- [Voiceover] Okay, so, how do we get at this? Well, there's a couple approaches that have been tried, and again, I'm by far not the only person working on this question of source-to-sink. There's other people who have tried other approaches to getting at this. But here's one approach. This is the Catchment Approach. In the Catchment Approach, what you do is you say I have a area of sink, so I have some area here of deposition. So, right here. Somewhere I'm depositing sediment. So sediment is coming out here into this basin and depositing. And so, that's what I have in the rock record. So to get at how much sediment would have been delivered to this sink, what I will do is I will drop back up in here into the source, and I'll say let's reconstruct the conditions in the source area, in terms of rainfall, slope, bluffology, and just simply make a forward model calculation of how much sediment a source like that would generate. Of course, in order to do that, you have to know quite a lot about the source area. You have to have actually had some amount of knowledge as to what the catchment of this basin would have looked like. Know something about the temperature conditions, the rainfall conditions. In other words, it's a very, very data-hungry way to try to get at the total amount of sediment that would've been delivered to your sink. That said, it's a commonly-used approach looking in modern systems. And somewhat in quaternary systems. But as you get further and further into the rock record, you know less and less and less about what was going on in the catchment. So calculating how much sediment would likely end up in your depositional sink becomes increasingly difficult by this method as you get deeper into the ancient, so this is just a work by Philip Allen where he's trying to use some simple variables to approximate it. But again, it's very coarse once you get in the rock record. If it's in order of magnitude, sediment supply to your sink, you feel pretty good about it.