Abstract

Note: This paper is dedicated to Aaron and Elizabeth Waters on the occasion of Dr. Waters' retirement.

Eocene limestone bodies on the Olympic Peninsula were deposited as nannoplankton-foraminiferal oozes upon a sea floor of volcanic rocks. Successive episodes of basaltic submarine volcanism caused substantial modifications of the sediments. Some of the oozes were disrupted and metamorphosed when they were intruded by diabase or pillow basalt. Others were eroded by volcanic breccia flows. In some places, the pelagic ooze infiltrated into cavities between and within basalt pillows where it is now preserved as small pockets of limestone.

These complex relations contribute to the lenticularity of the limestone bodies. In some cases, they also make it difficult to determine relative ages of spatially associated sediments and volcanic rocks, not only on the Olympic Peninsula but also in present oceanic regions where marine geologists may recover only small specimens. Some of the characteristics noted in this limestone may be useful in making relative age evaluations on oceanic samples. The presence or absence of thermal baking in sediments, often considered the best petrologic evidence for comparative age determinations, is commonly difficult to recognize in the limestones, even where field evidence indicates they were intruded.

Observations on the Olympic Peninsula suggest that the sedimentary record on sea-mounts and oceanic ridges will be incomplete or confusing because of volcanic activity, but systematic facies relations of sediments and volcanic rocks may be affiliated with such edifices.

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