Guest Blog: How Speleothems Are Used To Determine Past Climates?

About author: Alex Graham is an undergraduate student at University of Newcastle, Australia. He is interested in Geology as a whole but his major interests include fluvial processes, karst systems and ocean science. During his visit to New Zealand, he has obeserved the glow worms in Waitomo Caves and spelunking in Nikau Caves.

Speleothems, more commonly known as stalactites or stalagmites, consist of calcium carbonate (calcite or aragonite) crystals of various dimensions, ranging from just a few micrometers to several centimetres in length, which generally have their growth axis perpendicular to the growth surface. Speleothems are formed through the deposition of calcium carbonate minerals in karst systems, providing archives of information on past climates, vegetation types and hydrology, particularly groundwater and precipitation. However, they can also provide information on anthropogenic impacts, landscape evolution, volcanism and tectonic evolution in mineral deposits formed in cave systems.

Stalagmite Formation

Rainfall containing carbonic acid weathers the rock unit (generally either limestone or dolomite) and seeps into the cracks, forming caverns and karst systems. The groundwater, percolating through such cracks and caverns, also contains dissolved calcium bicarbonate. The dripping action of these groundwater droplets is the driving force behind the deposition of speleothems in caves.

Core drilling of an active stalagmite in Hang Chuot cave.

Speleothems are mainly studied as paleoclimate indicators, providing clues to past precipitation, temperature and vegetation changes over the past »500,000 years. Radioisotopic dating of speleothems is the primary method used by researchers to find annual variations in temperature. Carbon isotopes (d^13C) reflect C3/C4 plant compositions and plant productivity, where increased plant productivity may indicate greater amounts of rainfall and carbon dioxide absorption. Thus, a larger carbon absorption can be reflective of a greater atmospheric concentration of greenhouse gases. On the other hand, oxygen isotopes (d^8O) provide researchers with past rainfall temperatures and quantified levels of precipitation, both of which are used to determine the nature of past climates.

Stalactite and stalagmite growth rates also indicate the climatic variations in rainfall over time, with this variation directly influencing the growth of ring formations on speleothems. Closed ring formations are indicative of little rainfall or even drought, where-as wider spaced ring formations indicate periods of heavy rainfall or flooding. These ring formations thus enable researchers to potentially predict and model the occurrence of future climatic patterns, based off the atmospheric signals extrapolated from speleothems. Researchers also use Uranium –Thorium radioisotopic dating, to determine the age of speleothems in karst formations. Once the layers have been accurately dated, researchers record the level of variance in groundwater levels over the lifetime of the karst formation. Hydrogeologists specialise in such areas of quantitative research. As a result, speleothems are widely regarded as a crucial geological feature that provide useful information for researchers studying past climates, vegetation types and hydrology.


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Explore Fascinating Geology of Lofoten Islands, Norway

It is probably going to be boring what you are going to read, but if you are a geologist, please continue reading.

 What started as a simple fun trip with some friends to Lofoten Islands in northern Norway, just became a unique geological experience. This, because I think that, as a geologist, it is completely impossible to separate fun from my profession while traveling. It's just amazing to mix your profession with your favorite hobby. 
Trying to understand the rocks, the configuration of the landscapes and their phenomena, is simply priceless.

Reinebringen Mountain, Norway.
View to the town of Reine and Fjords.
Photo Credits: J. Sebastian Guiral

This time I got completely impressed with the beauty of the Fjords in Lofoten (help: what is a fjord? well basically, a fjord is a narrow and deep channel that allows the sea to enter to the land. They can be several kilometers long, so they are often confused with rivers or lakes, and can reach great depths, exceeding 1000 m. These geomorphological units are the product of sea flooding of valleys created by glacial activity).

Reinebringen mountain, Reine, Norway.
View to the town of Reine and Kirkefjord. U-shaped valleys and geomorphological features associated with intense tectonic activity. Glacial lake
Photo Credits: J. Sebastian Guiral

Hiking through the perfectly carved U-shaped valleys left me speechless (above mentioned glacial valleys). In each valley, it was possible to appreciate the sediments associated with the activity of the glacier, that is, the Moraines (frontal and lateral), till and reworked proglacial sediments.

Skelfjord, Lofoten, Norway.
Photo Credits: J. Sebastian Guiral

In addition, the typical vegetation of Tundra is impressive (help: what is Tundra? In simple words, it is a biome characterized by the lack of trees, the soils are mainly covered with mosses and lichens, characteristic of circumpolar latitudes. The subsoil is almost permanently frozen). This vegetation covered the base of the mountain chains and snowy hills, contrasting in a perfectly artistic way and offering a breathtaking view. 

Å, Moskenes, Norway.
Mosses on Precambrian gneisses and migmatites.
Photo Credits: J. Sebastian Guiral

Reine, Lofoten Norway.
View to Reinefjorden and snowy peaks
Photo Credits: J. Sebastian Guiral

Hamnøy, Lofoten Norway. Snowy Peaks.
Photo Credits: J. Sebastian Guiral

Haukland beach, Leknes, Lofoten, Norway

Snowy Peaks at Hamnøy, Lofoten Norway.
Photo Credits: J. Sebastian Guiral

What about lithologies? Well, broadly all those landscapes are conformed by a Precambrian basement represented by an Archean and Paleoproterozoic metamorphic complexes of ortho- and paragneisses, intruded by anorthosites and suites of charnokite-granites. This basement is in tectonic contact with amphibolites and paragneisses, which were intruded by tonalitic magmas at 470 Ma. Subsequently, at the top of the sequence, in a rather complex structural context, volcano-sedimentary sequences are found, ranging from the Permian to the Paleogene. These volcano-sedimentary sequences are part of the sea floor between Greenland and Norway. All these units are in well-marked tectonic contacts.

Utakleiv Beach, Leknes, Lofoten, Norway.
Paleoproterozoic amphibolites and gneisses.
Photo Credits: J. Sebastian Guiral

Utakleiv Beach, Leknes, Lofoten, Norway.
Paleoproterozoic amphibolites and gneissesPhoto Credits: J. Sebastian Guiral 

Paleoproterozoic amphibolites and gneisses at Haukland beach, Leknes, Lofoten, Norway
Photo Credits: J. Sebastian Guiral 

Finally, in addition to the geological stuff, the sunsets, perfect beaches, rainbows, snowstorms, the strong rain and a whole bunch of climatic phenomena associated with these high latitudes, make the Lofoten Islands one of the places. I have enjoyed a lot being a geologist. 

Reine, Lofoten Norway.
View of Reinefjorden and snowy peaks
Photo Credits: J. Sebastian Guiral 

 This is what I like about this profession, trying to understand a bit about such a complex, beautiful and huge planet.

If you are a geologist and feel the same as me while traveling, let me congratulate you.

You have a beautiful profession!

Sebas enjoying rain in Å, Moskenes, Norway.
Photo Credits: J. Sebastian Guiral 
  

Sebas exploring Paleoproterozoic amphibolites and gneisses at Utakleiv Beach, Leknes, Lofoten, Norway.
Photo Credits: J. Sebastian Guiral 

About author: J. Sebastian Guiral is a Geological Engineer from the National University of Colombia. He is currently pursuing his master's program in Georesources Engineering at the Luleå University of Technology in Sweden. He also has  studied at the University of Liege in Belgium and at University of Lorraine in France. As a geologist, he has worked in important engineering and research projects in his country, which include geomechanics of underground excavations, geodynamics and geomorphology. Currently, his interests are focused on economic geology, exploration, mining and mineral processing techniques. 

You can contact with J. Sebastian Gujral at sebasguiralv@gmail.com or at Instagram: @sebasguiralv

We are grateful to J. Sebastian Gujral for sharing his knowledge and adventures with us. You can also contribute share your geological adventures with us. See details here.

Deposition Associated with Glaciation

Deposition Associated with Glaciation 

The Glacial Conveyor 

The glacial conveyor and the formation of lateral and medial moraines on glaciers.

Glaciers can carry sediment of any size and, like a conveyor belt, transport it in the direction of flow (that is, toward the toe;  figure above a). The sediment load either falls onto the surface of the glacier from bordering cliffs or gets plucked and lifted from the substrate and incorporated into the moving ice. Geologists refer to a pile of debris carried by or left by glaciers as a moraine. Sediment dropped on the glacier’s surface moves with the ice and becomes a stripe of debris. Stripes formed along the side edges of the glacier are lateral moraines. When a glacier melts, lateral moraines lie stranded along the side of the glacially carved valley, like bathtub rings. Where two valley glaciers merge, the debris constituting two lateral moraines merges to become a medial moraine, running as a stripe down the interior of the composite glacier (figure above b). Trunk glaciers created by the merging of many tributary glaciers contain several medial moraines. Sediment transported to a glacier’s toe by the glacial conveyor accumulates in a pile at the toe and builds up to form an end moraine.

Alpine Glacier Basics