Model simulation of mid-cretaceous ocean circulation.

tween Eurasia and Africa that result in a primary eastward-directed, low-velocity current flow along the mid-Cretaceous Eurasian, northern Tethys margin. This conclusion appears to be at odds with sedimentologic and paleontologic field evidence (2, 3) obtained from the Helvetic tectonic unit that is exposed in the northern Alps and represents the former northern Tethys margin in southern Europe. Cretaceous, Helvetic sediments document the presence and physical imprint of an uniform and erosive, westbound, current system that contoured the southern European border and persisted throughout Aptian to early Cenomanian times (2, 3). A conspicuous zonation of sediments aligned parallel to the shelf break is preserved and consists of a proximal inner-shelf zone of moderate-to-low sediment accumulation rates, in which glauconitic sands dominate; a distal inner-shelf zone of ultralow sediment accumulation rates, where strongly condensed phosphatic beds formed; a zone along the break between the inner and outer shelf, where redeposited, inner-shelf-derived sediments accumulated in channel and fan systems; and an outer-shelf zone of hemipelagic and turbiditic sedimentation. This zonation or parts of it are traceable throughout the Helvetic Alps; beyond the Helvetic zone, it extends from southeastern Spain along the northern Tethys margin to the western Carpathians (3). The zonation is interpreted as the "fingerprint" of the Tethyan current system, the zone ofstrongly condensed phosphatic beds having been formed within the erosive zone along the current axis. Prominent proximal-distal shifts in the locations of the zones are considered to reflect relative sea-level changes. The unidirectional westward flow of this