The Berbice Valley and Canyon System of Guyana: A Cross-Shelf Incised Feeder of Giant Cretaceous Age Deepwater Fans

Abstract

The Guyana-Suriname margin of NE South American played host in the Cretaceous to one of the largest point-sourced feeder system in geologic time that pushed enormous volumes of sediment northward to form the deepwater fans of the Stabroek block discoveries. The Berbice paleo-incision is likely the largest documented river-associated, shelf-incised valley/canyon system in the margin. Incised during the late Coniacian to early Santonian, the Berbice formed through six major phases of incision, fill and re-incision over several million years. Several phases of constructional clinoforms fill the incision and valley walls shows scalloping and side wall failure. Clinoforms within the canyon prograde both axially and laterally, suggesting sediment sourced and/or distributed by river- and ocean-current processes, respectively. Individual phases of incision in the ~ 80 km long cross-shelf valley range from 20 to 33 km in width and are 800 to 1250 m deep, forming in composite a huge system linked directly to the proto-Berbice River bypassing sediments at a rate of 20.5 M/yr. Berbice clinoforms are progradational with foreset heights of 280 m and foreset slopes of 3.5 degrees. The proto-Berbice drainage was one of the largest in South American during the Mesozoic. However, subduction of the Nazca plate beneath western South American in the Miocene induced stream capture by the Amazon drainages effectively shutting off clastic sediment to the margin. The exact processes that drove this incision to develop are still under study but suffice to say, these valleys types feed the deepwater giant fans of the world.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019