Three orders of aeolian bounding surface are arranged in a hierarchy based on their extent and regularity. First order surfaces are the most extensive. They are flat‐lying bedding planes cutting across all other aeolian structures and are attributed to the passage of the largest aeolian bedforms—draas—across an area. First order surfaces cut across second order surfaces, which are gentle to moderately dipping surfaces bounding sets of cross‐strata. Second order surfaces are attributed to the passage of dunes across draas, or to longitudinal dunes migrating across the lower ice slopes of draas. Third order surfaces bound bundles of laminae within coscts of cross laminae and are due either to local fluctuations in wind direction and velocity or to changes in airflow patterns caused by configurational changes in dune patterns. All these bounding surfaces could be explained by wind variations and dune migration, but the rates of dune migration relative to probable sediment deposition rates are incompatible with this general explanation of the form and spacing of the bounding surfaces. The concept of climbing bedforms of different hierarchical order together with subsidence provides a better explanation. Analogous bounding surfaces in aqueous bedforms have already been attributed to climbing bedforms of differing hierarchical order.

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A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO 2 . The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie's Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO 2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date.astrochronology | CO2 | Jurassic | large igneous provinces | n-alkane P lants record through photosynthetic pathways the atmospheric values of δ 13 C that in turn reflect the exchangeable surface oceanic carbon reservoir (1). One of the most direct known plant proxies is the δ 13 C alk measurements of n-C 25 -n-C 31 n-alkanes derived from leaf wax lipids of plant cuticles (2). We analyzed δ 13 C alk , the carbon isotopic composition of wood (δ 13 C wood ), and total organic carbon (δ 13 C toc ) from sediments from two overlapping lacustrine sections interbedded with the lavas of the Central Atlantic magmatic province (CAMP) (3) in eastern North America to obtain a carbon isotope record unambiguously tied to the eruptions and climate proxies to compare with and calibrate organic carbon and carbonate δ 13 C records from elsewhere (3-7). This allows direct determination of the relationship between one of the largest Phanerozoic mass extinctions, the end-Triassic extinction (ETE) (8), carbon isotopic and CO 2 (9) excursions, the biocalcification crisis (10), and their proposed cause, the CAMP (3, 11-13). Core and outcrop samples were obtained from the Newark (New York, New Jersey, and Pennsylvania) and Hartford (Connecticut and Massachusetts) rift basins at 19-20°N paleolatitude (14) in the tropical humid to arid transition of central Pangea (Fig. 1). A hierarchy of Milankovitchforced lake level cycles permeate the sampled strata in these basins, and in conjunction with a high sediment accumulation rate and ...

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