Seismoacoustic Study of the Shallow Gas Transport and ... - E-LIB

Chapter 2
volcanoes between 66 and 88 ms TWT and at 164 ms TWT at Vassoevitch mud volcano
(Table 3).
We use the MSU mud volcano as an example to study the details of the subsurface
structures of the mud volcanoes, as we can analyze three seismic Lines GeoB02-030,
GeoB02-035 and GeoB02-036 across the top, which can reveal its internal structure in
three different directions: WNW-ESE, N-S and SW-NE (Fig. 6). A close-up of the depth
range 3250 to 3500 ms TWT is shown beneath each line. The MSU mud volcano has a
flat top of ~1360 m width, while the other mud volcanoes have the cone-shaped tops. The
feeder channel was clearly identified from reduced reflection amplitudes. Its diameter
varies with depth. Two mud chamber structures Chamber 1 and Chamber 2 (Fig. 6) and a
small chamber beneath the Chamber 1 (Fig. 6b) can be clearly seen at the seafloor and
from 3200 to 3500 ms TWT. The mud chambers are distinguished by low reflection
amplitudes next to parallel undisturbed seismic reflections. Also, transparent to chaotic
reflectors can be observed in the inner parts. The transparent to discontinuous reflectors
between Chamber 1 and Chamber 2 are bent downward, and can be traced to adjacent
reflectors of sediment. A few small bright spot patches distribute at those reflectors and
the edge of the feeder channel. Large bright spot zones BSZA are found beneath
Chamber 2, with a maximum lateral extent of ~1700 m, and at the depth of ~400 ms
TWT bsf around the feeder channel. Beneath Chamber 2, reflectors are also bent
downward. The feeder channel connects to the wider acoustic curtain at greater depth. A
high amplitude and reverse polarity reflector was clearly observed in Figure 6i with a
depth of ~520 ms TWT bsf.
2.6. Interpretation and Discussion
2.6.1. Sedimentary processes
Based on its complex seismic facies (Table 2), the middle to upper part of U1 can be
attributed to the Danube and Dniepr deep sea fan complexes, as interpreted by Winguth
et al. (2000), representing e.g. channel-levee deposits and mass transport deposits. The
lower part of U1 with parallel and continuous reflectors is predominantly constructed by
fine-grained deposits, which are likely formed by the unchannelized distal fan deposition
during earlier stages of fan development. U2 is interpreted as a more coarse-grained unit
possibly representing sandy terminal lobes from surrounding rivers, e.g. the Paleo-Don
River in the Northeast which entered the Black Sea during the middle Pliocene to late
Pliocene (Popov et al., 2004; Barg, 2007; Tari, 2011). According to Wagner-Friedrichs
(2007) who studied sediments in the Sorokin Trough to the Northeast of the study area,
the Paleo-Don River fan was observed during the early Pleistocene in the Sorokin Trough,
which was likely formed earlier than the Danube and Dniepr fan. Therefore, the Paleo-
Don River might enter the Black Sea during the middle Pliocene to late Pliocene and
form a large deep sea fan during the early Pleistocene. U2 probably indicated the sandy
terminal lobes from Paleo-Don River. Unit U3 and U4 are characterized by parallel and
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