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okay welcome so today I'm going to be

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talking about stromatolites and

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traumatic shirts of the straw a pool

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formation which is 3.4 billion years old

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in the Paley archaean in Western

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Australia luckily I don't have to go

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over too much about what a stromatolite

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is because it seems like this crowd is

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pretty savvy about that so the first

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goal this project was what we're all

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trying to do basically detect and

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characterize paleo archaean habitats

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that we might be able to use for a proxy

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as other habitats on you know planetary

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systems the other goal was basically

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just to use Institute isotopic analysis

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of these shirts and courts to better

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piece together the petrographic story of

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these rocks so these are the three field

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areas that we used you're looking at the

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pill bark raid time again I think you've

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actually seen this map a couple of times

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today but we're in Western Australia so

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we are in the northwestern corner and

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the three sampling areas are

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unconformity Ridge and then there's a

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lot of data from the trendle locality

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and then camel creek a quick note about

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this the towbar kraton basically has all

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of these granitic complexes that are

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doming the sediments in the area and so

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the stroll a pool formation is this red

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formation that is basically wrapping

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around those domes within the area okay

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so here's a field shot of straw a pool

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formation we're looking directly down

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one of the underrated chert ridges the

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australia formation is bounded

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underneath by the couch aruna volcanics

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at around 34 26 million years old above

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the countryand volcanics we have an

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unconformity so there's some erosion and

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erosional period at that time and then

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basically at the base of the Strela pool

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we have these course clastic rocks and

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that grades upward into finer salissa

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classics and then finally into church

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and stromatolite éclairs towards the top

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and then it's capped again by this

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course clastic interval

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so going through those here's the basal

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conglomerate of the straw a pool you

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move up one and you're getting into a

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little bit finer sedimentary rocks sand

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stones and shirts up a little further

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and you're into the bedded shirts and

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then all of our favorites stromatolites

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is what you start to see after that on

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the Left we have stromatolites that are

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dolomitic stromatolite so there's

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actually some carbonaceous stromatolites

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preserved and you can see that parts of

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these stromatolites have been solicited

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so these there's these little salissa

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fication fronts that come through and

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and just partially replace and some of

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you doing stromatolite research I'd love

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to ask about this later but and then

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anyway on the left or sorry on your

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right we have a completely solidified

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stromatolite which is what we more often

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see in the Cyrillic pool formation and

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then finally we have basically druzy

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coliform quartz veins that cut across

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the strongly pool formation and

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sometimes these breeches up towards the

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top so just a quick review on oxygen

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isotopes I know most of you know what's

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going on with this but we have a plot

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here showing temperature on the y-axis

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and Delta 18 on the x-axis and then

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these curves that you see are

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representing different values of water

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and so meteoric water tends to be light

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that's the evaporated water that we've

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talked about sea water tends to be at

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around 0 per mil that comprises the

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Vienna standard mean ocean water

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standard and then finally we have

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formation brians which are just

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basically base know Brian's that have

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undergone long interactions with rocks

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and have become ice topically heavier

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due to that and so you can see that this

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is basically representing church forming

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at equilibrium with these waters and so

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if you form a church at equilibrium at

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100 degrees Celsius with the water of

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say zero then you should get a value of

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about 21 22 per mil okay so precambrian

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shirts tend to be light

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over here in this 10 to 15 per mil which

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means that they're either warmer or that

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the oceans were basically isotopically

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negative vana Rizzo cherts format these

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higher isotopic values indicating

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probably cooler formation temperatures

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so the reason I bring this up is there's

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this long-standing debate basically

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about what this curve through time means

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so shirts in the past tend to be ice

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topically lighter and then through time

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they become heavier so scientists have

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offered basically three different

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mechanisms for this trend at the secular

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trend that we see through time it is

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either due to oceans being lighter in

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the past temperatures being warmer in

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the past or just the fact that all of

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these rocks over here have SAT around

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longer so it's more likely that they're

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altered and seeing some hydro

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hydrothermal activity basically the gray

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curve you see here is from oberon

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Chalcedon and this is what they propose

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as the least altered shirts because any

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post meteoric or hydrothermal alteration

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should lower those isotopic values so

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then we bring up some of our data and we

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see that we've got this one group of

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data from the trendle location that's

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significantly above that curve so what

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does that mean so then we start getting

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into the textures micro quartz is

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basically one of the earliest textures

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petrographic textures that I see then I

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see this mezzo quartz which is a

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slightly coarse inversion of micro

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chords then we move into mega quartz

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which is often found in veins and then

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just throughout the sample and then we

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have cavity megachords cavity megachords

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is this euhedral quartz that's growing

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into cavities and voids like a geode in

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a way then there's detrital courts and

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sandstone cements and for any of you who

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have looked in a petrographic microscope

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I just want to mention this is a thickly

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cut section so that's why you're seeing

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high interference colors in courts

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and then finally we see Chow said me

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which is basically these banded

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radiating courts okay so that basically

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brings me to these two different groups

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that we see we see an earlier or sorry

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we see a lower Delta eight teen group

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and a higher deltoid teen group and the

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question was what is this higher Delta

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18 group and so with Sims basically

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going in we see that we really break

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this rule from robear in Chalcedon with

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this higher deltoid teen group basically

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that higher deltoid teen group is found

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in kept in this cavity mega courts and

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then basically all of these coarser

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textures which is telling us something

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Petra graphically and then finally these

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lower groups are found in these Petra

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graphically earlier textures and finer

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groups so moving into this a little bit

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out here you can see the groups that are

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basically this is that drusy cavity

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quartz I talked about earlier and then

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if we look at that with an SEM into one

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of the voids then you can see the sort

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of geode like texture I was describing

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and then further if I look at that with

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cl which is cathode a luminescence you

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see this really incredible zone texture

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in these and these in my mind are

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clearly late they're clearly growing in

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and coming in later so one of the

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questions we had was is this late druzy

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cavity megachords also present at depth

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and so we checked into the so we sampled

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from the court we sampled a core that

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was drilled through the stroller pool

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formation the Strela pool is in yellow

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and then the drill core traces in blue

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here and then basically we found that

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the outcrop Trent or we found the earth

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we sampled a transect at the outcrop

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above the drill core and then we sampled

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the drill core at depth and then we

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compared them and basically we found

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that we have sand stones and

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conglomerates of base once again then

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moving up into the

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is bedded shirts this is all ice topic

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lighter because it's volcanic courts and

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so this is the actual detrital grains of

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quartz and then we saw this step up

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whoops and we saw this step up right at

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the BET right at the boundary between

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shirts and sandstones and glamour 'it's

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in both the samples at depth and on the

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surface but you'll notice over here the

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delta 18 does not get up to that 30 per

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mil that you saw earlier okay so here's

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some of the enca to work we did we found

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that the micro court cements we're right

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around 14 per mil and then that the

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dreidel quartz was right around this

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kind of 10 to 11 12 per mil this is an

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example of that there's the 14 per mil

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courts in the cements and then the trial

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court's is right around 12 so what we

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found based on all of this is that we

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have these Petra graphically early

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textures that define this lower group so

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these are the sandstones this peak ends

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up being basically sandstone right here

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that 14 per mil that I showed you

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earlier and then these end up being

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those Petra graphically early micro

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courts from the trundle locality

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straddle it exert and so that's so once

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again we can see that these early

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textures tend to be within that that

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range of precambrian turrets that we see

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and then finally the later textures tend

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to be in that 22 to 30 per mil range so

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what we conclude from this is that we

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think this there's an early salissa

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fication front possibly hydrothermal

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that comes through and forms these low

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delta 18 microcrystalline and earlier

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textures in the courts we think that

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late diagenesis or some sort of warm

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heavy delta 18 fluid probably forms this

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drusy cavity megachords and this is a

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little difficult to constrain we're not

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the exact timing of this just that it's

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late it's Petra graphically late to the

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story drill core samples tend to be very

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similar to the samples at depth

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indicating that at least in this area we

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didn't have that presence of drusy

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cavity megachords we didn't have that

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high delta 18 group for one reason or

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another in that sampling area and then

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finally what we've concluded from this

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is at least within the Strela pool

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information shirts are probably not a

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viable proxy for either the temperature

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of paleo archaean sea water or the Delta

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18 at paley are key in sea water and

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with that I'll take any questions that

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oh sure you're in my blind spot thank

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you not knowing anything about the feel

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I have a stupid question is there any

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evidence about the you're experiencing a

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critical global warming in the history

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of the earth it's I know Easter 11 but I

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I think what we found is actually that

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but most of this is probably due in my

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mind to hydrothermal activity if I were

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to give a single answer to why I think

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the trend that there's the secular trend

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in church through time it could be that

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there's just increased hydrothermal

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activity throughout the Precambrian and

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that you know your charts are forming at

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this sea water you know sea water

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sediment inter interface at the base of

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the sea floor and that's where those

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circulation cells would be and so it's a

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potential that this whole trend that

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we're reading into and trying to figure

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out ambient sea water temperatures we're

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really just were just reading that the