Separation of Gagua Rise from Great Benham Rise in the West Philippine Basin during the Middle Eocene

The West Philippine Basin (WPB) has started opening at ~ 58 Ma and ceased spreading at ~ 33 Ma, developing a fast spreading (~ 44 mm/yr half-spreading rate) magmatic episode between 58 and 41 Ma and the second amagmatic episode between 41 and 33 Ma. The occurrence of the first stage of spreading is closely related to the Oki-Daito mantle plume and related Benham Rise (BR) and Urdaneta Plateau (UP) activity. To the east of the Luzon–Okinawa Fracture Zone (LOFZ), BR was the most active volcanism from 48 to 41 Ma. The geomagnetic ages on both sides of the LOFZ have been determined; however, their causal relationship and evolution in the WPB remain unclear. In this study, we performed integrated analyses of multichannel seismic data and swath bathymetry data for the area to the west of the LOFZ. To the west of the LOFZ, the Gagua Rise (GR), is identified by a high residual free-air gravity anomaly, volcanic seamount chains and an overlapping spreading center. The GR is located at magnetic isochrons C20/C22 (50 to 44 Ma) and shows a thick oceanic crust of at least 12.7 km. We first propose an oceanic plateau named Great Benham Rise (GBR) which includes GR, UP and BR. We infer that the GR was a portion of the GBR since ~ 49 Ma and was separated from the GBR at ~ 41 Ma by the right-lateral LOFZ motion. Later, the relict GBR magmatism only continued in the area to the east of the LOFZ. Overall, the GBR dominates the spreading history of the WPB.

A Data-Driven Framework for Automated Detection of Aircraft-Generated Signals in Seismic Array Data Using Machine Learning

Ground motions associated with aircraft overflights can cover a significant portion of the seismic data collected by shallowly emplaced seismometers, such as new nodal and Distributed Acoustic Sensing systems. This article describes the first published framework for automated detection of aircraft on single channel and multichannel seismic data. The seismic data are converted to spectrograms in a sliding time window and classified as aircraft or nonaircraft in each window using a deep convolutional neural network trained with analyst-labeled data. A majority voting scheme is used to convert the output from the sequence of sliding time windows onto a decision time sequence for each channel and to combine the binary classifications on the decision time sequences across multiple channels. Precision, recall, and F-score are used to quantify the detection performance of the algorithm on nodal data using fourfold time-series cross validation. By applying our framework to data from the Sage Brush Flats nodal array in Southern California, we provide a benchmark performance and demonstrate the advantage of using an array of sensors.

Footprints of palaeocurrents in sedimentary sequences of the Cenozoic across the Maurice Ewing Bank

<p>High-resolution 2D multichannel seismic data collected by the Alfred Wegener Institute in 2019 across the Maurice Ewing Bank, the high-altitude easternmost section of the Falkland Plateau in the SW South Atlantic, are integrated with information from DSDP Leg 36, Sites 327, 329, and 330 and Leg 71 Site 511. A seismostratigraphic model is defined, including five units ranging in age from the Middle Jurassic to Quaternary and are interpreted with respect to the evolutional history of the oceanic circulations in the South Atlantic sector of the Southern Ocean. Sedimentary sequences of late Cretaceous and early Paleogene include little and restricted evidence of current activity, attributable to shallow-intermediate depth connections between the developing South Atlantic and Southern Ocean. In contrast, sedimentary sequences of the late Eocene/Oligocene and Neogene reveal a strong history of current-related erosion and deposition. These features exhibit specific water-depth expressions attesting to the long-term activity of different water masses, in stable circulation patterns as those of the present day. We thus suggest that proto-Upper and -Lower Circumpolar Deep Waters have been shaping the bank since the Oligocene. This implies that this bathymetric high has been acting as a barrier for the deep and bottom water masses flowing within the Antarctic Circumpolar Current since its establishment about the Eocene-Oligocene boundary.</p>

A comparison of legacy and recently acquired multichannel seismic data on 95 Ma Pacific oceanic crust south of the Hawaiian Islands

<p>The oceanic crust in the vicinity of the Hawaiian Islands is of tectonic interest because it formed at a fast spreading mid-oceanic ridge during the Late Cretaceous (Turonian) and has been deformed since the Late Miocene by volcanic loads generated at a deep mantle hotspot. We have used legacy and recently acquired multichannel seismic reflection data to determine the character of oceanic crust and the Moho in a region south of the Hawaiian Islands where the Pacific plate has been flexed upwards partly by volcano loading and partly by the dynamics of the hotspot. The legacy data is based on Common Depth Point (CDP) and Constant Offset Profile (COP) data acquired onboard R/V <em>Robert D. Conrad</em> and R/V <em>Kana Keoki</em> during August/September 1982. <em>Conrad</em> was equipped with a 3.6 km long streamer and a 1864 cu. in. airgun array and <em>Kana Keoki</em> was equipped with a 1864 cu. in. array. During the COP experiment the two ships steamed on a similar heading and a separation distance of 3.6 km, yielding an effective offset for reflection data of 7.2 km. Original field data have been re-processed with ‘state-of-the-art’ seismic processing work flows using Shearwater REVEAL software. The recently acquired data was acquired during October 2018 with R/V <em>Marcus G. Langseth</em>, equipped with a 15 km long streamer and a 6600 cu. in. airgun array. Comparisons between the legacy and recently acquired reflection data have been informative, revealing new methods to process <em>Conrad’s</em> legacy of multichannel data acquired on 31 cruises during 1975 to 1989 and new insights on the structure and nature of the Moho in 95 Ma oceanic crust.</p>

Tectonic controlled sedimentary features at the NE marigin of the Sorgenfrei-Tornquist Zone (STZ), southern Sweden

<p>The Hanö Bay basin was formed during Late Cretaceous transgression as a sedimentary trough on the NE margin of the Sorgenfrei-Tornquist Zone (STZ), a narrow NW-SE striking intraplate inversion zone within the Fennoscandian Border Zone. Sedimentation within the basin was primarily controlled by inversion tectonics, resulting in a coarse-grained syn-inversion clastic wedge forming adjacent to the basin-bounding fault in the Santonian-Maastrichtian. Previous studies have highlighted the deposition of contourite sediments associated with topographic relief of the chalk sea created by such local inversion-induced uplift. Imaged upper Cretaceous clinforms in the marginal trough show a NE-ward progadational character, that is, away from the uplifted and eroded inversion zone. These extend along the inversion axis all the way to NE of the Mid-Polish trough.</p><p>To gain detailed stratigraphic constraints and to better understand the interaction of these syn-sedimentary features that developed during inversion tectonics, we use a combination of high-resolution multichannel seismic data (MCS) from the 2019 AL526 cruise and a number of key profiles from reprocessed 70-80’s legacy industry MCS. Preliminary results suggest a drift-moat system developed during a stepwise uplift of the SW shoulder of the STZ, with the uplift driven by transpressional reactivation of basement faults. The resultant aggradational wedge formed a shelf-margin extending fairly far into the basin. The overlying clinoform depositional successions clearly demonstrate several depositional stages; including highstand-progradation, highstand-aggradation and distinct transgression-retrogradation, during which an overall landward migration of the paleo-shoreline position is revealed. The results constrain relative sea-level changes in this area that were primarily related to tectonic events during the Santonian-Campanian.</p>

Image improvement of Late Miocene (Messinian) to Plio-Quaternary units in the Algero-Balearic basin

<p>This study intends to contribute to the understanding of the Mediterranean Salt Giant in the Western Mediterranean, formed about 6 Ma ago during the Messinian Salinity Crisis. It provides reprocessed multichannel seismic reflection data that aim at improving our knowledge of the stratigraphy in the Algero-Balearic deepwater basin and its continental margins, in the absence of lithological information from wells.</p><p>We investigate the seismic expression of the Messinian salinity crisis from the south-east of the Balearic promontory to the central Algero-Balearic abyssal basin and the salt tectonic processes associated to these facies. Here the segmentation of salt structures has been previously described using shallow chirp sonar data, low-resolution vintage multichannel seismic data and high-resolution multi-channel seismic data post-stack migrated with a constant velocity field. The structure of the northern Algero-Balearic basin is controlled by two abrupt fault scarps oriented SW–NE (mainly the Emile Baudot Escarpment transform fault) and WSW-ENE (mainly the Mazarron Escarpment transform fault) emplaced during the basin extension, and later intruded by steep and narrow volcanic ridges of Pleistocene age. It is a good analogue to early stage salt tectonic for older and more complex salt giants in the North Sea or the Gulf of Mexico.</p><p>We reprocessed 2D Kirchhoff PSTM multichannel seismic data acquired by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS (SBALDEEP Cruise of 2005 and SALTFLU cruise of 2012; the latter within a Eurofleet cruise) spanning the South-East continental margin of the Balearic islands and the Algero-Balearic basin. The reprocessing was designed for improving the continuity of the reflectors by applying Kirchhoff PSTM using a detailed velocity model, while preserving amplitude information. The objectives are to better apprehend the structural complexity of the area and to retrieve the amplitude variation within the Messinian units, in an attempt to derive the composition of the salt and the pressure regime.</p><p>We present preliminary results where we delineate four different domains based on i) the seismic facies, ii) the amount of salt deformation, iii) the thickness of the overburden and iv) the pre-salt configuration. We try to assess the presence of the Messinian trilogy in the south-eastern continental slope. We attempt to reconstitute the paleo-depositionnal environment of the various depositional units, and the effect of crustal structures and salt tectonic gravity spreading and gliding on their syn to post-depositional evolution. Finally, we search for evidence of fluid circulation within the Messinian and the Plio-Quaternary deposits over the study area.</p>