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>

Bio-electrosequence interpretation of late cretaceous sediments of the Southern Bornu Basin, Nigeria

Integrated analysis that involves physical sedimentological, standard palynological and electrofacies analyses on ditch cuttings and suite of wireline logs from Gaibu–1 Well, southern Bornu were examined to identify critical sequence elements and construct a bio-sequence stratigraphical framework. Four (4) palynozones consisting of Triorites africaensis, Cretacaeiporites scabratus - Odontochitina costata, Droseridites senonicus and Syncolporites/Milfordia spp Assemblage Zones construed to be Late Cretaceous – younger successions. Nine (9) depositional sequences each with candidate maximum flooding surfaces (375, 900, 1875, 2250, 2600, 3050, 3400, 3800, 4300 m) marked by marker shales with high abundance and diversity of palynomorphs. Thus, equate with the local lithostratigraphy and global large-scale depositional cycles with candidate sequence boundaries (50, 725, 1625, 2175, 2490, 2850, 3300, 3610, 3960, 4470 m) ranging about 96.28 to 70.07 Ma. The delineated transgressive surfaces along the built sequences mark the subjected onset of marine flooding characterised with interchange of progradational to retrogradational facies. Delineated sequence elements generally show up-hole from progradational to retrogradational and aggradational that represents Lowstand Systems Tracts (LSTs), Transgressive Systems Tracts (TSTs) and Highstand Systems Tracts (HSTs) respectively. The LSTs are seen in form of prograding complex and slope fans, suggestive of good reservoirs. The TSTs consist of channel sand units and shales that depict retrogradational marine units, which could serve as both seals and source rocks for the sand units. The HSTs are made up of interplay of aggradational to progradational sediment packages that could serve as a potential source rock. The palaeoenvironmental indices depict the successions are deposited within continental to open marine settings.

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.

Depositional Environment of Deep-Water Fan Facies: A Case Study of the Middle Miocene Interval at the Kutei and North Makassar Basins

Massive exploration effort in the study area was conducted in 1996-2014 when deep-water drilling campaign found significant oil and gas discoveries but yet to optimally reach the middle Miocene deep-water sandstone reservoirs. Outcrops, well bores and 2D-seismic data had been incorporated in this study. Datum age from several taxon indicators have been utilized to correlate and unify various markers across the study area into four key biostratigraphy markers: M40, M45, M50, and M65. These four markers are at that point tied to the 2D seismic data in the act of the main horizons in conducting the seismic stratigraphy analysis over the study area not reached by wells. Identifying candidate of sub-regional sequence boundaries onshore and offshore that correspond with relative sea-level drops are the main result of this study. These results were integrated to generate the deep-water fan facies of the middle Miocene's gross depositional environment (GDE) maps, which generally show prograding succession easterly in the various shelf-breaks shifting laterally. The angle of slope and the horizontal length of the shelf-to-slope breaks significantly change from the Middle to Late Miocene until Recent time.Keywords: GDE, deep-water fan, Middle Miocene, Kutei, North Makassar.

Late Cretaceous (Turonian-Coniacian) sequence stratigraphy, sea level, and deltaic facies, Magothy Formation, U. S. Middle Atlantic Coastal Plain

ABSTRACT: The peak "hothouse" interval of the Turonian-Coniacian (93-87 Ma) is represented on the U.S. middle Atlantic Coastal Plain by sequences of the Raritan/Bass River, Magothy, and Cheesequake Formations deposited on a passive continental margin as mixed wave-, tide-, and river dominated deltas. We apply sequence stratigraphy integrated with biostratigraphy to identify and map two major sequence boundaries separating the Raritan/Bass River, Magothy, and Cheesequake Formations and four to five (Mg1, Mg2, Mg3, ?Mg4, Mg5) Magothy sequences using continuous cores, outcrops, and geophysical logs in New Jersey. We extend correlations into New York and Delaware using well logs. The Magothy sequences disconformably overlie the well-dated (>93 Ma) lower Turonian to Cenomanian marine Raritan/Bass River sequences and are disconformably overlain by the marine Cheesequake Formation, which straddles the Coniacian/Santonian boundary. A "mid-Turonian" hiatus (ca. 93-90 Ma) associated with this major disconformity is a global sequence boundary (K-Tu4) reflecting a ~ 25 m sea-level lowering based on published NJ and Russian Platform backstripping records that indicate this was a major lowering of Global Mean Sea Level (GMSL).Higher-order (~1 Myr scale) sequence boundaries bracketing Mg1-Mg5 apparently correlate with global sequences but are only associated with low-amplitude (<25 m) sea-level falls.Mapping of sequences within the Magothy Formation shows the influence of 2 to 3 moderate-sized river sources, with thickening northeastward toward Long Island, New York, and thinning southwestward toward Delaware. Thick northern depocenters contrast with the preceding Potomac Formation (Barremian-early Cenomanian) with thick southern depocenters. This seesawing of basins on the 100-300 km and 2-10+ Myr scales is due to tectonism likely from changes inmantle dynamic topography. The remarkably widespread distribution of Magothy sequences and facies indicates stability of this deltaic depositional system over ~ 4Myr despite low-amplitude (less than 25m) sea-level variations.Widespread facies correlation provides a predictable distribution of aquifer sands and confining-unit clays tied to sea-level changes on complex deltaic facies.

NEW RESULTS OF INTEGRATED LITHOFACIES AND BIOSTRATIGRAPHICAL STUDY OF THE LOWER CAMBRIAN OSA HORIZON IN THE SOUTH OF THE SIBERIAN PLATFORM (BOLSHETIRSKAYA 7 WELL)

The section of the Osa Subformation of the Usolka Formation of the Lower Cambrian Tommotian stage penetrated by the Bolshetirskaya 7 well in the south of the Nepa-Botuoba anteclise has been studied. As a result of lithological-facies investigations, seven lithological types of rocks were identified, they are regularly replaced by each other along the section. Facies environments of the reef complex were dеtected: bar bank, rear part of the reef, organogenic bioherm bildup, reef rear bars, reef buildup, core of reef buildup. In the section of the subformation, three fourth-order sequences are identified. The sequence boundaries are fixed by subaerial hiatuses represented in the core by sedimentation breccias, karst zones. The largest lowering of sea level, in terms of amplitude and duration, is confined to the border of the second and third sequences. The conducted biostratigraphic analysis confirms the Lower Cambrian age. Remains of calcareous algae Renalcis polymorphum, R. gelatinosum, R. granosum, Botomaella zelenovi were found. Small shell fauna of the genus of Namacalathus Grotzinger, Watt ers et Knoll. also was found. It has global distribution in the Lower Vendian (Ediacaran) deposits in Namibia, Brazil, Canada, Oman, Spain, China, Russia, etc.

The Hell Creek Formation, Montana: A Stratigraphic Review and Revision Based on a Sequence Stratigraphic Approach

The Upper Maastrichtian fluvial Hell Creek Formation of the Fort Peck Lake area, Montana (and regional equivalents) is notable for its vertebrate fossils and for the K-Pg mass extinction at or near its upper contact. Despite intense study, internal stratigraphy of the Hell Creek Formation is still poorly constrained, hindering study. This work reviews the stratigraphy of the Hell Creek Formation, as currently understood, and proposes important revisions to the recently proposed type section, particularly concerning complexity of the Hell Creek Formation basal contact. This work also subdivides the Montanan Hell Creek Formation into four 4th order depositional sequences, superimposed over a 3rd order marine transgression. Sequence boundaries are defined by four, laterally continuous disconformities formed by pauses in the creation of accommodation space, marked by overlying amalgamated channel complexes, or less commonly, correlative interfluve paleosols. Cyclicity in Montana may be correlative with similar 4th order cyclicity and marine influence documented in North and South Dakota, Alberta, and Saskatchewan. Magnetostratigraphy and new biostratigraphic data support correlation of the upper Montanan sequence with the North Dakotan Cantapeta tongue (and overlying fines) and Canadian Scollard and Frenchman Formations.

Sequence stratigraphy of the late Carboniferous Clifton Formation, New Brunswick

The Maritimes Basin of Atlantic Canada contains a rich record of Pennsylvanian cyclothems. Previous studies have focused on rapidly subsiding depocenters in the central part of the basin where Carboniferous successions feature cyclic alternations between terrestrial and marginal marine strata. In contrast, the Pennsylvanian Clifton Formation was deposited on the relatively stable New Brunswick platform and contains almost entirely terrestrial strata. Although early studies of the Clifton Formation noted a cyclic architecture, particularly within Member B, this unit has remained understudied. We provide a sedimentological and sequence stratigraphic framework for the lower 85 m of Member B and interpret our results relative to a broader regional framework. Near the base of the study interval, the highstand systems tract is composed of red floodplain mudrocks; overlying sequence boundaries are composed of calcretes and (or) channels. The transgressive systems tract and maximum flooding surface are represented by coals and aquatic bivalve-bearing mudrocks. Moving upward through the section, the architecture of the highstand systems tract remains largely unchanged while sequence-bounding paleosols become less well developed, the transgressive systems tract becomes thinner and eventually not preserved, and the maximum flooding surface is only occasionally preserved, possibly represented by carbonaceous shales. These changes in cyclic architecture may be attributed to changes in the magnitude of glacioeustatic fluctuations, climate, and (or) the accommodation/sediment supply ratio. The results of this study show that the Clifton Formation represents the terrestrial/proximal endmember for cyclicity in the Maritimes Basin and provide new insight into paleotopography as a possible control on cyclothem architecture.

Prestack simultaneous inversion for delineation of the Lower Wilcox erosional remnant sandstone beneath the Texas Gulf Coastal Plain: A case study

The Lower Wilcox lowstand sand deposits encased between two sequence boundaries along the Texas Gulf Coastal Plain are of good reservoir quality and usually gas productive. However, the sedimentation is sparsely scattered within such a depositional environment and it is hard to predict by qualitative interpretation methods. Simultaneous inversion of elastic parameters such as P-impedance, S-impedance, and density by the integration of prestack data and well logs allows us to quantitatively characterize the reservoirs and to distinguish them from the surrounding rocks. We have used prestack simultaneous inversion of the elastic parameters for delineation of the gas reservoir in an active field with limited log availabilities. For wells that are missing sonic and density logs, we estimate the parameters using the time-average equation (TAE) and Gardner’s equation, respectively. The shear wave velocity estimation methods are tested and compared using the measured log value. The estimation results are verified using well-log correlations in adjacent wells. Rock-physics analyses on wells are conducted to find the optimal elastic parameters for characterizing the gas-bearing sand. We successfully delineate the reservoir using the crossplot of VP/ VS versus S-impedance values. The inversion results are quality controlled by a producing well in the reservoir zone, and probability maps of each lithology are calculated by the probability density function. Our results from the Lower Wilcox Formation indicate that simultaneous inversion based on the estimated parameters using TAE is feasible, and the gas-bearing reservoirs can be recommended with high confidence.