Today, we completed the third and final borehole near Winterstettenstadt (Tannwald Site) at a total depth of 166 meters after drilling 10 meters into the host rock of the Tannwald basin, which consists of marl and fine sandstone of the Tertiary molasse sequence.
This week the borehole at the Basadingen-Schlattingen 5068-2 site was refilled and closed. We teamed up with local hydrogeologist to design an environmentally safe and stable filling that protects the local groundwater aquifers.
On monday we have finally reached the bedrock (Tertiary molasse deposits) of the basin at a depth of 155.35 meters. We will now continue drilling for another 10 meters to ensure that we did not hit an allochtonous (i.e. transported) slab of molasse.
We have arrived at a sequence of diamicts at a depth of 143 meters that likely represents the bottom of the overdeepened basin. The sediments are compact and therefore we have little losses.
We are still drilling through the basinal fine-grained clastics and the image nicely demonstrates how compact the sediments are. The bottom of one core had to be cut off and it perfectly fits to the top of the next core (140-141 m).
This week we completed the downhole logging at the Basadingen-Schlattingen 5068-2 site. The borehole proved to be very stable so the open-hole measurements could be completed as planned. Many thanks to the LIAG Logging Crew!
We have now decided to switch to a rotary core barrel system, since the fine sediments we currently encounter are too stiff to hammer through. In turn a rotating crown as shown in the image can nicely cut through these sediments.
We are still drilling through sand at a depth of 80 m and there is yet no sign of the expected fine basin sediments. Sometimes because of the sand the liner gets stuck in the casing and up to 3 people are needed to pull it out
While we encounter a few meters of well sorted sand from a depth of 74 m on the local farmers are harvesting corn on the nearby fields. We have reached a final depth of 77 m this week.
We have now reached the lake sediments at a depth of 65 m. The clay is perfect for taking noble-gas pore water samples, which we store in special sample containers. A total of 12 samples will be analyzed at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) in Zürich after the drilling is completed.
Thanks to our colleagues from Bern the core boxes have finally arrived. Also drilling is progressing very well in silty (more and more clayey) sediments and we have reached a depth of 64 m this week.
Finally, after 5 weeks of forced inactivity due to technical and other challenges, drilling operation continues. We have not reached a depth of 242 m drilling through sands and waiting for the bedrock to occur.
In these soft silty sediments we sometimes recover a core longer than the actually drilled distance. It is very difficult to identify the additional, most likely disturbed material. Hence, we eventually had to split parts of the core to have a more detailed look. The image shows sections through disturbed so-called re-core material on the left and original sediment on the right hand side.
Despite the fine sands, we are still encountering problems with larger clasts. When they fall down from the shallower gravel layers, they sometimes get stuck between the core and the outer casing. In some cases, the crew has to pull the whole casing out and remove the clasts by hand.
As we continue drilling we find sediments to be finer than expected, which allows for good progress as these fine sands are easy to hammer through. We have reached a final depth of 46 m today.
We have finally reached the sands of the Scholterhaus subformation (Rissian age, part of the Dietmanns formation). Even though they are softer and therefore easier to drill we sometimes need heavy machinery to pull the core due to the instability of the sands. Nevetheless, we have recovered a total of 6.6 meter today.
Today we are installing a new toughened crown at the bottom of the casing that will hopefully deal with the Illmensee gravels more easily. The core quality is worth the effort. We have now reached 31 m depth.
Drilling the permeable Illmensee gravels, which lacks a fine matrix, proves difficult since it causes significant loss of the drilling fluid. In addition, we need to re-set the casing every couple of meters.
Basadingen site (5068-2): For the final stretch, our drilling contractor switched to a larger drill rig. After some down time for installation, we should be back drilling in the beginning of next week.
The gravels of the Illmensee formation keep slowing us down. This week the clasts were abrasing the crown severely so that we had to replace it. Still, we are using percussion coring and the recovered cores are of excellent quality.
Drilling operations have come to a temporary standstill at the Tannwald site due to technical problems. We use our time to explore the end moraine that surrounds the Tannwald Basin.
The third Tannwald borehole has reached a depth of 17 meters. We recover excellent cores despite the devious geology by using an additionally armored crown and the Nordmeyer technology. From a depth of 15 meters downward a drilling fluid with bentonite had to be added to reduce the enormous friction caused by the gravel layers.
With slow but steady progress the Basadingen site (5068-2) stands now at 227 m depth; the lithology alternates between sand and challenging-to-drill gravelly diamicts.
We are slowly making our way through the very hard and compacted gravels in the uppermost part of the Tannwald Basin. Drilling is hampered by big clasts, which are hard to hammer through, but we are already at a depth of 10 m and making slow but steady progress.
Today we are happy to announce that we have recovered the first cores down to a depth of 4 m. Even though, we are located in challenging sediments (loose sands with large clasts) the drilling team managed to use a hammer technique, which will likely provide good core quality. Furthermore, the first DNA Sample to discover the Deep Biosphere was taken.
Here we go again: After the longer than expected break for the installation of an additional casing, the DOVE drilling in Basadingen-Schlattingen is now at 142 m. We are currently coring through a challenging alternation of diamicts, gravels and sands.
Once more we had to be well equipped because of long enduring rainfall. We measured a walkaway vertical seismic profile, which only had to be interrupted because of a helicopter flying by.
Since last week the drilling depth is at 126m due to challenges while forcing down the casing to 126 m in sediments partly consisting of thick gravel layers
The science teams at the two drill sites keep in close touch and share their know-how. This week PhD student Bennet Schuster is helping out PhD student Sebastian Schaller at the Basadingen drill site. With borders reopening, this is all so much easier again. Current depth at Basadingen is 125 m.
Ice and fire: This is the wonderful view from the Hochwacht Tower. The area contains an exceptionally rich archive of Quaternary sediments and landforms including the buried Basadingen Overdeepening that we explore within the DOVE project (drill site hidden in the forest in the middleground on the right). On the left (north) you can see the remains of the majestic Hegau volcanoes that were active during Miocene.
Tannwald: After reaching the final drilling depth on Wednesday, we are currently fitting the 80mm PVC pipes into the second borehole, so it can be used for seismic measurements and water sampling.
Second flush borehole reaches the Molasse at the bottom of the Quarternary basin at 153 m, about 2 m above the unconformity in the first borehole. The image shows cuttings of the Molasse on the driller's sieve. We had some help from nature - this sample was washed by 45 mm of heavy rain last night.
The second borehole in Tannwald is going very well and the drilling team is flooding us with samples. Meanwhile the hot weather is challanging us even more. Still, we like to think that the second flush drilling will be finished next week.
The second flush drilling of the Tannwald basin started on 31st of May and we now reached > 40 m depth. Interestingly, the borehole reveals a rather different geology than what we have seen just 30 m apart in the first borehole. Despite these differences, thunderstorms and torrential rainfall, which have been rather constant companions during this last week, drilling is progressing well.
Basadingen: After drilling and on-site MSCL measurements, the cores of DOVE Site 2 (BASA1) are brought to the cool storage room at the University of Bern. The cores will then be opened in the core lab in Bern starting in late summer.
