81-4 Resolving the origin and emergence of animals with continental drilling

Session: Investigating Earth’s History With Continental Scientific Drilling

Presenting Author:

Francis Macdonald

Authors:

Macdonald, Francis A.¹, Tasistro-Hart, Adrian², Koran, Isabel³, Rose, Catherine⁴, Prave, Tony⁵, Kasemann, Simone⁶, Nduutepo, Andreas⁷, Pruss, Sara B.⁸, Scharf, Andreas⁹, Trindade, Ricardo¹⁰, Brocks, Jochen¹¹, Bergmann, Kristin¹², Shipman, Samuel Raymond¹³, Rooney, Alan¹⁴, Swanson-Hysell, Nicholas¹⁵

(1) UC Berkeley, Berkeley, CA, USA, (2) University of California, Berkeley, Berkeley, California, USA, (3) UC Berkeley, Berkeley, California, USA, (4) University of St Andrews, St Andrews, United Kingdom, (5) University of St Andrews, School of Earth and Environ. Sciences, St Andrews, United Kingdom, (6) Bremen, Berlin, Germany, (7) Ministry of Mines and Energy, Windhoek, Namibia, (8) Smith College Geosciences, Northampton, MA, USA, (9) Sultan Qaboos University, Muscat, Oman, (10) University of Sao Paulo, Sao Paulo, Brazil, (11) Australian National University, Canberra, Australia, (12) MIT, Cambridge, MA, USA, (13) Yale University, New Haven, CT, USA, (14) Yale University, New Haven, CT, USA, (15) Department of Earth & Environmental Sciences, University of Minnesota, Minneapolis, MN, USA,

Abstract:

The origin of animals was a milestone in ecology and evolution. However, macrofossils provide limited insight into the early evolution of animals as they were likely small, soft-bodied, and not readily preserved. Although molecular clock analyses have suggested either a pre-Cryogenian, syn-Cryogenian, or post-Cryogenian origin of animals, these models rely on fossil calibration, which is lacking. The discovery of putative Neoproterozoic demosponge biomarkers and concomitant changes in photosynthetic primary producers have provided key data points for relating the emergence of animals with environmental changes. Yet, the age of their first appearance in Oman is at best loosely constrained to be between the end of the Sturtian Snowball Earth glaciation at ca. 661 Ma and the Cryogenian-Ediacaran boundary at ca. 635 Ma. It has alternatively been suggested that animals did not appear until later in the Ediacaran Period, after the proliferation of green algae in multiple locations.

 

With Geological Research through Integrated Neoproterozoic Drilling–Cryogenian (GRIND-CRY), we aim to resolve these uncertainties by obtaining cores through archetype Cryogenian successions in Oman, Brazil, and Namibia. In January 2026, with ICDP support, we intend to begin drilling the Neoproterozoic siliciclastic-dominated succession in southern Oman (Dhofar) near Mirbat. Outcrop studies demonstrate that these successions contain evidence for glaciation and retain organic matter that has not been heated over ~90^oC. We will integrate geochemical, paleomagnetic, and sedimentological data from these cores with that from both outcrop and previously drilled industry cores. These data will provide a refined age model and paleoenvironmental context for the diversification of eukaryotic steroid biomarkers, the rise of green algae to ecological dominance and the origin of animals relative to ocean oxygenation and Snowball Earth glaciation.

 

Over the next three years, we will subsequently drill Cryogenian strata in Brazil and Namibia. Both locations preserve shelf-slope transects of a mixed carbonate-siliciclastic sequence with interstratified diamictite and iron formation, which are well-suited to a variety of geochemical studies. Although the succession in Namibia is thermally overmature, it preserves the Trezona carbon isotope excursion and hosts abundant and diverse microfossil assemblages, which will complement data from other sites.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8411

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