Third-order Sequence Boundaries Research Articles

Transgressive–regressive (T–R) sequence analysis of the Jurassic succession of the Sverdrup Basin, Canadian Arctic Archipelago

Transgressive–regressive (T–R) sequence analysis has been applied to the Jurassic succession of the Sverdrup Basin with sequence boundaries drawn at subaerial unconformities or the correlative transgressive surfaces. A hierarchal system of sequence order that reflects the different nature of the boundaries has been formulated on the basis of boundary characteristics. Second- through fifth-order sequences have been recognized in the Jurassic succession, which itself is part of a first-order sequence of mid-Permian – Early Cretaceous age.The Jurassic strata occur within four second-order sequences. The boundaries of these sequences are characterized by widespread subaerial unconformities across which major changes in depositional and subsidence regimes occur. These boundaries are earliest Rhaetian, earliest Pliensbachian, earliest Bajocian, earliest Oxfordian, and Hauterivian in age.Each second-order sequence is divisible into a number of third-order sequences bounded mainly by basin-wide transgressive surfaces with subaerial unconformities present on the basin margins. The ages of the 10 Jurassic third-order sequences are Rhaetian – Hettangian, Sinemurian, Pliensbachian – Toarcian, late Toarcian – Aalenian, Bajocian, Bathonian, Callovian, Oxfordian – early Kimmeridgian, late Kimmeridgian – early Tithonian, and late Tithonian. The third-order sequences commonly contain three to six fourth-order sequences. These sequences are bound entirely by transgressive surfaces that can be correlated only over a portion of the basin.A good correlation between the second- and third-order transgressive events of the Sverdrup Basin and proposed global events is observed. This worldwide occurrence suggests that the events in part reflect eustatic sea-level changes. The characteristics of the second- and third-order boundaries also indicate that each had a tectonic influence that resulted in a rapid relative sea-level fall (uplift) followed by a rapid rise (subsidence). Given the apparent combination of tectonic and eustatic influence on the generation of the second- and third-order sequence boundaries, they are interpreted to reflect significant plate-tectonic reorganizations that affected the intraplate stress regimes of the oceanic (eustatic) and continental (tectonic) portions of each lithospheric plate.

Borehole Magnetostratigraphy, Absolute Age Dating, and Correlation of Sedimentary Rocks, with Examples from the Paris Basin, France

Total and CEA have conceived and developed two new logging tools which allow continuous, precise, and accurate in-situ magnetic measurements within weakly magnetized sedimentary rocks encountered in uncased industry drilled wells. The combination of these magnetic measurements permits for the first time continuous determination of natural remanent magnetization (NRM) polarities occurring in the logged section. The resulting well magnetostratigraphic sequence (WMS) which may be recognized from well to well (magnetostratigraphic correlations), may also be correlative to a geomagnetic polarity time scale (GPTS) or reference magneto-stratigraphic scale (RMS), given adequate dating tie points and lack of noticeable remagnetizations. Application of this method to the Upper Jurassic formation in four wells of the Paris basin has yielded promising results for both stratigraphic and near absolute age correlations as well as determination of facies diachronisms. The comparison of results obtained from magnetic measurements and from sequence stratigraphy analysis shows that third-order sequence boundaries may be correlative to geomagnetic reversals, but may also be diachronous in wells 80 km or less apart. The potential of borehole magnetic measurements as presented in this paper is still under investigation. However, these encouraging initial results show that this new investigating and dating method could be of great help in the analysis of subsurface stratigraphy by extending the concepts of magnetostratigraphy from the outcrops and laboratory directly into borehole logging.

Relationship of Facies and Sequence Stratigraphy to Paleokarst and Fracture Overprints in the Carbonates of the Arbuckle Group in the Evaluation of Exploration and Horizontal Drilling Potential

The mid-continent region, especially in Oklahoma and Arkansas, contains thick dolomite Paleozoic carbonate sections with karstic character. These sections commonly exhibit strong structural overprints, including intense fracturing, due primarily to Pennsylvanian orogenies. The Arbuckle Group is compose of multiple parasequences that are the result of cyclic peritidal deposition on a broad shallow shelf. Sequence stratigraphy evaluation indicates that significant unconformities or disconformities occur within the Arbuckle Group along third-order sequence boundaries. Arbuckle carbonates were subjected to very early dolomitization (Ordovician through Devonian). Sequences in which intercrystalline porosity was developed with little or no vuggy porosity usually have low permeability and effective porosity. However, these dolomitic sequences are quite susceptible to fracturing and they may produce in structural traps. These fractured sequences in the Arbuckle also are particularly susceptible to karstification associated with multiple unconformities, especially in areas where there has been significant orogenic activity such as the Criner uplift in southern Oklahoma. Fracturing and subsequent karstification have significant influence on porosity development and can produce extremely heterogeneous reservoirs. Exploration for oil and gas in the Arbuckle Group has been a difficult task. Problems with seal and source along with complex diagenetic and structural histories still plague efforts to understand Arbucklemore » reservoir development. There is new evidence that dolomitization, fracturing and karstification may be related to particular sequence positions and their related facies and disconformities. Innovative advances in geologic concepts, such as sequence stratigraphy, and in techniques, such as horizontal drilling, may lead to new discoveries in the Arbuckle Group.« less

Magnetic Logging: Detection of the Earth's Magnetic Field Reversals and Application to Borehole Magnetostratigraphy

TOTAL CFP and CEA (the French Atomic Energy Commission) designed and developed two magnetic logging tools for precise and reliable in-situ magnetic measurements in the low magnetized sedimentary formations encountered when drilling for oil. The tools, measuring respectively the magnetic field and the magnetic susceptibility of the rocks, are operated as standard logging tools, and logs are recorded during standard logging operations. A proper combination of these magnetic respectively the magnetic field and the magnetic susceptibility of the rocks, are operated as standard logging tools, and logs are recorded during standard logging operations. A proper combination of these magnetic measurements leads to the determination, every meter, of natural remanent magnetization polarity, from which the direction of the Earth's magnetic field at the time of sedimentation is derived. A magnetostratigraphic sequence is obtained for each well and appears to be similar to the magnetostratigraphic reference scale. Application of this method to wells in the North Sea gives good results for correlations and absolute age determination, as well as facies diachronism. Further comparison of results obtained from magnetic measurements and from sequence stratigraphy applied to conventional logs shows that third-order sequence boundaries can be diachronous in wells 80 km apart. Although themore » potential of magnetic measurements is still under investigation, the first encouraging results clearly show that the new dating method presented in this paper can be very helpful in petroleum geology.« less

Variations of the Sequence Stratigraphic Model: Past Concepts, Present Understandings, and Future Directions

The working hypothesis upon which the sequence concepts are based is that the relative sea level change results in changes in the capacity of a basin to accommodate sediment, which, in turn, results in a succession of sequences. The interplay between eustasy, tectonics, sediment flux, and physiography yields a predictable geologic response in carbonate, clastic, as well as mixed carbonate/clastic settings. The criteria for recognition of sequence boundaries can be varied within a given basin as well as between basins. They include but are not restricted to (1) a basinward shift of facies across a sharp bedding contact, (2) onlapping stratal geometry, and (3) truncation of strata. The key to the correct utilization of these concepts is to recognize sequence stratigraphy as an approach or a tool rather than a rigid template. Observations from the upper Albian, Cretaceous, Viking Formation of the western Canadian sedimentary basin are presented to illustrate the stratigraphic expression of clastic depositional sequences on a ramp margin. In this setting, forced regressions and lowstand shorelines commonly occur, incised valleys sometimes occur, and submarine fans rarely occur, in response to fluctuations of relative sea level. The base of the Viking Formation sometimes is characterized by relatively coarse-grainedmore » sediments sharply overlying fine-grained offshore muds and is interpreted as a third-order sequence boundary. Pebbles occasionally are observed at this contact. Subsequently, a number of higher-order sequences within the lower to middle Viking are observed and are characterized by the occurrence of forced regressions and lowstand shorelines without associated incised valleys.« less

Biostratigraphic Calibration in Sequence Stratigraphic Analysis: Pliocene-Pleistocene Case Study from Gulf of Mexico: ABSTRACT

Biostratigraphic analysis provides chronostratigraphic data for correlating depositional sequences and paleoecologic data helpful in identifying depositional facies. These data sets are essential for correct analysis of sequence stratigraphy in areas of complex depositional architecture and structural style. The most useful sequence stratigraphic element for correlation is the condensed section. The condensed section is a facies consisting of thin marine beds of hemipelagic or pelagic sediments deposited at very slow rates. They are most extensive during the time of regional transgression of the shoreline. Condensed sections are excellent correlation data because they contain abundant hemipelagic and pelagic fossil materials and form regionally continuous high-amplitude seismic reflectors. In well samples condensed sections are recognized by peaks in marine fossil abundance and diversity and by high carbonate content; on electric logs they are recognized as high-resistivity clays. Three types of condensed sections are recognized in the Galveston area-South Addition A-158 No. 1 well. Condensed sections deposited in paleowater depths of less than 600 ft occur within the third-order depositional sequences, indicating relatively thick lowstand and high-stand sediments. Condensed sections deposited in paleowater depths of 600-3000 ft occur at or just below the third-order depositional sequence boundaries, indicating relatively thin or absent sediments ofmore » the highstand systems tract. Condensed sections deposited at paleowater depths deeper than 3000 ft extend through most of the third-order sequence, suggesting essentially no eustatic influence on sediment accumulation.« less