Paleoecologic techniques make important contributions to basin analysis. The Neogene Humboldt basin of northern California is an excellent example of a basin whose history of development is being increasingly understood owing to paleoecologic study. Before the geologic history of a basin can be well understood, correlation of stratigraphic units must be established. This has been a problem in the Humboldt basin, but improved zonation based on planktonic foraminfera, diatoms, paleomagnetics, and dated ash beds offers promise of improved correlation. Several paleoecological techniques have been used to determine depositional environments: (1) taxonomic uniformitarianism; (2) biogeochemistry (especially oxygen isotopic analysis); (3) skeletal structure; (4) functional morpho ogy; (5) trace fossils; (6) population dynamics; (7) community analysis; and (8) biogeography. These techniques are especially valuable as supplements to sedimentologic and stratigraphic study.

The Humboldt basin formed in late Miocene time and deepened rapidly. Most of the basin fill is a thick regressive sequence of deep basin, slope, shelf, and finally continental deposits. At least the landward part of the basin was strongly deformed in mid-Pleistocene time. The basin was probably considerably more extensive both in the landward and seaward directions than suggested by the present outcrop pattern. The offshore part of the basin may still be an active site of deposition with nonmarine sedimentation still occurring in the lower Eel River valley, lagoonal sedimentation in Humboldt Bay, and shelf and deeper sedimentation continuing offshore into the Pacific Ocean basin.

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