Figure 5. Multichannel seismic profiles acquired south of Icy Point
(Balster-Gee et al., 2020); profile locations shown on Figure 2b. (a)
Seismic reflection profile A-A’ shows the Icy Point-Lituya Bay thrust
fault and the Finger Glacier fault, which both dip northeast and offset
an erosional unconformity probably formed during the Last Glacial
Maximum (LGM). Between the two thrust faults, the LGM unconformity is
displaced by bedding-parallel flexural slip reverse faults and by normal
faults related to extension above a growing fold. (b) Profile B–B’
shows an active fold between the blind Icy Point-Lituya Bay fault on the
west and the Queen Charlotte fault on the east. The fold is deformed by
bedding-parallel reverse faults and normal faults. (c) In profile C–C’
a single, near-vertical strand of the Queen Charlotte fault juxtaposes
horizontal strata on the east and possible moraine deposits overlying
west-dipping beds below an unconformity on the west. (d) Two strands of
the Queen Charlotte fault form a small pull-apart basin in profile
D–D’. West-dipping beds below an uncomformity indicate folding west of
the fault and south of Icy Point. M, sea-floor multiple.
Four multichannel seismic reflection profiles cross the Queen Charlotte
fault to the south of Icy Point (Figure 2; Figure 5); these profiles
reveal, as one approaches incrementally northward to within 4 km of Icy
Point, a growing contractional structure that overlies the buried Icy
Point-Lituya Bay fault on the west and is bounded to the east by the
Queen Charlotte fault. The contractional structure is defined by the
deformation of a prominent unconformity. The unconformity records
erosion by advancing ice during the Last Glacial Maximum, (Figure 5),
followed by deposition and deformation after the glacial-interglacial
transition ca. 17 ka. Beds below the unconformity, which dip to the
west, are likely Topsy and Yakataga sediment, which were deposited from
late Miocene to Pleistocene and started to be deformed ca. 300,000 years
ago based on thermochronometry (Lease et al., 2021). The profiles show
that the deformation of Miocene to Pleistocene sediment commenced
>15 km south of Icy Point, before the Topsy and Yakataga
beds reach the southern end of the restraining bend. Despite the
proximity of the northernmost seismic reflection profile to Icy Point
(panel A, Figure 5), the profile shows no expression of the Fairweather
fault, which implies that the 3 km right stepover is north of the
profile. Although the structures shown in profiles A and B (Figure 5)
show the initial contractional strain associated with offshore reverse
faults, the uplift of Icy Point is north of the fault step over and
bounded on the east by the principal strand of the Fairweather fault,
which strikes obliquely to the relative plate motion vector (Figure 6)
(Brothers et al., 2020).