It’s Complicated

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 . . .

. . . 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.

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.

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.

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.

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.

© Graham Young, 2013