Abstract The Lower Jurassic Kayenta Formation along the Echo Cliffs of northern Arizona represents an excellent analog for arid to semi-arid continental strata. Wet/dry climatic cycles exerted a major control on the regional distribution of facies tracts during deposition of the Kayenta Formation. Two scales of wet/dry climatic cyclicity can be recognized in the record of the Kayenta Formation. Long-term climatic cycles are represented by three sequence sets that span the Kayenta and its transition to the Navajo Sandstone. Superimposed on this long-term signal is a series of high-frequency sequences expressed by an alternation of widespread fluvial and eolian deposition. Dry portions of the cycles are characterized by low lake levels, fluvial incision, depressed water tables, and the development of extensive deflationary surfaces. Consequently, sequence boundaries at the base of incised valleys correlate with broad deflationary surfaces in a landward direction. Incised valleys, along the lower reaches of the system, are filled with fluvial strata deposited by ephemeral streams during lowstands of the lake level. Eolian facies of regional to sub-regional extent are preserved during rises of the water table and serve as prominent stratigraphic markers. The top of these deposits is interpreted as the transgressive surface because it represents the peak of the first significant base-level rise. Wet portions of the cycle consist of widespread fluvial deposits that correlate with lacustrine parasequences arranged in aggradational to progradational stacking patterns. Fluvial deposits in this part of the cycle are typically represented by amalgamated sandy facies punctuated by fine-grained overbank deposition.

Abstract This volume grew out of an AAPG-sponsored field trip led by an Exxon team—J.C. Van Wagoner, C.R. Jones, D.C. Jennette—and Dag Nummedal from Louisiana State University. The purpose of the trip was to provide a venue on the outcrop for discussing rapidly evolving opinions and points of view about sequence stratigraphy concepts and applications. These different opinions have been captured in the papers in this volume. Although foreland basin setting is a common theme for all of the papers, the ideas and observations presented in this volume have a broader significance and application to many other basin types. The purposes of this introduction to the volume are to provide a historical perspective to the terminology used in the papers, to summarize the papers for the reader’s benefit, and to provide a glossary for sequence stratigraphy terminology to facilitate communication. As sequence stratigraphy has evolved, terminology has grown more complex and confusing. This is in part because of an early dichotomy embedded in seismic stratigraphy (see Mitchum et al, 1977). The following section reviews the evolution of the terms and contrasts several different ways of looking at sequences and systems tracts.

Abstract Parasequence architecture and the nature of parasequence boundaries in marine to nonmarine strata are well illustrated in the Spring Canyon Member of the Upper Cretaceous Blackhawk Formation. Parasequences and parasequence sets are stratal successions which are the building blocks of sequences. In marine strata, parasequences result from basinward progradation of the shoreline, and typically shallow and coarsen upward; in the nonmarine, parasequences show a distinct vertical facies succession which begins with lagoon-fill deposits and ends with freshwater coals. A flooding surface (parasequence boundary), indicating an abrupt increase in water depth, accompanied by minor submarine erosion and nondeposition separates individual parasequences within a parasequence set. The parasequence boundary is a continuous, single surface that can be traced from updip in the coastal plain to downdip in the distal shelf. The parasequence boundary has different physical expressions depending on where it is observed, and enables correlation of nonmarine /marginal marine rocks to coeval marine strata within the same parasequence. Parasequence evolution and deposi- tional reconstruction is dependent on the application of sequence stratigraphic concepts. Outcrop examples from the Spring Canyon Member document parasequence expression. Both wave-dominated shoreface sandstone and river-dominated deltaic sandstone exist laterally in the marine portion of the same parasequence. Both are terminated by a flooding event marked by a rapid landward shift in facies, with no transgressive lag. A number of marginal marine and nonmarine subenvironments exist laterally within the same parasequence. The parasequence boundary provides a temporal framework to link the genetically related subenvironments, allowing reconstruction of the entire depositional system, as opposed to evaluation of outcrops as isolated systems or facies. Continuous coal seams occur immediately beneath parasequence boundaries and are markers used to trace parasequence boundaries from nonmarine sections into the marine.

Abstract The Desert Member of the Blackhawk Formation and the Castlegate Sandstone in the Book Cliffs of Utah and Colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins. Stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries, and at least six surfaces of incision and subaerial exposure with more limited lateral extent, interpreted as minor sequence boundaries. Each sequence boundary is a regionally correlatable, single surface. Major sequence boundaries can be traced from marine into proximal alluvial plain environments. Sequence boundaries have different physical expressions depending upon where in the basin they are observed. Strata beneath sequence boundaries are unrelated to strata above, and time lines cannot be carried across these boundaries. Flooding surfaces, called parasequence or parasequence set boundaries, also exert an important control on facies architecture. Based on parasequence stacking patterns, position of sequence bound-aries, and facies associations, the Desert Member and Castlegate Sandstone have been divided into sequences with durations of 200,000 to 300,000 yr. There are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of Haq et al. (1988). The major sequences have been divided into the following systems tracts or sequence sets: (1) Grassy highstand sequence set below the Desert sequence bound-ary, named for the Grassy Member of the Blackhawk Formation, (2) Desert lowstand, transgressive, and highstand systems tracts between the Desert and Castlegate sequence boundaries, (3) Castlegate lowstand sequence set resting on the Castlegate sequence boundary, and (4) Castlegate transgressive systems tract. Parasequence stacking patterns suggest that the Grassy highstand sequence set and the Desert highstand systems tract were deposited during a relative rise in baselevel. The Grassy highstand sequence set is punctuated by minor relative falls in baselevel. Both of these stratal units contain thick, amalgamated lower-shoreface sandstones with sharp, slightly erosional lower boundaries. These boundaries are interpreted to be caused by storm processes and are unrelated to sea level falls or forced regressions (Posamentier et al., 1992). Lowstand strata in both the Desert and Castlegate sequences are braid-ed-stream deposits forming fluvial sheet sandstones contained within incised valleys at least 50 mi wide. Sheet sandstones are regionally wedge- shaped and thin and fine basin ward. These fluvial lowstand deposits form megafans that prograded to the east off of the Sevier thrust belt. In both Desert and Castlegate lowstand systems tracts, fluvial systems do not connect to the sea, but die out into a broad, swampy complex of shallow lakes. Lowstand fluvial sandstones have no coeval siliciclastic lowstand beaches or deltas in the study area. Instead, the lowstand shoreline is marked by oolites in the Castlegate. Distal ends of these mega fans behave similarly to terminal fans described in literature (Friend, 1978). Channelized sediment at the distal end of these terminal fans downlaps onto the sequence boundaries. The incised valleys within which the mega fans are contained are interpreted to form and fill in response to relative falls in baselevel and upstream migration of knickpoints through highstand alluvial channels. In the Castlegate lowstand sequence set, interpreted intersection of upstream- migrating knickpoints with alluvial fans in front of the Sevier thrust belt result in a significant increase in discharge causing deeper incision of the valley and development of the observed wedge-shaped, basinward-thin-ning sandstone body. This occurs independently of sea level change. Sequence boundaries and systems tracts within the Desert and Castlegate can be continuously traced in both outcrop and subsurface, moving updip from the marine to totally nonmarine parts of the system. These relationships are used to develop an integrated model for nonmarine sequence stratigraphy applicable to the subsurface elsewhere. Nonmarine sequences fine upward. The lowstand systems tract is commonly a multi-story, high net/gross sandstone with excellent lateral continuity filling the updip end of an incised valley. The transgressive systems tract is composed of thinner, single-story sandstones, commonly deposited by point bars and associated overbank and crevasse-splay strata, forming a moderate to low net/gross interval. Trace-fossil assemblages typical of brackish water commonly occur in this systems tract. The highstand systems tract is dominated by muddy levee, lake margin, and crevasse-splay deposits punctuated by thin, singlestory channels, forming a low net/gross interval. Major sequence boundaries split the Desert Member and Castlegate Sandstone. For this reason, the more downdip strata, called Desert and Castlegate using formation names, are temporally and physically different from updip strata with the same names. This difference between sequence stratigraphy and lithostratigraphy reflects alternative ways of thinking about the stratigraphic and paleogeographic evolution of these units, with signifi-cant practical implications for basin exploration and production of hydrocarbons.

Abstract The Upper Cretaceous sediments of the Blackhawk Formation of the Mesa Verde Group are interpreted as a complex of wave-dominated, prograding, siliciclastic shoreline parasequences. The Spring Canyon Member, of the Blackhawk Formation is representative of the shoreline deposits and was preserved in core of the Exxon Production Research Co. Price River "C" well. The core illustrates the trace fossil assemblages throughout the offshore to shoreface environments on a wave-dominated shoreline. The transition between the lower shoreface and the upper shoreface can be readily defined through the packaging of facies-dependent, diagnostic trace fossil assemblages. These assemblages allow the offshore and shoreface facies to be accurately divided into distal and proximal facies, providing a greater range of facies control for correlation between well logs. The development of opportunistic trace fossil assemblages, formed in response to storm sedimentation can be differentiated from the background resident trace fossil assemblages by interpreting the ethology of the individual traces as a response to increases in the rate of sedimentation, oxygenation and corresponding changes in the substrate. Trace fossil assemblages can be used to define the flooding surfaces that bound parasequences, with deeper water facies resting sharply on more shallow water facies. There are no transgressive deposits, such as lags, that can be identified, associated with the sharp-based parasequence boundaries. Trace fossil assemblages can be used to identify and interpret key stratal surfaces. Recognition of the Glossifungites ichnofacies is important for delineating potential sequence boundaries.

ABSTRACT The Exxon global cycle chart demonstrates a hierarchy of interpreted glacio-eustatic cyclicity. The fundamental third-order cycles (1-2 m.y. duration) stack into related groups (second-order cycles: 9-10 m.y. duration). A much larger pattern (about 200 m.y.) is interpreted as tectonically-controlled eustacy probably related to sea-floor spreading rates. One and probably two higher orders of cyclicity (fourth-order: 0.1-0.2 m.y.; and fifth-order: 0.01-0.02 m.y.) are now observed in work with high-resolution data from well logs, cores, and outcrops in areas of very rapid deposition. These frequencies are in the range of Milankovitch cycles, and may represent part of the Milankovitch hierarchy. High-frequency (fourth-order) sequences, which form at a 0.1-0.2 m.y. cyclicity, have all the stratal attributes of conventional sequences, including constituent parasequences and systems tracts, and play a dominant role in controlling reservoir, source, and sealing rock distribution. A consistent hierarchy of stratigraphy is observed. Sets of parasequences (probable fifth-order cyclicity) stack to form systems tracts in fourth-order sequences. Groups (sets) of fourth-order sequences are deposited between major third-order boundaries within third-order composite sequences. These sets stack in prograding and backstepping patterns to form third-order lowstand, transgressive, and highstand sequence sets. Third-order sequence boundaries subdivide groups of fourth-order sequences. They are marked by greater basinward shifts in facies, by larger more widespread incised valleys, and by more extensive onlap than are fourth-order sequence boundaries. Third-order condensed sections commonly are widespread, faunally rich, and widely correlated biozone and mapping markers. Fourth-order sequence analysis helps to understand reservoir, source, and seal distribution at the play and prospect scale. Examples from the Gulf of Mexico are discussed.

Abstract OBJECTIVES: The Lower Sego provides an opportunity to study well-exposed, high-frequency sequences and their systems tracts. Criteria for identification of sequence boundaries will be presented. Sequences and their boundaries will be contrasted with parasequences and their bounding surfaces. The Upper and Lower Sego contain well-exposed tidal deposits within the lowstand systems tracts of high-frequency sequences. These tidal deposits and their relationship to incised valleys and systems tracts will be examined. The incised valleys interpreted to form during relative falls in sea level will be contrasted with distributary channels related to autocyclic mechanisms. 0.0 Leave the parking lot of the Grand Junction Hilton, Grand Junction, Colorado. Turn left onto Horizon Drive. Pass under the 1-70 bridge. Turn left onto the entrance ramp for 1-70 west. 0.2 Enter 1-70 heading west toward the Colorado-Utah State line. For the next 20 miles the Interstate will parallel the Colorado River flowing along the west side of the Grand Valley. The Interstate is built on the gray Cretaceous Mancos Shale. To the west of the Colorado River are the red cliffs of the Colorado National Monument. The Monument is operated by the National Parks Service. These cliffs are the eastern edge of the Uncompahgre Uplift As you drive north along the Interstate, the steeply dipping eastern limb of the Uncompahgre is clearly visible. This tight monoclinal fold is the result of horizontal compressional tectonics associated with Laramide deformation (Heyman, 1983). The red rocks in the Monument include, from stratigraphically oldest to youngest: the Chinle Formation

Abstract The Lower Sego, Anchor Tongue of the Mancos Shale, and the Upper Sego are well exposed along the Book Cliffs in western Colorado and eastern Utah. For the most part these strata crop out on public lands and access is excellent due to the constantly maintained roads leading to the gas fields along the front of the cliffs. Nine sequences and their component systems tracts can be seen in these strata. Because of the high-quality exposure and access, the Lower and Upper Sego are excellent units to study the geometry and expression of sequence boundaries and the facies contained between these regionally extensive surfaces. This paper discusses the sequence stratigraphy of the Lower and Upper Sego between Prairie Canyon on the Colorado-Utah border and Sulphur Canyon in eastern Utah. The discussion includes criteria for recognizing sequence boundaries in outcrop, the geometry of incised valleys and the nature of their fill, and the facies of the transgressive and highstand systems tracts within the sequence.

Abstract OBJECTIVES : The Desert and updip Castlegate provide an opportunity to study well-exposed sequences and systems tracts in nonmarine to marine settings. Because of the excellent quality of the outcrops, sequence boundaries can be traced continuously from the nonmarine, where the identification of sequence boundaries has historically been less certain, to the marine, where sequence boundaries can be well defined based on basinward shifts in facies. These outcrops also allow regional correlation of systems tracts and identification of exploration-scale facies changes within systems tracts. These stops demonstrate that sequence boundaries are regionally extensive, single physical surfaces that can be used to correlate in outcrop and the subsurface. These stops also show that strata between sequence boundaries are arranged in predictable packages and that facies within these packages commonly, but not always, have predictable characteristics. 0.0 Leave the parking lot of the Best Western River Terrace Motel in Green River, Utah. Turn right on the main road, Highway 6. 0.2 Turn left on the paved road. Drive north toward the Book Cliffs. This road parallels the Green River and is built on the Mancos Shale. 5.3 After ascending a hill which climbs on top of the Mancos out of the Green River alluvial valley, turn off of the paved road onto a gravel road that heads northeast directly toward Tuscher Canyon. 6.0 STOP ONE . Pull over to the side of the gravel road for an overview of the stratigraphy of the Desert Member of the Blackhawk Formation and the Castlegate Sandstone. This

Abstract OBJECTIVES : Today the Castlegate will be traced to the most basinward facies exposed in the Book Cliffs completing an updip to downdip analysis of the Castlegate sequence boundary and systems tracts. The Desert will be seen only at STOP ONE. As the Castlegate sequence boundary is traced basinward, changes in the sequence-boundary expression will be examined. These expressions will be compared with the expression of the sequence boundary seen yesterday. Changes in incised-valley geometry will also be studied, especially in the Horsepasture area of STOP THREE, time and weather permitting. Laramide deformation appeared to influence the Castlegate sequence boundary around the Colorado-Utah border. This influence will be examined later in the day. Leave the motel parking lot in Moab. Drive north on Highway 191. The road log begins at the bridge crossing the Colorado River outside of Moab. 0.0 Crossing the Colorado River on the north side of Moab. 2.7 Passing the entrance to Arches National Park. This park contains the greatest density of natural arches in the world from a three-foot opening to the largest, Landscape Arch. This 105-foot high ribbon of rock measures 291 feet across. Much of the faulting in the Jurassic and Triassic rocks around Moab is controlled by movement of Pennsylvanian salt, 1000's of feet thick in some places. 8.6 Pass the turnoff to Dead Horse Point. 25.0 The Mancos, Desert, and Castlegate can be seen along the Book Cliffs to the north. 29.1 Turn right onto the access road for 1-70. Drive east toward

Abstract The Desert Member of the Blackhawk Formation and the Castlegate Formation are well exposed along the Book Cliffs in eastern Utah and western Colorado. The cliffs are oriented relative to the southeasterly paleotransort direction within the Desert and Castlegate so that outcrops expose both strike and dip views of these strata] units. Starting in Tuscher Canyon outside of Green River, Utah and ending in West Salt Creek Canyon, one can traverse the Castlegate and Desert from a totally nonmarine depositional environment updip to shelf mudstones, in the case of the Desert, and red, ferruginous oolites in the case of the Castlegate downdip. Three sequence boundaries are developed in the interval, one within the Desert and and two within the Castlegate. Because of the high-quality of the exposures, the superb access to the rocks, and the orientation of the cliffs, these two units provide an unsurpassed natural laboratory to study nonmarine to marine sequence stratigraphy. Variations in sequence-boundary expression from updip to downdip, systems tract variations across a basin, changes in incised-valley geometries, and fluvial architecture in nonmarine lowstand deposits can all be analyzed in the Castlegate and Desert

Abstract OBJECTIVE : For the next two days we will examine the stratigraphy and lithofacies of Turanian- and Coniacian-age strata in northwestern New Mexico, on the lands of the Navajo Nation (see location map Figure 6-1). We will focus on the Gallup (shallow marine and coastal plain), Torrivio (predominantly braided-fluvial) and Tocito (estuarine to shallow marine) sandstone formations. An overview of the stratigraphy, lithofacies and hydrocarbon-trapping styles pertaining to these sandstones, in outcrop and from extensive subsurface well-log correlations, is presented in the accompanying paper entitled ‘High- resolution sequence stratigraphy of the Upper Cretaceous Tocito Sandstone…’. A briefer overview is also presented under STOP 1 below. The stratigraphy of the San Juan Basin is summarized in Figures 6-2, 6-3 and 6-4. These are increasingly higher resolution stratigraphic columns, with Figure 6-4, being specifically designed for this field trip. This figure reflects some of the latest ideas on the distribution of significant sequence-stratigraphic surfaces in the Late Turanian and Coniacian parts of the section. The discussion in the text at each of the field stops is designed to present two somewhat different sequence-stratigraphic interpretations of the rocks; an Exxon (Jones, Van Wagoner and Jennette) and L.S.U. (Nummedal and Riley) interpretation. The reader can draw his/her own conclusions from the observations made at outcrop and in the subsurface (see accompanying papers). Any person wishing to conduct geological investigations on the Navajo Reservation, including visiting the stops described in this guidebook, must first obtain a permit from the Navajo Nation Minerals Department, P.O. Box 146,

Abstract In the subsurface of the San Juan Basin, New Mexico, the Coniacian Tocito Sandstone is composed of four sequences (Tocito-1, Tocito-2, Tocito-3 and Tocito-4). Over their extent, each basal sequence boundary is marked by erosion and truncation of underlying strata and onlap by shallower water, typically estuarine strata. Axes of erosion are typically narrow, straight to slightly sinuous and locally join to form tributary-like junctures. These patterns are interpreted to be incised valleys cut by fluvial and estuarine systems during lowstands in relative sea level. The four sequences stack in a backstepping pattern to form a retrogradational sequence set. Toward the outcrop belt (southwest), the sequence boundaries merge to form a composite surface which everywhere separates Tocito strata from underlying Gallup strata. Sandstone accumulations occur along sinuous lows associated with incised sequence boundaries. Two end-member types of lowstand facies exist: an open-marine facies dominated by marine mudstone with minor thin-bedded and bioturbated sandstone beds and a sand-prone, tidally influenced facies consisting of beds of medium to coarse grained, highly glauconitic sandstone. Tidal indicators include double clay drapes, flaser and lenticular bedding and large- to small-scale sigmoidal and trough cross bedding. Iron-cemented shale rip-up clasts, quartz and phosphatic pebbles, sharks teeth, Inoceramus and oyster shell fragments also characterize the Tocito Sandstone. Ichnofauna are dominated by Thalassinoides, Paleophycus and Planolites burrows with locally abundant robust Ophiomorpha burrows. Bedding and ichnofauna indicate sand deposition within estuaries. Reactivated basement-involved faults were the dominant influence on Tocito drainage patterns. These northwest-trending basement-involved faults, which were active episodically throughout the Phanerozoic, created linear pathways that acted as catchments for southeast-directed stream and estuarine systems. Reactivation of these structures during the Tocito lowstands led to a reorientation of regional sediment transport directions nearly perpendicular to that of the underlying Gallup shoreline deposits. The close vertical juxtaposition of erosional sequence boundaries and variably filled incised valleys created abundant stratigraphic traps. Most hydrocarbon traps are dependent on a combination of trapping elements which can include a bend in the valley axis (lateral-trapping clement), valley edges where valley-fill sandstones thin to zero (lateral and updip seals), and truncation of sandstone valley-fill by younger, shale-filled valleys (lateral, updip and top seals). Through time, valleys tend to become broader and shallower and are filled with strata that are more shale-prone and more open marine in character. Hydrocarbon production is chiefly from the older, sand-prone valley systems. Previous workers viewed the composite erosional surface at the base of the Tocito sequences as a single erosional unconformity which was progressively onlapped through time by beaches, offshore bars and shelf-sand ridges. In these models, hydrocarbon-trapping mechanisms relied on gradual facies changes of the sandy bars into marine shale. The incised-valley model accounts for the lidal and estuarine indicators, complex erosional patterns and hydrocarbon-trapping styles of the Tocito Sandstone.