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Tectonic and depositional evolution of an active forearc basin based on 2-D multi-channel seismic reflection data, Sandino Basin, offshore Nicaragua

Tectonic and depositional evolution of an active forearc basin
based on 2-D multi-channel seismic reflection data,
Sandino Basin, offshore Nicaragua

Jay Stephens
PhD Candidate


Friday, Nov. 20, 2009, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.


Seminar Room 1.603, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758


Gail Christeson, UTIG

High-resolution (20-250 Hz) multichannel seismic reflection data, totaling approximately 4620 line km, were collected in November-December 2004 (cruise EW04-12) on the inner shelf to slope in the Sandino forearc basin, offshore Nicaragua and Costa Rica. Approximate age constraints are provided by industry well data.

The Mesozoic basement is uplifted to the southeast as it nears the Cocos Ridge and becomes subaerially exposed on the Nicoya Peninsula. Immediately northwest of the peninsula, only a thin (approximately 0.2- 0.4 s) layer of Neogene sediment overlies a prominent unconformity truncating basement. Approximately 50 km farther to the northwest, buried clinoforms that prograde northwestward, perpendicular to the present shelf break, may record episodes of this uplift in the south during the Pliocene.

The Sandino Basin outboard of southern Nicaragua displays multiple phases of deformation and is dominated by shortening. Deformation began with an outer arc high related to subduction initiation. Uplift of a broad anticline in the middle shelf of the southern Sandino region initiated during Late Eocene to Early Oligocene and was subsequently deformed by large offset normal faults (100s of meters). During the Miocene, the southern region's inner shelf underwent arc-normal shortening and uplift resulting in an angular unconformity on the inner shelf and prograding sigmoidal clinoforms at the shelf edge as a response to the corresponding increased sediment input.

The central Sandino Basin region undergoes initial subsidence followed by shortening in the late Oligocene to early Miocene resulting in a series of folds in the middle shelf. Deformation of strata continues to the present as evidenced by truncation of anticlines and faults that intercepting the seafloor. The northern Sandino region experiences initial uplift at the outer arc high and then undergoes continued subsidence resulting in the accumulation of >16km of sediment. The northern region does not appear to have undergone shortening in the middle or inner shelf but is affected by Pliocene extension and right lateral-shear within the Nicaraguan Depression as imaged by transects in the Gulf of Fonseca. Isopach and structure maps illustrate basin evolution with respect to timing of major tectonic events. In general, the basin thickens to the northwest, though some areas thin due to locally uplifted structures. The northwestern area of the survey images a thick (> 4 s) forearc basin, where a series of angular unconformities truncate heavily faulted Cenozoic strata. At their landward ends, dip profiles from show strata with steep basinward dips truncated by an angular unconformity near the seafloor. Continuing basinward, these strata are deformed by a series of approximately trench-parallel folds. Near the shelf edge, the sub-horizontal strata become clinoformal and the section is commonly cut by landward dipping normal faults. Beneath the slope, the faulted top of basement (margin wedge) is overlain by approximately 1.0 s of slope sediment. Deformational features of Cenozoic units onshore can be correlated to similar offshore features. The Rivas and Cayenta folds located on the Nicaraguan isthmus are likely related to margin sub-parallel folds found offshore in the central and southern Sandino Basin. The age of deformation is at least Early Miocene and probably dates to the Late Oligocene.