you will also find that all the largest "meteorites" found on earth are all the special iron ones and none of them have an impact crater. there is a list of the main ones here, some photos and some links. i cant be bothered to copy them to here as its all ready written.
Lloyd
Re: Help Us Explain Crater Formation!
* Thanks for your link, Matt. I think I came across some of your images of possible huge [limestone?] fulgurites on Malta yesterday. Apparently, Lichtenberg figures, shatter cones and fulgurites are basically the same thing, just in different media. Feel free to provide more info here, if you like. * Thanks for your theory on the Carolina Bays, Gary. If you have the theory well developed, feel free to mention it here, or in another thread, with a link here. I know hail is considered to possibly formed by electrical forces and I know Marklund convection takes heat away from outer areas and concentrates it into inner areas, so I suppose hail could form in an outer area, while the lightning obviously occurs in inner areas. Regarding anything coming through the atmosphere, though, it seems that anything moving very fast through air would get very hot before hitting the ground. Do you have a theory about how the atmosphere would be moved aside or something? * I thought I should mention, that, In my previous posts above, in which I condensed and paraphrased info from some TPODs, I generally only included my own ideas in brackets, usually in the form of questions.
Lloyd
Re: Help Us Explain Crater Formation!
CRATERS WITH SHATTER CONES * I searched the world crater data at http://sci2.lefora.com/2011/01/18/17-2 to find out which craters have shatter cones. The list is below. Most possible shatter cones in Africa are considered more likely signs of wind abrasion, instead of shatter cones. However, as I found in crater TPODs above, EU theory says shatter cones are actually Lichtenberg figures formed by lightning. Therefore, it's not necessary for them to be cone-shaped. The report for the Glikson crater in Australia below mentions "poorly developed horse-tailing striations", but, again, Lichtenberg figures need not be "fully" developed. One report below says "Shatter fracturing forms striated sets of cleavages more commonly than well developed shatter cones". So what causes striated sets of cleavages? * If you find any of the data below interesting, you can see more details at the link above. If you live near any of these craters, you may like to go have a look at them.
AFRICA __El-Mrayer: Wind abrasion striations reminiscent of shatter cones are present in the area. No evidence of impact related rocks was found (Rossi, 2002). The impact origin thus appears unlikely. __Arkenu 2: Cited evidence for impact includes "shatter cones" close to the northeastern inner ridge and pointing to the center of the structure, [also] breccia and "planar fractures" ... The presented "shatter cones" ... could represent wind ablation features common in desserts. Incidentally, all photographs show only cone-shaped polished surfaces; none shows cones on freshly broken inner surface as could be expected for shatter cones. All studied cones are located in the NE quadrant of the structure, thus the pointing of their apexes toward the structure center is also consistent with the direction of prevailing winds indicated by the sand dunes in the area. The presence of breccia is also consistent with non-impact, possibly endogenic, origin. The reported planar fractures are not planar in fact ... and PFs are not considered diagnostic shock features __Arkenu 1: Cited evidence for impact includes [same as previous] __El-Baz: The basalt exposed at the rim shows wind erosional striations at its surface, reminiscent of shatter cones __Tarek (GKCF59): [There are] at least 50 circular structures ... [X] studied 13 craters 20-1300m in diameter with possible shatter cones and planar structures in quartz ... They reported raised rims, breccias at most of the studied structures and shatter cone-like features and subplanar microdeformation in quartz grains at some of the structures. ... They found the planar microdeformations in quartz, shatter cone-like features and breccias consistent with impact origin but recognized that it is an insufficient evidence. ... Di Martino et al. (2006) argued that the shatter cone-like features are clearly wind-born with directions aligned with prevailing wind orientation and the features crosscutting the breccia. ... Orti et al. (2008) ... found ... shatter cone –like features are surface wind abrasion striations affecting both clasts and matrix of the breccia and consistent with dominant wind directions. __Vredefort: Impact evidence: PDFs in quartz, shocked zircon, coesite, stishovite, shatter cones, melting
ASIA __Jebel Waqf as Suwwan: Well-developed shatter cones occur on numerous locations within the central zone. __Ishim: [X] also reported shattercones in Proterozoic microquartzite east of the village of Novocherkasskoe __TOKRAUSKAYA: [X reported] shatter cones, breccias and glass.-Listed by (Moilanen, 2004) __Ambar Lake: [X] found suevite and many shatter cones (Master, 1999). __Ramgarh: [X] reported tilted quartzite beds with possible shatter cones, anomalous nature of the feature with respect to surrounding geology. ... [X] found ... PDF's in quartz from multiple locations, no shatter cones. __Bigach: Shatter cones occur in the rim. __Beyenchime-Salaaty: Carbonates are brecciated within 0.5-1 km zone beyond the rim. Breccias within this zone contain shatter cones.
AUSTRALIA __Glikson: Macdonald et al. (2005) documented a conical feature with poorly developed horse-tailing striations and interpretted it to be a shatter cone. __Goat Paddock: [X] reported well developed shatter cones in the drilled rocks and some in the rim outcrops. ... [X] confirmed ... [with] photographs of poorly developed shatter cones and PFs, PDFs and melt in quartz. __Skirmish: [X] observed a ring of strongly fractured outwardly dipping quartzite with possible shatter cleavage __Matt Wilson: Joint and fracture surfaces within the central zone are undulating and striated with slightly divergent striae - different from slickensides but not quite shatter cones. These "shatter cleavage" surfaces were steeply dipping in a restored position __Gosses Bluff: The impact origin of the Gosses Bluff has been documented with multiple shock indicators (shatter cones, high pressure minerals, shock deformation in minerals, melting) __Strangways: [X] suggested impact origin based on the presence of shatter cones, melt breccias, central uplift, shocked minerals and radially and concentrically faulted target rocks ... Shatter fracturing forms striated sets of cleavages more commonly than well developed shatter cones ... [X] described various breccias, poorly developped shatter cones and shocked material __Kelly West: Shatter cones are abundant in the central uplift ... [There are] shatter cone photographs __Amelia Creek: ... "unequivocal" shatter cones. Shatter cones nearly 1 m long also occur in felsic volcanics. Shatter cones occur within area of ~6 km^2. After restoring beds in horizontal position, the shatter cones point toward south at ~5-10 º inclination ... Thin sections from shatter cones display planar microstructures, which appear to be cleavage and not true PDFs. Common are "feather features" stemming from the fractures at an angle and could represent incipient PDFs __Goyder: Shock evidence: insitu shatter cones within structural uplift with radial faults, one to multiple sets of PDFs in quartz typically decorated with fluid inclusions __Acraman: An impact origin was first demonstrated by Williams (1986) based on the discovery of shatter cones, PDFs in quartz, and devitrified melt rock veins in isolated shattered dacite outcrops on islands near the centre of the lake. __Lawn Hill: Well developed shatter cones and "planar lamellae" in quartz occur in Proterozoic siltstone and sandstone ... [X] confirmed the presence of shatter cones and suevite in the central uplift. __Crawford: Striated fracture surfaces (in some cases resembling shatter cones) and thin pseudotachylite veins are present. __Flaxman: Higly fractured rocks with thin pseudotachylites show "shatter cleavage", possible shatter cones and PDFs and mosaicism in quartz
EUROPE __St. Imier: Shatter cone? - feature is actually a head scarp of a landslide? __LAGO DI TREMORGIO: Shatter cone? __Dobele: The central uplift consists of upper and middle Devonian rocks, which are ~300 m above their original stratigraphic position. The rocks contain occasional shatter cones and shocked quartz. __Keurusselkä: [X] reported 10-km diameter (corresponding to where the shatter cones were originally discovered) __KIURUJÄRVI: Shatter cone? __Suvasvesi S: Shatter cones, PDFs, diaplectic and melt glass, brecciation, kink bands and fluidal textures reported __Jänisjärvi: The discovery of shatter cones and planar deformation features (PDFs) in a quartz clast from a breccia sample (Hopeasaari Island) proved the impact origin of the structure ... Shatter cones up to 20–30 cm long occur in metasiltstones (Masaitis et al., 1976). These metasiltstones probably belong to the Late Precambrian cover, which was overlain by the crystalline basement at the time of impact __Zeleny Gai: The drill hole near the center encountered 58 m of recent Cenozoic sands and clays, and 150 m of sandy- argillaceous Paleogene lake deposits with redeposited shocked crystalline gravels and boulders. Below it is 120 m of polymict allogenic breccia with shocked minerals and melt. Further below is cataclased granite with shatter cones and shock features. The shock transformations attenuate by the bottom of the drillhole at 380 m depth __Obolon: The impact evidence includes polymict breccias with melt, multiple sets of PDFs in quartz, kinked biotite, diaplectic glasses, coesite, diamonds and shatter cones. __Kamensk: Shock indicators include shatter cones, fragments of vesicular glass with rock fragments in the allogenic breccia, coesite in redeposited sediments. Quartz grains in the alogenic breccia also contain up to three sets of rare poorly defined planar elements.
NORTH AMERICA __Avak: Repeated intervals of Barrow sand host shatter cones, cataclastic deformation and increased percussion fracturing in quartz, chert and feldspar ... and planar deformation features __Black Rock: The central area of the structure (Black Rock Point) displays common centimeter to meter scaled features interpreted as possible eroded shatter cones ... The reported shatter cones do not appear convincing on the pictures. Nevertheless, if this is an impact site, there appears enough material preserved that should contain wide range of shock indicators __Beaverhead: Shatter cones and shocked rocks in southwestern Montana: The Beaverhead impact structure. __Upheaval Dome: described some shatter cone–like features in the center of the structure, but they did not fulfill the strict diagnostic criteria of shock-produced shatter cones __Santa Fe: [X] report the occurrence of possible shatter cones and anomalous megabreccia in the area ... [X] confirmed that unusually large shatter cones (up to 2 m long and 0.5 m wide at the base) occur within Paleoproterozoic granitoids and supracrustal metamorphic rocks over an 5.5 km2 area. The study further described random fractures, fluid micro-inclusions, sericite replacement in feldspar, rare kink bands in mica, optical mosaicism, decorated planar fractures (PFs) and planar deformation features (PDFs) in quartz, and probable melt pockets within the surface layer of the shatter cones ... [There is] basal (0001) crystallographic orientation indicating a peak shock pressure of ~5–10 GPa that is consistent with shatter cone formation __Pecos: shatter cones in a siliceous shale within the central uplift __Red Wing: breccia, shatter cones.... PDF's in quartz __Hico: probable shatter cone __Marquez: Evidence for impact origin of the structure includes shatter cones in Pecan Gap limestone and PDFs and glass in breccias in the central uplift __Howell: couple of shatter cones __Sudbury: Impact evidence: PDFs, shatter cones, impact melt __unnamed: Chibougamau tillite, instead of being glaciogenic, is better explained as the product of an ejecta blanket owing to an impact event, maybe the one responsible for the shatter cones observed within the stromatolitic dolomite unit of the paleoproterozoic Mistassini Basin which displays a suggestive curved geomorphic pattern __Mistassini: Breccia dikes and associated shatter cone like features reported in dolomites of the Proterozoic Mistassini Group from an island in Mistassini Lake __CONCEPTION BAY: shatter cones 20 km NNE from Holyrood Bay ... [T]here is disturbed basement rocks with breccias, shattercones and other shock metamorphic features
SOUTH AMERICA __Meseta de la Barda Negra: Possible shatter cones and breccia found on middle to upper crater slope __São Miguel do Tapuio: features similar to shatter cones and PDFs in deformed sandstones. ... Other observations: 1) the general absence of breccias or breccia-dikes, 2) the absence of shattercones, 3) the absence of shock-melt products in outcrop or thinsection, and 4) the absence of other shock-metamorphic indicators __Panela: occurrence of breccias with evidence of partial melting and shatter cones. Photographs document a rusty colored breccia hand sample and several fragments with striated surfaces but no clear shatter cones.
Lloyd
Re: Help Us Explain Crater Formation!
Problem regarding Reversed Strata around Meteor Crater * A TPOD about Meteor Crater said: A rotating electric arc worked down from the surface through layers of soil, spraying the material outward roughly in layers that reversed the original strata. * I thought that sounded reasonable, until I think I found that conventional theory seems to deal with the issue too. I don't remember if I read it, or just figured it out, but, if a meteorite impacted as a fireball that then exploded, it seems that the explosion from a few hundred feet underground could have pushed up and turned over the upper strata all at once and laid it on the surrounding rim. * I think the difference in the effects would be that a rotating electric arc would mess up the strata quite a bit, but would not leave big triangular gaps all around the rim, whereas an underground fireball explosion would not mess up the overturned strata much, but would leave big triangular gaps, which would fill in from ejecta.
Contradiction in 2 versions of EU Crater Theory #1. - The above-mentioned E.D. theory that - A rotating electric arc worked down from the surface through layers of soil, spraying the material outward roughly in layers that reversed the original strata - seems to contradict #2. - the theory from the Tycho Crater TPOD, which said: - A plasma leader stroke came down from space. - Triggering electrons then were assembled by atmospheric breakdown from distant points in all directions and attracted charged rocks and sand from hundreds of km. - The stroke hauled them to a common collection point and mounded them up loosely, due to like charges. - A secondary stroke then jumped upward, pulling out the center of the mound like a rotating auger of fire. - Raised rims are the remains of the original mound of loose material.
* In the 1st case the raised rim would have roughly reversed strata. * In the 2nd case the raised rim would have no stratification, but just be a jumble of rock and dust.
MattEU
Skylight craters
Lloyd wrote: * Thanks for your link, Matt. I think I came across some of your images of possible huge [limestone?] fulgurites on Malta yesterday. Apparently, Lichtenberg figures, shatter cones and fulgurites are basically the same thing, just in different media. Feel free to provide more info here, if you like.
good stuff in this thread Lloyd
as always for me something obvious and i could not see it or did not think about it. shatter cones as fulgurites. i had thought of shatter cones as created by the discharge and had them a scalability of the Kimberlite pipes but never connected them with fulgurites! Doh.
you may be interested in the The Kaali crater field in Estonia as one of its small craters has a cone in the middle and uplifted dolomite blocks. you can read the official pdf The Kaali crater field and other geosites of Saaremaa Island (Estonia): the perspectives for a geopark or i have done an EU based study on it including folklore. if you look at my study you will understand why i have not pasted it all here! obviously more than happy to discuss it all here or people to post images/content here from it if they ever wanted to.
The shape of Crater 4 has been strongly affected by geological excavations. Initially it was bowl-like, oval in shape and 14–20 m in diameter. On the distorted bedrock surface of its bottom, a funnel-shaped trace of the impact was discovered ... The largest number of meteorite fragments was found at the crater bottom itself, 3–4 m away from the impact trace.
what i have found when looking at craters is that they are in certain patterns and sizes. with roughly the same shapes and width and depths found in various places. some are the same shape and width but much deeper than others though.
for example the mysterious oval Meres of Norfolk, the Il-Muqluba in Malta, the Martian skylights and the Moon Skylights are very similar with only the depth varying
you also have the kidney shaped mere Fowl Mere Norfolk that is a similar kidney shape if not size to one of the crater lakes in Australia, one of the lunettes, around the Lake Mungo area.
Lloyd
Re: Help Us Explain Crater Formation!
* Well, Matt, I wasn't actually picturing shatter cones as fulgurites myself, but only as Lichtenberg figures. However, I can see the similarities among all three. * And thanks for the links etc. * By the way, at this thread http://thunderbolts.info/forum/phpBB3/viewtopic.php?f=10&am~ I just posted about YOUNGER DRYAS, AIRBURSTS, IMPACTS, SATURN FLARES, which is about the global cataclysm that occurred about 10,000 years ago and how both kinetic and electrical effects may have been involved in crater formation, because of increased electric current into the Saturn System at that time.
Lloyd
Re: Help Us Explain Crater Formation!
Problem with Central Uplifts via E.D. * Central Uplifts in craters on Earth may not conform to E.D. theory. They also may not conform to impact expectations. E.D. theory suggests that strata in central uplifts should be undisturbed by E.D., whereas impact rebound from a bolide should leave little or no stratification in the uplift. * I searched the world crater database, that I posted at http://sci2.lefora.com/2011/01/18/17-2, for central uplifts, to see if any descriptions matched E.D. crater with central peak theory. I only checked North America and Australia. I found a few in North America that are descriptive enough, but none in Australia. * The E.D. theory for formation of craters with central peaks at this TPOD, http://www.thunderbolts.info/tpod/2005/arch05/050811richatr~, says:
- The twisted Birkeland current of the discharge channel usually doesn't machine as intensely in the center of the crater and it leaves a formation of undisturbed material ranging from a slightly elevated mound to a tall spike of rock. The type of central "peak" depends on many factors: the narrowness, focus and intensity of the Birkeland current, the type of material being excavated and the material's current carrying capacity. - When the current is narrow and intense, and the material is dense, most of the excavated material is accelerated away from the area. The result is deep canyons and/or craters with steep walls and central spikes. Conversely, broad, less intense currents machine out shallow craters with central mounds, less steep walls, and material piled up along the edge and strewn around the more immediate area.
* From this I gather that the central uplift should consist of "undisturbed material". * This TPOD, http://thunderbolts.info/tpod/2006/arch06/061222twinpeaks.h~, seems to confirm this, saying that the central uplift "will show the same geologic structure" "as the surrounding terrain". "In other words", the central uplift's "geologic structure" "will be continuous with the surrounding strata."
* Here's what the database says about these 3 craters [central uplifts are disturbed].
__Avak crater in Alaska - (1) a central uplift about 4 km in diameter in which Lower Cretaceous rocks have been uplifted more than 500 m above their regional structural position, - (2) a surrounding annular structural depression, or ring syncline, about 1.6 km wide in which the top of Franklinian argillite lies as much as 300 m below its regional structural position, __Upheaval Dome in Utah - a central uplifted area with a stratigraphic rise of ~250 m.... - The inner part of the central uplift forms a morphological depression that is ~1.4 km wide and 300 m deep. __Calvin crater in Michigan - central dome ~4 km in diameter , with some strata anomalously thickened or missing and uplifted 415 m relative to the surrounding stratigraphy.
* If E.D. was involved in forming these craters, I can imagine that the pulling force, like that described for forming raised mounds, called fulgamites, could be involved in raising and distorting the central uplifts, but I don't see how it could form a syncline, or dip in strata, as described in the case of the Arak crater above. * Does anyone have a solution?
MattEU
Re: Help Us Explain Crater Formation!
GaryN wrote: Excellent work, Lloyd, can't argue with much of what you propose so far. I only have one comment at the moment, and that would be about the Carolina Bays. I believe they may have been produced by a combination of impact and electricity, from large, icy and charged 'hailstones' produced within the ionosphere. We don't give electronic cooling processes enough credit for either past or present events, IMO.
really interested in this idea, can you explain it further?
something like tunguska or Comet Shoemaker-Levy 9? the "hailstones" either cause a discharge crater when they hit or get very close to the ground. this would help to explain so many of them and why they point in certain directions. or could they be the result of the fragments of a meteorite and discharging?
GaryN
Re: Help Us Explain Crater Formation!
Hi MattEU,
really interested in this idea, can you explain it further?
I haven't put a serious proposal together MattEU, and perhaps when I get around to it I should put it 'downstairs'. But cold protons streaming into a region with increasing oxygen atom density, and the charge differential between inner and outer regions, well, I think something might add up here. The Bays just look like some kind of fluid impactor may have been involved.
dahlenaz
Re: Help Us Explain Crater Formation!
Greetings All, I just put an interesting picture up at the para-az.com site for Mars images in 3d. Its title, from the HiRISE site is "Interaction of cratered cone and crater ejecta". There are some real strange aspects of the features shown but the one that caught my eye is awhat looks like a crater made below and under the lip of an overhang. Here is the link to the 3D image http://para-az.com/dzpspm-9906.10196_2225-lrzcl.jpg
How can a crater become tucked under a the lip of an overhang? If it is a crater, ofcourse.
From an electric discharge crater perspective, as seen in CRT experiments, a crater chain is the result of a discharg from the surface adjacent to a previous discharge but not far enough away as to involve or create a fully circular crater. This feature has me wondering. 3dzp
Lloyd
Re: Help Us Explain Crater Formation!
CENTRAL UPLIFTS * I finished a search at http://sci2.lefora.com/2011/01/18/17-2 for data on Earth craters that have central uplifts and info as to whether the strata in the uplifts are continuous with strata outside the crater, or whether the uplift strata are at a higher level. Most of the uplifts appear to be raised up above the original strata, but some are not, such as Hudson Bay. The data includes suggestions by the researchers that some of the structures are not actually impact craters, but I include them because their suggestions may be wrong. * So far, I can't imagine how central uplifts could have strata intact after impact. It seems that the contents of the uplifts would have to be chaotic, rather than stratified, if they were due to rebound after impact. __Dobele: Latvia, Europe, 56.58, 23.25, 4.5 km dia, The central uplift consists of upper and middle Devonian rocks, which are ~300 m above their original stratigraphic position. __Boltysh: Ukraine, Europe, 48.95, 32.285, ~24 km dia, buried under ~30 m of Quaternary sediments ... Central uplift is 4 km in diameter at a flat top and records ~600 m stratigraphic uplift. __Mazoula: Algeria, Africa, 28.3779, 7.2085, .8km dia, Anticlinal dome rising 30-35 m above the surrounding horizontal strata. No trace of fracturing, brecciation or shatter coning found. The structure could be a result of diapirism of underlying soft rocks or a Cretaceous marine reef __Kebira: Libya/Egypt, Africa, 24.677, 24.97, 27x30km dia, Central core with positive relief surrounded by annular trough filled with sand. The rocks in the center appear to have a flat top suggestive of horizontal bedding similar to surrounding lanscape. __Habhab (=Oman ring): Oman, Asia, 19.87, 56.93, 6km dia, Chondrites found in the area but salt identified below the structure, no shock effects, ejecta, brecciation or fracturing found, the same strata in the rim found undisturbed inside the structure; suggested salt dissolution origin __unnamed (34.879, 65.354), Ghowr, Afghanistan, Asia, 34.879, 65.354, 12-16km dia, A round structure defined by perfect half-circle scarp 12 km in diameter, a more irregular remaining round rim 16 km in diameter, central elevation 5-6 km in diameter extending also further north. The central elevation reaches max elevation 2960 m asl, the rim elevation is ~2500 m asl, the annular depression in between varies around ~2000-2500 m asl. Bedding in the central high can be traced over long distance and appears gently inclined - rather inconsistent with an impact structure uplift or a volcano. __Matt Wilson, Northern Territory, Australia, Australia, -15.5, 131.18, 5.5km dia, A circular structure within Proterozoic flat and nearly horizontal siliciclastic sediments (shale to sand). The central ~1.5 km wide zone is intensely faulted, has steeply dipping fractured strata uplifted 300-500 m. Joint and fracture surfaces within the central zone are undulating and striated with slightly divergent striae - different from slickensides but not quite shatter cones. __Avak crater in Alaska, 71.233, -156.483, 12km dia, (1) a central uplift about 4 km in diameter in which Lower Cretaceous rocks have been uplifted more than 500 m above their regional structural position, (2) a surrounding annular structural depression, or ring syncline, about 1.6 km wide in which the top of Franklinian argillite lies as much as 300 m below its regional structural position, __Upheaval Dome in Utah, 38.4373, -109.9284, 10.4km dia, a central uplifted area with a stratigraphic rise of ~250 m.... The inner part of the central uplift forms a morphological depression that is ~1.4 km wide and 300 m deep. __Bee Bluff , Texas, USA, North America, 29.0275, -99.8458, 6.75km dia, exposed structure located in south Texas near Uvalde in Zavala County. A well was drilled in the center of the structure to a total depth of 356 m to test a strong gravity maximum. The well encountered a stratigraphic sequence, which was the same as the sequence drilled east of the structure but it was uplifted by 74 m. __Calvin crater in Michigan, 41.8257, -85.9457, 8km dia, central dome ~4 km in diameter , with some strata anomalously thickened or missing and uplifted 415 m relative to the surrounding stratigraphy. __Hudson Bay: Canada, North America, 57.9, -80.03, 230km dia, proposed impact origin of the Hudson Bay coastal arc with a coherent upraised rim forming 155 dg arc and basin filled with Proterozoic sediments, possibility of Hudson Bay being an impact structure with a minimum diameter 450 km. The best fit circle has a diameter 230 km ... no evidence of shock metamorphism or any indication that it might have been produced by an impact event. The Belcher Islands, which are often suggested as representing a central uplift, consist of a series of metasediments, unfractured and unbrecciated, from a higher stratigraphic level than the surrounding basement rocks outcropping on the shores of Hudson Bay. One would expect that the central uplift be composed of fractured and brecciated rocks from lower stratigraphic levels if Hudson Bay were an impact structure. Moreover, these sediments have been folded and thrusted during the Paleoproterozoic Orogeny (~1.85-1.80 Ga) by extremely slow tectonic processes quite incompatible with the rapid events that accompany impacts. Hudson Bay is still isostatically adjusting after retreat of the ice cover and it appears fortuitous that is has a circular form.
Lloyd
Re: Help Us Explain Crater Formation!
HOW DOES STANDARD MODEL EXPLAIN CENTRAL UPLIFTS? * Does anyone know how the standard model explains how strata in central uplifts are raised up without obliterating or mixing up the strata? It seems to me that, if the central uplifts were due to rebound of bedrock after impact, the rebounding rock would be all broken up and mixed together without any strata, i.e. stratification, being discernible. * I found one example of a cross-section of a central uplift of Sierra Madera Crater in Texas here: which is from this website: http://ceed.utpb.edu/geology-resources/west-texas-geology/s~ where there are some other images, including a top view of the crater. * I don't know if that image has enough detail, but it looks to me like a bolide impact would not produce such a cross-section. What do you think? * Here's a cross-section of Manson Crater: http://www.activetectonics.coas.oregonstate.edu/main_pages/~. It's from this website: http://www.activetectonics.coas.oregonstate.edu/main_pages/~. The cross-section shows fracturing of the floor, but no fracturing under the central uplift. Again, that doesn't seem to me to support a bolide impact. * At this site, http://ottawa-rasc.ca/wiki/index.php?title=Odale-Articles-C~ is the following image, which is similar to the Manson Crater cross-section:
GaryN
Re: Help Us Explain Crater Formation!
To me, that 'complex crater' image would be exactly what I would expect an electrical excavation to produce. The impact ejecta could be from surrounding material being attracted towards the central discharge, the fractured bedrock from electrical stress, the same for the breccia, with the addition of partial heat fusing, and the melt from resistance heating. The center would be pulled up or not depending on the intensity and duration of the event. A perfectly feasible alternative explanation, IMO. I'll modify that image to explain such. Just some more info on impact breccias: http://www.impact-structures.com/breccia/breccia.htm
Lloyd, I'm not sure if this will be helpful, but there is a very small "Richat-like" structure at: 28.543176°, 18.800508°
It might just be a dried pond, and it happens to be in the vicinity of many other (take your pick) "craters" or "dried ponds" (or else they are something that hasn't occurred to me). But it certainly looks interesting on Google Earth. It is about a half-kilometer in diameter, and here's a Google Maps link:
