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1. Loess in eastern equatorial Pangea archives a dusty atmosphere and possible upland glaciation

   https://doi.org/10.1130/B35590.1  

   Pfeifer, Lily S.; Soreghan, Gerilyn S.; Pochat, Stéphane; Van Den Driessche, Jean (June 2020, GSA Bulletin)

   null (Ed.)

   Abstract Carboniferous–Permian strata in basins within the Central Pangean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (Pangea assembly, ice-age collapse, megamonsoon inception). The voluminous (∼1.5 km) succession of exclusively fine-grained red beds that comprises the Permian Salagou Formation (Lodève Basin, France) has long been interpreted to record either lacustrine or fluvial deposition, primarily based on a local emphasis of subaqueous features in the upper ∼25% of the section. In contrast, data presented here indicate that the lower-middle Salagou Formation is dominated by up to 15-m-thick beds of internally massive red mudstone with abundant pedogenic features (microscale) and no evidence of channeling. Up-section, limited occurrences of ripple and hummocky cross-stratification, and mudcracks record the intermittent influence of shallow water, but with no channeling nor units with grain sizes exceeding coarse silt. These data suggest that the most parsimonious interpretation for the Salagou Formation involves eolian transport of the sediment and ultimate deposition as loess in shallow, ephemeral lacustrine environments. Provenance analyses of the Salagou Formation indicate coarse-grained protoliths and, together with geochemical proxies (chemical index of alteration [CIA] and τNa) that correspond respectively to a low degree of chemical weathering and a mean annual temperature of ∼4 °C, suggest that silt generation in this case is most consistent with cold-weathering (glacial and associated periglacial) processes in the Variscan highlands. Together with previous studies that detailed voluminous Permian loess in western equatorial Pangea, this work shows a globally unique distribution of dust at low latitudes that can be linked either directly to glaciated alpine terranes or to reworked and deflated deposits of other types (e.g., fluvial outwash) where fine-grained material was originally generated from glacial grinding in alpine systems. These results further support a revised model for early Permian climate, in which extratropical ice sheets coexisted with a semiarid tropics that may have hosted significant ice at moderate elevation. 

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2. Spatiotemporal quantification of organic matter accumulation in the Eocene Green River Formation, Bridger Basin, Wyoming

   https://doi.org/10.31711/ugap.v50i.117  

   Tofte, Marshal; Carroll, Alan (September 2022, Geosites)

   It has long been recognized that lakes can bury large amounts of organic carbon (CORG) in their sediment, with important consequences for conventional and unconventional petroleum resources and potentially for the global carbon cycle. The detailed distribution of lacustrine organic carbon through space and time is important to understanding its commercial and climatic implications, but has seldom been documented in detail. The Green River Formation offers a unique opportunity to improve this understanding, due to extensive Fischer assay analyses of its oil generative potential and to recently published radioisotopic age analyses of intercalat ed volcanic tuffs. Fischer assay analyses reveal distinctly different patterns of organic matter enrichment that correlate with different lacustrine facies associations. Histograms of oil generative potential for evaporative facies of the Wilkins Peak Member exhibit an approximately exponential distribution. This pattern is interpret ed to result from episodic expansion and contraction of Eocene Lake Gosiute across a low-gradient basin floor that experienced frequent desiccation. In contrast, histograms for fluctuating profundal facies of the upper Rife Bed of the Tipton Member and the lower LaClede Bed of the Laney Member exhibit an approximately normal or log normal distribution, with modes as high as 16–18 gallons per ton. This pattern is interpreted to reflect generally deeper conditions when the lake often intersected basin-bounding uplifts. Within the Bridger basin, burial of CORG was greatest in the south during initial Wilkins Peak Member deposition, reflecting greater rates of accommodation near the Uinta uplift. The locus of CORG burial shifted north during upper Wilkins Peak Member deposition, coincident with a decrease in differential accommodation. CORG burial during deposition of the upper Rife and lower LaClede Beds was greatest in the southeast, due either to greater accommodation or localized influx of river-borne nutrients. Average CORG burial fluxes are consistently ~4-5 g/m2 yr for each interval, which is an order of magnitude less than fluxes reported for small Holocene lakes in the northern hemisphere. Maximum rates of CORG burial during deposition of organic-rich mudstone beds (oil shale) were likely similar to Holocene lakes however. Deposition of carbonate minerals in the Bridger basin resulted in additional, inorganic carbon burial. Overall it appears that carbon burial by Eocene lakes could have influenced the global carbon cycle, but only if synchronized across multiple lake systems. 

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3. Pliocene Glacial-Interglacial Cyclicity in Sedimentation Offshore the Amundsen Sea, West Antarctica

   Passchier, Sandra (October 2022, 2022 American Geophysical Union Fall Meeting: Chicago, IL)

   Pliocene sediments were recovered during IODP Expedition 379 within the Resolution Drift offshore the Amundsen Sea. Site U1533 was drilled on the margin of a submarine channel extending landward to the continental margin, and Site U1532 was drilled in a more distal position on the thicker portion of the drift. We present new data collected on both sites. Facies assemblages consist of greenish gray clast-bearing mud with a biosiliceous component, interbedded with dark brownish gray laminated silty clay. Due to the close proximity of Sites U1532 and U1533 and the continuous sedimentation in the early Pliocene, individual beds of each facies can be correlated between sites. The red-green channel (a*) in shipboard reflectance spectroscopy and colorimetry data for Site U1533 covaries with the facies descriptions, Ba/Rb and Br in XRF data, ICP-MS bulk elemental ratios such as Sm/Zr, and clay mineralogy. This suggests that a more greenish color of the facies is partially attributed to a larger biogenic component in the sediment relative to the terrigenous supply, and a different provenance from the gray facies. Terrigenous particle size distributions (0-2000 mu) of Site U1533 show that the gray facies are relatively uniform silty clay, whereas greenish gray units show more variability, and a sand component. Sand-rich beds are present in both facies between the top of the greenish units and the bottom of the overlying gray units, and these have a uniform fine-sand mode. Greenish gray units are tentatively interpreted as deposition during ice retreat, with reduced terrigenous supply and higher primary productivity. Although these greenish grey facies can be interpreted as interglacial units, beds with this character do not occur evenly spaced throughout the stratigraphy. Greenish grey facies coincide with low Al/Ti ratios in XRF data for Site U1533. However, Al/Ti ratios change over evenly spaced intervals with orbital frequency and likely record a more complete record of glacial-interglacial cyclicity in sediment delivery than the irregular occurrence of greenish grey facies. This would suggest that some early Pliocene interglacials did not yield suitable conditions for the deposition of the greenish gray facies, and highlights the complex interactions between the ice sheet and the ocean embedded within these paleoarchives. PLAIN LANGUAGE SUMMARY Layers of sediment extracted via deep-sea drilling from beneath the seafloor off the Amundsen Sea, Antarctica, were stacked up over millions of years. The layers were built by pulses of sediment supplied from land ice and biogenic blooms, with distribution of material by ocean currents. The changing color and composition of the layers is an indication of the dominant imprint of ice-related processes versus ocean processes on the sediments that were raining down on the seafloor at any given time. Sedimentation related to the ice and the ocean follows different rhythms related to distribution of heat over time at different latitudes on Earth. The climate archive studied here records how the interference of these rhythms produces ice ages in Antarctica in a previous warm period about 3 to 5 million years ago with atmospheric greenhouse conditions that were like those of today. Investigations of these polar geological climate archives help provide context for the current ice mass loss observed in this same area of Antarctica and its potential sea-level effects. 

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4. Age and Paleoenvironmental Significance of the Frazer Beach Member—A New Lithostratigraphic Unit Overlying the End-Permian Extinction Horizon in the Sydney Basin, Australia

   https://doi.org/10.3389/feart.2020.600976  

   McLoughlin, Stephen; Nicoll, Robert S.; Crowley, James L.; Vajda, Vivi; Mays, Chris; Fielding, Christopher R.; Frank, Tracy D.; Wheeler, Alexander; Bocking, Malcolm (January 2021, Frontiers in Earth Science)

   null (Ed.)

   The newly defined Frazer Beach Member of the Moon Island Beach Formation is identified widely across the Sydney Basin in both outcrop and exploration wells. This thin unit was deposited immediately after extinction of the Glossopteris flora (defining the terrestrial end-Permian extinction event). The unit rests conformably on the uppermost Permian coal seam in most places. A distinctive granule-microbreccia bed is locally represented at the base of the member. The unit otherwise consists of dark gray to black siltstone, shale, mudstone and, locally, thin lenses of fine-grained sandstone and tuff. The member represents the topmost unit of the Newcastle Coal Measures and is overlain gradationally by the Dooralong Shale or with a scoured (disconformable) contact by coarse-grained sandstones to conglomerates of the Coal Cliff Sandstone, Munmorah Conglomerate and laterally equivalent units. The member is characterized by a palynological “dead zone” represented by a high proportion of degraded wood fragments, charcoal, amorphous organic matter and fungal spores. Abundant freshwater algal remains and the initial stages of a terrestrial vascular plant recovery flora are represented by low-diversity spore-pollen suites in the upper part of the unit in some areas. These assemblages are referable to the Playfordiaspora crenulata Palynozone interpreted as latest Permian in age on the basis of high precision Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-IDTIMS) dating of thin volcanic ash beds within and stratigraphically bracketing the unit. Plant macrofossils recovered from the upper Frazer Beach Member and immediately succeeding strata are dominated by Lepidopteris (Peltaspermaceae) and Voltziopsis (Voltziales) with subsidiary pleuromeian lycopsids, sphenophytes, and ferns. Sparse vertebrate and invertebrate ichnofossils are also represented in the Frazer Beach Member or in beds immediately overlying this unit. The Frazer Beach Member is correlative, in part, with a thin interval of organic-rich mudrocks, commonly known as the “marker mudstone” capping the Permian succession further to the north in the Bowen, Galilee and Cooper basins. The broad geographic distribution of this generally <5-m-thick mudrock unit highlights the development in eastern Gondwana of extensive, short-lived, shallow lacustrine systems with impoverished biotas in alluvial plain settings in the immediate aftermath of the end-Permian biotic crisis. 

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5. FACIES AND ICHNOFABRICS IN THE PALEOCENE OF CHICXULUB: A RECORD OF THE RECOVERY OF LIFE POST-IMPACT

   Whalen, M; O’Malley, K; Lowery, C; Rodriguez-Tovar, F; Morgan, J; Gulick, S. (January 2017, Lunar and planetary science conference abstracts)

   Introduction: IODP/ICDP Expedition 364 recovered core from 505.7-1334.7 m below the seafloor (mbsf) at Site M0077A (21.45° N, 89.95° W) atop the peak ring in the Chicxulub impact structure. The core penetrated Paleogene sedimentary rocks, impactrelated suevite, melt rock, and granitic basement [1]. Approximately 110 m of post-impact, hemipelagic and pelagic sedimentary rocks were recovered, ranging from middle Eocene (Ypresian) to basal Paleocene (Danian) in age [1]. The transition between suevite and basal Paleocene sedimentary rocks is a remarkable succession of fining upward gravel to sand-sized suevite (Unit 2A) overlain by laminated carbonate-rich siltstone (Unit 1G, “impact boundary cocktail” [2]) that records the settling of fine-grained material postimpact [1]. This study concentrates on the carbonaterich Paleocene sedimentary rocks of overlying Unit 1F [1]. The degree of bioturbation, or ichnofabric index (II) [3, 4], provides a semiquantitative estimate of the density of burrowing within sedminentary facies. Collection of II data within the context of facies analysis thus yields insight into the initial and then continued disturbance of sediment by burrowing organisms recording the return of life to the crater (Fig. 1). Unit 1G: The unit extends from 616.58-617.33 mbsf (Fig. 1) and consists mainly of dark brown to dark grayish brown calcareous siltstone but is complex with several different lithologies and post-depositional pyrite nodules that disrupt bedding. The base of the unit is a sharp, stylolitized contact overlain by two ~1 cm thick, normally graded beds. Overlying, up to 617.17 mbsf, the siltstone contains internally finely laminated cm-scale beds that alternate between dark brown and grayish brown. Above, up to 616.97 mbsf is a package with mm bedded couplets of dark brown and grayish brown calcareous siltstone that grade upward into similarly colored cm bedded couplets that then thin upward into mm bedded couplets again. Above this interval bedding is indistinct and appears to be obscured by soft sediment deformation from 616.66- 616.97 mbsf. The upper part of the unit is slightly deformed with greenish marlstone and interbedded lighter gray siltstone displaying a distinct downwarp from 616.58-616.66 mbsf. Rare oval structures, that are potential individual burrows, occur down to 616.65 mbsf. Unit 1F: The unit records the remainder of the Paleocene and extends from 607.27-616.58 mbsf (Fig. 1). The base of the unit is a sharp contact at the base of a greenish claystone (II 2) that overlies Unit 1G [1]. It consists dominantly of interbedded light gray to light bluish gray wackestone and packstone (II 3-5) and light to dark bluish gray marlstone (II 2) at cm-dmscale. All lithologies contain wispy stylolites. The lower portion of the unit (616.58 and 607.74) is cyclic with cm-dm-scale bedding and light greenish-blue to bluish marlstone bases (II 2-3) that grade upward into light gray or light bluish gray wackestone and packstone (II 3-5). Contacts between lithologies are usually gradational due to burrowing. The upper portion of the unit from 610.25 to 607.74 mbsf is a light yellowish brown burrowed packstone (II 4) intercalated with gray marlstone (II 2). The uppermost 7.5 cm is calcite cemented with 1 cm wide burrows (II 3-4). Clasts are fine to coarse sand size and include foraminifera. The upper surface of this unit is a hardground and minor unconformity overlain by Eocene rocks [1]. Ichnofabric Index: II data provides a window onto the return of life post-impact (Fig. 1). Rare structures in the upper most sandy suevite (Unit 2A) and in Unit 1G (Core 40R-1) resemble bioturbation structures but may also represent fluid escape [1]. The first welldefined oval structures that appear to be burrows occur in the upper part of Unit 1G (Fig. 1, 616.58-616.65 mbsf). Unequivocal burrows (II 2) that disturb sedimentary facies occur just above, at 616.56 mbsf in Unit 1F (Fig. 1). II of 3-4 are reached 5-6 cm above indicating significant disruption of original sedimentary strutures. An II of 5 is first documented at 616.16 mbsf (Fig. 1). Above this level through the Paleocene succession II largely varies between 2 and 5 with rare laminated intervals (II 1). Bioturbation intensity correlates well with facies changes and more marly facies display lower levels of bioturbation than more carbonate- rich facies. This correlation implies a depth and/or paleoredox control on the distribution of bioturbating organisms. Discussion: II and the return of life: The II data indicate that burrowing organisms were likely reestablished in the crater before the end of deposition of Unit 1G. Biostratigraphic analyses document a mix of Late Cretaceous and earliest Danian taxa within Unit Lunar and Planetary Science XLVIII (2017) 1348.pdf 1G and lowermost Danian zone Pα documented in the lowermost part of Unit 1F down to 616.58 mbsf [1]. P1a taxa occur down to 616.29 mbsf with P1b-P4 recorded upward through 607.27 m [1]. Burrowing organisims were thus active by earliest Danian indicating a rapid return of life to the crater. Hydrocode modeling implies that much of the deformation and peak ring formation was completed within minutes of the impact [5]. Deposition and reworking of impact breccia by tsunami and seiches likely extended for several days [6]. More refined estimates for the return of life to the crater may be possible with more detailed analysis of the deposition of laminae within Unit 1G that records marine settling of fine-grained material that may have taken days to months. 

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