Process length variation of the cyst of the dinoflagellate Protoceratium reticulatum in the North Pacific and Baltic‐Skagerrak region: calibration as an annual density proxy and first evidence of pseudo‐cryptic speciation

Process length variation of cysts of the dinoflagellate Protoceratium reticulatum (Claparède et Lachmann) Bütschli in surface sediments from the North Pacific was investigated. The average process length showed a significant inverse relation to annual seawater density: σ_{t annual} = ?0.8674 × average process length + 1029.3 (R² = 0.84), with a standard error of 0.78 kg m^?3. A sediment trap study from Effingham Inlet in British Columbia revealed the same relationship between average process length and local seawater density variations. In the Baltic–Skagerrak region, the average process length variation was related significantly to annual seawater density: σ_{t annual} = 3.5457 × average process length ? 993.28 (R² = 0.86), with a standard error of 3.09 kg m^?3. These calibrations cannot be reconciled, which accentuates the regional character of the calibrations. This can be related to variations in molecular data (small subunit, long subunit and internal transcribed spacer sequences), which show the presence of several genotypes and the occurrence of pseudo‐cryptic speciation within this species. Copyright © 2012 John Wiley & Sons, Ltd.     

Computational parameter estimation for a maize crop

During a whole growing season, the evolution of the displacement height, d, and roughness length, z ₀, of a maize crop has been estimated by a measurement programme. The results have been used to check different types of existing models to calculate these parameters from canopy characteristics only; a simple geometric model and two matching models have been investigated. A geometric model is based on geometric features of the surface only. After a simple modification, the geometric model gives good results for the displacement height as well as for the roughness length.A matching model, based on gradient-diffusion theory, yields good results for the displacement height. The roughness parameter, however, is overestimated by 17%. By a simple modification, the model results could be improved considerably.A matching model, based on a second-order closure procedure, yields excellent results for the displacement height and good results for the roughness length. But it appears that, when applying this model, the plant density index and plant area density distribution as a function of height must be well known.     

Dynamical stability of convection cells in the upper mantle

Summary A two-dimensional flow model of an incompressible fluid with constant viscosity has been used to study the changes in the large-scale flow pattern (aspect ratio 4). Implications for convection in the Earth's mantle are discussed.

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High-frequency sequences and their stacking patterns: sequence-stratigraphic evidence of high-frequency eustatic cycles

A hierarchy of interpreted eustatic cyclicity in siliciclastic sedimentary rocks has a pattern of superposed cycles with frequencies in the ranges of 9–10 m.y., 1–2 m.y., 0.1–0.2 m.y., and 0.01–0.02 m.y. (second- through fifth-order cyclicity, respectively). Stratigraphic units displaying this cyclicity include composite sequences, sequences, and parasequences. On the Exxon global cycle chart, fundamental third-order cycles (1–2 m.y. average duration) stack into related groups (second-order cycles: 9–10 m.y. duration). A much larger pattern (about 200 m.y.) is interpreted as tectonically controlled eustasy probably related to sea-floor spreading rates.

One and probably two higher orders of cyclicity (fourth-order: 0.1–0.2 m.y.; and fifth-order: 0.01–0.02 m.y.) are now observed in work with well logs, cores, and outcrops in areas of very rapid deposition. These frequencies are in the range of Milankovitch cycles, and may represent part of the Milankovitch hierarchy which has been widely interpreted for cyclical units in carbonate rocks.

High-frequency (fourth-order) sequences, which form at a 0.1–0.2 m.y. cyclicity, have all the stratal attributes of conventional sequences, including constituent parasequences and systems tracts, and play a dominant role controling reservoir, source, and sealing rock distribution. A consistent hierarchy of stratigraphy is observed. Parasequences (probable fifth-order cyclicity) stack into sets to form systems tracts in fourth-order sequences. Groups (sets) of fourth-order sequences are deposited between major third-order boundaries within third-order composite sequences. Sequences in these sets stack in prograding and backstepping patterns to form third-order lowstand, transgressive, and highstand sequence sets.

Third-order sequence boundaries are marked by greater basinward shifts in facies, by larger more widespread incised valleys, and by more extensive onlap than are fourth-order sequence boundaries. Third-order condensed sections commonly are widespread, faunally rich, and widely correlated biozone and mapping markers. Fourth-order sequence analysis helps to understand reservoir, source, and seal distribution at the play and prospect scale. An example from the Gulf of Mexico is discussed.