Stratigraphic development and petroleum prospectivity of northern Zealandia

<p>Northern Zealandia lies between Australia, New Zealandia, and New Caledonia. It has an area of 3,000,000 km2 and is made up of bathymetric rises and troughs with typical water depths of 1000 to 4000 m. I use 39,309 line km of seismic-reflection profiles tied to recent International Ocean Discovery Program (IODP) drilling and three boreholes near the coast of New Zealand to investigate stratigraphic architecture and assess the petroleum prospectivity of northern Zealandia. Sparse sampling requires that stratigraphic and petroleum prospectivity inferences are drawn from better-known basins in New Zealand, Australia, New Caledonia, TimorLeste and Papua New Guinea. Five existing seismic-stratigraphic units are reviewed. Zealandia Seismic Unit U3 is sampled near New Zealand and may contain Jurassic Muhiriku Group coals. Elsewhere, Seismic Unit 3 may have oil-prone equivalents of the Jurassic Walloon Coal Measure in eastern Australia; or may contain Triassic-Jurassic marine source rocks, as found in offshore Bonaparte Basin, onshore Timor-Leste, and the Papuan Basin in Papua New Guinea. Seismic Unit U2b (Mid-Cretaceous) is syn-rift and may contain coal measures, as found in Taranaki-Aotea Basin and New Caledonia. Seismic Unit U2a (Late Cretaceous to Eocene) contains coaly source rocks in the southeastern part of the study area, and may also contain marine equivalent carbonaceous mudstone, as found at Site IODP U1509. Unit U2a is transgressive, with coaly source rocks and reservoir sandstones near its base, and clay, marl and chalk above that provides a regional seal. Seismic Unit U1b (Eocene-Oligocene) is mass-transport complexes and basin floor fans related to a brief phase of convergent deformation that created folds in the southern part of the study area and regionally uplifted ridges to create new sediment source areas. Basin floor fans may contain reservoir rock and Eocene folding created structural traps. Seismic Unit U1a is Oligocene and Neogene chalk, calcareous ooze, and marl that represents overburden. Mass accumulation rates (MAR) and climatic temperatures were high in the late Miocene and early Pliocene, resulting in peak thermal maturity and hydrocarbon expulsion at ~ 3 Ma. Approximately one-fifth of the region has adequate source rock maturity for petroleum expulsion at the base of Seismic Unit U2: Fairway Basin (FWAY), southern New Caledonia Trough (NCTS) and Reinga Basin (REIN). Plays may exist in either Seismic Unit U3 or U2, with many plausible reservoir-seal combinations, and several possible trapping mechanisms: unconformities, normal faults, folds, or stratigraphic pinch-out. The rest of the region could be prospective, but requires a source rock to exist within Seismic Unit U3, which is mostly unsampled and remains poorly understood.</p>

Stratigraphic development and petroleum prospectivity of northern Zealandia

<p>Northern Zealandia lies between Australia, New Zealandia, and New Caledonia. It has an area of 3,000,000 km2 and is made up of bathymetric rises and troughs with typical water depths of 1000 to 4000 m. I use 39,309 line km of seismic-reflection profiles tied to recent International Ocean Discovery Program (IODP) drilling and three boreholes near the coast of New Zealand to investigate stratigraphic architecture and assess the petroleum prospectivity of northern Zealandia. Sparse sampling requires that stratigraphic and petroleum prospectivity inferences are drawn from better-known basins in New Zealand, Australia, New Caledonia, TimorLeste and Papua New Guinea. Five existing seismic-stratigraphic units are reviewed. Zealandia Seismic Unit U3 is sampled near New Zealand and may contain Jurassic Muhiriku Group coals. Elsewhere, Seismic Unit 3 may have oil-prone equivalents of the Jurassic Walloon Coal Measure in eastern Australia; or may contain Triassic-Jurassic marine source rocks, as found in offshore Bonaparte Basin, onshore Timor-Leste, and the Papuan Basin in Papua New Guinea. Seismic Unit U2b (Mid-Cretaceous) is syn-rift and may contain coal measures, as found in Taranaki-Aotea Basin and New Caledonia. Seismic Unit U2a (Late Cretaceous to Eocene) contains coaly source rocks in the southeastern part of the study area, and may also contain marine equivalent carbonaceous mudstone, as found at Site IODP U1509. Unit U2a is transgressive, with coaly source rocks and reservoir sandstones near its base, and clay, marl and chalk above that provides a regional seal. Seismic Unit U1b (Eocene-Oligocene) is mass-transport complexes and basin floor fans related to a brief phase of convergent deformation that created folds in the southern part of the study area and regionally uplifted ridges to create new sediment source areas. Basin floor fans may contain reservoir rock and Eocene folding created structural traps. Seismic Unit U1a is Oligocene and Neogene chalk, calcareous ooze, and marl that represents overburden. Mass accumulation rates (MAR) and climatic temperatures were high in the late Miocene and early Pliocene, resulting in peak thermal maturity and hydrocarbon expulsion at ~ 3 Ma. Approximately one-fifth of the region has adequate source rock maturity for petroleum expulsion at the base of Seismic Unit U2: Fairway Basin (FWAY), southern New Caledonia Trough (NCTS) and Reinga Basin (REIN). Plays may exist in either Seismic Unit U3 or U2, with many plausible reservoir-seal combinations, and several possible trapping mechanisms: unconformities, normal faults, folds, or stratigraphic pinch-out. The rest of the region could be prospective, but requires a source rock to exist within Seismic Unit U3, which is mostly unsampled and remains poorly understood.</p>

Sedimentary Processes on a Mixed Turbidite-Contourite System - Northern Campos Basin, SE Brazil

&lt;p&gt;A new mixed turbidite-contourite system is described in the northern Campos Basin, southeastern Brazilian margin. This system is developed in a middle slope setting and was formed through non-synchronous interaction between the turbidity current and a contour current in the same stratigraphic interval (Miocene). Different depositional cycles were accounted based on their diagnostic seismic features. Seismic attributes, seismic facies, and isochron maps were used to identify alternating cycles of downslope and alongslope processes in the study area, along with the intermediate stage with features from both processes (mixed system). Seismic units were then associated with the dominant type of current. Depositional processes resulted from alongslope current activity can be distinguished from the downslope current activity, based on the acoustic characteristics (root-mean-square (RMS) amplitude values), internal architecture, and external geometry pattern. While alongslope currents deposits consist of mainly low RMS amplitude values clinoforms with an alongslope trend; the downslope gravity deposits present high-amplitude or chaotic seismic facies, usually higher values of RMS amplitude, channel or channel-lobe features, erosive surfaces, and a basinward depositional trend. The first and oldest seismic unit (S1) was interpreted as a dominantly alongslope system, with aggrading sigmoidal clinoforms and high-frequency, low-amplitude reflections commonly associated with fine-grained sedimentary deposits, typical of a plastered drift. Basinward mass transport deposit derived from previous drift instability are often identified. Seismic unit S2 represents the intermediate stage where both gravity-driven and along-slope currents act asynchronously. It is referred to as a mixed turbidite-contourite sequence that shows high-amplitude sediment waves migrating upslope and a moat feature carved in its upslope front. The interfingering between high- and low-amplitude reflectors, distal chaotic facies, together with sediment waves and a channel moat, points to a sand-rich deposit reworked by northward-flowing contour currents. Seismic units S3 and S4 show downslope features with chaotic facies (S3) and paleochannels with coarse basal lag deposits interpreted after the high RMS amplitude values (S4). In S4, a series of long-lived submarine channels formed. The last seismic unit, S5, referred to as the second plastered drift sequence, is marked by low-amplitude clinoforms that thin basinward. Important information on the paleocurrents' direction was also made based on the final deposits display (e.g. terraces, sediment waves, paleochannels), where a northward-flowing bottom current was assumed. Research on alternating dominant processes and transitional stages or mixed depositional systems may provide a better understanding of deep-water depositional processes. Because these processes do not always fit previous depositional models that are mainly described for synchronous systems, new insights on cyclic non-synchronous mixed systems can improve our understanding of how mixed systems are organized through time and space. We can also determine which were the dominant processes that controlled the sedimentation by indicating periods where the margin was mostly submitted to sediment transfer from continent to the basin and periods where the oceanic currents prevailed by redistributing sediments along the isobaths and replacing the axis of downslope transfer conduits. Setting new models on cyclic deposits and intermediate stages can have a future economic impact on potential hydrocarbon reservoir architecture.&lt;/p&gt;

Rapid response to the Mw 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics.

Assessment of a seismo-neotectonic origin for the New Liskeard–Thornloe scarp, Timiskaming graben, northeastern Ontario

To test an inference that the New Liskeard–Thornloe scarp (NLTS), Timiskaming graben, Ontario, is a deglacial–postglacial seismo-neotectonic fault, we collected shallow geophysical data along lines 7.2, 0.28, and 0.52 km long, located on three roads crossing the middle portion of the scarp. Data revealed a valley subsurface composed of bedrock (seismic unit a), glaciolacustrine–lacustrine deposits (units b to f), mass movement deposits (units ls 1 to ls 3), wave-worked sediments, mass wasting deposits and (or) artificial fill (unit g), and a minor occurrence of roadfill (unit h). The bedrock surface exhibits only minor undulations in the area underlying the scarp, indicating that the scarp morphology is unrelated to the underlying bedrock topography. Parallel reflectors in glaciolacustrine seismic units b and c conformably overlie the minor bedrock undulations and there is an absence of disturbed or offset zones within the reflectors underlying the scarp. This lack of disturbance or offset provides strong evidence that the scarp is not the product of deglacial–postglacial seismo-neotectonic faulting. The erosive truncation of glaciolacustrine seismic units d and e indicate that the scarp is an erosive feature cut into the glaciolacustrine deposits. It is likely a bluff formed by shoreline erosion, as is consistent with a geomorphic setting previously inundated by a large glacial lake and subsequent recessional lake stages. The non-fault origin for the NLTS limits the northern extent of the hypothesized Timiskaming East Shore Fault to within the Lake Timiskaming basin and, hence, constrains estimates of maximum rupture length.

Southern continuation of the Wakeham Group and Robe-Noire mafic suite (eastern Grenville Province) from hydrocarbon-targeted seismic reflection data on Anticosti Island, Quebec, Canada

Hydrocarbon-targeted seismic reflection profiles acquired on eastern Anticosti Island (Quebec) image subparallel reflections with significant continuity below the Paleozoic St. Lawrence Platform. These intra-basement reflections define a seismic unit with a relatively simple geometry characterized by broad open folds, an array of subparallel markers, and east-northeast-dipping faults. The reflective seismic unit likely corresponds to the southern extension of the Mesoproterozoic Wakeham Group and Robe-Noire mafic sills that are exposed on the nearby north shore of the Gulf of St. Lawrence, in the eastern Grenville Province of Quebec.

GEOLOGI BAWAH PERMUKAAN DASAR LAUTPERAIRAN LEMBAR PETA 0421, DAERAH ISTIMEWA ACEH

Hasil kegiatan penelitian geologi kelautan Lembar Peta 0421menghasilkan data seismik dan pemeruman sepanjang lebih kurang 963,73 kilometer. Dari peta batimetri ditemukan beberapa kelurusan dengan arah hampir baratlaut-tenggara dan diduga merupakan sesar. Hasil penafsiran data menunjukkan bahwa stratigrafi rekaman seismik, daerah penelitian secara garis besar dapat dibagi menjadi 4 (empat) unit yaitu unit 1; unit 2; unit 3, dan unit 4. Jika dikaitkan dengan geologi regional daerah penelitian, unit 1 diduga dapat disebandingkan dengan Formasi Peunasu berumur Miosen, unit 2 diduga dapat disebandingkan dengan Formasi Seurula & Formasi Julurayeu berumur Pliosen, unit 3 diduga dapat disebandingkan dengan endapan volkanik Toba berumur Plistosen, dan unit 4 diduga dapat disebandingkan dengan aluvial berumur Holosen. Pembagian unit tersebut berdasarkan pada adanya bidang tidakselarasan (onlap), dan pepat erosi (erosional truncation). Kata kunci : lembar peta 0421, unit seismik, ketidakselarasan. The results of marine geological investigation of map of sheet 0421 gave a data of seismic and sounding approximately 963.73 kilometers long. Bathymetric map indicates some alignment with the direction of nearly northwest-southeast and presumed to be faults. Seismic data interpretation indicate that the stratigraphy of the study area can broadly be divided into 4 (four) units those are unit 1; unit 2; unit 3, and unit 4. Correlation balance with regional geology, show that seismic, unit 1 correlates with Peunasu Formation of Miocene, unit 2 correlates with Seurula Formation and Julurayeu Formation of Pliocene, unit 3 correlates with Old Toba volcanic deposites of Pleistocene, and unit 4 correlates with Alluvium of Holocene. The division of seismic units was based on unconformity (onlap) and (erosional truncation). Keywords: map of sheet 0421, seismic units, unconformity.

The Late Holocene sediment infilling and beach barrier dynamics of the Thau lagoon (Gulf of Lions, Mediterranean sea, SE France)

A study combining very high resolution seismic and sediment core data has been carried out on the Thau lagoon (Mediterranean coast, microtidal setting, SE France) in order to understand more clearly the dynamics and Holocene chronology of its closure through the different stages of its filling. One main seismic unit (U2) has been defined into the infill, above the rocky basement (U0) and a composite unit U1, which is interpreted as remnants of Pleistocene fluvial terraces or/and to early marine Holocene deposits. Unit U2, that reaches locally 9 m in thickness, rests conformably on U1 in the central part of the lagoon and onlaps U0 or U1 close to the edge of the lagoon. It is divided in two sub-units, U2-1 and U2-2. U2-2 rests paraconformably on U2-1 in the central part of the lagoon where the infill is the thickest, while a marked erosional unconformity is observed between U2-1 and U2-2 on topographic highs of the basement and on the seaward edge of the lagoon. A total of seven elementary sequences have been observed in U2-1 and U2-2. According to core data, U2 consists in a series of mud-dominated sequences, with shell fragments dispersed at the base. The vertical distribution of the fauna into U2-1 and U2-2 reveals a lagoonal environment. However in U2-1, marine species are more abundant in the south of the lagoon. 14C AMS dating provides three ages: ~ 6000 cal yr B.P. in the lower part of U2-1 on CAL1, ~ 5400 cal yr B.P. just above the boundary between U2-1 and U2-2 on CAL4, ~ 3000 cal yr B.P. in the middle of U2-2 on CAL4. A scenario to explain the lagoon infill stratigraphy and geometry is proposed. The beginning of the lagoon infill occurred with the initiation of the barrier construction, as soon as the sea-level rise slowed down significantly, i.e. between 7000–6000 yr B.P. The sediment-fill began into the back-barrier system, with a high rate of sedimentation for U2-1, according to the radiocarbon data. At 5400 yr B.P., the barrier is assumed to be totally closed leading to the deposition of the fully lagoonal U2-2 succession. The unconformity between U2-1 and U2-2 is interpreted as the result of a rapid landward retreat of the barrier. This severe retreat could be related to climate forcing and/or brutal change in sediment discharge driven by the Rhône River, which is the main sediment source of the longshore drift. In this scenario, the last sub-unit, U2-2, represents most of the late Holocene infill. In this framework, the elementary sequences observed in U2-2 could be related to high frequency climate changes of about 1000–1500 years periodicity according to 14C dates.