Microbial Carbonate Reservoirs and Analogs from Utah

Multiple oil discoveries reveal the global scale and economic importance of a distinctive reservoir type composed of possible microbial lacustrine carbonates like the Lower Cretaceous pre-salt reservoirs in deepwater offshore Brazil and Angola. Marine microbialite reservoirs are also important in the Neoproterozoic to lowest Cambrian starta of the South Oman Salt Basin as well as large Paleozoic deposits including those in the Caspian Basin of Kazakhstan (e.g., Tengiz field), and the Cedar Creek Anticline fields and Ordovician Red River “B” horizontal play of the Williston Basin in Montana and North Dakota, respectively. Evaluation of the various microbial fabrics and facies, associated petrophysical properties, diagenesis, and bounding surfaces are critical to understanding these reservoirs. Utah contains unique analogs of microbial hydrocarbon reservoirs in the modern Great Salt Lake and the lacustrine Tertiary (Eocene) Green River Formation (cores and outcrop) within the Uinta Basin of northeastern Utah. Comparable characteristics of both lake environments include shallowwater ramp margins that are susceptible to rapid widespread shoreline changes, as well as compatible water chemistry and temperature ranges that were ideal for microbial growth and formation/deposition of associated carbonate grains. Thus, microbialites in Great Salt Lake and from the Green River Formation exhibit similarities in terms of the variety of microbial textures and fabrics. In addition, Utah has numerous examples of marine microbial carbonates and associated facies that are present in subsurface analog oil field cores.

The second North American fossil horntail wood-wasp (Hymenoptera: Siricidae), from the early Eocene Green River Formation

Eoteredon lacoi gen. et sp. nov., is described from the early Eocene Green River Formation in Wyoming, the second fossil siricid genus and species described from North America. We propose Eoteredon as sister to the genus Teredon, whose sole species is one of the rarest of extant Siricidae. The majority of siricids today inhabit temperate Northern Hemisphere forests; Teredon cubensis, however, is one of its few species that live in megathermal tropical lowlands. The Eocene forest that Eoteredon inhabited had a mesothermal to megathermal climate. We place Eoteredon in the context of broad Cenozoic climate change.

Depositional system and lake-stage control on microbialite morphology, Green River Formation, eastern Uinta Basin, Colorado and Utah, U.S.A.

ABSTRACT Lake-margin lacustrine carbonates of the Green River Formation, in the eastern Uinta basin of Colorado and Utah, occur interbedded with fluvial and shoreline-parallel sandstone and shale. Microbial bindstones were deposited in a saline-alkaline lake during and after the Early Eocene Climate Optimum (EECO) (52–50 million years ago) that is characterized by global hot-house conditions, elevated atmospheric CO2, and highly fluctuating climate conditions. The stratigraphic architecture, chemostratigraphy, and morphology of the microbialites and other associated carbonate beds can be related to these climatic conditions. Three facies associations are recognized in the carbonate units across the lake margin from upper littoral to lower sublittoral environments: facies association 1, delta proximal non-microbial carbonates, characterized by quartzose bioclastic, peloidal, intraclastic packstones and grainstones–rudstones, quartose peloid wackestones and sandy oil shale; facies association 2, microbialite associated non-microbial carbonates, composed of ostracod, ooilitic, peloidal packstones–grainstones and intraclastic packstones, grainstones and rudstones; and facies association 3, microbial carbonates, consisting of diverse forms of stromatolitic and thrombolitic lithofacies. Multiple scales of carbonate cyclicity are suggested by shifts of δ18O and δ13C stable isotopes and deepening-upward microbialite facies. High-frequency cycles, on the order of 1 to 5 m thickness, are characterized by positive shifts in stable isotopes and interpreted deepening trends from littoral to lower sublittoral conditions. Large-scale trends, on the order of tens to hundreds of meters thickness record long-term lake changes, including: 1) sparse microbialite deposition during initial fresh conditions in lake stage 1, with low macro-structure diversity and light δ18O and δ13C isotope values; 2) transitional lake stage 2 corresponding to moderate macro-structural diversity, large meter-scale biostromal and biohermal buildups, and a positive shift in δ18O and δ13C isotope values that suggest increasing saline and alkaline conditions; 3) a highly fluctuating lake stage 3 that contains the highest microbialite macro-structural diversity and marks the interval of heaviest δ18O and δ13C isotope values, suggesting the greatest lake restriction, and the highest salinity and alkalinity conditions; and 4) a rising lake stage 4 that marks the lowest microbialite macro-structure diversity and a reversal in trend of δ18O and δ13C isotope values, that indicate deepening and freshening conditions.

First record of the subfamily Sagrinae (Coleoptera: Chrysomelidae) from the Eocene of North America

A new genus, Palaeatalasis gen. nov. (type species P. monrosi sp. nov.), from the tribe Megamerini (Chrysomelidae: Sagrinae) from the early-middle Eocene Green River Formation is described and illustrated. The new genus is similar to the Recent Atalasis Lacordaire, 1845 but differs from it in the subparallel sides of the pronotum, metafemora without teeth, and non-emarginate eyes. It differs from the Eocene Eosagra Haupt, 1950 in the large, convex, non-emarginate eyes, wide elytra, and transverse pronotum. The new genus is distinguished from the Paleocene Gallopsis Legalov, Kirejtshuk et Nel, 2019 in the wide forehead and convex eyes. It is the first record of the Sagrinae from North America and the fourth known species of the family Chrysomelidae from the Green River.

Early Eocene snakeflies (Raphidioptera) of western North America from the Okanagan Highlands and Green River Formation

Four new species of Raphidiidae are described from the early Eocene of western North America: Megaraphidia antiquissima sp. nov. from McAbee, M. ootsa sp. nov. from Driftwood Canyon, M. hopkinsi sp. nov. from the Allenby Formation (all from British Columbia, Canada), M. klondika sp. nov. from Republic (Washington, United States of America). Archiinocellia Handlirsch, 1910, Archiinocellia oligoneura Handlirsch, 1910 from Horsefly River (British Columbia, Canada), and A. protomaculata (Engel, 2011), comb. nov., from the Green River Formation (Colorado, United States of America) are redescribed. Archiinocellia is assigned to Raphidiidae, sit. nov. The apparent absence of sclerotized gonocoxites 9 in the Archiinocellia protomaculata male is probably plesiomorphic at the family level. As some modern snakeflies do not require a cold interval to complete their development and Eocene Inocelliidae and Raphidiidae lived in regions of warm winters (especially A. protomaculata), adaptation to cold winters in many modern snakeflies is a post-Eocene phenomenon. Eocene Raphidiidae of Europe (Priabonian) differ greatly from those of North America (Ypresian and Priabonian). This pattern might reflect dispersal in either direction or ranges established prior to continental separation. Eocene Inocelliidae of Europe (Priabonian), however, are more similar to those of North America (Ypresian and Lutetian).