaRC/JPL, MISR Team)

  • Can we use the increasing resolution of topographic and sedimentary data to derive past tectonic and climatic conditions? Will we ever know enough about the erosion and transport processes? Was also the stocasticity of meteorological and tectonic events relevant in the resulting landscape? And how much has life contributed to shape the Earth’s surface?
  • Can classical geomorphological concepts such as ‘peneplanation’ or ‘retrogressive erosion’ be understood quantitatively? Old mountain ranges such as the Appalachian or the Urals seem to retain relief for > 10^8 years, while fluvial valleys under the Antarctica are preserved under moving ice of kilometric thickness since the Neogene. What controls the time-scale of topographic decay? (Egholm, Nature, 2013)
  • What are the erosion and transport laws governing the evolution of the Earth’s Surface? (Willenbring et al., Geology, 2013) Rivers transport sediment particles that are at the same time the tools for erosion but also the shield protecting the bedrock. How important is this double role of sediment for the evolution of landscapes? (Sklar & Dietrich, Geology, 2011, tools and cover effect); (Cowie et al., Geology, 2008, a field example).
  • Can we predict sediment production and transport for hazard assessment and scientific purposes? (NAS SP report, 2010)
  • What do preserved 4D patterns of sediment flow tell us from the past of the Earth? Is it possible to quantitatively link past climatic and tectonic records to the present landforms? Is it possible to separate the signals of both processes? (e.g. Armitage et al., Nature Geosc, 2011).

    Smaller-scale patterns at the limit between river channels and hillslopes (Credit: Perron Group, MIT)

    Smaller-scale patterns at the limit
    between river channels and hillslopes (Credit: Perron Group, MIT)

  • Can we differentiate changes in the tectonic and climate regimes as recorded in sediment stratigraphy? Some think both signals are indeed distinguishable(Armitage et al., Nature Geosc, 2011). Others, (Jerolmack &Paola, GRL, 2010), argue that the dynamics intrinsic to the sediment transport system can be ‘noisy’ enough to drown out any signal of an external forcing.
  • Does surface erosion draw hot rock towards the Earth’s surface? Do tectonic folds grow preferentially where rivers cut down through them, causing them to look like up-turned boats with a deep transverse incision? (Simpson, Geology, 2004).
  • How resilient is the ocean to chemical perturbations? What caused the huge salt deposition in the Mediterranean known as the Messinian Salinity Crisis? Was the Mediterranean truly desiccated? What were the effects on climate and biology, and what can we learn from extreme salt giants like this? (e.g. Hsu, 1983; Clauzon et al., Geology, 1996; Krijgsman et al., Nature, 1999; Garcia-Castellanos & Villaseñor, Nature, 2011). Were the normal marine conditions truly reestablished by the largest flood documented on Earth, 5.3 million years ago? (Garcia-Castellanos et al., Nature, 2009).

The next post will be our final post in the series and we will list open questions on how climate has contributed to shape the surface of planet Earth, from its surface to the emergence of life and beyond.

Have you been enjoying the series so far? Let us know what you think in the comments section below, particularly if you think we’ve missed any fundamental questions.

By Laura Roberts Artal, EGU Communications Officer, based on the article previously posted on RetosTerricolas by Daniel Garcia-Castellanos, researcher at ICTJA-CSIC, Barcelona


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