Abstract

Limestone and diabase from 11 sites in the Permanente Quarry, the largest outcrop of Calera limestone in the Franciscan terranes, have been studied by paleomagnetic and biostratigraphic methods. Observation of the upper Albian-uppennost Albian boundary at one outcrop provides age and polarity control; we propose a primary origin for a magnetic component identified in this unit. Another unit has been remagnetized by the diabase sill. However, predeformational inclinations are in agreement, suggesting that remagnetization occurred shortly after deposition. Inclinations from these sites and another farther north at Royce Quarry successfully pass a megaconglomerate test and suggest a depositional paleolatitude of 24°N ± 4°. This agrees with a plate model in which the Calera limestone was deposited on the Farallon plate at about 100 Ma and was accreted to North America at about 70 Ma.

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