The importance of strike-slip faulting was recognized near the turn of the century, chiefly from investigations of surficial offsets associated with major earthquakes in New Zealand, Japan, and California. Extrapolation from observed horizontal displacements during single earthquakes to more abstract concepts of long-term, slow accumulation of hundreds of kilometers of horizontal translation over geologic time, however, came almost simultaneously from several parts of the world, but only after much regional geologic mapping and synthesis. Strike-slip faults are classified either as transform faults which cut the lithosphere as plate boundaries, or as transcurrent faults which are confined to the crust. Each class of faults may be subdivided further according to their plate or intraplate tectonic function. A mechanical understanding of strike-slip faults has grown out of laboratory model studies which give a theoretical basis to relate faulting to concepts of pure shear or simple shear. Conjugate sets of strike-slip faults form in pure shear, typically across the strike of a convergent orogenic belt. Fault lengths are generally less than 100 km, and displacements along them are measurable in a few to tens of kilometers. Major strike-slip faults form in regional belts of simple shear, typically parallel to orogenic belts; indeed, recognition of the role strike-slip faults play in ancient orogenic belts is becoming increasingly commonplace as regional mapping becomes more detailed and complete. The lengths and displacements of the great strike-slip faults range in the hundreds of kilometers. The position and orientation of associated folds, local domains of extension and shortening, and related fractures and faults depend on the bending or stepping geometry of the strike-slip fault or fault zone, and thus the degree of convergent or divergent strike-slip. Elongate basins, ranging from sag ponds to rhombochasms, form as result of extension in domains of divergent strike slip such as releasing bends; pull-apart basins evolve between overstepping strike-slip faults. The arrangement of strike-slip faults which bound basins is tulip-shaped in profiles normal to strike. Elongate uplifts, ranging from pressure ridges to long, low hills or small mountain ranges, form as a result of crustal shortening in zones of convergent strike slip; they are bounded by an arrangement of strike-slip faults having the profile of a palm tree. Paleoseismic investigations imply that earthquakes occur more frequently on strike-slip faults than on intraplate normal and reverse faults. Active strike-slip faults also differ from other types of faults in that they evince fault creep, which is largely a surficial phenomenon driven by elastic loading of the crust at seismogenic depths. Creep may be steady state or episodic, pre-seismic, co-seismic, or post-seismic, depending on the constitutive properties of the fault zone and the nature of the static strain field, among a number of other factors which are incompletely understood. Recent studies have identified relations between strike-slip faults and crustal delamination at or near the seismogenic zone, giving a mechanism for regional rotation and translation of crustal slabs and flakes, but how general and widespread are these phenomena, and how the mechanisms operate that drive these detachment tectonics are questions that require additional observations, data, and modeling. Several fundamental problems remain poorly understood, including the nature of formation of en echelon folds and their relation to strike-slip faulting; the effect of mechanical stratigraphy on strike-slip-fault structural styles; the thermal and stress states along transform plate boundaries; and the discrepancy between recent geological and historical fault-slip rates relative to more rapid rates of slip determined from analyses of sea-floor magnetic anomalies. Many of the concepts and problems concerning strike-slip faults are derived from nearly a century of study of the San Andreas fault and have added much information, but solutions to several remaining and new fundamental problems will come when more attention is focused on other, less well studied strike-slip faults.

Strike-Slip faults

/pdf/towards-the-standardization-of-sequence-stratigraphy-b61e2b7dm7.pdf

Towards the standardization of sequence stratigraphy

Summary
Fluvial landforms and deposits provide one of the most readily studied Quaternary continental records, and alluvial strata represent an important component in most ancient continental interior and continental margin successions. Moreover, studies of the long-term dynamics of fluvial systems and their responses to external or ‘allogenic' controls, can play important roles in research concerning both global change and sequence-stratigraphy, as well as in studies of the dynamic interactions between tectonic activity and surface processes. These themes were energized in the final decades of the twentieth century, and may become increasingly important in the first decades of this millennium.

This review paper provides a historical perspective on the development of ideas in the fields of geomorphology/Quaternary geology vs. sedimentary geology, and then summarizes key processes that operate to produce alluvial stratigraphic records over time-scales of 103−106 years. Of particular interest are changes in discharge regimes, sediment supply and sediment storage en route from source terrains to sedimentary basins, as well as changes in sea-level and the concept of accommodation. Late Quaternary stratigraphic records from the Loire (France), Mississippi (USA), Colorado (Texas, USA) and Rhine–Meuse (The Netherlands) Rivers are used to illustrate the influences of climate change on continental interior rivers, as well as the influence of interacting climate and sea-level change on continental margin systems.

The paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea-level change. At present, empirical field-based research on fluvial response to climate and sea-level change lags behind: (a) the global change community's understanding of the magnitude and frequency of climate and sea-level change; (b) the sequence-stratigraphic community's desire to interpret climate and, especially, sea-level change as forcing mechanisms; and (c) the modelling community's ability to generate numerical and physical models of surface processes and their stratigraphic results. A major challenge for the future is to catch up, which will require the development of more detailed and sophisticated Quaternary stratigraphic, sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings. There is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter (102−103 years) and longer (104−106 years) time-scales than has commonly been the case to date, as well as in larger river systems, from source to sink. Studies of Quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre-Quaternary rock record.

Fluvial responses to climate and sea‐level change: a review and look forward

/pdf/morphologic-and-facies-trends-through-the-fluvial-marine-28tnn15m7c.pdf

Morphologic and facies trends through the fluvial–marine transition in tide-dominated depositional systems: A schematic framework for environmental and sequence-stratigraphic interpretation

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. 10. Diagram showing the GMTED2010 layer extents (minimum and maximum latitude and longitude) are a result of the coordinate system inherited from the 1-arc-second SRTM

Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010)

Shoreline migration patterns can be described in terms of the shoreline trajectory, which is the shoreline path viewed along a cross-sectional depositional-dip section. Discrete classes of shoreline trajectories can be defined: accretionary and non-accretionary forced regression; normal regression; and accretionary and non-accretionary transgression. "Accretionary" implies that sediment supplied to the shoreline participates in determining the shoreline trajectory, whereas "non-accretionary" implies that existing topography dictates the trajectory. In the latter case, translation of the shoreline takes place without significant deposition. The directions of the shoreline trajectories and the above classes provide a basis for describing variable shoreline behavior for individual shorel ne excursions, for stacked shoreline migration patterns, for systems tracts, and for depositional cycles. A non-accretionary forced regression takes place when little or no sediment is deposited at the shoreline as sea level falls. Accretionary forced regressions occur when sea-level fall is accompanied by coastal sediment accumulation. The architecture of accretionary forced regressions is controlled by the slopes of the alluvial and marine environments, and the shoreline trajectory. A regressive surface of marine erosion is most likely to be formed when the path of the shoreline converges with the fronting depositional foundation. During normal regression, the shoreline trajectory and the depositional foundation usually diverge, with accompanying deepening of water in front of the prograding shoreline. A non-accretionary transgression is defined as a transgression with a shoreline trajectory coinciding with the alluvial depositional surface at the onset of transgression. Accommodation may or may not be present at the landward side of the shoreline at the onset of transgression, but will not be generated there during transgression. An accretionary transgression takes place when the shoreline trajectory diverges relative to the alluvial depositional surface at the onset of transgression. This implies that accommodation is continuously generated and filled behind the retreating shoreline. If a ravinement surface is formed during transgression, its chronostratigraphic significance is maintained only if sediments accumulating during transgression are solely preserved seaward (and not lan ward) of the transgressing shoreline. As the shoreline migrates in various directions, composite stacking patterns, systems tracts, and depositional cycles, as well as surfaces or thin intervals of slow deposition, nondeposition, or erosion are formed. These levels can be used to envelop the depositional cycles. The cycles can be subdivided into two or four systems tracts. The maximum transgressive surface is the most applicable for delineation of cycles. A ravinement surface that merges with or erodes into the subaerial unconformity, in combination with the maximum regressive surface, can also be useful for bracketing cycles.

Shoreline Trajectories and Sequences: Description of Variable Depositional-Dip Scenarios

Shoreline and shelf- edge trajectories describe the migration through time of sedimentary systems, using geomorphological breaks-in- slope that are associatedwith key changes in depositional processes and products. Analysis of these trajectories provides a simple descriptive tool that complements and extends conventional sequence stratigraphic methods and models. Trajectory
analysis offers four advantages over a sequence stratigraphic interpretation based on systems tracts: (1) each genetically related advance or retreat of a shoreline or shelf edge is viewed in the context of a continuously evolving depositional system, rather than as several discrete systems tracts; (2) subtle
changes in depositional response (e.g. within systems tracts) can be identi¢ed and honoured; (3) trajectory analysis does not anticipate the succession of depositional events implied by systemstract models; and (4) the descriptive emphasis of trajectory analysis does not involve any a priori assumptions about the type or nature of the mechanisms that drive sequence development.These
four points allow the level of detail in a trajectory-based interpretation to be directly tailored to the available data, such that the interpretation may be qualitative or quantitative in two or three dimensions. Four classes of shoreline trajectory are recognized: ascending regressive, descending regressive, transgressive and stationary (i.e. nonmigratory). Ascending regressive and high-angle (accretionary) transgressive trajectories are associated with expanded facies belt thicknesses, the absence of laterally extensive erosional surfaces, and relatively high preservation of the shoreline
depositional system. In contrast, descending regressive and low-angle (nonaccretionary) transgressive trajectories are associated with foreshortened and/or missing facies belts, the presence of laterally extensive erosional surfaces, and relatively low preservation of the shoreline depositional system.
Stationary trajectories record shorelines positioned at a steeply sloping shelf edge, with accompanying bypass of sediment to the basin £oor. Shelf- edge trajectories represent larger spatial and temporal scales than shoreline trajectories, and they can be subdivided into ascending, descending and stationary (i.e. nonmigratory) classes. Ascending trajectories are associated with a relatively large number and thickness of shoreline tongues (parasequences), the absence of laterally extensive erosional surfaces on the shelf, and relatively low sediment supply to the basin floor. Descending trajectories are associatedwith a few, thin shoreline tongues, the presence of laterally extensive erosional surfaces on the shelf, and high sediment supply to basin- floor fan systems. Stationary trajectories record near-total bypass of sediment across the shelf and mass transfer to the basin floor.

Trajectory analysis: concepts and applications

Conceptual basis and variability in sequence stratigraphy: a different perspective

The study of source‐to‐sink systems relates long‐term variations in sediment flux to morphogenic evolution of erosional–depositional systems. These variations are caused by an intricate combination of autogenic and allogenic forcing mechanisms that operate on multiple time scales – from individual transport events to large‐scale filling of basins. In order to achieve a better understanding of how these mechanisms influence morphological characteristics on different scales, 29 submodern source‐to‐sink systems have been investigated. The study is based on measurements of morphological parameters from catchments, shelves and slopes derived from a ∼1 km global digital elevation model dataset, in combination with data on basin floor fans, sediment supply, water discharge and deposition rates derived from published literature. By comparing various morphological and sedimentological parameters within and between individual systems, a number of relationships governing system evolution and behaviour are identified. The results suggest that the amount of low‐gradient floodplain area and river channel gradient are good indicators for catchment storage potential. Catchment area and river channel length is also related to shelf area and shelf width, respectively. Similarly to the floodplain area, these parameters are important for long‐term storage of sediment on the shelf platform. Additionally, the basin floor fan area is correlative to the long‐term deposition rate and the slope length. The slope length thus proves to be a useful parameter linking proximal and distal segments in source‐to‐sink systems. The relationships observed in this study provide insight into segment scale development of source‐to‐sink systems, and an understanding of these relationships in modern systems may result in improved knowledge on internal and external development of source‐to‐sink systems over geological time scales. They also allow for the development of a set of semi‐quantitative guidelines that can be used to predict similar relationships in other systems where data from individual system segments are missing or lacking.

Relationships between morphological and sedimentological parameters in source-to-sink systems: a basis for predicting semi-quantitative characteristics in subsurface systems

The concept of stratigraphic base level, or the ratio between accommodation and sediment supply (A/S ratio), has been used to analyse the Rusty and Canyon Creek Members of the Campanian Ericson Sandstone in the Rock Springs Uplift, SW Wyoming, USA. The Ericson Sandstone was deposited under fluvial to estuarine conditions in a foreland basin setting influenced both by Sevier-style (thrust belt) tectonism and by more local, Laramide-style, foreland uplifts. The depositional setting was situated several tens to a few hundred kilometres from the nearest shoreline. Therefore, sea level change at the contemporaneous shoreline probably had little, if any, influence on the development of the sedimentary architecture.



The Rusty Member shows an alternation between incised valleys filled by multi-storey estuarine channel sandstones showing palaeoflow to the south and delta plain sediments with single-storey channels with no evidence of tidal influence, which show palaeoflow to the east. This cyclicity is interpreted as recording repeated uplift of the Wind River Range to the north, causing valley incision and reduction of the A/S ratio. During quiescent periods, the A/S ratio increased allowing the valleys to fill and delta plain conditions to be subsequently re-established because of increased sediment supply from the thrust belt in the west.



A regional unconformity at the base of the Canyon Creek Member truncates the Rusty Member, and represents a significant reduction of the A/S ratio caused by Laramide tectonic uplift. The Canyon Creek Member is a multi-storey, multi-lateral fluvial channel sandstone, where channel preservation and thickness increase upwards, suggesting an increase of the A/S ratio. The Canyon Creek Member channels are interpreted to have been sinuous, meandering channels from the observed sedimentary structures and fill patterns, despite their sand-rich nature. It is argued that grain size is a poor indicator of channel planform, and that there was very low preservation potential for fine material because of a relatively low A/S ratio.



The top of the Canyon Creek Member is a regionally correlative surface marking an abrupt increase of the A/S ratio. This surface is termed an expansion surface, denoting an abrupt increase in accommodation. The overlying Almond Formation shows a single-storey alluvial architecture with a very high preservation of fine-grained material. An assumed correspondence in time of the Late Absaroka thrust phase in the Sevier belt to the west and the formation of the sharp top of the Canyon Creek Member suggests that the thrust phase caused a basin-wide abrupt increase of subsidence that changed the alluvial architecture.



As an alternative to sequence stratigraphic nomenclature defined for strata controlled by shoreline movements, a scheme relating systems tracts and surfaces to changes in stratigraphic base level is proposed. Such a scheme is useful where correlations to shoreline strata are ambiguous or cannot be made, or where tectonics and climate are important controls.

William Helland-Hansen

Papers

Shoreline Trajectories and Sequences: Description of Variable Depositional-Dip Scenarios

Trajectory analysis: concepts and applications

Conceptual basis and variability in sequence stratigraphy: a different perspective

Relationships between morphological and sedimentological parameters in source-to-sink systems: a basis for predicting semi-quantitative characteristics in subsurface systems

Stratigraphic base level and fluvial architecture: Ericson Sandstone (Campanian), Rock Springs Uplift, SW Wyoming, USA