Pedogenic Phreatic Lacustrine Carbonate Their Use in Interpreting

Pedogenic, Phreatic, & Lacustrine Carbonate & Their Use in Interpreting Significant Surfaces in the Upper Triassic Chinle Formation, Southeastern Utah Stephen T. Hasiotis & Sean J. Fischer

Key Findings • Three types of carbonate occur in continental deposits of the Upper Triassic Chinle Formation, Canyonlands area, SE UT: pedogenic, phreatic, & lacustrine. • Pedogenic carbonates most abundant; phreatic carbonate overprint sediments & soils; lacustrine carbonate as oncolites fluvially reworked as laterally extensive lateral accretion. • Pedogenic carbonate accumulation in floodplain & alluvial paleosols as stages I, II, & III reflecting increasing landscape stability & paleosol development; four corners area stage IV is reached. • Pedogenic carbonates as compound, composite, or cumulic soil profiles that reflect interplay between sedimentation, pedogenesis, bypass, & erosion. • Stratigraphic occurrence of stage I–III paleosols as well as other paleosol types reflect distribution of valleys cut by landscape degradation & filled by aggradation.

Goals • Document spatial (lateral) & temporal (vertical) stratal patterns produced by paleosol development resulting in stages of pedogenic carbonate intervals in predominantly siliciclastic sedimentary systems; • Determine how various stages of pedogenic carbonate accumulation reflects landscape stability in relationship to landscape aggradation & degradation; • Integrate data from Chinle paleosols with ichnologic & sedimentologic data (i. e. , ichnopedofacies) & local tectonism to understand how climate change affected depositional systems, soil formation, & carbonate accumulation.

Background: Late Triassic Paleogeography Chinle Basin Ron Blakey at http: //cpgeosystems. com

Background: Chinle Basin Modified from Dickinson 1983; Blakey and Gubitosa 1983; Blakey 1989; Dubiel 1989, 1994; Dubiel et al. 1991; Riggs et al. 1996; Dickinson and Gehrels 2008

Study Area Modified from Stewart (1972)

Stratigraphy of the Canyonlands • Four members of the Chinle Formtion observed in this study • Moss Back Member – braided rivers • Petrified Forest Member – palustrine, high sinuosity rivers; CARBONATE • Owl Rock Member – lacustrine and high sinuosity rivers; CARBONATE • Church Rock Member – fluvial systems, playa lakes; CARBONATE

Methods • Measure & trench stratigraphic sections & stick sections • Describe lithofacies, facies associations, trace fossils, & paleosols • Thin-section analysis—pedogenic & bioturbation • Construct ichnopedofacies (IP) from paleosols & ichnocoenoses Nonsteady • XRF & XRD analysis—chemical composition & clay mineralogy From Kraus (1999) • Determine controls on IP development: (A) autocyclic or (B) allocyclic processes, or (C) hydrology • Reconstruct MAP for Chinle Fm, northeast Chinle Basin Steady • Compare IP to modern latitudinal landscape analogs: Tanzania, central India, & Australia

FORMATION OF SOIL PROPERTIES (STEADY STATE) VS. TIME A) Maximum expression of properties associated with soil horizons B) Soil profile development for various soil orders *Time for development dependent on seasonal annual temperature & precipitation *Also on sediment accumulation rates & groundwater profile (Birkeland, 2001)

105– 106 101– 102 Pedogenic Carbonate Development through Time (After Giles et al. , 1966) • Stages of carbonate development, depending on compound to cumulative sedimentation patterns, form from 102– 106 years • Typically represent longer term surface stability of physicochemical properties for carbonate accumulation

Ichnopedofacies Distribution Steady Nonsteady From Kraus (1999) Palustrine

Ichnopedofacies: Petrified Forest Mbr Composite Therapsid Calcic Inceptisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Therapsid Paleosol: Calcic Inceptisol Interpretations Autocyclic Events: Rare Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: Low, nonsteady Climate: 1100– 1300 mm/yr

Ichnopedofacies: lower Owl Rock Mbr Cumulative & Compound Camborygma Vertisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Camborygma Paleosol: Vertisol Interpretations Autocyclic Events: Rare Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: Low, nonsteady Climate: >1300 mm/yr

Ichnopedofacies: lower Owl Rock Mbr Composite Naktodemasis Calcic Alfisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Naktodemasis Paleosol: Calcic Alfisol Interpretations Autocyclic Events: Rare Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: Low, nonsteady Climate: ~700– 1100 mm/yr

Ichnopedofacies: lower Owl Rock Mbr Composite Rhizolith Calcic Alfisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Rhizolith Paleosol: Calcic Alfisol Interpretations Autocyclic Events: Rare Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: Low, nonsteady Climate: ~400– 700 mm/yr

Ichnopedofacies: middle Owl Rock Mbr Composite Camborygma Calcic Alfisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Camborygma Paleosol: Calcic Inceptisol Interpretations Autocyclic Events: Rare Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: Low, nonsteady Climate: ~700– 1100 mm/yr

Ichnopedofacies: middle Owl Rock Mbr Compound Rhizolith Inceptisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Rhizolith Paleosol: Inceptisol Interpretations Autocyclic Events: Common Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: High, nonsteady Climate: ~700 mm/yr

Ichnopedofacies: middle Owl Rock Mbr Observations Lithofacies: Laterally accreted conglomerate with oncoids Interpretations Oncoids originally formed in lakes Local salt tectonic uplift Lacustrine deposits reworked by meandering rivers Oncoids redeposited in laterally accreted conglomerate

Ichnopedofacies: upper Owl Rock Mbr Composite Naktodemasis Alfisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Naktodemasis Paleosol: Alfisol Interpretations Autocyclic Events: Rare Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: High, nonsteady Climate: ~1100 mm/yr

Ichnopedofacies: upper Owl Rock Mbr Composite & cumulative Naktodemasis Calcic Inceptisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Naktodemasis Paleosol: Calcic Inceptisol Interpretations Autocyclic Events: Rare Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: High, steady Climate: ~700 mm/yr

Ichnopedofacies: Church Rock Mbr Cumulative Naktodemasis Calcic Inceptisol Observations Lithofacies: Massive siltstone Ichnocoenosis: Naktodemasis Paleosol: Calcic Inceptisol Interpretations Autocyclic Events: Rare Fluvial Style: Braided river Basin Subsidence: Low Accommodation: Low Sedimentation: High, steady Climate: ~400 mm/yr

Ichnopedofacies: Moss Back Mbr Compound Rhizolith Entisols Observations Lithofacies: ripplelaminated sandstone Ichnocoenosis: Rhizolith Paleosol: Entisols Interpretations Autocyclic Events: Common Fluvial Style: Braided River Basin Subsidence: Low Accommodation: Low Sedimentation: High, nonsteady

Ichnopedofacies: middle Owl Rock Mbr Compound Camborygma Entisol Observations Lithofacies: Ripple-laminated sandstone Ichnocoenosis: Camborygma Paleosol: Entisol Interpretations Autocyclic Events: Common Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: High, nonsteady Climate: ~700 mm/yr

Ichnopedofacies: upper Owl Rock Mbr Compound Naktodemasis-Camborygma Entisol Observations Lithofacies: ripple-laminated sandstone Ichnocoenosis: Naktodemasis. Camborygma Paleosol: Entisol Interpretations Autocyclic Events: Common Fluvial Style: Meandering River Basin Subsidence: High Accommodation: High Sedimentation: High, nonsteady Climate: ~700 mm/yr

Ichnopedofacies: Church Rock Mbr Compound Shallowly Burrowed Entisol Observations Lithofacies: Planar-laminated and ripple-laminated siltstone to very fine sandstone Ichnocoenoses: Cylindrichum Paleosol: Entisol Interpretations Autocyclic Events: Common Fluvial Style: Braided river Basin Subsidence: Low Accommodation: Low Sedimentation: High, nonsteady Climate: ~25– 325 mm/yr

Stratigraphic Distribution of Paleosols & Incised Valleys

Climate Reconstruction • Petrified Forest Mbr • 1100– 1300 mm/yr • lower Owl Rock Mbr • Decrease from >1300 mm/yr to 400– 700 mm/yr • Multiple wet-dry fluctuations • middle & upper Owl Rock mbrs • Two upward drying cycles from 700– 1100 mm/yr • Church Rock Mbr • Decrease from 400 mm/yr to 25– 325 mm/yr • Overall decrease in MAP • Megamonsoon persisted until end of Chinle Fm deposition

Conclusions • Ichnopedofacies—lateral & vertical stratigraphic changes in landscape, sedimentation rate, climate, & groundwater profile 1. Depositional energy, sedimentation rate, & water table decrease with increasing distance from fluvial system 2. Sedimentation: Moss Back Mbr high, nonsteady; Petrified Forest & lower Owl Rock mbrs low, nonsteady; middle Owl Rock Mbr shifted to high, nonsteady, upper Owl Rock Mbr high, steady, & Church Rock Mbr high, nonsteady 3. Overall decrease in MAP up section with smaller wet-dry fluctuations 4. Water table controlled by MAP, decreases in depth up section; however, high water tables in proximal fluvial deposits from losing rivers • Oncoids: only evidence of lakes; lacustrine deposits not preserved due to salt tectonic uplift & fluvial reworking • Signatures of seasonality & decreasing MAP throughout Chinle Fm deposition in the NE Chinle Basin • Ichnopedofacies: megamonsoonal circulation continued through Chinle Fm deposition

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