Stratigraphy and paleoecology at the Wenlock/Ludlow boundary on Saaremaa Island, Estonia — An abstract submitted to the Geological Society of America for the 2011 annual meeting

July 7th, 2011

KURESSAARE, ESTONIA–Editor’s note: The Wooster Geologists in Estonia found enough material, and had enough time, to write abstracts for posters at the Geological Society of America Annual Meeting in Minneapolis this October. The following is from student guest blogger Nick Fedorchuk in the format required for GSA abstracts:

STRATIGRAPHY AND PALEOECOLOGY AT THE WENLOCK/LUDLOW BOUNDARY ON SAAREMAA ISLAND, ESTONIA

FEDORCHUK, Nicholas D., WILSON, Mark A., MATT, Rachel M., Dept of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691-2363, VINN, Olev, Dept of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia

The boundary between the Wenlock Series and the Ludlow Series can be easily observed on the island of Saaremaa in western Estonia. Here, the boundary is distinguished by a major disconformity that can be correlated to a regional regression described in several previous studies. During this time, western Saaremaa was a lagoonal facies that reflected sea-level changes within the Baltic Basin. We measured and described this Wenlock-Ludlow boundary interval at Soeginina Cliff on the western shore of Saaremaa. Here this boundary consists of the Vesiku Beds of the Rootsiküla Formation (Wenlock) overlain by the Soeginina Beds of the Paadla Formation (Ludlow). The Vesiku Beds (Wenlock) record a carbonate lagoonal environment with finely laminated beds and Thalassinoides burrows (indicating oxygenated bottom conditions). The fauna is much less diverse than that in normal marine sediments of the Wenlock. The top surface of these beds (the primary discontinuity surface) shows a microtopography and dissolution consistent with exposure and abrasion. The top 20 centimeters also show diagenetic alteration of the laminated sediments, probably from fluids traveling through the Thalassinoides burrow systems. The Soeginina Beds (Ludlow) show pulsating transgressive sediments with multiple discontinuity surfaces. Large oncoids are common in these beds. They have distinctive shapes because they were initially spherical and later stabilized and grew like small stromatolites upwards. These forms may indicate periodic energy reductions in these transgressive waters. There are also storm beds with biogenic debris including oncoids nucleated on gastropods. This boundary interval is topped by thin dolomites and stromatolites. This example of the Wenlock-Ludlow boundary can be correlated with other such disconformities recorded in a variety of depositional environments, such as in the equivalent reef complexes of Gotland, Sweden.

8 Responses to “Stratigraphy and paleoecology at the Wenlock/Ludlow boundary on Saaremaa Island, Estonia — An abstract submitted to the Geological Society of America for the 2011 annual meeting”

  1. Leann Doon 07 Jul 2011 at 6:47 pm

    I understood none of this! But yaaaay! Proud of you.

  2. Rosie Fedorchukon 07 Jul 2011 at 11:33 pm

    I would like to ditto Leann’s comment. I can’t wait to hear more about all the Wooster discoveries! Thanks for the daily blog updates…..I’ve really enjoyed them!

  3. Nick Fedorchukon 08 Jul 2011 at 1:27 am

    haha thanks guys

  4. [...] To our surprise, the Kaali Museum had a thorough display on the geology of Saaremaa, including this polished cross-section through Nick’s critical Wenlock/Ludlow section. [...]

  5. [...] found an excellent collection of eurypterids from the Rootsiküla Formation (Wenlock) in Estonia. He worked with these rocks in the field, but did not find any recognizable eurypterid fossils. Now [...]

  6. [...] America annual meeting. Above is Nick Fedorchuk who talked about his work in Estonia studying the Wenlock-Ludlow boundary on Saaremaa Island and its implication for Silurian stratigraphy and depositional environments in [...]

  7. [...] Thjis was exciting for me because these are the same beds Nick Fedorchuk worked on last year during his Independent Study. The Kübassaare Clff exposures, though, are many kilometers to the east and show extensive bedding [...]

  8. [...] those of Nick Fedorchuk (’12) who worked last year on the equivalent beds 70 km west during his Independent Study. There are some immediate clues to the general environment, such as the halite crystal mold [...]

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