ABSTRACT Meighen Island, in the Canadian Arctic Archipelago, is one of the most important localities for study of the late Neogene Beaufort Formation because of the presence of marine sediments interbedded with terrestrial fossiliferous sands. The stratigraphic succession, fossils from the marine beds, correlation with reconstructions of sea level, and paleomagnetic data from the Bjaere Bay region of the island suggest that the Beaufort Formation on Meighen Island was likely deposited either at 3.2–2.9 Ma or during two intervals at ca. 4.5 Ma and 3.4 Ma. The exposed Beaufort Formation on Meighen Island probably encompasses at least one warm interval and eustatic sea-level highstand of the Pliocene. Fossils of plants and arthropods are abundant in the alluvial sands exposed in the Bjaere Bay region. The lower part of the sequence (Unit A), beneath the muddy marine sequence (Unit B), contains plant taxa that have not been seen above the marine beds. Sediments below the marine beds are dominated more by fossils of trees, whereas the organic debris from above marine beds contains many fossils of plants, insects, and mites characteristic of open treeless sites. Regional tree line probably occurred on Meighen Island during deposition of the upper sediments, which implies a mean July climate at least 9 °C warmer than at present. When the marine sediments were deposited, nearshore water temperatures probably did not fall below 0 °C; hence, the Arctic Ocean probably lacked perennial ice cover. This confirms recent modeling experiments exploring the causes of Arctic amplification of temperature that have found the removal of sea ice to be a key factor in resolving previous proxy-model mismatches.

ABSTRACT Newark Valley lies between the two largest pluvial lake systems in the Great Basin, Lake Lahontan and Lake Bonneville. Soils and geomorphology, stratigraphic interpretations, radiocarbon ages, and amino acid racemization geochronology analyses were employed to interpret the relative and numerical ages of lacustrine deposits in the valley. The marine oxygen isotope stage (MIS) 2 beach barriers are characterized by well-preserved morphology and deposits with youthful soil development, with Bwk horizons and maximum stage I+ carbonate morphology. Radiocarbon ages of gastropods and tufas within these MIS 2–age deposits permit construction of a latest Pleistocene lake-level curve for Newark Valley, including a maximum limiting age of 13,780 ± 50 14 C yr B.P. for the most recent highstand, and they provide a calibration point for soil development in lacustrine deposits in the central Great Basin. The MIS 8–age to MIS 4–age beach barriers are higher in elevation and represent a larger lake than existed during MIS 2. The beach barriers have subdued morphology, are only preserved in short segments, and have stronger soil development, with Bkm and/or Bkmt horizons and maximum stage III+ to IV carbonate morphology. Newark Lake reached elevations higher than the MIS 2 highstand during at least two additional pluvial periods, MIS 16 and MIS 12, 10, or 8. These oldest lacustrine deposits do not have preserved shoreline features and are represented only by gravel lags, buried deposits, and buried soils with similar strong soil development. This sequence of middle and latest Pleistocene shorelines records a long-term pluvial history in this basin that remained internally drained for the last four or more pluvial cycles. Obtaining numerical ages from material within lacustrine deposits in the Great Basin can be challenging. Amino acid D/L values from gastropod shells and mollusk valves proved to be a valuable tool to correlate lacustrine deposits within Newark Valley. Comparison of soils and geomorphology results to independent 36 Cl cosmogenic nuclide ages from a different study indicated unexpected changes in rates of soil development during the past ~200,000 yr and suggested that common stratigraphic changes in lake stratigraphy could obscure incremental changes in soil development and/or complicate 36 Cl cosmogenic nuclide age estimates.

Abstract: Organic compounds are ubiquitous in the Earth’s surface, sediments and many rocks, and preserve records of geological, geochemical and biological history; they are also critical natural resources and major environmental pollutants. The naturally occurring stable isotopes of volatile elements (D, 13 C, 15 N, 17,18 O, 33,34,36 S) provide one way of studying the origin, evolution and migration of geological organic compounds. The study of bulk stable isotope compositions (i.e. averaged across all possible molecular isotopic forms) is well established and widely practised, but frequently results in non-unique interpretations. Increasingly, researchers are reading the organic isotopic record with greater depth and specificity by characterizing stable isotope ‘structures’ – the proportions of site-specific and multiply substituted isotopologues that contribute to the total rare-isotope inventory of each compound. Most of the technologies for measuring stable isotope structures of organic molecules have been only recently developed and to date have been applied only in an exploratory way. Nevertheless, recent advances have demonstrated that molecular isotopic structures provide distinctive records of biosynthetic origins, conditions and mechanisms of chemical transformation during burial, and forensic fingerprints of exceptional specificity. This paper provides a review of this young field, which is organized to follow the evolution of molecular isotopic structure from biosynthesis, through diagenesis, catagenesis and metamorphism.