Eocene to Miocene tectonostratigraphic evolution of northwest New Zealand

<p>Reinga Basin is located northwest of New Zealand, along strike structurally from Northland and has a surface area of ~150,000 km². The basin contains deformed Cretaceous and Cenozoic strata, flat unconformities interpreted as sea level-modulated erosion surfaces and is intruded by volcanics. Persistent submarine conditions and moderate water depths has led to preservation of fossil-rich bathyal sedimentary records. This thesis presents the first seismic-stratigraphic analysis tied to dredged rock samples and recent International Ocean Discovery Program (IODP) drilling. The Cenozoic tectonic evolution of Reinga Basin comprises four main phases. (1) Folding and uplift from lower bathyal water depths occurred at 56-43 Ma along West Norfolk Ridge to produce wave ravinement surfaces. This phase of deformation in Reinga Basin pre-dates tectonic events onshore New Zealand. (2) Basin-wide 39-34 Ma compression and reverse faulting exposed early to middle Eocene strata at the seabed. This phase of deformation is also observed farther south in Taranaki. (3) Oligocene uplift is recorded by late Oligocene shallow-water fauna at Site U1508, and led to a 6 Myr hiatus (34-28 Ma) associated with flat wave ravinement surfaces nearby. The unconformity is temporally associated with: normal faulting near West Norfolk Ridge that created topography of Wanganella Ridge; onset of Reinga Basin volcanism; and emplacement of South Maria Allochthon. Thin-skinned deformation and volcanism post-date thick-skinned reverse faulting and folding. The end of reverse faulting near South Maria Ridge is determined from undeformed Oligocene strata that have subsided 1500-2000 m since 36-30 Ma. (4) During the final phase of Reinga Basin deformation, South Maria Ridge subsided ~900-1900 m from middle shelf to bathyal depths from 23-19 Ma. Deformation migrated southeastwards, culminating in Northland Allochthon emplacement (23-20 Ma) and onshore arc volcanism at 23-12 Ma. Eocene onset of tectonic activity in northern New Zealand is shown to be older than previously recognised and it was broadly synchronous with other events related to subduction initiation and plate motion change elsewhere in the western Pacific.</p>

Eocene to Miocene tectonostratigraphic evolution of northwest New Zealand

<p>Reinga Basin is located northwest of New Zealand, along strike structurally from Northland and has a surface area of ~150,000 km². The basin contains deformed Cretaceous and Cenozoic strata, flat unconformities interpreted as sea level-modulated erosion surfaces and is intruded by volcanics. Persistent submarine conditions and moderate water depths has led to preservation of fossil-rich bathyal sedimentary records. This thesis presents the first seismic-stratigraphic analysis tied to dredged rock samples and recent International Ocean Discovery Program (IODP) drilling. The Cenozoic tectonic evolution of Reinga Basin comprises four main phases. (1) Folding and uplift from lower bathyal water depths occurred at 56-43 Ma along West Norfolk Ridge to produce wave ravinement surfaces. This phase of deformation in Reinga Basin pre-dates tectonic events onshore New Zealand. (2) Basin-wide 39-34 Ma compression and reverse faulting exposed early to middle Eocene strata at the seabed. This phase of deformation is also observed farther south in Taranaki. (3) Oligocene uplift is recorded by late Oligocene shallow-water fauna at Site U1508, and led to a 6 Myr hiatus (34-28 Ma) associated with flat wave ravinement surfaces nearby. The unconformity is temporally associated with: normal faulting near West Norfolk Ridge that created topography of Wanganella Ridge; onset of Reinga Basin volcanism; and emplacement of South Maria Allochthon. Thin-skinned deformation and volcanism post-date thick-skinned reverse faulting and folding. The end of reverse faulting near South Maria Ridge is determined from undeformed Oligocene strata that have subsided 1500-2000 m since 36-30 Ma. (4) During the final phase of Reinga Basin deformation, South Maria Ridge subsided ~900-1900 m from middle shelf to bathyal depths from 23-19 Ma. Deformation migrated southeastwards, culminating in Northland Allochthon emplacement (23-20 Ma) and onshore arc volcanism at 23-12 Ma. Eocene onset of tectonic activity in northern New Zealand is shown to be older than previously recognised and it was broadly synchronous with other events related to subduction initiation and plate motion change elsewhere in the western Pacific.</p>

Formation of the crater suevite sequence from the Chicxulub peak ring: A petrographic, geochemical, and sedimentological characterization

This study presents a new classification of a ∼100-m-thick crater suevite sequence in the recent International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364 Hole M0077A drill core to better understand the formation of suevite on top of the Chicxulub peak ring. We provide an extensive data set for this succession that consists of whole-rock major and trace element compositional data (n = 212) and petrographic data supported by digital image analysis. The suevite sequence is subdivided into three units that are distinct in their petrography, geochemistry, and sedimentology, from base to top: the ∼5.6-m-thick non-graded suevite unit, the ∼89-m-thick graded suevite unit, and the ∼3.5-m-thick bedded suevite unit. All of these suevite units have isolated Cretaceous planktic foraminifera within their clastic groundmass, which suggests that marine processes were responsible for the deposition of the entire M0077A suevite sequence. The most likely scenario describes that the first ocean water that reached the northern peak ring region entered through a N-NE gap in the Chicxulub outer rim. We estimate that this ocean water arrived at Site M0077 within 30 minutes after the impact and was relatively poor in rock debris. This water caused intense quench fragmentation when it interacted with the underlying hot impact melt rock, and this resulted in the emplacement of the ∼5.6-m-thick hyaloclastite-like, non-graded suevite unit. In the following hours, the impact structure was flooded by an ocean resurge rich in rock debris, which caused the phreatomagmatic processes to stop and the ∼89-m-thick graded suevite unit to be deposited. We interpret that after the energy of the resurge slowly dissipated, oscillating seiche waves took over the sedimentary regime and formed the ∼3.5-m-thick bedded suevite unit. The final stages of the formation of the impactite sequence (estimated to be &lt;20 years after impact) were dominated by resuspension and slow atmospheric settling, including the final deposition of Chicxulub impactor debris. Cumulatively, the Site M0077 suevite sequence from the Chicxulub impact site preserved a high-resolution record that provides an unprecedented window for unravelling the dynamics and timing of proximal marine cratering processes in the direct aftermath of a large impact event.

Comparison of stress orientation indicators in Chicxulub’s peak ring: Kinked biotites, basal PDFs, and feather features

ABSTRACT During hypervelocity impacts, target rocks are subjected to shock wave compression with high pressures and differential stresses. These differential stresses cause microscopic shear-induced deformation, which can be observed in the form of kinking, twinning, fracturing, and shear faulting in a range of minerals. The orientation of these shear-induced deformation features can be used to constrain the maximum shortening axis. Under the assumption of pure shear deformation, the maximum shortening axis is parallel to the maximum principal axis of stress, σ1, which gives the propagation direction of the shock wave that passed through a rock sample. In this study, shocked granitoids cored from the uppermost peak ring of the Chicxulub crater (International Ocean Discovery Program [IODP]/International Continental Drilling Project [ICDP] Expedition 364) were examined for structures formed by shearing. Orientations of kink planes in biotite and basal planar deformation features (PDFs) in quartz were measured with a U-stage and compared to a previous study of feather feature orientations in quartz from the same samples. In all three cases, the orientations of the shortening axis derived from these measurements were in good agreement with each other, indicating that the shear deformation features all formed in an environment with similar orientations of the maximum principal axis of stress. These structures formed by shearing are useful tools that can aid in understanding the deformational effects of the shock wave, as well as constraining shock wave propagation and postshock deformation during the cratering process.

Introduction

ABSTRACT This paper does not have an abstract. CONFERENCE The Large Meteorite Impacts and Planetary Evolution Conference VI (LMI VI) took place between 30 September and 3 October 2019 on the campus of the University of Brasília (UnB) in Brasília, Brazil. This series of essentially quintennial conferences has been a mainstay for three decades. It was initiated with the aim to review major research outcomes, share ideas, and fertilize new collaborations in the impact cratering and planetary science fields. The timing for LMI VI, related to the state of impact cratering research, was a good one. For example, the studies resulting from the important IODP-ICDP (International Ocean Discovery Program–International Continental Scientific Drilling Program) project, in which a deep drill core was retrieved from the peak ring of the Chicxulub impact structure—the smoking gun for the Cretaceous-Paleogene (K-Pg) boundary impact event coincident with the mass extinction at that time—were nearing completion and could be presented, in part, at LMI VI. Numerous other advances in impact research had been made in the preceding years (for example, state-of-the-art microstructural studies on accessary minerals with electron backscatter diffraction [EBSD]) and were extensively discussed at the conference. And, finally, interest in impact cratering has significantly increased in recent years, not only...

Intra-oceanic submarine arc evolution recorded in an ~1-km-thick rear-arc succession of distal volcaniclastic lobe deposits

International Ocean Discovery Program (IODP) Expedition 351 drilled a rear-arc sedimentary succession ~50 km west of the Kyushu-Palau Ridge, an arc remnant formed by rifting during formation of the Shikoku Basin and the Izu-Bonin-Mariana arc. The ~1-km-thick Eocene to Oligocene deep-marine volcaniclastic succession recovered at Site U1438 provides a unique opportunity to study a nearly complete record of intra-oceanic arc development, from a rear-arc perspective on crust created during subduction initiation rather than supra-subduction seafloor spreading. Detailed facies analysis and definition of depositional units allow for broader stratigraphic analysis and definition of lobe elements. Patterns in gravity-flow deposit types and subunits appear to define a series of stacked lobe systems that accumulated in a rear-arc basin. The lobe subdivisions, in many cases, are a combination of a turbidite-dominated subunit and an overlying debris-flow subunit. Debris flow–rich lobe-channel sequences are grouped into four, 1.6–2 m.y. episodes, each roughly the age range of an arc volcano. Three of the episodes contain overlapping lobe facies that may have resulted from minor channel switching or input from a different source. The progressive up-section coarsening of episodes and the increasing channel-facies thicknesses within each episode suggest progressively prograding facies from a maturing magmatic arc. Submarine geomorphology of the modern Mariana arc and West Mariana Ridge provide present-day examples that can be used to interpret the morphology and evolution of the channel (or channels) that fed sediment to Site U1438, forming the sequences interpreted as depositional lobes. The abrupt change from very thick and massive debris flows to fine-grained turbidites at the unit III to unit II boundary reflects arc rifting and progressive waning of turbidity current and ash inputs. This interpretation is consistent with the geochemical record from melt inclusions and detrital zircons. Thus, Site U1438 provides a unique record of the life span of an intra-oceanic arc, from inception through maturation to its demise by intra-arc rifting and stranding of the remnant arc ridge.

Using past interglacial temperature maxima to explore transgressions in modern Maldivian coral and Amphistegina bleaching thresholds

Tropical corals and Amphistegina, an example genus of symbiont-bearing larger benthic foraminifera, are presently living close to their thermal bleaching thresholds. As such, these essential reef-building organisms are vulnerable to the future prospect of more frequent sea surface temperature (SST) extremes. Exploring the earth’s paleo-climatic record, including interglacials warmer than present, may provide insights into future oceanographic conditions. We analyse foraminiferal shell geochemical compositions, from Recent surface sediments and Marine Isotope stage (MIS) 9e and MIS11c aged sediments, from the International Ocean Discovery Program Expedition 359 Site U1467 drilled in the Inner Sea of the Maldives. We illustrate through traditional (pooled) geochemical analysis (δ18O, Mg/Ca) that tropical temperatures were indeed marginally warmer during MIS9e and MIS11c in comparison to the modern ocean. Individual foraminiferal analysis (IFA) from the Recent (representing the last few hundred years) and MIS9e samples shows SSTs occasionally breached the coral bleaching threshold similarly to the modern-day. Significantly, the number of transgressions was four times higher during MIS11c, a recognised analogue for a warmer modern world. This new knowledge and novel IFA insight and application is invaluable given thermal stress is already obvious today with an increasing number of bleaching events over the last few decades.

Potential microbial contamination from drilling lubricants into subseafloor rock cores

International Ocean Discovery Program (IODP) Expedition 357: “Serpentinization and Life” drilled shallow cores into the Atlantis Massif near the Mid-Atlantic Ridge in October 2015 using seabed drills. Serpentinization and other geochemical processes occurring within the Atlantis Massif release hydrogen, methane, and other chemicals that can potentially fuel microorganisms through chemosynthesis. The subseafloor rock cores collected during IODP Exp. 357 are the first of their kind, meaning the analysis and interpretation of these samples required new methodologies, including a specialized approach for distinguishing endemic subsurface inhabitants from potential contaminants from various sources. Background samples of various potential contamination sources were collected during sampling: 109 samples of seawater collected before, during, and after drilling; 20 samples of greases and oils associated with the drilling equipment; and samples of the laboratory's ambient air. Despite the widespread usage of drilling lubricants and the importance of controlling contamination in drill-core samples for microbiological analyses, no studies to date have looked at DNA in drilling greases and oils. In this study, drilling lubricants were analyzed as possible sources of microbial contamination of subseafloor rock core samples by environmental sequencing of 16S rRNA genes. We find that microbial signatures from drilling lubricants are only found in low abundance in seafloor samples (at most a few percent of total sequence counts), with laboratory contaminants being a greater source of contamination.

Shock-deformed zircon from the Chicxulub impact crater and implications for cratering process

Large impact structures with peak rings are common landforms across the solar system, and their formation has implications for both the interior structure and thermal evolution of planetary bodies. Numerical modeling and structural studies have been used to simulate and ground truth peak-ring formative mechanisms, but the shock metamorphic record of minerals within these structures remains to be ascertained. We investigated impact-related microstructures and high-pressure phases in zircon from melt-bearing breccias, impact melt rock, and granitoid basement from the Chicxulub peak ring (Yucatán Peninsula, Mexico), sampled by the International Ocean Discovery Program (IODP)/International Continental Drilling Project (IODP-ICDP) Expedition 364 Hole M0077A. Zircon grains exhibit shock features such as reidite, zircon twins, and granular zircon including “former reidite in granular neoblastic” (FRIGN) zircon. These features record an initial high-pressure shock wave (&gt;30 GPa), subsequent relaxation during the passage of the rarefaction wave, and a final heating and annealing stage. Our observed grain-scale deformation history agrees well with the stress fields predicted by the dynamic collapse model, as the central uplift collapsed downward-then-outward to form the peak ring. The occurrence of reidite in a large impact basin on Earth represents the first such discovery, preserved due to its separation from impact melt and rapid cooling by the resurging ocean. The coexistence of reidite and FRIGN zircon within the impact melt–bearing breccias indicates that cooling by seawater was heterogeneous. Our results provide valuable information on when different shock microstructures form and how they are modified according to their position in the impact structure, and this study further improves on the use of shock barometry as a diagnostic tool in understanding the cratering process.

The Upper Cretaceous foraminiferal record of IODP Site U1512 (Great Australian Bight, Indian Ocean)

&lt;p&gt;Site U1512 was drilled during Expedition 369 of the International Ocean Discovery Program (IODP), which is located in the Great Australian Bight, southern Indian Ocean. It provides exceptional insights into the benthic foraminiferal biostratigraphy and paleoecology of a high southern latitude restricted marginal marine basin during the Late Cretaceous hot greenhouse climate and the rifting between Australia and Antarctica. The sedimentary sequence recovered at Site U1512 presents a rare record of a deep water agglutinated foraminifera (DWAF) community from the Southern High Latitudes. The Cretaceous record at Site U1512 covers the lower Turonian through Santonian (nannofossil zones UC8b to UC12/CC10b to CC16, &lt;em&gt;H. helvetica&lt;/em&gt; to &lt;em&gt;Marginotruncana&lt;/em&gt; spp. - &lt;em&gt;Planoheterohelix papula&lt;/em&gt; - &lt;em&gt;Globotruncana linneana&lt;/em&gt; planktonic foraminifera zones). Diverse benthic foraminiferal assemblages yield many new taxa that are yet to be described.&lt;/p&gt;&lt;p&gt;Agglutinated forms dominate the assemblage in most intervals. In lower to mid Turonian and Santonian strata, calcareous benthic as well as planktonic foraminifera are frequent. Abundant radiolaria are recovered from the mid Turonian, and they increase up-section and exceed 50% of the microfossil assemblage. We documented a diverse benthic foraminiferal assemblage consisting of 162 taxa (110 agglutinated and 52 calcareous). The most common taxa of the DWAF assemblage are tubular (i.e., &lt;em&gt;Kalamopsis grzybowskii,&lt;/em&gt; &lt;em&gt;Bathysiphon&lt;/em&gt; spp.) and planispiral forms (i.e., &lt;em&gt;Ammodiscus&lt;/em&gt; spp., &lt;em&gt;Haplophragmoides&lt;/em&gt; spp., &lt;em&gt;Buzasina&lt;/em&gt; sp., &lt;em&gt;Labrospira&lt;/em&gt; spp.).&lt;/p&gt;&lt;p&gt;The Turonian strata yield highly abundant &lt;em&gt;Bulbobaculites problematicus&lt;/em&gt; and &lt;em&gt;Spiroplectammina navarroana&lt;/em&gt;. The presence of the agglutinated foraminiferal marker taxa &lt;em&gt;Uvigerinammina jankoi&lt;/em&gt; and &lt;em&gt;Bulbobaculites problematicus&lt;/em&gt; provides a tie-point to the Tethyan DWAF biozonation of Geroch and Nowak (1984). The composition of foraminiferal assemblages and the increase in radiolaria abundance suggest unstable environmental conditions at Site U1512 during the early Turonian through Santonian. These characteristics refer to changes in bathymetry associated with changing ocean chemistry. Results of quantitative analyses of the benthic foraminiferal assemblages indicate a restricted paleoenvironmental regime, dictated by changes in paleobathymetry, unstable patterns in ocean circulation, and the discharge of a nearby river delta system.&lt;/p&gt;&lt;p&gt;References: Geroch, S., Nowak, K., 1984. Proposal of zonation for the Late Tithonian &amp;#8211; late Eocene. based upon arenaceous Foraminifera from the Outer Carpathians, Poland, 225-239, In: Oertli, H.J. (Ed.), Benthos &amp;#180;83; 2nd international 915 Symposium on Benthic Foraminifera, Pau (France) April 11-15, 1983, Elf Aquitaine, ESO REP and TOTAL CFP, Pau and Bordeaux.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;