Pelagic Cover Research Articles

Rheology and Biostratigraphy of the Mariana Serpentine Muds Unravel Mud Volcano Evolution

AbstractIn late 2016, the IODP Expedition 366 drilled 21 holes on summits and flanks of three serpentinite mud volcanoes (SMVs) of the Mariana Forearc: Yinazao (Blue Moon), Fantangisña (Celestial), and Asùt Tesoru (Big Blue). The drilling reached the forearc sediments underneath the SMVs only at Site U1498 where, according to data from this study, the biostratigraphic age of Fantangisña appears to be well constrained, with a pelagic cover on top of the serpentine mud flows of 0.44 Ma and an age of the forearc sediments of 11.21 Ma. With an estimated age of at least 10.77 Myr this is, to our knowledge, the oldest mud volcano ever dated. To link the age of the edifice with its eruptive dynamics, we performed rheological tests of natural samples of serpentine mud from the Fantangisña SMV for the first time. These experiments not only confirm the highly viscous characteristic of the mud breccia but also identify different muds' mineralogical compositions (i.e., serpentine‐rich vs. serpentine‐poor sediments) and water contents as being responsible for the main rheological variations. The viscosity from the rheological data, together with the physical properties of the mud breccia and the clasts measured onboard IODP366, under several assumptions, allow us to estimate of flow velocities and a depth of the mud source at ∼8.4 km below seafloor. Moreover, comparison of erupted mud breccia volumes from bathymetry, seismic data, and calculations shows how the SMV evolution is linked to episodic events, highlighting that Fantangisña has actively been expelling sediments during 2.41% of its life span.

The last 2 Myr of accretionary wedge construction in the central Hikurangi margin (North Island, New Zealand): Insights from structural modeling

AbstractThree depth‐converted and geologically interpreted seismic profiles provide a clear image of the offshore outer accretionary wedge associated with oblique subduction of the Pacific Plate beneath the central Hikurangi margin. Plio‐Quaternary turbidites deposited over the pelagic cover sequence of the Hikurangi Plateau have been accreted to the margin by imbrication along E‐verging thrust faults that propagated up‐section from the plate boundary décollement. Growth stratigraphy of piggy‐back basins and thrusting of progressively younger horizons trace the eastward advance of the leading thrust front over ∼60 km in the last 2 Myr. Moderate internal shortening of fault‐bounded blocks typically 4–8 km wide reflects rapid creation of thrust faults, with some early formed faults undergoing out‐of‐sequence reactivation to maintain critical wedge taper. Multistage structural restorations show that forward progression of shortening involves: (1) initial development of a ∼10–25 km wide “proto‐thrust” zone, comprising conjugate sets of moderately to steeply dipping low‐displacement (∼10–100 m) reverse faults; and (2) growth of thrust faults that exploit some of the early proto‐thrust faults and propagate up‐section with progressive break‐through of folds localized above the fault tips. The youngest, still unbreached folds deform the present‐day seafloor. Progressive retro‐deformations show that macroscopic thrust faults and folds account for less than 50% of the margin‐perpendicular shortening imposed by plate convergence. Arguably, significant fractions of the missing components can be attributed to mesoscopic and microscopic scale layer‐parallel shortening within the wedge, in the proto‐thrust zones, and in the outer décollement zone.

The Owen Ridge uplift in the Arabian Sea: Implications for the sedimentary record of Indian monsoon in Late Miocene

The pelagic cover of the Owen Ridge in the Arabian Sea recorded the evolution of the Indian monsoon since the Middle Miocene. The uplift of the Owen Ridge resulted from tectonic processes along the previously unidentified Miocene India–Arabia plate boundary. Based on seismic reflection data tied with deep-sea drilling to track the Miocene India–Arabia plate boundary, we propose a new timing for the uplift of the Owen Ridge and highlight its impact on the record of climate changes in pelagic sediments. The new dataset reveals a fracture zone east of the Owen Ridge corresponding to the fossil plate boundary, and documents that the main uplift of the Owen Ridge occurred close to ∼8.5 Ma, and is coeval with a major uplift of the east Oman margin. Late Miocene deformation at the India–Arabia plate boundary is also coeval with the onset of intra-plate deformation in the Central Indian Ocean, suggesting a kinematic change of India and surrounding plates in the Late Miocene. The uplift of the Owen Ridge above the lysocline at ∼8.5 Ma accounts for a better preservation of Globigerina bulloides in the pelagic cover, previously misinterpreted as the result of a monsoon intensification event.

Mass wasting processes along the Owen Ridge (Northwest Indian Ocean)

The Owen Ridge is a prominent relief that runs parallel to the coast of Oman in the NW Indian Ocean and is closely linked to the Owen Fracture Zone, an 800-km-long active fault system that accommodates today the Arabia–India strike–slip motion. Several types of mass failures mobilizing the pelagic cover have been mapped in details along the ridge using multibeam bathymetry and sediment echosounder. Here we present a synthetic map of the different types of mass wasting features observed along the ridge and we further establish a morphometric analysis of submarine landslides. The spatial variation of failure morphology is strongly related to the topography of the basement. The highest volumes of multi-events generated slides are mobilized along the southern portion of the ridge. There, the estimated volume of evacuated material during a slide is up to 45km3. Combining these new observations with re-interpreted ODP seismic lines (Leg 117) documents sporadic mass wasting events through time along the southern segment of the ridge since its uplift in the Early Miocene, with a typical recurrence rate of the order of 105–106years. Although seismicity may still be the final triggering process, mass wasting frequency is mainly controlled by the slow pelagic sedimentation rates and hence, time needed to build up the 40–80m thick pelagic cover required to return to a mechanically unstable pelagic cover.

Ophiolite‐bearing mélanges in southern Italy

AbstractIn southern Italy two ophiolite‐bearing belts, respectively involved in the Adria‐verging southern Apennines and in the Europe‐verging thrust belt of the northern Calabrian Arc, represent the southward extension of the northern Apennines and of ‘Alpine Corsica’ ophiolitic units, respectively. They form two distinct suture zones, which are characterized by different age of emplacement and opposite sense of tectonic transport. The ophiolite‐bearing units of the southern Apennines are represented by broken formation and tectonic mélange associated with remnants of a well‐developed accretionary wedge emplaced on top of the Adria continental margin, with an overall NE direction of tectonic transport. These units consist of a Cretaceous‐Oligocene matrix, which includes blocks of continental‐type rocks and ophiolites with remnants of their original Upper Jurassic to Lower Cretaceous pelagic cover. The innermost portion of the accretionary wedge is represented by a polymetamorphosed and polydeformed tectonic units that underwent a Late Oligocene high pressure/low temperature (HP/LT) metamorphism. The northern Calabria ophiolitic‐belt is indeed composed of west‐verging tectonic slices of oceanic rocks which, embedded between platform carbonate units of a western continental margin at the bottom and the basement crystalline nappes of the Calabrian Arc at the top, are affected by a Late Eocene‐Early Oligocene HP/LT metamorphism. The main tectonic features of these two suture zones suggest that they can be interpreted as the result of the closure of two branches of the western Neotethys separated by a continental block that includes the crystalline basement rocks of the Calabrian Arc. We thus suggest that the north‐east verging southern Apennine suture constituted by a well‐developed accretionary wedge is the result of the closure of a large Late Jurassic‐Early Cretaceous oceanic domain (the Ligurian Ocean) located between the African (the Adria Block) and European continental margins. The northern Calabria suture derives indeed from the deformation of a very narrow oceanic‐floored basin developed during the Mesozoic rifting stages within the European margin separating a small continental ribbon (Calabrian Block) from the main continent. Copyright © 2008 John Wiley & Sons, Ltd.

Biogeographical and geological evidence for a smaller, completely‐enclosed Pacific basin in the Late Cretaceous: a comment

Biogeographical and geological evidence for a smaller, completely‐enclosed Pacific basin in the Late Cretaceous: a comment

The Misis–Andırın Complex: a Mid-Tertiary melange related to late-stage subduction of the Southern Neotethys in S Turkey

The Mid-Tertiary (Mid-Eocene to earliest Miocene) Misis–Andırın Complex documents tectonic-sedimentary processes affecting the northerly, active margin of the South Tethys (Neotethys) in the easternmost Mediterranean region. Each of three orogenic segments, Misis (in the SW), Andırın (central) and Engizek (in the NE) represent parts of an originally continuous active continental margin. A structurally lower Volcanic-Sedimentary Unit includes Late Cretaceous arc-related extrusives and their Lower Tertiary pelagic cover. This unit is interpreted as an Early Tertiary remnant of the Mesozoic South Tethys. The overlying melange unit is dominated by tectonically brecciated blocks (>100 m across) of Mesozoic neritic limestone that were derived from the Tauride carbonate platform to the north, together with accreted ophiolitic material. The melange matrix comprises polymict debris flows, high- to low-density turbidites and minor hemipelagic sediments.The Misis–Andırın Complex is interpreted as an accretionary prism related to the latest stages of northward subduction of the South Tethys and diachronous continental collision of the Tauride (Eurasian) and Arabian (African) plates during Mid-Eocene to earliest Miocene time. Slivers of Upper Cretaceous oceanic crust and its Early Tertiary pelagic cover were accreted, while blocks of Mesozoic platform carbonates slid from the overriding plate. Tectonic mixing and sedimentary recycling took place within a trench. Subduction culminated in large-scale collapse of the overriding (northern) margin and foundering of vast blocks of neritic carbonate into the trench. A possible cause was rapid roll back of dense downgoing Mesozoic oceanic crust, such that the accretionary wedge taper was extended leading to gravity collapse. Melange formation was terminated by underthrusting of the Arabian plate from the south during earliest Miocene time.Collision was diachronous. In the east (Engizek Range and SE Anatolia) collision generated a Lower Miocene flexural basin infilled with turbidites and a flexural bulge to the south. Miocene turbiditic sediments also covered the former accretionary prism. Further west (Misis Range) the easternmost Mediterranean remained in a pre-collisional setting with northward underthrusting (incipient subduction) along the Cyprus arc. The Lower Miocene basins to the north (Misis and Adana) indicate an extensional (to transtensional) setting. The NE–SW linking segment (Andırın) probably originated as a Mesozoic palaeogeographic offset of the Tauride margin. This was reactivated by strike-slip (and transtension) during Later Tertiary diachronous collision. Related to on-going plate convergence the former accretionary wedge (upper plate) was thrust over the Lower Miocene turbiditic basins in Mid–Late Miocene time. The Plio-Quaternary was dominated by left-lateral strike-slip along the East Anatolian transform fault and also along fault strands cutting the Misis–Andırın Complex.

Quantifying the sequence stratigraphy and drowning mechanisms of atolls using a new 3‐D forward stratigraphic modelling program (CARBONATE 3D)

ABSTRACTThis paper describes a new 3‐D forward numerical model (CARBONATE 3D) that simulates the stratigraphic and sedimentological development of carbonate platforms and mixed carbonate–siliciclastic shelves by simulating the following sedimentary processes: (1) Carbonate shallow, open‐marine production, dependent on water depth, restriction and sediment input; (2) Carbonate shallow, restricted‐marine production, dependent on water restriction; (3) Pelagic sediment production and deposition; (4) Coarse and fine siliciclastic input; (5) Erosion, transport and redeposition of sediment, dependent on currents, slope, depth and restriction as well as sediment grain‐size and composition; (6) Dissolution of subaerially exposed carbonate. In this paper the model is used to investigate the controlling mechanisms on the sequence stratigraphy of isolated carbonate platforms and atolls and to predict distinctive architectural signatures from different drowning mechanisms. Investigation of the mechanisms controlling atoll strata shows that although relative sea‐level is the major control, antecedent topography, environmental setting and early diagenesis have profound influence on what stratigraphic geometries and facies develop. Hence care must be taken if sea‐level curves are interpreted from real stratigraphies. Atoll drowning by fast sea‐level rise, by lowered production and by repeated exposure and fast subsequent sea‐level rises are investigated and different stratigraphic signatures for the respective mechanisms predicted. A fast relative sea‐level rise results in a bucket‐shaped morphology developed prior to drowning and a sharp transition from the platform margin facies to a pelagic cover. Drowning caused by lowered platform margin production is predicted to result in the development of a dome‐shaped, shallow‐water shoal over the whole platform top prior to drowning. Fourth order amplitudes of several tens of metres, typical of ‘icehouse’ settings, cause atoll drowning at subsidence rates where atolls subject to fourth order amplitude of only a few metres, typical of ‘greenhouse’ settings, can keep up with the rising sea‐level. In the resultant strata, vertical facies belts are less well developed but horizontally extensive facies bands are more prominent. High fourth order amplitudes (up to 80 m) without sufficient third order scale subsidence will not lead to drowning, however, as the platform can recover in each fourth order lowstand. These results suggest that atolls might be easier to drown in ‘icehouse’ rather than in ‘greenhouse’ conditions but only in situations with suitably high rates of longer‐term relative sea‐level rise or sufficient lag times.

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

Geochemical characteristics of accreted material beneath the Pozanti-Karsanti ophiolite, Turkey: Intra-oceanic detachment, assembly and obduction

The mid- to late Cretaceous sub-ophiolitic dynamothermal metamorphic sole and the underlying unmetamorphosed Aladag melange, defined here as the Aladag accretionary complex, were accreted to the base of the Pozanti-Karsanti ophiolite in southern Turkey during intra-oceanic subduction, transport and final obduction of the ophiolite onto the Menderes-Taurus block. Geological, geochemical and structural investigations of the dynamothermal metamorphic sole and melange indicate that these units represent a progression of high to low temperature accreted appendages to the base of the Pozanti-Karsanti ophiolite formed within the Neo-Tethyan ocean in the mid to late Cretaceous. Intra-oceanic detachment of the Pozanti-Karsanti ophiolite appears to have begun in the vicinity of ocean islands generated at an off-axis plume or at a plume-centered spreading ridge within Neo-Tethys during the early late Cretaceous. During the early stages of the intra-oceanic subduction, the dynamothermal metamorphic sole formed through accretion of portions of the downgoing oceanic slab to the base of the Pozanti-Karsanti ophiolite. This ophiolite formed the forearc basement and leading edge of the southerly vergent upper plate. The highest temperature accretion to the base of the overthrust ophiolite occurred at ∼90–94 Ma, and involved dominantly OIB-like alkali basalts metamorphosed under lower to upper amphibolite facies conditions. Subsequently, because of decreasing temperature and pressure and continued subduction of the oceanic crust unaffected by intra-plate volcanism, tholeiitic MORBs and their open ocean pelagic cover were metamorphosed and accreted to the base of the amphibolite facies rocks under greenschist facies conditions. Formation of the greenschist facies rocks was succeeded by igneous activity in which unmetamorphosed mafic to intermediate dyke swarms intruded the ophiolite and dynamothermal metamorphic sole, apparently due to a ridge subduction event. Later, low-temperature accretion occurred during intra-oceanic subduction and final emplacement of the ophiolite forearc basement onto the Menderes-Taurus block. This is recorded by development of the Aladag melange complex accreted to the base of the higher-temperature metamorphic sole. The melange is composed of three major thrust-fault-bounded tectonic packages, each of which has a different block and matrix lithology, geochemical signature and deformation style. The geochemical analyses of the pelitic protoliths in the metamorphic sole and pelitic matrix in the Aladag melange complex suggest that the sediments accreted to the base of the overriding plate in the early stages were primarily derived from open-ocean pelagic sediments and juvenile oceanic island-arc volcanic sources, whereas the sediments accreted in the relatively later stages were derived from mixed sources that included mafic/oceanic and felsic/continental sources. These were probably orogenic in nature and presumably formed as the forearc encroached on the Menderes-Taurus stable margin. During its final emplacement and obduction, the Pozanti-Karsanti ophiolite was thrust onto the northward-facing Devonian-early Cretaceous Menderes-Taurus carbonate margin. These high- to low-temperature accreted packages and continental margin sediments are strongly folded and disrupted along southward-directed thrust surfaces and now represent an allochthonous to para-autochthonous sequence of thrust sheets resting on the eastern Tauride autochthon.

Oceanic crust of the Grenada Basin in the Southern Lesser Antilles Arc Platform

Seismic refraction data permit the southern Lesser Antilles arc and surrounding regions to be divided by the velocity of their basement. We propose that high‐velocity basement of the arc platform beneath the Grenadine islands and below a part of the Tobago Trough forearc basin is oceanic and continuous and was originally connected with oceanic crust of the Grenada Basin. Low‐velocity basements of the Tobago terrane and the arc platform from St. Vincent north lie south and north, respectively, of the high‐velocity basement of the arc platform. An oceanic origin of this high‐velocity crust in the Grenadines is argued to be more plausible than an origin as unroofed lower arc crust. The segment of probable oceanic crust in the arc platform was greatly uplifted during development of the present island arc, mainly in late Neogene time, relative to the Grenada Basin and Tobago Trough. Accepting the proposition of shallow oceanic crust in the Grenadines, early middle Eocene and possibly older pillow basalts of Mayreau, the oldest rock unit of the southern Lesser Antilles arc platform, may be an exposure of such basement. Major and minor element compositions of Mayreau Basalt are indicative of a spreading rather than arc origin. The stratigraphy of the pillow basalts indicates extrusion in an open marine environment, distant or shielded from sources of arc or continental sediment, followed by a period of pelagic sedimentation above the carbonate compensation depth. The Eocene basalt and pelagic cover formed a relatively deep floor of a marine basin in which arc‐derived turbidites and pelagic sediments accumulated over the succeeding 25–30 ma. Such basalts thus indicate a probable spreading origin of the Grenada Basin and an age of cessation of spreading in the region of Mayreau in Eocene time. The configuration of the Eocene basin and the direction of spreading, however, are unknowns. Regional structural relationships imply the spreading was probably backarc, an origin also hinted at by Ce/Zr ratios of Mayreau Basalt. Although the Aves Ridge probably was the remnant arc, the existence and position of an early middle Eocene frontal arc are unresolved. The early Paleogene tectonic architecture of the southeastern Caribbean differed substantially from that of the Neogene.