Late Pleistocene Tephrostratigraphy of the Eastern Bay of Plenty Region, New Zealand

<p>This thesis has produced the compilation of a complete tephrostratigraphic record of the eastern Bay of Plenty, New Zealand. About fifty Late Pleistocene tephras (i.e. those older than the Rotoiti eruption), ranging in age from c. 600 to 50 ka, are recorded in a terrestrial sequence of loess and paleosols in the eastern Bay of Plenty. Tephra correlations are based on the distinctive physical characteristics of the airfall beds and confirmed by microprobe analysis of glass shards ("fingerprinting"). Chemical analysis of hornblendes and titanomagnetites is used as a supplementary correlation tool where the tephras are too weathered to retain glass. The eastern bay of Plenty deposits are divided into seven subgroups with their boundaries marked either by major tephras or by significant changes in the paleo-climate indicator deposits such as loess and paleosols. These subgroups, and their estimated age ranges, are: Age control on the eastern Bay of Plenty tephras has been obtained by fitting the paleoclimatic information inferred from field observations to the Low Latitude Stack (LLS) and SPECMAP oxygen isotope curves, with correlations to a few well dated eruptives providing key time planes within this record; in particular, the Mamaku Ignimbrite (correlates to the Kutarere Tephra), and the Kaingaroa (Kaingaroa), Matahina (Matahina) and Rangitaiki (Kohioawa) Ignimbrites. Tentative correlations of several eastern Bay of Plenty tephras to the western, coastal central, and Southeast-central Bay of Plenty areas (Tauranga Matata cliffs and Reporoa, respectively) have been achieved. Three additional subgroups are proposed: the Welcome Bay (with at least 6 tephras) in the west, the Ohinekoao (14 tephras) in the coastal central, and the Reihana (13 tephras) in the southeast-central Bay of Plenty; all of which overlap in time with the eastern Bay of Plenty stratigraphy. The tephras recorded in the Bay of plenty have been used to estimate the ages of formation and uplift rates for many of the landforms that are observed throughout the region. A tectonic regime of subsidence in the west towards Tauranga, block faulting on either side of the subsiding Whakatane Graben in the central Bay of Plenty, and further large scale block faulting towards the far eastern margin of the Bay of Plenty has been proposed. Activity at the Okataina Volcanic Centre is now thought to have initiated at or before c. 370 ka, with the eruption of the Paerata Tephra. This tephra has a distribution pattern consistent with an Okataina source, and contains abundant cummingtonite, which is a signature mineral within tephras from the Okataina Volcanic Centre during the late Quaternary time period. However, the much older, but less well understood, Reeves-A and Wilson Tephras - both with estimated ages of c. 0.5 Ma - also contain cummingtonite, which indicates that activity may have been initiation at a much earlier time, or that a volcanic centre other than Okataina has produced cummingtonite. Activity in the Rotorua Volcanic Centre prior to the eruption of the Mamaku Ignimbrite is also indicated, as is activity at the Reporoa Volcanic Centre prior to the Kaingaroa Ignimbrite eruption.</p>

Late Pleistocene Tephrostratigraphy of the Eastern Bay of Plenty Region, New Zealand

<p>This thesis has produced the compilation of a complete tephrostratigraphic record of the eastern Bay of Plenty, New Zealand. About fifty Late Pleistocene tephras (i.e. those older than the Rotoiti eruption), ranging in age from c. 600 to 50 ka, are recorded in a terrestrial sequence of loess and paleosols in the eastern Bay of Plenty. Tephra correlations are based on the distinctive physical characteristics of the airfall beds and confirmed by microprobe analysis of glass shards ("fingerprinting"). Chemical analysis of hornblendes and titanomagnetites is used as a supplementary correlation tool where the tephras are too weathered to retain glass. The eastern bay of Plenty deposits are divided into seven subgroups with their boundaries marked either by major tephras or by significant changes in the paleo-climate indicator deposits such as loess and paleosols. These subgroups, and their estimated age ranges, are: Age control on the eastern Bay of Plenty tephras has been obtained by fitting the paleoclimatic information inferred from field observations to the Low Latitude Stack (LLS) and SPECMAP oxygen isotope curves, with correlations to a few well dated eruptives providing key time planes within this record; in particular, the Mamaku Ignimbrite (correlates to the Kutarere Tephra), and the Kaingaroa (Kaingaroa), Matahina (Matahina) and Rangitaiki (Kohioawa) Ignimbrites. Tentative correlations of several eastern Bay of Plenty tephras to the western, coastal central, and Southeast-central Bay of Plenty areas (Tauranga Matata cliffs and Reporoa, respectively) have been achieved. Three additional subgroups are proposed: the Welcome Bay (with at least 6 tephras) in the west, the Ohinekoao (14 tephras) in the coastal central, and the Reihana (13 tephras) in the southeast-central Bay of Plenty; all of which overlap in time with the eastern Bay of Plenty stratigraphy. The tephras recorded in the Bay of plenty have been used to estimate the ages of formation and uplift rates for many of the landforms that are observed throughout the region. A tectonic regime of subsidence in the west towards Tauranga, block faulting on either side of the subsiding Whakatane Graben in the central Bay of Plenty, and further large scale block faulting towards the far eastern margin of the Bay of Plenty has been proposed. Activity at the Okataina Volcanic Centre is now thought to have initiated at or before c. 370 ka, with the eruption of the Paerata Tephra. This tephra has a distribution pattern consistent with an Okataina source, and contains abundant cummingtonite, which is a signature mineral within tephras from the Okataina Volcanic Centre during the late Quaternary time period. However, the much older, but less well understood, Reeves-A and Wilson Tephras - both with estimated ages of c. 0.5 Ma - also contain cummingtonite, which indicates that activity may have been initiation at a much earlier time, or that a volcanic centre other than Okataina has produced cummingtonite. Activity in the Rotorua Volcanic Centre prior to the eruption of the Mamaku Ignimbrite is also indicated, as is activity at the Reporoa Volcanic Centre prior to the Kaingaroa Ignimbrite eruption.</p>

Chapter 24 Carboniferous–Neogene tectonic evolution of the Fennoscandian transition zone, southern Sweden

The Fennoscandian transition zone, including the Sorgenfrei–Tornquist Zone, constitutes the weakened and faulted bedrock between a craton, including the ancient continent Baltica to the north, and the boundary between Baltica and Avalonia along the Trans-European Fault Zone to the south. Early Permian subsidence in this transition zone resulted in the development of various basins and the initiation of a more or less continuous Permian–Paleogene depositional cycle. In southwestern Sweden, magmatic activity associated with transtensional deformation along the Sorgenfrei–Tornquist Zone prevailed during the Late Carboniferous–Permian. However, the transition zone is dominated by a Mesozoic sedimentary rock succession displaying both hiatuses and great lateral variability in composition and thickness, which can be related to several tectonic events including the progressive break-up of Pangaea. Much of the deposition took place in continental, coastal and shallow-marine settings. Early–Middle Jurassic block faulting and basanitic or melanephelinitic volcanism, as well as Late Cretaceous tectonic inversion along the Sorgenfrei–Tornquist Zone, related to a changeover to a predominantly compressive tectonic regime coeval with the Alpine orogeny, significantly influenced the depositional setting. Subsequent Paleogene–Neogene regional uplift of the southwestern margin of Baltica resulted in significant erosion of the bedrock.

Remote Predictive Mapping 7. The Use of Topographic–Bathymetric Lidar to Enhance Geological Structural Mapping in Maritime Canada

An airborne topo-bathymetric lidar survey was conducted at Cape John, on the north shore of Nova Scotia, Canada, using the shallow water Leica AHAB Chiroptera II sensor. The survey revealed new bedrock features that were not discovered using previous mapping methods. A thick blanket of glacial till covers the bedrock on land, and outcrops are exposed only along the coastal cliffs and offshore reefs. The seamless landseabed digital elevation model produced from the lidar survey revealed significant bedrock outcrop offshore where ocean currents have removed the glacial till, a significant finding that was hitherto hidden under the sea surface. Several reefs were identified offshore as well as a major fold structure where block faulting occurs along the limbs of the fold. The extension of the Malagash Mine Fault located ~10 km west of Cape John is proposed to explain the local folding and faulting visible in the submerged outcrops. The extension of this fault is partially visible on land, where it is obscured by glacial till, and its presence is supported by the orientation of submerged bedding and lineaments on both the south and north sides of Cape John. This paper demonstrates how near-shore high-resolution topography from bathymetric lidar can be used to enhance and refine geological mapping.RÉSUMÉUn levé lidar topo-bathymétrique été réalisé à Cape John, sur la rive nord de la Nouvelle-Écosse, Canada, en utilisant un capteur Leci AHAB Chiroptera II. Ce levé a permis de repérer des affleurements que les méthodes de cartographie plus anciennes n’avaient pu détecter. Une épaisse couche de till glaciaire recouvre la roche en place sur le continent, et la roche affleure seulement le long des falaises côtières et des récifs côtiers. Le modèle numérique de dénivelé en continu terres et fonds marins obtenu par le levé lidar a révélé l’existence d’affleurement rocheux considérables au large des côtes, là où les courants océaniques ont emporté le till glaciaire, une découverte importante demeurée cachée sous la surface de la mer jusqu’alors. Plusieurs récifs ont été identifiés au large des côtes, ainsi qu’une structure de pli majeure, à l’endroit où se produit un morcellement en blocs le long des flancs du pli. Une extension de la faille de la mine Malagash situé ~ 10 km à l’ouest de Cape John est proposé pour expliquer les plis et les failles locaux visibles dans les affleurements submergés. L’extension de cette faille est partiellement visible sur la terre, voilée par le till, et sa présence est étayée par l’orientation de la stratification et des linéaments submergés tant du côté sud que nord de Cape John. Cet article montre comment la topographie haute résolution du lidar bathymétrique peut être utilisée pour améliorer et affiner la cartographie géologique.

Apatite fission-track evidence for regional exhumation in the subtropical Eocene, block faulting, and localized fluid flow in east-central Alaska

The origin and antiquity of the subdued topography of the Yukon–Tanana Upland (YTU), the physiographic province between the Denali and Tintina faults, are unresolved questions in the geologic history of interior Alaska and adjacent Yukon. We present apatite fission-track (AFT) results for 33 samples from the 2300 km2 western Fortymile district in the YTU in Alaska and propose an exhumation model that is consistent with preservation of volcanic rocks in valleys that requires base level stability of several drainages since latest Cretaceous–Paleocene time. AFT thermochronology indicates widespread cooling below ∼110 °C at ∼56–47 Ma (early Eocene) and ∼44–36 Ma (middle Eocene). Samples with ∼33–27, ∼19, and ∼10 Ma AFT ages, obtained near a major northeast-trending fault zone, apparently reflect hydrothermal fluid flow. Uplift and erosion following ∼107 Ma magmatism exposed plutonic rocks to different extents in various crustal blocks by latest Cretaceous time. We interpret the Eocene AFT ages to suggest that higher elevations were eroded during the Paleogene subtropical climate of the subarctic, while base level remained essentially stable. Tertiary basins outboard of the YTU contain sediment that may account for the required >2 km of removed overburden that was not carried to the sea by the ancestral Yukon River system. We consider a climate driven explanation for the Eocene AFT ages to be most consistent with geologic constraints in concert with block faulting related to translation on the Denali and Tintina faults resulting from oblique subduction along the southern margin of Alaska.

STUDI POTENSI MIGAS DENGAN METODE GAYABERAT DI LEPAS PANTAI UTARA JAKARTA

Anomali Bouguer dapat dibagi kedalam dua kelompok yaitu: Anomali gayaberat rendah terbentuk pada kisaran nilai 15 mGal hingga -40 mGal sebagai rendahan sinklin. Anomali gayaberat tinggi terbentuk pada kisaran nilai 40 mGal hingga 60 mGal sebagai tinggian antiklin. Formasi batuan dari atas hingga bawah sebagai berikut: Formasi Cisubuh rapat massa batuan 2.5 gr/cm³ ketebalan pada penampang ±1400 meter. Formasi Parigi rapat massa batuan 2.7 gr/cm³ ketebalan ± 400 meter. Formasi Cibulakan rapat massa batuan 2.6 gr/cm³ ketebalan ± 1600 meter. Formasi Jatibarang rapat massa 2.8 gr/cm³ ketebalan ± 1000 meter. Batuan reservoir didominasi lensa-lensa batupasir Formasi Cibulakan Atas, Cibulakan Bawah serta batugamping Formasi Parigi dan batupasir Formasi Talangakar. Batuan induk migas adalah serpih lakustrin halus Anggota Cibulakan Bawah (Formasi Talang Akar). Tinggian batuan reservoir pada anomali sisa antara 0 mGal hingga 16 mGal dan kedalaman pada penampang ± 1500 meter dengan rapat massa batuan 2.7 gr/cm³ Sesar normal terbentuk arah Utara-Selatan dan sesar naik arah Timur-Barat dikontrol oleh pematahan bongkah pada batuan alas metamorf dengan rapat massa 3.0 gr/cm³. Kata kunci: gayaberat, antiklin, anomali sisa, lepas pantai. Bouguer anomaly can be grouped into two parts: Low Gravity anomaly formed at 15 mGal to 40 mGal as syncline lower. High gravity anomaly formed at 40 mGal to 60 mGal as anticline high. Rock formation from the top to the bottom as follows: Cisubuh Formation rock of density with 2.5 gr / cm³ thickness at section of ± 1400 metre. Parigi Formation rock density of 2.7 gr / cm³ thicknees ± 400 metre. Cibulakan Formation density with 2.6 gr / cm³ thickness ± 1600 metre. Jatibarang Formation with density 2.8 gr / cm³ of thickness ± 1000 metre. Reservoir rock is dominated by lens of sandstone upper Cibulakan Formation, Lower Cibulakan and also Parigi Formation limestone and Talangakar Formation sandstone. Sourced rock of oil and gas from shales lacustrine of Cibulakan Lower or Talang Akar Formation. High Rocks reservoir at recidual anomaly range from 0 mGal to 16 mGal at section deepness ± 1500 metre with density of 2.7 gr / cm³, formed by normal fault of Northern-Southern direction and reverse fault Eastern-Western direction controlled by block faulting metamorphics bedrock with density of 3.0 gr / cm³. Keywords: gravity, anticline, recidual anomaly, offshore.

The Permian and Triassic in the Albanian Alps

The sedimentary succession of the Permian to Middle Triassic of the Albanian Alps is described, as part of the eastern Adria passive margin towards the Tethys. A carbonate ramp deepening towards NE in present day coordinates developed during the Middle Permian and was affected by block faulting with the deposition of carbonate breccia. The Early Triassic was characterized by intense terrigenous deposition with several cobble conglomerate units up to 80 m-thick, and by oolitic carbonate shoals. The fine clastic deposition ended gradually during the earliest Anisian and a wide calcarenitic ramp occupied the area, with small local carbonate mounds. Basinward, the red nodular limestone of the Han Bulog Formation was interbedded with calcarenitic material exported from the ramp. Drowning to more open conditions occurred towards the end of the Pelsonian. Subsequently, cherty limestone and tuffitic layers spread over the entire area. Towards the end of the Ladinian, with the end of the volcanic activity, red pelagic limestone was deposited locally for a short period. By the latest Ladinian most of the area returned to shallow-water conditions, with a peritidal carbonate platform. In the Theth area, in contrast, a basin with black organic-rich dolostone and limestone developed which seems to be unique in that part of the Adria passive margin. The occurrence of cobble conglomerate units in the Lower Triassic testifies to very active block faulting and high accommodation, not yet described for the area.