Fault-related biogenic mounds in the Ceduna Sub-basin, Australia. Implications for hydrocarbon migration

Geochem Geophys Geosyst

Holford

Schofield

et al. 2017

Submarine lava flows are the most common surficial igneous rock on the Earth. However, they are inherently more difficult to study than their subaerial counterparts due to their inaccessibility. In this study, we use newly acquired 3‐D (three‐dimensional) seismic reflection data to document the distribution and morphology of 26 ancient, buried lava flows within the middle Eocene‐aged Bight Basin Igneous Complex, offshore southern Australia. Many of these lava flows are associated with volcanoes that vary from 60 to 625 m in height and 0.3 to 10 km in diameter. Well data and seismic‐stratigraphic relationships suggest that the lava flows and volcanoes were emplaced offshore in water depths of <300 m. The lava flows range from 0.5 to 34 km in length and 1 to 15 km in width and are typified by tabular and dendritic forms. This morphological variation may result from differing lava effusion rates and/or the volumes of lava erupted. We demonstrate that: (1) the dendritic flows contain complex lava distribution systems and kipukas, features never‐before observed from seismic data; and (2) the distribution and morphology of the lava flows was strongly controlled by the emplacement of magmatic intrusion‐induced forced folds. This suggests that magmatic intrusions may play an important role in controlling the distribution of lava flows elsewhere. Our study highlights the usefulness of seismic data in studying the manifestation of submarine volcanism, and provides quantitative data on the extent and distribution of an ancient submarine volcanic province along the southern Australian margin.

Section: Description and Interpretation Of The Lava Flowsmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Three‐Dimensional Seismic Imaging of Ancient Submarine Lava Flows: An Example From the Southern Australian Margin

Geochem Geophys Geosyst

Holford

Schofield

et al. 2017

“…The vents are distinguished from biogenic mounds since they are much smaller than these features and they do not form above faults (e.g. Langhi et al, 2016). Furthermore, the vents we describe are ubiquitously associated with sills (e.g.…”

Section: Interpretation Of Sill and Hydrothermal Vent Complexesmentioning

confidence: 80%

Hydrothermal vent complexes offshore Northeast Greenland: A potential role in driving the PETM

Earth and Planetary Science Letters

Millett

Jerram

et al. 2017

Continental rifting is often associated with voluminous magmatism and perturbations in the Earth's climate. In this study, we use 2D seismic data from the northeast Greenland margin to document two Paleogene-aged sill complexes ≥18 000 and ≥10 000 km 2 in size. Intrusion of the sills resulted in the contact metamorphism of carbon-rich shales, producing thermogenic methane which was released via 52 newly discovered hydrothermal vent complexes, some of which reach up to 11 km in diameter. Mass balance calculations indicate that the volume of methane produced by these intrusive complexes is comparable to that required to have caused the negative δ 13 C isotope excursion associated with the PETM. Combined with data from the conjugate Norwegian margin, our study provides evidence for margin-scale, volcanically-induced greenhouse gas release during the late Paleocene/early Eocene. Given the abundance of similar-aged sill complexes in Upper Paleozoic-Mesozoic and Cretaceous-Tertiary basins elsewhere along the northeast Atlantic continental margin, our findings support a major role for volcanism in driving global climate change.

“…1). Cold-water, giant bryozoan reef mounds penetrated by the Potoroo-1 well are also found downlapping the base of the top of the Wobbegong Supersequence (Langhi et al, 2016) suggesting that the volcanoes and lava flows were emplaced in a submarine environment (Schofield and Totterdell, 2008;Jackson, 2012;Magee et al, 2013;Reynolds et al, 2017d). Dredging from incised canyons collected detrital volcanic fragments that were characterised as amygdaloidal, possibly pillowed, alkali basalts (Clarke and Alley, 1993) suggesting that the volcanoes have a similar composition (Schofield and Totterdell, 2008;Magee et al, 2013).…”

Section: Controls On Intrusive:extrusive Ratios In Intraplate Volcanic Provincesmentioning

confidence: 94%

The importance of subsurface lithology in controlling magma storage v. eruption: an example from offshore southern Australia

Holford

Schofield

et al. 2018

JGS

The volumetric relationship between the intrusive and extrusive components of volcanic fields are difficult to constrain. This is because the erupted products are commonly either eroded, or the intrusions are concealed by overburden. 3D seismic data therefore offers a unique opportunity to study ancient volcanic provinces, since these datasets can image both components without the need for erosional dissection. This study is based on 3D seismic data from the Bight Basin Igneous Complex (BBIC); a volcanic province constructed within a sedimentary basin, offshore southern Australia. We demonstrate that the BBIC contains abundant sills and laccoliths emplaced within deltaic sediments. The intrusions have a total volume of 92−111 km 3 whilst the lava flows and volcanoes have a combined volume of 66−76 km 3 (Dense Rock Equivalent). This indicates that the ratio of intrusive:extrusive Article textClick here to download Article text jgs_reynolds_et_al_revised_240118.docx Controls on intrusive:extrusive ratios in intraplate volcanic provinces 2 products for the BBIC is between 1:1 and 2:1. The architecture of the BBIC contrasts markedly with the neighbouring Newer Volcanics Province (NVP), which lacks abundant sills and laccoliths. Since lava flows and volcanoes in the NVP were dominantly fed by dykes hosted in basement rock, we suggest subsurface lithology plays an important role in causing sill formation and determining the total volume of magma stored in the subsurface.