Tectonic versus Eustatic Control on Neogene Sedimentation in the Cibao Basin of the Dominican Republic: Tectonic Dominance near an Active Plate Boundary

ERIKSON, JOHAN P., Dartmouth College, Hanover, NH

Continuous Neogene subsidence, transgression, and brief periods of accelerated subsidence are indicated by the Yaque Group sediments of the Cibao basin of northern Dominican Republic, in which the generally fining-upward sediments are punctuated by two, thick, conglomeratic sequences. Lithologic and paleontologic evidence supports continuous subsidence and a tectonic control on sedimentation and is in conflict with an interpretation of one or both of the conglomeratic sequences as being due to a rapid regressive-transgressive cycle and a correlation with a second-order fluctuation (supercycle) on a Vail-type sea-level curve. Coralline clasts are noticeably absent from the conglomerates that are dominated by volcanic and plutonic clasts, lithified tuff, and chert pebbles. Igneous pebbl s 150 m below the upper, igneous, clast-rich conglomerate indicate that deposition of coarse, arc-derived sediments occurred quasi-continuously. The flow structures and internally repetitive nature of the less than 20 m of fining-upward conglomerates are inconsistent with an origin as transgressive lags. The upper conglomerate is locally conformable with the underlying shale; sedimentation was continuous, though accelerated. Subsidence generally outpaced sedimentation, such that water depths almost continuously increased during deposition of all but the uppermost Yaque Group (when the basin shallowed prior to subaerial exposure), as interpreted from detailed paleontological analyses.

The depositional history of the entire approximately 1 km exposed section and approximately 5 km subsurface section of the Yaque Group is best explained by a single, continuous, east to west, middle Miocene to earliest Pliocene transgression due to asymmetric basin subsidence. Deposition of the igneous clast-rich conglomerates was probably caused by accelerated basement subsidence at the northern edge of the basin, which oversteepened the depositional slope, led to accelerated transgression of the northern flank of the Central Cordillera, and produced brief pulses of coarse, partially Cordilleran-derived conglomerates. Varying subsidence in the Cibao basin is correlated with episodic uplift and sedimentation in the Cordillera Septentrional.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)