Apogean–perigean signals encoded in tidal flats at the fluvio–estuarine transition of Glacier Creek, Turnagain Arm, Alaska; implications for ancient tidal rhythmites
Apogean–perigean signals encoded in tidal flats at the fluvio–estuarine transition of Glacier Creek, Turnagain Arm, Alaska; implications for ancient tidal rhythmites
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DOI：
10.1111/j.1365-3091.2010.01220.x
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发表时间：
2011-10
期刊：
影响因子：
3.5
通讯作者：
S. Greb;A. W. Archer;Darron G. DeBoer
中科院分区：
文献类型：
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作者：
S. Greb;A. W. Archer;Darron G. DeBoer
TURNAY ARM是一个大型潮汐峡湾式河口。冰川小溪是一条冰川滋养的小溪，在阿拉斯加的吉德伍德附近以切线的方式流入河口。2003年以来的几个夏季，对冰川河口过渡段的泥滩进行了逐日泥沙测量和沟槽观测。每年，这些平地似乎在冬季被侵蚀，然后在春季和夏季垂直共生。在研究的每一年中，在小潮-大潮周期中，每天两次潮汐沉积垂直加厚和变薄的片束中的潮汐片层。2004年，在平地的沟渠中发现了一束束加厚和变薄的叶片对联。5个叶片束在粗束和细束之间交替，对应于近地点(高春季)和远地点(低春季)潮汐。保存完好的远地点-近地点旋回在现代潮滩沉积物中很少有记载。在这个位置，潮汐韵律具有良好的小潮旋回性，这是因为与前一年相比，潮汐节律几乎完全被移除，这为垂直吸积创造了可容纳空间，而不需要进行重大的返工。巨大的潮汐条件，无底栖无脊椎动物的返工，砾石坝保护主要潮汐水道，以及围绕平原的莎草沼泽凹陷保护免受风暴和河流侵蚀，所有这些都有助于在沉积期间保存韵律。平地相对于潮差的位置允许积累完整的春季周期和不完整的小潮周期。2004年夏季，远地点和近地点与新月和满月紧密对准，导致连续的强烈近地点和远地点潮汐，这可能有助于积累连续的粗细春季周期，编码远地点和近地点潮汐周期。在接下来的几年里，没有观测到远地点-近地点信号。
Turnagain Arm is a macrotidal fjord‐style estuary. Glacier Creek is a small, glacially fed stream which enters the estuary tangentially near Girdwood, Alaska. Trenches and daily sedimentation measurements were made in a mudflat along the fluvio–estuarine transition of Glacier Creek during several summers since 2003. Each year, the flats appear to erode during the winter and then accrete vertically in the spring and summer. In each of the years studied, tidal laminae in vertically thickening and thinning laminae bundles were deposited by twice daily tides in neap–spring tidal cycles. In 2004, bundles of thickening and thinning laminae couplets were noted in trenches cut into the flats. Five laminae bundles alternated between thicker and thinner bundles, corresponding to the perigean (high spring) and apogean (low spring) tides. Well‐preserved apogean–perigean cycles have rarely been documented in modern tidal flat sediments. At this location, vertical accretion of tidal rhythmites with well‐developed neap–spring cyclicity is possible because of the near‐complete removal of the flat from the previous year, which creates accommodation space for vertical accretion without significant reworking. Macrotidal conditions, no reworking by infaunal invertebrates, protection from the main tidal channel by a gravel bar and protection from storm waves and fluvial erosion by a recess in the sedge marsh that surrounds the flats all aid in preservation of rhythmites during aggradation. The position of the flats relative to tidal range allows for accumulation of complete spring cycles and incomplete neap cycles. In the summer of 2004, apogee and perigee were closely aligned with the new and full moons, resulting in successive strong perigee and apogee tides which probably aided in the accumulation of successive thick–thin spring cycles encoding the apogean and perigean tidal cycle. The apogean–perigean signal was not observed in subsequent years.