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Geological Society, London, Petroleum Geology Conference series Vol. 7, 2010 Petroleum Geology: From Mature Basins to New Frontiers— Proceedings of the 7th Petroleum Geology Conference B. A. Vining, Baker Hughes, UK and S. C. Pickering, Schlumberger, Gatwick, UK Global petroleum systems in space and time 1. S. May1, 2. R. Kleist2, 3. E. Kneller1, 4. C. Johnson1 and 5. S. Creaney2 6. Abstract Each of the Earth's approximately 900 sedimentary basins is a unique result of geologic, hydrologic, atmospheric and biologic processes. The interaction of these processes results in complex histories that are palaeogeographically linked within tectonic provinces. Process-based genetic analysis provides the fundamental framework for predicting the distribution and character of petroleum systems. New technologies enable the exploitation of this predictability and are themselves the origin of new ideas and improved systems understanding. Petroleum geoscience embraces both forward modelling of processes as well as observation, calibration and inverse modelling. This approach of forward and inverse modelling promotes a general scientific methodology of simulation, prediction, testing and learning that allows us to describe the genetics of sedimentary basins. Genetic analysis can be applied to the spectrum of resource types from hydrocarbon to groundwater to mineral systems and across the range of scales from regional to play to prospect. Like the study of evolution through the fossil record, fundamental characteristics of petroleum systems can be recovered from the patterns of their distribution within the framework provided by plate motion, palaeogeography and palaeoclimate. These fundamental drivers control regional tectonics, subsidence, fill history and deformation that result in the phenotypic expression of individual basins and their fluid systems. Genetic analysis results in a taxonomic hierarchy that facilitates prediction and guides resource exploration. Although genetic analysis provides a framework for understanding the distribution and nature of petroleum systems, that framework itself is insufficient to address the challenges now facing the petroleum industry. New technologies are required to enable exploration in frontier settings, to identify new opportunities in mature basins, to maximize recovery from existing fields, and to unlock the potential of unconventional resources. Future success in all of these areas is fundamentally dependent on our ability to conceptualize new ideas. 3.3. Tectonics of Rifting and Drifting: Pangea Breakup 3.3.1. Rift Basin Architecture and Evolution Roy W. Schlische & Martha Oliver Withjack Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854-8066 U.S.A. Rift basins have been increasingly the focus of research in tectonics, structural geology, and basin analysis. The reasons for this interest include: (1) Rift basins are found on all passive (Atlantic-type) continental margins and provide a record of the early stages of (super)continental breakup. (2) The architecture of these basins and the basin fill are strongly influenced by the displacement geometry on the bounding normal fault systems (e.g., Gibson et al., 1989). Thus, aspects of the evolution of these fault systems, including their nucleation, propagation and linkage, can be extracted from the sedimentary record. (3) Many modern and ancient extensional basins contain lacustrine deposits (e.g., Katz, 1990) that are sensitive recorders of climate. Milankovitch cycles (e.g., Olsen and Kent, 1999) recorded in these strata provide a quantitative test of the predictions of basin-filling models (e.g., Schlische and Olsen, 1990) that can, in turn, be used to infer aspects of crustal rheology during rifting (e.g., Contreras et al., 1997). (4) Many of the major petroleum provinces of the world are associated with rift basins (e.g., the North Sea basins, the Jeanne d'Arc basin, the Brazilian rift basins). This section provides a brief overview of the rift basins related to Pangean breakup, especially those along the central Atlantic margin (e.g., Olsen, 1997). In particular, we examine: (1) the structural architecture of rift basins; (2) the interplay of tectonics, sediment supply, and climate in controlling the large-scale stratigraphy of rift basins; (3) how the sedimentary fill can be subdivided into tectonostratigraphic packages that record continental rifting, initiation of seafloor spreading, basin inversion, and drifting; and (4) how coring can be used to answer fundamental questions related to these topics. Structural Architecture A typical rift basin is a fault-bounded feature known as a half graben (Fig. 3.3.1.1a). In a cross section oriented perpendicular to the boundary fault (transverse section), the half graben has a triangular geometry (Fig. 3.3.1.1b). The three sides of the triangle are the border fault, the rift-onset unconformity between prerift and synrift rocks, and the postrift unconformity between synrift and postrift rocks (or, for modern rifts, the present-day depositional surface). Within the triangular wedge of synrift units, stratal boundaries rotate from being subparallel to the rift-onset unconformity to being subparallel to the postrift unconformity. This fanning geometry, along with thickening of synrift units toward the boundary fault, are produced by syndepositional faulting. Core from the Newark basin confirms the thickening relationships (see Section 3.3.2). Synrift strata commonly onlap prerift rocks. In a cross section oriented parallel to the boundary fault (longitudinal section), the basin has a synclinal geometry (Fig. 3.3.1.1c), although more complicated geometries are associated with segmented boundary fault systems (e.g., Schlische, 1993; Schlische and Anders, 1996; Morley, 1999). Figure 3.3.1.1. Geometry of a simple half graben. (a) Map-view geometry. (b) Geometry along a cross section oriented perpendicular to the boundary fault, showing wedge-shaped basin in which synrift strata exhibit a fanning geometry, thicken toward the boundary fault, and onlap prerift rocks. (c) Geometry along a cross section oriented parallel to the boundary fault, showing syncline-shaped basin in which synrift strata thin away from the center of the basin and onlap prerift rocks. The half-graben geometry described above is directly controlled by the deformation (displacement) field surrounding the boundary fault system (Gibson et al., 1989; Schlische, 1991, 1995; Schlische and Anders, 1996; Contreras et al. 1997). In a gross sense, displacement is greatest at the center of the fault and decreases to zero at the fault tips (Fig. 3.3.1.2a); this produces the syncline-shaped basin in longitudinal section. In traverse section, the displacement of an initially horizontal surface that intersects the fault is greatest at the fault itself and decreases with distance away from the fault. This produces footwall uplift and hanging-wall subsidence, the latter of which creates the sedimentary basin (Fig. 3.3.1.2b). However, this geometry is affected by fault propagation and forced folding (e.g., Withjack et al., 1990; Gawthorpe et al., 1997). As displacement accumulates on the boundary fault, the basin deepens through time. Because the width of the hangingwall deflection increases with increasing fault displacement (Barnett et al., 1987), the basin widens through time. Because the length of the fault increases with increasing displacement (e.g., Cowie, 1998), the basin lengthens through time. The growth of the basin through time produces progressive onlap of synrift strata on prerift rocks (Fig. 3.3.1.3). Figure 3.3.1.2. Fault-displacement geometry controls the first-order geometry of a half graben. (a) Perspective diagram before (left) and after faulting showing how normal faulting uplifts the footwall block and produces subsidence in the hangingwall block. The yellow dashed line shows the outer limit of hanging-wall subsidence and marks the edge of the basin. Displacement is a maximum at the center of the fault (only the right half of the fault is shown) and decreases toward the fault tip. (b) Traverse section before faulting (left) and after faulting and sedimentation showing footwall uplift and hanging-wall subsidence. The latter produces a wedge-shaped basin (half graben). Figure 3.3.1.3. Simple filling model for a growing half-graben basin shown in map view (stages 1-4), longitudinal cross section (stages 1-5), and transverse cross section (stages 1-4). Dashed line represents lake level. The relationship between capacity and sediment supply determines whether sedimentation is fluvial or lacustrine. For lacustrine sedimentation, the relationship between water volume and excess capacity determines the lake depth. Modified from Schlische and Anders (1996). The simple structural architecture described above may be complicated by basin inversion, in which a contractional phase follows the extensional phase (e.g., Buchanan and Buchanan, 1995). Typical inversion structures include normal faults reactivated as reverse faults, newly formed reverse and thrust faults, and folds (Fig. 3.3.1.4, 3.3.1.5). Basin inversion occurs in a variety of tectonic environments (e.g., Buchanan and Buchanan, 1995), including several passive margins related to the breakup of Pangea (e.g., Doré and Lundin, 1996; Vagnes et al., 1998; Withjack et al., 1995, 1998; Hill et al., 1995; Withjack & Eisenstadt, 1999). The causes of inversion on these passive margins is not well understood. Section 4.2.1 describes how coring, in combination with other methods, may help further our understanding of basin inversion on passive margins. Figure 3.3.1.4. Examples of positive inversion structures. a) Cross section across part of Sunda arc. During inversion, normal faults became reverse faults, producing synclines and anticlines with harpoon geometries (after Letouzey, 1990). b) Interpreted line drawings (with 3:1 and 1:1 vertical exaggeration) of AGSO Line 110-12 from Exmouth sub-basin, NW Shelf Australia (after Withjack & Eisenstadt, 1999). During Miocene inversion, deep-seated normal faults became reverse faults. In response, gentle monoclines formed in the shallow, postrift strata. Figure 3.3.1.5. Experimental models of inversion structures. Cross sections through three clay models showing development of inversion structures (after Eisenstadt and Withjack, 1995). In each model, a clay layer (with colored sub-layers) covered two overlapping metal plates. Movement of the lower plate created extension or shortening. Thin clay layers are prerift; thick clay layers are synrift; top-most layer is postrift and pre-inversion. Top section shows model with extension and no shortening; a half graben containing very gently dipping synrift units is present. The middle section shows model with extension followed by minor shortening; a subtle anticline has formed in the half graben, and is associated with minor steepening of the dip of synrift layers. Bottom section shows model with extension followed by major shortening. The anticline in the half graben is more prominent, and is associated with significant steepening of the dip of synrift strata. New reverse faults have formed in the prerift layers. Although the inversion is obvious in this model, erosion of material down to the level of the red line would remove the most obvious evidence of inversion in the half graben. Furthermore, the prominent reverse faults cutting the prerift units could be interpreted to indicate prerift contractional deformation, as is common in the rift zones related to the breakup of Pangea. Stratigraphic Architecture Numerous non-marine rift basins of varied geography and geologic age share a remarkably similar stratigraphic architecture (Lambiase, 1990; Schlische and Olsen, 1990; Fig. 3.3.1.6). Known as a tripartite stratigraphy, the section begins with basin-wide fluvial deposits overlain by a relatively abrupt deepening-upward lacustrine succession overlain by a gradual shallowing-upward lacustrine and fluvial succession. The key to understanding the significance of this tripartite stratigraphy rests in the relationships among basin capacity and sediment and water supply (Schlische and Olsen, 1990; Carroll and Bohacs, 1999). Tectonics creates accommodation space or basin capacity. Sediment supply determines how much of that basin capacity is filled and whether or not lake systems are possible (Figure 3.3.1.7). In general, fluvial deposition results when sediment supply exceeds capacity, and lacustrine deposition results when capacity exceeds sediment supply. Figure 3.3.1.6. Stratigraphic architecture of Triassic-Jurassic rift basins of eastern North America. For tectonostratigraphic (TS) package III, nearly all basins exhibit all or part of a tripartite stratigraphy: 1, basal fluvial deposits; 2, "deeper-water" lacustrine deposits; 3, "shallow-water" lacustrine and fluvial deposits. The southern basins do not contain TS-IV. TS-I is only recognized in the Fundy basin and may or may not be a synrift deposit. Where TS-II is recognized, a significant unconformity (in terms of missing time) commonly separates it from TS-III. Modified from Olsen (1997), Olsen et al. (2000), and Schlische (2000). Figure 3.3.1.7. [BELOW] Relationships among basin capacity, sediment supply, and volume of water determine the large-scale depositional environments of terrestrial rift basins. In example 1, basin-wide fluvial sedimentation is predicted. In example 2, shallow-water lacustrine sedimentation is predicted. For the basin capacity and available sediment supply shown in this example, no very deep lakes are possible because the excess capacity of the basin (and thus lake depth) is limited. Thus, under these conditions, climate is a relatively unimportant control on lake depth. In example 3, deep-water lacustrine sedimentation is predicted. The relationships shown in Figure 3.3.1.7 allow us to interpret the large-scale stratigraphic transitions observed in many non-marine rift basins. The fluvial-lacustrine transition may result from an increase in basin capacity and/or a decrease in sediment supply. The shallow-water lacustrine to deep-water lacustrine transition may result from an increase in basin capacity, a decrease in sediment-supply, and/or increase in the available volume of water. The deep-water lacustrine to shallow-water lacustrine transition may result from a decrease or an increase in basin capacity (depending on the geometry of the basin's excess capacity), an increase in the sediment supply, and/or decrease in the available volume of water. How do we go about choosing the more likely interpretation? Interestingly, all of the major stratigraphic transitions can be explained by an increase in basin capacity, for which a simple basin-filling model is shown in Figure 3.3.1.3. Other basin filling models are described by Lambiase (1990), Smoot (1991), and Lambiase and Bosworth (1995). As discussed in Section 3.3.3, long cores from rift basins, combined with basin modeling (e.g., Contreras et al., 1997) and seismic reflection data (e.g., Morley, 1999), are required to test the predictions of these basin-filling models. Figure 3.3.1.8. Idealized rift basin showing unconformity-bounded tectonostratigraphic packages. Thin black lines represent stratal truncation beneath unconformities; red half-arrows represent onlaps. In eastern North America, TS-I may not be a synrift deposit, and thus the geometry shown here would be incorrect. TS-II is much more areally restricted and more wedgeshaped than TS-III. The transition between TS-III and TS-IV is likely related to an increase in extension rate. An offset coring technique (vertical orange lines), as used in the Newark basin coring project, does not sample TS-I and most of TS-II. A deep core (vertical yellow line) is necessary to recover TS-I and TS-II. Modified from Olsen (1997). Tectonostratigraphic Packages and Basin Evolution Olsen (1997) subdivided the synrift strata of central Atlantic margin rift basins into four tectonostratigraphic (TS) packages (Fig. 3.3.1.6, 3.3.1.8). An individual TS package consists of all or part of a tripartite stratigraphic succession, is separated from other packages by unconformities or correlative conformities, and generally has a different climatic milieu compared to other TS packages. TS-I is a Permian deposit that may or may not be synrift, whereas TS-II, TS-III, and TS-IV are Late Triassic and Early Jurassic synrift deposits (Olsen et al., 2000). The unconformities between TS-I, TS-II, and TS-III represent significant geologic time. However, it is not yet clear if these unconformities are related to regional tectonic changes (e.g., pulsed extension) (Olsen, 1997) or to relatively local processes such as strain localization (a change from distributed extension on lots of small faults to extension on a few large ones; e.g., Gupta et al., 1998) (Fig. 3.3.1.9). Given their geometry and location in the rift basin, TS-I and TS-II can generally only be sampled through deep coring and not the relatively shallow offset coring utilized in the Newark basin (Section 3.3.3). The rift-onset unconformity between prerift rocks and various synrift units should not be taken as evidence of regional uplift preceding rifting; rather, it more likely reflects erosion and non-deposition occurring over a topographically elevated region resulting from the assembly of Pangea. Figure 3.3.1.9. Stages in the evolution of a rift basin. (a) Early rifting associated with several minor, relatively isolated normal faults. (b) Mature rifting with through-going boundary fault zone, widespread deposition, and footwall uplift and erosion. TS-III and TS-IV were deposited in much larger basins or subbasins than was TS-II, and the unconformity between them is small to non-existent (Olsen, 1997). TS-IV includes the widespread CAMP basalts that were erupted in a geologically short interval at ~202 Ma (e.g., Olsen et al., 1996; Olsen, 1999) (The CAMP basalts comprise a large-igneous province or L.I.P.; see Section 3.1.3). Significantly, TS-IV is absent in all of the southern basins of the central Atlantic margin. As discussed more fully in Withjack et al. (1998), TS-IV was probably never deposited in this region, indicating that synrift subsidence had ceased prior to TS-IV time. [A postrift basalt sequence, which may or may not be the same age as CAMP, is present in the southern region and plausibly can be connected to a seaward-dipping reflector sequence at the continental margin (Oh et al., 1995). The temporal and spatial relationships of these igneous rocks is a critical coring target; see sections 4.2.1 and 4.2.2.] Also significantly, basin inversion in the southern basins occurred shortly prior to and during TS-IV time, while inversion in the northern basins occurred after TS-IV time. (During TS-IV time, the northern basins underwent accelerated subsidence; see Figure 3.3.2.7). Thus, the end of rifting, the initation of inversion, and probably the initiation of seafloor spreading are diachronous along the central Atlantic margin (i.e., during earliest Jurassic time in the southeastern United States and Early to Middle Jurassic time in the northeastern United States and Maritime Canada) (Withjack et al., 1998). Coring, field analysis, and seismic-reflection profiles of synrift and immediately overlying postrift deposits and the structures formed in them, are necessary to clarify the important events occurring at the rift-drift transition. The inferred diachronous initiation of seafloor spreading along the present-day margin of the central North America Ocean is part of larger trend that reflects the progressive dismemberment of Pangea. As the North Atlantic Ocean continued to develop, seafloor spreading propagated northward. For example, seafloor spreading between the Grand Banks and southwestern Europe began during the Early Cretaceous (e.g., Srivastava and Tapscott, 1986); seafloor spreading between Labrador and western Greenland began during the early Tertiary (anomaly 27N) (e.g., Chalmers, et al., 1993); whereas seafloor spreading between eastern Greenland and northwestern Europe began slightly later during the early Tertiary (anomaly 24R) (e.g., Talwani and Eldholm, 1977; Hinz et al., 1993). References: Barnett, J. A. M., Mortimer, J., Rippon, J. H., Walsh, J. J., and Watterson, J., 1987, Displacement geometry in the volume containing a single normal fault: American Association of Petroleum Geologists Bulletin, v. 71, p. 925-937. Buchanan, J. G., and Buchanan, P. G., eds., 1995, Basin Inversion: Geological Society of London Special Publication 88, 596 p. Carroll, A.R., and Bohacs, K.M., 1999, Stratigraphic classification of ancient lakes: Balancing tectonic and climatic controls: Geology, v. 27, p. 99-102. Chalmers, J. A., Pulvertaft, C. R., Christiansen, F. G., Laresen, H. C.,Laursen, K. H., and Ottesen, T. G., 1993, The southern West Greenland continental margin: Rifting history, basin development, and petroleum potential, in Parker, J. R., ed., Petroleum Geology of Northwest Europe, Proceedings of the 4th Conference: Geological Society of London, v. 2, p. 915-931. Contreras, J., Scholz, C. H., King, G. C. P., 1997, A general model of rift basin evolution: constraints of first order stratigraphic observations: Journal of Geophysical Research, v. 102, p. 7673-7690. Cowie, P. A., 1998, Normal fault growth in three-dimensions in continental and oceanic crust, in Faulting and Magmatism at Mid-Ocean Ridges: Geophysical Monograph 106, American Geophysical Union, p. 325-348. Dore, A. G., and Lundin, E. R., 1996, Cenozoic compressional structures on the NE Atlantic margin: nature, origin, and potential signficance for hydrocarbon exploration: Petroleum Geoscience, v. 2, p. 299-311. Eisenstadt, G., and Withjack, M. O., 1995, Estimating inversion: results from clay models, in Buchanan, J. G., and Buchanan, P. G., eds., 1995, Basin Inversion: Geological Society of London Special Publication 88, p. 119-136. Gawthorpe, R.L., Sharp, I., Underhill, J.R., and Gupta, S., 1997, Linked sequence stratigraphic and structural evolution of propagating normal faults: Geology, v. 25, p. 795-798. Gibson, J. R., Walsh, J. J., and Watterson, J., 1989, Modelling of bed contours and cross-sections adjacent to planar normal faults: Journal of Structural Geology, v. 11, p. 317-328. Gupta, S., Cowie, P. A., Dawers, N. H., and Underhill, J. R., 1998, A mechanism to explain rift-basin subsidence and stratigraphic patterns through fault-array evolution: Geology, v. 26, p. 595-598. Hill, K. C., Hill, K. A., Cooper, G. T., O'Sullivan, A. J., O'Sullivan, P. B., and Richardson, M. J., 1995, Inversion around the Bass basin, SE Australia, in Buchanan, J.G., and Buchanan, P.G., eds., 1995, Basin Inversion: Geological Society of London Special Publication 88, p. 525-548. Hinz, K., Eldholm, O., Block, M., and Skogseid, J., 1993, Evolution of North Atlantic volcanic continental margins, in Parker, J. R., ed., Petroleum Geology of Northwest Europe, Proceedings of the 4th Conference: Geological Society of London, v. 2, p. 901-913. Katz, B. J., ed., 1990, Lacustrine basin exploration--case studies and modern analogs: AAPG Memoir 50, 340 p. Lambiase, J.J., 1990, A model for tectonic control of lacustrine stratigraphic sequences in continental rift basins, in Katz, B.J., ed., Lacustrine Exploration: Case Studies and Modern Analogues: AAPG Memoir 50, p. 265-276. Lambiase, J. J., and Bosworth, W., 1995, Structural controls on sedimentation in continental rifts, in Lambiase, J.J., ed., Hydrocarbon habitat in rift basins: Geological Society Special Publication 80, p. 117-144. Morley, C. K., 1999, Patterns of displacement along large normal faults: Implications for basin evolution and fault propagation, based on examples from East Africa: AAPG Bulletin, v. 83, p. 613634. Oh, J., Austin, J. A., Jr., Phillips, J. D., Coffin, M. F., and Stoffa, P. L., 1995, Seaward-dipping reflectors offshore the southeastern United States: Seismic evidence for extensive volcanism accompanying sequential formation of the Carolina trough and Blake Plateau basin: Geology, v. 23, p. 9-12. Olsen, P. E., Schlische, R. W., and Fedosh, M. S., 1996, 580 kyr duration of the Early Jurassic flood basalt event in eastern North America estimated using Milankovitch cyclostratigraphy, in Morales, M., ed., The Continental Jurassic: Museum of Northern Arizona Bulletin 60, p. 11-22. Olsen, P. E., 1997, Stratigraphic record of the early Mesozoic breakup of Pangea in the LaurasiaGondwana rift system: Annual Reviews of Earth and Planetary Science, v. 25, p. 337-401. Olsen, P. E., and Kent, D. V., 1999, Long-period Milankovitch cycles from the Late Triassic and Early Jurassic of eastern North America and their implications for the calibration of the early Mesozoic time scale and the long-term behavior of the planets. Transactions, Royal Society of London, Series A, v. 357, p. 1761-1786. Olsen, P. E., 1999, Giant lava flows, mass extinctions, and mantle plumes [perspective on Marzoli, et al.]: Science, v. 284, p. 604 - 605. Rosendahl, B. R., 1987, Architecture of continental rifts with special reference to East Africa: Annual Review of Earth and Planetary Science, v. 15, p. 445-503. Schlische, R. W., 1991, Half-graben filling models: New constraints on continental extensional basin development: Basin Research, v. 3, p. 123-141. Schlische, R. W., 1993, Anatomy and evolution of the Triassic-Jurassic continental rift system, eastern North America: Tectonics, v. 12, p. 1026-1042. Schlische, R. W., 1995, Geometry and origin of fault-related folds in extensional settings: American Association of Petroleum Geologists Bulletin, v. 79, p. 1661-1678. Schlische, R. W., 2000, Progress in understanding the structural geology, basin evolution, and tectonic history of the eastern North American rift system, in LeTourneau, P.M., and Olsen, P.E., eds., Aspects of Triassic-Jurassic Rift Basin Geoscience: New York, Columbia University Press, in press. Schlische, R. W., and Anders, M. H., 1996, Stratigraphic effects and tectonic implications of the growth of normal faults and extensional basins, in Beratan, K. K., ed., Reconstructing the Structural History of Basin and Range Extension Using Sedimentology and Stratigraphy: GSA Special Paper 303, p. 183-203. Schlische, R. W., and Olsen, P. E., 1990, Quantitative filling model for continental extensional basins with applications to early Mesozoic rifts of eastern North America: Journal of Geology, v. 98, p. 135155. Smoot, J. P., 1991, Sedimentary facies and depositional environments of early Mesozoic Newark Supergroup basins, eastern North America: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 84, p. 369-423. Srivastava, S. P., and Tapscott, C. R., 1986, Plate kinematics of the North Atlantic, in Vogt, P. R., and Tucholke, B. E., eds., The Geology of North America, v. M., The Western North Atlantic Region: Geological Society of America, p. 379-404. Talwani, M., and Eldholm, O., 1977, Evolution of the Norwegian-Greenland Sea: GSA Bulletin, v. 88, p. 969-999. Vågnes, E., Gabrielsen, R. H., and Haremo, P., 1998, Late Cretaceous-Cenozoic intraplate contractional deformation at the Norwegian continental shelf: timing, magnitude and regional implications: Tectonophysics, v. 300, p. 29-46. Withjack, M.O., Olson, J., and Peterson, E., 1990, Experimental models of extensional forced folds: AAPG Bulletin, v. 74, p. 1038-1054. Withjack, M. O. and Eisenstadt, G., 1999, Structural history of the Northwest Shelf, Australia -- an integrated geological, geophysical and experimental approach: AAPG Annual Meeting Abstract, v. 8, p. A151. Withjack, M.O., Olsen, P.E., and Schlische, R.W., 1995, Tectonic evolution of the Fundy rift basin, Canada: Evidence of extension and shortening during passive margin development: Tectonics, v. 14, p. 390-405. Withjack, M.O., Schlische, R.W., and Olsen, P.E., 1998, Diachronous rifting, drifting, and inversion on the passive margin of central eastern North America: An analog for other passive margins: AAPG Bulletin, v. 82, p. 817-835. 3.3. Tectonics of Rifting and Drifting: Pangea Breakup 3.3.2. Extracting Tectonic Information from Cores in Rift Basins Roy W. Schlische Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854-8066 U.S.A. Rift basins are tectonic features. Thus, a goal of any large-scale study involving rift basins should be a better understanding of the tectonic processes controlling basin formation and infilling. The NSF-funded Newark Basin Coring Project (NBCP) demonstrated that it is possible to extract tectonic information from cores in rift basins. This section reviews the successes of NBCP in terms of tectonics and basin evolution and briefly highlights some of the unanswered questions. Figure 3.3.3.1. Schematic cross section of the Newark basin showing offset coring technique; marker unit at the base of one core correlates with same marker unit at top of adjacent core. From Schlische (2000). NBCP used an offset drilling technique (e.g., Olsen et al., 1996a) to take advantage of the eroded half-graben geology of the Newark basin. Core sites were positioned so that the bottom of one hole overlapped with the top of an adjacent hole in a distinctive stratigraphic interval (Figure 3.3.2.1). Correlations are based on cyclostratigraphy and magnetostratigraphy (Olsen et al., 1996a; Kent et al., 1995). The overlap sections allowed construction of a composite stratigraphic section (Olsen et al., 1996a; section 3.2.2). In addition, the overlap sections by themselves provide useful tectonic information. For example, the overlap section between the Rutgers and Somerset cores shows that stratigraphic units thicken by ~12% across the 10 km between these holes (Figure 3.3.2.2). In addition, lake facies are deeper in Somerset than Rutgers. All overlap sections thicken from the lateral edge of the basin toward the basin center (e.g., Rutgers-Titusville) and from the hinged margin toward the intrabasinal faults and/or border fault system (e.g., Nursery-Titusville) (Figure 3.3.2.3). The simplest interpretation of these variations in thickness and facies is variations in basin subsidence caused by syndepositional faulting (see Figure 3.3.2.1). Figure 3.3.3.2. Overlap section of the Rutgers and Somerset cores, showing pronounced increase in thickness and proportion of deeper-water mudstones (gray and black units) from Rutgers to Somerset. Based on data in Olsen et al. (1996a). Click on the image at left to view a larger version. Figure 3.3.3.3. Geologic map of the north-central part of the Newark basin showing the locations of the seven NBCP drill sites. Arrows indicate the amount of thickening between overlap sections of stratigraphically adjacent cores based on correlations in Olsen et al. (1996a). Abbreviations for drill holes are: M, Martinsville; N, Nursery; P, Princeton; R, Rutgers; S, Somerset; T, Titusville; W, Weston. From Schlische (2000). Correlations of the NBCP cored sections to outcrop sections is also extremely useful (e.g., Silvestri, 1994, 1997; Olsen et al., 1996a; Schlische, 1999). The Perkasie Member of the Passaic Formation extends across 125 km of the Newark basin (Figure 3.3.2.4). Variations in thickness of the Perkasie Member indicate that the Newark basin is a large longitudinal syncline, consistent with border-fault displacement being highest near its center and declining towards its lateral ends (e.g., Schlische, 1992) (also see Figure 3.3.2.1). Additional core-to-outcrop correlations, coupled with seismic-reflection profiles, indicate that a hierarchy of fault-related folds along the border fault system and intrabasinal faults formed, at least in part, syndepositionally (Jones, 1994; Schlische, 1992, 1995; Reynolds, 1994; Olsen et al., 1996). Figure 3.3.3.4. Basinwide correlation of the Perkasie Member of the Passaic Formation showing variations in thickness and facies. Inset sketch map of Newark basin shows locations of sections. Modified from Olsen et al. (1996a). Click on the image at left for a larger version. The large-scale basin geometry outlined above, the large-scale stratigraphic architecture present in the NBCP composite section (see Figures 2.4 and 3.3.1.5), and onlap relationships revealed by seismic data can be reproduced in quantitative basin-filling models (see Figure 3.3.1.3). Although these basin-filling models successfully explain many aspects of the stratigraphy of the Newark basin and many other non-marine rift basins (e.g., Lambiase, 1990; Schlische and Olsen, 1990; Olsen, 1997), this simply indicates that the models are viable. The models are bolstered because they also make quantitative predictions about accumulation rates. In the Newark basin, accumulation rates are derived from Milankovitch lacustrine cycles in the NBCP composite section (Figure 3.3.2.5a; Contreras et al., 1997; Olsen and Kent, 1999). The most sophisticated numerical basin filling models (which incorporate self-similar faulting, flexure, isostasy, and sediment diffusion; Contreras et al., 1997) broadly account for observed trends in accumulation rates in the NBCP data (Figure 3.3.2.5b). In addition, the basin-filling models place constraints on the boundary conditions of the rifting process (constant strain-rate conditions are favored over constant fault-lengthening rate), the rheology of the crust and lithosphere, and the nature of fault growth (Schlische, 1991; Schlische and Anders, 1996; Contreras et al., 1997). Figure 3.3.3.5. Accumulation rate data derived from NBCP cyclostratigraphy (a) and constant strain-rate basin-filling model (b). The two accumulation rate data sets were normalized by the maximum accumulation rate in each data set to facilitate comparisons. The numbered curves in (b) were derived from vertical drill holes through the model rift basin shown in map view on right. Curve 2 fits the Newark basin data reasonably well, but fails to reproduce the marked increase in accumulation rates at ~27.5 M.yr. since the onset of extension (Early Jurassic extrusive interval). Modified from Olsen (1997), Contreras et al. (1997), and Schlische (2000). Deviations from the predictions of the models are also important. The most notable deviation in the Newark basin concerns the markedly higher accumulation rates (Figure 3.3.2.5) and deeper lake facies present in the Early Jurassic strata (tectonostratigraphic (TS) package IV; see Figure 3.3.1.5) compared with those in TS-III (Olsen et al., 1996a, b). Strata belonging to TS-IV are interbedded with a series of lava flows (CAMP flows) that were emplaced in as little as 650 kyr (Olsen et al., 1996b). Schlische and Olsen (1990) postulated that accelerated faulting and tilting would markedly increase basin asymmetry. This would cause sediments and water to shift toward the basin depocenter, increasing accumulation rates and average lake depths. This anomaly is not just limited to the Newark basin: a plot of cumulative stratigraphic thickness versus age (Figure 3.3.2.6) shows marked increases in accumulation rates for all of the eastern North American rifts containing Early Jurassic strata (Schlische and Anders, 1996). Thus, tectonics is likely responsible for this "anomaly", although the relationship of CAMP volcanism to this tectonic anomaly is not clear. Figure 3.3.3.6. Cumulative stratigraphic thickness versus geologic age for various exposed rift basins in eastern North America. The Culpeper (C), Deerfield (D), Fundy (F), Hartford (H), and Newark (N) basins all show pronounced increases in stratal thickness in earliest Jurassic time (extrusive interval). Other abbreviations are DR, Deep River; DV, Danville; and R, Richmond basins. Modified from Schlische and Anders (1996). References: Contreras, J., Scholz, C.H., King, G.C.P., 1997, A general model of rift basin evolution: constraints of first order stratigraphic observations: Journal of Geophysical Research, v. 102, p. 7673-7690. Jones, B.D., 1994, Structure and stratigraphy of the Hopewell fault block, New Jersey and Pennsylvania: M.S. Thesis, New Bruswick, NJ, Rutgers University. Kent, D.V., Olsen, P.E., and Witte, W.K., 1995, Late Triassic-earliest Jurassic polarity sequence and paleolatitudes from drill cores in the Newark rift basin, eastern North America: Journal of Geophysical Research, v. 100, p. 14,965-14,998. Lambiase, J.J., 1990, A model for tectonic control of lacustrine stratigraphic sequences in continental rift basins, in Katz, B.J., ed., Lacustrine Exploration: Case Studies and Modern Analogues: AAPG Memoir 50, p. 265-276. Olsen, P.E., 1997, Stratigraphic record of the early Mesozoic breakup of Pangea in the LaurasiaGondwana rift system: Annual Reviews of Earth and Planetary Science, v. 25, p. 337-401. Olsen, P.E. and D.V. Kent, 1999, Long-period Milankovitch cycles from the Late Triassic and Early Jurassic of eastern North America and their implications for the calibration of the early Mesozoic time scale and the long-term behavior of the planets: Transactions of the Royal Society of London, series A, in press. Olsen, P.E., Kent, D.V., Cornet, B., Witte, W.K., and Schlische, R.W., 1996a, High-resolution stratigraphy of the Newark rift basin (early Mesozoic, eastern North America): Geological Society of America Bulletin, v. 108, p. 40-77. Olsen, P.E., Schlische, R.W., and Fedosh, M.S., 1996b, 580 kyr duration of the Early Jurassic flood basalt event in eastern North America estimated using Milankovitch cyclostratigraphy, in Morales, M., ed., The Continental Jurassic: Museum of Northern Arizona Bulletin 60, p. 11-22. Reynolds, D.J., 1994, Sedimentary basin evolution: tectonic and climatic interaction: Ph.D. thesis, New York, Columbia University. Schlische, R.W., 1991, Half-graben filling models: new constraints on continental extensional basin development: Basin Research, v. 3, p. 123-141. Schlische, R.W., 1992, Structural and stratigraphic development of the Newark extensional basin, eastern North America; Implications for the growth of the basin and its bounding structures: Geological Society of America Bulletin, v. 104, p. 1246-1263. Schlische, R.W., 1995, Geometry and origin of fault-related folds in extensional settings: AAPG Bulletin, v. 79, p. 1661-1678. Schlische, R.W., 1999, Progress in understanding the structural geology, basin evolution, and tectonic history of the eastern North American rift system, in LeTourneau, P.M., and Olsen, P.E., eds., Aspects of Triassic-Jurassic Rift Basin Geoscience: New York, Columbia University Press, in press. Schlische, R.W., and Anders, M.H., 1996, Stratigraphic effects and tectonic implications of the growth of normal faults and extensional basins, in Beratan, K.K., ed., Reconstructing the Structural History of Basin and Range Extension Using Sedimentology and Stratigraphy: GSA Special Paper 303, p. 183203. Schlische, R.W., and Olsen, P.E., 1990, Quantitative filling model for continental extensional basins with applications to early Mesozoic rifts of eastern North America: Journal of Geology, v. 98, p. 135155. Silvestri, S.M., 1994, Facies analysis of Newark basin cores and outcrops: Geological Society of America Abstracts with Programs, v. 26, p. A-402. Silvestri, S.M., 1997, Cycle correlation, thickening trends, and facies changes of individual paleolake highstands across the Newark basin, New Jersey and Pennsylvania: Geological Society of America Abstracts with Programs, v. 29, p. 80. 3.3.3. Large Igneous Provinces Millard F. Coffin, Institute for Geophysics. The University of Texas at Austin, 4412 Spicewood Springs Rd., Suite 600, Austin, Texas 78759-8500 Plate tectonic theory has provided a breakthrough in understanding how the continuous opening and closing of ocean basins reflects convection in the Earthís upper mantle. Among the terrestrial planets and moons of our solar system, however, global plate tectonics may well be unique to Earth. Even on Earth, current plate tectonic theory does not predict major crustal growth events termed large igneous provinces, LIPs (Figure 3.3.3.1). LIPs are a continuum of voluminous magmatic constructions which include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups, and ocean basin flood basalts. They form in massive volcanic events that result from a mode of mantle convection different from that driving plate tectonics on Earth. Furthermore, unlike the magmatism associated with plate tectonics that creates new crust exclusively in the ocean basins or at ocean margins, LIPs form independently of plate setting; they form on the continents, in the oceans, and along margins between the two, and either wholly within plates or at plate boundaries. The alternative mode of convection manifested by LIPs is probably how other terrestrial planets and moons lose most, if not all, of their interior heat. Figure 3.3.3.1: Global LIPs, including oceanic plateaus, volcanic passive margins, continental flood basalts, submarine ridges, seamount groups, and ocean basin flood basalts. The CAMP is shown in red. (Modified after Coffin and Eldholm, 1994). LIPs represent enormous outpourings of predominantly basaltic magma that commonly cover areas of 105 km2 or more. The largest appear to occur in ocean basins, where giant plateaus such as the Ontong Java Plateau in the western Pacific and the Kerguelen Plateau in the Indian Ocean have formed. Similarly, flood basalts were erupted along many "volcanic passive margins" (e.g., Eastern North America, Greenland, Norway, Brazil, Namibia, NW Australia) during continental breakup, as well as in continental settings (e.g., Columbia Plateau in the Pacific Northwest, Deccan in India, Karoo/Ferrar in South Africa/Antarctica, Parana in Brazil, Siberian in Asia). Primarily because of ease of access, continental flood basalts are the best sampled and documented type of LIP. Studies of continental flood basalts illustrate the evolution in thinking regarding the importance of such events for Earth evolution. Twenty years ago, when systematic studies of continental flood basalts began, flood volcanism was largely viewed as produced by continental rifting - a "standard" plate tectonic interpretation. Improvements in geochronology, however, have demonstrated that all well-dated continental flood basalt provinces initially thought to have formed over many tens of millions of years instead formed, for the most part, in a million years or less. The rapid melt production rates documented by the eruption of huge volumes of magma in such short time intervals implies a generation mechanism other than rifting, since passive rifting cannot produce such high melting rates. This realization has led to other models involving either the melting of a plume of hot, mantle that rises to the surface from a deep thermal boundary layer, such as that between the core and mantle, or upflow of deep upper mantle in areas where the plate thickness varies greatly. Neither the initial phase of activity that produces the LIPs ("plume head") nor the subsequent volcanic activity that commonly produces trailing volcanic ridges and island chains ("plume tail") in the ocean basins (Figure 3.3.3.2, below) below are directly related to, or predicted by, the standard cycle of plate formation, aging, and destruction described by plate tectonic theory. Figure 3.3.3.2: Model of Wilsonian periods and MOMO (mantle overturn, major orogeny) episodes. During Wilsonian periods (left), the normal mode of plate tectonics prevails, with opening and closing of oceans and mantle convection with isolated upper and lower mantle. Plumes originate predominantly from the base of the upper layer, and continental growth is dominated by arc accretion. During MOMO episodes (right), accumulated cold material descends from the 660knm boundary layer into the lower mantle, and multiple major plumes rise from the core-mantle boundary to form large igneous provinces (LIPs) at the surface, thus creating a major overturn. (After Stein and Hofmann, 1994) The magnitude of such igneous events is perhaps best illustrated by oceanic plateaus. The Ontong Java Plateau in the western Pacific, for example, consists of more than 50 million km3 of mafic volcanic and plutonic rocks which form a ~30 km thick plateau encompassing an area equal to one third of Australia. Events of this magnitude are unknown to human experience, but the consequences are dramatic. For example, 1 million km3 of basalt, the size of an average continental flood basalt province, would bury the area east of the Appalachians from Maine to Florida under more than a kilometer of basalt. The release of gases (CO2, SO2, Cl, F, H2O, etc.) accompanying such great eruptions must have had tremendous consequences for the composition of the ocean and atmosphere, with dramatic impact on climate and environment. Indeed, LIP formation correlates temporally with ecological changes and extinction of life forms. For instance, the eruption of the Siberian continental flood basalt province 250 million years ago at the Permian-Triassic boundary coincided with the largest extinction of plants and animals in the geologic record. Ninety percent of all species became extinct at the boundary. Similarly, eruption of the Central Atlantic Magmatic Province (CAMP) correlates temporally with the Triassic-Jurassic boundary mass extinctions. On Iceland, the 1783-84 eruption of Laki provides the only human record of experience with the type of volcanism that constructs igneous provinces. Although Laki produced a basaltic lava flow which represents only 1% of the volume of a typical LIP flow, the eruptionís environmental impact resulted in the deaths of 75% of Icelandís livestock and 25% of its population from starvation. If such a relatively small eruption happened today, all air traffic over the North Atlantic would likely be halted for three to six months. Observational and modeling efforts to understand LIP formation and development are at an early stage and are comparable to investigations of the mid-ocean ridge system prior to development of the plate tectonics paradigm, in that no one theory adequately explains large-volume basaltic magmatism on Earth and the other terrestrial planets and satellites. Understanding the processes in the Earthís mantle and crust, and the effects of LIPs on the oceans, atmosphere, and biosphere (Fig. Figure 3.3.3.3: Temporal correlations among 3.3.3.3), is of particular importance. Because geomagnetic the scientific problems associated with LIPs polarity, crustal production rages, LIPs, sea range widely, scientists from many disciplines water Strontium are involved in their study. These fields include (Sr), sea level, climate, black shales, and mass geochronology, marine geophysics, petrology, extinctions. geochemistry, mineral physics, rock (After Coffin and Eldholm 1994), Click on deformation, oceanic and atmospheric image for a chemistry, physical volcanology, more legible figure. paleomagnetics, tectonics, seismology, geodynamics, micropaleontology, paleoclimatology, paleoceanography, sedimentology, remote sensing, and planetary geology. References: Coffin, M. F., and Eldholm, O., 1994. Large igneous provinces: crustal structure, dimensions, and external consequences, Reviews of Geophysics, 32, 1-36. Stein, M., and Hofmann, A. W., 1994. Mantle plumes and episodic crustal growth, Nature, 372, 63-68.