- [Voiceover] So, I'll introduce my contribution to the source and sink approaches, is the fulcrum test. So, this is the fulcrum approach. So, in the fulcrum approach, I would begin by simply saying it also has the issue of you're making a lot of assumptions and there's only so much accuracy to this at this point and it's in its embryotic stages, too, but it's at least something we can start with. So, here's the principle behind the fulcrum test. In the fulcrum test you still have a source and a sink for your sediment. However, somewhere between the source and the sink there's some cross section that all sediment going from the source to the sink must've crossed. So, therefore, that means that from the source to the sink that there is some place between where the source volume certainly equals the sink volume, but it also has to equal the amount of sediment that passed from the source to the sink through some fulcrum cross section. So, the idea here is then, of course, thus the name, the fulcrum test, is that there is going to be some fulcrum, some cross section in your system whereby the sediment has had to pass through that and the sediment source and sink must balance across that fulcrum and therefore if you knew how much sediment was moving through that fulcrum, you'd have your source and sink volumes. Okay, as a general rule, when you look at the source and sink, of course, what we're trying for in the fulcrum is you're looking at the, what you're looking for is for the fulcrum, is you're trying to assess how much sediment has moved through the axis of the fluvial system that transferred the sediment from the source to the sink. So, all those valley fills and so forth that exist that fed the summering fans, fed the deltas, fed the coastlines, those fluvial systems that are draining from the source just as they're approaching the sink, that's your fulcrum. So, what we really wanna do, then, is to look at those fluvial channels and ask ourselves the question: how much sediment were those channels actually moving? So, what we're gonna do is we're gonna walk through, approach this, and the good thing about this particular approach is that is uses Data Requirements that really only call for Story Thickness. In other words, how thick are the individual channel belt deposits that were deposited by these rivers? And the Grain Size that these channels were moving, which, of course, we're going to assume that that's the grain size that was actually deposited in the channels. So, from the rock record we commonly record how thick are the channel fills and what's the grain size of the channel fills. So, these are the only two actual Data Requirements we have. So, once again, common data information. So, we can get grain size from cores. We can get story thickness from Well Logs or from cores. And so, figuring out how thick the individual channel fills and the individual bar deposits are is a common exercise that we do in the rock record, as well as looking at the cores and working out the stories from the cores. Of course, now we have the grain sizes for the grains that's actually been deposited in the core. So, these are data that we can actually get our hands on.