Tectonic history from vitrinite reflectance

Summary. The degree of organic metamorphism of carbonaceous matter is expressed in terms of the reflectance of vitrinite. Vitrinite reflectance is a function of temperature and time. A model relating vitrinite reflectance to temperature and time is proposed from published vitrinite reflectance—temperature—time nomograms. A plot of the logarithm of vitrinite reflectance versus depth gives a linear curve (for vitrinite reflectance greater than 0.3 per cent) in a sedimentary basin which has had a constant geothermal gradient throughout its tectonic history; the geothermal gradient (°C km⁻¹) is equal to the slope of the curve multiplied by 194.8. The model is also applied to sedimentary basins with decreasing geothermal gradient with time (i.e. cooling continental-margin basins). The vitrinite reflectance model is demonstrated to be consistent with observed reflectance data and tectonic information from the Sydney, Bowen-Surat and Gippsland basins in eastern Australia.     

Thermal history and exhumation of the Northern Apennines (Italy): evidence from combined apatite fission track and vitrinite reflectance data from foreland basin sediments

ABSTRACT Apatite fission track ages of 20 samples collected from turbidite successions deposited in foreland basins adjacent to the Northern Apennines range between ∼3 and ∼10 Ma. The youngest fission track ages are concentrated in a NW–SE elongated belt, which approximately runs through the centre of the study area, while gradually increasing ages are distributed towards the south-western and north-eastern borders. Integration of apatite fission track data and published vitrinite reflectance values indicate this region of the Apennines experienced continuous but variable exhumation starting from ∼14 Ma. The extent of exhumation and uplift range between 5 and 6 km at the south-western and north-eastern borders of the study area, and ∼7 km in the central part. Exhumation was driven mainly by erosion, with minor faulting in response to structural readjustment related to differential exhumation. Regional exhumation and erosion are interpreted as the result of isostatic rebound following crustal thickening in the lower part of the orogen.     

New insights on measured and calculated vitrinite reflectance

Measurement of dispersed vitrinite reflectance in organic sediments is one of the few regional data sets used for placing bounds on the thermal history of a sedimentary basin. Reflectance data are important when access to complementary information such as high‐quality seismic data is unavailable to place bounds on subsidence history and in locations where uplift is an important part of the basin history. Attributes which make vitrinite reflectance measurements a useful data set are the relative ease of making the measurement, and the availability of archived well cores and cuttings in state, provincial, and federal facilities. In order to fully utilize vitrinite data for estimating the temperature history in a basin, physically based methods are required to calibrate an equivalent reflectance from a modelled temperature history with measured data. The most common method for calculating a numerical vitrinite reflectance from temperature history is the EASY%R_o method which we show systematically underestimates measured data. We present a new calculated reflectance model and an adjustment to EASY%R_o which makes the correlation between measured vitrinite values and calculated vitrinite values a physical relationship and more useful for constraining thermal models. We then show that calibrating the thermal history to vitrinite on a constant age date surface (e.g., top Cretaceous) instead of calibrating the thermal history in depth removes the heating rate component from the reflectance calculation and makes thermal history calibration easier to understand and more directly related to heat flow. Finally, we use bounds on the vitrinite–temperature relationships on a constant age date surface to show that significant uncertainty exists in the vitrinite data reported in most data sets.     

Thermal history analysis by integrated modelling of apatite fission track and vitrinite reflectance data: application to an inverted basin (Buller Coalfield, New Zealand)

Integrated analysis and modelling of apatite fission track with vitrinite reflectance (VR) data allows the timing, magnitude and pattern of Palaeogene subsidence and Neogene inversion to be established for an uplifted and largely denuded basin: the Buller Coalfield, New Zealand. At the time of maximum subsidence in the late Oligocene, the basin consisted of an extensional half graben, bounded to the west by the Kongahu Fault Zone (KFZ), with up to 6 km of upper Eocene to Oligocene section adjacent to it; currently, only a few tens of metres of basal coal measures on basement are preserved on top of a range 800–1000 m above sea level. Integrated modelling of the VR and fission track data show that the deepest parts of the basin were inverted during two Miocene compressional phases (24–19 Ma and 13–8 Ma), and are consistent with a further phase of inversion during the Quaternary that formed the present topography. Palinspastic restoration of the three phases of inversion shows that the basin was not inverted in a simple way: most of the rock uplift/denudation adjacent to the KFZ occurred during the early Miocene phase, and at the same time burial occurred in the south-eastern part of the basin (maximum temperatures were experienced at different times at different places in the basin); during the middle to late Miocene there was broad uplift in the central and eastern parts of the coalfield. Because the timing and magnitude of uplift have been derived from the zone of inversion, they can be compared independently with the timing of unconformity development and rapid subsidence in the adjacent foredeeps, particularly the Westport Trough. For the middle to late Miocene phase of inversion, we show that during the first 1–2 million years of compression, the uplift within the coalfield also involved the margins of the Westport Trough, contributing to unconformity development; subsequently, uplift continued on the inversion structure but the margins of the Westport Trough subsided rapidly. This is explained by a model of stick slip behaviour on the boundary faults, especially for the KFZ. When compression started the fault zone has locked and uplift extends into the basin, whereas subsequently the fault zone unlocks, and the inversion structure overrides the basin margin, thereby loading it and causing subsidence.     

Thermal effects of intrusion below the Taranaki Basin (New Zealand): evidence from combined apatite fission track age and vitrinite reflectance data

A high surface heat-flow anomaly on the northern Taranaki Peninsula in the Taranaki Basin (New Zealand) coincides spatially with Quaternary volcanic edifices, but the temporal aspects of heating of the sedimentary column associated with volcanism and any related plutonism have been unclear. A combined analysis of fission track age and vitrinite reflectance data, in particular comparing data from within the high heat-flow anomaly to calibration wells elsewhere in the Taranaki Basin, provides important new constraints. Within the high heat-flow region, apatite fission track (AFT) ages are older and vitrinite reflectance ( R _o) values are lower than in samples from elsewhere in the basin that have undergone similar burial histories. Modelled AFT ages and R _o values suggest gradual heating to within about 20  °C of maximum temperature followed by rapid heating of sedimentary strata in the last 1 Myr, perhaps as recently as the last 0.1 Myr. The inferred age of this heating event is younger than the age of the volcanic edifice on which it is centred, suggesting that volcanism precedes heating that may be related to plutonism under the northern peninsula. These results suggest that, if the heating is caused by intrusion, then the intrusion is probably in the upper crust.
     

Basin tectonic history and paleo‐physiography of the pelagian platform,northern Tunisia,using vitrinite reflectance data

Constraining the thermal, burial and uplift/exhumation history of sedimentary basins is crucial in the understanding of upper crustal strain evolution and also has implications for understanding the nature and timing of hydrocarbon maturation and migration. In this study, we use Vitrinite Reflectance (VR) data to elucidate the paleo‐physiography and thermal history of an inverted basin in the foreland of the Atlasic orogeny in Northern Tunisia. In doing so, it is the primary aim of this study to demonstrate how VR techniques may be applied to unravel basin subsidence/uplift history of structural domains and provide valuable insights into the kinematic evolution of sedimentary basins. VR measurements of both the onshore Pelagian Platform and the Tunisian Furrow in Northern Tunisia are used to impose constraints on the deformation history of a long‐lived structural feature in the studied region, namely the Zaghouan Fault. Previous work has shown that this fault was active as an extensional structure in Lower Jurassic to Aptian times, before subsequently being inverted during the Late Cretaceous Eocene Atlas I tectonic event and Upper Miocene Atlas II tectonic event. Quantifying and constraining this latter inversion stage, and shedding light on the roles of structural inheritance and the basin thermal history, are secondary aims of this study. The results of this study show that the Atlas II WNW‐ESE compressive event deformed both the Pelagian Platform and the Tunisian Furrow during Tortonian‐Messinian times. Maximum burial depth for the Pelagian Platform was reached during the Middle to Upper Miocene, i.e. prior to the Atlas II folding event. VR measurements indicate that the Cretaceous to Ypresian section of the Pelagian Platform was buried to a maximum burial depth of ~3 km, using a geothermal gradient of 30°C/km. Cretaceous rock samples VR values show that the hanging wall of the Zaghouan Fault was buried to a maximum depth of <2 km. This suggests that a vertical km‐scale throw along the Zaghouan Fault pre‐dated the Atlas II shortening, and also proves that the fault controlled the subsidence of the Pelagian Platform during the Oligo‐Miocene. Mean exhumation rates of the Pelagian Platform throughout the Messinian to Quaternary were in the order of 0.3 mm/year. However, when the additional effect of Tortonian‐Messinian folding is accounted for, exhumation rates could have reached 0.6–0.7 mm/year.     

Constraining the burial history of the Ghadames Basin, North Africa: an integrated analysis using sonic velocities, vitrinite reflectance data and apatite fission track ages

Constraining the burial history of a sedimentary basin is crucial for accurate prediction of hydrocarbon generation and migration. Although the Ghadames Basin is a prolific hydrocarbon province, with recoverable oil discovered to date in excess of 3.5 billion bbl, exploration on the eastern margin is still limited and the prospectivity of the area depends on the identification of effective source rocks and the timing of hydrocarbon generation. Sonic velocity, apatite fission track (FT) and vitrinite reflectance analysis offer three complementary methods to determine burial history and provide independent analytical techniques to evaluate the timing and amount of exhumation. The results indicate that two phases of tectonic activity had the biggest influence on basin evolution: the Hercynian (Late Carboniferous–Triassic) and Alpine (Late Mesozoic/Cenozoic) tectonic events. Exhumation during the Hercynian tectonic event increases from the SE, where an almost complete Palaeozoic section is preserved, towards the NW. This study quantifies the significant regional Alpine exhumation of the southern and eastern margins of the basin, with important implications for the timing of hydrocarbon maturation and expulsion, particularly for the Silurian source rock interval. Incorporating elevated Alpine exhumation values into burial history models for wells in the eastern (Libyan) part of the basin allows calibration with available maturity (Ro_eq) data using moderate values of Hercynian erosion. The result is preservation of the generation potential of Silurian (Tanezzuft) source rocks until maximum burial during Mesozoic/Cenozoic time, which improves the chance for preservation of hydrocarbon accumulations following entrapment.     

Joint inversion of temperature,vitrinite reflectance and fission tracks in apatite with examples from the eastern North Sea area

As sediment accumulation indicates basin subsidence, erosion often is understood as tectonic uplift, but the amplitude and timing may be difficult to determine because the sedimentary record is missing. Quantification of erosion therefore requires indirect evidence, for example thermal indicators such as temperature, vitrinite reflectance and fission tracks in apatite. However, as always, the types and quality of data and the choice of models are important to the results. For example, considering only the thermal evolution of the sedimentary section discards the thermal time constant of the lithosphere and essentially ignores the temporal continuity of the thermal structure. Furthermore, the types and density of thermal indicators determine the solution space of deposition and erosion, the quantification of which calls for the use of inverse methods, which can only be successful when all models are mutually consistent. Here, we use integrated basin modelling and Markov Chain Monte Carlo inversion of four deep boreholes to show that the erosional pattern along the Sorgenfrei–Tornquist Zone (STZ) in the eastern North Sea is consistent with a tectonic model of tectonic inversion based on compression and relaxation of an elastic plate. Three wells in close proximity SW of the STZ have different data and exhibit characteristic differences in erosion estimates but are consistent with the formation of a thick chalk sequence, followed by minor Cenozoic erosion during relaxation inversion. The well on the inversion ridge requires ca. 1.7 km Jurassic-Early Cretaceous sedimentation followed by Late Cretaceous–Palaeocene erosion during inversion. No well demands thick Cenozoic sedimentation followed by equivalent significant Neogene exhumation. When data are of high quality and models are consistent, the thermal indicator method yields significant results with important tectonic and geodynamic implications.     

Thermal modelling of magmatic intrusions in the Gjallar Ridge, Norwegian Sea: implications for vitrinite reflectance and hydrocarbon maturation

Extensive magmatic activity took place in the Vøring Basin, offshore Norway, related to the Early Cenozoic rifting. The break‐up of the North‐Atlantic at the Palaeocene–Eocene transition induced strong volcanism. There are numerous magmatic sills below 3 km depth in the area. They are predominantly layer parallel and thin compared with their lateral extent. Igneous intrusions, sills and dykes affected the temperature history, and thus need to be taken into account in petroleum prospect analysis. We have calculated the temperature and maturity effects in the sedimentary layers in the Gjallar area associated with the emplacement of single sill and sill complexes. A 120‐m‐thick sill produces a theoretical vitrinite reflectance (%R₀) 0.8% higher than normal at a distance of 100 m from the sill. Vitrinite reflectance changes caused by a swarm of seven sills varying from 8 to 80 m in thickness were calculated. It is shown that the calculated thermal profile can account for the observed shift in vitrinite reflectance in the well. A two‐dimensional section crossing the Gjallar Ridge, consisting of numerous magmatic intrusions, is also modelled. The modelled geological development and temperature history over the profile show that there are significant maturation effects in the interval under investigation. Based on this work, the sill swarm observed in the area could more than double the fraction of the kerogen that has been transformed to petroleum at the (present) depth of 4 km.     

Unravelling the multi-stage burial history of the Swiss Molasse Basin: integration of apatite fission track, vitrinite reflectance and biomarker isomerisation analysis

A complex basin evolution was studied using various methods, including thermal constraints based on apatite fission‐track (AFT) analysis, vitrinite reflectance (VR) and biomarker isomerisation, in addition to a detailed analysis of the regional stratigraphic record and of the lithological properties. The study indicates that (1) given the substantial amount of data, the distinction and characterisation of successive stages of heating and burial in the same area are feasible, and (2) the three thermal indicators (AFT, VR and biomarkers) yield internally consistent thermal histories, which supports the validity of the underlying kinetic algorithms and their applicability to natural basins. All data pertaining to burial and thermal evolution were integrated in a basin model, which provides constraints on the thickness of eroded sections and on heat flow over geologic time. Three stages of basin evolution occurred in northern Switzerland. The Permo‐Carboniferous strike–slip basin was characterised by high geothermal gradients (80–100°C km^?1) and maximum temperature up to 160°C. After the erosion of a few hundreds of metres in the Permian, the post‐orogenic, epicontinental Mesozoic basin developed in Central Europe, with subsidence triggered by several stages of rifting. Geothermal gradients in northern Switzerland during Cretaceous burial were relatively high (35–40°C km^?1), and maximum temperature typically reached 75°C (top middle Jurassic) to 100°C (base Mesozoic). At least in the early Cretaceous, a stage of increased heat flow is needed to explain the observed maturity level. After erosion of 600–700 m of Cretaceous and late Jurassic strata during the Paleocene, the wedge‐shaped Molasse Foreland Basin developed. Geothermal gradients were low at this time (≤20°C km^?1). Maximum temperature of Miocene burial exceeded that of Cretaceous burial in proximal parts (<35 km from the Alpine front), but was lower in more distal parts (>45 km). Thus, maximum temperature as well as maximum burial depth ever reached in Mesozoic strata occurred at different times in different regions. Since the Miocene, 750–1050 m were eroded, a process that still continues in the proximal parts of the basin. Current average geothermal gradients in the uppermost 2500 m are elevated (32–47°C km^?1). They are due to a Quaternary increase of heat flow, most probably triggered by limited advective heat transport along Paleozoic faults in the crystalline basement.     

Some terms of nutation derived from the BIH data

Summary. The z -term of latitude and the w -term of UT, as computed by the BIH, are suitable for investigating imperfections in the representation of the real nutation in space. They have been previously used for deriving only the amplitude of the principal term of nutation (Feissel & Guinot). In this study they are used more generally for deriving the amplitudes of two terms of nutation and searching for a possible nutation in space due to the nearly-diurnal wobble.
Two kinds of data are used for this purpose: the values of z and w from 1962.0 to 1980.0 at 0.05 yr intervals and the values of z from 1967.0 to 1980.0 at 5 day intervals. The first ones have been used previously by Feissel & Guinot (using the values up to 1974.0 and 1976.95 respectively). The second ones have not previously been used for such studies.
The derived amplitudes of the principal and the fortnightly terms of nutation are in good agreement with other values deduced from observations, and with the theoretical ones corresponding to the best models of a non-rigid earth. The values obtained are not yet sufficiently precise to distinguish between these models, but could become so in the near future.
The least-squares fits, performed among the z and w data in order to look for any error in the representation of nutation, show the existence of a retrograde term, of a 434 day period for z and 444 day for w and an amplitude of the order of 0.01 arcsec. It may be due to the nearly-diurnal wobble.     

Motions at the core surface derived from SV data

Summary. Examples of core motions which generate the observed secular variation field – as given by various models for 1970 and 1980 – from the main field have been computed in the frozen flux approximation, assuming that the spectrum of the motion is of low degree and decreases with wave-number. No mode of degree > 4 in the expansion of the motion can be derived with any degree of confidence. Among the low degree modes, some appear to be stable (they come out with the same magnitude whatever the inversion scheme used). The flow made of these stable modes is then examined. An outstanding feature of the flow is the body westward drift. But it seems necessary, if one looks for such a regular flow, to consider both toroïdal and poloïdal components, which would imply upwelling and down-welling in the upper layers of the core. The toroïdal part of the flow appears to be enhanced by the 1969 impulse, although its geometry is nearly unchanged. On the contrary the geometry of the computed poloïdal part is different in 1980 and in 1970;     

Kinematics of a landslide derived from archival photogrammetry and GPS data

The evolution of the Patigno landslide, a deep-seated gravitational slope deformation in the Northern Apennine range (Italy), was investigated using archival photogrammetry, and GPS observations from a permanent station located inside the landslide. Historical aerial photographs of the area taken in 1975 (scale 1:13,000), 1987 (1:13,000) and 2004 (1:30,000) were co-registered into the same reference frame using an unconventional method based on the detection of homologous points in multi-temporal models. Three DTMs were produced using a Digital Photogrammetric Workstation and compared. The displacement vectors of 293 points in the landslide were determined. The average movement velocity of the GPS station since 2004 (about 3.5 cm yr^− 1) agrees with the mean displacement rate obtained from photogrammetry. Furthermore, the estimated velocity varies seasonally between 3 and 6 cm yr^− 1. This variability correlated with rainfall suggests that the creep of the landslide is influenced by hydrological factors.     

综合地理数据与MODIS物候特征的区域土地覆盖制图(英文)

The study developed a feasible method for large-area land cover mapping with combination of geographical data and phenological characteristics, taking Northeast China (NEC) as the study area. First, with the monthly average of precipitation and temperature datasets, the spatial clustering method was used to divide the NEC into four ecoclimate regions. For each ecoclimate region, geographical variables (annual mean precipitation and temperature, elevation, slope and aspect) were combined with phenological variables derived from the moderate resolution imaging spectroradiometer (MODIS) data (enhanced vegetation index (EVI) and land surface water index (LSWI)), which were taken as input variables of land cover classification. Decision Tree (DT) classifiers were then performed to produce land cover maps for each region. Finally, four resultant land cover maps were mosaicked for the entire NEC (NEC_MODIS), and the land use and land cover data of NEC (NEC_LULC) interpreted from Landsat-TM images was used to evaluate the NEC_MODIS and MODIS land cover product (MODIS_IGBP) in terms of areal and spatial agreement. The results showed that the phenological information derived from EVI and LSWI time series well discriminated land cover classes in NEC, and the overall accuracy was significantly improved by 5.29% with addition of geographical variables. Compared with NEC_LULC for seven aggregation classes, the area errors of NEC_MODIS were much smaller and more stable than that of MODIS_IGBP for most of classes, and the wall-to-wall spatial comparisons at pixel level indicated that NEC_MODIS agreed with NEC_LULC for 71.26% of the NEC, whereas only 62.16% for MODIS_IGBP. The good performance of NEC_MODIS demonstrates that the methodology developed in the study has great potential for timely and detailed land cover mapping in temperate and boreal regions.     

A data model and algorithms for a spatial data marketplace

A data marketplace is a platform that facilitates online data trading. It gives sellers the capabilities of publishing data, defining the price function, the authorization rules and the data contract. It gives customers the capabilities to search for data services, to query for their price, to invoke them and to pay for the usage. As data are more and more emphasized as a payable asset, the need for data marketplaces rises. There is a lack of marketplace proposals for spatial data. This paper contributes to fill-in this gap. We propose a data model for representing the different types of data involved. The logical representation of data is a quadtree, and the physical representation fits into a key-value store. The model is thus logically simple and extensible, and physically scalable and highly available. We discuss price queries in detail and propose evaluation algorithms.     

Current channelling and three-dimensional effects detected from magnetotelluric data from a sedimentary basin in Sierras Pampeanas, Argentina

Aquifer-bearing intermontane sedimentary basins of the Sierras Pampeanas in the northwest of Argentina are in general very deep and narrow and contain economically important deposits of Tertiary sediments. This paper presents the results of a study to characterize the sedimentary basin bounded to the west by Sierra de Famatina and to the east by Sierra de Velasco, where an electromagnetic sensing technique, the magnetotelluric (MT) method, was applied. 12 MT sites were deployed along a 30  km E–W transect. Some of the data collected were used to derive a 2-D resistivity model of the basin. The model shows a subsurface trough with a thick (approximately 8  km) sedimentary sequence above it. Anomalous behaviour of the E–W electric-field component ( E _y ) was detected in the period range 1–100  s, where the amplitude of this component was below the instrumental noise level. The cause of this anomaly is not known, but it might be due to the presence of an embedded conducting body between 8 and 10  km, which would give rise to N–S current channelling.