POTENTIAL ICE CRYSTAL MARKS FROM PENNSYLVANIAN–PERMIAN EQUATORIAL RED-BEDS OF NORTHWEST COLORADO, U.S.A.

ABSTRACT The Pennsylvanian–Permian Maroon Formation of northwest Colorado is an up to 4,600 m thick succession of mainly siliciclastic continental red-beds deposited in equatorial intermontane basins of the Ancestral Rocky Mountains. Sedimentary surfaces of fluvio-lacustrine to eolian siltstones and fine-grained sandstones from various stratigraphic levels within the Maroon Formation preserve cm-sized straight to gently curved sediment-filled acicular structures referred to five morphological groups: single, branched, stellate, rosette, and bunched. Depositional environment, shape, and size of the structures are most similar to ice crystal marks that result from freezing of water-saturated fine-grained substrate at the sediment-air interface. They differ from other syngenetically produced crystals and crystal pseudomorphs in sedimentary rocks mainly by crystal shape and environmental conditions. The potential ice crystal marks of the Maroon Formation are notable for the fidelity and morphological diversity of the crystal casts and could be a key for the understanding of similar but hitherto often only called enigmatic structures of the sedimentary rock record. The ice crystal mark occurrences in the Maroon Formation suggest that night frost affected lower elevation equatorial areas during the climax of the Late Paleozoic Ice Age and may stimulate research on evolutionary adaptations of early terrestrial biota to overcome significant air temperature fluctuations.

CO2 Storage Potential Reconnaissance of the Newly Identified Red Beds of Hazlehurst in the Southeastern United States

The states of Georgia and South Carolina emitted ∼100 million tons (Mt) of CO2 in 2019 from point sources. Integration and interpretation of subsurface data enabled identification of a previously unrecognized, regionally extensive, and thick (up to 450 m) sedimentary sequence—the Red beds of Hazlehurst (RbH)—as a potential saline reservoir for CO2 storage in the southeastern United States. Based on the renewed stratigraphic framework and structural interpretation of the RbH interval, we analyzed detailed well logs and the depositional environments to provide reconnaissance-level regional scale estimations of the storage resource. The volumetric results suggest the effective storage area (∼85,000 km2) has a maximum resource potential for 390 gigatons (Gt) of anthropogenic CO2. Petrophysical measurements suggest the permeability of RbH ranges from 0.001 to 48 mD, and the porosity ranges from 11.1 to 18.4%. Residual/capillary trapping and solubility trapping act as the main trapping mechanisms for long term storage and prevent vertical migration of CO2 into the shallow freshwater aquifers. Due to the heterogeneity observed in geophysical logs and the scarcity of well penetrations, future data collection is needed to characterize the storage aquifer and confining aquitards of a site-specific system at this stage.

Diamicton facies in the vicinity of Duhlata cave, Bosnek karst region, Southwestern Bulgaria

Karst caverns in the Upper Triassic dolostones of the Rusinovdel Formation are filled with allochthonous clastics (brecciaconglomerates with maximum boulder size) and locally with speleothems (flowstones). Deposition of the former (diamicton facies) by debris flows resulted from extreme flood events along the upper reaches of Struma river. The polymict material reflects erosion of various rock types in the source area but is dominated by resedimented Lower Triassic red beds. The diamictons are more or less similar to the few known examples from Quaternary karst caves.

A prolonged, two-step oxygenation of Earth’s early atmosphere: Support from confidence intervals

The Great Oxidation Event (GOE), among Earth’s most transformative events, marked the sustained presence of oxygen above 10–5 times the present atmospheric level. Estimates of the onset of the GOE span 2501–2225 Ma and are based primarily on the loss of mass-independent fractionation of sulfur isotopes (MIF-S) in pyrite. To better constrain the timing of the GOE, we apply probabilistic techniques to estimate the confidence intervals of four proxies: MIF-S, redox-sensitive detrital minerals, "red beds," and I/(Ca + Mg). These GOE proxies are drawn from a highly fragmentary geologic record, and consequently, estimates of the 95% confidence intervals span tens to hundreds of millions of years—orders of magnitude larger than suggested by radiometric constraints on individual successions. Confidence interval results suggest that red beds and nonzero I/(Ca + Mg) values may have appeared earlier than 2480 Ma and 2460 Ma, respectively, whereas redox-sensitive detrital minerals and MIF-S may have disappeared after 2210 Ma and 2190 Ma, respectively. These data suggest a delay of potentially >300 m.y. between initial and permanent oxygenation of the atmosphere and a delay of tens of millions of years between onset of the Lomagundi-Jatuli carbon isotope excursion and permanent oxygenation of the atmosphere.

Evidencias de canibalización de secuencias Cretácicas y Paleógenas de la Cuenca Oriente en la cuña orogénica de los Andes ecuatorianos

Al sureste de la Cordillera Real, en la sección del río Miriumi, rocas sedimentarias e ígneas metamorfoseadas fueron agrupadas sin discriminación en la Unidad Upano, y la falla Palanda-Méndez-Cosanga fue considerada un límite de terreno en anteriores investigaciones. El objetivo de esta investigación es caracterizar y discriminar rocas sedimentarias e ígneas metamorfoseadas de la Unidad Upano, de rocas sedimentarias de la Cuenca Oriente. Esta discriminación está soportada en datos litoestratigráficos, identificación de estructuras sedimentarias, registro de fósiles, estudios petrográficos y análisis de datos estructurales. Rocas meta-volcánicas y meta-pelíticas afloran en la parte occidental de la sección; mientras que hacia el este de la sección, secuencias estratodecrecientes de conglomerados de cuarzo, cuarzo-areniscas, lodolitas y areniscas con estructuras mareales; calizas mudstone y wackstone, lutitas negras con abundantes trazas de amonites y bivalvos son afectadas por un pliegue anticlinal. En el río Upano, calizas y lutitas fosilíferas son cubiertas en discordancia por limolitas multicolores y red beds. Considerando la descripción inicial de la Unidad Upano, se restringe a esta secuencia a rocas meta-volcánicas y meta-pelíticas de bajo grado de metamorfismo en facies de sub-esquistos verdes relacionadas a la dinámica regional. En este estudio, cuarzo-areniscas y lodolitas con estructuras mareales son incluidas en la Formación Hollín, calizas y lutitas con Inoceramus sp. y Harleites sp. (?) son asociadas a la Formación Napo; y secuencias de red beds son vinculadas a la Formación Tena. La presencia de bloques y escamas tectónicas compuestos por las formaciones Hollín, Napo y Tena de la Cuenca Oriente en el frente de la cuña orogénica, afectadas por zonas de corrimiento y pliegues de arrastre indican que la falla Palanda-Méndez-Cosanga, no constituye un límite de terreno entre secuencias metamórficas de la Cordillera Real y secuencias sedimentarias de la Cuenca Oriente. Al contrario, nuestros datos concuerdan con el modelo de canibalización de secuencias de foreland.