Tuesday, August 1, 2017

Axel Heiberg Adventures Part I

Okay, now that I’ve had a week to recover and sort through things, I am delighted and excited to share some of my field experiences with you!  July 5th-20th marked a two-week adventure into the Canadian High Arctic. Our goal: Axel Heiberg Island.  This is why this blog is called, “Arctic Resolution” after all! In a sense, this trip is the epitome of my M.Sc thesis because it gave me the opportunity to “ground-truth” all the observations and analysis I’ve been doing remotely up to now. In essence, I got to see what my radar and spectroscopy images look like in person! It was seriously cool to be able to have that opportunity.

If you need to recap quickly what my thesis is about you can watch me explain it in three minutes:

We are trying to see how radar can be used for remote predictive geological mapping. Remote predictive mapping is not only useful on Earth to save time and money – it is often the only way we are able to learn about the surfaces of other planets and moons. The techniques we are developing are important for planetary science, as Earth is the only planet humans like us can go and check in person. Thus the need for terrestrial analogue studies, which is one of the focuses and strengths of the University of Western Ontario’s Centre for Planetary Science and Exploration. My project is largely grounded in economic geology (salt diapirs -> petroleum + ore deposits -> $$$ = 😊), but I like that this project also has potential analogues for radar mapping and is helping me develop skillsets vital to planetary sciences.

So, what did we see?

This blog post, for the sake of avoiding rambling on and on, will contain summaries of Part I of our field adventures. About half way through our time on Axel Heiberg we moved campsites from Lost Hammer Spring to Strand Fjord, so I will cover our work done around the first campsite.
We found one of our first scientific findings before the Twin Otter even landed. Remember how I was puzzling over the nature of secondary salts? The strong ASTER thermal infrared spectral signatures for gypsum or anhydrite that weren’t confined to salt domes, but rather in gullies and river floodplains? I was wondering if those signatures were the result of:
1. Rubble and gravel of mechanically eroded diapir materials (chunks of salt rock)
            2. Precipitated salt minerals that geochemically dissolved out through water flow

Number 2 is our winner! Just looking out the Twin Otter windows the secondary, precipitated salt is abundant and widespread. 
Salt minerals precipitating in gullies and floodplains
Of course, we confirmed that it is salt minerals on the ground later, and have collected many samples that we will XRD to identify, but it is incredible that we solved one of our biggest field objectives before even landing! These hillslopes and floodplains are predominantly radar-smooth soils, with some colluvial or fluvial pebbles and cobbles.  The salt bearing gullies and stream channels contain larger pebbles, cobbles, and sporadic boulders, but I think these features are too localized to affect the CPR images at the scale of RADARSAT-2 or PALSAR-1 multilooked CPR image resolution. The salt encrustations are <1 mm in thickness on the surfaces. Although boulders and cobbles of salt have mechanically broken off diapiric structures, like the flanks of Wolf Diapir, these likely contribute to the rougher radar signatures seen in the CPR images in association with the diapirs. Later, I also found that there are at least two types of salt minerals precipitating: halite, and what is likely gypsum or anhydrite. I discovered the halite using the classic method all new students learn in Earth Science 101 – licking the samples.
However, what sort of surprised us was the weather-dependence of these surficial salts. When we first arrived, on a beautiful, clear, sunny day, these salts were very sharp in contrast against the landscape. When I walked up the stream at our first campsite, the rocks in the riverbed exposed above water were coated in a white crust. Then the rain and snow came. After three days of snow, almost all of the white encrustations disappeared! There were still white patches on the hillslopes and in gullies, but they weren’t nearly as stark as before. After a day or two of the weather clearing up, the white minerals appeared again, almost as abundant as when we arrived. We think the snow and rain dissolved the salt minerals and they were able to precipitated again from the surface water after the ground was able to start drying.
Salt minerals encrusting some rocks on hillslope

Our first campsite was at Lost Hammer Spring. Lost Hammer Spring is a perennial spring, one of many places on Axel Heiberg Island where brines upwell to surface and deposit large precipitated structures of salt. It is entirely possible that the source of the salt in these fluids derives from the core of the adjacent Wolf Diapir, but this has not been conclusively proven. The salt that makes up Lost Hammer is very sodium rich, implying that the groundwater has interacted with subsurface halite (i.e. table salt) (Battler et al. 2013) but no halite has yet been found at Wolf Diapir. The only diapir at which halite has been found is at Stolz Diapir, which we visited and sampled later in the trip. It is entirely likely that many diapirs on Axel Heiberg Island contain halite in their cores, and that this is simply not exposed at surface. Curiouser and curiouser! Halite was even found precipitating in small patches a few kilometers downriver from Lost Hammer. Like the secondary salts, Lost Hammer Spring exhibited a similar wet/dry cycle. Upon arrival to the field site, the Lost Hammer Spring was a dazzling white, but during the snowfall the spring became greyer and muddier. Either the surface layer of salt was exfoliated, or mud was transported onto the spring during the wet interval. 

Not a snow bank, this is all salt! Lost Hammer Spring (aka Wolf Spring) has accumulated an almost 2 m high vent of halite, calcite, gypsum,
thernardite, and microbilite. The shape of the perennial spring changes seasonally, with periods of partial dissolution and reprecipitation

               Wolf Diapir is characterized by having steep slopes and heavy erosion compared to surrounding rocks from the Isachsen Formation and the Invisible Point Member of the Christopher Formation. The contrast in surface texture is sharp between Wolf Diapir and the other formations. Whereas the adjacent rock formation has regularly distributed gravel in soil, the flanks of the Wolf Diapir are characterized poorly sorted very angular colluvium from sand to block sized particles. Two textures were pervasive amongst all the diapirs we visited this trip - solid, crystalline anhydrite, and weathered, heavily altered vuggy gypsum. 
Wolf Diapir. You can see how the surface of the mountain is far rougher and more gullyied than the surrounding hills.

Close up, you can see how heterogenous and blocky the surface of the diapirs are. Broken fragments range from granule to block sized. It is frequently difficult to determine which blocks are in situ or broken

This weathered, vuggy crust is pervasive across all diapirs we visited.

Other intact anhydrite (or gypsum?) has different lithologies across different diapirs.
At Wolf, the crystalline material was very friable (likely still altered) and highly veined with what might be limestone.

A long gully with 2 m high levees made up of large angular boulders runs down the eastern flank of the structure. We mapped this using a portable LiDAR system.
Dr. Osinksi stands adjacent to the 2 m high colluvial levee flanking a prominent gully coming down Wolf Diapir
              On one of our helicopter traverse days, we could visit Stolz and Whitsunday Bay diapirs are located outside of the WABS region, on the eastern side of the island. Right now we don’t have  RADARSAT-2 or PALSAR-1 coverage over these sites, but I contacted a gentleman at the CSA about using our SOAR-E proposal to get some. For now, we are interested in their chemistry and spectral responses. The top of the diapir is encrusted with a thick, weathered crust of gypsum/anhydrite.  The slopes are steep, with large blocks broken off on the flanks and in the valleys. The topography on Stolz Diapir is karstic, with tall, jaggaed pillars of eroded diapir material.
In some places, the erosion characteristics of Stolz Diapir appeared karstic in nature.
We saw some of this later on at Colour Peak as well.
Like Wolf, Stolz Diapir is very rough and blocky.
                Large vugs within and beneath the altered crust and small dissolution caves run throughout. Two streams run through the structure, converging along the eastern flank. These two streams have different water chemistries and sediment load. One stream has distinctively more halite than the other, and likely runs through Stolz’s halite core. Halite is exposed in outcrop downstream of where the streams converge. Textures within the halite range from white powdery massive structureless to colourless/grey clear crystalline halite with perfect cubic cleavage. Some areas of crystalline halite are green tinged from localized yellow spots which may be endolith colonies.
Dr. Osinksi stands in front of large halite outcrop

In certain places, the halite could be seen growing in framboidal bulbs of small cubes

There are extreme, extensive, thick perennial springs deposits downstream.  They are seriously insane. It looks and feels like walking through snow! These salts have varying textures, colours, banding, and crystal structure. Upstream are alternating light and dark grey salts. Downstream by a pool are pure white, snow-like salts with bladed/rod crystal structures. The strength of anhydrite/gypsum over the spring deposits is notably weaker than the signature over the diapir itself, likely because the spring is predominantly formed from precipitated halite or calcite travertine.

Extensive, massive perennial springs! The white and grey is all salt!
Note the differences in colour and texture between the white and grey salts.
Mark sampled each, and so hopefully he'll be able to tell us what they are.

Salt salt salt!  Everywhere! So that concludes the first part of Arctic updates. Stay tuned for part II within the next fortnight.

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