Cyclo and chemostratigraphic characteristics of the Middle Silurian in Gotland, Sweden M.C.M. Arts1, B. Cramer2, M. Calner3, C. M.Ø. Rasmussen4 5, A. M. Bancroft5, S. C. Oborny2, E. Hartke2, E. Biebesheimer2, A.C. Da Silva1 3Lithosphere and Biosphere Science, Lund University, Sweden 1 Sedimentary Petrology, Geology Department, Liège University, Belgium 4Natural History Museum of Denmark, University of Copenhagen, Denmark corresponding author: [email protected] 5GLOBE Institute, University of Copenhagen, Denmark 2 Earth and Environmental Sciences, University of Iowa, U.S.A. 6Indiana Geological Survey, University of Indiana, U.S.A Introduction The Silurian Period which was once thought as warm and climatically stable time interval is in fact punctuated by numerous paleoenvironmental perturbations or events. These Silurian events follow a similar pattern where an extinction event precedes a carbon isotope excursion (Jeppsen 2000 &1997). Many theories have been brought forward to explain these events ranging from glaciations, to changes in precipitations patterns, ocean currents, volcanism induced ocean anoxia and SEDEX formation. Constraints on the duration and timing of these extinction events and subsequent positive carbon isotope excursions are weak, which hampers a full understanding of the processes at play. The Altajme well drilled in South Central Gotland in Sweden in 2015 spans the latest Ordovician to Homerian succession of Gotland. The data from the Altajme core provides us with a unique opportunity to look at climatic perturbations during the Silurian. The Altajme core spans both the Sheinwoodian Ireviken event and the Homerian Mulde event. The Altajme core dataset includes a litholog, high-resolution δ13C data, correlated bentonites with U-Pb dates and a new highresolution XRF core scan. The new high resolution (0.5-1cm resolution) XRF-dataset was gathered in December 2019. The δ13C data in combination with the high resolution XRF scan gives us insights into the changes in the ocean before during and after the events, while the XRF data and U/Pb dated bentonites give cyclostratigraphic age constraints for the events and for core as a whole. XRF Aluminiun 58°N Hangvar Fm. 800 A B Tofta Fm. 600 N ELLESMERIAN Högklint Fm. 400 10o 200 Lower Visby Fm. Al (ppm) Upper Visby Fm. roup Slite G N Visby Halla Fm. 0 50 100 150 200 250 300 350 depth (metres) 6 20 km 4 Mulde Excursion EDONIAN B Altajme 2 L Fröjel Fm. 13C Ireviken CAL 19°E δ 0 20o g Fm. Excursion C -2 Klinteber Han./Tof. ALACHIAN Fröjel U. & L Visby P Klinteberg Fm. Halla Fm. Slite Group P A Fm. Hög. Fm. Gotland Strat. Fm. 60°N

o 40 57°N Gotland Litho. 0 50 100 150 200 250 300 350 Modified after Cramer et, al. 2012 18°E 20°E depth (metres) Investigated section A. Silurian paleogeography B. Geological map of Gotland, with the Altajme well location as red dot Homerian ? Sheinwoodian Telychian Rh. Hir. C. Map of Northern Europe with Gotland Wenlock Llandovery Up. Silurian Ord. Chemostratigraphy Cyclostratigraphy To provide insights into the paleoclimatological To asses the presence of orbital cycles the Wavelet spectrum role of different elements a Principle Component XRF Aluminium record was analyzed using C. 3.3e4 Analysis was conducted using the FactoMineR the R Astrochron and Biwavelet packages spectral power

Period (metres) 1 (Le et al., 2008) function from R. The results (A) (Meyers 2014 and Gouhier. et al.,). 1.0e3 show that Dim 1 and 2 cover almost 50% of the precession 4 3.2e2 variance and that 3 clusters can be defined: The core contains 3 U/Pb dated obliquity 1 Cluster 1: detrital elements bentonites: Ireviken 281.5m 431.83Ma 100ky eccentricity 16 Cluster 2: carbonate associated elements +/- 0.23, 3.1e-2 Grotlingbo: 134m 428.45 Ma +/- 0.35 405ky eccentricity Cluster 3: Chalcophile/low oxygen elements 64 9.8e-4 and Djupvik: 62.9m 428.06Ma +/- 0.35 Barnes. et al. (2019). The U/Pb dates 3.1e-5 Aluminium a detrital element is selected for the 256 tuning. Gotland was located In mid to lower indicate that the 281.5-134m interval has an 0 50 100 150 200 250 300 latitudes during the Silurian. Higher summer average sedimenation rate of ~4cm/kyr and depth (metres) insolation should lead to higher precipitation the 134-62.9m interval has an average and thus higher aluminium values thus a maxima EHA: EHA: EHA: spectral power normalized in the 405-kyr filtered aluminium record should sedimentation rate of D. Harmonic F-test (1) Harmonic F-test (2) Harmonic F-test (3) correspond to a 405-kyr eccentrcity maxima. ~19cm/kyr. The 1 1 320 1 bentonite data allows depth (metres) 280 200 The XRF chemostratigraphic record also us to idntifiy precession, 0.8 260 0.8300 0.8 shows enrichments in P, Mn, Zn, S, Ba obliquity,long and short 0.6 240 0.6 and Pb at and and during the onset of the eccentricity in the 280 0.6 A. 150 220 carbon isotope excursions (B). Elemental wavelet spectra (C). 0.4 200 0.4 0.4 enrichments before carbon isotope excursions could be associated with volcanic events but as indicated in 260 100 0.2 Emsbo. (2017) the elemental enrichment of P, Mn, Zn, S, Ba and Pb could also be indicative of the formation of The stable 405kyr 0.2 180 0.2 240 Sedimentary exhalative deposits (SEDEX). The pre-excursion extinction and subsequent δ13C excursion point eccentrcity cycle can 0 160 0 0 to a release of SEDEX brines. be used to create a Mn Zn S Ba Pb 0.008 0.02 0.02 0.12 0.5 P floating time scale for 0.15 10000 20000 30000 40000 50000 10000 15000 20000 25000 (ppm) 10000 (ppm) (ppm) 10000 (ppm)20000 30000 (ppm) Frequency (cycles/metre) 2000 4000 6000 8000 (ppm) 1000 2000 3000 4000 (Laskar et al., 2004). Black dotted lines are 405-kyr cycle traced in spectra 20 40 60

-2 δ13C Litholog 0 2 4 6 The 405kyr cycle was y

0 0 0 0 0 0 0 traced in the EHA windowed spectra (D). Three k Sedimentation rate from EHA / 30

different sized spectral analysis windows with overlap m

c 25

in the depth domain were used to account for the e t 20 a

large changes in sedimenation rate in the core and r 50 50 50 50 50 50 50 15 provide a complete trace ofthe 405-kyr cycle in the n Mulde o i 10 t

Excursion depht domain. The traced results are combined and a

t 5

converted to a new composite sedimentation rate (E). n e 0 100 100 100 100 100 100 100 The sedimentation rate is used to convert the data m 0 50 100 150 200 250 300 350 i

from the depth to the time domain (F). d depth (m) e

S Red lines are mayor formation/lithological boundaries Left to right shale ->marl ->carbonate Depth (metres) The duration of the Ireviken event is 5*405-kyr E. 150 150 150 150 150 150 150 eccentricity cycles giving a duration of 2.025Myr for the whole event. The rise in δ13C values for both events took place within a 200-400 kyr time window indicating that the Mulde and Ireviken excursions were created by single environmental perturbations. 200 200 200 200 200 200 200 1.5 Al based Tuning Altajme core F. 6 1.0 250 250 4 250 Ireviken 250 250 250 250 Excursion 0.5 2

300 300 300 300 300 300 300 δ13C (promille) -1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 Al Al 405ky -0.5 -2 d13C Normalized Al. values 350 350 350 350 350 350 350 B. (filtered and unfiltered) floating age (in kyrs) Conclusions References

A new cyclostratigraphy based age model for the Telychian to Homerian of Gotland is presented. The duration Barnes. L., Trayler R. B., Cramer B. D., Calner M., Bancroft A. M., Oborny S.C., Jeppsson, Lennart & Calner, Mikael. (2002). The Silurian Mulde Event and a (2019) A Bayesian Age-Depth Model for the Silurian Altajme Core, Gotland, Sweden. scenario for secundo–secundo events. Earth and Environmental Science of the Ireviken event is 2.025Myrs eg. 5*405-kyr eccentricity cycle. The rise in δ13C values for both events took 10.1130/abs/2019AM-337871. Transactions of the Royal Society of Edinburgh. 93. 135 - 154. 10.1017/S0263593300000377. place within a 200-400 kyr time window indicating that the Mulde and Ireviken excursions were created by a Cramer, & Condon, Daniel & Söderlund, Ulf & Marshall, & Worton, & Thomas, Alan & Calner, Mikael & Ray, David & Perrier, Vincent & Boomer, & Patchett, & Jeppsson,. Laskar J., Robutel P., Joutel F., Gastineau M., Correia A. C. M., and Levrard B. single environmental perturbations. The enrichments of P, Mn, Zn, S, Ba and Pb before and during the (2012). U-Pb (zircon) age constraints on the timing and duration of Wenlock (Silurian) A&A, 428 1 (2004) A long-term numerical solution for the insolation quantities of the paleocommunity collapse and recovery during the ‘Big Crisis’. Geological Society of Earth, 261-285 DOI: https://doi.org/10.1051/0004-6361:20041335 excursions indicate that the δ13C excursions might be the result of a sudden release of SEDEX brines. America Bulletin. 124. 1841-1857. 10.1130/B30642.1. Le, S., Josse, J. & Husson, F. (2008). FactoMineR: An R Package for Multivariate Emsbo P., (2017). Sedex brine expulsions to Paleozoic basins may have changed Analysis. Journal of Statistical Software. 25(1). pp. 1-18. global marine 87Sr/86Sr values, triggered anoxia, and initiated mass extinctions, 86. http://www.jstatsoft.org/v25/i01/ 474-486. https://doi.org/10.1016/j.oregeorev.2017.02.031 \. Acknowledgments Meyers, S.R. (2014). Astrochron: An R Package for Astrochronology. https://cran.r- Gouhier T. C., Grinsted. A., Viliam S., https://CRAN.R-project.org/package=biwavelet project.org/package=astrochron Jeppsson, L (1997). "The anatomy of the Mid-Early Silurian Ireviken Event and a scenario for P-S events". In Brett, C.E.; Baird, G.C. (eds.). Paleontological Events: This poster is made with support of FNRS grant FNRS.PDRT.T.0051.19. Stratigraphic, Ecological, and Evolutionary Implications. New York: Columbia This poster is a contribution to IGCP-652 “Reading Geologic time in Paleozoic Sedimentary rocks” University Press. pp. 451–492.