Climate impact on fluvial-lake system evolution, Eocene Green River Formation, Uinta Basin, Utah, USA

2019 ◽  
Vol 132 (3-4) ◽  
pp. 562-587 ◽  
Author(s):  
L.P. Birgenheier ◽  
M.D. Vanden Berg ◽  
P. Plink-Björklund ◽  
R.D. Gall ◽  
E. Rosencrans ◽  
...  

Abstract In light of a modern understanding of early Eocene greenhouse climate fluctuations and new highly seasonal fluvial system faces models, the role of climate in the evolution of one classically-cited continental, terminal lake system is re-examined. Detailed stratigraphic description and elemental abundance data from fifteen cores and seven outcrop regions of the Green River Formation were used to construct a ∼150 km cross section across the Uinta Basin, Utah, USA. Lake Uinta in the Uinta Basin is divided into five lake phases: (1) post-Paleocene Eocene Thermal Maximum, (2) peak Eocene hyperthermal, (3) waning hyperthermal, Early Eocene Climatic Optimum (EECO), (4) post-hyperthermal, and (5) post-EECO regimes, based primarily on climatically driven changes in fluvial style in combination with sedimentary indicators of lacustrine carbonate deposition, organic matter preservation, salinity, and lake depth. Basinwide siliciclastic dominated intervals were deposited by highly seasonal fluvial systems and record negative organic carbon isotope excursions associated with early Eocene abrupt, transient global warming (hyperthermal) events. Carbonate dominated or organic rich intervals record stable, less seasonal climate periods between hyperthermals, with lower siliciclastic sediment supply allowing the development of carbonate and organic matter preservation. The stratigraphic progression from alternating organic rich and lean zones to the overlying organic rich Mahogany and R8 zones represents the global transition out of the pulsed early Eocene hyperthermal climate regime to a time of sediment starvation and lake stratification, sequestering sedimentary organic carbon. This study provides a novel approach to terrestrial paleoclimate reconstruction that relies largely on unique sedimentary indicators and secondarily on isotopic proxy records within the context of a large basin-wide sedimentologic and stratigraphic data set, thus setting the stage for future detailed geochemical terrestrial paleoclimate proxy development.

2020 ◽  
Vol 90 (4) ◽  
pp. 429-447
Author(s):  
Andrew P. Walters ◽  
Stephen R. Meyers ◽  
Alan R. Carroll ◽  
Tina R. Hill ◽  
Michael D. Vanden Berg

ABSTRACT The Green River Formation preserves an extraordinary archive of terrestrial paleoclimate during the Early Eocene Climatic Optimum (EECO; ∼ 53–50 Ma), expressing multiple scales of sedimentary cyclicity previously interpreted to reflect annual to Milankovitch-scale forcing. Here we utilize X-ray fluorescence (XRF) core scanning and micro X-ray fluorescence (micro-XRF) scanning in combination with radioisotopic age data to evaluate a rock core record of laminated oil shale and carbonate mudstone from Utah's Uinta Basin, with the parallel objectives of elucidating the paleo-environmental significance of the sedimentary rhythms, testing a range of forcing hypotheses, and evaluating potential linkages between high- and low-frequency forcing. This new assessment reveals that the ∼ 100-μm-scale laminae—the most fundamental rhythm of the Green River Formation—are most strongly expressed by variations in abundance of iron and sulfur. We propose that these variations reflect changes in redox state, consistent with annual stratification of the lake. In contrast to previous studies, no support was found for ENSO or sunspot cycles. However, millimeter- to centimeter-scale rhythms—temporally constrained to the decadal to centennial scale—are strongly expressed as alternations in the abundance of silicate- versus carbonate-associated elements (e.g., Al and Si vs. Ca), suggesting changes in precipitation and sediment delivery to the paleo-lake. Variations also occur at the meter scale, defining an approximate 4 m cycle interpreted to reflect precession. We also identify punctuated intervals, associated principally with one phase of the proposed precession cycle, where Si disconnects from the silicate input. We propose an alternative authigenic or biogenic Si source for these intervals, which reflects periods of enhanced productivity. This result reveals how long-term astronomical forcings can influence short-term processes, yielding insight into decadal- to millennial-scale terrestrial climate change in the Eocene greenhouse earth.


2016 ◽  
Vol 53 (3) ◽  
pp. 119-223 ◽  
Author(s):  
James Borer

Lacustrine strata of a portion of the Green River Formation studied in outcrops along Raven Ridge and in the subsurface around Red Wash Field in the northeastern Uinta Basin represent cyclic storm-dominated shoreface to deep lake deposition within a syntectonic embayment on the margin of Eocene Lake Uinta. The study interval consists of the lower Green River Formation, including the Douglas Creek, Garden Gulch, and lower Parachute Creek members, from the top of the underlying Wasatch to the Mahogany Zone of the Parachute Creek Member. Data consists of 11,900 ft (3627 m) of section measured at 23 locations across Raven Ridge, including 7,800 ft (2377 m) of hand-held gamma-ray scintillometer measurements, and over 500 wells in the greater Red Wash Field area, including pay zone analysis correlated to stratigraphy in the field. Facies analysis, as the basis for an integrated stratigraphic approach, reveals a seven-fold hierarchy of stratigraphic cycles ranging from two orders of large-scale cycles to five orders of progressively higher-frequency (smaller scale) shoreface-lake cycles across an 18-mile (29 km) long and 1900-ft (579 m) thick dip-oriented stratigraphic transect. This study recognized twenty-two facies grouped into eight facies tracts using Walther’s Law for two composite shoreface successions: one for a siliciclastic storm-graded shoreface profile that was dominant during times of regression and one for a carbonate profile that dominated in times of transgression. Two important regional facies trends across Raven Ridge include: 1) greater proportions of mudstone facies present in the southern, upper portion of the Green River Formation; and 2) significantly higher proportion of bioturbated sandstone in the northern, lower portion of the formation. The long-term 2nd-order transgression of Lake Uinta from base to top of the study interval results in an evolution from a low-gradient shoreline with marshes, ponds, and sand/mud flats to a high-gradient high-energy profile composed of spits and shorefaces that grew southward away from the emergent highlands. A composite storm-graded shelf profile shows how trough, hummocky, and swaley cross stratification type and amalgamation style change offshore proportionally to contain mud-dominated tempestites, erosional storm furrows, and oil shale. In the most offshore positions, diastasis cracks caused by differential loading are common. The lacustrine shoreface profile is compressed in the Green River Fm. in the study area with narrow facies tracts and large local gradient changes as a result of different responses to sediment supply. As a lake grows and shorelines migrate, the increase in accommodation is balanced, or in-phase, by a corresponding increase in sediment supply resulting in shoreface progradation keeping up with lake-level rise. As the shoreface stacks vertically during the rise, over steepening and failure of the profile generates gravity-flow sandstone facies. Little reworking of hummocky cross stratification high on the profile was observed, probably because wave power was limited by a shallow fair-weather wave-base. These differences also result in more symmetrical lacustrine shoreface cycles, with a large proportion of sediment partitioned into rise hemicycles, as opposed to the classical fall-asymmetric marine para-sequence which tends to have little to no strata preserved in the rise hemicycle along most of the shoreface profile. Landward-stepping lacustrine shoreface cycles are more common during the early rise portions of larger-scale 3rd-order megacycles for similar reasons. Strata at Raven Ridge support the concept that Eocene Lake Uinta was chemically stratified, or meromictic, at least during certain periods. The equable subtropical Eocene paleoclimate is interpreted to be the most important control on meromixis. Chemical stratification played a critical role in the development and preservation of organic matter, as evidenced by oil shale facies. The equable climate, however, might also have made the lake prone to thermal stratification. A paradox exists in the storm dominance of the lacustrine shorefaces and the coeval lake stratification: wave energy apparently was insufficient to break through the strong chemocline. Red Wash Field, directly downdip from the Raven Ridge outcrop belt, is an example of an oil field in a setting where the lake margin is not coincident with a structural feature: a “non-coincident” margin. Reservoirs mostly are present in the 6th-order aggradational shoreface cycles that are interpreted to have accumulated in the rise portions of 3rd-order megacycles. The best reservoir facies are trough, hummocky, and swaley cross-stratified sandstone deposited by storm processes and structureless sandstone probably derived from over steepening and failure of the shoreface during transgression. A petroleum accumulation model encompassing the Red Wash-Raven Ridge area proposes that lacustrine-sourced petroleum originated from an over-pressured mature cell in the Altamont-Bluebell field region. Oil migrated updip through leaky seals and became trapped in reservoirs within the non-coincident lake margin strata. An irregular shoreline configuration and compaction folds at Red Wash Field trapped petroleum. After reaching spill point at Red Wash Field, oil migrated farther updip to Raven Ridge and Asphalt Ridge, forming tar sand accumulations.


2016 ◽  
Vol 53 (1) ◽  
pp. 5-28 ◽  
Author(s):  
Grace Ford ◽  
David Pyles ◽  
Marieke Dechesne

A continuous window into the fluvial-lacustrine basin-fill succession of the Uinta Basin is exposed along a 48-mile (77-kilometer) transect up the modern Green River from Three Fords to Sand Wash in Desolation Canyon, Utah. In ascending order the stratigraphic units are: 1) Flagstaff Limestone, 2) lower Wasatch member of the Wasatch Formation, 3) middle Wasatch member of the Wasatch Formation, 4) upper Wasatch member of the Wasatch Formation, 5) Uteland Butte member of the lower Green River Formation, 6) lower Green River Formation, 7) Renegade Tongue of the lower Green River Formation, 8) middle Green River Formation, and 9) the Mahogany oil shale zone marking the boundary between the middle and upper Green River Formations. This article uses regional field mapping, geologic maps, photographs, and descriptions of the stratigraphic unit including: 1) bounding surfaces, 2) key upward stratigraphic characteristics within the unit, and 3) longitudinal changes along the river transect. This information is used to create a north-south cross section through the basin-fill succession and a detailed geologic map of Desolation Canyon. The cross section documents stratigraphic relationships previously unreported and contrasts with earlier interpretations in two ways: 1) abrupt upward shifts in the stratigraphy documented herein, contrast with the gradual interfingering relationships proposed by Ryder et al., (1976) and Fouch et al., (1994), 2) we document fluvial deposits of the lower and middle Wasatch to be distinct and more widespread than previously recognized. In addition, we document that the Uteland Butte member of the lower Green River Formation was deposited in a lacustrine environment in Desolation Canyon. Two large-scale (member-scale) upward patterns are noted: Waltherian, and non-Waltherian. The upward successions in Waltherian progressions record progradation or retrogradation of a linked fluvial-lacustrine system across the area; whereas the upward successions in non-Waltherian progressions record large-scale changes in the depositional system that are not related to progradation or retrogradation of the ancient lacustrine shoreline. Four Waltherian progressions are noted: 1) the Flagstaff Limestone to lower Wasatch Formation member records the upward transition from lacustrine to fluvial—or shallowing-upward succession; 2) the upper Wasatch to Uteland Butte records the upward transition from fluvial to lacustrine—or a deepening upward succession; 3) the Uteland Butte to Renegade Tongue records the upward transition from lacustrine to fluvial—a shallowing-upward succession; and 4) the Renegade Tongue to Mahogany oil shale interval records the upward transition from fluvial to lacustrine—a deepening upward succession. The two non-Waltherian progressions in the study area are: 1) the lower to middle Wasatch, which records the abrupt shift from low to high net-sand content fluvial system, and 2) the middle to upper Wasatch, which records the abrupt shift from high to intermediate net-sand content fluvial system.


2017 ◽  
Author(s):  
Megan Rohrssen ◽  
◽  
Gordon N. Inglis ◽  
Gordon N. Inglis ◽  
Alice Charteris ◽  
...  

2017 ◽  
Author(s):  
Lauren P. Birgenheier ◽  
◽  
Ryan D. Gall ◽  
Ellen M. Rosencrans ◽  
Michael D. Vanden Berg

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