Tectonic and depositional history of an active forearc basin, Sandino basin, offshore Nicaragua




Stephens, Jason Henry

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High-resolution (20-250 Hz) multichannel seismic (MCS) reflection data with record lengths of 4-8 s TWT, totaling approximately 4620 line km on the shelf and slope of the Sandino forearc basin of offshore western Nicaragua, were acquired in November-December 2004 (cruise EW04-12) and subsequently processed at the University of Texas Institute for Geophysics. Seismic sequence interpretation was conducted using these MCS data in conjunction with deeper penetration (16-20. s TWT) MCS profiles from a previous survey (cruise EW00-05). Age estimates were based on cuttings from intersecting industry wells. Structure and isochron maps were created for 16 sequences and used to identify structural and depositional trends within the Sandino basin. The Tectonostratigraphic evolution of the basin varies considerably along-strike and is divided into five general stages from Late Cretaceous to recent. Evidence for multiple episodes of terrane accretion is observed from Late Eocene to Late Oligocene and potentially during Mid- to Late Miocene as well. Stratal stacking patterns suggest the Nicaraguan margin has not been dominated by subduction erosion during its history and extensional features beneath the slope are interpreted to have originated as a result of processes related to collision of allochthonous terrane of the downgoing plate, sediment underplating, and slab roll-back. With more precise age control, the stable northwestern region of the Sandino basin, where sediment is relatively undeformed since Late Oligocene and measures ≥ 16 km thick, offers a unique convergent margin setting for investigations of forcings on sequence development.



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