Top Trilo Posted January 22, 2021 Share Posted January 22, 2021 I know the cretaceous period ended 65-66 million years ago but when exactly did it end? Did it end as soon as the meteor touched the Earth's surface? As soon as all dinosaurs went extinct? After a certain amount of species went extinct? There may not be a definitive answer but if it was up to you where would you decide where the end of the cretaceous meets the beginning of the paleogene? “If fossils are not "boggling" your mind then you are simply not doing it right” -Ken (digit) "No fossil is garbage, it´s just not completely preserved” -Franz (FranzBernhard) "With hammer in hand, the open horizon of time, and dear friends by my side, what can we not accomplish together?" -Kane (Kane) "We are in a way conquering time, reuniting members of a long lost family" -Quincy (Opabinia Blues) "I loved reading the trip reports, I loved the sharing, I loved the educational aspect, I loved the humor. It felt like home. It still does" -Mike (Pagurus) “The best deal I ever got was getting accepted as a member on The Fossil Forum. Not only got an invaluable pool of knowledge, but gained a loving family as well.” -Doren (caldigger) "it really is nice, to visit the oasis that is TFF" -Tim (fossildude19) "Life's Good! -Adam (Tidgy's Dad) Link to comment Share on other sites More sharing options...
Troodon Posted January 22, 2021 Share Posted January 22, 2021 The cretaceous ended 66mya not 65. Its identified by the K-T boundary found around the world which contains a higher concentration of iridium than normal. The layer was deposited shortly after the impact. ChronostratChart2020-03.pdf 1 Link to comment Share on other sites More sharing options...
Thecosmilia Trichitoma Posted January 22, 2021 Share Posted January 22, 2021 From what I know, the mass extinction is what defines the K-T boundary, and the impact of the asteroid was the cause. People knew about the extinction event before they new about the asteroid that caused it. I would assume there was a transition period, as the effects of the asteroid killed off the species. It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt -Mark Twain Link to comment Share on other sites More sharing options...
Thecosmilia Trichitoma Posted January 22, 2021 Share Posted January 22, 2021 I would assume there was a transition period in between. For me, I consider the Cretaceous to end when the asteroid’s effects ended, as that (as Troodon says) is when the iridium layer would have stopped being deposited too. 2 It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt -Mark Twain Link to comment Share on other sites More sharing options...
Tidgy's Dad Posted January 22, 2021 Share Posted January 22, 2021 I think it is now known as the K-Pg boundary (Cretaceous-Paleogene) and was 66.043 mya, plus or minus 0.011 million years and is marked by the iridium anomaly, a thin layer that is also associated with the mass extinction. 4 1 Life's Good! Tortoise Friend. Link to comment Share on other sites More sharing options...
Top Trilo Posted January 22, 2021 Author Share Posted January 22, 2021 Yes I know of the iridium layer deposited from the meteor so from what I've heard it is at the top of the layer or the iridium layer is still part of the creteacous. Thanks guys very helpful “If fossils are not "boggling" your mind then you are simply not doing it right” -Ken (digit) "No fossil is garbage, it´s just not completely preserved” -Franz (FranzBernhard) "With hammer in hand, the open horizon of time, and dear friends by my side, what can we not accomplish together?" -Kane (Kane) "We are in a way conquering time, reuniting members of a long lost family" -Quincy (Opabinia Blues) "I loved reading the trip reports, I loved the sharing, I loved the educational aspect, I loved the humor. It felt like home. It still does" -Mike (Pagurus) “The best deal I ever got was getting accepted as a member on The Fossil Forum. Not only got an invaluable pool of knowledge, but gained a loving family as well.” -Doren (caldigger) "it really is nice, to visit the oasis that is TFF" -Tim (fossildude19) "Life's Good! -Adam (Tidgy's Dad) Link to comment Share on other sites More sharing options...
piranha Posted January 22, 2021 Share Posted January 22, 2021 18 minutes ago, Top Trilo said: Yes I know of the iridium layer deposited from the meteor so from what I've heard it is at the top of the layer or the iridium layer is still part of the creteacous. The iridium layer is placed at the base of the Paleogene. Gradstein, F.M. et al. 2020. Geologic Time Scale 2020. Elsevier Publishing, 1357 pp. 5 Link to comment Share on other sites More sharing options...
DPS Ammonite Posted January 22, 2021 Share Posted January 22, 2021 21 minutes ago, piranha said: The iridium layer is placed at the base of the Paleogene. Gradstein, F.M. et al. 2020. Geologic Time Scale 2020. Elsevier Publishing, 1357 pp. Forgive my asking, is the iridium layer fully within the Danian? 1 My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
Jeffrey P Posted January 22, 2021 Share Posted January 22, 2021 In New Jersey there is the Pinna Layer which lies right above the iridium. This roughly foot thick layer of clay contains a "Cretaceous" fossil assemblage that includes ammonites and baculites (well over a 100 invertebrate species in all) that appear to have survived the asteroid impact for at least a few years though it is unclear how long. It has been theorized that during this time due to the sharp reduction in sunlight, micro organisms were rapidly dying off and sinking down through the water column creating a temporary food surplus for the macro fauna that survived until this food source was exhausted and the entire ecosystem collapsed. Above this layer, fossils are scarce, the beginning of the Paleogene. 7 Link to comment Share on other sites More sharing options...
piranha Posted January 22, 2021 Share Posted January 22, 2021 24 minutes ago, DPS Ammonite said: Forgive my asking, is the iridium layer fully within the Danian? Gradstein et al. 2012 showing the same info. Gradstein, F.M. et al. 2012 The Geologic Time Scale 2012. Elsevier Publishing, 1144 pp. 2 Link to comment Share on other sites More sharing options...
DPS Ammonite Posted January 22, 2021 Share Posted January 22, 2021 7 minutes ago, piranha said: Gradstein et al. 2012 showing the same info. Gradstein, F.M. et al. 2012 The Geologic Time Scale 2012. Elsevier Publishing, 1144 pp. So the answer to my question is yes? The boundary, (a plane), between the Cretaceous and the Paleocene is the bottom side of the iridium layer as apposed to the middle or top of the iridium layer. 1 My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
piranha Posted January 22, 2021 Share Posted January 22, 2021 6 minutes ago, DPS Ammonite said: So the answer to my question is yes? The boundary, (a plane), between the Cretaceous and the Paleocene is the bottom side of the iridium layer as apposed to the middle or top of the iridium layer. The answer appears to be self-evident. 2 Link to comment Share on other sites More sharing options...
DPS Ammonite Posted January 22, 2021 Share Posted January 22, 2021 I disagree. To say that the iridium rich layer is a “marker” bed or the Cretaceous/Paleocene boundary is “at” an iridium layer does not specifically tell you where the boundary is. It could be below the iridium layer, in the middle of the iridium layer or on top of the iridium layer. I think that the boundary is placed just below the iridium layer; is that correct? 1 My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
piranha Posted January 22, 2021 Share Posted January 22, 2021 32 minutes ago, DPS Ammonite said: I disagree. To say that the iridium rich layer is a “marker” bed or the Cretaceous/Paleocene boundary is “at” an iridium layer does not specifically tell you where the boundary is. It could be below the iridium layer, in the middle of the iridium layer or on top of the iridium layer. I think that the boundary is placed just below the iridium layer; is that correct? I have no idea what you're arguing. The charts and the info in the cited publications appear to indicate the the iridium layer is defined at the base of the Paleogene. Sounds like you need to contact a specialist that can elaborate further. 1 Link to comment Share on other sites More sharing options...
FossilDAWG Posted January 22, 2021 Share Posted January 22, 2021 Presumably the iridium layer was deposited after the impact, as fine dust from the vaporized meteor and bedrock was distributed around the world and settled out. Since the impact itself defines the end of the Cretaceous, it seems to me the iridium layer would be entirely in the Paleocene, at least as originally deposited. I think there is evidence that some iridium has migrated down into underlying layers with groundwater movement, so it is important to take this possibility into account. The associated extinction event was likely more complex, as different taxa may have persisted for a shorter or longer time depending on their ability to tolerate the severe environmental disruption. Don 6 Link to comment Share on other sites More sharing options...
FranzBernhard Posted January 22, 2021 Share Posted January 22, 2021 2 hours ago, piranha said: The answer appears to be self-evident. 1 hour ago, DPS Ammonite said: I disagree. It is not totally self-evident and not explicitly stated in that table (I am a fan of redundancy!). The Ir-layer, while very thin, is a 3D-object. The boundary between C/Pg is 2D. But this makes it clear: 1 hour ago, FossilDAWG said: Presumably the iridium layer was deposited after the impact, as fine dust from the vaporized meteor and bedrock was distributed around the world and settled out. Since the impact itself defines the end of the Cretaceous, it seems to me the iridium layer would be entirely in the Paleocene, at least as originally deposited. However, all this depends on definition. Franz Bernhard 2 Link to comment Share on other sites More sharing options...
Norki Posted January 22, 2021 Share Posted January 22, 2021 3 hours ago, Jeffrey P said: This roughly foot thick layer of clay contains a "Cretaceous" fossil assemblage that includes ammonites and baculites (well over a 100 invertebrate species in all) that appear to have survived the asteroid impact for at least a few years though it is unclear how long. This has interested me for awhile, and from what I've read there seems to be pretty good evidence for some ammonoid survival into the Danian, especially among scaphitids. Apparently the main thing that eventually killed them off was ocean acidification, because the the shells of freshly hatched, planktonic ammonoids would reliably dissolve once ocean pH levels got low enough. This theory also accounts for why nautiloids survived and they didn't - nautiloids hatch as subadults and skip the vulnerable planktonic stage altogether. Anyway, the acidification process probably would have taken a fair amount of time, just like the delayed food chain collapse, so I suspect that at least a few species of ammonoids were around for a couple thousand years into the Danian. 1 Link to comment Share on other sites More sharing options...
Ludwigia Posted January 22, 2021 Share Posted January 22, 2021 Not to forget of course that the conclusions leading to the above described definition followed up on years of intensive field study and deliberation by the International Commission on Stratigraphy and its pertinent Subcommissions. In other words, human scientific conclusions, which, as far as dating is concerned, are relatively specific, but nevertheless always approximate given the inevitable +/- factor. A border is 2D, as Franz has pointed out (when do you actually leave or enter your house?), at least when viewed and defined by the human intellect, and the members of the Commission decided in this case to place the iridium layer in the Danian and the impact in the Cretaceous. It would be practically impossible to define a younger world-wide layer where the dinosaurs and "a certain amount of species" went instinct as the border between the Cretaceous and the Paleogene. However, the "no man's land" in front of and behind a border is of no set magnitude, depending on the circumstances, which can often give arise to doubt as to exactly where the border is. 2 Greetings from the Lake of Constance. Roger http://www.steinkern.de/ Link to comment Share on other sites More sharing options...
LabRatKing Posted January 22, 2021 Share Posted January 22, 2021 Late to the game as usual...makes my snide comment of "It ended when the Paleogene began..." moot. 2 Link to comment Share on other sites More sharing options...
Al Dente Posted January 22, 2021 Share Posted January 22, 2021 As Don pointed out, the iridium layer has a tendency to migrate. There are some who think there were multiple impacts thousands of years apart and the iridium layer could be from a different event than the impact that created the tektites. Here's one opinion on the Brazos River boundary section. Taken from "The Cretaceous-Paleogene boundary on the Brazos River, Falls County, Texas: is there evidence for impact-induced tsunami sedimentation?" 1 Link to comment Share on other sites More sharing options...
siteseer Posted January 26, 2021 Share Posted January 26, 2021 I always understood the iridium layer to be neither Cretaceous nor Paleocene but THE boundary - the line/zone between them. If there was more than one impact over hundreds or thousands of years and the layer/layers was/were deposited over that amount of time, it would still be virtually instantaneous from a geologic standpoint. It's like asking what time of day the Cretaceous ended (relative vs. absolute as we learned in geology class). We will likely never reach that level of resolution so the boundary might still move or get thinner or thicker. When I was a kid, the number was 60-65 million years ago. Jess 1 Link to comment Share on other sites More sharing options...
LabRatKing Posted January 26, 2021 Share Posted January 26, 2021 Keep in mind the iridium layer didn’t form overnight. It took thousands of years to form. 1 Link to comment Share on other sites More sharing options...
doushantuo Posted January 26, 2021 Share Posted January 26, 2021 can recommend: maybe in conjunction with: and(e.g.) 2 Link to comment Share on other sites More sharing options...
doushantuo Posted January 26, 2021 Share Posted January 26, 2021 some of you may like(less than 3 Mb) Iridium_profiles_and_delivery_across_the.pdf Link to comment Share on other sites More sharing options...
jeannie55 Posted January 26, 2021 Share Posted January 26, 2021 Wow! I was feeling a little guilty about my plan to skip my doctors appointment today but the second cup of coffee and first gingerbread cookie with this thread totally se t the guilt packing. Of course my non- scientific brain feels stretched. That’s why I love that you big brained guys (male and female) allow those of us who are enjoying our hobby access to this forum. 1 Link to comment Share on other sites More sharing options...
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