Permian Triassic Extinction Event Boundary - Bulli Coal Measures | Discovery Geology

Today I just wanted to take you on a little bit of an interesting journey into the Permian-Jurassic extinction event. I'm at the base of the Seacliff Bridge which is located in Coal Cliff in the Sydney Basin on the south coast of New South Wales. And I'm just going to go around and check out the Bullay Coal Seam and the top of the Coal Seam which marks the beginning of the Jurassic or the Permian-Jurassic extinction event. I shot this video pretty haphazardly so I'm not going to spend a great deal of time editing it so I apologise for that. I'm just going to kind of narrate over the top and talk about some of the features that we kind of see within the shots. So starting off what we're looking at here is some of the sedimentary deposits that were deposited on top of the Bullay Coal. And this is early Jurassic sedimentary deposits. So it's interesting to see the various fluvial processes involved in these deposits. We can see that the quartz crystals have been rounded due to the action of being transported by water. This interesting conglomerate kind of bed may indicate sort of an abraded river or creek system. And the sandstone without much sort of carbonaceous material sort of indicates what we'll talk about a little later is the lack of plant material that can be found after the Permian-Jurassic extinction event boundary. So just looking here we can see various cross stratification. The size of these beds may be a little difficult to interpret in some of the shots but I'll try to kind of give some kind of reference. So panning around I found this clump of rock with fairly carbonaceous material embedded. So this may have been deposited within the fluvial settings. I didn't actually spend much time investigating the grain sizes and things like that associated with some of the stuff we're looking at. But as you can see here this deposit is on top of the Permian-Jurassic extinction event boundary and within fluvial setting and we can see some of the carbonaceous material. Later on interestingly I found a large clump of rock that had fallen off and we've got some great examples of some large branches and things like that. So again just looking around we can see sort of various water deposited sediments and it is interesting to note that it doesn't contain much sort of carbonaceous material. I've got some ironstone concretions and things like that and better examples of that stuff coming up later on. So most of the information I'm going to talk about is by G.J. Retallack and the paper is called Post-apocalyptic greenhouse paleoclimate revealed by early Jurassic paleo soils within the Sydney Basin. So what it might do is it might stagger the information based off what we're looking at and keep it fairly brief and concise. So just starting off what we see here is the Bulleye coal seam and what we've come to investigate is the area at the top of that seam which marks the Permian-Jurassic extinction boundary. And underneath the coal it's interesting to see various horizontals and planar laminations which indicates various sort of seasonal deposits. So this coal seam, the Bulleye coal measures, is the last of coals found anywhere in the world for all of the early Jurassic time. It also marks the extinction of Glossopteris. However, various papers indicate that remnants of Glossopteris may exist into the mid-Permian times, however this is a little bit of a controversial matter. So now we're just looking north and we can see in that last shot the Wombara formation on top of the Coal Cliff formation on top of the Bulleye coal. So what we're looking at here is a close-up of the Bulleye coal and coming up is the Permian-Jurassic extinction boundary. So this bed is 10-15cm and is black kaolinitic claystone breakup and this is what is thought to mark the Permian-Jurassic extinction boundary. The temperature of the Permian was cool temperate and marginally frigid. It's believed that it possibly had snow cover in the cooler winter months but was able to support forest biomes with trees such as Glossopteris that could grow up to 16m high. The Glossopteris is believed to have been deciduous, dropping its leaves in autumn in response to this cool change. Above that we see an increase in temperature and humidity and a change from the marginally frigid swampland to cool temperate broadleaf and conifer forests. Underneath the coal we see the fossil roots going down into the clay paleo soil. Maybe in a later video I'll show you some of the Erkesley formation and this has some great examples of some well-preserved Glossopteris roots. So what this indicates is that before the peat accumulated the clay was freely drained and influenced by rainfall. The rainfall during the Permian and early Jurassic is believed to have been about 1,000 to 1,300 mm. So looking closely at this coal, peat deposits of this nature are believed to have been deposited between 1 and 0.5 mm a year. And are compacted to roughly 13% of their former thickness. So moving along now we see the former Bulleye Coal Jetty and the Coal Cliff Mine that as this plaque says was sealed in 1992. So they used to extract coal from this location and put it directly onto ships. So looking at sedimentation rates, it is believed that the early Jurassic sedimentation rate was about 0.16 mm a year. The maximum thickness from the base of the PN group to the base of Mitchenberry Sandstone and the Winnematta group is 1,157 m. And it is believed that the thickness represents no more than 7.2 million years from the Permian-Jurassic extinction event boundary. So the sedimentary accumulation was fairly rapid during the early Jurassic times. So moving around now I'm just heading south and I just want to check out another part of where the Bulleye Coal scene can actually be seen. Interestingly I just want to show you some of these large rockfalls that have some great examples of some large tree branches and things like that. Sort of coalified logs which have been coalified due to the heat and pressure due to the sediment on top of it. But these are great examples of possibly some, I'm not going to say glossopterous, but some large trees that may have been deposited within the fluvial settings on top of the, or in the beginning of the early Jurassic. So I'll give you a bit of a reference. So we've got the Bulleye Coal scene here and if I tilt up you'll see where this large chunk came from. And I think I've got some shots of where, here we go, where this coalified wood is actually seen within the sedimentary deposits. Yeah, that's tilting up to it now. This is some of the coalified logs still remaining within the cliff. So this is interesting as it indicates that either these are parts of the conifer, more humid forests, or the remnants of glossopterous. I didn't spend much time having a close look at the structure to see which it was, but it does indicate that large trees existed at this period of time. It has been reported that the sediment on top of the Permian-Turassic extinction boundary is, as you can see here, heavily bleached. So these kind of conditions are not great for preserving phosphor remains of bones and shells and things like that. Back to some of this carbonaceous material, we can see various stems and small tweaks and stuff like that that have been deposited within the mudstone. Referring back to the paper that I mentioned earlier, it is mentioned that some glossopterous was found 17cm from the top of the Bulleye Coal. So if this rockfall is an indication of glossopterous, then it is interesting to see that glossopterous may have existed into the early Turassic times. So down below the Bulleye Coal Seam you can see in the Oaksley Formation a lot of examples of large pre-mineralised trees and again some references from these indicate that these trees may have grown up to 16m in height. So just returning again to the rockfalls, I'm just going to make my way back through. I can't tell exactly where these have come from, but what we can see is a variety of blooming processes involved with that. So just to go into a little bit more detail, during the end of the Permian in this area there was actually a volcanic arc that extended up the east coast with possibly extinct volcanoes during the end of the late Permian. Some good examples of some ash that can be seen from this can be seen in the Tongara Coal Measures which I may take you to another day. We can see large tarfaceous ashfall deposits.