2,669 research outputs found
Mixed sandâmud bedforms produced by transient turbulent flows in the fringe of submarine fans: Indicators of flow transformation
The fringe of fineâgrained deepâmarine systems often exhibits complex sedimentary facies and facies associations, because the presence of clay promotes the development of transient turbulent flows with complex depositional properties. Relatively little is known about the variation of currentâinduced sedimentary structures found within these facies. This study provides the first comprehensive description and interpretation of mixed sandstoneâmudstone bedforms observed in the fringe of the mudârich submarine fan that makes up the Aberystwyth Grits Group and Borth Mudstone Formation (Wales, United Kingdom). Using textural and structural descriptions, 158 bedforms in sediment gravity flow deposits were characterized into three main types: âclassicâ sandy current ripples, large current ripples and lowâamplitude bedâwaves. The sandy current ripples comprise clean sandstone, with average heights and lengths of 11 mm and 141 mm, respectively. The large current ripples are composed of mixed sandstoneâmudstone and possess greater dimensions than the sandy current ripples, with an average height of 19 mm and an average length of 274 mm. The lowâamplitude bedâwaves are long thin bedforms composed commonly of mixed sandstoneâmudstone, with an average height and length of 10 mm and 354 mm, respectively. The large current ripples and lowâamplitude bedâwaves are strikingly similar to experimental bedforms produced under decelerating mixed sandâmud flows and are interpreted to form beneath transitional flows with enhanced and attenuated nearâbed turbulence, respectively. From the fringe to the distal fringe of the fan, the dominant bedform type changed from sandy current ripples, via large current ripples, to lowâamplitude bedâwaves, suggesting that the flows changed from turbulent to increasingly turbulenceâmodulated. It is proposed that the flow Reynolds number reduced, reflecting this flow transformation, from a combination of constant or decreasing flow height, flow deceleration from sediment deposition, and increasing flow viscosity due to the shearâthinning nature of clayârich suspensions. Large current ripples and lowâamplitude bedâwaves are likely to be common in the fringe of other submarine fans. The presence and spatial trends in mixed sandâmud bedform types may be an important tool in interpreting fan fringe environments
A 2:1 cocrystal of 6,13-dihydropentacene and pentacene
6,13-Dihydropentacene and pentacene cocrystallize in a ratio of 2:1, i.e. C22H16·0.5C22H14, during vapour transport of commercial pentacene in a gas flow. The crystal structure is monoclinic, space group P21/n, and contains one dihydropentacene molecule and half a pentacene molecule in the asymmetric unit.
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