Abstract Autogenic dynamics and self-organization in sedimentary systems are increasingly viewed as significant and important processes that drive erosion, sediment transport, and sediment accumulation across the Earth’s surface. These internal dynamics can dramatically modulate the formation of the stratigraphic record, form biologically constructed depositional packages, affect ecological patterning in time and space, and impact aspects of geochemical sedimentation and diagenesis. The notion that autogenic processes are local phenomena of short duration and distance is now recognized as false. Understanding autogenic dynamics in sedimentary systems is thus essential for deciphering the morphodynamics of modern sedimentary systems, accurately reconstructing Earth history, and predicting the spatial and temporal distribution of sedimentary and paleobiologic features in the stratigraphic record. The 13 papers in the publication, Autogenic Dynamics and Self-Organization in Sedimentary Systems, present exciting new ideas and research related to sedimentology, stratigraphy, ecology, paleobiology, sedimentary geochemistry, and diagenesis. Five papers summarize the current state of thinking about autogenic processes, products, and patterns in fluvial–deltaic, eolian, and carbonate depositional systems, and in paleobiologic and geochemical contexts. A second group of papers provides perspectives derived from numerical modeling and laboratory experiments. Thefinal section consists of field studies that explore autogenic processes and autogenically modulated stratigraphy in five case studies covering modern and ancient fluvial, deltaic, and shelf settings. These papers should stimulate further research into how self-organization might promote a better understanding of the sedimentary record.

Abstract The science of the internally generated behavior and spatial organization of depositional systems has come a long way since Beerbower first coined the term “autocycles” to refer to fining-upward sequences generated by river meander migration, cutoff, and eventual return. Ongoing research has broadened the scope and scale range of known autogenic dynamics, even as a unifying theme—sediment storage and release—has emerged. Many internally generated processes do not have a single characteristic length or time scale but rather occupy a broad scale range (hence, “autocyclic” has been gradually replaced by “autogenic”). But even where they are broad, the scale ranges for autogenic processes are bounded by limiting time and length scales. The central role of sediment storage and release provides a means of estimating these limiting length and time scales based on mass balance, geometry, and mean sediment flux. Recent research has also allowed us to expand the upper limits of autogenic behavior to time scales of 10 5 to 10 6 years. Finally, we recognize that autogenic dynamics is not simply superimposed on allogenic signals but interacts strongly with, modifies, and even destroys allogenic input. That the autogenic imprint on the stratigraphic record is stronger and more complex than once thought can be seen as an opportunity to focus on using the record to learn about intrinsic surface behavior under pre-human conditions, rather than simply as an archive of externally imposed signals.

Abstract Eolian dune fields self-organize through a hierarchy of autogenic processes that culminate at the dune-field pattern level. Interactions that occur between flow and grains, flow and dunes, and dunes and dunes define the levels of this hierarchy. These autogenic processes occur within sets of boundary conditions, which impart a uniqueness to each emergent dune-field pattern. The interpretation of allogenic forcing on dune-field patterns and their stratigraphic record requires an understanding of how these external environmental variables are manifested at the dune-field pattern level. The fundamental process in eolian systems is a wind event with basic boundary conditions of sediment supply, sediment availability, and the transport capacity of the wind. It is hypothesized that the basic high-frequency boundary conditions are remade at each level of the hierarchy of autogenic processes or have a cumulative effect over many wind events. The influence of these boundary conditions “trickles up” to and is manifested at the dune-field pattern level. Tectonic, climatic and hydrologic boundary conditions are low frequency and operate over much longer timescales than a wind event. It is hypothesized that these “trickle down” to be remade as high-frequency boundary conditions, which then trickle up. Analysis of the White Sands Dune Field in New Mexico supports these hypotheses by the manifestation of the influence of boundary conditions in the dune-field pattern. The dune field originated by wind deflation of a lacustrine sediment supply, which was made available episodically by climatic forcing that controlled the hydrodynamics of the tectonic basin. Although the dune-field pattern arose through autogenic dune interactions, the morphologies of which are ubiquitous throughout the field, the influence of boundary conditions is evident in the dune morphologies and field-scale pattern heterogeneity.

Abstract Self-organization refers to the emergence of large-scale ordered pattern starting from initially disordered conditions through small-scale interactions between components of a system. Although the influence of biological agents on sediments and landscapes is widely appreciated by sedimentary geologists, the role of life in sedimentary self-organization is less familiar. One of the oldest ecological concepts relevant to self-organization is ecological succession, which is the idea that species colonization of a virgin or a disturbed landscape follows a series of more or less orderly and predictable changes in taxonomic composition and habitat structure. Many early studies of ecological succession in the fossil record confounded allogenic facies succession reflecting environmental shifts with autogenic ecological changes driven by organism interactions. However, evidence for autogenic ecological succession can be found in a variety of depositional contexts and is particularly evident in environments that are influenced by ecosystem engineers (organisms that affect other species by physically modifying or building their habitats), like reefs and shell beds. In addition to influencing change in an ecosystem over time, biologically mediated feedbacks can also produce highly organized spatial patterns. The basic mechanism of spatial self-organization requires at least one negative feedback loop that acts at a distance. Although relatively few examples have been documented in the rock record, self-organized spatial dynamics have the potential to greatly influence the nature of depositional environments by altering the flow of matter and energy. Recognition of biotic feedbacks is necessary for a complete and predictive understanding of the architecture of the stratigraphic record, and it seems likely that with greater awareness of self-organization and autogenesis in the sedimentary record, the numberof biologically mediated examples will increase.

Abstract Spatial self-organization, the process where coherent spatial patterns emerge through internal interactions, is widely observed in modern natural systems. Compelling examples range from ripple and dune formation in aquatic and terrestrial systems to formation of patterned coral reefs and vegetation in arid regions. Despite this wide range of contemporary cases, the concept of self-organization and its potential effects on geological patterns have not yet been widely discussed by the geological community, especially in carbonate depositional systems. We present four case studies from modern bivalve beds, coral reefs, microbial carbonates, and tidal channels, and one from the rock record considering carbonate cyclicity, where spatial self-organization could explain regularity in preserved strata. Only two of these five case studies, bivalve beds and tidal channel systems, are accompanied by a firm understanding of the mechanisms that generate emergent patterning. Three types of ecosystem spatial self-organization—scale-dependent feedback creating regular patterns, criticality behavior causing scale-free patterns, and oscillating consumer resource interactions causing consumer waves—are well documented. The first two of those appear to hold most relevance for carbonate depositional environments. Considerable work remains to understand the processes and products of spatial self-organization in carbonate deposystems.

Abstract Geochemical self-organization is a process whereby a geochemical system acquires oscillatory behaviors or spatially repetitive patterns through its own internal autogenic dynamics. The concept of self-organization provides a new perspective for understanding the formation of repetitive patterns in sedimentary rocks, without invoking any unjustified external periodic allogenic force or template. Geochemical self-organization requires a system to be far from equilibrium and to have a positive feedback among the physical and chemical processes involved. Identification of a plausible mechanism for a specific self-organizational phenomenon usually boils down to finding a positive feedback consistent with laboratory and field observations. In this paper, we review the concepts and principles of geochemical self-organization, highlight some of the driving mechanisms and examples that typify sedimentary geochemical systems, and consider some of the basic techniques for model analysis. Two specific examples, formation of banded iron formations and development of periodic patterns in the distribution of porosity in dolomites, are presented in some detail to illustrate the insights generated from numerical modeling and linear stability analysis. Last, we offer some speculations on other chemical sedimentary and diagenetic features that might have self-organizational origins. Testing those hypotheses will require new types of sampling strategies and analyses not normally employed by sedimentologists and sedimentary petrologists.

Abstract One of the most common and straightforward ways to explicitly represent spatial heterogeneity in simulations is with the use of some form of a lattice. Lattices are two- or three-dimensional grids in which entities are connected using various forms of local rules. They are thus ideal for representing systems with different levels of local interactions and, thus, for exploring the processes and impacts of self-organization. Models based on lattices have found wide usage in ecology and geology and often use the same basic formalism, despite the differences in the entities being studied. Groups of models, such as cellular automata, self-organized criticality, and diffusion limited aggregation, show how complex spatial structures and temporal behaviors can arise from local interactions only in the absence of external forcing. Other models that incorporate external processes, such as percolation-based models of fire and diseases, demonstrate that self-organization can strongly affect the signal produced by exogenous disturbances. Most lattice models are best used as tools for improving understanding of the dynamics of systems under various sets of assumptions of internal dynamics and external forcing, rather than as a means for accurate predictions of actual system behaviors. Lattice models that integrate ecology and sedimentology could be used to introduce an explicit spatial component into studies of Earth system history.

Abstract Bedforms that develop at the interface between a fluid flow and a loose sediment bed are among some of the most fundamental morphodynamic processes, perhaps among the greatest examples of canonical autogenic adjustments between flow and sediments. Because different types of bedforms develop under specific combinations of flow and sediment properties, these sedimentary features have commonly been used to aid interpretations of flow conditions and infer the nature of depositional environments. While subaerial (river) bedforms are relatively well understood, their counterparts in deep water (i.e., related to gravity underflows, namely, density or turbidity currents) remain somewhat elusive, largely due to the difficulty of direct observation in their natural setting, due to the limited number of experimental studies, and due to their inherent process complexity. Although widely practiced, extrapolation of equilibrium regime diagrams developed for subaerial bedforms to the deep-water realm remains questionable, particularly in light of recent experimental and field observations that suggest some departures from the subaerial counterpart. Herewe present results from an experimental program aimed at investigating equilibrium bedforms resulting from saline density currents under bypass conditions. Saline density currents have been typically treated as the surrogate of muddy turbidity currents for which sediments never settle. More than 500 separate experiments were run, comprising currents that spanned a wide range of the densimetric Froude number including all flow regimes (supercritical, critical, subcritical: Fr d = 0.6 to 2.8). Results confirm some similarities between subaerial and gravity flow bedforms both in process and product but also reveal some interesting differences. For example, ripples form under both subcritical and supercritical density currents, while supercritical currents yield dunes and both small-wavelength, downstream-migrating, and long-wavelength, upstream-migrating antidunes, where the latter may transition to cyclic steps. Supercriticality of the flow, the proportion of bedload to suspended load (when looking at the sediment composing the bed), and the bed characteristic sediment size are the major controls on the prevailing bedform observed. To investigate the flow and morphodynamic mechanisms related to some of the observed bedforms (e.g., supercritical dunes), detailed analyses of flow structure over the bed features were performed using particle image velocimetry techniques. Outcrop examples are presented to demonstrate that the gravity flow bedforms we observed experimentally might have counterparts at the field scale. Our findings underscore the rich spectrum of potential bed states produced by dense underflows and their deviation from bed behavior in open-channel flows. As a result, we argue that inversion of gravity flow bed features based on known subaerial bedform regimes might be potentially misleading.

Abstract A series of alluvial fan experiments was compared to a series of submarine fan experiments in order to explore the similarities and differences of autogenic supercritical avulsion cycles in the two environments. Both systems have cycles of: distributive channel formation and basinward extension, deceleration and mouth bar deposition, flow interaction with the aggrading mouth bar, propagation of the channel-to-lobe transition in the upstream direction, and flow reorganization. The channel-to-lobe transition in both alluvial fan and submarine fan experiments was located at the supercritical-to-subcritical flow transition. Channel-to-lobe transitions were also the primary locus of deposition in each case, and their aggradation in turn forced upstream accretion. The commonalities between the two environments are striking and lend evidence toward the hypothesis that supercritical vs. subcritical flow in distributary channels is a more significant distinction than subaerial vs. subaqueous environment in termsof the hydraulic and sediment transport properties.

Abstract Autogenic fluvial dynamics, including river avulsion, influence the distribution of channel sand bodies in alluvial deposits. Over long timescales, autogenically organized avulsions can generate stratigraphic patterns such as clusters of sand bodies when avulsions preferentially return to previous channel locations, or evenly spaced sand bodies when avulsions preferentially fill topographic lows. Consequently, quantifying stratigraphic patterns may provide an avenue for reconstructing paleoavulsion dynamics from ancient deposits. Several quantitative approaches have been used to quantify the degree to which channel-belt deposits are distributed randomly, evenly, or with clustered patterns; however, to date, there are only a few examples where these metrics have been applied in outcrop studies. Here we present a quantitative analysis of stratigraphic architecture in the lower Williams Fork Formation (Cretaceous, Colorado) to quantify the paleoavulsion pattern in this interval. A spatial-point-process statistic (the K function) and the compensation statistic are applied to stratigraphic data mapped from a terrestrial lidar digital outcrop model. Both analyses show random channel-body distributions and random basin filling at short (less than 200 m) spatiotemporal scales, which suggests that lower Williams Fork channels avulsed randomly. To evaluate the sensitivity of the K function to different degrees of stratigraphic organization, we use a two-dimensional (2D) geometric model to build synthetic stratigraphy with different degrees of sand-body clustering. Model results show that the lower Williams Fork data set should be of sufficient size and resolution to detect strong clustering signals, if they were present. This type of sensitivity analysis is helpful for comparing results of spatial-point-process analyses among outcrop examples with confidence. The random paleoavulsion pattern inferred from lower Williams Fork stratigraphy in this locality contrasts with previously published analyses that show qualitative clustering at larger scales; however, these results are not incompatible if avulsions remained clustered regionally over long timescales.

Abstract The Kayenta Formation, Warner Valley, Utah, shows lateral and vertical clustering of mud-delta propagating-channel sand bodies within a matrix of fine-grained open-lake deposits and further provides opportunity to develop a fluvio-deltaic depositional-process model. Clustering due to nonrandom stream avulsion is well documented for high-accommodation fluvial systems operating in alluvial plains but not well established for lacustrine systems with abundant fluvio-deltaic lobes. Kayenta Formation delta lobes have similar spatial clustering to those observed in fluvial channel belts and possibly extend this clustering concept to fluvio-lacustrine systems. Lithofacies were mapped on three large photo panoramas, and architectural-element analysis was used to identify bounding surfaces of fluvial channel-deltaic lobes. Fluvio-lacustrine delta lobes reflect linear channels that propagate across mud deltas with negligible bifurcation and generate fluvial channel belts incised into lake mudstone. Channels are associated with thin sand sheets or “blow-out wings” that extend multiple channel widths from the channel and cover levee and mud-delta deposits, but delta-front sand beds are absent. The stages of evolution for these propagating channels is preserved in the variation of channel-lobe architecture and reflects mud-delta propagation at the mouth of each channel in the absence of delta-front sand. Sand is outpaced by mud in the ever-lengthening channel, which reduces sand at the channel mouth and diminishes necessity for channel bifurcation. The resulting deposit is thus a frontal mud-delta lobe bisected by a later single sandy channel belt with lateral sand wings. Statistical analysis of these channel belts shows clustering. Clustering of fluvial bodies within shallow lakes is significant in predictive reservoir models because it improves connectivity and localization of delta-lobe reservoirs. The clustering of delta lobes in fluvio-lacustrine systems is theorized to reflect the preferential channel avulsion centered on the axis of the primary channel feeding into the lake and preferential avulsion fairways of feeder channels. Both the segregation of sand and mud though channel lengthening and the clustering are explainable in fully autocyclic terms. The needed allocyclic driver to trigger these fluvio-lacustrine processesis an accommodation rate sufficiently low compared with lake filling rate as to maintain shallow-water conditions across the lake system through multiple generations of channel propagation.