Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements

Sequence stratigraphy, structural style, and age of deformation of the Malaita accretionary prism (Solomon arc-Ontong Java Plateau convergent zone)

Possibilities for the fate of oceanic plateaus at subduction zones range from complete subduction of the plateau beneath the arc to complete plateau–arc accretion and resulting collisional orogenesis. Deep penetration, multi-channel seismic reflection (MCS) data from the northern flank of the Solomon Islands reveal the sequence stratigraphy, structural style, and age of deformation of an accretionary prism formed during late Neogene (5–0 Ma) convergence between the 33-km-thick crust of the Ontong Java oceanic plateau and the 15-km-thick Solomon island arc. Correlation of MCS data with the satellite-derived, free-air gravity field defines the tectonic boundaries and internal structure of the 800-km-long, 140-km-wide accretionary prism. We name this prism the “Malaita accretionary prism” or “MAP” after Malaita, the largest and best-studied island exposure of the accretionary prism in the Solomon Islands. MCS data, gravity data, and stratigraphic correlations to islands and ODP sites on the Ontong Java Plateau (OJP) reveal that the offshore MAP is composed of folded and thrust faulted sedimentary rocks and upper crystalline crust offscraped from the Solomon the subducting Ontong Java Plateau (Pacific plate) and transferred to the Solomon arc. With the exception of an upper, sequence of Quaternary? island-derived terrigenous sediments, the deformed stratigraphy of the MAP is identical to that of the incoming Ontong Java Plateau in the North Solomon trench

Sequence stratigraphy, structure, and tectonic history of the southwestern Ontong Java Plateau adjacent to the North Solomon Trench and Solomon Island Arc

The Ontong Java Plateau (OJP) is the largest and thickest oceanic plateau on Earth and one of the few oceanic plateaus actively converging on an island arc. We present velocity determinations and geologic interpretation of 2000 km of two-dimensional, multi-channel seismic data from the southwestern Ontong Java Plateau, North Solomon Trench, and northern Solomon Islands. We recognize three megasequences, ranging in age from early Cretaceous to Quaternary, on the basis of distinct interval velocities and seismic stratigraphic facies. Megasequence OJ1 is early Cretaceous, upper igneous crust of the OJP and correlates with basalt outcrops dated at 122–125 Ma on the island of Malaita. The top of the overlying megasequence OJ2, a late Cretaceous mudstone unit, had been identified by previous workers as the top of igneous basement. Seismic facies and correlation to distant Deep Sea Drilling Project/Ocean Drilling Program sites indicate that OJ2 was deposited in a moderately low-energy, marine environment near a fluctuating carbonate compensation depth that resulted in multiple periods of dissolution. OJ2 thins south of the Stewart Arch onto the Solomon Islands where it is correlated with the Kwaraae Mudstone Formation. Megasequence OJ3 is late Cretaceous through Quaternary pelagic cover which caps the Ontong Java Plateau; it thickens into the North Solomon Trench, and seismic facies suggest that OJ3 was deposited in a low-energy marine environment. We use seismic facies analysis, sediment thickness, structural observations, and quantitative plate reconstructions of the position of the OJP and Solomon Islands to propose a tectonic, magmatic, and sedimentary history of the southwestern Ontong Java Plateau. Prior to 125 Ma late Jurassic and early Cretaceous oceanic crust formed. From 125 to 122 Ma, the first mantle plume formed igneous crust (OJ1). Between 122 and 92 Ma, marine mudstone (OJ2 and Kwaraae mudstone of Malaita, Solomon Islands) was deposited on Ontong Java Plateau. At 92 Ma a second mantle plume caused widespread volcanism on the plateau. From 92 to 15 Ma, pelagic carbonate sediment (OJ3) was deposited. At ?15 Ma the southern Ontong Java Plateau was deformed by normal faults during its approach toward the North Solomon Trench. Finally, from 4 to 0 Ma, the Malaita Accretionary Prism formed during collision between a substantially thicker portion of the Ontong Java Plateau and the Solomon Islands arc. Flexure of the Ontong Java Plateau near the trench caused coeval normal faulting. <br/

Oligocene to Recent tectonic history of the Central Solomon intra-arc basin as determined from marine seismic reflection data and compilation of onland geology

Systematic analysis of a grid of 3450 km of multichannel seismic reflection lines from the Solomon Islands constrains the late Tertiary sedimentary and tectonic history of the Solomon Island arc and its convergent interaction with the Cretaceous Ontong Java oceanic plateau (OJP). The OJP, the largest oceanic plateau on Earth, subducted beneath the northern edge of the Solomon arc in the late Neogene, but the timing and consequences of this obliquely convergent event and its role in the subduction polarity reversal process remain poorly constrained. The Central Solomon intra-arc basin (CSB), which developed in Oligocene to Recent time above the Solomon arc, provides a valuable record of the tectonic environment prior to and accompanying the OJP convergent event and the subsequent arc polarity reversal. Recognition of regionally extensive stratigraphic sequences—whose ages can be inferred from marine sedimentary sections exposed onland in the Solomon Islands—indicate four distinct tectonic phases affecting the Solomon Island arc. Phase 1: Late Oligocene–Late Miocene rifting of the northeast-facing Solomon Island arc produced basal, normal-fault-controlled, asymmetrical sequences of the CSB; the proto-North Solomon trench was probably much closer to the CSB and is inferred to coincide with the trace of the present-day Kia-Kaipito-Korigole (KKK) fault zone; this protracted period of intra-arc extension shows no evidence for interruption by an early Miocene period of convergent “soft docking” of the Ontong Java Plateau as proposed by previous workers. Phase 2: Late Miocene–Pliocene oblique convergence of the Ontong Java Plateau at the proto-North Solomon trench (KKK fault zone) and folding of the CSB and formation of the Malaita accretionary prism (MAP); the highly oblique and diachronous convergence between the Ontong Java plateau and the Solomon arc terminates intra-arc extension first in the southeast (Russell subbasin of the CSB) during the Late Miocene and later during the Pliocene in the northwest (Shortland subbasin of the CSB); folds in the CSB form by inversion of normal faults formed during Phase 1; Phinney et al. [Sequence stratigraphy, structural style, and age of deformation of the Malaita accretionary prism (Solomon arc-Ontong Java Plateau convergent zone)] show a coeval pattern of southeast to northwest younging in folding and faulting of the MAP. Phase 3: Late Pliocene–early Pleistocene arc polarity reversal and subduction initiation at the San Cristobal trench. Effects of this event in the CSB include the formation of a chain of volcanoes above the subducting Australia plate at the San Cristobal trench, the formation of the broad synclinal structure of the CSB with evidence for truncation at the uplifted flanks, and widespread occurrence of slides and “seismites” (deposits formed by seismic shaking). Phase 4: Pleistocene to Recent continued shortening and synclinal subsidence of the CSB. Continued Australia-Pacific oblique plate convergence has led to deepening of the submarine, elongate basin axis of the synclinal CSB and uplift of the dual chain of the islands on its flanks.<br/

3. SEISMIC STRATIGRAPHY OF THE ONTONG JAVA PLATEAU 1

International audienceThe Ontong Java Plateau, a large, deep-water carbonate plateau in the western equatorial Pacific, is an ideal location for studying responses of carbonate sedimentation to the effects of changing paleoceanographic conditions. These carbonate responses are often reflected in the physical properties of the sediment, which in turn control the appearance of seismic reflection profiles. Seismic stratigraphy analyses, correlating eight reflector horizons to each drill site, have been conducted in an attempt to map stratigraphic data. Accurate correlation of seismic stratigraphic data to drilling results requires conversion of traveltime to depth in meters. Synthetic seismogram models, using shipboard physical properties data, have been generated in an attempt to provide this correlation. Physical properties, including laboratory-measured and well-log data, were collected from sites drilled during Deep Sea Drilling Project Legs 30 and 89, and Ocean Drilling Program Leg 130, on the top and flank of the Ontong Java Plateau. Laboratory-measured density is corrected to in-situ conditions by accounting for porosity rebound resulting from removal of the sediment from its overburden. The correction of laboratory-measured compressional velocity to in situ appears to be largely a function of increases in elastic moduli (especially shear rigidity) with depth of burial, more than a function of changes in temperature, pressure, or density (porosity rebound). Well-log velocity and density data for the ooze intervals were found to be greatly affected by drilling disturbance; hence, they were disregarded and replaced by lab data for these intervals. Velocity and density data were used to produce synthetic seismograms. Correlation of seismic reflection data with synthetic data, and hence with depth below seafloor, at each drill site shows that a single velocity-depth function exists for sediments on the top and flank of the Ontong Java Plateau. A polynomial fit of this function provides an equation for domain conversion: Depth (mbsf) = 44.49 + 0.800(traveltime[ms]) + 3.308 × 10" 4 (traveltime[ms] 2) Traveltime (ms) =-35.18 + 1.118(depth[mbsf])-1.969 × KT* (depth[mbsf] 2) Seismic reflection profiles down the flank of the plateau undergo three significant changes: (1) a drastic thinning of the sediment column with depth, (2) changes in the echo-character of the profile (development of seismic facies), and (3) loss of continuous, coherent reflections. Sediments on the plateau top were largely deposited by pelagic processes, with little significant postdepositional or syndepositional modification. Sediments on the flank of the plateau are also pelagic, but they have been modified by faulting, erosion, and mass movement. These processes result in disrupted and incoherent reflectors, development of seismic facies, and redistribution of sediment on the flank of the plateau. Seismic stratigraphic analyses have shown that the sediment section decreases in thickness by as much as 65% between water depths of 2000 m water depth (at the top of the plateau) and 4000 m (near the base of the plateau). Thinning is attributed to increasing carbonate dissolution with depth. If this assumption is correct, then changes in the relative thicknesses of seismostratigraphic units at each drill site are indicative of changes in the position of the lysocline and the dissolution gradient between the lysocline and the carbonate compensation depth. We think that a shallow lysocline in the early Miocene caused sediment thinning. A deepening of the lysocline in the late-early Miocene caused relative thickening at each site. Within the middle Miocene, a sharp rise in lysoclinal depth occurs, concurrent with a steepening of the dissolution gradient. These events result in sediment thinning at all four sites. The thicker sections in the late Miocene likely correspond to a deepening of the lysocline, and a subsequent rise in the lysocline again hinders accumulation of sediment in the very late Miocene and Pliocene