Miocene to Recent sediments of the northern Apennines

The materials we were studying in the Northern Apennines were very young sediments (geologically speaking, at least, where 1 million years is not much time at all). Below is a series of photos and descriptions that attempt to lay out the sequence of these rocks in the way they would be seen in a geologic column, youngest on top.


At the top of the section are the very recent Quaternary terraces, Qt8 and Qt9. These are 50-year old floodplain deposits that have been incised by downcutting related to gravel mining that began shortly after WWII.

Each of the surfaces separating these units in an unconformity (time passed without deposition of sediment). The lower boundary of Qt8 in this picture is an excellent example of an angular unconformity.


Here we see Qt3 on top of Qt2. The top of Qt2 has a deeply weathered "fossil" soil or paleosol. The presence of carbonate nodules in that soil indicate a prolonged period of warm and dry climate. The lower gravel (Qt2) was deposited about 450,000 years ago and the soil developed about 400,000 years ago





Here is Qt2 on top of Qt1. Qt1 is the oldest Quaternary gravel stream terrace in the region. It is moderately tilted everywhere along the mountain front and is characterized by a reddish weathering soil at its top. This soil developed about 630,000 years ago







This is the upper mud in the AEI (Association Emilliano Inferiore - Lower Emillia Association). The AEI consists of alternating lake muds, representing glacial periods, gravels, representing glacial melting, and soils developed on top of the gravels, representing interglacial times. These sediment cycles occur due to 100,000 year cycles in the eccentricity of Earth's orbit. The reddish strata in the background are debris flow gravels that lie on top of this mud.





Here is another mud interval (yellow and grey material at the bottom of the photo), overlain by a thin fluvial gravel and then by debris flows. This is the second of three such cycles in AEI.
















Here is a fossil cypress(?) stump at the top of the lowermost AEI mud unit This shows the unit was deposited on land,or in very shallow water








This is the lowest unit in AEI. This mud contains terrestrial fossils and was deposited in a lake on land. The base of this mud is roughly 800,000 years old.

Somewhere in the AEI unit, should be the most recent magnetic reversal in Earth's history. At this time, the magnetic field went from a period of reversed polarity (Matuyama chron) to a period of normal polarity (Brunhes chron). The Brunhes-Matuyama reversal occurred 780,000 years ago.




These interbedded sands and gravels lie at the very top of the Sabbie Gialle.

This unit is approximately 1 million to 800,000 years old








The muds of the Argille Azzure are overlain by medium to thick bedded sands and gravels of the Sabbie D'Imola (Sand of Imola), locally known as the Sabbie Gialle (Yellow Sand)








In the upper part of the Argille Azzure, fossils are abundant. In particular, there are beds of very coarse calcarenite (calcite sands) made of shells and shell fragments. These beds range from 3.1 Ma (million years ago) to 1.8 Ma, corresponding to the Gelasiano and Piacenzian Ages of the middle Pliocene Epoch.







These grey muds of the Argille Azzure show distinct bedding. Much of the Argille Azzure is completely homogeneous mud with no evident bedding. The differences between the bedded and unbedded parts may reflect differences in the depositional environment, in the sediment supply, r in the degree of bioturbation (churning of the sediment by living creatures). The Argille Azzure was deposited between approximately 4.9 and 1 Ma (million years ago).



Cross-bedded sandstones of the upper Miocene Colobacci Formation. This formation is 5.6-5.3 Ma in age. There is an unconformity (time without deposition) between the Colombacci and the overlying Argille Azzure.










Beneath the Colombacci is a very unique rock unit, formed roughy 6 million years ago. These are the Messinian evaporites. This picture shows bedded gypsum that grew out of the evaporating waters of the Mediterranean Sea. Above these rocks lie layers of gysum crystal conglomerates (resedimented gypsum).












Here is a detailed view of the gypsum crystals that make up the Messinian evaporites in this section.

Catching up after Italy

Well, I didn't get nearly as much blogging done in Italy as I might have hoped. Two big reasons - one is that we spent most of our waking hours as you see on the left, up to our knees in Torrente Stirone.



The other, as you see in the second picture, is that our apartment was a bit remote and had no Internet access of any sort.

So now, I'm back and I'm finally caught up with what was waiting on my desk, so I can get a few updates posted on my time in Italy.

We had a great time. The grad student, whose project this is, Kellen, three faculty working with him, and I all had a chance to work together and we got a lot done. The primary work involved measuring the stratigraphic section and sampling for magnetic intensity and for magnetic reversals. For magnetic intensity, we took bulk samples of the sediment every 0.75 meters or 1 meter of section. Because the rocks were tilted, this corresponded to about 2 to 2.5 meters along the river bank. We needed a way to mark the sample sites and the normal method of using a dot of spray paint was not going to work on these soft and wet muds.

On our very first day, inspiration hit when we stopped for gelato on our way home. The little plastic gelato spoons were brightly colored, had a flat area where we could write a number, and a relatively stiff stem that could be pushed into the mud. Our one Italian speaker asked the proprietor if we could buy some and he responded "This is not a spoon store." We persevered and the next morning, we were able to buy a big bag of gelato spoons from the owner. Here is one of those spoons marking a sample site.



After all the samples had been collected, we removed the spoons. Here's is the first day's take.


When I left Italy, we had collected over 500 of these samples. They will be analyzed for their magnetite content to test the hypothesis that there will be a periodicity to the magnetic intensity that matches the 100,000 year and 400,000 years cycles of eccentricity in Earth's orbit around the sun. These cycles are paralleled by climate cycles, making the magnetic intensity measurements a proxy for climate and allowing the project to evaluate possible links between climate cyclicity and patterns in deformation, if there are any. As this data comes in, I will be working to figure out how students can engage with this data set to understand more about basic concepts in earth science, but first we wait and hope that all those boxes yield something useful.

Coming up next: 6 million years of mountain building and climate, recorded in sediments.

Little Boxes on the Hillside... (or at least on the riverbank

The free Internet at the local library won't talk to Blogger, so it's time for a cell phone update. We have been busy collecting samples of mud for the magnetic study. Every two meters along the bank, we stuff a 2 cm plastic cube with sediment, mostly mud. The boxes have been pre-weighed and numbered, so we have to keep track of which is which and where they get filled. Today, we collected oriented samples to look for magnetic reversals. In order to preserve the orientation while getting it into the box, we had to carve little pedestals of mud and slip the boxes over them, then measure the orientation of the box before cutting the box off of the outcrop, trimming off the excess, and putting on the lid. 9 boxes took 6 hours.

Tomorrow is a field trip then one more day in the river before heading home.

Day 3 in the field: we have measured and sampled more than 60 meters of sand and mud, sampling every .75 m. The rocks are Miocene and Pliocene and are barely lithified. They look like rocks, but you sink in to your ankles when you step in a wet spot. We've also seen a whole set of Quaternary gravel terraces, some of which are tilted by deformation.

More details on Thursday!