Deep fault-controlled fluid flow driving shallow
stratigraphically-constrained gas hydrate formation: Urutī Basin,
Hikurangi Margin, New Zealand
Abstract
The Hikurangi Margin east of New Zealand’s North Island hosts an
extensive gas hydrate province with numerous gas hydrate accumulations
related to the faulted structure of the accretionary wedge. One such
hydrate feature occurs in a small perched upper-slope basin known as
Urutī Basin. We investigate this hydrate accumulation by combining a
long-offset seismic line (10-km-long receiver array) with a grid of
high-resolution seismic lines acquired with a 600-m-long hydrophone
streamer. The long-offset data enable quantitative velocity analysis
while the high-resolution data constrain the three-dimensional geometry
of the hydrate accumulation. The sediments in Urutī Basin dip landward
due to ongoing deformation of the accretionary wedge. These strata are
clearly imaged in seismic data where they cross a distinct bottom
simulating reflection (BSR) that dips, counterintuitively, in the
opposite direction to the regional dip of the seafloor. BSR-derived heat
flow estimates reveal a distinct heat flow anomaly that coincides
spatially with the upper extent of a landward-verging thrust fault. We
present a conceptual model of this gas hydrate system that highlights
the roles of fault-controlled fluid flow at depth merging into
strata-controlled fluid flow into the hydrate stability zone. The result
is a layer-constrained accumulation of concentrated gas hydrate in the
dipping strata. Our study provides new insight into the interplay
between deep faulting, fluid flow and the shallow processes involved in
gas hydrate formation.