Science. 1984 Mar 16;223(4641):1174-7. doi: 10.1126/science.223.4641.1174.
The results of a detailed study of the brachiopods of the most complete Cretaceous-Tertiary boundary in Denmark, Nye Klslashed circlev, show an extinction pattern for this marine invertebrate group compatible with that reported for pelagic foraminifera and coccoliths and with the impact scenario. The extinction is abrupt, coinciding with the Maastrichtian-Danian boundary. There is no warning in the form of decreasing density, decreasing diversity, or early extinction of specialized groups. The basal few meters of the Danian are almost devoid of brachiopods, and a Danian brachiopod fauna starts almost as abruptly as the Maastrichtian fauna disappeared. The new fauna is similar to the Maastrichtian as regards density and diversity, and at maximum six species are common to both stages. The northwest European Masstrichtian chalk is composed mainly of the remains of coccoliths and pelagic foraminifera. The mass extinction of these groups led to a total cessation of chalk production. The chalk is overlain by a thin clay bed deposited partly under anoxic conditions. This combination of anoxia and clay deposition coupled with a cessation of productivity led to the extinction of specialized groups such as the chalk brachiopods. The surviving species included forms that could survive in well-aerated shallow marine waters on substrates other than chalk.
对丹麦最完整的白垩纪-第三纪交界地区腕足动物的详细研究结果表明，这种海洋无脊椎动物群的灭绝模式与浮游有孔虫和颗石藻的灭绝模式以及撞击情景相吻合。灭绝是突然的，与马斯特里赫特阶-丹尼尔阶边界一致。没有以密度降低、多样性减少或特化群早期灭绝的形式发出警告。丹尼尔阶的底部几厘米几乎没有腕足动物，丹尼尔阶的腕足动物群几乎与马斯特里赫特阶动物群同时突然消失。新动物群在密度和多样性方面与马斯特里赫特阶相似，在最大程度上，有 6 种共同存在于两个阶段。西北欧的马斯特里赫特阶白垩主要由颗石藻和浮游有孔虫的遗骸组成。这些群体的大规模灭绝导致白垩岩的生产完全停止。白垩岩之上覆盖着一层薄薄的粘土床，部分是在缺氧条件下沉积的。缺氧和粘土沉积的这种组合加上生产力的停止导致了专门化群体的灭绝，如白垩纪腕足动物。幸存的物种包括那些能够在含氧丰富的浅海水中、在不是白垩的基质上生存的形式。
