Remotely India: Folding At Margins Of The Vindhyan Sedimentary Basin

Remotely India # 9 (a post series about landforms and geological structures imaged by remote sensing satellites).

This is a geology rich image!

Source: Rajasthan Tourism

It shows Gagron Fort in the Jhalawar district of Rajasthan. I came across it while watching a history show on EPIC channel. Looking at the steeply dipping strata I identified them as the metamorphosed and deformed Aravalli Group sediments of early Proterozoic age.

I then checked a geological map and realized I had gotten the stratigraphy completely wrong. These steeply dipping rocks belong to the mid-late Proterozoic Vindhyan Group of sediments.

There are two distinct categories of Proterozoic basins in India. There are the mobile belts. An example of a mobile belt is the Aravalli orogenic belt. As the name suggests, these basins formed as linear depressions at the margins of Archaean cratonic blocks. They are filled with volcano-sedimentary successions, intruded by granitic bodies and subjected to intense deformation and metamorphism during convergence and collision between different cratonic blocks. They are economically important. Lead, zinc, copper, iron ore is mined from various mobile belts. The Aravalli belt formed due to the collision between the Aravalli craton and the Bundelkhand craton. Sedimentation in the Aravalli basin was initiated around 2 billion years ago. Their deformation and metamorphism has been dated to around 1.7-1.6 billion years ago.

The second category of basins are the epicratonic basins, developed as either rift basins or foreland basins within cratonic blocks. Volcanic activity is mostly restricted to the early stages of basin evolution. Sedimentary successions are sandstones, shale and limestone. Collectively these are known as the 'Purana' (ancient) basins. They show very light to no metamorphism and relatively gentle deformation. Flat lying strata form mesas and plateaus in the interior of such basins. The degree of deformation usually increase at the basin margins. In proximity to basin margins faults, sediments are often spectacularly folded. The Vindhyan Basin is a 'Purana' style basin.

I am putting up a few examples of folding in Vindhyan Basin sediments. These range in age from about 1.7 billion to 650 million years.

The first one is the Jhalawar anticline in proximity to the Mukundara Fault. Fort Gagron was built  on the steep NE dipping limb made up of the Kaimur sandstones.

Mukundara Fault is an easterly directed thrust fault. See this cross section across the Jhalawar anticline.

Source: Rajeev Bhoj, Avdhesh Nautiyal and Rajesh Sharma 2011:  Regional Structural Style of Chambal Valley Vindhyan Basin, Rajasthan, India

This second example of folding is south and east of the famous fort at Chittorgarh. Lower Vindhyan Group sediments have been folded into N-S trending tight anticlines and synclines. 

This folded zone abuts the Great Boundary Fault which structurally juxtaposes the Bundelkhand Craton with the Aravalli Craton. The fault brings into contact the Aravalli mobile belt and the Vindhyan 'Purana' basin. The Great Boundary Fault is a NW dipping thrust fault (ref).

Finally, northeast of the previous location, also along the Great Boundary Fault in the vicinity of the town of Bundi are these folded Upper Vindhyan sediments. These are the sandstones and limestones of the Rewa and Bhander Group.

And below is a geological map of the region to give some context to these structures. The Great Boundary Fault and the Mukundara Fault are orthogonal to each other, testimony to differently oriented compressive forces  affecting the Vindhyan Basin.

Source: Rajeev Bhoj, Avdhesh Nautiyal and Rajesh Sharma 2011:  Regional Structural Style of Chambal Valley Vindhyan Basin, Rajasthan, India

Three distinct structural trends can be seen in this part of the Vindhyan Basin. A NE-SW trend of the Great Boundary Fault. A N-S trend of the tight folds south and east of Chittorgarh. And a NW-SE  trend of the Mukundara Fault and associated folds. The other major structural trend in the Vindhyan Basin is the E-W trend of  Narmada rift fault zone which forms the southern boundary of the basin.

All satellite images from the Indian Remote Sensing satellite Cartosat series, accessible through ISRO's web mapping application Bhuvan.

Cartosat 1 DEM- Two Strike Slip Faults

My two favorite strikes slip faults in India as rendered by Cartosat 1 Digital Elevation Model-

1) Yamuna Left Lateral Fault-

Source: Cartosat 1 DEM National Remote Sensing Center, ISRO

You can see that the Siwalik hills are breached by the Yamuna and dislocated in a left lateral sense, i.e. one would have to turn left to follow the narrow marker rock bed across the fault.

From a previous post on this fault-

Miocene onwards a thick wedge of fluvial sediments filled up a foreland basin that formed in front of rising thrust sheets uplifted along the active Main Boundary Thrust (MBT). That phase ended about 0.5 to 1 mya.

This fluvial wedge over the last half a million years has been deformed into the Siwalik mountains. These mountains form broad synclines and tight anticlines cut by north dipping thrust faults, a result of the continuing compression of the sediment wedge. The southernmost of these thrusts which brings into tectonic contact the anticlinal Frontal Range of the Siwaliks over the alluvial plains in called the Himalayan Frontal Thrust (HFT).

The HFT is broken into segments and the amount of displacement along these segments or thrust blocks is unequal. For example the blocks west of the Yamuna and east of the Ganga have moved southwards with an opposite sense of movement relative to the central block known as the Dun block. To view this, turn on labels and pan southeastwards in embeddable map below until the town of Haridwar where the Ganga enters the plains.

Thus the Yamuna fault has a left lateral sense of movement while the Ganga fault has a right lateral sense of movement. These faults can be thought of as lateral ramps of the HFT accommodating the displacement caused by the southwards movement of the HFT blocks. 

Structural considerations indicate that during the last 0.5 my there has been about 8 km of displacement along the Yamuna and Ganga faults, a slip rate of approx. 16 mm year. - See more at: http://suvratk.blogspot.in/2010/12/remotely-india-3-left-lateral-yamuna.html#sthash.H9K4tfrI.dpuf

 Miocene onwards a thick wedge of fluvial sediments filled up a foreland basin that formed in front of rising thrust sheets uplifted along the active Main Boundary Thrust (MBT). That phase ended about 0.5 to 1 mya.

This fluvial wedge over the last half a million years has been deformed into the Siwalik mountains. These mountains form broad synclines and tight anticlines cut by north dipping thrust faults, a result of the continuing compression of the sediment wedge. The southernmost of these thrusts which brings into tectonic contact the anticlinal Frontal Range of the Siwaliks over the alluvial plains in called the Himalayan Frontal Thrust (HFT).

The HFT is broken into segments and the amount of displacement along these segments or thrust blocks is unequal. For example the blocks west of the Yamuna and east of the Ganga have moved southwards with an opposite sense of movement relative to the central block known as the Dun block. To view this, turn on labels and pan southeastwards in embeddable map below until the town of Haridwar where the Ganga enters the plains.

Thus the Yamuna fault has a left lateral sense of movement while the Ganga fault has a right lateral sense of movement. These faults can be thought of as lateral ramps of the HFT accommodating the displacement caused by the southwards movement of the HFT blocks.

Structural considerations indicate that during the last 0.5 my there has been about 8 km of displacement along the Yamuna and Ganga faults, a slip rate of approx. 16 mm year.

The Digital  Elevation Model also brings out beautifully the Quaternary alluvial fans with tiers of river terraces deposited in the valley between the Siwaliks and the Lesser Himalayas and the intricate drainage on the southern slopes of the Siwalik frontal range.

2) Gani Kalava Fault-

This too has a left lateral movement and has a prolonged history of being reactived during different phases of sedimentation in the Proterozoic Cuddapah Basin of south India.  I  did my M.Sc dissertation on this area, concentrating on the asymmetric anticline with a gentler dipping southern limb and a nearly vertical dipping northern limb located south of Gani village.

Source: Cartosat 1 DEM, National  Remote Sensing Center, ISRO

From a previous post on this fault-

The feature is an ENE plunging asymmetric anticline with spectacular dip slopes of quartz arenites making up the southern limb of the fold and left-lateral movement along a regional fault steepening the northern limb of the fold. There is some copper mineralization along the fault. The Cuddapah basin is an intra-cratonic basin which was filled up in several depositional mega cycles. Sections of two of these mega cycles are exposed in this area. The older mega cycle comprising the Cuddapah subgroup is exposed in the core of the anticline. An angular unconformity separates the older cycle from the younger Kurnool cycle (sub group) which is exposed along the limbs.

Brown arrows shows the offset marker beds (grey arrows show sense of movement) of the oldest sedimentary formation of the Cuddapah basin, the early Proterozoic Gulcheru Quartzites and Vempalle limestones of the Papaghani Group. These lie unconformably on the Archean Peninsular  Gneiss which is the fawn colored peneplain in the left part of the DEM. The very distinct dip slopes of  the Gani anticline (south of Gani village) are made up of a much younger sedimentary unit, the Banganpalle  Quartzites of the Kurnool Group. They were deposited in energetic shallow seas, forming a vast sand shelf, wherein waves and currents winnowed out unstable minerals, leaving behind a nearly pure well sorted and rounded quartz sand. The quartz grains are polycyclic, meaning they show evidence of being derived by weathering of older sandstones, the most likely source being the Gulcheru Quartzites.

Remember this is a Digital Elevation Model,  same color means the same altitude range and not mineral composition.

Free Download- Cartosat 1 India 1 Arc Sec Digital Elevation Model

I've been writing periodic updates on Bhuvan and have been critical about some of its features before. Today I sing its praise.

Bhuvan is the Indian Space Research Organization's web mapping portal. It was  launched with much hype in 2009, touted by the media as a Google Earth killer.  That it hasn't turned out to be. Google Earth /Maps is still the most used application for browsing imagery and exploring the world's surface.

This need not have been portrayed by the media as a Google versus Bhuvan competition. I always felt Bhuvan would offer real value by making available India specific natural resources and earth science datasets to overlay imagery. That in fact is the direction Bhuvan has been evolving for the past few years.

Bhuvan now offers a variety of  India datasets for overlay, analysis and download. I have been playing around with the Digital Elevation Model (DEM) derived from Cartosat 1 stereo imagery. The DEM is available as 1 degree tile corresponding to the Survey of India topo map sheets. The interface  to  select and download the DEM is easy to use. Technical documentation of the DEM is also available. Spatial resolution is 1 Arc Sec, which corresponds to around 30 meters. The vertical margin of  error is about 8 meters. Analysis shows that the Cartosat DEM compares well with other widely used DEM such as SRTM (90 m res) and ASTER (30 m res).

Below is  a Digital Elevation Model of the Nallamalai Hills in Andhra Pradesh with a 0.5 deg graticule overlain. I've generated this representation in Manifold GIS. The geological terrain is part of the Proterozoic Cuddapah Basin. Remember, the color scheme assigned to the DEM is not demarcating different rock types but elevation ranges. However, as a nod to the prominent geological feature that I wanted to highlight, I have assigned a color of the common rock in outcrop. These are the Bairenkonda Quartzites and Sandstones of the Nallamalai Group which form folded ridges, part of the Nallamalai fold belt. The green low relief areas are mostly underlain by shales and limestones.

And check out the drainage in color black (lowest elevation). You can make out the drainage divide between the Godavari and Krishna basins. In the upper right part of the image, streams are draining north towards the Godavari river. In the left lower part of the DEM, streams are flowing south towards the Krishna river.

Source: Cartosat 1 DEM, National Remote Sensing Centre, ISRO

I'm planning to tell more stories about Indian geology using these DEM 's. For that I  have to thank ISRO for making this dataset available.

Bhuvan Continues To Be A Mixed Bag As A Citizen Mapping Tool

After my last post on the use of Google Earth to identify illegal mining in Goa, I was curious to find out if I could replicate the same in Bhuvan, India's public mapping portal.

I was disappointed:

1)  There is no historical imagery available, or at least none that I could find.  So I could not pull out older imagery to verify claims made about the presence /absence of mining before a certain date.  This is not due to a lack of older imagery. The Indian Space Research Organization has had a remote sensing satellite program since the late 1980's and imagery  of at least 23 m resolution is available for  the last couple of decades and imagery of 5.8 meter resolution is available for the last 12 years or so (IRS - 1D). The 5.8 m resolution images are fine grained enough to identify large features like open pit mines.

2) I could not find the open pit mines using "search by name". In Google Earth I could zoom onto the area of the open pit mines by searching for the nearest settlement "Maina" which was mentioned in the article on the Goa mining scam by the newspaper Herald.   In Bhuvan, the search by name database works best for towns and cities. The village level data is still incomplete. Even when a small village is present in the database the imagery does not always zoom to that area, nor is the village annotated to allow easy navigation to it. These are the basics of interactive map navigation design and Bhuvan is falling short.

On a general note, its been close to three months since the government announced that 1 meter resolution data will now be available without need for security clearances. Yet Bhuvan still is not streaming imagery finer than 5.8 meter resolution.

On the data download front, elevation data of CartoDEM 1 arc second (Digital Elevation Model derived from Cartosat 1 imagery- 1 arc second corresponds to roughly 30 meters) and Resourcesat-1: AWiFS imagery (56m) of the Indian region can be downloaded from the NRSC Open EO Data Archive. You can choose the product and the area of interest from the Bhuvan interface. The DEM download is a welcome addition. You could previously download 1 km resolution DEM of India from the USGS and also 30 m relative DEM generated from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) from NASA.

However, regarding imagery the government's all too cautious approach is perplexing. If 5.8 meter resolution and 1 meter resolution data are available and now cleared for access to all users without further security checks, why not let users download that data too?

Does The Indian Govt Prefer Google Over Bhuvan?

From a note in Geospatial World I learn that the Election Commission (EC) of India might be using Google satellite images as a background layer on which to placemark the locations of polling booths along with relevant information. The project will be initiated in the state of Bengal.

If this report of using Google is true, I am curious to know why the EC chose Google over Bhuvan which also serves out satellite images and is advertised by the Indian Space Research Organization (ISRO) to be customizable to incorporate the kind of functionality the EC wants.

Is it because - a) the EC was not aware of Bhuvan and its capabilities? In that case, ISRO has not done a good job of educating potential users about Bhuvan.

Or is it because - b) the Application Programming Interface i.e. the programming tools that allow developers to customize the application is not good enough?

Or is it because - c) Data policy restricts even government departments from accessing very high resolution imagery (1 meter) from Indian satellites for web applications, even internal ones like the proposed polling booth app. Government users may obtain without clearances high res images of a pre-defined extent i.e. images of one particular geographic area, but is a high res seamless image stream available to them through  Bhuvan?

Currently the data policy allows only imagery of resolution 5.8 meters and coarser to be released free of clearances in the public domain. Due to this policy Bhuvan can only stream images of 5.8 meters and coarser to the general public. The policy is supposed to be up for a review this year.

Whatever the reasons, it's a shame that Bhuvan and high resolution imagery captured by Indian satellites is being kept away from being utilized in innovative applications.

The government and ISRO need to introspect.