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Tuesday, November 17, 2009
Logical Fallacies
Here's a quick description of some commonly employed logical fallacies. I've observed similar arguments made by scientists on occasion, so it's useful for more than just E/C issues.
1 why do you assume orogeny occurred immediatley after deposition? 2 why do you assume sediments are unconsolidated soon after deposition? Is it possible for sediments to consolidate soon after deposition from pore pressure, overburden, electrostatic flocculation of clay size particles, etc. 3 also, is it possible that the rounded clasts at Echo Cny are exotic? Were they transported from elsewhere?
tillites, You've got some good questions - I think I should do a separate post or two about some of the aspects of #2.
I assume you are referring to the previous post about syntectonic deposition. Here's some response:
1) I'm not assuming this - although that is the implication of the flood-geology model. However, this entirely depends on your definition of "immediately." To a human, immediately generally means a few seconds or hours. In geologic terms, "immediately" could refer to hundreds, thousands, or even a couple million years. It's a somewhat useful term, but only in a relative sense.
2) What do you mean by "unconsolidated?" This is a commonly used, yet somewhat useless geologic term. Consolidated denotes individual particles brought together into a more coherent whole. This may or may not mean "turned into rock." I assume you are referring to the previous post about syntectonic deposition.
I specifically said unlithified because "unconsolidated" may mean that the sediment has some apparent cohesion due to the "consolidation" of individual grains. Because yes, during deposition, individual particles are "brought together" and may act as a somewhat cohesive material (subject to the usual laws of physics).
Secondly, I'm not sure how some amount of fluid pressure between grains of sediment can act to bring those particles together. It seems counter-intuitive since "pore pressure" implies that each sedimentary particle is experiencing a force directed onto the grain, away from the pore space - thereby forcing one grain away from another.
Third, electrostatic flocculation of clays may indeed bring clay particles close together (this is a fascinating behavior of clay). However, these "flocs" are packed together loosely, while clays that may settle without flocculation are packed together more closely (think of a floc as a house of cards, while non-flocculated clays are stacked flat, like a deck). So, while they both bay be considered "consolidated," the flocculated clays will behave differently. Try it sometime - take a beaker of mud, and pour one part of it into a larger beaker of salt water, and another part into a beaker of fresh water. Then, let the clay settle, the water evaporate, and then observe the behavior of the two clays.
3) It is possible that some rounded clasts are exotic. But it is also unlikely that ALL the clasts are exotic. You can see many clasts that are identical intact rock formations nearby - including fossils. So I suppose it is not impossible to have some exotics. But then what do you mean by "elsewhere?" You can get a sense of transport direction from sedimentary structures. These structures show the upstream direction (in a general "uphill sense" not necessarily the exact same channel) is towards the region of uplift. This uplifted region contains the rock formations that we can observe as clasts within the Echo Canyon cgt.
1 why do you assume orogeny occurred immediatley after deposition?
ReplyDelete2 why do you assume sediments are unconsolidated soon after deposition? Is it possible for sediments to consolidate soon after deposition from pore pressure, overburden, electrostatic flocculation of clay size particles, etc.
3 also, is it possible that the rounded clasts at Echo Cny are exotic? Were they transported from elsewhere?
tillites,
ReplyDeleteYou've got some good questions - I think I should do a separate post or two about some of the aspects of #2.
I assume you are referring to the previous post about syntectonic deposition. Here's some response:
1) I'm not assuming this - although that is the implication of the flood-geology model. However, this entirely depends on your definition of "immediately." To a human, immediately generally means a few seconds or hours. In geologic terms, "immediately" could refer to hundreds, thousands, or even a couple million years. It's a somewhat useful term, but only in a relative sense.
2) What do you mean by "unconsolidated?" This is a commonly used, yet somewhat useless geologic term. Consolidated denotes individual particles brought together into a more coherent whole. This may or may not mean "turned into rock." I assume you are referring to the previous post about syntectonic deposition.
I specifically said unlithified because "unconsolidated" may mean that the sediment has some apparent cohesion due to the "consolidation" of individual grains. Because yes, during deposition, individual particles are "brought together" and may act as a somewhat cohesive material (subject to the usual laws of physics).
Secondly, I'm not sure how some amount of fluid pressure between grains of sediment can act to bring those particles together. It seems counter-intuitive since "pore pressure" implies that each sedimentary particle is experiencing a force directed onto the grain, away from the pore space - thereby forcing one grain away from another.
Third, electrostatic flocculation of clays may indeed bring clay particles close together (this is a fascinating behavior of clay). However, these "flocs" are packed together loosely, while clays that may settle without flocculation are packed together more closely (think of a floc as a house of cards, while non-flocculated clays are stacked flat, like a deck). So, while they both bay be considered "consolidated," the flocculated clays will behave differently. Try it sometime - take a beaker of mud, and pour one part of it into a larger beaker of salt water, and another part into a beaker of fresh water. Then, let the clay settle, the water evaporate, and then observe the behavior of the two clays.
3) It is possible that some rounded clasts are exotic. But it is also unlikely that ALL the clasts are exotic. You can see many clasts that are identical intact rock formations nearby - including fossils. So I suppose it is not impossible to have some exotics. But then what do you mean by "elsewhere?" You can get a sense of transport direction from sedimentary structures. These structures show the upstream direction (in a general "uphill sense" not necessarily the exact same channel) is towards the region of uplift. This uplifted region contains the rock formations that we can observe as clasts within the Echo Canyon cgt.