Is there only geological literature on this topic? I have now read some geological papers, about the subduction of the northern fringe of the Arabian plate. This could be interpreted [by me] as the possibility that shell bearing deposits have been ""swallowed"" by a covering European plate. Due to the collision of the plates this Neo-Tethyan Sea disappeared and the fossil containing beds with it? Thus the connection between the Western Tethys and the Proto Indian Ocean, the area with the connection, stays a black box this way for the gastropod and bivalves (and other creatures)?

The closure of a seaway is quite challenging and spectacularly flexible, and depending on the perspective, ages and mechanisms can be quite different. I see three main ways to define the "closure":

• a. A seaway closes when the last aquatic obstacle is removed and land fauna can "cross" the former boundary. In this case, the closure between the Mediterranean and the Indian realms would be of the early Miocene age (Gomphotherium land bridge – Harzhauser et al., 2007; doi:10.1016/j.jcz.2007.05.001 ), however, the seaway opened briefly in the middle Miocene (Sun et al 2021; https://doi.org/10.1016/j.palaeo.2020.110172). This is however a very terrestrial perspective.
• b. A seaway is lost when ocean currents cease to flow properly (triggering climate and biological changes on a large, Planetary scale). In this case, the closure between the Mediterranean and the Indian realms would likely be of the Eocene-Oligocene age (Allen and Armstrong, 2008; https://doi.org/10.1016/j.palaeo.2008.04.021).
• c. Another way of looking at closure is when marine organisms and water masses are no longer able to cross the "seaway". This can appear blurry, because submerged obstacles would quite different for faunas or water masses flow, but is essential in understanding the gradual decrease of connectivity. From this perspective, the closure between the Mediterranean and the Indian realms would show as gradual steps (in the interval between the two extremes mentioned above - (e.g., Bialik, https://doi.org/10.1016/j.palaeo.2008.04.021).

However, evidence needs to be weighed in carefully – the closure between the Mediterranean and the Indian realms is not necessarily the closure of one “seaway”. Several strait configurations (shallow, deep etc.) existed, favouring particular aquatic exchanges.

As for stacks of such marine sediments trapped in modern mountains, such a suture zone is well expressed from south Iran so SE Turkey.

hope this is useful

And please don't hesitate to correct me if I missed something.

beste,

Dan

Thanks for your contribution Dan! In my opinion, a seaway is not yet (fully) closed when the last crawlers or fish are able to crawl or swim from one basin to the other. Thus not limited to stopping of currents bringing veligers to another basin. I have seen several DNA-analyses (mostly mollusca) where the differentation between Atlantic/mediterranean lineages and Indo-Pacific lineages is set around 17-18 mio years ago. In those cases the connection should have been lost slightly earlier to give time for divergence.

For the fossil records, I would love to have more literature on the south of Iran and SE Turkey as that would have been the area of the last connection of the 2 oceans. I have all works of Harzhauser & co.

It might be that fossil bearing limestones were ultimately disappeared by the tectonics, the Arabian Plate getting under the Eurasian Plate. Is there any literature that you know of, pointing in that direction?

I will look into it. As the "full" closure would likely correspond to a post subduction phase of the collision, so the fossil-bearing sediments should be trusted and exposed in the collision zone. However, in this particular case, there is a second gateway further south. I will try to prepare a list of publications in the upcoming days.

thanks Dan! looking forward ti it!

Thanks! But it is not in English, so that is a job to translate it ...

Wow, this is super interesting Nazik - did not know bout the first publication.

One word of caution, the region contains two types of basins: the passage - south of the Bitlis suture (former Bitlis ocean) in the south and some extensional basins north of Bitlis (eg. Mus and Elazig), that are likely to be marginal basins connected only with the Mediterranean but not linked with the Indian Ocean.

Maybe this will give a better perspective (ex. Fig. 10):

Article Oligocene-Miocene basin evolution in SE Anatolia, Turkey: co...

A bit to the south and of course more to the East, north Irak might be a potential hotspot for your search Aart:

Article The Miocene Sequence in Iraq, a Review and Discussion, with ...

Article The palaeoshoreline of Early Miocene formations (Euphrates a...

https://www.iasj.net/iasj/download/69dc8b89346aa713

You can also check fig. 6 of this paper"Paleomagnetic constraints on the Early Miocene closure of the southern Neo-Tethys (Van region; East Anatolia): Inferences for the timing of Eurasia-Arabia collision, 10.1016/j.gloplacha.2019.103089"

""However the region is tectonically very complicated. I believe it is a topic that should be investigated deeper"" : so true. It is even possible that the last marine deposits are only connecting to one side, not both! That would be interesting to know as it would outdate the connection.

I found an interesting geological paper: Pourteau, A., Oberhänsli, R., Candan, O., Barrier, E., & Vrielynck, B. (2015). Neotethyan closure history of western Anatolia: a geodynamic discussion. International Journal of Earth Sciences, 105(1), 203–224. doi:10.1007/s00531-015-1226-7. It is about the subduction in Turkey. The conclusion [from the abstract] is: "Thence, we put forward a favoured tectonic scenario featuring two successive phases of subduction of a single lithospheric slab and episodic accretion of two continental domains separated by a continental trough, representing the eastern end of the Cycladic Ocean of the Aegean. The lack of univocal evidence for slab break-off in western Anatolia and southward-younging HP/LT metamorphism in continental tectonic units (from ~85, 70 to 50 Ma) in the Late Cretaceous–Palaeogene period suggests continuous subduction since ~110 Ma, marked by roll-back episodes in the Palaeocene and the Oligo-Miocene, and slab tearing below western Anatolia during the Miocene". Other scenarios are represented in the article. But all have in common the subduction - hence the lack of layers with marine fossils. The authors favour continuous subduction into the Miocene.

Thanks for your help,it was very useful

Thanks Nazik! Impressive list ... reading will take some time but i will certainly do!