Dip Profiles Research Articles

Subsidence Modeling of the Sabah Basin, a Foreland Basin, Northwest Borneo, Malaysia: ABSTRACT

The Sabah Basin is located on the northwestern side of Borneo. It is a piggy back northeast-southwest-trending basin, riding on a north-westward directed imbricate thrust system. The basin contains approximately 10 to 12 km of sediment in the deepest part deposited in two main episodes of basin development; (1) a pre-early middle Miocene phase of generally deep-marine clastic deformation, which was later subjected to compression and (2) a post-early middle Miocene episode of clastic deposition, comprising bathyal to upper coastal plain sediments. Tectonic subsidence of the post-middle Miocene sequence was determined using the 1-D Airy and 2-D flexure backstripping techniques and wells and selected dip profiles, where the effects of compaction and sediment loading were removed. Variation in paleowater depth was also taken into account. The results show an extremely rapid subsidence phase dominating the earlier part of the basin history, with the later part corresponding to passive basin infilling. The boundary between these two phases becomes younger toward the northwest. The rapid subsidence phase is attributed to tectonic loading, possibly as a result of continuing thrusting at the basin margin. The results also imply that sedimentary sequences formed during the earlier phase were tectonically controlled and marked by transgressivemore » events, while those deposited during the later phase bear the imprints of both tectonic and eustasy.« less

Comparison of Magnetotelluric Data with Drilling Results in Papua New Guinea

Since 1988, more than 800 magnetotelluric (MT) stations have been acquired in Papua New Guinea. Most of the stations have been acquired in the highlands where conventional exploration (seismic) is difficult owing to the outcropping limestone, intense karstification and severe topography. The seismic data that are acquired are expensive and, in many cases, poor to no-record. In an effort to provide useful geophysical data in the exploration effort, several companies have acquired MT data. The survey size has ranged from nine to over one hundred MT stations. Most of the data have been acquired along profiles, with station spacing of between 200 m and 1500 m. With the release of MT and drilling data by the PNG government, a comparison of MT data with well data can now be shown. MT data have now been acquired at more than 15 well locations, which were drilled either before or after the MT data surveys. These comparisons confirm the usefulness and application of the MT technique in tough exploration regions such as PNG. Although MT does not have the accuracy of seismic, it can be very useful in predicting pre-drill depths and lithologies, at best to within 5% of depth. Perhaps MT is more useful in determining gross structure at depth, such as mapping repeats of thrusted section and structural style, which combined with geologic modelling can help to determine the best well location or, in some cases, lower the prospectivity of a prospect. When recorded properly as closely-spaced stations along dip profiles, and interpreted using 2-D algorithms integrated with geology, MT can be very successful in predicting pre-drill depths and helping to determine well locations.

Gravitational dip profiles of the microwave background radiation temperature towards rich clusters of galaxies

The anisotropies of the temperature of the microwave background radiation due to gravitational effects of clusters of galaxies are studied in the frame of the potential approximation method. To describe a typical cluster, the general spherical model of a pure infall of a compensated lump is applied and the resulting density profiles to the Coma cluster density field are normalized. The predicted values of the temperature dip amplitude towards the cluster turn out to be well below the accuracy of present measurements

Applications of magnetotellurics to petroleum exploration in Papua New Guinea: A model for frontier areas

Magnetotelluric (MT) data have been acquired at more than 500 stations in the fold belt of Papua New Guinea since 1988. The MT stations were recorded for several clients and in various Petroleum Prospecting Licenses (PPLs). Most of the MT stations were acquired along dip profiles, trending across the Papuan fold belt. A total of 32 profiles were recorded across mapped surface structures and faults. The data were collected primarily on outcrops of (often heavily karstified) Darai limestone. The spacing between MT stations on the profiles varied from 400–2500 m.

Continental-shelf progradation by sediment-drift accretion

Multi-channel seismic profiles from the Canterbury Basin on the eastern margin of the South Island of New Zealand reveal the importance of current activity in shaping a Neogene shelf sediment prism. The shelf prism prograded across a broad, near-horizontal platform in water depths of 1,000 to 1,750 m. The platform was formed above a condensed section of late Eocene to late Oligocene limestones which overlie Cretaceous to Paleogene rift-fill and transgressive sediments. The Neogene sediment prism contains sediment drifts which are as much as 25 km long and 15 km wide and extend up to 1,600 m (uncompacted) vertically. Individual drifts migrated westward and can be traced between dip profiles, revealing that the long axes of most are subparallel to the present coastline and shelf-edge. Channel-like features at the landward edges of the drifts correspond to residual space left between the landward-prograding off-shelf sediment drift and the adjacent shelf foreslope. Erosion or slow deposition characterized the foreslope. Progradation of the shelf was by the accretion of successive sediment drifts. Before ca. 11.5 Ma (= Pink Horizon), the shelf-edge-parallel drifts were distributed across the central part of the basin, whereas subsequently they were concentrated to the northeast. The seismic architecture of the Neogene sediment prism results from the interplay of an abundant western sediment source and an offshore boundary current system. Present-day ocean circulation involves northward flow along the east coast of the South Island. The basin may have been subjected to a middle Miocene to late Pliocene phase of intensified flow, caused by local topographic enhancement and/or global paleoceanographic events. Current activity has played a crucial role in the sedimentary evolution of the Canterbury Basin Neogene shelf prism.

Sediment accumulation rates in time and space: Paleogene genetic stratigraphic sequences of the northwestern Gulf of Mexico basin

The Paleogene fill of the northwestern Gulf of Mexico basin consists of eight genetic stratigraphic sequences bounded by regional marine flooding surfaces. Calculation of sediment accumulation rates along dip profiles through four subbasins shows that regional changes in accumulation rate - and by inference, rate of sediment supply - of fivefold to tenfold repeatedly occurred over time spans of 1 to 3 m.y. Major sequences record episodes of high supply and accommodation-limited accumulation. Periods of declining and low supply were characterized by short-term over-accommodation and consequent transgressive flooding of the basin margin. Within sequences, depositional rates varied with position relative to the contemporaneous shelf margin, with type of depositional system, and between subbasins. Normal patterns of load-induced basin-margin subsidence and creation of accommodation space were modified by perturbation of the crustal stress regime.

A Preliminary Study of Seismic Stratigraphy of the Late Cenozoic Sequences in the Tainan Basin off Southwestern Taiwan

This study investigates the late Cenozoic strata in the Tainan basin off southwestern Taiwan. The nature and development history of late Cenozoic sequences are discussed in terms of seismic stratigraphy. Multichannel seismic profiles more than 330 km long were acquired and processed, including 4 dip profiles and 3 strike lines. The quality of the seismic profiles range from fair to good. Seismic profiles show that late Cenozoic strata are relatively conformable stratigraphic successions from. which Pleistocene and Pliocene seismic sequences are defined. The seismic reflection configurations of the late Cenozoic sequences are characterized by parallel, subparallel and divergent patterns. The parallel pattern suggests that sediments accumulated at a relatively uniform rate on a shallow shelf within the study area. The divergent reflection pattern and the external wedge- shape of the sequences indicate lateral changes in depositional rates and progressive tilting of the shelf facies. Seismic facies analysis indicates that late Cenozoic sediments were deposited mainly in the fluvial-nearshore environments. The regional trends of the Pliocene and Pleistocene sequences represent relatively smooth parts of the shelf without the characteristic shelf-slope breaks. The shelf breaks in the Pliocene and Pleistocene sequences are probably situated farther seaward than today’s shelf edge. Velocity models indicate an interval velocity ranging from 1,800 m/s to 4,000 m/s suggesting that the late Cenozoic sequences are composed mainly of sands and shales. Vertical distribution of the interval velocity shows that the yelocity of the sequences increases with depth as a result of compaction (i.e. depth of burial). Analyses of seismic sequences, seismic facies and velocity suggest that the Pleistocene and Pliocene sequences developed into a clastic wedge. The sequences form parts of the South China continental margin which has undergone tilting and subsiding during the past ten or more million years.

The relevance of dip profiles from outcrops as reference for the interpretation of SHDT dips

Abstract The ability of SHDT processing techniques to produce detailed sedimentological information has been evaluated by comparing the data with 3000 ft of cores covering shallow marine, deltaic, lacustrine, fluvial and aeolian sedimentary environments. It has been shown previously that, by using side-by-side processing, realistic sedimentary dip sequences through sedimentary bodies can be obtained from SHDT data under normal conditions. However, optimum results require processing parameters to be chosen compatible with the scale of the sedimentary structures present. Furthermore, post-processing selection procedures are required to remove noise and to identify dips representing foreset inclination which can be interpreted in terms of flow direction and sand body orientation. The sedimentological interpretation of downhole dips is often difficult. It may be improved by comparison with vertical dip sequences from outcrops. Sedimentary dip profiles have been measured as part of field work carried out in the Pocahontas Basin of Kentucky. Extensive roadcuts not only enable an unambiguous sedimentological interpretation, but also exhibit numerous relict blast-boreholes, in which vertical dip profiles can be measured under conditions similar to downhole logging. The data now available show that even contradictory dip sequences may be a proper representation of the reality. Systematic collection of sedimentary dip sequences will provide guidelines for a realistic interpretation of downhole records of sedimentary dips.

Example of fault identification using dipmeter data

Abstract Dip results obtained by conventional processing techniques are not always suitable for the identification of faults. Dipmeter identification of faults is usually based on the recognition of increasing angles of dip associated with drag zones adjacent to fault zones. Several case studies confirm this relationship. Interpreting faults in this way is, however, risky, and can lead to erroneous data being integrated into structural interpretation. By reviewing original log quality and processing methods, much erroneous information can be eliminated. The influence of faulting on raw dipmeter curves is studied, and actual fault geometries from outcrops are compared with dipmeter patterns. Outcrop data are taken from several tectonic contexts in order to provide a significant amount of information, in spite of the restricted vertical perspective of the outcropping faults. Reliable detailed fault interpretation from dipmeter data is enhanced by reconstruction of dip profiles from field examples, in particular where similar data are available from other wells and local structural geological knowledge is available.

Late Tertiary Sediment Basin on Continental Slope off Western Nova Scotia: ABSTRACT

The continental slope off Nova Scotia was shaped during the Cenozoic by progradation, erosion, and intrusion by salt-cored diapirs termed the No evidence has previously been reported that Cenozoic sediment accumulation on the slope landward of the Sedimentary ridge was affected by sea-floor deformation owing to growth of diapirs. As part of a regional survey, seismic stratigraphy in reflection profiles shot on the slope between 61° and 64°W was tied to wells on the upper slope and shelf. Dip profiles show three reflector sequences, each about 0.5 sec two-way travel time thick, which terminate in a seaward direction against diapirs of the Sedimentary ridge. Whereas reflectors within the upper and lower sequences dip at least 2° seaward, reflectors within the middle sequence lie flat, lap out onto an unconformity postdating the Eocene-Oligocene canyon-cutting event along the Scotian shelf, and are truncated seaward by a sharp Pliocene-Pleistocene(?) unconformity. Neither rotation along listric faults nor back-tilting by uplift in the Sedimentary ridge can account for the geometry and along-strike ontinuity (200 km) of the middle sequence. It is proposed that sediments forming the flat reflectors were ponded landward of a sea-floor ridge in the present position of the Sedimentary ridge. The dam was formed in the late Paleogene by sediments uplifted above linear salt ridges. Subsequently, erosion removed both the dam and the outward portion on the ponded sediments, and diapirs rose from the salt ridges. End_of_Article - Last_Page 310------------

Crustal structure of the Lomonosov Ridge and the Fram and Makarov Basins near the North Pole

Reversed refraction surveys were conducted along and across the Lomonosov Ridge as part of the 1979 Lomonosov Ridge Experiment. Interpretation of the strike profiles indicates a 5‐km‐thick upper crustal layer with a velocity of 4.7 km/s overlying a 15‐ to 20‐km‐thick layer of 6.6 km/s material. An upper mantle velocity of 8.3 km/s is indicated by a few pn arrivals. High‐amplitude reflection events recorded from this boundary can be successfully modeled by a transition zone of rapidly changing velocity over a depth interval of 5 km. Ray trace modeling of the dip profiles suggests a root structure extending to about 28‐km depth flanked by crust thinning to a depth near 13 km beneath the Makarov Basin and a more gradual thinning to near 16 km beneath the Fram Basin. The similarity between the crust of the Lomonosov Ridge and that beneath the Barents and Kara seas supports the suggestion that the ridge is a slice rifted from the Baltic Shelf.

Influence of mode coupling on differential mode delay

The manner in which the differential mode delay (DMD) pulse response is affected by ellipticity- and microbending-induced mode coupling has been analyzed numerically. We have considered both a fiber profile containing a central index dip and fiber profiles with sinusoidal ripples. We find that slowly varying profile components can be correctly estimated from DMD results even in the presence of substantial mode coupling.

Lifetime-effect relations in the blocking technique for a thick crystal

Abstract The change in blocking dip profiles due to compound nuclei recoil displacement during the lifetime (lifetime-effect relations) has been studied experimentally using the 27Al(p, α) 24Mg resonance reaction at an energy Er=633 keV and treated theoretically using the multistring model and the Fokker-Planck equation. The influence of the crystal thickness traversed by outgoing α-particles and the radiation defects present in the crystal on the lifetime-effect relations has been investigated. The importance of the inclusion of defects in calculations is demonstrated.

Dip-Profile Method of Constructing Structural and Stratigraphic Cross Sections: ABSTRACT

Dip profiles are graphs that show apparent dip as a function of distance along selected horizontal, vertical, or inclined lines on cross sections. Such profiles not only serve to integrate structural control of all kinds (surface dips, dipmeter dips, and dips derived from contour maps and migrated seismic sections) into a single numerical package, but they also provide a foundation for sophisticated geometric constructions based on the concepts of curvature trajectories and dip isogons. A curvature trajectory is a smooth line that connects points on a cross section where the bedding curvature has a distinctive property not shared by points on either side. (The trace of an axial plane is a familiar example.) Eight kinds of curvature trajectories (of which two relate to dip slip faults) occur in nature. Each kind is distinguished on dip profiles by a specific, mathematically-defined special point. A dip isogon is a smooth line that connects points of equal apparent dip on those parts of a cross section where the bedding is curved. (The trace of a crestal plane is a familiar example.) Reliable procedures for extrapolating and interpolating curvature trajectories and dip isogons (based on the known or deduced tectonic style) can be used to establish a network of primary and secondary dip profiles--thereby insuring structural and stratigraphic interpretations that are statistically and End_Page 898------------------------------ geometrically consistent with all observed data. The methods described are especially useful for resolving sparse or erratic data and predicting subtle traps and deep structures from shallow control. End_of_Article - Last_Page 899------------