The cyclic nature of late Neogene climate is reflected in the relative frequency diagrams of palynomorphs deposited in the northern Gulf of Mexico. A general cooling through the late Neogene and at least five glacial cycles for the Quaternary are indicated. An additional prominent cold cycle in latest Miocene time is interpreted from the frequency diagram of Picea, spruce. The Pliocene-Pleistocene boundary is marked by an abundance of Ambrosia and Helianthus types of Compositae pollen below and increased frequency of Alnus and Exesisporites above. A new species of fungal spore occurs abundantly in the lower part of the Pleistocene and also lower in the Neogene.

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