Abstract
Detailed geologic mapping of the Fondo Negro-Sierra de Martin
Garcia region of the Southwestern Dominican Republic establishes
that this area is part of a broad and diffuse Northern Caribbean
plate boundary zone (PBZ). Faulting in the study area is
predominantly left lateral strike-slip, with secondary compression
(thrusting) causing both substantial, and rapid, uplift of the
region. Folding associated with the wrench faulting affects rocks
of all ages in the field area from Paleocene limestones to
Quaternary alluvial fans.
New stratigraphic designations are proposed for mappable
litho-units in the area, and these are correlated with Hispaniola
stratigraphy in general based on biostratigraphic age
determinations. Thus a new formation name, the Fondo Negro
Formation is proposed for a thick (2650 m. exposed) predominately
calcareous siltstone, marl and sandstone sequence which is exposed
between the village of Fondo Negro and the Sierra de Martin Garcia
where it lies in tectonic contact with Paleocene to early Miocene
carbonates. The Fondo Negro Formation contains microfauna
belonging to the Tortonian and Messinian intervals. The lowest
exposed section of the Fondo Negro Formation contains distinctive,
ridge forming, sandy limestones and this unit is described as the
Gajo Largo member. The 400m. of predominantly grey calcareous
shales apparently conformably overlying the Fondo Negro Formation
are redefined as the Bao Formation, also of Messinian age, and
conformably above that the Pliocene, Arroyo Blanco Formation, also
more specifically defined than previous studies. The Arroyo Blanco
Formation comprises sandy marls, and resedimented carbonate shelf
debris, as well as coarse sandstones and conglomerates. In the
east it is approximately 100m thick, and it varies as a facies
transition into evaporites in the northwest of the field area. The
evaporite faeies, including massive pure gypsum beds are probably
thicker than the facies in the east.
The carbonates of the Sierra de Martin Garcia were not mapped in
detail, but paleontological determinations for samples collected
indicate a broader age range for the carbonates than suggested on
existing maps (Blesch, 1967), from Paleocene to Early Miocene.
In addition to the primary field mapping, reconnaissance studies
and paleontological analysis of samples from the Tavera Basin
suggest that it is the earliest basin yet identified related to
the initiation of the northern Caribbean PBZ. That is that this
basin can be related to strike-slip faulting in probably early
Oligocene times and this represents movement along the Cayman
Trough.
An interpretive cross-section across Hispaniola is presented which
suggests that present strike-slip activity is greatest in the
Cibao Valley, the Enriquillo Valley and in the northern, offshore
areas of Hispaniola, and that the Island is cut by a great number
of splay faults. The mountain ranges, the Sierra de Neiba and the
Sierra de Bahoruco are compressional structures related to bends
in the strike-slip fault system. An attempt is made to integrate
this in the perspective of the Cainozoic evolution of the Greater
Antilles.
Cooper, J.C., 1983. Geology of the Fondo Negro region, Dominican
Republic.
Unpublished MSc. thesis, State University of New York at Albany.
145pp., +xiv; 4 folded plates (maps)
University at Albany Science Library call number: SCIENCE
Oversize (*) QE 40 Z899 1983 C66
MS thesis (scanned text pdf - 14.8 MB)
Plate 1 - Geological
map
of
the Fondo Negro - Martin Garcia Region, Dominican Republic (west
part)
(uncoloured geological map;
scale 1:25,000) pdf file 3MB
Plate 1 - Geological
map
of
the Fondo Negro - Martin Garcia Region, Dominican Republic (east
part)
(uncoloured geological map;
scale 1:25,000) pdf file 4MB
Plate 2 - Geological
cross
sections
of the Fondo Negro Region (Dominican Republic)
(uncoloured; scale 1:25,000)
Plate 3 - Hispaniola geological cross
section
(uncoloured; scale
1:250,000)
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the Geological Sciences Program, University at Albany