Flood Surfaces and Deflation Surfaces Within the Cutler Formation and Cedar Mesa Sandstone (Permian), Southeastern Utah

Flood surfaces and deflation surfaces within the Cutler Formation and Cedar Mesa Sandstone (Permian), southeastern Utah

RICHARD LANGFORD 1 „ „ . tr, , . „ , . „ . . , rr . r , , , . 0,,,, MARJORIE A CHAN J Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112

ABSTRACT of dune masses and intervening interdune deposits results in the formation of first-order bounding surfaces (Mckee and Moiola,1975; Brookfield, Areally extensive erosion surfaces in eolian deposits have been 1977; Rubin and Hunter, 1982). First-order surfaces are limited in areal interpreted as long hiatuses in eolian deposition. Such erosion surfaces extent (several square kilometers) and form during relatively continuous form during deflationary episodes or during periods of erg stabiliza- eolian deposition. tion or contraction). They are called "super surfaces" and can be useful for stratigraphic correlation because of their regional extent. TOie Permian Cedar Mesa Sandstone and Cutler Formation contain a type of super surface (herein termed "flood surfaces"), -10-400+ tan2. Flood surfaces form as a result of fluvial floods into active dune seas. The surfaces may expand through nonclimbing migration of eolian dunes but do not imply long hiatuses in eolian deposition as do other types of super surfaces. Cutler and Cedar Mesa flood surfaces are overlain by shales and sandstones which thicken laterally and merge with fluvial channel-fill deposits. Flooding of active dune fields in the Cedar Mesa Sandstone is suggested by intertonguing of eolian dune and fluvial deposits. Flood surfaces can easily be mistaken for deflationary super surfaces but are distinguished by evidence of dune migration coincident with flood events and by an increase in the number of surfaces adjacent to associated aqueous deposits.

INTRODUCTION

Purpose

How are eolian strata deposited and preserved? Does the deposition of an eolian sandstone proceed relatively continuously, or is it episodic with long hiatuses? Areally extensive erosion surfaces which truncate dune deposits are a distinctive and common feature of eolian sandstones and are the keys to answering these questions. This paper documents a type of areally extensive erosion surface, herein termed "flood surfaces" (hundreds of square kilometers), in the Cutler Formation and Cedar Mesa Sandstone that formed during relatively short breaks in eolian deposition. Previously these same surfaces were interpreted as deflation surfaces (super surfaces), formed during extended hiatuses (Loope, 1985). The criteria that distinguish flood surfaces are identified.

Background

Theories for the formation of extensive erosion "bounding" surfaces Figure 1. Outcrop map of Cutler Formation and Cedar Mesa in eolian sandstone have been derived from two schools of thought on the Sandstone with Paleozoic Uncompahgre uplift. Box depicts study nature of eolian deposition. One school proposed that the subcritical climb area.

Geological Society of America Bulletin, v. 100, p. 1541-1549, 13 figs., 1 table, October 1988.

1541

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surface which formed as dunes in the Sahel deflated to a degraded, rolling, vegetated topography following a change to a wetter climate. Blakey and Middleton (1983), Kocurek (1984, 1988), Talbot (1985), and Loope (1985) argued that extensive erosion surfaces can represent significant hiatuses in eolian deposition over significant portions of ergs (sand seas). Kocurek (1988) discussed the origin of regionally extensive erosion surfaces and referred to them as "super surfaces." He discussed three categories of super surfaces: (1) super surfaces formed through the termination of ergs through a change in climate, (2) super surfaces formed through erg contraction due to eustatic or tectonic events, or (3) super surfaces formed through erg migration. All of these mechanisms invoke long hiatuses in eolian deposition. Rubin.and Hunter (1984) proposed an alternative process for creating areally extensive erosion surfaces. Migrating dunes cease to climb, and moving parallel to the depositional surface, they cut an extensive erosion surface. The Cutler Formation and Cedar Mesa Sandstone contain extensive erosion surfaces which appear to have formed in this manner. The surfaces are defined initially through fluvial floods into eolian strata and expand through nonclimbing migration of the dunes. Flood surfaces are a fourth category of super surface. In contrast to the other three categories described by Kocurek (1988), they do not mark significant hiatuses in eolian deposition.

Depositional Setting

Permian sedimentation patterns in the northeastern Colorado Plateau were influenced by the Uncompahgre Uplift (Fig. 1). A thick sequence of fluvial arkosic sandstones and conglomerates were shed from the southwestern flank of the uplift to form the Cutler Formation (Fig. 1). Paleocurrent indicators suggest west and northwest dispersal of Cutler fluvial arkoses, oblique to the Uncompahgre range front (Baars, 1970). Over most of the exposure of the Cutler Formation in eastern Utah, fluvial arkosic sandstones and shales are interbedded with eolian sandstones. Fluvial strata predominate near the Uncompahgre Uplift, northeast of Castle Valley (Fig. 1). Here eolian strata compose only 3% of the strata in 2 measured sections. Eolian strata, however, make up 51% to 78% of 12 measured sections southwest of Moab, farther from the Uncompahgre Uplift (Fig. 1). The eolian deposits occur as discontinuous tabular bodies, surrounded by fluvial sandstones and shales. The Cutler Formation intertongues with the Cedar Mesa Sandstone to the southwest (Figs. 1, 2, 3), a cliff-forming sandstone which has been Figure 2. Geologie map of study area showing locations referred interpreted both as marine and eolian in origin (Baars, 1962; Loope, to in text. Line A-A' is location of Figure 3. B-B' is location of Figure 1984a). Strata within the Cedar Mesa Sandstone intertongue with ma- 5, and C-C' is location of Figure 8. rine limestones on the west, and fluvial and eolian strata of the Cutler Formation on the east (Fig. 1) (Baars, 1962). Loope (1981, 1984a) has argued convincingly for an eolian setting. In 21 measured sections, the Cedar Mesa Sandstone consists of 90% to 97% cross-stratified sandstone in The alternative model is based on episodic eolian deposition. Stokes thick tabular beds (Fig. 4). Loope (1981) described erosion surfaces and (1962) suggested that extensive parallel erosion surfaces formed through thin lenticular shales and limestones between the tabular bodies. He also deflation of dunes to the water table. Loope (1981, 1984b, 1985) sug- observed terrestrial plant and vertebrate remains and sedimentary struc- gested that regionally extensive erosion surfaces within the Cedar Mesa tures formed through desiccation and eolian deposition (Loope, 1981, Sandstone formed as water-table-controlled deflation surfaces. Kocurek 1984a). Eolian deposition in the Cedar Mesa Sandstone was contempo- (1984) reported a similar deflation surface from the Jurassic Entrada raneous with the fluvial and eolian deposition in the Cutler Formation. Sandstone. In discussion papers, Kocurek (1984), Loope (1984), and Rubin and Stratigraphic Relations Hunter (1984) agreed that both theories were correct and that deflation surfaces might form during interruptions in the climbing migration of Eolian and fluvial strata within the Cutler Formation and Cedar eolian dunes. Thus, deflation surfaces should truncate first-order surfaces. Mesa Sandstone were examined in an area extending from Moab to the Talbot (1985) described a second type of regional erosional bounding Needles District in Canyonlands National Park (Fig. 2). Thirty-five strati-

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Moab Fault 10 Km Indian Creek Needles

Moenkopl Formation

.Organ Rock Formation/ '/y^Fluvlai and eolian

Figure 3. North-to-south cross section showing Permian stratigraphie relations along a folton and fluvial north-south lime (A-A\ see Fig. 2) across the study area. Eolien

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lower Cutler beds (Elephant Canyon Fm WÊÊmEollan, Fluvial, and Marine tmm-. v.,- J.

graphic sections were measured through the Cedar Mesa and Cutler For- Cedar Mesa is 15-18 m higher stratigraphically in the south (Figs. 2, 3) mations in this area. Near Indian Creek, in the southern part of the study (McKnight, 1940). area, cross-stratified eolian sandstones of the Cedar Mesa Sandstone inter- The limestones mark the top of a section of intertonguing fluvial, tongue with fluvial deposits of the Cutler Formation (Figs. 1, 2, 3). eolian, and marine strata. These beds have been the subject of some debate The Cedar Mesa Sandstone and stratigraphically equivalent Cutler and have been referred to as the "Elephant Canyon Formation" (Baars, Formation are -250 m thick throughout the study area. Both formations 1962) and as the "Rico Formation" (Loope, 1981, 1985). Due to the overlie and intertongue with thin fossiliferous limestones (McKnight, nature of this debate, we informally refer to this section as the "lower 1940). In the study area, the base of the Cedar Mesa Sandstone rests on Cutler beds" (suggested by Loope, 1987, personal commun.). From the and intertongues with two limestones. The upper limestone pinches out Moab fault to the Uncompahgre Uplift, the lower Cutler beds are included near the confluence of the Green and Colorado Rivers, and the base of the as part of the Cutler Group Undifferentiated (McKnight, 1940; Baars, 1962). In the study area, the Cedar Mesa Sandstone is overlain by the Organ Rock Shale (Fig. 3) (Baars, 1962). The latter formation is a fluvial and eolian unit containing abundant rip-up clasts derived from the Cedar Mesa Sandstone. Here, the Organ Rock Shale is a conglomeratic arkose and is properly a tongue of the Cutler Formation. The Shale nomenclature is misleading. Stratigraphic sections measured through the Organ Rock Shale contain 22% to 40% eolian strata. Farther north, the Organ Rock Shale grades into the Cutler Formation (Figs. 2, 3).

SURFACES

The most notable feature of the Cedar Mesa Sandstone and Cutler Formation is composed of tabular sandstone bodies containing cross- stratified eolian dune deposits (Fig. 4) (Loope, 1984b, 1985). Each sandstone body is capped by an areally extensive erosion surface (Fig. 4).

Deflationary Super Surfaces

Figure Tabular eolian sandstone bodies separated by flood and Loope (1985) identified 17 erosion surfaces from the Cedar Mesa deflationary? super surfaces, marked by arrows, in the lower half of Sandstone and interpreted them to be regional deflation surfaces. Loope the Cedar Mesa Sandstone. Eolian dune cross-strata in foreground. (1984b, 1985) used three lines of evidence to support this interpretation.

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B NE Section I

Figure 5. Cross section B-B' (location in Fig. 2) in Cedar Mesa Sandstone showing southwest-to-northeast increase in flood surfaces "F," approaching fluvial strata. Possible deflationary super surfaces are marked with "S." Asterisks mark deflationary super surfaces described by Loope (1985).

Limestone at top of lower Cutler beds.

First, the erosion surfaces have great areal extent. Loope (1981) originally flat planes and not irregular surfaces covered with stabilized, mapped one over a 225-km2 area. degrading dunes, an alternative suggested by Talbot (1985). Second, the deflation surfaces are parallel to each other and to thin limestone beds in the underlying lower Cutler beds for great distances (Fig. Flood Surfaces 5). Because the surfaces do not rise with respect to the general depositional surface of the underlying limestones, they do not represent climbing bed- The Cutler Formation contains many areally extensive erosion sur- form migration (Loope, 1984b). faces that appear identical to those described in the Cedar Mesa Sandstone Third, eolian sandstones underlying the erosion surfaces are com- by Loope (1981, 1985). They are flat and planar; they overlie extensive, monly bleached, and they contain burrows, root casts, and rhizocretions tabular, eolian sandstone bodies (Fig. 7); and they parallel each other and (Loope, 1981) (Fig. 6). Thin lenses of aqueously deposited horizontally underlying marine limestones. They have a gently irregular topography bedded sandstone, limestone, or shale which overlie the surfaces were with ~ 10 m of relief (Fig. 8). In addition, flood surfaces are covered with interpreted as deposits of ephemeral lakes and ponds (Loope, 1981,1985). isolated, thin lenses of limestone, shale, and sandstone; and the tops of The abundance of water-laid deposits overlying the surfaces was related to the underlying sandstones are bleached and contain roots and burrows a high water table. The vegetation was inferred to have grown when the (Fig. 6A). surfaces deflated down to the water table (Loope, 1981,1985). Flood surfaces also exhibit evidence of fluvial floods. They vary The low relief on the surfaces and the lack of sand reworked from widely in areal extent, from a few square kilometers to several hundred dunes in low areas on the surfaces indicate that the erosion surfaces were square kilometers. The shales and sandstones overlying the flood surfaces

Figure 6. A. Thin horizontal beds of shale and fine-grained sandstone covering flood surface "F." Rhizoliths and rhizocretions "R" extend through the flood surface into the underlying eolian sandstone. B. Horizontally bedded shales and algal limestone covering deflationary? super surface "S?". Note the large sand-filled mudcrack "M" and the sandstone dike "D." A flood surface "F" covered directly by eolian sandstone is 3 m above stick. Stick is 1.5 m long.

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Figure 7. Relationships between eolian strata and playa/overbank shale deposits. A. Lower arrows indicate 12-m-thick eolian dune strata terminating into thinly bedded shales. Upper arrow shows 25-m-thick eolian dune bed being broken up into thinner beds by thin, dark, recessively weathering shale beds. Cross-bed dip is from right to left (northwest to southeast). B. Ar- rows indicate 20-m-thick eolian-dune deposit dividing into thinner sheets separated by thin, dark shales. Cross-bed dip (paleowind) direction is out of photo toward observer.

grade laterally into thick, pebbly, coarse-grained, arkosic, fluvial channel also seems to be a common feature of modern streams which interact with deposits and are interpreted as dune localized playa/overbank deposits dunes (Langford, unpub. data). The lenticular limestones are interpreted as (Fig. 9). Lack of well-developed overbank deposits is characteristic of the deposits of wet interdune areas. They contain mudcracks and other evi- Cutler fluvial-eolian deposits (Langford and Chan, unpub. data). This lack dence of repeated flooding and desiccation (Fig. 6B).

Section 8 Section

Figure 8. Cross section showing relief on flood surfaces (location C-C' shown in Fig. 2). Sections are aligned on marine limestone at top of lower Òi Cutler bsdls. 5 kilometers

Top lower Cutler beds

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Figure 9. Two darker, coarse- grained, fluvial-channel sandstones (indicated by arrows) incised into flood surfaces and underlying light colored eolian sandstones. Right-hand channel is 7.5 m thick.

The overlying shales locally intertongue with the foresets of eolian MODEL FOR FLOOD SURFACES dunes (Fig. 7). The shales thicken through this intertonguing until entire eolian sandstone bodies pinch out (Fig. 7 A). Local soft-sediment deforma- Two modern dune fields which interact with fluvial systems provided tion in eolian sandstones extends into underlying shales. This deformation clues for a model for formation of flood surfaces. Repeated flooding of continues through a few of the shales and warps the underlying erosion dune fields indirectly promoted the formation of low-relief erosion sur- surfaces and eolian sandstones. The lower portions of eolian beds also faces. Large areas covered with shallow playas were formed through contain numerous lenses of shale which increase in abundance downward obstruction of streams by eolian dunes. Playa and channel sediments filled toward fluvial/playa strata (Fig. 10). low-lying areas. Interdune areas were expanded through erosion of dunes Interpretation. The flood surfaces represent flooding of parts of ac- by playa and channel waters. Sand-sheet development was enhanced tive ergs rather than erosion and extensive deflation. The low-relief sur- through increased vegetation and a higher water table. Fluvial activity thus faces (Fig. 8) are too flat to have formed as degrading stabilized dunes tends to reduce eolian topography and to establish a low-relief surface. (Talbot, 1985). Shale intertongued with eolian dune foresets requires dune This surface, partially vegetated and covered with clay and gravel, is migration coincident with flooding (Figs. 7, 10). Lateral pinch-out of resistant to eolian deflation. The low-relief surface allows flood waters to entire tabular eolian sandstone bodies indicates simultaneous eolian and spread widely across the erg. fluvial deposition rather than fluvial flooding of previously formed defla- The four-stage model for the formation of flood surfaces in the Cutler tion surfaces (Fig. 7). Deformation of shales and flood surfaces results Formation is summarized in Figure 11. from loading by overlying dunes and indicates a high water table during (A) A dry erg aggrades through the migration and climb of dunes and dune migration. Some root casts extend from the overlying interdune/ playa shales through the flood surfaces (Fig. 6A), suggesting that the growth of vegetation which resulted in bleaching and bioturbation of the underlying sandstones was related to flooding of the playas. Widespread fluvial floods are common in many modern ergs (Mab- butt, 1977). A good analog for the floods which produced flood surfaces within the Cedar Mesa Sandstone was the 1967 Finke River flood in southern Australia (Williams, 1970,1971). The flood inundated an 1,100 km2 area adjacent to the river channel (Williams, 1970). Fluvial channels extended into the erg and were filled with sand. Clays were deposited between dunes, creating extensive "flood flats" which cover thousands of square kilometers along the western edge of the Simpson Desert (Wil- liams, 1970). Several modern dune fields in the southwestern United States also record fluvial flood events (Langford, unpub. data). These fields show characteristic features similar to the Cutler Formation and Cedar Mesa Sandstone. Features include extensive playas interspersed with active dunes, and intertonguing between eolian dunes and shales deposited during fluvial floods. The flood deposits produced in this manner, however, are discontinuous and restricted to those interdunes accessible to the fluvial system. The Figure 10. Photograph showing the downward increase in uninterrupted nature of the Cutler Formation flood surfaces requires that number of shale (dark-weathered) beds in the lowest 6 m of a 20-m- the interdune areas were subsequently connected, probably through non- thick eolian-dune deposit. Below this unit, there is 16 m of fluvial climbing migration of the intervening dunes. channel and overbank strata.

interdunes (Rubin and Hunter, 1982) (Fig. 11 A). During this stage, the tips of first-order erosion crop out in interdune areas. (B) Flooding of a dune field partially buries interdune areas beneath playa mud (Fig. 1 IB). Topographically higher areas are eroded, and fluvial sand and mud accumulate in topographically low areas, establishing a smooth generalized interdune surface graded to the slope of the fluvial system. The fluvial influx raises the water table and allows vegetation of low-lying areas (Fig. 11C). Thus, the discontinuous erosion surfaces from stage A are buried and preserved (Fig. 1 IB) to form a flood surface. (C) The dunes migrate across the alluvial/interdune plain (Fig. 11C). If the dunes climb as they migrate, the flood surface remains as a discontinuous surface. If the dunes do not climb while migrating, they will connect the discontinuous erosion surfaces buried beneath the playa sediment, producing a single areally extensive flood surface parallel to the alluvial plain, (Figs. 11C, 1 ID). This seems to have been the case within the Cutler Formation, where surfaces are usually continuous. Repeated flooding and continued dune migration created intertongued shales and dune Figure 11. Model for forming flood surfaces. A. Dunes and in- foresets above the flood surfaces (Figs. 11C, 1 ID). ierdunes climb while migrating, and preserve underlying dune depos- (D) Eventually, periodic or seasonal flooding of the erg ceases, and its. First-order surfaces terminate up-dip as a discontinuous string of sand is re-established in interdune areas. Climbing migration of dune and erosional areas in interdune and stoss areas. B. Flooding occurs. Flu- interdune areas resumes and produces an eolian sandstone body which vial channels are incised into underlying eolian sands. Interdune buries the flood surface (Fig. 1 ID). surfaces are buried by flood deposits, creating a discontinuous flood surface. C. Continued migration of dunes is nonclimbing, across MODEL FOR DEFLATIONARY SUPER SURFACES flooded surfaces, forming a continuous flood surface. The rise in water table associated with flooding allows vegetation of low-lying areas, Loope (1984a, 1985) presented a model for deflation surfaces in the producing a rooted horizon. Continued dune migration and flooding Cedar Mesa Sandstone. Sand-rich depositional periods alternated with produce intertonguing shales and dune foresets. D. Eolian aggrada- sand-poor deflationary periods (Fig. 12). The changes in sand supply may tion resumes, burying the flood surface. coincide with eustatic changes (Loope, 1985). Climbing migration of eolian dunes occurred during eustatic sea-level fall, as sand supply was uncovered by the receding sea (Fig. 12A). Sand supply was rapidly de- pleted, and deposition ceased. Dune migration continued during this period of net erosion, cutting an erosion surface of regional extent, the super surface (Fig. 12B). Eventually, the erg deflated until it could no longer support dunes (Figs. 12C, 12D). The stabilized surfaces were colonized by plants and animals which bioturbated the underlying sandstones, producing prominent burrowed horizons in the underlying eolian sandstones (Figs. 12D, 12E).

DISCUSSION

The principal difference between the models for flood surfaces and other types of super surfaces is that flood surfaces are formed within an active dune field, whereas other super surfaces form during an interruption of eolian deposition. The deflationary super-surface model assumes that the Cedar Mesa Sandstone was formed by at least 17 separate ergs, separated by significant hiatuses (Loope, 1985). Loope (1985) gauged the time represented by these surfaces at -370,000 yr. He estimated the active dune fields to represent 30,000 yr, less than one-tenth of the time represented by Figure 12. Model illustrating the formation of deflationary super the erosion surfaces. This model has gained general acceptance (Kocurek, surfaces in eolian sandstones (modified from Loope, 1985). A. Dunes 1988; Loope, 1985; Talbot, 1985), and the possibilities of using super and interdunes climb while migrating and preserve underlying dune surfaces such as the deflation surfaces as stratigraphic and depositional deposits. First-order surfaces separate dune foresets. B. Dunes cease tools have generated much interest. to climb. Continued migration of dunes without deposition truncates In contrast, flood surfaces may mark only a flood event interrupting first-order surfaces. Nondeposition or erosion occurs. C. Deflation to otherwise continuous eolian deposition. Most flood surfaces within the ground-water table results in a low-relief erosion surface. D. Growth Cedar Mesa and Cutler are continuous, and not composed of isolated of vegetation on deflation surface creates bioturbated horizons be- interdunes. This geometry requires a period of nondeposition, during neath the erosion surface. which migrating dunes did not climb. The extensive bioturbated horizons

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cumulate soil carbonates in the southwestern United States range from hundreds to thousands of years (Gile and others, 1966; Leeder, 1975; Machette, 1985). Although the rates of carbonate accumulation and bioturbation are uncertain for the Permian Cedar Mesa, periods of nondeposition from hundreds to thousands of years probably are a good order of magnitude estimate. During these periods of nondeposition, one flood or many floods covering hundreds of square kilometers may have inundated the exposed portions of the flood surfaces.

DIFFERENTIATION OF FLOOD AND SUPER SURFACES

How can flood surfaces be differentiated from deflationary super surfaces? Flood surfaces extend from fluvial channels in the Cutler Forma- tion into the stratigraphically equivalent eolian Cedar Mesa Sandstone. Fluvial deposits of the Cutler Formation are well exposed at Indian Creek, where they intertongue with the Cedar Mesa Sandstone. Here flood surfaces may be directly traced into the Cedar Mesa Sandstone where eolian deposition was uninterrupted. The extent of flood surfaces into the erg may be determined, and flood surfaces may be compared with the deflationary super surfaces described by Loope (1984b, 1985). Figure 13. Map of distribution of areally extensive erosion sur- Surfaces were traced through the continuously exposed lower 110 m faces in the lower 110 m of the Cedar Mesa Sandstone. Contours of the Cedar Mesa Sandstone in its northern outcrop (Figs. 5, 13). Loope indicate number of surfaces. Stratigraphic sections shown as dots. (1985) described eight super surfaces from this section of the Cedar Mesa Cross section B-B' is Figure 5. Sandstone (Fig. 5). Fifteen surfaces (spaced 4-12 m apart) are found in this section near Indian Creek where the fluvial sandstones of the Cutler Formation intertongue with the Cedar Mesa Sandstone. Only four sur- beneath the flood surfaces suggest that the time of nondeposition was faces, however, proved to be continuous throughout the mapped area measurable. The horizons usually lack identifiable soil carbonates but are (Figs. 5, 13). These surfaces are potentially deflationary super surfaces. thoroughly bioturbated. Talbot (1985) noted eolianites which were sim- The other 11 surfaces terminate to the south and west. Many of these ilarly bioturbated within 6,000 yr. Estimates of the time required to ac- surfaces were traced into fluvial channel and overbank deposits near In- dian Creek, suggesting that the 11 terminating surfaces are flood surfaces. TABLE I. FEATURES OF FLOOD AND DEFLATIONARY SUPER SURFACES Discontinuous shales up to 2 m thick cover the flood surfaces near Indian Creek (Fig. 6A) but are very rare 15 km to the southwest. Feature Super surface Rood surface The average areal extent of the correlated flood surfaces is 200 km2

Areal extent 800 km2 and larger 10-400 km2 (Fig. 13). Strata containing several flood surfaces at the erg margin (Indian

Topography Planar with gentle Planar with gentle Creek) correspond to thick, continuous eolian dune deposits in the hummocky relief hummocky relief (up southwestern part of the study area. Deflation surfaces have been sug- (up to 10 m) to 10 m) gested to correlate with marine transgressions (Loope, 1985; Blakey and Geometry Parallel to general Parallel to general depositional depositional Middleton, 1983; Kocurek, 1988). The paleoshoreline for the Cedar Mesa surface surface Sandstone, however, lay to the west (Baars, 1962). Flood surfaces are Spacing 5-20 m, fairly Irregularly spaced regularly spaced (6-20 m) in clusters clustered toward the northeastern edge, adjacent to fluvial strata of the Underlying eolian Cutler Formation (Figs. 5, 13). Higher in the section, close to the fluvial strata Geometry Tabular sheets Tabular sheets Organ Rock Shale, surfaces also become more abundant and more closely

Texture Burrowed and rooted Burrowed and rooted spaced. Although the surfaces in this section are untraceable, this relation- at top, commonly at top, commonly ship suggests that most of these upper surfaces are probably flood surfaces. massive massive Overlying aqueous strata It is impossible to unambiguously identify deflationary super surfaces Geometry Thin lenses in low Thin lenses in low within the study area. Super surfaces and flood surfaces should, however, areas on the areas on the surface surface, laterally be differentiatable through sedimentologic or stratigraphic relations (for thickening example, tracing surfaces laterally). Table 1 provides a list of the character- Lithology Limestone, Same, but shale istic features of the flood and deflationary super surfaces in the Cedar Mesa sandstone, and more abundant shale Sandstone and Cutler Formation. Features Mudcracks Same, but shales Sedimentologically, the flood surfaces are identifiable through evi- sandstone dikes, intertongue with soft sediment overlying eolian dence of flooding coincident with dune migration and eolian deposition. deformation dune foresets, soft This relationship is suggested by the intertonguing of dune foresets and features sediment deformation of surface-capping shales or syndepositional deformation of underlying shales erosion surfaces underlying strata and surfaces. The thin, discontinuous shales and limestones within the

Spacing 5-20 m, fairly Closely (~ 1 m) lower portions of eolian dune strata provide further support for flooding regular spaced near the during dune migration. These distinguishing features, however, are only bottom of the sandstone sheets; locally present on flood surfaces. Other types of super surfaces should lack absent toward top these features.

Flood surfaces are distinguishable through their lateral and vertical ACKNOWLEDGMENTS associations. Laterally equivalent aqueous deposits may suggest that erosion surfaces are flood surfaces. The number of flood surfaces and thick- We thank David Loope, Steven Fryberger, and Mario Caputo, who ness of aqueous, surface-capping sediments increase laterally and vertically provided critical reviews and significantly improved the manuscript. This toward the aqueous deposits. In the Cedar Mesa Sandstone, these deposits research was funded by National Science Foundation Grant EAR- are fluvial, but lacustrine and marine events could also produce flood 8618235 to M. Chan. Chevron USA was generous in providing funding to surfaces. begin this research. The eolian strata adjacent to the line of termination of other types of super surfaces should show evidence of an extended hiatus. Evidence might include partially vegetated remnant dune forms; or concentrations of REFERENCES CITED

zibars, lag gravels, or sand sheets adjacent to the termination of the super Baars, D. L., 1962, Permian system of the Colorado Plateau: American Association of Petroleum Geologists Bulletin, surfaces. Another test for super surfaces is to correlate the surface through- v. 46, p. 146-218. 1970, Permian System, in Geologic Atlas ofthe Rocky Mountains: American Association of Petroleum Geologists, out the erg, demonstrating a regional areal extent. We have neither at- Rocky Mountain Section, Denver, Colorado, p. 148-165. Blakey, R. C., and Middleton, L. T., 1983, Permian shoreline eolian complex in central Arizona: Dune changes in response tempted to correlate the four potential deflationary super surfaces to cyclic sea level changes, in Brookfield, M. E., and Ahlbrandt, T. S., eds., Eolian sediments and processes: throughout the Cedar Mesa erg, nor have we been able to observe the Developments in Sedimentology 38: Amsterdam, the Netherlands, Elsevier, p. 551-581. Brookfield, M. E., 1977, The origin of bounding surfaces in ancient eolian sandstones: Sedimentology, v. 28, p. 303-332. termination of these surfaces. They may, in fact, prove to be flood surfaces Gile, L. H-, Peterson, F. F., and Grossman, R. B„ 1966, Morphological and genetic sequences of carbonate accumulation in desert soils: Soil Science, v. 101, p. 347-360. of great areal extent. Kocurek, Gary, 1984, Origin of first-order bounding surfaces in aeolian sandstones—Reply: Sedimentology, v. 31, p. 125-127. 1988, First-order and super bounding surfaces in eolian sequences—Bounding surfaces revisited: Sedimentary CONCLUSIONS Geology, v. 56 (in press). Leeder, M. R., 1975, Pedogenic carbonates and flood sediment accretion rates: A quantitative model for alluvial arid-zone lithofacies: Geology Magazine, v. 112, p. 257-270. Loope, D. B., 1981, Deposition, deflation, and diagenesis of upper Paleozoic eolian sediments, Canyonlands National 1. Major fluvial floods or a sequence of floods can mark extensive Park, Utah [Ph.D. dissert.]: Laramie, Wyoming, University of Wyoming, 170 p. surfaces (termed "flood surfaces") in eolian deposits through filling of 1984a, Eolian origin of upper Paleozoic sandstones, southeastern Utah: Journal of Sedimentary Petrology, v. 54, p. 563-580. interdunes with flood-derived sediment. In the Cedar Mesa Sandstone and 1984b, Origin of extensive bedding planes in aeolian sandstones: A defense of Stokes Hypothesis—Discussion: Sedimentology, v. 31, p. 123-125. Cutler Formation, the interdunes were commonly connected through sub- 1985, Episodic deposition and preservation of eolian sands: A late Paleozoic example from southeastern Utah: sequent nonclimbing migration of eolian dunes to form continuous flood Geology, v. 13, p. 73-76. Mabbutt, J. A., 1977, Desert landforms: An introduction to systematic geomorphology. Volume 2: Cambridge, Massachu- surfaces. These surfaces are keys to the preservation of eolian strata in the setts, MIT Press, 340 p. Machette, M. N., 1985, Calcic soils of the southwestern United States, in Weide, D. L., ed., Soils and Quaternary geology Permian Cedar Mesa Sandstone, as portions of the erg were buried be- of the southwestern United States: Geological Society of America Special Paper 203, p. 1-22. neath the shales derived from the laterally equivalent Cutler Formation. Mckee, E. D., and Moiola, R. J., 1975, Geometry and growth of the White Sands dune field, New Mexico: U.S. Geological Survey Journal of Research, v. 3, p. 59-66. 2. Previous models for super surfaces, regional erosion surfaces of McKnight, E. T., 1940, Geology of the area between Green and Colorado Rivers, Grand and San Juan Counties, Utah: U.S. Geological Survey Bulletin 908, 147 p. higher than first order, have inferred long hiatuses in eolian deposition Rubin, D. M., and Hunter, R. E., 1982, Bedform climbing in theory and nature: Sedimentology, v. 29, p. 121-138. 1984, Origin of first-order bounding surfaces in aeolian sandstones—Reply: Sedimentology, v. 31, p. 128-132. (Talbot, 1985; Kocurek, 1988). Flood surfaces are a new type of super Stokes, W. L., 1968, Multiple parallel-truncation bedding planes—A feature of wind-deposited sandstone formations: surface which may form during continuous eolian deposition. Journal of Sedimentary Petrology, v. 38, p. 510-515. Talbot, M. R., 1985, Major bounding surfaces in aeolian sandstones—A climatic model: Sedimentology, v. 32, 3. Deflationary super surfaces, marking hiatuses in eolian sedimenta- p. 257-265. Williams, G. E., 1970, The central Australian stream floods of February-March 1967: Journal of Hydrology, v. 11, tion, are less common than previously thought in the Cedar Mesa Sand- p. 185-200. stone. Only 4 of the 15 mapped erosion surfaces in the lower half of the 1971, Flood deposits of sand-bed ephemeral streams of central Australia: Sedimentology, v. 17, p. 1-40. Cedar Mesa Sandstone are potentially deflationary super surfaces. Defla- MANUSCRIPT RECEIVED BY THE SOCIETY SEPTEMBER 8, 1987 REVISED MANUSCRIPT RECEIVED FEBRUARY 23, 1988 tionary super surfaces are difficult to distinguish from flood surfaces. MANUSCRIPT ACCEPTED FEBRUARY 23, 1988

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