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It’s Complicated

August 5, 2013
tubes in channel 3

What are these strange structures in a tidal channel?

The Anchorage, Grand Manan Island, New Brunswick

We stroll along the beach at golden hour, but the haze of shore-fog this evening is far more silver than gold. The waves are dull steel,  the wet sand is burnished copper, and the fog . . .

tidal flat 3

. . . the fog is really quicksilver. It may look still and static, but don’t let that fool you. One minute it is a thick grey blanket, the next a wispy white cloud. When I look away briefly it evaporates completely, to rematerialize moments later along the shore.

tidal flat 2

When the fog is in its grey blanket phase, our attention is focused in close. We consider the sediment at our feet because there is little else to look at. Between our footprints the sand is dissected by small dendritic tidal outflow channels.


These originate  near the top of the intertidal zone, and develop gently downslope.The channels become pervasive and intertwined, like giant meiosing chromosomes.


As they grow, the channels scour deeper into the sediment, washing away sand and pebbles.

tubes in channel 1

Looking into a larger channel, we wonder about some unusual structures that look like little vertical pillars of sand and gravel. What put them there?  How do they stand up?

These appear to be mucus-lined vertical burrows. These were made by invertebrates (worms, perhaps?) that burrowed downward through the sand of the tidal flat. When the outflowing water scoured the channel’s course it removed the sediment around them, but the thoroughly cemented burrows held fast, becoming little pillars of sediment.

tubes in channel 2

The remarkable pillars stand up because the “worms” glued them together so well.

Now, imagine if this beach was buried deep by further episodes of sedimentation, and ended up being turned into sedimentary rock. A future scientist trying to understand that rock might have a very difficult task, examining clues that could explain the relationship between burrows and sediment.

tubes 1

This is the kind of complicated sequence that those of us studying ancient environments have to make sense of all the time.  Natural processes are rarely linear and straightforward; daily, monthly, and yearly episodes all pile on top of one another, often jumbled into various orders and juxtapositions.

It may tax the human imagination to make sense of a succession of sedimentary events, even when examining a little piece of a tidal flat. Still, the more we put ourselves out there in the modern world, contemplating its messy complexity, the more likely we are to be able to understand the ancient systems of long-past worlds.

tidal flat 1


© Graham Young, 2013

10 Comments leave one →
  1. zzinnia permalink
    August 5, 2013 10:33 pm

    Great post. I like the analogy.

  2. August 7, 2013 7:48 am

    Beautiful, beautiful! We get the same features here on the calmer Maine beaches. I love the worm tubes, and the outflow rivulets. All that artistry, all so ephemeral. So glad to have stumbled on this page.

    • Graham permalink*
      August 7, 2013 12:11 pm

      Harry, many thanks for your kind comment.

  3. August 7, 2013 11:30 am

    Wonderful landscape.

  4. August 12, 2013 5:26 am

    I wondered if you had come across the work “Biogeomorphology of coastal seas – How benthic organisms, hydrodynamics and sediment dynamics shape tidal sand waves” by Bas W. Borsje (2012) ISBN 978-90-365-3434-5. I thought it might have some bearing on your interest in the potential for traces of sand/mud dwelling creatures to be preserved in the geological record. The author is based in the Department of Civil Engineering of the University of Twente in the Netherlands. In his research he has a particular interest in sand-tube dwelling worms and their effect on the substrate in which they were living.

    (Very interesting place, Anchorage. I visited there in June but focused on the wonderful patterns and textures in the rocks rather than the seashore creatures).

    • Graham permalink*
      August 12, 2013 9:28 am

      Thank you Jessica, I will look that up! Interestingly there is quite a good fossil record for vertical burrows in peritidal environments, though I am not sure if any of them are from the sorts of features I saw on Grand Manan.

      You seem to have some very good travel opportunities!

  5. August 15, 2013 3:29 am

    Wonderful post as always, Graham. Love the photos.

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