Geology, domestic, mundane, and otherwise

This summer, for my first real professional geology job, I have been logging cores from boreholes drilled 100-200' into subterranean urban Seattle.

It is sandy down there. Lots of silty sand. Some clean sand, but lots and lots and lots of silty sand. There is advance outwash, till, meltout till, and recessional outwash from at least two glaciations. There are fluvial and lacustrine deposits from at least two interglacial periods. Sand, sand, a bit of silt and gravel, a tiny bit of clay, all mixed in with sand, sand, sand.

Living here, one's day-to-day visual input is from this mostly-paved, mid-latitude, low-altitude highly urbanized environment, and a brain isn't forced to think about periglacial processes much. Now, however, having logged a couple thousand feet of Quaternary core here in the Puget Lowland this summer, I have a new appreciation for the huge amount of mostly-sand that is dumped out of the front of glaciers and then pushed around by the huge amount of water that the glacier becomes. Huge. Darn big. Sandy.

Next week, I will put geology-for-money behind me for a couple weeks and head to the desert Pacific coast of southern Peru to hunt for the elusive, wild, Mio-Pliocene barnacle scuta and especially, terga. I am the bouncer and mule of the expedition. My tasks: glower at men trying to hit on the (female) PI. Bash rocks when rocks resist being collected. Carry rocks after they've been bashed. Act as ballast in the tiny rental car when the wind picks up.

The expedition's PI is testing hypotheses about climate-induced macroevoloution by measuring changes in species richness and abundance among balanoid barnacles in the uplifted littoral Pisco Fm.

A little light on details for you? Me, too. I don't really know much about the project yet. I have my script: glower, bash rocks, carry rocks, be weighty.

I will learn more there, and will blog when I can.

On phosphate and sulfide in sediments

Authigenic pyrite (FeS2) commonly forms in marine sediments during early diagenesis from microbially reduced iron and sulfide, both inorganic (from deepsea hydrothermal vents) and microbially produced. Authigenic pyrite is rare in fresh-water lacustrine sediments due to lack of sulfide.

Instead, in most lake sediments, reduced iron that has been released into the pore water during diagenesis of clay minerals is bound by phosphate, not sulfide, to form vivianite Fe3(PO4)2 8H2O.

However, pyrite is common in one fresh-water diagenetic setting: coal swamps. This is apparently because there is so much organic material that sulfide can reach high enough concentrations to compete with the phosphate for the available iron.

I don't know, but I suppose that the activation energy of pyrite formation is much lower than that of vivianite formation. Berner (1980) and Canfield et al (2005) will reveal more to me tonight.

On the quantization of precipitation

I guess rain falls in discrete drops because of water molecules' dipole moments. Does snow form in discrete flakes because a growing snowflake, once it forms on its nucleation site, scavenges all of the water vapor from the surrounding area?