now another thing we got to talk about are unconformities okay this indicates missing time in the geologic record so missing time there's two ways to get missing time it's either a period where there's no deposition so nothing was deposited so that means you know a lack of erosion and weathering or there was a period of erosion where materials were actually removed from the geologic record and deposited elsewhere so ripped away that top layer may be ripped away okay that's going to show you an unconformity and there's three types of unconformities and they can be a little tricky so make sure you know these write down these definitions for these okay so there's a disconformity a non-conformity and an angular unconformity if you get nervous and you're talking to somebody about um conformities disconformity non-conforming angular unconformity the number one way to not do anything wrong is just to say it's an unconformity that's your umbrella term that these three fall under okay so but i need you to know these three in this class you'll be tested on them so what's a disconformity let's start there this is where two horizontal beds are separated by an unconformable surface so a surface of erosion or non-deposition so this black line here that's wavy represents a disc conformity okay so we've got um a perfectly laid down b's perfectly down c is perfectly laid down and then the top of c has a weird kind of wavy sort of look that's because this was probably eroded away at some point and then e was laid on top of it so when it's not a nice perfect layer where it's nice and flat between the two you probably have a disc conformity and this is between two sedimentary beds okay disconformity check out this you got these nice paleo soil horizons through they got these nice horizontal layers and then whoa there's this weird smiley face looking thing that's a channel so this was a period in which this channel came through and ripped away this material that was pre-existing and then deposited its own material so this right here is where the disconformity is okay and then that river if you see smiley faces in a cliff by the way so this is what i see is a smiley face that's a channel that's evidence of literally water running through and ripping away at what was previously there in a nice u-shaped form or smiley face form is what i like to say and then deposits itself and then later on without you know that channel running through or that water running through you got more deposition above so this disconformity notice it's between two sedimentary layers okay now a non-conformity still under the umbrella of unconformities is the sedimentary beds overly an unconformable surface on igneous or metamorphic rocks okay so these are the hard rocks okay so that is when you've got these nice sedimentary beds above and you've got your hard rock below this surface that black line there that is what we're talking about as a non-conformity okay so that right there is the spot where we call a non-conformity here's an example of a non-conformity you've got your hard rock below and then you've got your horizontal nice sedimentary beds above this right here the image of that line between kind of the reddish and the whitish rock that is your non-conformity okay we also have angular unconformity so this is where flat sedimentary rocks overlay an unconformable surface with angled layers beneath so how do you get angled layers well you get faults and folds and things happening tectonically and then maybe that stops and then all of a sudden you start laying down nice flat surfaces again okay so there you go this is all folded and faulted and all angular and all you know weird looking not nice and horizontal right and then you got those nice horizontal layers just right above that transition this black just below this yellow is an angular unconformity okay here's a nice example we've got kind of vertical looking layers below and then you've got your horizontal layers above this is an angular unconformity and make sure you understand this is between sedimentary rocks okay so this is kind of a sedimentary style rock this is a sedimentary style rock above okay angular unconformity now take a look at this video it starts with a very complex picture and then breaks down the ways in which things will have been deposited in the relative ages of each and this is something you're going to be doing for your assignment so take close look at this video hope you enjoy this hypothetical cross section represents 100 million years of sediment accumulation protectionism and volcanism first to orient you let's look at what's on the surface this lake which is cut down through the surrounding sedimentary bedrock is near a volcanic dome that is surrounded by fallout deposits we'll remove the foreground to expose the cross section again in general young rock layers overlay older rock layers gaps in the sequence called unconformities are due to erosion absence of deposition folding or faulting we'll start with a layer of undeformed slowly subsiding bedrock that gets drowned by a broad sea most sedimentary rock is produced by two broad processes first by the accumulation of weathered rock debris that was distributed by water wind and gravity second though less abundant rock is produced by precipitation which is a chemical reaction where calcium carbonate and or silica settle out of solution forming limestone or chirp both processes result in sedimentary rock straight with varying quantities of organic matter the seas recede and the layers are subjected to regional compressive forces which deform the strata slowly wind-blown sediment blankets the area [Music] after millions of years of continued sediment accumulation regional extension stretches the plate until it drops along faults in basin range fashion during extension magma rises from the mantle and lava erupts on the surface normal faulting accompanied by large earthquakes offset the lava during continued extension sediment eroded from highlands out of view creates an angular unconformity over the faulted layers an invading inland sea precipitates limestone renewed extension causes faulting multiple processes contribute to the accumulation of sedimentary strata [Music] broad uplift due to renewed extension is accompanied both by down cutting as well as by the slow rise of magma below the thinned crust an explosive volcanic eruption through the lake and dome building punctuates its history [Music] okay great i hope that makes sense and if it doesn't go back and watch that video again because you will be doing an assignment on this you will be doing this yourself okay and i'm gonna i'm gonna have this set up in your modules for you to do so this is another assignment and if you have questions come ask me come ask me those questions come talk about it with me these are something that i love to do and i know some of you are going to love to do this as well as kind of break down the timing and the format in which these all occurred okay so here's another example of one of those geologic sequences and the numbers here might confuse you a little bit so let me just make sure we're all together on it um they're not including the numbers for this intrusive granite pluton or this basalt dike here or this fault okay so they're not including that or the sill they're just talking about the sedimentary layers here so you've got this first kind of brick two three four then they don't include this sill which has been offset from this fault and then five the sandstone above six this other layer here and then seven is the top another type of sandstone but they are not including this granitic pluton or this vertical dyke or this fault okay and that is something that you will have to include when you do your assignment okay so let's talk a little bit about sorting out these relative ages and you could sort this one out too but it's pretty complex all right look at these inclusions here as well from number five remember this granitic pluton these inclusions are older than the granite pluton okay so that's how that's one little step or key factor there and on top of that look at the fault the fault cuts through everything but it doesn't cut through the basalt dike so what does that mean this dike is actually younger than the fault okay because the basalt deck is cutting through and it's not offset at all now here's another example of one of the ones that maybe i'll have you try okay so we've got these layers a b c d e f g h i j k right we're trying to figure out how they're all sorted um and here we actually have an angular unconformity okay and we're gonna go through the sequence so let's let's check it out so in diagram one we've got a b c e okay all this is just laid out nice and beautifully principle of horizontality and superposition all acting as one right here when you get to two we actually have a little bit of uplift okay and that uplift um an intrusion of the sill layer d right ends up with some inclusions from e so now you know that d actually is older than e because e has the inclusions within d okay then later on you end up with this intrusive dike here of f and you know that f is younger than d because f cuts across d okay so that's how you would tell there and then for four you actually end up with some tectonic shift so they're tilted and the layers were eroded a little bit so over here these layers got eroded some everything was tilted and then substance occurred and you got a new ocean then you lay down g h i j and k so that is kind of like how you would build this slowly but surely and it makes sense with the water here at the start and then disappearing for a while kind of erosional surface and then a new depositional surface and a lot of times deposition occurs when water is there and erosion occurs when water is not and that makes perfect sense right when you have water everything falls out nice and easy and it's just like boom there you go and then uh depositing at least sediment and then when the water is not there you've got wind and um see floods coming through that are eroding away the surface all right um here's another example of kind of something to think about as far as what non-conformity angular unconformity might look like versus a disconformity go back and make sure you look through those definitions that i gave you and i need you to add those in to that diagram that i gave you as an assignment okay we're going to stop right here i want you to think through this chew on it a little bit and when you go on your next hike try and figure out if you can see any disconformities or non-conformities or angular unconformities or relative ages with dikes and sills and superposition and original horizontality think about all these things as you go out and you do your hikes okay so i'll be back with the next lecture to finish this up and i hope you have a good rest of your day enjoy