Sumner D Y, Grotzinger J P
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Insitute of Technology, Cambridge 02139, USA.
J Sediment Petrol. 1993 Sep;63(5):974-82. doi: 10.1306/d4267c5d-2b26-11d7-8648000102c1865d.
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.
鲕粒大小的时间变化反映了沉积环境物理和化学特征的重要变化。使用两个数值模型来评估影响鲕粒大小的几个过程的作用。第一个模型表明，新鲕粒核的低供应量和高皮层生长速率均会促进大鲕粒的生长。第二个模型表明，高平均水流速度和速度梯度也会增强鲕粒的生长。几个新元古代鲕粒岩含有异常大的鲕粒，有些直径可达16毫米。虽然在分泌碳酸盐的生物体演化之前可能普遍存在较低的核供应量和较高的鲕粒生长速率，但这两种差异都无法解释新元古代沉积物中巨型鲕粒的存在，因为太古宙至中元古代的鲕粒直径很少超过5毫米。在核供应量较低和生长速率较高的情况下，高平均水流速度可能使如此大的鲕粒得以生长。较高的平均水流速度可能是由于新元古代时期碳酸盐缓坡比镶边陆架更为普遍。
