Supplementary Material_Revised_MartinBarajas etal

Arturo Martín-Barajas*, Mario González-Escobar, John M. Fletcher, and Martín
División de Ciencias de la Tierra, CICESE, Ensenada, Baja California, CP. 22860
*Corresponding author: [email protected]
This Supplementary Material includes a cross-section that provides a more detailed
perspective of the crustal structure across the Delfín-Tiburón rift segment in the northern
Gulf of California (Fig. S1). A simple 2D crustal budget along this cross-section indicates
an excess of continental crust beneath the submarine part of the rift (Fig. S1). This
Supplementary Material also includes higher resolution seismic plots for three keys
seismic sections oriented sub-parallel to the direction of oblique extension. Lines 5471
(Fig. 4), 5450 (Fig. 5), and 5040 (Fig. 7) illustrate important stratigraphic and structural
relationships that support our interpretation that detachment faults control the delay of
continental rupture. These detachment faults are buried beneath a 2 to 7 kilometer-thick
sedimentary cover, principally built by deltaic sedimentation from the Colorado River
since late Miocene time.
Seismic reflection data collected by Petroleos Mexicanos (PEMEX) have a redundancy
of 4800 % and were acquired with a 48 channel, 2400 m-long streamer, a 1341 cubic inch
air-gun array, and using a shot interval of 25 m. Record length was 6.1 seconds with a
sampling rate of 2 ms. Data processing for workflows 1 and 2 includes spherical
spreading correction, predictive deconvolution, semblance velocity analysis, normal
move-out correction. Stacking and post-stack time migration was processed by commonmidpoint (CMP) sorting, band-pass filtering, velocity analysis, normal move out, inside
and outside muting, stacking, and post-stack time migration. Processing for workflow 3
was accomplished at Instituto Mexicano del Petroleo in the early 1980’s. Seismic line
5040 (Figures S4 and 7) was scanned from a film copy held at PEMEX archives and
vectorized using Landmark software.
Figure S1. Profile across Upper Delfín-Tiburón basins used for calculating the width of
old continental crust versus new crust along this rift segment (no vertical exaggeration)
(see Table S5). The area now occupied by old continental crust is more than 80% of the
total distance between the Baja California and Isla Tiburon (Sonora) shorelines and
difficult to reconcile with the ~265±10 km reconstruction by Oskin et al. [2001]. This is
similar with the 240-280 km of oceanic crust created in the Guaymas basin [c.f.
Lizarralde et al., 2007] and contrast with our ~25-40 km estimation of permissive new
oceanic crust. Thickness of continental lithosphere is after González-Escobar et al.
[2005] and Lewis et al. [2001]. SSPM-Sierra San Pedro Mártir, SPMF-San Pedro Mártir
Fault, AGD-Angel de la Guarda Detachment, US-Upper Sequence, LS-Lower Sequence.
Seismic line location is shown in the inset.
Figure S2. Interpreted seismic line 5471 across the Upper Delfin basin. The seismic
horizon in red marks an important sequence boundary that indicates that the lower
sequence was deposited in both the Upper Delfín and the Tiburón basins (see also Figure
S4), whereas the upper sequence is thin over the Intrabasin Structural High and becomes
progressively thicker towards the Upper Delfín basin. The horizon in light blue is the
Pliocene-Pleistocene boundary as defined in well T-1 in the Tiburón basin [Helenes et
al., 2009]. The upper horizon (dark blue) marks the base of the upper sequence that
indicates shifting of depocenters and bathymetric lows in the South Upper Delfin basin
(SUDB). A series of southeast-dipping listric normal faults above the Intrabasin
Structural High merge at depth into the basement. This basement high is interpreted as
the lower plate of a detachment that juxtaposes the sedimentary sequence in the hanging
wall against continental crust in the footwall. The listric normal faults are main
breakaway faults that merge at depth into the Angel de la Guarda Detachment fault
(AGD). Note the flower structure at the left (NW) side of the profile, interpreted as a
dextral strike-slip fault on the San Felipe-Puertecitos continental shelf. Seismic line
location is shown in the inset.
Figure S3. Stacked multichannel seismic data (MSD) (below) and interpretation (above)
along seismic line 5451 across the Upper Delfín basin. Seismic processing of workflow 1
as described in the Summary of this Supplementary Material. The horizon in yellow
is the acoustic basement interpreted as continental crust (inferred when dashed).
The red horizon is the sequence boundary between the Upper and Lower sequences.
The upper horizon (dark blue) marks the base of the upper sequence that indicates
shifting of depocenters and bathymetric lows in the South Upper Delfin (SUD) and
North Upper Delfín (NUD) basins. In this seismic section the South Upper Delfin
basin (SUDB) has a more prominent bathymetric expression and a deeper and
narrower axial through as compared to the NUD. Seismic line location is shown in the
Figure S4. Seismic line 5040 across the Tiburón basin. To the left (NNW) the
structural high constitutes the footwall block of a low angle normal fault that
juxtaposes late Neogene sedimentary deposits in the hanging wall against
continental basement in the footwall. The acoustic basement is poorly defined near
5.0 seconds (TWTT) between kilometers 65 to 120 in this profile. In the Central
domain, NE-striking dip-slip faults with opposed slip direction cut the Late Miocene
and Pliocene strata and produce a broad antiform with strata gently dipping
towards both the NW and SE. The West Desemboque and East Desemboque faults
offset and lower the continental shelf offshore Isla Tiburón (South domain). Here,
the continental crust is likely composed of Paleozoic-Mesozoic crystalline and
metamorphic rocks that underlie pre-rift and syn-rift Mid to Late Miocene volcanic
rocks exposed on Isla Tiburón [Oskin and Stock, 2003; Gastil et al., 1999]. Seismic
line location is shown in the inset.
Table S5. Areas from the regional cross-section of Figure S1 used for calculating the
width of old continental crust versus new crust along this rift segment. Crustal
thicknesses across de Upper Delfín and Tiburón basins are from González-Fernández et
al. [2005]. Thickness of continental crust in Baja California is from Lewis et al [2001]
and Persaud et al [2005].
Areas in regional cross-section
Mobilized lower crust beneath Baja California
Baja California lower crust
Baja California upper crust
San Felipe-Puertecitos shelf upper crust
San Felipe-Puertecitos shelf lower crust
Central Delfin lower crust
Intrabasin high lower crust
Central Tiburón lower crust
South Tiburón lower crust
South Tiburón upper crust
Isla Tiburón lower crust
Isla Tiburón upper crust
Calculations between coastlines
Existing upper crust
Existing lower crust
Initial coastline separation (35 km thick)
Initial coastline separation (17 km upper crust)
Initial volume of lower crust
Excess lower crust
Lower crust from Baja California
Lower crust from Sonora
93 %
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