Upper Cretaceous strata of the Mahajanga Basin, northwestern Madagascar, yield some of the most significant and exquisitely preserved vertebrate fossils known from Gondwana. The sedimentology of these strata and their stratigraphic relations have been the focus of renewed geological investigations during the course of five expeditions since 1993. We here designate stratotypes and formalize the terrestrial Maevarano Formation, with three new members (Masorobe, Anembalemba, Miadana), and the overlying marine Berivotra Formation. The Maevarano Formation accumulated on a broad, semiarid alluvial plain bounded to the southeast by crystalline highlands and to the northwest by the Mozambique Channel. The Berivotra Formation was deposited in an open marine setting that evolved from a clastic‐ to a carbonate‐dominated shelf, resulting in deposition of the overlying Betsiboka limestone of Danian age. New stratigraphic data clearly indicate that the Maevarano Formation correlates, at least in part, with the Maastrichtian Berivotra Formation, and this in turn indicates that the most fossiliferous portions of the Maevarano Formation are Maastrichtian in age, rather than Campanian as previously reported. This revised age for the Maevarano vertebrate assemblage indicates that it is approximately contemporaneous with the vertebrate fauna recovered from the Deccan basalt volcano‐sedimentary sequence of India. The comparable age of these two faunas is significant because the faunas appear to be more similar to one another than either is to those from any other major Gondwanan landmass. The revised age of the Maevarano Formation, when considered in the light of our recent fossil discoveries, further indicates that the ancestral stocks of Madagascar's overwhelmingly endemic modern vertebrate fauna arrived on the island in post‐Mesozoic times. The basal stocks of the modern vertebrate fauna are conspicuously absent in the Maevarano Formation. Finally, the revised age of the Maevarano Formation serves to expand our global perspective on the K/T event by clarifying the age of a diverse, and arguably the best preserved, sample of Gondwanan vertebrates from the terminal Cretaceous.

中文翻译：

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马达加斯加西北部 Mahajanga 盆地上白垩统岩石的地层分析：对古代和现代动物群的影响

马达加斯加西北部 Mahajanga 盆地的上白垩纪地层出产了冈瓦纳大陆已知的一些最重要、保存最完好的脊椎动物化石。自 1993 年以来的五次探险过程中，这些地层的沉积学及其地层关系一直是新地质调查的重点。我们在这里指定地层并正式确定陆地 Maevarano 地层，其中有三个新成员（Masorobe、Anembalemba、Miadana），以及上覆的海相 Berivotra 组。Maevarano 地层堆积在广阔的半干旱冲积平原上，东南部以结晶高地为界，西北部以莫桑比克海峡为界。Berivotra 组沉积在开阔的海相环境中，从碎屑岩为主的陆架演化为碳酸盐为主的陆架，导致上覆的大年时代贝齐博卡石灰岩沉积。新的地层数据清楚地表明 Maevarano 地层至少部分地与 Maastrichtian Berivotra 地层相关，这反过来表明 Maevarano 地层中化石含量最高的部分是马斯特里赫特地层，而不是之前报道的坎帕尼亚地层。Maevarano 脊椎动物群的修正年龄表明它与从印度德干玄武岩火山沉积序列中恢复的脊椎动物群大致同时期。这两个动物群的可比年龄很重要，因为与来自任何其他主要冈瓦纳大陆的动物群相比，这两个动物群似乎更相似。Maevarano组的修正年龄，考虑到我们最近的化石发现，进一步表明马达加斯加绝大多数地方性现代脊椎动物群的祖先种群是在后中生代时期到达岛上的。现代脊椎动物群的基础种群在 Maevarano 组中明显不存在。最后，修正后的 Maevarano 组年龄有助于扩大我们对 K/T 事件的全球视野，通过澄清来自白垩纪末期的冈瓦纳脊椎动物样本的年龄，可以说是保存最完好的。