Geology Of Basin Research Articles

Regional geology and hydrogeology of the Yellow River basin

The paper reviews regional geology in the Yellow River basin from viewpoints of stratigraphy and structure. Based on the geologic features, water-bearing formations are classified into following 5 types: Loose sediment type pore water-bearing formation, Clastic rock type fissurepore water bearing formation, Carbonate rock type formation, Magmatic and metamorphic rock type formation, and Frozen layer type formation. Groundwater in the Yellow river basin is classifi ed into 12 systems on the basis of hydrogeological conditions and characteristics of recharge, runoff and discharge of groundwater. Each system is described in detail, and distribution map for classifi ed systems are shown in the map. Three cross sections are illustrated as representative examples for upper, middle and lower reaches respectively.

Geochemistry, petrogenesis and tectonic setting of the Samothraki mafic suite, NE Greece: Trace-element, isotopic and zircon age constraints

The Samothraki mafic suite in the north-eastern Aegean Sea, Greece, is an ‘in situ’ magmatic complex comprising gabbros, sparse dykes and basalt flows and pillows cut by late dolerite dykes. We have determined the age of the complex by SHRIMP zircon geochronology of a gabbro as 159.9 ± 4.5 Ma (i.e. Oxfordian; early Late Jurassic), which precludes any correlation with the so-called Lesvos ophiolite further south (253.1 ± 5.6 Ma; Latest Permian). Six distinct, hitherto unrecognised, geochemical groups have been identified among the basalts and dolerites of the Samothraki mafic suite on the basis of trace-element and Nd–Sr isotopic characteristics. All groups show the presence of an enriched component in their source region, be that a long-term enriched mantle reservoir or an enriched melt. They also invariably show evidence of the addition of subduction-related hydrous fluids. Some groups testify to recent depletion events of long-term enriched mantle, some to the involvement of strongly depleted, recently refertilised mantle, and others to significant addition of melts either from subducted sediments or continental crust. None of the groups bear resemblance to mid-ocean ridge or back-arc basin basalts thus suggesting that the Samothraki mafic suite cannot represent mature back-arc basin crust. In view of recent advances in back-arc basin geology and the data collected here, the Samothraki mafic suite could represent a slab-edge segment of an evolved back-arc basin near the trench, a situation that satisfies the inflow of fertile mantle, the strong signature of sediment melts and the rare occurrence of boninite-like melts. Alternatively, it could represent the embryonic stages of back-arc basin formation either by a propagating rift tip into continental crust or by oblique subduction causing back-arc rifting of continental crust and creation of nascent transtensional basins. Restoration of block configuration in NE Greece before extensional collapse of the Hellenic hinterland and exhumation of the Rhodope Metamorphic Core Complex (mid-Eocene to mid-Miocene) results in a continuous ophiolite belt from Guevgueli to Samothraki, thus assigning the latter to the Innermost Hellenic Ophiolite Belt. We propose that the Samothraki mafic suite originated via rift propagation of the Sithonia ophiolite spreading ridge into the Chortiatis calc-alkaline arc (and its basement) which was partly assimilated. Our model does not favour southward intra-oceanic subduction of the Meliata–Maliac Ocean under the Vardar Ocean whereby Samothraki is located in the back-arc spreading centre. The autochthonous rift-related origin, the enriched geochemical characteristics and the lack of common features with known ophiolite types suggests calling the igneous complex of Samothraki Island a “mafic suite” rather than an “ophiolite”.

Liquefaction severity map for Aksaray city center (Central Anatolia, Turkey)

Abstract. Turkey having a long history of large earthquakes have been subjected to progressive adjacent earthquakes. Starting in 1939, the North Anatolian Fault Zone (NAFZ) produced a sequence of major earthquakes, of which the Mw 7.4 earthquake that struck western Turkey on 17 August 1999. Following the Erzincan earthquake in 1992, the soil liquefaction has been crucial important in the agenda of Turkey. Soil liquefaction was also observed widely during the Marmara and the Düzce Earthquake in 1999 (Sönmez, 2003). Aksaray city center locates in the central part of Turkey and the Tuzgolu Fault Zone passes through near the city center. The fault zone has been generated to moderate magnitude earthquakes. The geology of the Aksaray province basin contains Quaternary alluvial deposits formed by gravel, sand, silt, and clay layers in different thickness. The Tuzgolu Fault Zone (TFZ) came into being after the sedimetation of alluvial deposits. Thus, the fault is younger from lithological units and it is active. In addition, the ground water level is very shallow, within approximately 3 m from the surface. In this study, the liquefaction potential of the Aksaray province is investigated by recent procedure suggested by Sonmez and Gokceoglu (2005). For this purpose, the liquefaction susceptibility map of the Aksaray city center for liquefaction is presented. In the analysis, the input parameters such as the depth of the upper and lower boundaries of soil layer, SPT-N values, fine content, clay content and the liquid limit were used for all layers within 20 m from the surface. As a result, the category of very high susceptibility liquefaction class was not observed for the earthquake scenario of Ms=5.2, 4.9% of the study area has high liquefaction susceptibility. The percentage of the moderately, low, and very low liquefied areas are 28.2%, 30.2%, and 36.3%, respectively. The rank of non-liquefied susceptibility area is less than 1%.

Where do floodplains begin? The role of total stream power and longitudinal profile form on floodplain initiation processes

Research Article| January 01, 2008 Where do floodplains begin? The role of total stream power and longitudinal profile form on floodplain initiation processes Vikrant Jain; Vikrant Jain 1Department of Physical Geography, Division of Environmental and Life Sciences, Macquarie University, North Ryde, NSW, 2109, Australia Search for other works by this author on: GSW Google Scholar Kirstie Fryirs; Kirstie Fryirs 1Department of Physical Geography, Division of Environmental and Life Sciences, Macquarie University, North Ryde, NSW, 2109, Australia Search for other works by this author on: GSW Google Scholar Gary Brierley Gary Brierley 2School of Geography and Environmental Science, University of Auckland, P.O. Box 92019, Auckland, New Zealand Search for other works by this author on: GSW Google Scholar GSA Bulletin (2008) 120 (1-2): 127–141. https://doi.org/10.1130/B26092.1 Article history received: 18 Aug 2006 rev-recd: 04 Jun 2007 accepted: 24 Jun 2007 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Vikrant Jain, Kirstie Fryirs, Gary Brierley; Where do floodplains begin? The role of total stream power and longitudinal profile form on floodplain initiation processes. GSA Bulletin 2008;; 120 (1-2): 127–141. doi: https://doi.org/10.1130/B26092.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Understanding downstream transitions in river character and behavior is a basic concept in fluvial geomorphology. Downstream patterns of depositional processes can be differentiated between channel and floodplain components. In this study a generic set of methods is used to analyze floodplain initiation and continuity in relation to downstream changes in total stream power (slope and discharge) and longitudinal profile form for river courses in the upper Hunter catchment, Australia. Absolute values of these controlling factors are shown to be poor indicators of threshold conditions at which floodplains begin to form along river courses. Catchment-scale patterns of stream power and the form of longitudinal profiles provide better predictors of this transitional zone. The total stream power plot derived along longitudinal profiles represented by a second-order exponential curve has a bimodal pattern. In most cases, floodplains begin to form in a transition zone characterized by a trough area within the bimodal stream power distribution. This bimodal stream power pattern provides a better means to identify this transition in depositional processes along longitudinal profiles than more conventional single peak stream power analyses based on first-order exponential longitudinal profiles. Indirect controls such as basin geology and accommodation space also influence the initiation and pattern of floodplains. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Estudo mineralógico dos sedimentos de fundo do Lago Paranoá, Distrito Federal

Much informations about the geology and chemical composition of a drainage basin is recorded in the fluvial and lacustrine sediments. The Paranoa Lake basin is formed of rocks from the Paranoa Group, which is composed of shales, overlain by sand-siltic rhytmite and quartzites. The Paranoa Lake lies on violet shales, costituted by illite and kaolinite. The streams that form the Paranoa Lake also drain the sand-siltic rhytmite and its lateritic soil cover, as well as the quartzite. The lateritic soil cover is formed by kaolinite and gibbsite. The mineralogical characterization of the sediments from the Paranoa Lake indicates their provenance. This work presents the results of the characterization of the detritic materials of the bottom of the Paranoa Lake in order to identify the sediments provenance and the dynamical system. The material was analysed by X-ray diffraction in a whole sample and also in a clay fraction successively oriented and air-dried, etileno-glicol solvated and heated until 490 o C. The main minerals found are quartz, illite, kaolinite and gibbsite; accessory constituents are vermiculite, goethite, anatase, hematite and sepiolite. Quartz is the dominant mineral in the margin samples, while in the middle lake samples it can also appear as a minor constituent. Its distribution depends upon the tributaries that cut quartzitic levels and upon the lake’s hydrodynamics, which promoted its accumulation on the margins. Gibbsite is also a major constituent in most of the analysed points and in the whole sample, as well as in the clay fraction, on the margins and in the middle of the lake. It is derived from the lateritic soil erosion. Kaolinite is the dominant mineral in the clay fraction, indicating an important contribution from shales and soil, transported by the tributaries, or the reworking of margins and bottom materials. Illite is major constituent mainly in the fine fraction from the middle of the lake, while in the margins it can be a minor or lacking constituent. It results from the reworking of the margins and bottom materials, or is transported by streams that cut the shales.

Caracterização de parâmetros hidráulicos em depósitos fluviais paleogênicos na Bacia de Volta Redonda, RJ

The present study aims for the characterization of the hydrogeological parameters of the Paleogenic fluvial deposits of Volta Redonda Geological Basin, through hydraulic conductivity determinations and grain sized analyses. The overall goal was to produce a hydrogeological data base applicable to the characterization of hydrofacies (interconnected sedimentary bodies with distinct hydraulic properties) and the modeling groundwater flow. The used methods used consisted of in situ permeability determinations (Guelph permeameters) and laboratory tests (variable head permeameter), besides grain size analyses carried out in each sedimentary facies in the study area. These sedimentary facies were characterized by Marques (2006) and belong to the Resende and Pinheiral formations. The permeameter results were coherent to the sedimentological characteristics. The Resende Formation sedimentary deposits are constituted by medium to fine sand with presence of argillaceous matrix and present moderate to very low hydraulic conductivity, varying between 10-4 to 10-8 cm/s, which indicates a poor reservoir. The Pinheiral Formation presents sandy layers with conglomeratic lenses, limited by small thickness pelitic intervals, with a very low permeability, with a hydraulic conductivity varying between 10-5 to 10-7 cm/s. The upper layer has the maximum permeability, around 10-3 cm/s. This formation presents a medium reservoir characteristics and it must be taken into consideration that the upper layer has as role in recharge to the aquifer. From the results of hydraulic conductivity, that varies from 10-8 to 10-3 cm/s for the Resende and Pinheiral formations, it is concluded that these deposits a low to medium hydraulic conductivity, explaining the low productivity of the water-bearing multilayered aquifer of Volta Redonda Basin.

Chemical weathering of carbonates and silicates in the Han River basin, South Korea

A detailed investigation of the fluvial geochemistry of the Han River system allows to estimate the rates of chemical weathering and the consumption of CO 2. The Han River drains approximately 26,000 km 2 and is the largest river system in South Korea in terms of both water discharge and total river length. It consists of two major tributaries: the North Han River (NHR) and the South Han River (SHR). Distinct differences in basin lithology (silicate vs. carbonate) between the NHR and SHR provide a good natural laboratory in which to examine weathering processes and the influence of basin geology on water quality. The concentrations of major elements and the Sr isotopic compositions were obtained from 58 samples collected in both summer and winter along the Han River system in both 2000 and 2006. The concentrations of dissolved loads differed considerably between the NHR and SHR; compared with the SHR, the NHR had much lower total dissolved solids (TDS), Sr, and major ion concentrations but a higher Si concentration and 87Sr/ 86Sr ratio. A forward model showed that the dissolved loads in the NHR came primarily from silicate weathering (55 ± 11%), with a relatively small portion from carbonates (30 ± 14%), whereas the main contribution to the dissolved loads in the SHR was carbonate weathering (82 ± 3%), with only 11 ± 4% from silicates. These results are consistent with the different lithologies of the two drainage basins: silicate rocks in the NHR versus carbonate rocks in the SHR. Sulfuric acid derived from sulfide dissolution in coal-containing sedimentary strata has played an important role in carbonate weathering in the SHR basin, unlike in the NHR basin. The silicate weathering rate (SWR) was similar between the NHR and SHR basins, but the rate of CO 2 consumption in the SHR basin was lower than in the NHR basin due to an important role of sulfuric acid derived from pyrite oxidation.

Petroleum systems of Indonesia

Indonesia contains many Tertiary basins, several of which have proven to be very prolific producers of oil and gas. The geology and petroleum systems of these productive basins are reviewed, summarized and updated according to the most recent developments. We have linked the recognized petroleum systems to common stages in the geological evolution of these synrift to postrift basins and classified them accordingly. We recognize four Petroleum System Types (PSTs) corresponding to the four main stages of geodynamic basin development, and developed variably in the different basins depending on their depositional environment history: (i) an oil-prone Early Synrift Lacustrine PST, found in the Eocene to Oligocene deeper parts of the synrift grabens, (ii) an oil and gas-prone Late Synrift Transgressive Deltaic PST, located in the shallower Oligocene to early Miocene portions of the synrift grabens, (iii) a gas-prone Early Postrift Marine PST, characteristic of the overlying early Miocene transgressive period, and (iv) an oil and gas-prone Late Postrift Regressive Deltaic PST, forming the shallowest late Tertiary basin fills. We have ascribed the petroleum systems in each of the basins to one of these types, recognizing that considerable mixing of the predominantly lacustrine to terrestrial charge has taken place. Furthermore, we have grouped the basins according to their predominant PSTs and identified “basin families” that share important aspects of their hydrocarbon habitat: these have been termed proximal, intermediate, distal, Borneo and eastern Indonesian, according to their palaeogeographic relationship to the Sunda craton of Southeast Asia.

Return to rifts – the next wave: fresh insights into the petroleum geology of global rift basins

Rift basin exploration has provided the oil and gas industry with almost one third of discovered global hydrocarbon resources. The maturity of prolific passive margin sequence plays has necessitated a shift in technical emphasis to understanding petroleum geology of the deeper precursor rift basin megasequences. Modelling of these petroleum systems relies extensively on theoretical stretching hypotheses for whole-crust evolution and heat flow prediction. Several alternatives have emerged to account for anomalous rift-related thermal stress, asymmetry of structural styles and origin of thick syn-rift ‘sag-basin’ subsidence patterns at passive continental margins. These observations cannot be predicted by the pure shear uniform stretching model first introduced by McKenzie in 1978. Newly acquired, 2D long cable deep seismic records provide empirical evidence that supports more complex, polyphase, depth-dependent stretching origins for rift-basin formation. Heterogeneities are believed to be inherent in the brittle upper crust, in the ductile lower crust and lithospheric mantle and so result in the complex distribution of accommodation space recorded by syn-rift megasequence deposition during episodes of orthogonal or oblique extension. No single stretching model uniquely describes the varied structural response of the anisotropic crust to plate-scale extension. A hybrid of phased simple and pure shear deformation mechanisms separated by regional lateral, and possibly vertical crustal discontinuities, may explain the apparent paradox of along-strike co-existence of uniform versus depth-dependent stretching structural geometries.

Geology and tectonics of the South Atlantic Brazilian salt basins

Abstract This paper first reviews the salt basins and depositional ages in the South Atlantic salt province. This comprises a series of salt basins separated by basement highs, deep graben (that never dried up), later volcanic highs and subaerial ocean spreading ridges. Initial halite and anhydrite deposition occurred first in the Sergipe-Alagoas Basin of NE Brazil at c. 124.8 Ma, and was closely followed by deposition in the Kwanza Basin, Angola between 124.5 and 121 Ma. The later potassium-magnesium-rich salts were deposited in the Sergipe-Alagoas and Gabon-Congo basins before 114.5 Ma. The age of the main Santos-Campos salt is not known precisely, but the latest anhydrites deposited on the southern margin of the Santos Basin post-date volcanic rocks dated at 113.2 Ma. The paper then compares the salt tectonics of the wide Campos-Santos Basin segment with the narrow South Bahia basins segment. Sediment loading in the Santos Basin produced a landward-dipping base salt, which led to the development of counter-regional faults, and inhibited downslope sliding, and enhanced later contractional effects caused by either gravity spreading or regional tectonic compression. Folding occurred in simultaneous pulses across the Santos Basin, suggesting that regional tectonic compression occurred. The narrow salt basins of South Bahia have a steeply dipping base salt horizon (4°) and pronounced folding, which initiates at the oceanward pinch-out of the salt and propagates back up the slope. The topographic highs, above fold anticlines, are rapidly eroded on narrow margin slopes, which allows the folds to grow more easily to large amplitudes at the top salt horizon.

Aquifer and watercourse interaction in the Murray Darling Basin elucidated using electrical conductivity imaging

Imaging of groundwater that interacts with surface watercourses is essential for providing detail needed to accurately manage both resources. It is particularly important where one resource is saline or otherwise polluted, where spatial quantification of the interacting resources is critical to water use planning and where losses from surface waterways need to be minimized in order to transport water long distances. Geo-electric arrays or transient electromagnetic devices can be towed along watercourses to image electrical conductivity (EC) at multiple depths within and beneath those watercourses. It has been found that in such environments, EC is typically related primarily to groundwater salinity and secondarily to clay content. Submerged geo-electric arrays can detect detailed canal-bottom variations if correctly designed. Floating arrays pass obstacles easily and are good for surveying constricted rivers and canals. Transient electromagnetic devices detect saline features clearly but have inferior ability to detect fine changes just below beds of watercourses. All require that water depth be measured by sonar or pressure sensors for successful elimination of effects of the water layer on the data. Presentation of the data using a 3D presentation technique where EC is imaged along vertical ribbons drawn along the watercourses is almost essential for handling the data produced because the meandering paths of rivers and canals combined with the shear volume of data typically acquired results in a geo-referencing dilemma that cannot be accommodated using traditional presentation techniques. An extensive set of EC Imaging case studies, distributed across canals and rivers of the Australian Murray-Darling Basin, has been collected. They reveal the interaction of various rivers and canals with the underlying groundwater resources. At some sites, watercourses cross prior river channel sands that are being recharged and are suitable for use as water storages with low evaporation losses. Geophysical imagery can be used to optimize recharge and design of such underground storages. At some other sites, little connection between aquifers and surface watercourses is evident. Finally, at downstream ends of geological basins, sites where saline groundwater flows into, or is on the verge of flowing into rivers are evident.

Aragonite dissolution, sedimentation rates and carbon isotopes in deep-water hemipelagites (Livinallongo formation, Middle Triassic, northern Italy)

In a recent contribution to this journal Preto et al. (2005) present stratigraphic results and correlations of sediments of the Middle Triassic Buchenstein basin (Buchenstein/Livinallongo Fm.) of the Southern Alps. The data are then used for quantifying the rates of pelagic sedimentation and for the interpretation of observed dissolution features. Because we feel that some relevant conclusions presented therein are either not supported by field evidence or have been proposed previously, with this discussion we intend to clarify some aspects of the geology of the hemipelagic Buchenstein basin. The aspects discussed here address the following points: 1) the reliability of the proposed stratigraphic correlations and the importance of the post-depositional diagenetic modification for assessing the variations in rates of sedimentation; 2) the origin and rates of sediment accumulation of the Plattenkalke versus the Knollenkalke; 3) aragonite dissolution versus compation-driven diagenesis and the bias of the fossil record. Graphical logs of the Buchenstein sediments along with stratigraphic and sedimentologic analysis demonstrate that the Buchenstein basin was fed from different sediment sources whose relative importance has changed through time and space (e.g., Ogilvie Gordon, 1927; Viel, 1979; Bosellini and Stefani, 1991; Brack and Rieber, 1993; Maurer and Schlager, 2003). Relevant for the assessment of basinal sedimentation rates proposed in Preto et al. (2005) are the new data presented for two basinal sections (Rio Sacuz, San Marco) along with information mainly adapted from the literature (Seceda, Bagolino).

New unilateral problems in stratigraphy

This work deals with the study of some stratigraphic models for the formation of geological basins under a maximal erosion rate constrain. It leads to introduce differential inclusions of degenerated hyperbolic-parabolic type , where H is the maximal monotonous graph of the Heaviside function and E is a given non-negative function. Firstly, we present the new and realistic models and an original mathematical formulation, taking into account the weather-limited rate constraint in the conservation law, with a unilateral constraint on the outflow boundary. Then, we give a study of the 1-D case with numerical illustrations.

The environment and evolution of the West Antarctic ice sheet: setting the stage

The West Antarctic ice sheet is the last ice sheet of the type cradled in a warm, marine geologic basin. Its perimeter stretches into the surrounding seas allowing warmer ocean waters to reach the undersides of its floating ice shelves and its relatively low surface elevation permits snow-carrying storms to extend well into its interior. This special environment has given rise to theories of impending collapse and for the past quarter-century has challenged researchers who seek a quantitative prediction of its future behaviour and the corresponding effect on sea level. Observations confirm changes on a variety of time scales from the quaternary to less than a minute. The dynamics of the ice sheet involve the complex interaction of ice that is warm at its base and cold along the margins of ice streams; subglacial till that is composed of a combination of marine sediment and eroded sedimentary rocks; and water that moves primarily between the ice and bed, but whose flow direction can differ from the direction of ice motion. The pressure of the water system is often sufficient to float the ice sheet locally and small changes in the amount of water in the till can cause it to rapidly switch from very weak to very stiff.

Tectonic controls of the right-lateral Burro Negro tear fault on Paleogene structure and stratigraphy, northeastern Maracaibo Basin

The northeastern Maracaibo Basin in western Venezuela was deformed by Paleogene thrusting and an associated tear fault (Burro Negro right-lateral strike-slip fault zone), related to Paleogene oblique collision between the Caribbean and South American plates. Two different tectonic models have been previously proposed for the thick Paleogene depocenter located along the northeastern margin of the Maracaibo Basin. The first model proposes that the depocenter is a foreland basin controlled by southwestward-directed overthrusting during a late Paleocene–middle Eocene oblique collision between the Caribbean and South American plates. The second model, supported by data presented in this study, proposes that the asymmetric Paleogene Maracaibo sedimentary wedge was controlled by strike-slip displacement along a right-lateral tear fault, separating southeast-directed thrust sheets to the east (Lara nappes) from a more stable platform area to the west (Maracaibo Basin).Regional seismic lines recorded to 5 s two-way traveltime reveal the structure of the asymmetric Paleogene depocenter in the northeastern part of the Maracaibo Basin. The approximately 100-km (62-mi)-long Burro Negro fault is a right-lateral strike-slip fault separating less deformed, inner- to outer-shelf rocks of the western Maracaibo Basin from highly deformed, deep-marine rocks of the eastern Maracaibo Basin. Seismic lines northeast of the Burro Negro fault zone show elongate, subsurface basins bounded by partially inverted reverse and strike-slip faults filled with about 3 km (1.8 mi) of Oligocene and Miocene clastic marine sedimentary rocks. Structural highs of Eocene rocks are characterized at depth on seismic reflection lines by chaotic seismic reflections that underlie the more coherently stratified Oligocene and Miocene subbasins. We interpret these structural highs as steeply dipping fault zones and shale diapirs activated during Eocene–Oligocene oblique plate convergence.The geology and overall structural configuration of the northeastern Maracaibo Basin and the Burro Negro fault zone support its origin as a right-lateral tear fault. In our model, the Burro Negro fault zone accommodated southeastward migration of the thrust front in the deep-water area east of the fault in the present-day Falcn region. The Paleogene clastic wedge of the Maracaibo Basin exhibits many common features of a classic foreland basin, including onlap onto an arch or forebulge located near the center of the present-day Lake Maracaibo. This paleogeographic coincidence of the Burro Negro fault zone and the Maracaibo shelf edge suggests that the paleotrend of the South American passive margin prior to collision was serrated in map view. West-to-east migration of the Caribbean–South America oblique collision formed progressively younger, parallel tear faults to the east of the Maracaibo Basin that may have formed by the same tectonic process as the Burro Negro fault zone.

Geologic evolution and aspects of the petroleum geology of the northern East China Sea shelf basin

Analysis of multichannel seismic reflection profiles reveals that the northern East China Sea shelf basin experienced two phases of rifting, followed by regional subsidence. The initial rifting in the Late Cretaceous created a series of grabens and half grabens, filled by alluvial and fluviolacustrine deposits. Regional uplift and folding (Yuquan movement) in the late Eocene–early Oligocene terminated the initial rifting. Rifting resumed in the early Oligocene, while alluvial and fluviolacustrine deposition continued to prevail. A second phase of uplift in the early Miocene terminated the rifting, marking the transition to the postrift phase. The early postrift phase (early Miocene–late Miocene) is characterized by regional subsidence and westward and northwestward marine transgression. Inversion (Longjing movement) in the late Miocene interrupted the postrift subsidence, resulting in an extensive thrust-fold belt in the eastern part of the area. The entire area entered a stage of regional subsidence again and has become a broad continental shelf. Source rocks include synrift lacustrine facies, fluvial shales, and coal beds. Synrift fluvial, lacustrine, and deltaic deposits, postrift littoral and/or shallow-marine sandstones, and fractured basement have the potential to provide reservoirs. Various types of hydrocarbon traps (e.g., faulted anticlines, overthrusts, rollover anticlines, faults, unconformity traps, combination structural-stratigraphic traps, weathered basement, and stratigraphic traps) are recognized, but many of these traps have not been tested.

INITIAL REVIEW OF THE BIOSTRATIGRAPHY AND PETROLEUM SYSTEMS AROUND THE TASMAN SEA HYDROCARBON-PRODUCING BASINS

Understanding the genesis and habitat of hydrocarbons in a sedimentary basin takes knowledge of that basin at many levels, from basic infill geology to petroleum systems, plays, prospects and detailed sequence stratigraphy. While geophysics can define the basins and their internal structures, biostratigraphy and paleogeography provide greater understanding of basin geology. Micropaleontology and palynology are the chief tools that we need to define both the environment and dimension of time.As an example, the reconstruction of the Tasman Sea region to the mid-Cretaceous (ca 120 Ma) shows that the hydrocarbon-producing Gippsland and Taranaki petroleum basins developed at similar latitudes and in similar geological contexts. Other basins within the region have been lightly explored and need evaluation as to the value of further exploration.As paleontology has developed separately in Australia and New Zealand, comparison of biostratigraphic zones and their chronostratigraphy is critical to understand the similarity or otherwise of the sedimentary record of the two regions. Recent refinement of the NZ timescale and comparative studies on Gippsland Basin wells by NZ paleontologists have provided some key insights that enable us to compare the geological history of both regions more closely, and to recognise similarities in petroleum systems that may enhance petroleum prospects on both sides of the Tasman Sea.

Interaction between surface waves and absorbing boundaries for wave propagation in geological basins: 2D numerical simulations

Surface waves control the peak of the seismic records at regional and teleseismic distances. In complex structures, such as basins, their amplitude is produced by the interference between the topography and the wedges of the model. Therefore, they represent a challenging target for numerical simulations. When modelling low frequencies in thin media, such as basins and waveguides, some instabilities arise from the interaction between propagating evanescent waves and the artificial layer, required to avoid spurious reflection to be sent back into the elastic volume. Here we propose to generalize the absorbing boundary conditions, by adding a cut‐off frequency and an overdamping. The efficiency is demonstrated through a comparison with analytical solutions. Finally an analysis is performed by adopting a complex basin geometry, where we show that the pollution of classical absorbing conditions becomes significant near the edges of the model.

Occurrences of the fossil Dipnoiformes in Brazil and its stratigraphic and chronological distributions

n Recent records in new fossiliferous localities have widened the apparently limited paleogeographic distribution of Dipnoiformes in Brazil. The Dipnoiformes are registred from Devonian to Miocene/Pliocene in different Brazilian geologic basins. The Paleozoic of the ParanAE Basin, with five localities, is the most importat interval, including the largest concentration of Dipnoiformes dental plates in a Permian bone-bed of the CorumbataI Formation. The most fossiliferous localities occur in the ParanAE Basin (Sao Paulo State), Sao LuIs nGrajaœ Basin (Maranhao State) and the Acre Basin (Acre State). Fossils from these deposits show the greatest morphological variation and are most abundant, compared to material from other localities. It is presented here a check-list of the fossil dipnoan records in Brazil, providing stratigraphic, cronologic and correlation data of the localities.

The early Mesozoic Birdsboro central Atlantic margin basin in the Mid-Atlantic region, eastern United States: Discussion

[Faill (2003)][1] provides an important contribution to our understanding of the geology and evolution of the Triassic-Jurassic basins of the central Atlantic margin that formed during the breakup of Pangea (e.g., [Olsen, 1997][2]). In particular, Faill draws attention to the importance of fluvial