The Paleocene–early Eocene interval is punctuated by a series of transient warming events known as hyperthermals that have been associated with changes in the carbon isotope composition of the ocean-atmosphere system. Here we present and discuss a detailed record of calcareous nannofossil and foraminiferal assemblages coupled with high-resolution geochemical, isotopic, and environmental magnetic records across the middle Ypresian at the Contessa Road section (Gubbio, Italy). This allows characterization of the Eocene Thermal Maximum 3 (ETM3, K or X) and recognition of four minor (I1, I2, J, L) hyperthermals. At the Contessa Road section, the ETM3 is marked by short-lived negative excursions in both δ13C and δ18O, pronounced changes in rock magnetic properties, and calcium carbonate reduction. These changes coupled with the moderate to low state of preservation of calcareous nannofossils and planktonic foraminifera, higher FI and agglutinated foraminifera values, along with a lower P/(P + B) ratio (P—planktonic; B—benthic) and coarse fractions provide evidence of enhanced carbonate dissolution during the ETM3. A marked shift toward warmer and more oligotrophic conditions has been inferred that suggests unstable and perturbed environmental conditions both in the photic zone and at the seafloor.

We studied the oxidation state of Fe in silicate glasses produced during the first atomic bomb blast at the Trinity test site (New Mexico) by X-ray absorption–near edge spectroscopy (XANES). The sample consists of green glass resulting from melting of the quartz-bearing sand present at the test site; some relict unmelted sand is still fused to the bottom of the sample. Comparison of the pre-edge peak data with model compounds of known Fe oxidation state and coordination number shows that in the Trinity glass sample, Fe is in the divalent state and, on average, in a mixture of 4- and 5-fold coordination. XANES spectra collected at various heights of the sample, from the bottom of the sample up to the exposed surface, show no variation of the pre-edge peak and, thus, of the Fe oxidation state with the distance from the sand-glass interface. However, XANES analysis of a portion of the sand at the bottom of the sample shows Fe to be a mixture of Fe2+ and Fe3+, with a Fe3+/(Fe2+ + Fe3+) ratio close to 0.5. This demonstrates that during the nuclear explosion, the ground rock was instantaneously reduced, transforming all the iron from mostly trivalent state to almost exclusively divalent. Pre-edge peak features (intensity and energy) are consistent with those of tektites from the Ivory Coast studied here and with literature data of tektites from all the other known strewn fields (Australasian, Central European, and North American). The reduction of Fe to divalent state during Trinity glass formation, the homogeneity of the Fe oxidation state within the glass, and the Fe structural role suggest that this glass represents a good analog of tektite glass.

The ca. 2.45 Ga pyritic uraniferous quartz-pebble conglomerate (UQC) of the Matinenda Formation of the Elliot Lake Group, Huronian Supergroup, was used in this study to investigate the origin of pyrite. A laser-microprobe was used for analysis of the sulfur isotopic compositions of individual pyrite grains, and an electron-probe microanalyzer was used for analysis of the trace element compositions of pyrite grains with overgrowth texture. We found a variation in δ34S values among pyrite crystals (73 analyses) of various size and morphologies that occur in a small (∼1 cm3) rock chip: the total range in δ34S is −9.0‰ to +5.5‰ with respect to CDT (Cañon Diablo Troilite) with a mean value of +0.6‰ ±2.1‰ (1σ). The widest range of ∼15‰ is found among euhedral pyrite grains whereas variations of ∼4‰ to ∼6‰ are common in anhedral, subhedral, and rounded grains of pyrite. These values are in marked contrast to the δ34S values of pyrite from the Matinenda Formation that were obtained by previous investigators using bulk-rock sulfur isotope analyses. We found variable concentrations of Co (below detection to 4700 ppm), Ni (to 1900 ppm), and As (to 3400 ppm) among individual pyrite crystals and within single grains with overgrowth textures. These elemental concentrations are markedly different between core and overgrowth parts of pyrite. We demonstrate that the pyrite grains in the Paleoproterozoic UQC have been isotopically, chemically, and morphologically modified by post-depositional processes, suggesting that the pyrite grains have undergone multiple generations. The results of the present study cannot be explained solely by a detrital process. Therefore, one cannot use the preserved morphology and chemistry of pyrite (and possibly uraninite) to represent the original features at the time of deposition to support the hypothesis of an anoxic atmosphere prior to 2.2 Ga.

In the southeastern United States, identification of the Rocklandian Deicke and Millbrig K-bentonite Beds is based on differences in phenocryst mineralogy in the tuffaceous zones of each bed, and the two beds can be reliably and consistently distinguished on this basis. The common phenocrysts in the Deicke are labradorite and various Fe-Ti minerals, and in the Millbrig they are andesine, quartz, and biotite. Phenocrysts present in trace amounts are biotite and quartz in the Deicke, and apatite and zircon in both beds. The Deicke is altered dacitic or latitic ash, whereas the Millbrig is altered rhyodacitic ash. Both beds are interpreted as airfall deposits produced by huge volcanic eruptions, each of which was much larger and produced far more ash than the 1815 eruption of Tambora and even the great Toba eruption of 75 Ka. The principal authigenic minerals are feldspars (albite and K-feldspar), the clay minerals mixed-layer illite/smectite (I/S) and kaolinite, and ferroan and ferrotitanian minerals (pyrite, hematite, and the TiO2, polymorphs). The current lateral distribution of these authigenic minerals is the result of variations in regional geochemical conditions during burial diagenesis. The distribution of authigenic feldspars, together with regional changes in the percentage of illite in the I/S, indicates that maximum burial temperatures were higher in the Valley and Ridge province than along the Cincinnati Arch, and that the highest temperatures were in the Virginia Valley and Ridge. Regional variations in the distribution of the ferroan and ferrotitanian authigenic minerals in the K-bentonites and adjacent strata reflect variations in pore water redox conditions during diagenesis. Throughout the Cincinnati Arch and the westernmost Valley and Ridge, sediment pore waters were reducing. In the eastern Valley and Ridge of Alabama and Georgia the pore waters were oxidizing, and in the central and eastern Valley and Ridge from south of Roanoke to Knoxville the pore waters were initially reducing and then oxidizing. The stratigraphy of the Deicke and Millbrig is now very well known from their type area in the Upper Mississippi Valley to the easternmost exposures of Rocklandian strata in the southern Valley and Ridge from Alabama to Virginia. Many previous correlations are verified, and correlation of the two beds is extended along and across strike in the Valley and Ridge between Roanoke, Virginia, and Birmingham, Alabama. The Deicke and Millbrig are the thickest and most wide-spread of the several Rocklandian K-bentonites in this region. Of the two, the Deicke is more laterally persistent along the Cincinnati Arch, but in the southern Valley and Ridge the Millbrig is the more widespread and persistent of the two beds. The relationship of the K-bentonites to several regional and local unconformities is also now better understood. With this documentation of the great lateral extent of these two superb marker beds, it will be possible to link the vertical and lateral distribution of stratigraphically important faunal elements, especially conodonts and graptolites, with the stratigraphic position of the Deicke and Millbrig K-bentonite Beds.