Decoding sill emplacement and forced fold growth in the Exmouth Sub-basin, offshore NW Australia: implications for hydrocarbon exploration
File(s)
Accepted version
Author(s)
Magee, C
Jackson, CA-L
Hardman, JP
Reeve, MT
Type
Journal Article
Abstract
Igneous sills emplaced at shallow-levels in sedimen
tary basins commonly uplift the
overburden and free surface. Uplift produces dome-s
haped forced folds that may host
economic hydrocarbon accumulations. These intrusion
-induced forced folds are typically
assumed to develop instantaneously, whereby the old
est onlapping strata constrain the age of
sill emplacement, and accommodate the entire volume
of intruded magma. However, several
studies demonstrate that forced folds may grow over
geological timescales, with additional
space-making mechanisms (e.g., compaction) partly a
ccommodating the magma volume. It is
thus critical to understand when forced fold traps
form and how they evolve in relation to the
timing of source rock maturation and migration. We
analyze two forced folds imaged in 2D seismic reflection data from offshore NW Australia.
Analyzing the seismic stratigraphy of the
forced fold overburden allows us to recognize sever
al distinct phases of fold growth. Sub-
horizontal reflections onlapping onto the lower por
tion of the forced folds at a high angle
indicate that the first phase of sill emplacement a
nd fold development occurred rapidly,
facilitated by normal faulting, prior to deposition
of overlying strata during a period of
magmatic quiescence and regional hydrocarbon matura
tion in the Early Cretaceous. Renewed
magmatic activity resulted in a final, protracted p
hase of doming, which is recorded by a
package of onlapping growth strata that was increme
ntally deformed by successive intrusive
pulses. We also demonstrate that in addition to fol
ding and faulting, the magma volume was
likely accommodated by porosity within the folded s
trata. Our observations imply that the
age of the lowermost onlapping reflections only con
strain the onset of sill emplacement and
not the duration of magmatic activity. Constraining
the dynamic evolution of intrusion-
induced forced folds from the structure of onlappin
g reflections during hydrocarbon
exploration can thus provide critical insights into
the potential volume and charge history of
any hydrocarbon accumulations.
tary basins commonly uplift the
overburden and free surface. Uplift produces dome-s
haped forced folds that may host
economic hydrocarbon accumulations. These intrusion
-induced forced folds are typically
assumed to develop instantaneously, whereby the old
est onlapping strata constrain the age of
sill emplacement, and accommodate the entire volume
of intruded magma. However, several
studies demonstrate that forced folds may grow over
geological timescales, with additional
space-making mechanisms (e.g., compaction) partly a
ccommodating the magma volume. It is
thus critical to understand when forced fold traps
form and how they evolve in relation to the
timing of source rock maturation and migration. We
analyze two forced folds imaged in 2D seismic reflection data from offshore NW Australia.
Analyzing the seismic stratigraphy of the
forced fold overburden allows us to recognize sever
al distinct phases of fold growth. Sub-
horizontal reflections onlapping onto the lower por
tion of the forced folds at a high angle
indicate that the first phase of sill emplacement a
nd fold development occurred rapidly,
facilitated by normal faulting, prior to deposition
of overlying strata during a period of
magmatic quiescence and regional hydrocarbon matura
tion in the Early Cretaceous. Renewed
magmatic activity resulted in a final, protracted p
hase of doming, which is recorded by a
package of onlapping growth strata that was increme
ntally deformed by successive intrusive
pulses. We also demonstrate that in addition to fol
ding and faulting, the magma volume was
likely accommodated by porosity within the folded s
trata. Our observations imply that the
age of the lowermost onlapping reflections only con
strain the onset of sill emplacement and
not the duration of magmatic activity. Constraining
the dynamic evolution of intrusion-
induced forced folds from the structure of onlappin
g reflections during hydrocarbon
exploration can thus provide critical insights into
the potential volume and charge history of
any hydrocarbon accumulations.
Date Issued
2017-02-17
Date Acceptance
2016-12-01
Citation
Interpretation, 2017, 5 (3), pp.SK11-SK22
ISSN
0020-9635
Publisher
Interpretation
Start Page
SK11
End Page
SK22
Journal / Book Title
Interpretation
Volume
5
Issue
3
Copyright Statement
© 2017 Society of Exploration Geophysicists and American Association of Petroleum Geologists. All rights reserved.
Sponsor
Junior Research Fellowship
Subjects
2203 Philosophy
Publication Status
Published