Strontium isotope ratios of planktonic foraminifera from sediment samples acroos the K/T boundary

Seawater 87Sr/86Sr values increase abruptly by 28 * 10**-6 across the Cretaceous/Tertiary boundary (KTB). This small, but rapid shift is superimposed on the larger scale structure of the seawater Sr isotope curve. The time scale of radiogenic Sr addition appears to be too rapid to reconcile with sources associated with volcanism, and we show that the amount of Sr required to produce even this small increase is too large to be derived from: (1) a KT bolide of the size constrained by the Ir anomaly, (2) continental crust ejecta from the impact of such a bolide, (3) soot from global wildfires initiated by an impact, or (4) any combination of these sources. The probable source of the radiogenic Sr is enhanced continental weathering, but the high rate of increase appears to rule out processes such as sea level regression, glaciation or tectonism. A plausible mechanism for rapid addition of radiogenic Sr to the oceans is enhanced weathering associated with globally distributed acid rain (pH c. 1) which is a proposed by-product of a bolide impact (Prinn and Fegley, 1987, doi:10.1016/0012-821X(87)90046-X).

海水87Sr/86Sr比值（Seawater 87Sr/86Sr values）在白垩纪-古近纪界线（Cretaceous/Tertiary boundary，简称KTB）处骤然升高28×10^-6。这一幅度微小但变化迅速的偏移，叠加于海水锶同位素曲线的更大尺度变化格局之上。放射成因锶（radiogenic Sr）的补给时间尺度似乎过于短促，难以与火山作用相关的源区相契合；本研究证实，即便仅产生这一微小增幅，所需的锶总量也远超以下四类来源所能提供的规模：(1) 受铱异常（Ir anomaly）约束尺寸的KTB陨星（bolide），(2) 此类陨星撞击溅射的大陆地壳物质，(3) 撞击引发的全球野火所产生的煤烟，或(4) 上述来源的任意组合。放射成因锶的潜在源区为增强型大陆风化作用，但快速的升高速率似乎排除了海退（sea level regression）、冰川作用（glaciation）或构造作用（tectonism）等过程的可能性。一种合理的海洋放射成因锶快速补给机制，是与全球分布的酸雨（pH约为1）相关的增强型风化作用——该酸雨被认为是陨星撞击的副产物（Prinn和Fegley，1987，doi:10.1016/0012-821X(87)90046-X）。