Basic studies on growth bands (daily, monthly and annual bands) of corals

尽管人们普遍认为，根据珊瑚的每日和每年的生长增量，每年的天数在地质时期内有所减少，但我们的研究表明，在每日和每月的地理计时校准中应该重新考虑古代珊瑚生长带。本文用扫描电镜计数了日本更新世两种石珊瑚化石中的微小生长带，并测定了它们的氧稳定同位素比值，得到了它们的年生长率。在Truncatoflabellumformosum中，每隔半个月就有一条带形成，其带宽（0.05-0.20 mm）与皱纹珊瑚相当。在Tachyphyllia geoffroi中，每个带每天都形成，并且带的宽度比前一种要细得多。这项研究表明，来自皱纹珊瑚的“日常”带以前并不认为是每天形成的。此外，在古生代珊瑚中假设的月球月周期可能真的是一年一次。

Although it has been widely accepted that the number of days per year have decreased through geological time based on daily and annual growth increments of corals, our study indicates that ancient coral growth bands should be reconsidered for daily and monthly geochronometric calibrations. Minute growth bands in two fossil scleractinian coral species from the Pleistocene of Japan were counted by SEM and the oxygen stable isotope ratio was measured to obtain their annual growth rates.There are really two different types of bands and they have different origins. In Truncatoflabellum formosum, each band is demonstrated to have formed per half-month interval.The band widths (0.05-0.20 mm) are nearly equivalent with those of rugose corals. In Tachyphyllia geoffroi, each band was formed daily and the band widths are much finer than the former species. This study suggests that "daily" bands derived from the rugose corals were not previously thought formed daily. Furthermore, lunar monthly periodicities postulated in the Paleozoic corals were probably really annual.