Author Topic: NEW UPDATES  (Read 43 times)

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Re: UPDATES
« on: March 23, 2019, 04:09:43 pm »
Large cratonic basins likely of impact origin
https://creation.com/large-cratonic-basins
… Phase change problem. The mechanism of phase change seems to be the only viable uniformitarian mechanism for basin subsidence. For instance, if basalt or gabbro subside, the lithostatic pressure increases and the rock can change to eclogite, which is 15% denser with 15% less volume. The required pressure is that of the lower crust and upper mantle. So if basalt and gabbro can subside to about 40–60 km depth, this phase transformation can potentially occur and the basin will subside more. This is a reasonable idea, except where does the initial subsidence come from? Furthermore, the phase transformation from gabbro to eclogite requires water,18 and there is rarely any significant water at the depth of the lower crust and upper mantle.
_Properties of basins. … Thick sedimentary rocks
Basins are almost always filled with sedimentary rocks, which are sometimes extremely thick. Some depths will be given in the examples of basins below, but other basins not mentioned are the East Barents Basin in the Barents Sea, north of Norway, that has about 20 km of sedimentary rocks; the West Siberian Basin with about 8 km of sedimentary rocks; the Tarim Basin of central Asia with 15 km of sedimentary rocks; and the Paranà Basin in South America with about 7 km of sedimentary rocks.21
_Little deformation during sedimentation. An examination of those rocks reveals that the sediments underwent little deformation when deposited in the basin.13,22 Figure 1 shows sedimentary rocks of the Precambrian Belt Supergroup, which are typically undeformed within the bedding planes and formations, but the whole supergroup is deformed as a single unit, suggesting that deformation occurred after the whole supergroup was deposited.
_The crust is commonly thinned in basins. It has been discovered by seismic and gravity anomaly methods that the crust below a basin is commonly thinned. Artyushkov states: “Considerable thinning of the crystalline crust occurs under most deep basins located on continents.”15 Along with a thinned crust, the Moho, the boundary between the crust and mantle, is commonly raised (see figure 2).
_Some basins uplifted and deformed. Another significant observation on basins applies to sedimentary basins in which the sedimentary rocks are uplifted and folded by compression and differential vertical tectonics.22 Practically all uplift occurs after the sediments have been deposited and turned to sedimentary rock. During uplift, the sedimentary rocks are folded and faulted with the top eroded. Such uplifted sedimentary rocks form many of the mountain ranges of the world today and would not impress anyone that they were once in a deep basin.
_In the case of an impact origin, no subsidence is needed to form the basin; an instant circular ‘hole’ in the ground is blasted out. Subsidence or uplift may occur after the basin is filled with sediments.
_... the Flood impact submodel postulates thousands of impacts occurred early in the Flood. One major effect of such a large amount of impacts is to blast a huge amount of debris up into the air in the form of ejecta. All this sediment would end up in the floodwater and would eventually be deposited. A second major effect of so many impacts is that powerful currents would develop, sometimes interfering with each other. So, the combination of powerful currents and a huge amount of sediment would be rapid sedimentation in deep basins where currents are expected to be weaker and allow sedimentation. So, early Flood impact craters are expected to rapidly fill with sediments, since the crater acts like a sediment trap (see figure 8a). Sedimentation was likely so rapid that the sediments were little deformed by subsequent movements of the crater bottom and walls.
_Large basins of North America
There are five large basins on the stable craton of North America that I will briefly discuss. These basins are the Belt, Williston, Illinois, Michigan, and Hudson Bay Basins.
_Two basins of note on other continents. … The South Caspian Basin. … The Congo Basin.
_The two largest recognized Precambrian impact features, the Vredefort and Sudbury impact structures, have been eroded anywhere from 5 to 10 km.70 In a Flood setting, with thousands of impacts in a short time, turbulent currents would be expected to create significant erosion that also would destroy shatter cones, PDFs, and other impact features.
_Discussion. ... There are hundreds of cratonic basins that could be discussed, some of which have been discussed elsewhere.74 ... Tectonics, erosion, and sedimentation during the Genesis Flood are expected to destroy much of the evidence for impact craters. But, cratonic basins would be one of the most obvious evidences of large, modified impact craters.