Geomorphologic and Stratigraphic Evidence of Ongoing Transpressional
Deformation Across Lake Azuei (Haiti)
Abstract
he boundary between the North American and Caribbean plates cuts EW
across the island of Hispaniola. Relative motion on this part of the
plate boundary is transpressional and tectonic deformation is
partitioned between a NW-SE fold-and-thrust belt and two E-W
left-lateral faults 150 km apart. The southern fault, the
Enriquillo-Plantain Garden Fault (EPGF), is well defined in western
Haiti but looses its morphological expression as it nears Lake Azuei in
eastern Haiti. Since the sedimentation rate is high for this 20 km-long
lake, Holocene deformation should be recorded in its upper stratigraphy
and bottom morphology. To test this hypothesis, we analyzed 200 km of
subbottom (CHIRP) profiles collected in 2017 that imaged the upper 2 -
10 m of sediments. This dataset is complemented with other sonar data,
including 140 km of echosounder profiles (Moknatian et al., Rem. Sensing
2017) and 65 km of CHIRP profiles (Wang et al., Tectonics 2018).
Morphological and stratigraphic information extracted from the combined
dataset are compiled into a detailed geological map, which reveals: 1)
Gas-charged sediments occur across most of the flat lake floor. However,
where the gas front is deeper, the CHIRP data show the rhythmic
stratigraphy characteristic of turbidites; 2) Turbidite beds fold up
along the edges of the lake floor, documenting the ongoing deformation
of the basin margins; 3) In the southern part of the lake, en echelon
folds are trending EW, a trend compatible with fault-propagation folds
developing ahead of a S-dipping oblique-slip EPGF. We find no evidence
of fault scarp or stratigraphic offset in that same area, as might be
expected from a sub-vertical EPGF; 4) Deeper penetration seismic
reflection profiles acquired concurrently with the CHIRP reveal that the
west side of the lake is occupied by a NW-trending monoclinal fold,
possibly the expression of a SW-dipping blind thrust fault at depth.
Vertical faults across that monocline are associated with subtle breaks
in slope. Careful mapping of these slope breaks shows that these faults
strike NW-SE, subparallel to the monocline; 5) A < 2 kyr-old
paleoshoreline is uplifted 1-2 m across the monocline and soft-sediment
deformation suggestive of liquefaction also affects that area. A large
earthquake on the presumed underlying blind thrust fault could explain
these two features.