Palaeoenvironments associated with caddisfly‐dominated microbial‐carbonate mounds from the Tipton Shale Member of the Green River Formation: Eocene Lake Gosiute

Abstract

Caddisfly-dominated microbial-carbonate mounds and avian eggshell fragments are common in a nearshore, oolite facies of the Tipton Shale Member of the Eocene Green River Formation. The fossils occur in a 9 m thick carbonate sequence exposed on the south-west flank of Essex Mountain, Sweetwater County, Wyoming. The eggshell was determined to be of avian origin by examination of the radial eggshell microstructure by scanning electron microscopy and polarized light microscopy. Common allochems in the limestone include: ooids, pisoids, oncoids, ostracods, gastropods, intraclasts, caddisfly larval/pupal cases, fish bones, avian bones and avian eggshell fragments. Carbonate mineralogy varies between 95% calcite and 95% dolomite. Oxygen stable isotopes vary between )10AE1 and )1AE3& (V-PDB). Carbon and oxygen stable isotopes co-vary. Co-variance of oxygen and carbon stable isotopes indicates that Lake Gosiute was hydrologically closed during the formation of this oolite sequence. Positive excursions of oxygen stable isotope values are correlated with dolomite, caddisfly cases and avian eggshell fragments. These factors are probably associated with lake regression and more saline conditions. Negative excursions of oxygen stable isotope values are correlated with calcite, gastropods and intraclasts. These factors are probably associated with lake transgression and lake freshening. In the 9 m oolite sequence studied there are at least two inferred transgressions, three regressions and two storm events. The caddisfly cases and avian eggshell fragments occur in sediments formed only during low-stands of the lake as determined by other lake level proxies (dolomites and more positive oxygen stable isotope values). As avian eggshell fragments were formed under subaerial conditions, the avian eggshell fragments independently confirm lake regression. In addition, the occurrence of avian eggshell fragments during saline phases of the lake may indicate that the birds which produced the eggshell preferred saline conditions (or that their food preferred saline lake water).

Petrography and Environmental Interpretation of Tufa Mounds and Carbonate Beds In the Jurassic Navajo Sandstone of Southeastern Utah, U.S.A.

“…They are not layered, and multiple mounds are arrayed parallel to shoreline (Della Porta 2015). The best-studied ancient examples are from the Eocene Green River Formation (e.g., Sarg et al 2013;Awramik and Buchheim 2015); caddisfly mounds there also include laminated, columnar microbialites that are typical of lake-margin bioherms (Leggitt and Cushman 2001;Leggitt et al 2007). These features are not found in the Navajo Sandstone tufa mounds.…”

Petrography and characterization of microbial carbonates and associated facies from modern Great Salt Lake and Uinta Basin's Eocene Green River Formation in Utah, USA

“…Leggitt et al (2007) discussed palaeoenvironments associated with the caddisflydominated microbial mounds of the Tipton Member of the Green River in SW Wyoming, whereas Miller (2011) described branching in stromatolites and their biogenicity, also in the Tipton Member. Buchheim et al (2010 presented basic descriptions, stratigraphic architecture, sequence stratigraphy and a depositional model for microbialite 'bioherms' in the northwestern part of the Greater Green River Basin, whereas generally described the basic facies associations containing Green River microbialites to predict lacustrine microbialite distribution.…”

Microbial-caddisfly bioherm association from the Lower Cretaceous Shinekhudag Formation, Mongolia: Earliest record of plant armoring in fossil caddisfly cases

“…Multiple Early Cretaceous examples are documented from Asia including China, Korea, and Mongolia [ 7 , 9 , 10 ]. However, our current knowledge of caddisflies is mainly limited to Eocene and younger examples (e.g., Eocene Green River Formation, Oligocene Limestone Formation) due to excellent exposures and preservation in these sections [ 11 , 12 , 13 ].…”

“…Generally, carbonate facies of the lacustrine systems are altered by both biological and depositional processes, and thus these strata contain important insights to the paleoecosystem and paleoenvironment [ 17 , 18 ]. In the Green River Formation, the co-existence of fossil caddisfly cases and microbialites was used to infer a depositional model for carbonate bioherm facies [ 13 , 19 , 20 ], because each of these biologic components (caddisfly and microbialite) have environmental preferences and tolerances including light, oxygen, and nutrient availabilities that are fundamentally dependent on wave energy, bathymetry, lake hydrology, and lake chemistry [ 21 , 22 , 23 ]. Additionally, the debris incorporated in the caddisfly larval cases indicates the main detrital components of the environment [ 13 ].…”