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Thick evaporites and early rifting in Guaymas Basin, Gulf of
California
Abstract
Multichannel seismic transects reveal an ~2-km-thick, ~50 x 100 km evaporite body under the shelf
on the eastern margin of the Guaymas Basin, central Gulf of California (Mexico). These
thick newly discovered evaporites appear to be correlated with well-known gypsum beds
near Santa Rosalia to the northwest, on the Baja California peninsula. Closing the Gulf of
California along kinematic flow lines suggests that the thin, scattered, ca. 7 Ma Santa
Rosalia gypsum beds formed on the fringe of the much thicker evaporite deposit. This
correlation, and the large volume of the Guaymas evaporates, implies that substantial
marine incursions and subsequent evaporite deposition occurred during the Late Miocene
and prior to lithospheric rupture. Furthermore, the shape of the Guaymas evaporite is
indicative of a transtensional basin, suggesting that oblique extension existed in the
central Gulf of California ca. 7 Ma.
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Figure 1.
Shipboard free-air gravity anomaly (top), post-stack
time migration of MCS data (middle), and seismic data interpretations (bottom)
along Line 25 of cruise EW0210. EW0210 data were collected using the R/V Ewing’s
20-element airgun array and a 6-km-long hydrophone streamer. The shot spacing for
this line was 100 m. Data were processed by common-midpoint (CMP) sorting,
band-pass filtering, velocity analysis, normal move out, inside and outside muting,
stacking, post-stack wavenumber filtering to remove energy from the water-bottom
multiple, and post-stack time migration. Line location is shown in the inset.
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Figure 2.
(a) Crustal (left) and map-view (right) reconstruction
of Guaymas basin to ~7 Ma. The crustal model is based on removing 280 km of crust
produced by seafloor spreading from the velocity model of Lizarralde et al. (2007).
Similarly, the map-view reconstruction was produced by closing the North and South
Guaymas spreading segments by 280 km. This reconstruction places gypsum units from
the Santa Rosalia Basin (SrB) and Isla San Marcos (ISM) on the southern edge of the
east Guaymas evaporite (EGE). (b) Interpreted velocity model of Lizarralde et al.
(2007) showing the position of the EGE and seaward-dipping reflectors (SDRs) as
imaged by the multichannel-seismic data on Line 25 (Figure 1).
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