Neogene planktonic foraminiferal biostratigraphy of the southwestern Dominican Republic

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Abstract
The Azua Basin of the southwestern Dominican Republic contains a thick (as much as 4,000 m or more) Neogene marine sedimentary sequence that is here, for the first time, zoned in detail using planktonic foraminifera. Thirty-five species have been identified and are figured in this report. Age determination (early Miocene to early or middle Pliocene) are younger than assumed in previous geologic studies and demonstrate a southeastward time-transgression of Stratigraphic units. The lower part of the sequence reflects a change from a deep carbonate basin setting, represented by the Sombrerito Formation, to a prograding turbidite regime, represented by the Trinchera Formation. The Sombrerito ranges in age from early Miocene (stratigraphic level: Globigerinatella insueta chronozone) to middle Miocene (Globorotalia fohsi robusta chronozone). The Gajo Largo member of the Sombrerito is dated as late middle to earliest late Miocene (Globorotalia mayeri chronozone to lower Globorotalia acostaensis chronozone). The Trinchera spans an interval from near the middle-late Miocene boundary (equivalent of Globorotalia mendarii zone or Globorotalia acostaensis zone) to the early Pliocene (Globorotalia margaritae zone). The upper part of the sequence reflects a transition from shallow-marine to lagoonal paleoenvironments and contains planktonic foraminiferal faunas of variable richness. Blue-green siltstones of the Quita Coraza Formation overlie the Trinchera in the southern and eastern parts of the basin and contain faunas that generally indicate an early Pliocene age (Globorotalia margaritae chronozone). The lower part of the Arroyo Blanco Formation contains relatively poor planktonic foraminifereral faunas of latest Miocene (upper Globorotalia humerosa chronozone) to early or middle Pliocene age (Globorotalia margaritae or Globorotalia miocenica chronozone). Re-evaluation of earlier Caribbean region planktonic foraminiferal studies permitted correlation of the Azua Basin strata to nine other Neogene stratigraphic sequences. Greater resolution in region stratigraphic correlation would permit insights into the basin''s geologic evolution.

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