Oligocene and Early Miocene gastropods from Kutch (NW India) document an early biogeographic switch from Western Tethys to Indo-Pacific

Abstract

Shallow marine gastropod assemblages from Chattian, Aquitanian and Burdigalian sections in the Indian Kutch Basin are described. They provide insight into the composition and biogeographic relations of the gastropod assemblages at this junction between the Western Tethys and Proto-Indo-Pacific Ocean. For the first time, an improved biostratigraphy allows a clear separation of the assemblages, especially for the hitherto undifferentiated Early Miocene faunas. Throughout the Oligocene, about one-third of the species are also frequently found in the Western Tethys, documenting a passable Tethyan Seaway for nearshore molluscs. A considerable provincialism is evident as well. The expected turnover during the Early Miocene, due to the closing of the Tethyan Seaway, is reflected in the Miocene assemblages. Surprisingly, however, the cut appears very early, i.e. already during the Aquitanian, when the West-East interrelation drops to zero despite the passage having been open during this interval. In contrast, the Burdigalian assemblages witness a minor re-appearance of Western Tethys taxa, suggesting the re-establishment of rather ineffective migration pathways prior to the final closure of the Tethyan Seaway. Cerithium bermotiense and Lyria (Indolyria) maniyaraensis are introduced as new species.

The role of eastern Tethys seaway closure in the Middle Miocene Climatic Transition (ca. 14 Ma)

“…Therefore we suggest that, prior to approximately 14 Ma, a relatively deep seaway connected the Indian Ocean and the proto-Mediterranean, allowing the production of TISW. Moreover, the termination of TISW production during the MMCT (Woodruff and Savin, 1989;Wright et al, 1992;Kennett, 1994, 1995) suggests a middle Miocene age for the final closure of the Tethys seaway, which is consistent with oceanic palaeontological data (Rögl, 1999;Harzhauser et al, , 2009Reuter et al, 2009). Our results are in disagreement with the study of Hüs-ing et al (2009), who suggested that a connection between the Mediterranean Sea and the Indian Ocean still existed at 11 Ma.…”

“…During the Cenozoic, the collision between the AfroArabian and Eurasian plates closed the Tethys seaway which connected the proto-Mediterranean Basin and the Indian Ocean (Rögl, 1999;Harzhauser et al, , 2009). The timing of this seaway closure is still under debate.…”

“…Finally, stratigraphic and oceanic palaeontological data indicate that the Mediterranean Basin and the Indian Ocean were intermittently connected until at least the middle Miocene (Rögl, 1999;Harzhauser et al, , 2009Okay et al, 2010). The consensual view is that, after the initial collision between AfroArabia and Eurasia, the remaining eastern Tethys seaway was not floored by oceanic crust, and the re-opening phases were mainly due to sea-level changes (Rögl, 1999;Harzhauser et al, , 2009Allen and Armstrong, 2008;Hüsing et al, 2009;Reuter et al, 2009;Okay et al, 2010). The final closure of the Tethys seaway after the Langhian transgression (ca.…”

“…Many authors agree that the final closure of the eastern Tethys seaway, and the subsequent end of water exchanges between the proto-Mediterranean and the Indian Ocean, occurred during the middle Miocene, at approximately 14 Ma (Rögl, 1999;Harzhauser et al, , 2009). This age estimation coincides with the Middle Miocene Climatic Transition, and is one of the arguments supporting the hypothesis of the Tethys seaway closure as a driver of this transition (Woodruff and Savin, 1989;Wright et al, 1992;Flower and Kennett, 1995;Ramsay et al, 1998).…”

Cyclone trends constrain monsoon variability during late Oligocene sea level highstands (Kachchh Basin, NW India)

“…Cyclones are one of the most devastating weather phenomena that affect tropical coasts (Henderson-Sellers et al, 1998). For this reason, attempts to relate trends in tropical cyclone intensity and frequency with global change have become a challenging subject in recent years (e.g.…”