Stratigraphic Investigations into the Late Miocene-Early Pliocene of the Northern Aorangi Range, Wairarapa

<p>The late Miocene-early Pliocene geology of the Makara and Ruakokoputuna Valleys in the northern Aorangi Range, south-east Wairarapa, is described in detail. In this area, a succession of Neogene sedimentary units laps onto basement rocks of Cretaceous age, and late Miocene-early Pliocene stratigraphy varies markedly, from bathyal mudstone to high energy coastal environments, over distances of only a few kilometres. Sections were measured at four key locations, which provided reference sites for stratigraphic changes across the study area. Additional detailed field mapping was carried out around Te Ahitaitai Ridge. Depositional environments were interpreted using grain size analysis, macrofossil and foraminiferal assemblages, and palynology. Foraminiferal biostratigraphy was used to constrain the ages of samples. Data obtained by these methods were combined with previous authors’ work to produce a synthesis map, unit correlations, and geological cross-sections of the Makara and Ruakokoputuna Valleys. Late Miocene-early Pliocene geological history is interpreted, and a depositional model is proposed to explain the presence of giant cross-beds in the Clay Creek Limestone. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially laterally equivalent, while the overlying Makara Greensand is shown to be a diachronous unit which ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) in age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke Groups, and provides new insights into regional geological history. The late Miocene-early Pliocene stratigraphy records a history of regional subsidence, punctuated by episodes of deformation which caused localised uplift and erosion. Previous seismic imaging studies identified one such episode of accelerated crustal shortening and deformation in the Wairarapa region near the Miocene-Pliocene boundary. The Clay Creek Limestone has proven to be a useful marker horizon for constraining the timing and style of deformation, which is interpreted to have occurred prior to 7.2 Ma. Major differences in stratigraphy between the upthrown and downthrown sides of the Mangaopari Fault indicate that the fault was active during this deformational episode. Lithostratigraphic units from the study area have been correlated with units in other parts of the Wairarapa, and these correlations suggest that late Miocene deformation in the region may have propagated from south to north.</p>

Stratigraphic Investigations into the Late Miocene-Early Pliocene of the Northern Aorangi Range, Wairarapa

<p>The late Miocene-early Pliocene geology of the Makara and Ruakokoputuna Valleys in the northern Aorangi Range, south-east Wairarapa, is described in detail. In this area, a succession of Neogene sedimentary units laps onto basement rocks of Cretaceous age, and late Miocene-early Pliocene stratigraphy varies markedly, from bathyal mudstone to high energy coastal environments, over distances of only a few kilometres. Sections were measured at four key locations, which provided reference sites for stratigraphic changes across the study area. Additional detailed field mapping was carried out around Te Ahitaitai Ridge. Depositional environments were interpreted using grain size analysis, macrofossil and foraminiferal assemblages, and palynology. Foraminiferal biostratigraphy was used to constrain the ages of samples. Data obtained by these methods were combined with previous authors’ work to produce a synthesis map, unit correlations, and geological cross-sections of the Makara and Ruakokoputuna Valleys. Late Miocene-early Pliocene geological history is interpreted, and a depositional model is proposed to explain the presence of giant cross-beds in the Clay Creek Limestone. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially laterally equivalent, while the overlying Makara Greensand is shown to be a diachronous unit which ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) in age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke Groups, and provides new insights into regional geological history. The late Miocene-early Pliocene stratigraphy records a history of regional subsidence, punctuated by episodes of deformation which caused localised uplift and erosion. Previous seismic imaging studies identified one such episode of accelerated crustal shortening and deformation in the Wairarapa region near the Miocene-Pliocene boundary. The Clay Creek Limestone has proven to be a useful marker horizon for constraining the timing and style of deformation, which is interpreted to have occurred prior to 7.2 Ma. Major differences in stratigraphy between the upthrown and downthrown sides of the Mangaopari Fault indicate that the fault was active during this deformational episode. Lithostratigraphic units from the study area have been correlated with units in other parts of the Wairarapa, and these correlations suggest that late Miocene deformation in the region may have propagated from south to north.</p>

The Neogene seismic stratigraphy and uplift history of the Otago Shelf, New Zealand

<p>The Otago continental shelf is a prospective petroleum area on the east side of the South Island New Zealand. During the Neogene it evolved from a post-rift to passive margin as giant progrades extended eastward across the shelf, fed by tectonic uplift and erosion of the Southern Alps to the west. Seismic reflection profiles reveal an uplifted limestone horizon near the Dunedin Volcano. This may be caused by a buoyant load under the lithosphere and can be spatially and temporally linked to the Dunedin Volcano and geophysical anomalies in the area. This thesis utilises 2D and 3D seismic data to map Neogene sequence boundaries over the Otago Shelf. Seven such sequence boundaries have been mapped based on distinctive seismic characteristics above and below these surfaces. These surfaces have been tied to nearby petroleum and Integrated Ocean Drilling Project wells using biostratigraphic data and then used to generate a series of isopach and depth maps that document the Neogene evolution of this margin. The maps depict the deposition of Neogene sediment and provide age constraints to structural events in the basin such as the uplift near Dunedin and fault movement on the Endeavour High. The maps are then used to develop a lithospheric flexure model where uplift is interpreted to have been caused by asthenospheric upwelling beneath Dunedin. The model provides insight into the conditions that led to the flexure of the lithosphere, specifically the elastic thickness of the plate and the magnitude and depth distribution of buoyant intrusive material that fed the Dunedin Volcano. Asthenospheric upwelling explains elevated heat flow around Dunedin and would result in enhanced petroleum maturity. This highlights the potential for petroleum generation in source rocks immediately offshore from Dunedin.</p>

The Neogene seismic stratigraphy and uplift history of the Otago Shelf, New Zealand

<p>The Otago continental shelf is a prospective petroleum area on the east side of the South Island New Zealand. During the Neogene it evolved from a post-rift to passive margin as giant progrades extended eastward across the shelf, fed by tectonic uplift and erosion of the Southern Alps to the west. Seismic reflection profiles reveal an uplifted limestone horizon near the Dunedin Volcano. This may be caused by a buoyant load under the lithosphere and can be spatially and temporally linked to the Dunedin Volcano and geophysical anomalies in the area. This thesis utilises 2D and 3D seismic data to map Neogene sequence boundaries over the Otago Shelf. Seven such sequence boundaries have been mapped based on distinctive seismic characteristics above and below these surfaces. These surfaces have been tied to nearby petroleum and Integrated Ocean Drilling Project wells using biostratigraphic data and then used to generate a series of isopach and depth maps that document the Neogene evolution of this margin. The maps depict the deposition of Neogene sediment and provide age constraints to structural events in the basin such as the uplift near Dunedin and fault movement on the Endeavour High. The maps are then used to develop a lithospheric flexure model where uplift is interpreted to have been caused by asthenospheric upwelling beneath Dunedin. The model provides insight into the conditions that led to the flexure of the lithosphere, specifically the elastic thickness of the plate and the magnitude and depth distribution of buoyant intrusive material that fed the Dunedin Volcano. Asthenospheric upwelling explains elevated heat flow around Dunedin and would result in enhanced petroleum maturity. This highlights the potential for petroleum generation in source rocks immediately offshore from Dunedin.</p>

The Quaternary Kurobegawa Granite: an example of a deeply dissected resurgent pluton

The Quaternary Kurobegawa Granite, central Japan, is not only the youngest known granitic pluton exposed on the Earth’s surface, it is one of few localities where both Quaternary volcanics and related plutons are well exposed. Here, we present new zircon U–Pb ages together with whole rock and mineral geochemical data, revealing that the Kurobegawa Granite is a resurgent pluton that was emplaced following the caldera-forming eruption of the Jiigatake Volcanics at 1.55 ± 0.09 Ma. Following the eruption, the remnant magma chamber progressively cooled forming the voluminous Kurobegawa pluton in the upper crust (~ 6 km depth) until ~ 0.7 Ma when resurgence caused rapid uplift and erosion in the region. This is the first study to document the detailed spatiotemporal evolution of resurgent pluton for a Quaternary caldera system. Our new findings may contribute significantly to understanding the fate of active caldera systems that can produce supereruptions.

From marginal outcrops to basin interior: a new perspective on the sedimentary evolution of the eastern Pannonian Basin

Sedimentary successions exposed at basin margins as a result of late-stage inversion, uplift and erosion usually represent only a limited portion of the entire basin fill; thus, they are highly incomplete records of basin evolution. Small satellite basins, however, might have the potential of recording more complete histories. The late Miocene sedimentary history of the Șimleu Basin, a north-eastern satellite of the vast Pannonian Basin, was investigated through the study of large outcrops and correlative well-logs. A full transgressive–regressive cycle is reconstructed, which formed within a ca. 1 million-year time frame (10.6–9.6 Ma). The transgressive phase is represented by coarse-grained deltas overlain by deep-water lacustrine marls. Onset of the regressive phase is indicated by sandy turbidite lobes and channels, followed by slope shales, and topped by stacked deltaic lobes and fluvial deposits. The deep- to shallow-water sedimentary facies are similar to those deposited in the central, deep part of the Pannonian Basin. The Șimleu Basin is thus a close and almost complete outcrop analogue of the Pannonian Basin’s lacustrine sedimentary record known mainly from subsurface data, such as well-logs, cores and seismic sections from the basin interior. This study demonstrates that deposits of small satellite basins may reflect the whole sequence of processes that shaped the major basin, although at a smaller spatial and temporal scale.

Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic

The geology of North-East Greenland (70–78°N) exposes unique evidence of the basin development between the Devonian collapse of the Caledonian Orogen and the extrusion of volcanics at the Paleocene–Eocene transition during break-up of the North-East Atlantic. Here we pay special attention to unconformities in the stratigraphic record – do they represent periods of stability and non-deposition or periods of subsidence and accumulation of rocks followed by episodes of uplift and erosion? To answer that and other questions, we used apatite fission-track analysis and vitrinite reflectance data together with stratigraphic landscape analysis and observations from the stratigraphic record to study the thermo-tectonic history of North-East Greenland. Our analysis reveals eight regional stages of post-Caledonian development: (1) Late Carboniferous uplift and erosion led to formation of a sub-Permian peneplain covered by coarse siliciclastic deposits. (2) Middle Triassic exhumation led to removal of a thick cover including a considerable thickness of upper Carboniferous – Middle Triassic rocks and produced thick siliciclastic deposits in the rift system. (3) Denudation at the transition between the Early and Middle Jurassic affected most of the study area outside the Jameson Land Basin and produced a weathered surface above which Middle–Upper Jurassic sediments accumulated. (4) Earliest Cretaceous uplift and erosion along the rifted margin and further inland accompanied the Mesozoic rift climax and produced coarse-grained sedimentary infill of the rift basins. (5) Mid-Cretaceous uplift and erosion initiated removal of Cretaceous post-rift sediments that had accumulated above the Mesozoic rifts and their hinterland, leading to cooling of Mesozoic sediments from maximum palaeotemperatures. (6) End-Eocene uplift was accompanied by faulting and intrusion of magmatic bodies and resulted in extensive mass wasting on the East Greenland shelf. This event initiated the removal of a thick post-rift succession that had accumulated after break-up and produced a peneplain near sea level, the Upper Planation Surface. (7) Late Miocene uplift and erosion, evidenced by massive progradation on the shelf, resulted in the formation of the Lower Planation Surface by incision below the uplifted Upper Planation Surface. (8) Early Pliocene uplift raised the Upper and the Lower Planation Surfaces to their present elevations of about 2 and 1 km above sea level, respectively, and initiated the formation of the present-day landscape through fluvial and glacial erosion. Additional cooling episodes of more local extent, related to igneous activity in the early Eocene and in the early Miocene, primarily affected parts of northern Jameson Land. The three earliest episodes had a profound impact beyond Greenland and accompanied the fragmentation of Pangaea. Younger episodes were controlled by plate-tectonic processes, possibly including dynamic support from the Iceland Plume. Our results emphasise that gaps in the stratigraphic record often reflect episodes of kilometre-scale vertical movements that may result from both lithospheric and sub-lithospheric processes.

New Perspectives on the Stratigraphy of the Andaman Trough, offshore North Sumatra, Indonesia. Utilising Modern Quantitative Biostratigraphical Analysis, Integrated with Newly Acquired 3D Multi Client Seismic Data

The Andaman Trough, located offshore North Sumatra is currently defined as an emerging basin for exploration. Its location primarily in a remote deep-water environment has resulted in limited well data being acquired to date and although there has historically been abundant seismic data, imaging of pre-Miocene stratigraphy has been poor. New seismic data, including the regional PGS NSMC3D and proprietary and multi-client 2D reprocessed data, combined with high resolution biostratigraphical analysis, has enabled extrapolation of the stratigraphy from the well explored and established shelfal areas down into the deep-water areas. To establish the high-resolution stratigraphic framework, paleo-environment, and paleo-climate for the well penetrations in the Andaman Trough, re-evaluation of quantitative and semi-quantitative abundance charts based on nannofossil, micropaleontology, and palynology zonation and sequences was conducted. Integration of this updated biostratigraphic analysis with interpretation from the modern regional seismic datasets enabled the identification of and confirmation of sequence boundaries and flooding surfaces across the Andaman Trough. Insights into timing of rifting, uplift, and erosion were made, as well as an interpretation of depositional environments, paleo-bathymetry and paleo-climate throughout the Andaman Trough. Significant findings include the chronostratigraphic separation of Late Oligocene Parapat fluvialtile deposits from the overlying Bampo marine turbidites, absent or incomplete Bampo Formation penetrated by some wells, as well as the delineation of a previously unidentified Eocene unconformity and revised timing of basin formation. Further insights into source rock development for the Eocene stratigraphic package were also developed.

Central- and North-East Greenland Rifted Margin Composite Tectono-Sedimentary Element, From Onshore East Greenland to the Greenland Sea

The Devonian to lower Eocene Central-East and NE Greenland Composite Tectono-Sedimentary Element CTSE) is a part of the North-East Atlantic rift system. East and NE Greenland geology is therefore analogues to that of the prolific basins on the conjugate Atlantic margin and in the North Sea in many respects. None the less, hydrocarbon discoveries remain. The presence of world-class source rocks, reservoirs and seals, together with large structures, may suggest an East and NE Greenland petroleum potential, however. The TSE was established through Devonian - Carboniferous, Permian - Triassic and Jurassic - Cretaceous rifting interspersed by periods of uplift and post-rift sagging. Subsequently, Paleocene - Eocene magma-rich rifting accompanied the North-East Atlantic break-up. Depositional environments through time varied in response to the changing tectonism and climate. None-marine deposition dominated until the end of the Triassic, only interrupted by marine sedimentation during Late Permian - Early Triassic times. Subsequently, marine conditions prevailed during the Jurassic and Cretaceous. Volumetric series of basalt erupted over most of the CTSE during the latest Paleocene - early Eocene following a significant latest Cretaceous - Paleocene regression, uplift and erosion event. Since the Eocene, denudation pulses have removed much of these basalts uniquely exposing the up to 17 km strata of the CTSE.

The stratigraphic record of continental breakup, offshore NW Australia

Continental breakup involves a transition from rapid, fault-controlled syn-rift subsidence to relatively slow, post-breakup subsidence induced lithospheric cooling. Yet the stratigraphic record of many rifted margins contain syn-breakup unconformities, indicating episodes of uplift and erosion interrupt this transition. This uplift has been linked to mantle upwelling, depth-dependent extension, and/or isostatic rebound. Deciphering the breakup processes recorded by these unconformities and their related rock record is difficult because associated erosion commonly removes the strata that help constrain the onset and duration of uplift. We examine three major breakup-related unconformities and intervening rock record in the Lower Cretaceous succession of the Gascoyne and Cuvier margins, offshore NW Australia, using seismic reflection and borehole data. These data show the breakup unconformities are disconformable (non-erosive) in places and angular (erosive) in others. Our recalibration of palynomorph ages from rocks underlying and overlying the unconformities shows: (i) the lowermost unconformity developed between 134.98–133.74 Ma (Intra-Valanginian), probably during the localisation of magma intrusion within continental crust and consequent formation of continent-ocean transition zones (COTZ); (2) the middle unconformity formed between ~134–133 Ma (Top Valanginian), possibly coincident with breakup of continental crust and generation of new magmatic (but not oceanic) crust within the COTZs; and (iii) the uppermost unconformity likely developed between ~132.5–131 Ma (i.e. Intra-Hauterivian), coincident with full breakup of continental lithosphere and the onset of seafloor spreading. During unconformity formation, uplift was focused along the continental rift flanks, likely reflecting landward flow of lower crustal and/or lithospheric mantle from beneath areas of localised extension towards the continent (i.e. depth-dependent extension). Our work supports the growing consensus that the ‘breakup unconformity’ is not always a single stratigraphic surface marking the onset of seafloor spreading; multiple unconformities may form and reflect a complex history of uplift and subsidence during the development of continent-ocean transition.