赞尼特期（亦被称为兰登期或海尔斯期）是古新世的最后一个时期，与晚古新亚世相对应。其起止时间分别为58.7 ± 0.2百万年前和55.8 ± 0.2百万年前。该阶名字来源于在伦敦盆地发现的最古老的古新世沉积层——赞尼特岩层，该岩层的名字则来自肯特地区的赞尼特岛。

赞尼特期对应的地层为赞尼特阶，全球界线层型剖面和点位协定（Global Boundary Stratotype Section and Point，GSSP）将西班牙北部的祖玛亚（Zumaia）地区的岩层作为赞尼特阶的定义标准，并于2008年获得批准。

The Thanetian is, in the ICS Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or series. It spans the time between 59.2 and 56 Ma. The Thanetian is preceded by the Selandian age and followed by the Ypresian age (part of the Eocene). The Thanetian is sometimes referred to as the Late Paleocene sub-epoch.