Field Photos: Fluvial Bedforms

The Deccan Volcanic Province in best known as a thick pile of basalt lava. It is igneous rock country. In Maharashtra, the plateau east of the western ghats is drained by rivers small and big flowing ultimately into the Bay of Bengal. Many of these rivers originate in the very humid mountainous region known as the western ghats. Eastwards in the more arid climatic zone prevailing over the plateau these rivers have deposited a lot of sediment throughout the Quaternary and possibly earlier.

Here is the regional context:

Source: Mishra et al 2003

I was visiting a mineral museum north of the town of Sangamner a couple of weeks ago and came across some superbly preserved fluvial bedforms  along a road cut just south of Sangamner. Fluvial bedforms are sedimentary structures formed as sediment is moved and is deposited by current action in the river bed.  If you zoom and pan southwards along National Highway 50 south of Sangamner in the embedded image below you can see a trace of a small tributary of the river Pravara.


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The sediments in the images below were deposited by that tributary. The river has incised or cut into its own deposits and the active channel today is about 10-15 meters below the section seen in the images. So these deposits form an ancient probably late Pleistocene fluvial terrace a few hundred meters wide.

1) View of fluvial bedforms with pebbly and sandy planar and cross stratification clearly seen. At right center is a pebbly cross bedded wedge, possibly a point bar deposit. So, the sediment you see was being rolled along the bed of the river. The morphology of the sediment surface was like a sheet of sand and pebbles (the planar layers are a cross section of these sheets). Here and there the sediment sheet was wrinkled into large waves (the large cross beds are likely the cross section of these large wave forms). Some sediment was being deposited along the banks along inclined surfaces forming the point bar deposits.

2) Another wide view of planar and cross beds.

3) Shallow cut and fill structures. These are common features in the river bed as pulses of high energy events such as floods may scour the sand in the river bed and then fill up the trough formed by sediment.

4) A small channel filled by gravel and sand overlain by planar and cross bedded sand and pebbly layers.

I couldn't stay long at the outcrop as traffic was zooming perilously close to me and we had to go some distance. These deposits though have been interpreted to preserve a record of Quaternary climate change. The entire section records a phase of mid-late Pleistocene - early Holocene aggradation in which sediment was deposited and the river channel built upwards. This was followed by a phase of incision later in the Holocene when the river cut into its own deposits leaving stranded terraces.

I hope this outcrop survives for long. Apart from aiding our understanding of fluvial geomorphology and climate change it is a superb teaching tool for sedimentary geology and geomorphology classes. Unfortunately intensive farming activity and excavations for construction are slowly degrading these fluvial deposits near Sangamner.

Zeolite Photos Quiz

Some samples of zeolites and associated cavity minerals.

I had to take the pictures from behind a glass pane so excuse the lack of extreme close ups.

Take a stab at identifying the minerals and post your answers in the comments. I will put up the correct answers in this post in a few days.

Update: Answers at the bottom.

A)

B)

C)

These palm sized samples were selling in the range of Rs 5000 to Rs 10,000 (~ $100 to $200). Larger samples were in the range of Rs 25,000 to Rs 60,000. These are prices for the Indian market. I imagine there will be a significant markup for sale in the U.S and Europe, Japan etc.

Ornamental zeolites have become quite a lucrative business.

Answers: Lockwood got most of them right!

A)  pink - stilbite, green - apophyllite,  needles - scolecite , few crystals of heulandite in the centre of the sample.

B) blue- cavansite , white substrate - stilbite

C) cotton like puffs- okenite, small globules - gyrolite , prismatic crystals- apophyllite, with substrate of quartz.

Graphic Of Engineered Geothermal Energy Projects And India Update

The Economist on Engineered Geothermal Projects...

with a nice graphic...

Here is a graphic summarizing geothermal energy potential from India

 Source: Geothermal Energy Resources and its Potential in India

Gap along the Himalayan axis where high heat flow is associated with granitic intrusives is because the geothermal potential of Nepal is not shown. Within peninsular India all the high heat flow regimes fall along either old Precambrian weak zones which have been reactivated during late Paleozoic -Mesozoic rifting events or coincide with the evolution of the western margin of India during Mesozoic rifting from Africa /Madagascar / Seychelles. This rifting resulted in lithosphere stretching and thinning and hot mantle upwelling.

The focus in India has been on conventional geothermal energy exploration in the vicinity of volcanoes, geysers and hot springs where high heat flow occurs at shallow depths of a few hundred meters. These projects use naturally occurring steam and hot water to generate electricity. The estimate is that these shallow heat flow sites could potentially generate up to 10,300 MW of electricity. Engineered geothermal systems (EGS) projects in which water is circulated along drilled pathways to great depths to heat it up can be located in areas of relatively low heat flow. EGS have not yet been explored in any detail in India. These projects are more expensive but because they don't have to be located near unusually high heat regimes the aggregate energy potential may be even bigger than what is estimated for conventional projects.

Everything right now is still in the "estimates and potential" stage. Not much energy if any at all is being produced from any of these sites. So far at least the government has been neglecting this clean energy resource. We lack the right policies to make both conventional and engineered geothermal energy economically viable.

Perceptions And Future Of Earth Sciences In India

T.N Narasimhan writes a short correspondence in the latest issue of Current Science on the comparatively lesser importance given in India to earth sciences as compared to math, physics and chemistry.

The reasons as to why earth system science is considered a poor relative of the other sciences in India may be many and complex. Among these, the following two appear credible. First is the populist perception that mathematics, physics and chemistry demand highest levels of intelligence. The second is a more mundane reason of jobs, financial security and career opportunities. Currently India is pursuing a hope of economic growth based on physical and biological technologies, and entrepreneurship. Not surprisingly, India’s best young talents have little inclination to pursue earth sciences. However, it seems likely that India’s economic expectations may be seriously jeopardized if earth sciences continues to be a poor relative of the other sciences, and the country fails to nourish excellence in earth sciences as a means of sustainable management of water, land, ecosystems and the environment.

I don't disagree except that career opportunities have been improving recently with the entry of private operators in the oil and mining industries. So the earlier perception that geology = constricting government job is slowly going away.

K/Pg Boundary And An Emerging Database Of The Terrestrial Cretaceous From China

Nature News has an article by Jane Qiu detailing an ambitious drilling project ultimately aimed at recovering 10 km of core from a Cretaceous sedimentary section deposited in the Songlia Basin, northeast China. The Songlia basin is a rift basin that saw establishment of very long lived lakes fed by rivers throughout the Cretaceous, a geological period which saw great fluctuations in temperature, atmospheric carbon dioxide and sea / lake levels. Much of our understanding of the Cretaceous comes from marine sediments. Scientists have started analyzing portions of a two km core of terrestrial sediment in the hope of understanding how dramatic shifts in temperature and CO₂ content affected conditions on land.

Here is an interesting bit:

Other as-yet-unpublished results also point to a possible position for the K/Pg boundary. But it is about 100 meters below the depth determined by Wan Xiaoqiao, a palaeontologist at the Beijing-based China University of Geosciences who used fossils of spores, pollen, phytoplankton and ostracod to locate the boundary. The researchers are trying to determine why the estimates differ, and to nail the boundary down to 2–3 metres, so that detailed geochemical analysis can be performed to look for rare elements, such as iridium, that are common in meteorites and were spread around the globe by the cosmic impact.

The article doesn't say how the K/Pg boundary has been identified but one cannot help speculating on a topic like the end Cretaceous mass extinction.

Some scenarios:

1) The boundary has been incorrectly located and more detailed work will place it near the palaeontologically determined K/Pg boundary.

2) The physical location of the K/Pg boundary is correct and more detailed studies will show that it temporally coincides with the palaeontological boundary. This will imply that the intervening 100 meter or so of sediment was deposited very rapidly.

3) The identified boundary is indeed an event pointing to a large environmental perturbation caused by a meteorite impact but palaeontological evidence for a mass extinction occurs a considerable amount of time after this event as evidence in the 100 meter or so of intervening sediment will tell us. This is a scenario similar to what Gerta Keller and colleagues have been arguing using late Cretaceous sections from Texas and near the Chicxulub impact site i.e. the Chicxulub impact took place a few hundred thousand years before the mass extinction.

This might turn out to be an important section in the context of the mass extinction debate. Cretaceous geology is never dull.