Talk:Stac Fada Member

Article name

The current name is not used by any sources outside wikipedia and its mirrors/derivatives. The scholarly publications use the term 'eject blanket' but don't give it a separate name outside the 'Stac Fada Member'. I think that it would make more sense to move this page to Stac Fada Member, allowing both the historical and current interpretations of the deposit to be presented. Mikenorton (talk) 10:17, 21 May 2011 (UTC)

Fine by me - only question on that front is should the "m" be lower case? Any idea where the "Stac Fada" is? Ben MacDui 10:36, 21 May 2011 (UTC)

Upper case 'm' is used in 'The geology of Scotland', the Stewart Geol. Soc. Memoir 24 and both the Amor et al. and Parnell et al. papers - searching more widely on googlescholar the great majority (>90%) use upper case. Stac Fada is a small 'fin-shaped' sea stack in Stoer bay. Mikenorton (talk) 10:57, 21 May 2011 (UTC)

Well it took me the best part of four years, but I've moved to the new title. Mikenorton (talk) 12:00, 22 March 2015 (UTC)

Thickness of Stac Fada Member

This article currently assigns 3 different thicknesses to the Stac Fada Member: (1) 4 to 10.5 m (source is not cited), (2) 6 to 22 metres (source is a 2008 newspaper article) and (3) 10 to 15 metres (source is the British Geological Survey). Since the BGS has the definitive final say on British stratigraphic units, I suggest the article should use only the BGS's figure, unless a source can be found showing that the BGS is wrong. Any comments? GeoWriter (talk) 16:27, 23 March 2016 (UTC)

There are a lot of different numbers out there. Simms 2015 gives a range of 2m to about 12m. Amor et al. 2008 give a maximum of >20m. You would hardly think that they had been to the same outcrops, however, I think we have to live with this inconsistency and just say something like "varying from as little as 2m in thickness (Simms 2015) up to a maximum of >20m (Amor et al 2008), althought the BGS give a range of 10-15m (BGS)". Mikenorton (talk) 21:24, 23 March 2016 (UTC)

Lairg gravity low

I've made some minor updates to document the 2015 research with academic citations, reference a popular TV account (unsure if that's Wikipedia-appropriate), and correct occasional use of “miles” to “km”: while I'm aware that this is a UK article and UK articles should generally use miles for distance, earlier editors had used km, the scientific papers cited use km, and this is an article on a scientific topic — which I suspect would also argue for use of metric units. Happy to be corrected on this. Conrad Hughes (talk) 09:44, 17 August 2017 (UTC)

@GeoWriter (talk · contribs) re: secondary source wanted, what would satisfy here, given that the research is recent enough that there probably won't be many responses? You mentioned previously that there was some subsequent discussion in the PGA; with a bit of effort I might be able to access that. Helpful? Or is it ok to just leave it dangling until such time as further work is published? Or is it enough to just cite newspaper articles? --Conrad Hughes (talk) 09:44, 17 August 2017 (UTC)

Conrad Hughes, a problem with reporting recent scientific research on Wikipedia is that the scientific content of Wikipedia is supposed to report the current consensus among scientists working in a particular field. Wikipedia is not supposed to be a newspaper reporting latest scientific findings. That is the role of scientific journals (primary sources) and, of course, newspapers. I find newspaper articles about science to be problematic anyway because they usually just uncritically report the primary source's findings without any independent analysis. In my opinion, primary sources may be acceptable, in the absence of secondary sources, if they are only sourcing facts. If primary sources are used to source interpretations of data or advocacy of a hypothesis, then they are much more problematic and should be avoided. This article uses a primary source in the latter manner, so it is likely to result in deletion of the text if a reliable secondary source cannot be found in the near future. I suggest that we leave things as they are for a while, to see if a secondary source becomes available.

Any comments, Mikenorton?

GeoWriter (talk) 14:15, 17 August 2017 (UTC)

Removed the content in question as secondary sources are needed. Vsmith (talk) 14:41, 17 August 2017 (UTC)

Mildly at a loss here, and apologies if this appears to be timewasting: GeoWriter seemed to concur that it'd be worth mentioning the 2015 research in this article when I asked about it on talk here last April. The 2008 section cites a press release and a journal article, while the 2015 section that I tidied up cited a TV programme, some news coverage and (after my edit) a journal article. So surely both are only substantively backed by "primary sources" (given that news media are problematic as secondaries for science), and Vsmith should have removed the 2008 section too? If this article is to represent consensus, should it not give more prominence to the established volcanic interpretation (only mentioned incidentally in the 2008 section) that the 2008 and 2015 work seeks to overturn? Following Mikenorton's suggestion, would it be reasonable to remove the 2008 section (since 2008/2015 are now briefly mentioned in the introduction) and to add the pre-2008 consensus to the introduction? It may be that there's other published material which establishes the 2008 theory as "consensus", but it's not cited here, so far as I can see. Conrad Hughes (talk) 14:16, 21 August 2017 (UTC)

Originally the member was interpreted as volcanic in origin. Later is was reinterpreted as being impact-related. The paper on the Lairg anomaly proposes that as a likely location for the impact, but doesn't change the interpretation of the deposit at all. It is worth a mention, but it's not the main point of our article. Mikenorton (talk) 20:39, 21 August 2017 (UTC)

Sorry, should have tried to make my point more concisely: if the 2008 (impact not volcanic) view is now consensus, then shouldn't that be demonstrated by citing something other than the 2008 primary source? I'm failing to understand why the "secondary source needed" tag didn't get attached to the 2008 paper citation as well. While the 2011 paper also cited cites 2008, it's about age not origin, and explicitly seems to acknowledge that 2008 is not yet canon on p.356: "Although we have assumed an ejecta origin [..] volcanic origin would be similarly rapid". — Preceding unsigned comment added by Conrad Hughes (talk • contribs) 22:12, 21 August 2017 (UTC)

I've changed the section as described below. I'm adding in another 2015 paper, Reddy et al., which provides extra evidence of the impact origin. Mikenorton (talk) 12:57, 26 August 2017 (UTC)

I think that the main problem was the way it was presented. '2008 research' is an odd title for a section - I would prefer simply 'Interpretation'. Under such a heading two possible locations could be mentioned, the Minch and the Lairg anomaly. Virtually all the sources for an article like this are likely to be primary, unless this turns up in a book or a review paper. There is no direct evidence of the location of the impact, so everything else is just informed speculation. The article should in my view concentrate on describing the unit and its genetic interpretation, with just a mention for the likely impact location. Mikenorton (talk) 14:51, 17 August 2017 (UTC)

Please update from a new paper

This report in The Guardian says that new research has been published on this topic.

• Sample, Ian (10 June 2019). "Ancient asteroid crater located off coast of Scotland". The Guardian. London.

The report cites the following paper, which gives more details:

• Amor, Kenneth; Hesselbo, Stephen P.; Porcelli, Don; Price, Adam; Saunders, Naomi; Sykes, Martin; Stevanović, Jennifer; MacNiocaill, Conal (9 June 2019). "The Mesoproterozoic Stac Fada proximal ejecta blanket, NW Scotland: constraints on crater location from field observations, anisotropy of magnetic susceptibility, petrography, and geochemistry". Journal of the Geological Society: jgs2018-093. doi:10.1144/jgs2018-093.

I'm a bit out of my depth in this area, can a specialist please update the article? Verbcatcher (talk) 00:40, 10 June 2019 (UTC)

I have access to the paper, so I will use that, rather than the Guardian, to update the article. The paper proposes a possible location based on several lines of evidence, but there is still considerable uncertainty, which is why additional geophysical surveys have been suggested. Thanks for raising this. Mikenorton (talk) 09:20, 10 June 2019 (UTC)

I've added sections on the extent and description of the unit and rewritten the interpretation section to incorporate the new findings. Mikenorton (talk) 14:01, 12 June 2019 (UTC)

Questions that we should try to anticipate

We mention Evidence for a bolide impact in the Minch or near Lairg, which suggests that an impact in the Minch would have been into the sea. Is it known whether this area was sea at the time? If it was then presumably a tsunami would have been generated – is there any evidence of this or estimates of its magnitude? Can we say if it would have been a sea impact, or a land impact, or even if it is unclear whether it was land or sea? Should we say Evidence for a bolide impact in the area of the Minch or near Lairg?

We link to the bolide article. Presumably the 'Geology' section of that article is intended, which says:

• [...] For example, the Woods Hole Coastal and Marine Science Center of the USGS uses bolide for any large crater-forming impacting body whose origin and composition is unknown, as, for example, whether it was a stony or metallic asteroid, or a less dense, icy comet made of volatiles, such as water, ammonia and methane.

Does the presence of platinum group metals indicate a metallic asteroid? Should we change our terminology, or give a explanation of what bolide means in the context of this article?

Are there any estimates of the diameter of the bolide? Verbcatcher (talk) 20:14, 12 June 2019 (UTC)

I've made the change to the lead section that you suggested. It was definitely a land impact, but there is strong evidence for the presence of a significant amount of water at the impact site based on the amount of melt material included in the unit (that's in the recent paper), so perhaps a lake, but that's just speculation and is not addressed further by the authors. There is nothing else published to my knowledge to say what kind of impactor we're talking about. The sources do use "meteorite", so I am happy to see that used instead of "bolide". Mikenorton (talk) 20:57, 12 June 2019 (UTC)

You have changed bolide to meteorite in the lead, but we still have Evidence for a bolide impact close to Ullapool was published.... Verbcatcher (talk) 23:23, 12 June 2019 (UTC)

Now changed - thanks for pointing that out. Mikenorton (talk) 08:08, 13 June 2019 (UTC)

Another new paper

The latest addition to the literature on the Stac Fada Member is Osinki et al. (2020). They interpret the deposit to be a result of Melt Fuel Coolant Interactions (MFCI) rather than a true ejecta blanket. They argue that the general low number of shocked clasts and grains rule out there origin by ballistic fallout of an ejecta blanket, but are consistent with deposition from "high-energy ground-hugging sediment gravity flows". They compare the deposit to suevites from the Nordlinger Ries and Mistastin craters, which are very poorly sorted and ungraded, interpreted as ejecta blanket deposits, and with suevites from the Chicxulub crater (upper impact melt unit in the Peak ring borehole M0077A) and Sudbury impact structure (e.g. the Onaping Formation) which are well-sorted and graded, interpreted as the result of MFCI, with water re-entering the impact craters and interacting with the extremely hot impact melts, leading to repeated quenching and fragmentation similar to what is found in some phreatomagmatic volcanic eruptions. The Stac Fada Member is well-sorted and graded and does not appear to be a result of ballistic fallout, with other similarities to the Sudbury and Chicxulub examples. I'm not sure exactly how to incorporate this information and I've partly written this down to get it straight in my own head. Mikenorton (talk) 11:46, 25 October 2022 (UTC)