Excellent posts and pictures 
The usual "flood geology" answer to this is that they're all escape burrows which is shown to be incorrect by burrows which obviously are not escape burrows such as the horizontal networks provided by SteveF. The fact is we can find such tunneling going on in all directions – horizontally, vertically and diagonally. This includes an abundance of U-shaped burrows made when the creatures first dug down and then horizontally while looking for food, and finally dug back up. If a flood was depositing sediments at a rate necessary to be responsible for laying down most, if not all, of the Geologic Column, these U-shaped tunnels should resemble fishhooks in that the creatures would never be able to dig their way back out. Instead, they would continue tunnelling upward until they expired, leading one to conclude that these "escape burrows" must be filled with the remains of the creatures that died in vain trying to escape if they were made during Noah's Flood. But that isn't what we find. In fact, what we do find is evidence for activity that seems awfully strange for creatures tunnelling for their lives trying to escape entombment. For if that were the case, then many of them stopped to build nests and search for food. Many newer burrows cut through older ones. Some areas are so churned up that it is impossible to follow individual burrows. Something like this takes time to create and time was something they wouldn't have during the Flood. In the end, it appears that the vast majority of these burrows can be associated with typical day-to-day activity rather than signs of creatures desperately attempting to dig their way out.
What many young earth supporters seemingly don't understand is how extensive such burrowing is in the fossil record, I think they imagine a few being located here and there not realizing that it is an incredibly common feature in sedimentary rock. Hence, any explanations for them consisting of temporary lulls (eye of the storm, so to speak) doesn't wash, in that their frequency and abundance would mean that most of the planet had to be i that "temporary lull"
I have seen a few beds (pure sand) which show no evidence of burrowing, but as you say, burrows are so incredibly common, and stack up on top of each other. I took a field trip to carbonate country in South Texas in 1984. That trip alone caused me such serious doubt about YEC that I mark that point as the beginnings of my struggles to leave YEC. Here are 3 photos from that old field trip--they are old slides turned into pictures and the colors have faded over the years.
This is from my web page
http://home.entouch.net/dmd/hardgrounds.htm
In March of 1984, I was sent on an AAPG field trip to look at carbonates in South Texas. The area we examined has at least 15,000 feet of sedimentary rock below it. Global flood advocates claim that all of this sediment was deposited by Noah's catastrophe. The rocks we saw presented a serious challenge to that view, a view which at that time, I held.
One of the sites was along Bear Creek where we saw a series of hardgrounds. A hard ground is a slowly deposited carbonate which is very hard and resistant to erosion, which is why they form ledges along the banks of this creek. What happens is that the land subsides, and a softer form of carbonate is deposited, which then fills the void caused by the sea level drop. As the carbonate gets near the sea surface, the rate of deposition drops and the hardground carbonate is deposited. The fuzzy photo below is from a slide I took which shows the hardground limestone ledges jutting out from the cliff face.
{see first picture with lots of red arrows}
But that doesn't stop biological activity. In the shallow waters, especially when the softer carbonates were being deposited, dinosaurs walked in search of food. Below is a photo of a dinosaur track which walks in the softer sediment above the lowest observed hardground. If this was during the middle of the global flood, at a point in the flood where ,There are creatures, like clionid sponges, which burrow into carbonate rocks.
{see dinosaur footprint 2nd picture}
But an even more interesting record of the time it takes for this section to be deposited comes from the nature of the biologic activity seen on the hardgrounds. Each hardground is highly burrowed by animal life. These animals are clionid sponges which eat shell material as part of their search for food. Below is a rock I brought back from this sight. You can clearly see the burrows, and the fact that the waters were very shallow is shown in the crack which was filled by an evaporative mineral, celestite.
**end of page*
I will add that the evaporative mineral and desciccation cracks means that the water was very very shallow. It is as NeilUnreal says, a confluence of evidence.
Come on John, You made the claim that there was lots of evidence of an young earth in the rocks. You live your life among mathematics but never as a geophysicist actually get out to see the rocks. Please explain this kind of data so that those who admire YEC can see how superior YEC is. Of course, you won't because it would be too embarassing to acknowledge that you can't explain them. Just remember, I was staying out of the RATE issue until you made that highly misleading claim.
If you would but say all the geological features I am showing are miraculous, I could have no argument with you, but by saying that there is evidence of a young earth in the rocks, I can't go along. In that RATE thread you said you feared God so you remain YEC. I fear God because he is a God of Truth. How can I not mention the data I truly observed? How can I stand before God knowing that I ignored tough questions, and refused to answer any issue that challenged my belief system. Honesty requires answering questions one doesn't like answering.
Where would we be if God had not goaded Paul on that road to Damascus? Geology was God's way to goad me to leave YEC every bit as much as the bright light was God's goad to Paul to cease killing Christians.