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Fawton, T.F and Buck, B.J.. 2006, Geology

Fawton, T.F and Buck, B.J.. 2006, Geology

Implications of diapir-derived detritus and gypsic paleosols in Lower strata near the Castle Valley salt wall, ,

Timothy F. Lawton* Institute of Tectonic Studies, New Mexico State University, Las Cruces, New Mexico 88003, USA Brenda J. Buck Department of Geoscience, University of Nevada–Las Vegas, Las Vegas, Nevada 89154, USA

ABSTRACT conformities on the flanks of diapiric anti- Gypsum-bearing growth strata and sedimentary facies of the on clines (Shoemaker et al., 1958; Elston et al., the crest and NE flank of the Castle Valley salt wall in the Paradox Basin record salt rise, 1962; Cater and Elston, 1963; Trudgill et al., exposure, and salt-withdrawal subsidence during the Early Triassic. Detrital 2004; Matthews et al., 2004). Elston et al. gypsum and dolomite clasts derived from the middle Paradox Formation (1962) described carbonate-clast conglomerate were deposited in strata within a few kilometers of the salt wall and indicate that salt rise of possible Paradox Formation fragments in rates roughly balanced accumulation, resulting in long-term exposure of mobile strata near the crest of the Salt Valley evaporite. Deposition took place primarily in flood-basin or inland sabkha settings that , and Shoemaker et al. (1958) de- alternated between shallow subaqueous and subaerial conditions in a hyperarid climate. scribed gypsum detritus adjacent to the Sinbad Matrix-supported and clast-supported conglomerates with gypsum fragments represent Valley anticline in the Lower Triassic Moen- debris-flow deposits and reworked debris-flow deposits, respectively, interbedded with kopi Formation. These observations indicate flood-basin and during development of diapiric topography. - diapir exposure, but their significance to the rich flood-basin deposits with numerous stage I to III gypsic paleosols capped by eolian mechanics of salt rise was not recognized. We gypsum sheets accumulated during waning salt-withdrawal subsidence. Association present observations here demonstrating that of detrital gypsum, eolian gypsum, and gypsic paleosols suggests that the salt wall provided the evaporite of the Castle Valley diapir was a common source for gypsum in the surrounding strata. This study documents a previ- subaerially exposed throughout the Early Tri- ously unrecognized salt weld with associated growth strata containing diapir-derived de- assic, confirming that passive diapirism was tritus and gypsic palesols that can be used to interpret halokinesis. the primary mechanism of salt rise during that time. We describe the oldest gypsic paleosols Keywords: diapirism, Moenkopi Formation, Paradox Basin, gypsum, salt structures, paleosols. known in the rock record and ascribe them to diapiric exposure. These paleosols indicate ex- INTRODUCTION treme aridity during the Early Triassic and Passive diapirism, or downbuilding, where- represent a previously unrecognized type of in the rise of salt diapirs roughly keeps pace diapir-sourced material; thus, they are an im- with contemporaneous sediment accumula- portant indicator of proximity to the salt walls. tion, has long been inferred from geometric relations of flanking strata in outcrop and seis- GEOLOGIC SETTING mic reflection profiles (Barton, 1933; Rowan, The asymmetric Paradox Basin developed 1995) and experimental models (Vendeville in middle Pennsylvanian time adjacent to the and Jackson, 1991). Nevertheless, confirma- northwest-trending basement-cored Uncom- tion of the process requires evidence for pahgre uplift (Fig. 1; Baker et al., 1933; Wen- diapir-generated topography and possible gerd and Strickland, 1954; Elston et al., 1962). evaporite exposure, whether subaerial or sub- The proximal basin fill constitutes the undif- aqueous, in the form of detritus eroded di- ferentiated Cutler Group, a Pennsylvanian– rectly from the diapir and/or its thin overbur- Permian arkosic alluvial wedge ϳ5 km thick den and deposited in flanking strata (e.g., near the uplift; it grades southwestward Giles and Lawton, 1999; Rowan et al., 2003). through a thick section of cyclic middle Penn- In this paper we describe diapir-derived de- sylvanian evaporite, , and carbonate of tritus and the oldest recorded gypsic paleosols the Paradox Formation into middle and Late in growth strata of the Moenkopi Formation Pennsylvanian carbonates of the Paradox and at the northwest end of the Castle Valley salt Honaker Trail Formations on the southwest wall, one of several elongate salt diapirs in the Figure 1. Location map of Paradox Basin flank of the basin (Barbeau, 2003). The Paradox Basin of eastern Utah and south- and salt anticline province. Salt walls: CV, strongly progradational Early Permian part of western (Fig. 1). The salt walls Castle Valley; FV, Fisher Valley; GV, Gypsum the alluvial wedge grades southwestward into Valley; LVD, Lisbon Valley–Dolores; MSV, marginal marine, eolian, and fluvial siliciclas- formed by migration of middle Pennsylvanian Moab–Spanish Valley; PV, ; evaporite of the Paradox Formation during ST, Salt Valley; SV, Sinbad Valley. Commu- tic and subordinate carbonate strata of the Cut- Late Pennsylvanian, Permian, and Triassic nities: GJ, Grand Junction; GR, Green ; ler Group (Condon, 1997). The Lower Triassic time; minor salt movement continued beyond M, Moab. Edge of salt is from Condon Moenkopi Formation, which unconformably the Triassic. Evidence for syndepositional salt (1997); distribution of salt in salt walls is af- overlies the Cutler Group and was likewise ter Shoemaker et al. (1958). Explanation rise includes thinning of strata and angular un- shows distribution of selected geologic fea- derived from the Uncompahgre uplift, post- tures near end of Pennsylvanian. Inset rect- dated important shortening-related flexural *E-mail: [email protected]. angle indicates area of Figure 2. subsidence (Barbeau, 2003), but records con-

᭧ 2006 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. Geology; October 2006; v. 34; no. 10; p. 885–888; doi: 10.1130/G22574.1; 4 figures. 885

Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/34/10/885/3531439/i0091-7613-34-10-885.pdf by Rice University user on 27 February 2020 Figure 2. Geologic map and cross section of northwest end of Castle Valley anticline. Plunging crest of anticline is indicated by anticlinal symbol. Locations of measured sections of Figure 3: EM, East monocline; PM, Pariott Mesa; WM, West monocline. Map units of Moenkopi Formation are stratigraphic intervals dominated by lithologic associations (see text for details), except for Pariott Member, which is a formal lithostratigraphic unit (Shoemaker and Newman, 1959). Use of informal ‘‘lower Cutler beds’’ as a lithostratigraphic unit follows the recommendation of Condon (1997).

tinued diapirism in the salt anticline region in opposite sides of the structure dip steeply and gion represents terrestrial strata deposited in a the northeastern part of the Paradox Basin face outward away from the weld; (2) the hyperarid basin of low regional relief. On the (Shoemaker et al., 1958; Shoemaker and New- structure terminates downdip at exposures of northeast flank of the Castle Valley anticline, man, 1959; Trudgill et al., 2004). Paradox gypsum, shale, and dolostone; (3) the Moenkopi unconformably overlies arkosic The Castle Valley salt wall and associated strata on both sides of the structure thin to- sandstone and conglomerate of the Cutler For- anticline (Fig. 1) trend 310Њ from Oligocene ward it; (4) updip Cutler beds adjacent to the mation with ϳ10Њ of angular discordance. The intrusions on the southeast to a plunge ter- structure contain dolostone clasts derived basal bed consists of structureless fine- to mination at the on the north- from the Paradox Formation, although the coarse-grained gypsum-cemented sandstone. west. Gypsum, black shale, and dolostone of Paradox is no longer present there. The struc- This is overlain on both sides of the Castle the Paradox Formation crop out locally on the ture loses stratigraphic displacement upward Valley by a distinctive 0.7–1-m-thick bed of flanks and near the middle of the eroded salt and terminates into the upper hinge of a finely crystalline gypsum (Dane, 1935; Shoe- wall where not covered by a thin veneer of monoclinal panel of growth strata in the maker and Newman, 1959), locally with faint Neogene surficial deposits. Permian and Tri- Moenkopi Formation (Fig. 2). Maximum tabular cross-beds as high as 30 cm. We in- assic strata dip northeast and southwest away structural relief on the monocline decreases terpret this extensive bed of gypsum as an eo- from the diapir; dips are steep to overturned northward from 250 m at its southernmost ex- lian sand sheet. ϳ near the diapir and decrease away from the posure to 20 m near the Colorado River (a Four major lithologic associations are pres- diapir and upward through the section, indi- distance of 1600 m). On the western upthrown ent in the Moenkopi Formation adjacent to the cating decreasing amounts of halokinetic ro- block of the weld, laminated dolomicrite and Castle Valley salt wall (Figs. 2 and 3): (1) het- red sandstone that we interpret as upper tation in progressively younger strata. erolithic thin-bedded siltstone and sandstone; Pennsylvanian–Lower Permian ‘‘lower Cutler Structural and stratigraphic relations at the (2) thick-bedded sandstone; (3) interbedded beds’’ (e.g., Condon, 1997) underlie a com- plunging northwest end of the Castle Valley conglomerate and rippled sandstone; (4) - plete but thin section of undifferentiated Cut- anticline confirm rapid diapirism during Penn- stone and gypsum. The dominant heterolithic ler and White Rim Sandstone; the latter sylvanian and Permian time, with continuing association consists of thin-bedded siltstone is overlain by the basal Hoskinnini Member salt-withdrawal subsidence into the Early Tri- and very fine to fine-grained sandstone with of the Moenkopi Formation. The Cutler Group assic (Fig. 2). A previously unrecognized lis- is not exposed directly east of the weld, where oscillation, current, and combined flow rip- tric secondary salt weld (e.g., Jackson and a thick Moenkopi section is present. ples, and desiccation cracks filled with frosted Cramez, 1989), a fault-like structure formerly eolian sand. This is a widespread lithologic occupied by evaporite, juxtaposes Permian LITHOLOGIC ASSOCIATIONS OF association in the Moenkopi (e.g., McKee, and Triassic strata and trends 015Њ, oblique to MOENKOPI FORMATION 1954; Blakey, 1973); in the study area we in- the trend of the salt wall. Evidence for the Depositional relations indicate that the terpret it as deposits of a continental flood ba- weld interpretation is fourfold: (1) strata on Moenkopi Formation in the salt anticline re- sin or inland sabkha (sebkha of Glennie, 1970)

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Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/34/10/885/3531439/i0091-7613-34-10-885.pdf by Rice University user on 27 February 2020 Figure 4. Gypsum in Moenkopi Formation adjacent to Castle Valley salt wall. Scale bars are 20 cm. A: Detrital gypsum clast (g) and dolostone clast (d) derived from Para- dox Formation in conglomerate and sand- stone association. Photo by Ron Foster. B: Cumulative paleosol with stage II gypsum nodules (1–12 cm; examples indicated with arrows) and variable structure, ranging from Figure 3. Measured sections of Moenkopi Formation. Section locations are indicated in moderate to strong, fine to coarse, suban- Figure 2. Datum is base Pariott Member. gular blocky to columnar, in mudstone and gypsum association.

subject to alternating flooding and desiccation. ination, transverse climbing ripples, The oscillation and combined-flow ripples are casts, and occur singly or, less commonly, in rent ripples, adhesion ripples, and halite casts. interpreted to have formed during ephemeral multiple stories. Desiccation cracks, adhesion Uncommon desiccation cracks are restricted to lacustrine (sabkha) deposition. Although the structures, and well-sorted eolian sandstone a few horizons in the association. We interpret proportion of continental as opposed to mar- with compound foresets containing climbing this association as deposits of debris flows and ginal marine and tidal deposits in this asso- translatent strata are present in the upper parts wave- and/or current-reworked debris flows in ciation of the Moenkopi is debated (e.g., Blak- of some channel-fill successions. This litho- the lacustrine (sabkha) setting at the toes of ey, 1989), we infer a continental origin in the logic association records ephemeral and inter- debris cones derived from the topographic salt anticline region on the basis of distance mittent fluvial systems of a wadi environment high of the diapir. to a time-equivalent shoreline (Blakey, 1989) (e.g., Glennie, 1970) that impinged upon the The mudstone and gypsum association, and absence of evidence, other than hetero- inland sabkha. Although the sandstone bodies most common in the upper part of the section lithic character, for tidal deposition. are stratigraphically adjacent to the heterolith- (Fig. 3), is dominated by thick reddish-brown The thick-bedded sandstone association ic association, they lack features of tidal influ- mudstone containing repetitive cycles of gyp- consists of poorly to well-sorted, fine- to ence, notably inclined heterolithic bedsets sic paleosols 0.5–1.5 m thick capped by thin coarse-grained sandstone in beds 50–100 cm (e.g., Shanley and McCabe, 1995). Three flu- (0.1–2 m) tabular beds of gypsum interpreted thick, commonly with scour bases overlain by vial sandstone intervals (Trms1–Trms3 in as- as eolian sand-sheet deposits. The paleosols lags containing at least four clast types: (1) cending order) are present near the weld, range in development from stage I gypsum rounded ; (2) subangular dolostone; (3) where they onlap the anticline (Trms1 and snowballs (1–3 mm in diameter; Buck and angular to subangular intraclastic sandstone Trms2) and overlap the weld (Trms3). Van Hoesen, 2002), to stage II gypsum nod- and shale; (4) subangular white gypsum as The interbedded conglomerate and rippled ules (Ͻ20 cm), to stage III indurated gypsum much as 12 cm in diameter. Dolostone clasts sandstone association contains 5–40-cm-thick (Ͻ30 cm) with fine to coarse subangular include finely crystalline gray Paradox varie- beds of matrix-supported conglomerate with blocky and/or columnar structure (Fig. 4B). ties and very light gray laminated lower Cutler 1–20 cm clasts of dolostone derived from the Thin (2–30 cm) rippled sandstone beds with varieties. Both dolostone varieties are exposed Paradox Formation and ‘‘lower Cutler beds’’ and halite casts are also present. in the map area (Fig. 2); the Paradox dolo- (e.g., Condon, 1997); sugary textured crystal- The fine grain size and well-developed paleo- stones are in the diapir, and the lower Cutler line gypsum (Fig. 4A); and reddish-brown sols in this association indicate reduced rates dolostones are steeply dipping beds adjacent sandstone and siltstone intraclasts. Conglom- of deposition in the inland sabkha. to the diapir. Sandstone bodies fine upward erate beds are capped by fine-grained sand- The uppermost interval of the Moenkopi and contain trough cross-beds, horizontal lam- stone with oscillation, combined-flow and cur- Formation, the Pariott Member (Fig. 3; Shoe-

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Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/34/10/885/3531439/i0091-7613-34-10-885.pdf by Rice University user on 27 February 2020 maker and Newman, 1959), appears to repre- ACKNOWLEDGMENTS Annual Research Conference Program and sent deposits of lacustrine deltas and mean- We thank the Institute of Tectonic Studies at New Abstracts, p. 66–89. Mexico State University for financial support, Ann Matthews, W., Hampson, G., Trudgill, B., and Un- dering that record a changing climatic Foster and Ron Foster for field assistance, Robyn derhill, J., 2004, Impact of salt movement on regime. It was not assigned to a lithologic as- Howley for drafting assistance, and the Nature Con- fluvio-lacustrine stratigraphy and facies archi- sociation during our study. servancy for land access. Reviews by David Bar- tecture: Late Triassic , north- beau, Katherine Giles, Gary Hampson, Charles ern Paradox basin, southeast Utah, USA, in Kluth, and Mark Rowan substantially improved the Post, P.J., et al., eds., Salt-sediment interac- DISCUSSION manuscript. tions and hydrocarbon prospectivity: Con- A previously unrecognized listric secondary cepts, applications and case studies for the salt weld is associated with growth strata con- REFERENCES CITED 21st Century: Gulf Societies–Society of Baker, A.A., Dane, C.H., and Reeside, J.B., 1933, Economic Paleontologists and Mineralogists taining diapir-derived detritus and gypsic pa- Paradox Formation of eastern Utah and west- Foundation, 24th Bob F. Perkins Re- lesols in the Moenkopi Formation flanking the ern Colorado: American Association of Petro- search Conference Proceedings (CD-ROM), Castle Valley in Utah (Fig. 2). The exposed leum Geologists Bulletin, v. 17, p. 963–980. p. 931–964. evaporite was an important source for the gyp- Barbeau, D.L., 2003, A flexural model for the Par- McKee, E.D., 1954, Stratigraphy and history of the adox basin: Implications for the tectonics of Moenkopi Formation of Triassic age: Geolog- sic paleosols and gypsum eolian sand sheets the Ancestral Rocky Mountains: Basin Re- ical Society of America Memoir 61, 133 p. in the Moenkopi Formation. Proximity of the search, v. 15, p. 97–115, doi: 10.1046/j.1365- Rowan, M.G., 1995, Structural styles and evolution gypsic paleosols and the detrital gypsum clasts 2117.2003.00194.x. of allochthonous salt, central Louisiana outer to the salt wall indicates that the diapir was Barton, D.C., 1933, Mechanics of formation of salt shelf and upper slope, in Jackson, M.P.A., et domes with special reference to Gulf Coast the source of the gypsum. 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Coarse-grained diapiric Condon, S.M., 1997, Geology of the Pennsylvanian stratigraphic systems: Northern Paradox basin, and Permian Cutler Group and Permian Kai- in detritus is most abundant in the middle part of southeast Utah, USA, Post, P.J., et al., eds., bab in the Paradox basin, south- Salt-sediment interactions and hydrocarbon the Moenkopi Formation, suggesting compar- eastern Utah and southwestern Colorado: U.S. prospectivity: Concepts, applications and case atively high diapiric topography at that time Geological Survey Bulletin 2000-P, 55 p. studies for the 21st Century: Gulf Coast or fluctuations in climate-driven erosion and Dane, C.H., 1935, Geology of the Salt Valley anti- Societies–Society of Economic Paleontolo- cline and adjacent areas, Grand County, Utah: sediment supply during the Early Triassic. Ex- gists and Mineralogists Foundation, 24th Bob U.S. Geological Survey Bulletin 863, 184 p. F. Perkins Research Conference Proceedings tensive paleosol development higher in the Elston, D.P., Shoemaker, E.M., and Landis, E.R., (CD-ROM), p. 669–700. Moenkopi section suggests decreased topog- 1962, Uncompahgre front and salt anticline re- Vendeville, B.C., and Jackson, M.P.A., 1991, De- raphy along the salt wall, reduced rates of sub- gion of Paradox basin, Colorado and Utah: position, extension, and the shape of down- American Association of Petroleum Geolo- sidence due to salt withdrawal, and/or climate- building diapirs: American Association of Pe- gists Bulletin, v. 46, p. 1857–1878. troleum Geologists Bulletin, v. 75, induced decreases in erosion and sediment Giles, K.A., and Lawton, T.F., 1999, Attributes and p. 687–688. supply resulting in episodic geomorphic sta- evolution of an exhumed salt weld, La Popa Wengerd, S.A., and Strickland, J.W., 1954, Penn- bility. The Moenkopi paleosols represent the basin, northeastern Mexico: Geology, v. 27, sylvanian stratigraphy of Paradox basin, Four p. 323–326, doi: 10.1130/0091-7613(1999) oldest gypsic paleosols yet known in the rock Corners region, Colorado and Utah: American 027Ͻ0323:AAEOAEϾ2.3.CO;2. Association of Petroleum Geologists Bulletin, record, a distinction formerly held by Paleo- Glennie, K.W., 1970, Desert sedimentary environ- v. 38, p. 2157–2199. gene gypsic soils (Buck et al., 2003). The per- ments: New York, Elsevier Publishing Co., sistence of gypsic paleosols in the geologic 222 p. Manuscript received 3 January 2006 record thus has significant potential utility for Jackson, M.P.A., and Cramez, C., 1989, Seismic Revised manuscript received 9 May 2006 recognition of salt welds in salt tectonics re- Manuscript accepted 18 May 2006 the interpretation of salt tectonics and gimes: Gulf Coast Societies–Society of Eco- paleoclimate. nomic Paleontologists and Mineralogists 10th Printed in USA

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