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Stratigraphic backbone for the eleven stages of the Jurassic period, 200 to 135 m.y. ago, are ammonite zonations with local resolution close to 1 m.y. Micropaleontologic zonations largely have stage-level resolution. Facies-dependence and provincialism limit universal application, and calibration to ammonite and (at the Jurassic-Cretaceous boundary) to calpionellid zonations is limited. The geomagnetic reversal scale (with few events only), stage designations, and linear time scale are not well integrated either. Uncertainty may be on the order of a stage.
Two examples of recent progress in Jurassic stratigraphy are: (1) calibration of the Early Jurassic foraminifer and ostracod zonation for Portugal and Grand Banks to a standard ammonite scheme; it shows that the post-evaporite-dolomite marine transgression occurred at the Sinemurian-Pliensbachian boundary as in east Greenland and northwestern Europe; (2) acquistion of a continuously cored, fossiliferous Middle and Late Jurassic record in Deep Sea Drilling Site 534, Blake Bahama Basin, in the Jurassic magnetic quiet zone. Oceanic pillow basalt (31.5 m) occurs below a strong basement seismic reflector, which proves normal ocean crust exists under the Jurassic magnetic quiet zone.
The overlying dark shales are early-middle Callovian, which revises upward with 10 to 20 m.y., the age of the Blake Spur and M-28 anomalies, and the time of early spreading of the central North Atlantic. Widespread Callovian transgression may be an expression of rapid, early spreading.
The new bio- and magneto-stratigraphic data are being integrated with local zonal schemes for Atlantic basins to provide an improved Jurassic time scale of events.
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