From Clastic Detritus: Sea-Floor Sunday #22: A actively-growing mound on the sea floor (Hat tip: Anaconda)
A paper came out in Marine Geology last month (v. 250, p. 258-275) about a methane-seeping, actively-growing sea-floor mound in Santa Monica Basin (offshore Los Angeles, CA).Here is the abstract: Association among active seafloor deformation, mound formation, and gas hydrate growth and accumulation within the seafloor of the Santa Monica Basin, offshore California.
It’s like a zit on the sea floor!!
Continuous streams of methane gas bubbles emanate from the crest of the northeastern mound, and extensive methane-derived authigenic carbonate pavements and chemosynthetic communities mantle the mound surface.
ABIOTIC METHANE DIAPIR AND MOUND OFF CALIFORNIA COAST
ReplyDeleteThe geological feature depicted is a growing mound with diapir emanating methane. This is consistent with 'solfataric' vent activity. 'Solfatarism' associated with hydrocarbons is a key to Abiotic Theory.
This feature is in the Santa Monica Basin roughly 2600 feet below the water surface. These roughly 30 feet high by 300 feet long mounds protrude from the crest of broad anticlines that are part of a series, approximately 66 feet high and anywhere from slightly over half a mile to a mile and a half long. These anticlines formed within latest Quarternary-aged seafloor sediment associated with compression between lateral offsets in regional faults.
This feature is also consistent with characteristics of an underwater mud volcano.
Onshore there is evidence of 'solfataric' activity in association with the California oil fields. The growing mound suggests "active pressure" under the mound from a specific 'point source', much like the bulging flank of a volcano due to increased internal pressure.
The scientific paper states, "continuous streams of methane gas bubbles" rise from the diapir in the middle of the mound.
This writer suggests that methane or a combination of methane and oil is rising from a deep "source fault" in the basement related to larger tectonic faults in the region, and thus travels up through the stratigraphic column by way of vertical fissures acting as conduits ending with escaping methane and a bulging mound.
The key evidence which supports Abiotic Theory with regards to this sea-floor mound and protruding diapir is the continuous pressure as expressed by the growing mound and sustained stream of methane gas. These characteristics are consistent with a 'point source', which is 'solfataric' in nature.
Repeated field observations have documented the association between hydrocarbons gasses and 'solfataric' vents. This is more consistent with Abiotic theory than "fossil" theory.
WHAT "FOSSIL" THEORY SAYS:
ReplyDeleteOf course, "fossil" advocates wouldn't agree with the above Abiotic Theory description of this under-sea methane "zit."
They fall back on words like "diagenesis" to describe make believe "miracles" that oil geologists have never been able to reproduce in the laboratory or describe in quantitative terms (mathematical equations constrained by chemical and physical laws).
In this case, with the methane emitting diapir and bulging mound, "fossil" theorists maintain the gas rises after a "miracle" process, oops, diagenesis, in so-called source rocks.
Then the gas works its way up through vertical fissures acting as conduits for the gas -- in this geologic description, the two rival "schools" of thought are much the same.
The distinction is that "fossil" theory maintains diagenesis and categenesis combine to cause a "conversion" into oil out of so-called "kerogen" which somehow manages to emerge out of an impermiable veneer like layer of rock.
Abiotic Theory states no miracle happens in so-called "source rock," rather, this impermiable rock such as shale, acts as a channeling or trapping structure, and most definitely is not the source of the oil & gas.
Rather:
There are "source faults" in the bedrock out from which oil & gas emanate through a cycle of pressure & expansion & collaspe & subsidence & finally expulsion of hydrocarbons up toward impermiable sedimentary layers in the stratigraphic column where oil can't penitrate. The impermiable rock then serves, either, to channel the oil & gas until the oil & gas finds a fissure or crack to squeeze up through, or, to trap the oil & gas in an impermiable reservoir structure. The oil & gas that manages to continue squeezing up is then caught by a subsequent layer of impermiable rock in the column with its own trapping rock, acting to guide or block the hydrocarbon's upward travel.
This pattern is repeated, either, until the hydrocarbon escapes to the surface, or comes to ultimate repose in a impermiable trapping structure forming an oil reservoir.
In Abiotic Theory a key concept to remember is the emanation of oil & gas by cyclical expulsion through "source faults" in the crystalline basement. These "source faults" are usually related to a larger tectonic fault network.
The more active the network of faults the larger the oil deposits are likely to be.
"Fossil" theory only deals with tectonic faults as a secondary cause of oil deposits, as opposed to Abiotic Theory which states that tectonic faults are a primary cause of oil deposits.
This principle has been observed by the association between the location of tectonic faults and giant oil fields all over the world.
I don't see how such a formation could be abiotic. An abiotic formation just seems to be of a few orders of magnitude much greater than a biotic origin. 1.2 kilometers by 0.6 kilometers seems too small for something that theoretically should be coming from plate tectonics....at least in my opinion.
ReplyDeleteQuantum_Flux, let me guess? You're a geologist.
ReplyDeleteNo, but I see no reason why this particular process can't be biological though. If there is ever a discovery of close-to-the-surface biotic crude oil production, then I want to get a new microbial pet "fishtank". So far, all I officially know about is methane and hydrogen sulfide producing bacteria though. Who knows though, perhaps that woodchip eating, crude oil crapping bacteria experiment will pull through in just a couple weeks or so. The "London Times" is England's oldest and most respected newspaper so I'm giving them the benefit of the doubt on that article, but of course we'll find out soon enough.
ReplyDeleteAnaerobic Digestion
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ReplyDeleteAlthough, it is interesting that the carbon composition is as such:
ReplyDeleted12C = 28.8% (???)
d13C = 70.8‰
d14C =<0.4%
I'm not real sure where that carbon came from.... serpentine belts!? biologic detritus!? a combination of both!?
Anyhow, I can't quite draw conclusions from this since I have high uncertainties. I'm no geologist or deep sea biologist, so I certainly can't rule anything out just yet. I was making a size observation though, and my assumption is that 0.5 km^3 is not that much methane if you give algea a long enough time (millions of years) to settle into sludge at that spot.
RESPONSE TO QUANTUM_FLUX
ReplyDeleteEditorial note: It has been brought to my attention that my writing style has been obtuse and difficult to follow. In an effort to be more fluid, I will drop the "this writer," in order to be more readable.
To Quantum_Flux:
Abiotic Theory operates on a "continuum" scale. In many things "size does matter," but Abiotic Theory applies to geological phenomena at all points on the spectrum of geological activity.
Yes, Abiotic emanations start from plate tectonic activity, but on the course of traveling up the stratigraphic column through various sedimentary layers, the amount of hydrocarbons escaping to the next higher level can be quantitatively reduced in scale.
Also, not all expulsions start out equally. Some are larger than others.
Quantum_Flux, would you agree 'Solfataric' activity can exist on a variety of scales from small vents to Yellowstone's ol' Faithful geyser?
Abiotic Oil is no different.
Economically, the oil industry isn't interested in "small vents," but as to whether Abiotic oil can exist on a small scale I have no doubts.
As to this particular methane diapir, it's relatively small scale doesn't mean there aren't larger deposits deeper below in stratigraphic column.
This diapir is above a tectonic network. The abstract (I don't have access to the paper itself) makes reference to tectonic activity below the mound.
Also, you can have low activity tectonic faults like the ones in Oklahoma and Kansas, where the oil deposits aren't large. The Appalalchian fault system is relatively inactive, thus the oil deposits in Pennsilvania were relatively small.
In the early part of the 20th century folks were prospecting for all kinds of oil deposits in Ohio, Indiana, even Missouri, but the deposits were small -- reflecting the less active fault network in the region.
Once larger oil fields were discovered these smaller ones weren't pursued.
Sorry, Quantum_Flux, there are no "fossil" theory oil deposits. That's the big mistake geology made in its infancy that it never was able to outgrow.
It's why I pursue this issue tenaciously, its the biggest myth since people believed the Sun rotated around the Earth.
But geologists just can't come to grips with the fact they screwed up so badly.
Geologists are right there with the Spanish Inquisition.
Geologists and the Catholic church. Who would of thunk it.
To Quantum_Flux:
ReplyDeleteI'm curious, I've stuck your nose in the poop (science), like a bad puppy during "paper training."
How come you are so bent to avoid the real science of Abiotic Oil that is right here in front of your face?
That cognitive dissonance must be pretty strong by now.
Give it up. What you were taught as a kid is false.
Oil is Abiotic -- that's the science.
Stack up the science of the two rival theories. It's not even close.
Abiotic Theory has the science. "Fossil" theory has made-up words to describe made-up happenings.
"Fossil" theory has no more science than the Piltdown man hoax.
C14 is radioactive and has no connection with biological organisms.
ReplyDeleteWell, I see no reason why oil needs to be formed under extreme heat and pressure (although, it has been shown to form in that way by Russian scientists). To me, however, long chains of hydrocarbons seems like a process that can be biotically generated, like DNA or any other organic molecule....(glucose from photosynthesis; methane, ammonia, and hydrogen sulfide from anaerobic bacteria; plant and animal oils; alcohols; the all too numerous other stable and unstable organic compounds containing nitrogen, carbon, oxygen, hydrogen, and/or sulfur; etc).
ReplyDeleteAnyway, life is incredibly versatile, I would definantly be hesitant to rule that out as an origin of higher order hydrocarbons. There are seemingly endless possible combinations in which life has been shown to put organic molecules together on this planet (and maybe on other planets as well).
And yes, I would be ruling out abiotic oil origins at my own peril too if I were to reject it. There is good evidence of fault line oil production and perhaps in serpentine belt methane production.
However, for all I know, it could easily be a combination of both processes as in Gold's "Deep Hot Biosphere". Thermophile bacterias have been found at volcanic uprisings and ridges, so perhaps there are extremophiles (the theoretical limits for carbon-based life would be carbon-carbon bond ionization temperatures as per Gibbs Free Energy values, and there would also be a lower temperature limit for C-H bonding [actually, I have to check that particular statement though, C-C may be a weaker bond than C-H]).
I think it is wise to say that science simply does not know all of the factors conclusively at this point, and therefore I'll just keep my mind open to all of the possible crude-oil theories.
71% C13 would obviously be abiotic.
ReplyDeleteBut even if there were 0% C13 it would still be abiotic since carbon stars HD13716 and HD182040 show no trace of C13.
Oil is Mastery said "C14 is radioactive and has no connection with biological organisms."
ReplyDeleteOh yeah, thank you for reminding me.
How does C-13 form?
ReplyDeleteC13 is formed the same way all elements and compounds are formed, namely abiotically. Unless you believe the elements in the periotic table are biogenic because God created them.
ReplyDeleteC-12 forms in 3rd generation stars as a result of fusion of 3 alpha particles...I was just wondering how, nuclearly speaking, do you get C-13.
ReplyDeleteAnyhow, I found bond energies (kcal/mol)....
C-H 98
O-H 110
C-C 80
C-O 78
H-H 103
C-N 65
O=O 116 (2 x 58)
C=O 187* (2 x 93.5)
C=C 145 (2 x 72.5)
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ReplyDeletePeriodic, excuse me, pardon the typo.
ReplyDeleteRecall that the inventor of the periodic table of elements, Mendeleev, was an abiotic hydrocarbon theorist.
ReplyDeleteC-13, aha!
ReplyDeleteI guess if you bombard C-12 with a proton, then it releases a gamma particle forming unstable N-13, which then decays into C-13 with the release of a positron and a neutrino....which is why it is a stable isotope. C-13 is a transitional fusion phase on the way to the production of N-14 which is also stable.
ReplyDeleteI would say that extremophiles would require higher bond energies to survive....hmmm.
ReplyDeleteTo Quantum_Flux:
ReplyDeleteI see that you have worked your way through the problem, good -- that's science.
(My apology for being tough on you.)
But in the interest of accuracy and fairness an item must be clarified.
The figure you provided of 70.8% isn't a percentage of the total C13 in the methane.
The proper figure as supplied by BrianR on his blog, Clastic Detritus, in the comments section, as taken from the original paper is as follows:
d13C value of -70.8% (PDB).
PDB stands for Pee Dee Belemite.
As taken from J.F. Kenney's "Dismissal of Claims of a Biological Connetction for Natural Petroleum" (Available by direct link at left-hand column under Oil Science):
"The carbon isotopic ratio designated C13/C12, is simply the ratio of the abundance of the carbon isotopes C13/C12, normalized to the standard of a marine carbonate named Pee Dee Belemite. The values of measured C13 ratio is expressed as a percentage (compared to the standard)."
So -70.8% is a much lower number than for organic detritus which averages -20% to -30% PDB. This average is taken from a (Mello & Moldawan, 2005) diamondoid dismissal paper, also available on this website.
The authors of the paper in question state, "this methane must be migrating form a gas reservoir at greater depth because the continuous flow observed...could not be sustained by local methane production."
But because they are conventional geologists that can't or won't take an Abiotic explanation into account, they miss the obvious conclusion: The gas came from great depth because C13 was stripped out to a high degree due to the greater distance travelled up through the stratigraphic column.
Look at the PDB value, -70.8%. This is much lower than organic detritus which averages between -20% to -30% PDB: Per Kenney: The further the carbon travels, the more C13 is stripped out by the terrestrial environment.
This gas travelled a great distance through the stratigraphic column to reach that number. Likely deeper than where orgainic detritus would be located.
So we know the methane came from great depth, not just by qualitative deduction as presented by the papers authors, but also by inductive, quantifiable chemical observations compared against quantifiable laboratory experimental results.
That's solid scientific analysis, right there folks. That's not simply "rhetoric" as complained about by BrianR in the comments section on the posted article.
This leaves two viable options: It is Abiotic methane or Biogenic methane -- but the great depth weighs against the Biogenic conclusion.
And this result confirms something else: The laboratory experiments results as reported by Kenney are confirmed by field observations: This proves that isotopic ratios are not reliable to prove carbon's origin when collected from the sedimentary column.
Isotopic ratios can't be used to prove petroleums origins, just as Kenney argued in his paper.
Another strike against "fossil" theory, which has relied on this isotopic ratio as "proof" of oil's origin from organic detritus.
I hope my comment clarified the discussion.
Thank you anaconda.... this is all beginning to sound like a slam dunk to me.
ReplyDeleteIs that formula -71% =100*[(C13:C12)/(PDB)-1] then, or is it something else?
Also, does the C-13 get stripped out as it is upwelling simply because it is a heavier isotope?
THE COMMENTS SECTION ON THE LINKED POST IS INSTRUCTIVE
ReplyDeletePlease read the comments section on the post this Oil Is Mastery post is linked to and based on.
(can be directly linked from this post)
The comments are instructive -- both because they demonstrate errors and obtuseness on my part, but, also, while only one young geologist (please be nice to him, or refrain from commenting), his attitude reflects, I believe, the geological community as a whole.
Also, it reflects their tactics as well.
Hide the crazy uncle, Sir Charles Lyell, one of the two "Fathers of Modern Geology" by not wanting to talk about Uniformitarianism, which increasingly fails to explain Earth's geo-mechanics.
Uniformitarianism -- its maxim
"The present explains the past."
Also, try to sound reasonable and objective (as a good scientist), but when "push comes to shove" and you're confronted by specifics of Abiotic Theory, get nasty and dismissive.
I'm not going to hold him for failing to answer specific points because his "school" leaves him so utterly unprepared to engage in "cross-discipline discussions" or dealing with a perpective from a rival "school" of thought.
Make no mistake, Abiotic Theory, without question, is a rival "school" of thought.
Abiotic Theory amounts to a "Revolution" against the "science" of geology.
Actually, I give Brian credit for the discussion we did have because the normal reaction from those supportive of "fossil" theory is to roll up the sidewalk and not respond to honest assertions or comments from the Abiotic perspective, at all.
Worship for authority within the discipline is demonstrated -- instead of engaging on specifics, I brought up, he linked me to a 700 page tomb, which is out of print on petroleum geology.
Sorry, I said I wasn't going to criticise his failure to engage in debate, but "pointing" to an old book is too illustrative of the general attitude of geologists to pass up.
My apology to Brain.
I do sincerely extend an olive branch of peace in the shared quest for knowledge & understanding to geologists, but I will not acquiesce to arrogance & tactics that violate the scientific method.
Honest and open dialogue and discussion being one of the fundamental requirements of the scientific method.
To the Greeks we owe our thanks.
To Quantum_Flux:
ReplyDeleteMy understanding is that '0.0%' would mean the carbon being compared to the standard marine carbonate, Pee Dee Belemite, has the same proportion of C13 as the Pee Dee Belemite.
Carbon is mostly C12 isotope, only a very small percentage of the total carbon present in any given sample would be C13.
A negative value constitutes a smaller percentage of C13 than the "control" Pee Dee Belemite contains.
And in the reverse, a positive number means it has more C13 than Pee Dee Belemite.
Remember, math is over my head, but here goes:
-70.8% PDB means the standard control number divided into amount measured in the sample carbon one is measuring. Please don't hold me to that.
I'd like to know what the equation is myself. but I suspect it's a division or multiplication like equation.
Let me know.
I think I have the right equation then.
ReplyDeleteTo Quantum_Flux:
ReplyDeleteI neglected to answer your last question. It gets stripped out because the C13 has a higher propensity to react with the terrestrial medium as it travels through it.
To quote Kenney in his paper "Dismissal of Claims...":
"There is a slight preference for the heavier isotope of carbon to react chemically with the rock through which it passes...[this is] entirely consistent with the fundamental requirements of quantum mechanics and kinetic theory."
I hope these two comments have provided the information you were interested in.
It's in per mil, not percent ... this is the equation:
ReplyDeleted13Csample = {(13C/12C sample) / (13C/12C standard) - 1} x 1000
Since you don't have access to this particular paper, I recommend the ODP publications, they are freely available and might be useful to familiarize yourself with these measurements and analysis.
This one is actually by the same author as the Santa Monica Basin paper, from the Blake Ridge.
This is the table of contents for the entire Leg 164 volume.
And zooming out a bit more, this is a portal to about 100 ODP leg proceedings, each with numerous chapters discussing topics you would be interested in.
Finally, what is great about ODP is that this is essentially data available to the public. YOU can reinterpret, write, and then submit a paper ... researchers do it all the time. What's more, if for some reason you don't like/trust the analysis, you can request samples from the core itself and do your own analysis! A LOT of researchers do this. You can fill out the sample request form here.
This is FREE data available to interested researchers. You can make a graduate thesis out of it if you really want.
Brian, Thank you for the information. Hopefully Quantum_Flux can make use of it and I will study it.
ReplyDeleteThanks, again.
I'll be damned, I don't believe I've seen that 'per mil' notation before. Is that standard x10 or something?
ReplyDeleteWell, -7.08% would mean that it is a shallower source of methane then. I take it you are saying that it is generally -2.0% to -3.0% PDB then anaconda?
ReplyDeleteTo Quantum_Flux:
ReplyDeleteI'm not sure what you mean.
The basis of my opinion is that if it was organic detritus from shallow depth it would have a similar value as the one Mello&Moldawan gave in their paper for organic material which was -20 to -30. Essentially, the descriptive word is "lighter." As in lighter in C13. So -70.8% would mean the methane from the diapir is lighter in C13 than organic detritus. And the argument is that the greater the distance travelled in the rock medium the lighter the carbon will be in C13.
That's my understanding.
My thinking was if the carbon in the methane had a number similar to the -20 to -30, say -25 that would indicate it came from a shallow deposit and could be from organic detritus.
My contention is that -70.8 shows the distance is greater because of the lighter amount of C13.
So, I didn't follow your reasoning for determining it was shallower.
Please explain.
To Quantum_Flux:
ReplyDeleteWe need a contrarian, here, to provide objectivity:
...(PDB) and dissolved inorganic carbon (DIC; 13C range -37.7 to +10.8 PDB) have parallel profiles with depth, but with an offset of 12.5. Distinct downhole variations in the carbon isotopic composition of CH4 and CO2 cannot be explained by closed-system fractionation where the CO2 is solely derived from the locally available sedimentary organic matter (13C -2.0 ± 1.4 PDB) and the CH4 is derived from CO2 reduction. The observed isotopic profiles reflect the combined effects of upwards gas migration and decreased microbial activity with depth.
Brian provided excellent material.
"Distinct downhole variations in the carbon isotopic composition of CH4 and CO2 cannot be explained by closed-system fractionation..."
This sentence suggests my interpretation is still in the 'game'.
What is your opinion Quantum_Flux?
Oh, I was merely making the observation that the difference between -30 and -70 per mil, is a much smaller difference than between -30 and -70 percent.
ReplyDeleteActually, that makes the difference of -4.0% instead of -40% like I was originally thinking....but still, I don't know if a -4.0% difference is that much or not, but I can imagine a -40% difference being on the order of 10x deeper or so.
Quantum_Flux:
ReplyDeleteI was thinking the reason they do move the decimal place over is because small differences do matter.
Well, there are actually a couple diffent things I can think of regaurding that.
ReplyDelete(1) Perhaps the carbon gasses are upwelling through finer pore spaces (and hence being stripped out at a higher rate per linear foot), in which case there would be more pressure from underneath to counteract the pressure head losses, but that would mean that it is of shallower origins then.
(2) Perhaps the carbon gasses are upwelling through larger pore spaces and over a much longer distance. If that were the case, then there would need to be some form of siesmic strain activity in the region (California->check), in combination with miles deep less dense material that has a much smaller packing geometry (like spheres or something light and amorphous).
....but then again, I'm just trying to visualize the situation and make predictions (more surface area exposed=more stripping per meter, less surface area exposed=less stripping per meter), but I haven't really read the report or read any geology textbooks or whatnot. I'm just spreading laterally if I can, and taking my knowledge of math, science, and chemistry with me.
Correction .... in combination with miles deep less dense material that has a much "LARGER" (as in more volumous) packing geometry
ReplyDeleteDECODING THE NUMBERS ON THE DATA PROVIDED: FIGURE 2
ReplyDeleteOil Is Mastery was provided excellent data, from samples of drilling cores off the South Carolina coast (the "Atlantic" study).
First, scientists interpret findings of physical observations, based on the "scientific" framework they apply to the data recorded.
So, the tendency is for conclusions to be drawn, which are in sync with the the observer's education and experience in a particular scientific framework.
Seperate scientific disciplines can draw different conclusions about the same data.
This can be expected.
This post has moved to a consideration of the isotopic ratios of the CH4 (methane).
The conclusion I have drawn is that the isotopic ratio (-70.8) of C13 in the methane (of the "pacific" study) is that it's indicative of methane from a deep source, which is consistent with the conclusion reached by the authors of the paper.
Although, my conclusion was arrived at by different considerations of the data.
A parallel study of a seperate location off the coast of South Carolina in an area known as the Carolina Trough was provided to give some depth to the discussion and consideration of the Santa Monica Basin methane "zit."
There is an extensive amount of quantifide data in the parallel study.
Some discussion was had about the meaning and relevance of this data in relation to the Pacific sea-floor feature.
While not taking an exhaustive review and interpretation of the "Atlantic" study, I note that Abiotic Principles were not applied to the data from either the "Pacific" study or the "Atlanic" study.
The "Atlantic" study can be directly linked from BrianR's 6/25/08, 9:57PM comment. It's the first link titled, "This one."
Please review what is listed as "Figure 2."
This figure depicts a graph of observed data, specifically, isotopic ratio values for C13 in methane and other gas samples at various depths below the sea-floor: The graph shows that the "ratio" for a body of methane samples was fairly constant as the depth below the sea floor changed, with the samples of carbon getting "lighter" in C13 just as the core samples neared the surface.
A body of samples from the carbon in the methane is considerably lighter than the carbon from seperate bodies of samples.
This suggests that the carbon in the "lighter" samples has travelled further in the starigraphic column or some other unknown factor is effecting the sample's isotopic ratios.
This suggests that the conclusion I made concerning the "Pacific" study has merit.
Regarding d13C CH4 values near the top of Fig. 2, the authors state:
ReplyDelete"Very negative 13CCH4 values are known to occur at the top of the methane-bearing zone throughout this region and numerous other similar locations worldwide (Borowski et al., 1997). The extremely depleted 13CCH4 values (e.g., ~-100) found near the sulfate-methane interface (SMI) are in part a response to local CH4 recycling (Borowski et al., 1997). At the SMI, extremely 13C-depleted CO2 (i.e., -37.7, 20.40 mbsf, Site 995) is derived anaerobic methane oxidation (AMO). Thus, CH4 produced from this CO2 pool (via CO2 reduction) will exhibit progressively larger 13C depletion."
The full citation for the Borowski et al. paper is:
Borowski, W.S., Paull, C.K., and Ussler, W., III, 1997. Carbon cycling within the upper methanogenic zone of continental rise sediments: an example from the methane-rich sediments overlying the Blake Ridge fas hydrate deposits. Mar. Chem., 57:299-311.
To what extent (quantitatively) that the distance the methane traveled throught the stratigraphic column influences the results is not explicitly addressed. However, the effect of the sulfate-methane interface (and associated microbial activity) on the measurements is profound and, from what I can gather, is the primary reason for sharp interface seen on Fig. 2. Methane is isotopically light (compare to other gases on Fig. 2) but note how all the curves become very depleted around the same depth (~20 meters below sea floor) ... thus, whatever explanation one postulates for the excursion in d13C in CH4 must also address the other measurements.
To BrianR:
ReplyDeleteI appreciate your contribution and input. Thank you.
Would that be consistent with abiogenic & less so with fossil gas?
ReplyDelete