Making smear slides

Hi crew: So what is “ooze” anyway? Well, there are two flavors:siliceous ooze and calcareous ooze. There are many, many types of microscopic organisms that live in the sunlit surface waters of the world ocean (don’t drink the water!). But some produce mineralized hard parts that preserve to the sediments; that is why geologists study these beasts. Across vast areas of the deep-sea, these ‘microfossils’ are the sediment (i.e., little or no sand or mud from the continents).

Siliceous ooze is composed of the silica hard parts of microscopic plankton, including diatoms and radiolarians. Siliceous ooze is typical of the high latitudes and the equatorial Pacific.

Calcareous ooze is common in the low to mid-latitudes at water depths less than 5000 m. It is composed of the tiny shells and hard parts of single-celled plankton. Today,calcareous ooze covers nearly 40% of the seafloor. The “White Cliffs of Dover”are composed of chalk (the same stuff we use on the board), which began its life 90 million years ago as calcareous ooze.

The most common type of organisms in calcareous ooze are ‘calcareous nannofossils’, including coccolithophorids.These are very tiny, photosynthetic algal cells at the base of open ocean tropical food chains. They produce calcareous platelets that become the sediment after they are eaten and packaged into fecal pellets, which settle to the seafloor.

Today’s picture shows sedimentologists Kristen using a toothpick to take a tiny dab of sediment (that’s how tiny these little critters are) to make a smear slide, and Kathie examining a smear slide using a petrographic microscope to characterize the composition of the sediment. Tomorrow: the sand-sized critters in calcareous ooze. Mark L.

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