*Revised Manuscript (clean copy) © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http:// creativecommons.org/licenses/by-nc-nd/4.0/ A depositional model for spherulitic carbonates associated with 1 2 3 4 alkaline, volcanic lakes 5 6 7 8 1* 2 1 3,4 9 Ramon Mercedes-Martín , Alexander T. Brasier , Mike Rogerson , John J.G. Reijmer , Hubert 10 11 5 1 12 Vonhof and Martyn Pedley 13 14 15 16 1. School of Environmental Sciences, University of Hull, Cottingham Road, HU6 7RX, Hull, UK. (* Email: 17 18
[email protected]). 19 20 2. School of Geosciences, Meston Building, University of Aberdeen, Old Aberdeen, Scotland, UK. AB24 3UE. 21 22 3. Faculty of Earth and Life Sciences, VU University of Amsterdam, De Boelelaan 1085, 1081HV Amsterdam, 23 24 The Netherlands. 25 26 4. College of Petroleum Engineering and Geosciences, King Fahd University of Petroleum and Minerals, 27 28 Dhahran 31261, Saudi-Arabia 29 30 5. Max Planck Institut für Chemie, Hahn-Meitnerweg 1, 55128 Mainz, Germany. 31 32 33 34 35 ABSTRACT 36 37 The South Atlantic Aptian ‘Pre-salt’ reservoirs are formed by a combination of spherulitic 38 39 40 carbonates and Mg-rich clays accumulated in volcanic alkaline lake settings with exotic 41 42 chemistries. So far, outcrop analogues characterised by metre-thick successions deposited in 43 44 45 lacustrine scenarios are elusive so disentangling the genesis of spherulitic carbonates 46 47 represents a major scientific challenge with business impact. In particular the controls on 48 49 50 spatial distribution and the environment of spherulitic facies formation remain poorly 51 52 constrained, little studied, and hotly debated.