GeoLog

sedimentology

Imaggeo on Mondays: Small scale processes, large scale landforms

Imaggeo on Mondays: Small scale processes, large scale landforms

This picture was taken in a sea cliff gully landscape at the Portuguese coast. It shows the microrelief which small scale wash and erosional processes produce in these poorly consolidated sediments. These small scale landforms could be interpreted as initial stages of larger scale gully landforms, which can be seen in the back. This highlights the importance of regarding scales and scale linkages in the geosciences.

Description by Jana Eichel, as it first appeared on imaggeo.egu.eu.

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 http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Probing the Pliocene

Imaggeo on Mondays: Probing the Pliocene

The heights we go to for science…

This photograph shows a member of our team preparing to abseil down a cliff in the Charyn Canyon, in the Ili River basin of southeast Kazakhstan. The Charyn River and its tributaries, a branch of the Ili River north of the Tien Shan Mountains, have cut canyons up to 300 metres deep, carving through rocks of different geologic ages, some as old as 540 million years.

The name “Charyn” may derive from local Uighur or Turkic words for “ash tree” or “precipice” respectively, both of which are common in the area.

Charyn Canyon is presently characterized by a cold semi-arid climate, with dry summers and cold winters. However, these conditions are likely to have varied through time, becoming wetter, drier, warmer and cooler in response to major climate systems’ changing intensity and influence over the region.

Our research team investigates the past and present climate systems of the Cenozoic era, our current geological era which began 66 million years ago; the most recent 2.6 million years have been characterised by alternating ice ages and warmer so-called “interglacial” phases, and saw the evolution of humans. More specifically, we study climate systems in one of the most remote regions of Central Asia, known as the Eurasian Continental Pole of Inaccessibility. The area is a challenging place for climate research since it has no marine or ice core records, the most common calendars of ancient climate.

This region is poorly understood yet important within the global climate system, since it lies at the boundaries of the major northern hemispheric climate systems. These systems, such as the Siberian high pressure system and Asian monsoons, are likely to have shifted, expanded and contracted over time. These changes occur in response to factors like mountain uplift, and changes in the Earth’s orbital patterns and incoming solar radiation.

The aim of our study is to reconstruct climatic change over this period. By analysing various chemical and physical characteristics of the sediments, such as their age, magnetism, grain size and chemistry, we can reconstruct quantitative palaeoclimatic variability through time.

Here we focus on an 80-metre thick layer of sediment, which alternates between layers of river-transported gravels and wind-blown dust deposits, known as loess. Younger sedimentary layers have thicker dust deposits, reflecting a long-term aridification trend in the Ili Basin and, more broadly, Central Asia.

Our preliminary results from our fieldwork indicate that the canyon’s sediments represent an uninterrupted representation of the region’s climate from the Pliocene to early Pleistocene (from approximately 4.5 to 1 million years ago).

Achieving a comprehensive geological sampling of the Charyn Canyon was only possible by abseil. Our fieldwork, undertaken from May to June 2017, was a hot and dusty business, but ultimately a lot of fun. Definitely not for those with a fear of heights!

By Kathryn Fitzsimmons, Max Planck Institute for Chemistry, Germany and Giancarlo Scardia, São Paulo State University, Brazil

Imaggeo on Mondays: Angular unconformity

Imaggeo on Mondays: Angular unconformity

It is not unusual to observe abrupt contacts between two, seemingly, contiguous rock layers, such as the one featured in today’s featured image. This type of contact is called an unconformity and marks two very distinct times periods, where the rocks formed under very different conditions.

Telheiro Beach is located at the western tip of the Algarve; Portugal’s southernmost mainland region and the most touristic too.

The area, famous for its famous rocky beaches and great seefood, shows a spectacular Variscan unconformity between the highly-folded greywackes and shales of the Brejeira Formation (Moscovian-Carboniferous) and the horizontally placed red sandstones and mudstones of the Group Grés de Silves (of Late Triassic age: 237 and 201.3 million years old). There is a hiatus of about 100 million years between the two formations.

The Variscan period ranges from 370 million to 290 million year ago and is named after the formation of a mountain belt which extends across western Europe, as a result of the collision between Africa and the North American–North European continents.

The imposing sea cliffs produce a privileged place to observe the end of the Variscan Cycle and the beginning of the Alpine Cycle.

It is possible to visit the outcrop on foot, from the top of the cliffs to the beach, although the path is of high degree of difficulty. When going down to the beach one can begin to visualise the typical lithologies of the Grés de Silves. Toward its top you can see red to green Mudstones (dominant) intercalated with rare dolomites and immediately above the unconformity plane it is possible to observe the red sandstone with cross stratification. The highly-folded turbidites (a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean) of the Brejeira Formation are located below the unconformity.

The folds feature chevron geometries (where the rocks have well behaved layers, with straight limbs and sharp hinges, so that they look like sharp Vs). The folding is the result of the final deformation phase of the Variscan compression.

The beds of sedimentary rocks show sedimentary structures attributed to sedimentation in a turbidic environment (turbititic currents), namely the Bouma sequence and sole marks like flute, groove and load casts.

                                                                                                     By André Cortesão, Environmental Engineer and Geoscientist collaborator of the University of Coimbra Geosciences Centre

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 http://imaggeo.egu.eu/upload/

Imaggeo on Mondays: Viñales Valley

Imaggeo on Mondays: Viñales Valley

From last week’s unusual desert landscape to this week’s lush valley in Cuba…

The picture shows the Vinales Valley, a karstic depression with mogotes in western Cuba. Karst is the general term for landscapes formed when limestone is disolved by carbonic acid, in rain water. This leads, in particular, to the formation of an underground network of caves and rivers.

In the tropics, due to the heavy rains, the dissolution is fast. The ground collapses above the caves and the karst landscape may evolve to mogotes, which are isolated and steep-sided limestone hills; visible in this week’s featured image. Mogotes can also be found in Eastern Asia, for instance in Halong Bay (Vietnam) or Bohol Island (‘Chocolate Hills’) in the Philipines.

By Alexis Merlaud, Belgian Institute for Space Aeronomy

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 http://imaggeo.egu.eu/upload/.