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Published September 1993 | Published
Journal Article Open

Numerical Modeling of Ooid Size and the Problem of Neoproterozoic Giant Ooids

Abstract

Temporal variation in ooid size reflects important changes in physical and chemical characteristics of depositional environments. Two numerical models are used to evaluate the effects of several processes influencing ooid size. The first demonstrates that low supply of new ooid nuclei and high cortex growth rate each promote growth of large ooids. The second model demonstrates that high average water velocity and velocity gradient also enhance ooid growth. Several Neoproterozoic oolites contain unusually large ooids, some reaching diameters of up to 16 mm. While lower nuclei supply and higher ooid growth rate may have prevailed prior to the evolution of carbonate-secreting organisms, neither difference can explain the presence of giant ooids in Neoproterozoic deposits because Archean through Mesoproterozoic ooids rarely exceed 5 mm in diameter. In the presence of lower nuclei supply and higher growth rate, high average water velocity may have allowed growth of such large ooids. Higher average water velocity could have been due to a prevalence of carbonate ramps over rimmed shelves during Neoproterozoic time.

Additional Information

© 1993 Society for Sedimentary Geology. Received 22 January 1993; accepted 30 March 1993. This work was supported by a National Science Foundation Graduate Fellowship to DYS and by NASA Grant #NAGW-2795 to JPG. The authors would like to thank Peter S. Kaufman and Linda C. Kah for their extensive participation at the beginning of the project. In addition, reviews from Bruce H. Wilkinson, David Osleger, Mark R. Boardman, and John B. Southard provided direction for greatly improving the presentation of this research.

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August 22, 2023
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