From Mud to Microfossils: Processing Samples

Adriane here-

I work with tiny microfossils, called foraminifera, that accumulate on the seafloor. Here, I’ll show you how I, and other paleontologists that work with microfossils (micropaleontoloigsts) acquire our fossils!

Core 21 from Site 1208.

All of the sediment cores that have been drilled since the late 1960’s are kept in one of three core storage facilities (core repositories) located at universities around the world. The University of Bremen, German currently stores 154 km (95.7 miles!) of cores; Kochi University in Japan has 111.2 km (69 miles) of cores; and Texas A&M University in the USA currently houses 132 km (82 miles) of sediment cores. Samples from any cores stored in any of the three repositories can be requested by scientists, and usually arrive in the mail within a few weeks! But let’s back up a bit and talk about where the sediment samples come from.

For my research, I recently requested samples from three cores stored at Texas A&M University. The cores I requested samples from were drilled from the northwest Pacific Ocean (see the sea surface temperature and site location map on the ‘Our Research Explained‘ page). On the left is what a core looks like. All cores, after being drilled and pulled back up onto the drill ship, are cut in half. One half of the core is photographed and kept as a sort of reference, and the other half is used for research (we call this the ‘working half’).

The core pictured here was drilled from Leg 198 (all of the major drilling expeditions are given a number), Site 1208 (the specific site that has coordinates attached), Hole A (in a number of cases, more than one core will be drilled from the same location to ensure the scientists get enough sediment, or recovery). The last number, 21X, is the core number and the letter corresponds to the drill bit that was used to drill it. Because this is Core 21, that means that there are 20 cores younger, or that were drilled before, this one. This core was cut into 4 sections, each approximately 150 centimeters in length, plus the core catcher, which is the last bit of core brought up. Notice the white square of styrofoam labeled ‘PAL’ in the core catcher; this was the sample taken out of the core that was given to the paleontologists on the scientific expedition to determine the age of this sediment.

OK, now back to the samples! My samples arrived within 2 weeks in 3 large boxes. Notice the samples are just chunks of mud. First, I (with the help of my husband) sorted the samples according to what site they were from (1207, 1208, or 1209).

Then, I put the chunks of mud in glass jars and dried them in a low-temperature oven in our lab. This is done to evaporate any water from the mud so we can weigh the samples. After the samples are dried and weighed, they are put into bottles with water to break the mud apart (I call these bottles of mud my ‘Mud Milkshakes’). Notice the labels on each bottle: these indicate which site the sample is from (in this case, all are from Site 1208), the core (the samples in these bottles are from cores 24 and 25), the core section (the third number), and the depth from the top of that section where the sample was taken (125-127 and 127-129, measured in centimeters).

The samples soak for about a week and are then sieved over a small screen. The screen is small enough to let very tiny particles of clay through, but not the microfossils I’m interested in. The sieved samples are then put back into glass dishes and dried. When completely dry, the microfossils are put into small glass jars. Notice the jars are also labeled just like the bottles to indicate the exact location in the cores the sample was taken. This is very important information to know, as later  in my research, I convert depth in the core to age (more on that later)!

 

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