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FranzBernhard

Introduction to "Point 25"

For some general information, including some maps, about the Campanian St. Bartholomä-formation in Styria, Austria see:

http://www.thefossilforum.com/index.php?/topic/86433-rudist-hunting-in-st-bartholomä-styria-austria-13072018/

The rudist-bearing St. Bartholomä-formation covers an area of about 3km2. Within this area, there are a few sweet spots, where rudist can be found with some confidence: one of the creeks west of Kalchberg; a pile of rocks west of Kalchberg, collected during centuries from the nearby fields; a small, weathered outcrop along a narrow forest road, also west of Kalchberg; or simply an accumulation of fossiliferous limestone with some rudists in a steep forest east of Kalchberg.

But the sweetest spots of all, supplying a continuous flow of rudists, is a scree slope in a small quarry east of Kalchberg - called "Point 25" in my own documentation. The scree slope is located below an outcrop of „Knödelbrekzie“, which is a grain-supported, coarse conglomerate to breccia, exclusive composed of fossiliferous limestone clasts with the occasional rudist, as can be seen in this photo, taken 07/16/2017. The rudist is the cracked, horizontal cylinder-like object in the middle of the photo:

25_16072017_RudistinKnoedelbrekzie_kompr.jpg

 

The next photo is a frontal view of a part of the quarry. It was operated about 100 years ago for hydraulic marl and is heavily overgrown, in other words, its very dark there and the photos are so-so (as usual). „K“ denotes the exposure of the „Knödelbrekzie“, which was shown in the photo above; below you can see beds of fine grained calcareous sandstone. The „U“ denotes the entry to the underground workings, the entry is largely filled with debris from above. Below the „U“ is the scree slope, consisting of clasts of fossiliferous limestone, sandstone and marl. At the bottom is the „deep hole“, scale bar is 1 m, the red x will appear again. Photo taken 09/13/2018.

25_13092018_vertikal_kompr.jpg

 

Lateral view of the quarry. Out of operation since 100 years? It doesn´t seem so. I visited this spot for the first time at 07/16/2017 and two rudists were found instantaneously in the scree (beside the one in the outcrop itself). In October 2017, I decided to examine the material of the scree slope systematically. I began with the nearly horizontal left side and progressed to the steeper right side. Fossiliferous limestone (center left) and marl, sandstone, soil, organic material etc. (at the left edge) were dumped separately. Part of the „deep hole“ is visible in the right corner (note the big sandstone slab in the lower right corner, this slab is also visible in the photo above). I collected and dug at this site from October 2017 until 09/13/2018 about 34 times, each time for about 2 hours. Photo taken 09/13/2018.

25_13092018_Uebersicht_kompr.jpg

 

The „deep hole“. At 09/13/2018, it was about 1.8 x 1.8 x 1.6 m large and something like a quarry in the quarry. Note the red x on the sandstone slab… Photo taken 09/13/2018, scale bar is 1 m.

25_13092018_Tiefbau_kompr.jpg

Next entry: "Point 25" - What´s behind the red x??

FranzBernhard

"Point 25" - What´s behind the red x??

Now the sandstone slab behind the red x (last photo of the previous entry) has been removed. Can you spot it, just above the pocket knife? Photo taken 09/13/2018.

25_13092018_UebersichtmitRudist_kompr.jpg

 

Closer…

25_13092018_MittelmitRudist_kompr.jpg

 

Closest! There was a large rudist just behind the sandstone slab, lying in a depth of about 40 cm below the surface of the scree slope. Still in situ, only some roots and small stones removed for the photo. Pocket knife is 9 cm long, some tapering of the rudist is clearly visible. Such a nice surprise is very rare, normally the rudists are quite dirty there and you can only recognize a few rips or the typical conical or cylindrical outline.

25_13092018_DetailmitRudist_kompr.jpg

 

Rudist removed from the scree and photo taken of the uncleaned traverse fracture at the left end in the photo above. The apical view clearly shows two pillars (P1, P2) and a very thick shell, it´s a Hippurites nabresinensis. Photo taken 09/13/2018.

25_13092018_Rudist_kompr.jpg

 

Next entry: "Point 25" - Surprise at home!

FranzBernhard

"Point 25" - Summing up

Here are the numbers I promised ;):

From 07/16/2017 to 09/13/2018, about 140 hippuridit rudist specimens were found in the scree slope of "Point 25", the sweetest of all spots in St. Bartholomä. The species distribution is (approximate numbers, with examples):

Hippurites colliciatus: 80 (with 140 individuals – many pseudocolonies!) - F, G, H, J

Hippurites nabresinensis: 10 - I and possibly K

Vaccinites vesiculosus: 25 - A, B

Vaccinites alpinus: 10 - C

Vaccinites cf. sulcatus: 5 - D, E

Vaccinites sp.: 10 (no pillars visible, but to nice to be cut, or partial specimens)

 

Polished traverse sections of hippuritid rudists found at "Point 25" from 01/20/2018 to 03/23/2018:

Tafel_Hippuritidae_2018.jpg

 

Only hippuritids in this spot? No, during the same period, about 200 radiolitid rudists were also found, giving a total of about 340 rudist specimens from this spot. Thats about 70% of all rudists found in the St. Bartholomä-formation during my hunting and digging trips from 05/07/2017 to 09/13/2018. Ah, and about 10 coral colonies ware also found at "Point 25"...

 

It is difficult to estimate how many rudists are still waiting in the scree there. Judging from

- the amount of material already removed and dumped (about 3-4 m3),

- the distribution of fossiliferous limestone and other rocks in the scree slope (about 1:2, but highly variable), and

- considering the amount of „Knödelbrekzie“ that seems to be missing in the outcrop (and now lying in the scree),

I will try to make an estimate of 200 to 500 rudists that are still there to be found.

 

Now I am stopping!

Thanks for your patience!
Franz Bernhard

FranzBernhard

"Point 25" - Surprise at home!

Fine, a very nice rudist - a Hippurites nabresinensis -, one of the longest I have found so far in St. Bartholomä (18 cm). But it came even better! At home, I recognized that I have already seen a quite similar traverse fracture before. Indeed, here it is, with the cleaned traverse fracture of the newly found rudist below. Maximum diameter is about 7.5 cm.

HippuritesNabresinensis_25_3987a_adapical_kompr.jpg

HippuritesNabresinensis_25_3987b_apical_kompr.jpg

 

The two parts fit together (considering that there are at least 100 years of weathering between them), resulting in the by far tallest rudist found by me in St. Bartholomä up to now, having a total length of about 27 cm. The shorter part was found at 05/20/2018, about 2 m downslope of the second, longer part, in a depth of about 10-20 cm. Note that the longer part has a kink at the upper end.

HippuritesNabresinensis_25_3987aundb.jpg

 

The upper part is also the natural end of this rudist, as some parts of the upper valve are preserved (upper left).

HippuritesNabresinensis_25_3987a_lateral_kompr.jpg

 

I could stop now, but I don´t. Some people may like numbers, so I will present some in the next entry:

"Point 25" - Summing up

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