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Experimental Stratigraphy Under Precisely Controlled and Monitored Conditions of Sediment Supply, Subsidence, Base-Level Variation, and Transport Mechanics

Experimental Stratigraphy Under Precisely Controlled and Monitored Conditions of Sediment Supply, Subsidence, Base-Level Variation, and Transport Mechanics

field is the ultimate repository of information, but exposure is limited, and it is often difficult to constrain key governing variables independently. We have developed a novel experi- Experimental mental basin—nicknamed Tank—that allows us to produce experimental stratigraphy under precisely controlled and monitored conditions of supply, , base-level variation, and transport mechanics. The unique feature of the basin is a fully programmable subsiding floor. Stratigraphy In the first application of the , we looked for evidence of decoupling (out-of-phase behavior) between shoreline and base level, as has been predicted by some recent strati- graphic models. We found little support for this idea, but the results demonstrate the potential that experiments have for complementing field and theoretical studies of the filling of Chris Paola, St. Anthony Falls Laboratory, University of sedimentary basins. Minnesota, Minneapolis, MN 55414, USA, and Department of & , University of Before you read this, try solving the problem posed in Figure 1. Minnesota, Minneapolis, MN 55455-0219, USA INTRODUCTION Jim Mullin and Chris Ellis, St. Anthony Falls Laboratory, The central goal of sedimentary geology is to interpret the University of Minnesota, Minneapolis, MN 55414, USA ’s surface from sedimentary rocks. We develop competing hypotheses, debate, discuss, and compare, but un- David C. Mohrig, Department of Earth, Atmospheric and like areas of science that deal in accessible time and space Planetary Sciences, Massachusetts Institute of Technology, scales, in sedimentary geology it is often difficult to determine Cambridge, MA 02139, USA unambiguously who is right. The ultimate source of truth—the stratigraphic record itself—is like a fragmentary manuscript John B. Swenson, Department of Geological Sciences and written in a long-forgotten language. Deposits are imperfectly Large Lakes Observatory, University of Minnesota, Duluth, exposed and hard to date, seismic images are highly filtered MN 55812, USA and expensive, and the precise sequence of events that pro- duced real-world stratigraphy usually cannot be determined Gary Parker, St. Anthony Falls Laboratory, University of independently. Trying to understand the language of sedi- Minnesota, Minneapolis, MN 55414 USA ments using rocks alone would be like trying to understand Russian by opening War and Peace to the middle and staring Tom Hickson, Department of Geology, University of St. at the pages. Thomas, St. Paul, MN 55105, USA Sedimentary have long recognized this and Paul L. Heller, Department of Geology & Geophysics, sought Rosetta stones for the stratigraphic record through University of Wyoming, Laramie, WY 82071, USA

Lincoln Pratson, Earth and Ocean Sciences, Duke University, Durham, NC 27708-0230, USA

James Syvitski, Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309-0450, USA

Ben Sheets and Nikki Strong, St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA, and Department of Geology & Geophysics, University of Minnesota, Minneapolis, MN 55455-0219, USA

ABSTRACT Stratigraphy has been a descriptive science for most of its Figure 1. Can you interpret this panel? It shows a section of basin sed- iment taken parallel to transport (i.e., a dip section), with flow from history. Recently, thanks to the development of the mechanis- right to left. Darker material is lighter and hence more mobile. Distal tic view of Earth embodied in and to improve- part of deposit was formed under water, and proximal part is fluvial. ments in our understanding of sediment dynamics, the strati- Break between light and dark material is a good indicator of shoreline graphic community has developed a first generation of position. The challenge: Deduce history of sediment supply, subsi- quantitative models for the filling of basins and the formation dence, and base level for this section using only information above of stratigraphic patterns. How do we test such models? The and geometry of the preserved deposits. Answer is given in Figure 5.

4 JULY 2001, GSA TODAY studies of modern environments and apply our newly minted models to processes. Most of our understanding of the stratigraphic record—after all, an- sedimentary lithofacies, for instance, cient basins are one setting where it comes from synthesis of the mainly hori- is very hard to check our model results zontal information we have from mod- independently! ern depositional environments with the mainly vertical information provided by The Rationale for the eXperimental ancient deposits. A particularly fruitful EarthScape Facility line of research has clarified the origin In most sciences, carefully controlled of (e.g., cross- experiments are the preferred means of stratification) in terms of forms and testing theoretical models. For a variety other relatively generic features of sedi- of reasons, experimentation has not ment-depositing flows (Allen, 1984; played much of a role in stratigraphic Middleton and Southard, 1984). This re- science, but the experimental approach search, carried out in both field and lab- is well developed in other areas of sedi- oratory, has taught us much about the ment dynamics, particularly in civil engi- alphabet of the language of . neering and . One of the The paragraphs and chapters of the main logistical hurdles to experimental sedimentary narrative are written in the stratigraphy is the necessity of including form of larger-scale sequences of sedi- tectonic effects such as subsidence and mentary . A basic tenet in stratigra- uplift. We have addressed this by build- phy is that patterns in these sequences ing a large experimental basin that in- are controlled by three main indepen- corporates a unique, flexible subsiding dent variables: sea level, subsidence floor to simulate the development of Figure 2. Schematic diagram of subsidence (rate and distribution), and sediment sedimentary basins under a wide variety mechanism used in eXperimental EarthScape (XES) subsiding-floor experimental basin. supply (e.g., Sloss, 1962). To this trinity of subsidence conditions. This new ex- perimental facility (the eXperimental Pulses of water shot through narrow tubes we should add a fourth variable group knock gravel out of pipe, causing subsidence EarthScape or XES basin) can be used to that controls the efficacy of the transport of gravel surface. system (e.g., water supply for rivers, study the formation of stratigraphy un- wave climate or tidal range for the der completely controlled conditions of Formally, we use theory to link continental shelf). The first attempts to base-level change, subsidence, sediment experiments and field cases. Once a the- understand how changes in these inde- supply, and transport—the same influ- ory has had a good workout in a con- pendent variables are recorded strati- ences that control natural basin stratigra- trolled system, we can be more confident graphically were descriptive. However, phy. The experimental system includes about using it to scale the experimental the physical mechanisms that distribute the most fundamental physical pro- results to the field, to evaluate effects sediment (not to mention biological cesses associated with basin filling— that cannot be scaled down to experi- and chemical processes) are complex river, wave, current, and mass-flow sedi- ments, and to model cases where we enough that it is difficult to model ment transport—and it allows the cannot check the answer independently. stratigraphy using descriptive methods boundaries between transport environ- Stratigraphic experiments are especially alone. Two major developments have ments (e.g., the shoreline) to evolve on well suited for testing formal “inversion” allowed us to create a first generation of their own. The resulting data sets docu- models for reconstructing variables like physically based, quantitative strati- ment spatial and temporal changes in sea level and sediment supply directly graphic models (Cross, 1990; Harbaugh sediment budgets, morphodynamics, from the stratigraphic record (Lessenger et al., 1999; Paola, 2000; Slingerland et and stratigraphic response. and Cross, 1996), and for evaluating al., 1994): (1) development of quantita- The main advantages of experimental how unique such reconstructions are tive models of the mechanics of basin stratigraphy are that boundary condi- (Heller et al., 1993). subsidence, an outgrowth of plate-tec- tions can be controlled, processes with At a more informal level, experiments tonic theory; and (2) improvements in natural analogs that occur over long help build intuition. There is nothing our understanding of how sediment- time scales can be thoroughly docu- like watching a transport system evolve transport systems work. By coupling mented, the resultant deposits can be in front of you and then dissecting it to subsidence and transport, we produce dissected at high resolution and visual- see how the depositional filter has ren- theoretical models of stratigraphy. ized in three dimensions, and transport dered it in stratigraphy. We manipulate (Because of the complexity of the equa- processes can be directly related to de- only boundary conditions. Within the tion systems involved, quantitative strati- positional products. On the other hand, basin, the transport systems organize graphic models are nearly always nu- experimental systems leave some impor- themselves and do what they want merical.) These models should allow us tant things out (e.g., biogenic processes rather than what we programmed them to read the sedimentary record with and Coriolis effects), and they distort to do. Self-organization—the spontaneous greater subtlety and precision. However, others (e.g., topographic slopes tend to emergence of patterns and structures— it is worth pausing before rushing off to be exaggerated). is a hallmark of sediment-transporting

GSA TODAY, JULY 2001 5 generators, a high-resolution sonar sys- tem for recording underwater topogra- phy, and a system for rapid digital pho- tography of sectioned deposits.

INITIAL EXPERIMENTAL RESULTS The Experiment Our first study (XES 96-1) involved a small prototype basin with 10 subsi- dence cells (Heller et al., 2001; Paola, 2000; Pratson and Gouveia, 2002). It was designed to study the effects of Figure 3. Honeycomb floor of full eXperimental EarthScape (XES) basin, with 432 subsidence slow and rapid changes in base level on cells. A 10-cell version was used for experiment described in this paper. shoreline position and the resultant se- quence stratigraphy. The experimental design was inspired by theoretical mod- systems, and it gives even simple exper- smooth and continuous in time. The els proposed by Pitman (1978), iments the capacity to surprise us and subsidence also is spatially continuous: Angevine (1989), and Jordan and trump our expectations. These surprises The cells are separated only at floor Flemings (1991). This work suggested give us new ideas and things to look for level, so the gravel can flow laterally to that for slow (long-period) base-level in the field. As long as our intuition- accommodate differential subsidence changes, shoreline would not track base building is tempered by a good under- with no imprinting of the hexagonal pat- standing of the limitations and distor- tern onto the basement surface. The sys- tions of the experimental systems, it is tem provides ~1.3 m of usable accom- one of the most valuable uses of strati- modation space in the basin. Depending graphic experiments. on loading of the gravel basement, lat- eral slopes of up to 60° can be pro- THE XES FACILITY duced between adjoining cells. The XES facility is a large basin (13 m Premixed sediment and water can be × 6.5 m) developed and built with funds fed from anywhere along the perimeter from the National Science Foundation of the basin, and base level is indepen- and the University of Minnesota that dently set by a computer-controlled allows the accumulation of strata head tank mounted outside of the basin. through the use of a flexible subsiding More details of the design and mechanics substrate (Fig. 2). The basin floor is a of the basin are available on our Web honeycomb of 432 independent subsi- site: www1.umn.edu/safl/research/ dence cells (Fig. 3) through which a research.html. gravel basement is slowly extracted During an experiment, the surface- from below, providing space to accom- flow pattern is recorded using video and modate deposition. An experiment starts still cameras. In addition, a topographic with the basin filled with gravel. The top scanning system, based on the design of of the gravel is covered with a thin rub- Rice et al. (1988) and Wilson and Rice ber membrane, which forms the base of (1990), allows us to document the the experimental deposit. Each subsi- 3-dimensional of the surface dence cell is a hexagon forming the top topography during the run for later of a cone that tapers down into a stan- comparison with the surface-flow im- dard elbow pipe (Fig. 2), where the ages, the preserved deposits, and theo- Figure 4. Drawings from photographs show- gravel sits at the angle of repose. retical predictions. ing sediment surface at two times, 15 min- Subsidence is induced by firing a pulse Once an experiment is complete, the utes apart, during the rapid base-level fall. of high-pressure water into the gravel in resultant deposits are cut in a series of Numbers in parentheses give time after start the elbow, knocking a small volume precise parallel faces, beginning near of the base-level cycle. Basin centerline is into an exhaust line. Each subsidence one edge. Each face is photographed. shown by dashed line; sediment-feed point is cell has its own sealed pressure tube About every 10 faces, a peel is taken of shown by small cylinder. Locations of two sections shown in Figure 5 are shown by that drives the pulses via a computer- the cut face. This serial microtome pro- controlled solenoid valve. We have re- white lines (main and inset panels). Zone of cess allows us to build a 3-dimensional active flow is shown in black, and fault sym- fined the pulsing so that each pulse pro- image of the deposits by stacking the bols show normal faults associated with ex- duces ~0.12 mm of subsidence—the sequence of photographed slices. posure of delta front. Base-level history is “earthquake slip” in the experiments. Additional equipment being added to given in Figure 5, with time for these images Hence, the subsidence is effectively the basin includes rainfall and wave indicated by arrow.

6 JULY 2001, GSA TODAY level, as one would expect, but rather should track the rate of change of base level (i.e., shoreline would be 90° out of phase with base level). This idea is so strange—imagine that the high-water mark on your local beach occurred not at high tide but midway between low and high tide—that at first blush, it seems impossible. But over long time scales, the coastal plain is not a static surface on which sea-level rise and fall are passively imprinted. Rather, the surface mor- phology evolves along with changing sea level: Shelf transport produces different morphology from fluvial transport, and the boundary between the two regimes depends on where the shoreline is. If beaches could re- shape themselves during a tidal cycle, our intuition about the relationship between shoreline and tidal height might be quite different. Slow and rapid cycles are defined relative to a natural time constant for the basin (e.g., the “equilibrium time” defined in Paola et al. [1992]). Figure 5. Flow-parallel (dip) panel of experimental deposit from base-level run. Color bands al- Angevine’s (1989) analysis of the Pitman low correlation of deposit with base-level curve to left. Arrow in base-level curve shows time of images in Figure 4. Spatial subsidence pattern is indicated by basement position at bottom model also suggested that the shoreline of panel. Darker material is coal sand; lighter material is quartz sand. Inset shows upper part of response to base-level change would be stratigraphy from an area outside incised valley that formed during rapid base-level cycle. relatively weak for long-period base-level Locations of sections are shown in Figure 4. cycles. In contrast, rapid (short-period) base-level cycles were predicted to pro- duce strong shoreline response directly rate of volumetric accommodation in the rium time of 3.4 h. The rapid cycle had in phase with base level, just as our in- basin. We imposed two cycles of base- a duration of 2 h. tuition tells us. But it was the prediction level change separated by periods of What Happened? that shoreline could get out of phase steady-state deposition (Fig. 5) to allow Although some degree of incision oc- with base level that was most interesting, for relaxation of transient effects. The slow cycle had a total duration of 30 h, curred during both base-level falls, inci- because it is so counterintuitive and sion and valley formation were much because it has profound implications for nearly 10 times the estimated equilib- inferring sea level stratigraphically.

Unfortunately, Pitman’s theory has proved 1800 200 100 difficult to test in the field (e.g., Miller autocyclic amplitude, mm 1600 50 et al., 1985, 1993). Could we find evi- 1400 0 dence for it experimentally? -200 We fed a mixture of water and sedi- 1200 -50 ment into one end of the basin (Fig. 4). 1000 The sediment was a 50:50 mixture (by 800 -100 volume) of quartz and coal sand, prox- 600 -150 base level, mm shoreline position, mm ies for coarse and fine-grained clastics, 400 respectively. Absolute base level was in- -200 200 dependently controlled from the oppo- -250 site end of the basin. Subsidence was 0 10 20 30 40 50 induced in a bowl-shaped pattern with a time, hrs maximum in the center of the basin. Figure 6. Shoreline position (red and orange) and base level (blue) during base-level run. Red Constant rates of water and sediment shoreline curve was taken within incised valley, orange one just outside it. Gray curve is discharge and of subsidence were main- shoreline predicted with theoretical model of Swenson et al. (2000). Green curve at top tained throughout the run. The sediment shows high-frequency (autocyclic) variation in shoreline position. Classic “shazam” zigzag discharge was set to balance the total pattern that autocyclic variation produces in stratigraphy is clearly visible in Figures 1 and 5.

GSA TODAY, JULY 2001 7 but deviated somewhat after that. Transgression began immediately upon stabilization of base level, and the point of maximum trans- gression occurred during the rise, as the rate of rise began to decrease (Fig. 6). There was also a noticeable overshoot in the transgression: the point of maxi- mum transgression is landward by ~32% of the total shoreline excursion distance of the initial shoreline location. The same phenomenon occurred at the end of the rapid cycle, but the overshoot is proportionally much larger: 133% of the total excur- sion distance. Otherwise, the rapid-cycle–shoreline behavior closely tracked base level, as all existing theories would predict. On the whole, the experiment does not offer strong support for the idea that shoreline follows rate of change of base level Figure 7. Various ways of using eXperimental EarthScape (XES) experimental deposits. A. Sequence- rather than base level itself for stratigraphic analysis (Heller et al., 2001). B. Synthetic seismic panel. C. Predicted stratigraphy (grain long-period cycles. Theoretical size, warmer colors are larger) using the SEDFLUX model (Syvitski and Hutton, 2001). D. Predicted analysis of the shoreline-re- stratigraphy (time lines) using model of Swenson et al. (2000). sponse problem by Swenson et al. (2000) suggests that our fail- stronger for the rapid base-level fall interfluve areas would show features ure to observe the predicted shoreline (Fig. 4). The rapid fall was characterized such as soil development associated behavior cannot be explained by differ- by initial exposure of the delta front and with a period of prolonged exposure ences between the experimental geome- development of a narrow incised valley and nondeposition. try and the assumptions of Pitman (1978). many times deeper than the pre-incision In contrast, the slow base-level cycle Rather, it appears that Pitman’s result is flow depth that extended headward produced a nearly symmetric regressive closely linked to his assumption of a along the length of the basin. The strati- and transgressive stratigraphic record. constant rate at the shore- graphic signature of the base-level cycle Most of the base-level fall was accompa- line, a condition that is not satisfied in was quite different for sections inside nied by deposition and thus did not pro- the experiments or, generally speaking, and outside the incised valley (Fig. 5). duce an unconformity that, in sequence in nature. Within the valley, the fall resulted in an stratigraphic parlance, would mark a se- unconformable sequence boundary that quence boundary. The basin fill devel- Internally Generated Phenomena is easy to identify in stratigraphic cross oped during the slow cycle was also These fell into two categories. Growth sections. Significant valley filling, and re- much more laterally continuous than for faults evolved before and during the sultant onlap, did not commence until the rapid cycle. Overall, the rapid cycle rapid fall, trapping sediment at the fault the beginning of the subsequent base- had far greater impact on the distribu- breakaway zone (Fig. 5). The continu- level rise. During the rise, of the tion of sediment storage, the 3-dimen- ous increase of dip rotation with fault valley walls significantly widened the in- sional geometry of fluvial and subma- offset shows how steady the motion on cised valley. As a result, the cross-valley rine transport systems, and the the faults was. It is particularly striking profile as recorded in the stratigraphy development of clearly segregated re- that at no time prior to the rapid base- was substantially wider and more gently gressive and transgressive facies tracts. sloping than the actual valley at the end level cycle was there any surface mani- of the base-level fall. Although exagger- Test of Theoretical Predictions festation of the presence of the faults. ated because the sand in the experiment It had been predicted that shoreline The only visible fault motion during the was relatively erodible, we believe this response to the slow cycle would be experiment was a collapse of the delta to be a general effect: Incised valley attenuated and out of phase. First, it is front during the rapid fall (Fig. 4B), with profiles will generally be composites clear from Figure 6 that in no sense was an offset of no more than 20 mm. that reflect both incision and widening the slow-cycle response attenuated; the The second internally generated phe- by lateral erosion as the valley is filled. slow-cycle shoreline excursion was 417 nomenon was high-frequency fluctuation Areas outside the incised valley received mm, 2.1 times that for the rapid cycle. in shoreline position (Fig. 6) associated no sediment and experienced the base- The shoreline remained closely locked with shifting of the threads of maxi- level cycle as a hiatus. In the field, these to base level during the base-level fall, mum flow in the fluvial system. Such

8 JULY 2001, GSA TODAY autocyclic variation in shoreline position COMMUNITY INVOLVEMENT IN XES Jordan, T.E., and Flemings, P.B., 1991, Large-scale strati- graphic architecture, eustatic variation, and unsteady tec- will not surprise anyone familiar with One of our main motivations in writing tonism: A theoretical evaluation: Journal of Geophysical the stratigraphic record, but it is interest- this article is to get the word out that the Research, v. 96, p. 6681–6699. ing that it is prominent in such a small- XES basin, and associated facilities at St. Lessenger, M.A., and Cross, T.A., 1996, An inverse strati- graphic simulation model—Is stratigraphic inversion possible?: scale experiment. The amplitude of the Anthony Falls Laboratory, are by no means Energy Exploration & Exploitation, v. 14, p. 627–637. autocyclic variation does not change sig- a closed shop. Insofar as it is possible, Middleton, G.V., and Southard, J.B., 1984, Mechanics of nificantly during the slow base-level cy- we would like St. Anthony Falls sediment movement, in Short Course 3: Providence, Rhode Island, Society of Economic Paleontologists and cle, but it diminishes measurably after Laboratory to be a resource for the earth Mineralogists Eastern Section Meeting, p. 401. that. Persistent removal of sediment by sciences community. We are continuing Miller, K.G., Mountain, G.S., and Tucholke, B.E., 1985, subsidence on localized growth faults to work on making the experimental Oligocene glacio-eustasy and erosion on the margins of the may account for this during the steady- results available via the Internet and/or North Atlantic: Geology, v. 13, p. 10–13. Miller, K.G., Thompson, P.R., and Kent, D.V., 1993, state interval before the rapid base-level CD-ROM. We also invite you to provide Integrated Late Eocene—Oligocene stratigraphy of the fall. During the rapid fall, autocyclic input and suggestions for future experi- Alabama coastal plain: Correlation of hiatuses and stratal surfaces to glacioeustatic lowerings: Paleoceanography, variation is suppressed as incision focuses ments. We are, of course, especially in- v. 8, p. 313–331. and trains the flow. While the fluvial terested in input based on field experi- Paola, C., 2000, Quantitative models of sedimentary basin system was less constrained during the ence and in case studies we can use for filling: , v. 47 (suppl. 1), p. 121–178. rise, it was still sufficiently confined to comparison with experimental results. Paola, C., Heller, P.L., and Angevine, C.L., 1992, The large- scale dynamics of grain-size variation in alluvial basins, 1: inhibit fully developed lateral shifting. Experiments on small space and time Theory: Basin Research, v. 4, p. 73–90. scales can never replace careful field Pitman, W.C., 1978, Relationship between eustasy and TESTING OF STRATIGRAPHIC MODELS study of real examples. On the other stratigraphic sequences on passive margins: Geological Society of America Bulletin, v. 89, p. 1389–1403. The main goal of these experiments is hand, interpreting natural stratigraphy is Pratson, L., and Gouveia, W., 2002, Seismic simulations of to provide data to test and refine strati- difficult enough so that we must take experimental strata: American Association of Petroleum graphic models and other interpretive advantage of every opportunity for in- Geologists Bulletin (in press). tools. We are approaching this from sev- sight. Experimental stratigraphy is one Rice, C.T., Wilson, B.N., and Appleman, M., 1988, Soil topography measurements using image processing tech- eral directions. A sequence-stratigraphic more Rosetta stone that will help us niques: Computers and Electronics in Agriculture, v. 3, analysis of the section is shown in Figure decipher the language of sediments. p. 97–107. 7A. For comparison of the experimental Slingerland, R., Harbaugh, J.W., and Furlong, K., 1994, Simulating clastic sedimentary basins: Englewood Cliffs, results with seismic-stratigraphic inter- ACKNOWLEDGMENTS New Jersey, PTR Prentice Hall, 211 p. pretation techniques, we use the model This work has been supported by the Sloss, L.L., 1962, Stratigraphic models in exploration: stratigraphy to produce synthetic seismic National Science Foundation (grant EAR Journal of Sedimentary , v. 32, p. 415–422. cross sections. The methods for doing 97-25989), the University of Minnesota, Swenson, J.B., Voller, V.R., Paola, C., Parker, G., and Marr, J.G., 2000, Fluvio-deltaic sedimentation: A generalized this are explained in Pratson and Gouveia the Office of Naval Research (grant Stefan problem: European Journal of Applied Mathematics, (2002); the results are shown in Figure 7B. N00014-99-1-0603), and our industrial v. 11, p. 433–452. In addition, the experimental results can partners: Anadarko Petroleum Syvitski, J.P.M., and Hutton, E.H., 2001, 2D SEDFLUX 1.0C: An advanced process-response numerical model for be compared directly with existing the- Corporation, Conoco Inc., ExxonMobil the fill of marine sedimentary basins: Computers & ory. Apart from specific hypotheses like Upstream Research Company, Japan Geosciences (in press). out-of-phase shoreline behavior, we can National Oil Company, and Texaco Inc. Wilson, B.N., and Rice, C.R., 1990, An indoor soil erosion research facility: Journal of Soil and Water Conservation, also compare the experimental results We would also like to thank John Isbell v. 45, p. 645–648. directly with theoretical stratigraphy, as and Neal Driscoll for helpful reviews, Manuscript received January 8, 2001; illustrated in Figures 6, 7C, and 7D. In and Molly Miller for enthusiastic and in- accepted May 2, 2001. ▲ this case, the two models shown do a sightful help with the manuscript. reasonable job, although there are prob- lem areas, such as the modest shoreline REFERENCES CITED overshoot at the end of the first cycle, Allen, J.R.L., 1984, Sedimentary structures, their character and physical basis: Amsterdam, Netherlands, Elsevier, 1206 p. that are not predicted well. Angevine, C.L., 1989, Relationship of eustatic oscillations to Of course, one of the best and sim- regressions and transgressions on passive continental mar- plest things to do with experimental gins, in Price, R.A., ed., Origin and evolution of sedimentary basins and their energy and resources: Washington, stratigraphy is to deduce cause from D.C., American Geophysical Union, p. 29–35. stratigraphic pattern (Fig. 1). It’s a very Cross, T.A., 1990, Quantitative dynamic stratigraphy: hard problem, and in our experience, Englewood Cliffs, New Jersey, Prentice Hall, p. 615. the great temptation is to make the Harbaugh, J., Watney, L., Rankey, G., Slingerland, R., Goldstein, R., and Franseen, E., 1999, Numerical experi- causes more complicated than necessary. ments in stratigraphy: SEPM (Society for Sedimentary And this was a relatively simple experi- Geology) Special Publication 62, 362 p. ment! If nothing else, the difficulty of Heller, P.L., Burns, B., and Marzo, M., 1993, Stratigraphic solution sets for determining the roles of sediment supply, analyzing sections such as Figure 1 subsidence, and sea level on transgressions and regressions: should remind us to treat the more Geology, v. 21, p. 747–750. Heller, P.L., Paola, C., Hwang, I.-G., John, B., and Steel, R., difficult and underconstrained natural 2001, Geomorphology and due to cases with respect, along with a gener- slow and rapid base-level changes in an experimental sub- siding Basin (XES 96-1): American Association of Petroleum ous supply of Ockham’s famous razors. Geologists Bulletin, v.85, p. 817–838.

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