The study focuses on sand grain properties in different parts of a beach-dune system built entirely of heavy mineral particles. These properties are related to: (1) resistance of particular minerals to weathering and abrasion, (2) hydraulic sorting in the swash zone, and (3) aeolian sorting during grain transport inland from the upper beach. The main waterlain and windlain sand properties depend on settling velocity which results from grain density (reflecting grain mineralogy), size, shape and roundness. The study was performed on the beach and dunes at Patea on the west coast of the North Island of New Zealand, which are comprised of heavy minerals assemblage containing a ferromagnetic (dominated by titanomagnetite) and non-ferromagnetic (mainly pyroxene and amphibole) fractions. The result demonstrates that three zones of different sand properties can be distinguished: (1) a lower swash zone dominated by non-ferromagnetic, larger and more angular particles which are carried back from the upper swash zone down the foreshore by the backwash; (2) an uppermost swash zone and beach with almost 100% of ferromagnetic, smaller and more rounded particles deposited at the back of the beach by the uprush, which during high tide and storms can reach the cliff toe, and can be reworked by wind; and (3) a climbing dune composed of a more poorly sorted mixture of non- and ferromagnetic particles. In terms of both mineralogy and grain size and shape, the dune sand is less uniform than the beach sand. Aeolian segregation resulted here in sand textural features opposite to those found in dune sands composed of light minerals. The results highlight the density-dependent variability of grain size and shape of beach-dune deposits consisting of only heavy minerals, and broaden our understanding of mechanisms of sedimentary processes which is particularly important when reconstructing older sedimentary successions.

中文翻译：

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新西兰北岛帕提亚海滩沙丘系统中的黑沙特性

该研究侧重于完全由重矿物颗粒构成的海滩沙丘系统不同部分的沙粒特性。这些特性与：(1) 特定矿物对风化和磨损的抵抗力，(2) 斜盘带的水力分选，以及 (3) 在从上海滩向内陆的谷物运输过程中的风成分选。主要的水纹砂和风纹砂特性取决于颗粒密度（反映颗粒矿物学）、尺寸、形状和圆度的沉降速度。该研究是在新西兰北岛西海岸 Patea 的海滩和沙丘上进行的，它们由含有铁磁性（以钛磁铁矿为主）和非铁磁性（主要是辉石和闪石）部分的重矿物组合组成。结果表明，可以区分出三个不同砂质的带：（1）下冲带以非铁磁性为主，较大和更多角的颗粒被反冲从上冲带带回前滩；(2) 最上层的浪荡带和海滩，几乎 100% 的铁磁、更小、更圆的颗粒在上升过程中沉积在海滩的后面，在涨潮和暴风雨时可以到达悬崖脚趾，并且可以被风重新加工; (3) 由非磁性粒子和铁磁性粒子的分类较差的混合物组成的攀爬沙丘。就矿物学和粒度和形状而言，沙丘沙子的均匀性不如海滩沙子。风成偏析导致这里的沙子纹理特征与由轻矿物组成的沙丘沙子中的特征相反。