Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications
Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications
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DOI：
10.1007/s11001-013-9196-2
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发表时间：
2014-03
影响因子：
1.4
通讯作者：
N. Mitchell;N. Dubois
中科院分区：
文献类型：
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作者：
N. Mitchell;N. Dubois
如果赤道沉积物在赤道周围形成特征沉积物，可能有助于解决太平洋板块向北漂移的量。与这个问题相关的是，已经表明230Th在赤道海底的积累速度快于全新世期间上覆水柱中放射性衰变产生的速度（Marcantonio等人在Paleoceanography 16:260–267, 2001）。一些研究人员认为，这反映了底部电流携带的吸附有 230Th 的粒子沉积到赤道（“聚焦”）。如果正确的话，这种效应可能与同样以赤道为中心的高浮层生产力相结合，产生高积累率的特征，标志着较老矿床的古赤道。在这里，我们评估了地质过去存在这种赤道特征的潜在证据。七个经向样线的地震反射数据表明，受限制纬度的赤道增强积累带在空间和时间上都有不同程度的发育。它在 14.25–20.1 Ma 区间不存在，但在 8.55–14.25 Ma 区间发育良好。我们还检查了科学钻探数据生成的风成尘埃积累率历史。现代赤道附近的沙尘堆积率异常与热带辐合带关系不明显，解释为聚焦引起。 Ba 和 P2O5（出口产量的代表）的累积率揭示了静态赤道特征，这表明太平洋板块在 10-25 Ma 期间的运动是温和的。地震数据中 14.25 Ma 左右聚焦特征从缺失到发育良好的总体转变与新西兰近中新世中期西部边界流的发展相一致。该洋流为太平洋提供来自南极洲的深水，因此可能意味着潜在的古海洋或古气候起源。在 10.05–14.25 Ma，地震异常的纬度与太平洋板块热点模型预测的古赤道相差约 2°，这表明热点纬度相对于现在可能存在微小变化（尽管这一推论取决于赤道周围沉积的精确形式）。另一方面，Ba 和 P2O5 异常与预测板块缓慢向北移动超过 10-25 Ma 的板块模型广泛兼容。
If equatorial sediments form characteristic deposits around the equator, they may help to resolve the amount of northwards drift of the Pacific tectonic plate. Relevant to this issue, it has been shown that230Th has been accumulating on the equatorial seabed faster than its production from radioactive decay in the overlying water column during the Holocene (Marcantonio et al. in Paleoceanography 16:260–267, 2001). Some researchers have argued that this reflects the deposition of particles with adsorbed230Th carried by bottom currents towards the equator (“focusing”). If correct, this effect may combine with high pelagic productivity, which is also centered on the equator, to yield a characteristic signature of high accumulation rates marking the paleoequator in older deposits. Here we evaluate potential evidence that such an equatorial feature existed in the geological past. Seismic reflection data from seven meridional transects suggest that a band of equatorially enhanced accumulation of restricted latitude was variably developed, both spatially and temporally. It is absent in the interval 14.25–20.1 Ma but is well developed for the interval 8.55–14.25 Ma. We also examined eolian dust accumulation rate histories generated from scientific drilling data. A dust accumulation rate anomaly near the modern equator, which is not obviously related to the inter-tropical convergence zone, is interpreted as caused by focusing. Accumulation rates of Ba and P2O5(proxies of export production) reveal a static equatorial signature, which suggests that the movement of the Pacific plate over the period 10–25 Ma was modest. The general transition from missing to well-developed focusing signatures around 14.25 Ma in the seismic data coincides with the mid-Miocene development of the western boundary current off New Zealand. This current supplies the Pacific with deep water from Antarctica, and could therefore imply a potential paleoceanographic or paleoclimatic origin. At 10.05–14.25 Ma, the latitudes of the seismic anomalies are up to ~2° different from the paleoequator predicted by Pacific plate-hotspot models, suggesting potentially a small change in the hotspot latitudes relative to the present day (although this inference depends on the precise form of the deposition around the equator). The Ba and P2O5anomalies, on the other hand, are broadly compatible with plate models predicting slow northward plate movement over 10–25 Ma.