Modern Sedimentation in a Mixed Siliciclastic-Carbonate Coral Reel Environment, La Parguera, Puerto Rico
Modern Sedimentation in a Mixed Siliciclastic-Carbonate Coral Reel Environment, La Parguera, Puerto Rico
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混合硅质碎屑-碳酸盐珊瑚卷环境中的现代沉积，波多黎各拉帕尔格拉
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发表时间：
2009
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通讯作者：
J. Nittrouer
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作者：
K. Ryan;J. Walsh;D. Corbett;M. Dail;J. Nittrouer
摘要。混合的硅质碎屑 - 碳酸盐体系在全球热带地区均有分布，但在活跃沉积方面所受的研究关注有限。为了更好地理解位于波多黎各岛西南海岸、加勒比海边缘的这一混合体系，对波多黎各拉帕古拉附近的沉积作用进行了详细研究。本研究包括对拉帕古拉海底沉积物成分和质地的评估，以及对过量²¹⁰Pb活度剖面和沉积速率的检测。对陆架上的粒度分布以及碳酸盐和烧失量（LOI）百分比的变化进行了检测。更具体地说，很明显在向海方向碳酸盐百分比增加，烧失量分数降低。过量²¹⁰Pb活度剖面呈现稳态和非稳态剖面。稳态剖面最为常见，在表层混合层中显示出一系列厚度（3 - >20厘米）。在一些近岸环境中观察到非稳态剖面，这反映了间歇性沉积或人类影响。最大的沉积速率通常出现在近岸处，最大速率接近0.5厘米/年。在更靠海的珊瑚礁区域，沉积速率约为0.2厘米/年。根据成分和沉积速率数据计算出的质量沉积速率表明，向海底的陆地（非碳酸盐且无烧失量）沉积物通量在向海方向上减少。近岸地区陆地沉积物的通量通常要高几倍（>0.05对比0.01克/平方厘米·年）。这些成分和质量沉积的趋势反映了来自陆地和海洋源的沉积物供应和扩散，以及珊瑚礁庇护所导致的波浪作用减弱。一项初步的沉积物收支表明，供应到陆架的陆地沉积物大部分（61%）在当地储存。陆架上堆积的沉积物主要是碳酸盐（85%），并被认为是海洋来源的。陆地（12%）和烧失量（3%）物质在储存的沉积物中所占比例较小，但也是重要组成部分。总体而言，数据表明陆地沉积在拉帕古拉混合硅质碎屑 - 碳酸盐环境中是一个较小但不断增加的沉积组分。
Abstract. Mixed siliciclastic-carbonate systems are globally distributed throughout the tropics, but have received limited research attention on active sedimentation. A detailed examination of sedimentation near La Parguera, Puerto Rico has been conducted to better understand this mixed system on the border of the Caribbean Sea, along the southwest coast of the island. This study includes an assessment of the sediment composition and texture of material accumulating on the La Parguera seabed, as well as an examination of excess 210Pb-activity profiles and accumulation rates. Variations in grain-size distribution and carbonate and loss-on-ignition (LOI) percentages are examined on the shelf. More specifically, an increase in carbonate percentage and a decrease in the LOI fraction in the seaward direction are evident. Excess 210Pb-activity profiles display steady-state and non-steady-state profiles. Steady-state profiles are most common and display a range of thicknesses in surface-mixed layers (3 - >20 cm). Non-steady-state profiles are observed in some nearshore settings, reflecting episodic deposition or human influence. Greatest sediment accumulation rates are generally found close to shore, where maximum rates approach 0.5 cm y-1. Sediment accumulation rates in more seaward reef areas are approximately 0.2 cm y-1. Mass accumulation rates calculated from the composition and accumulation rate data indicate there is a seaward decrease in terrestrial (non-carbonate and LOI-free) sediment flux to the seabed. Fluxes of terrestrial sediment in nearshore areas are typically several times higher (>0.05 vs. 0.01 g cm-2 y-1). These trends in composition and mass accumulation reflect sediment supply and dispersal from terrestrial and marine sources along with the reduced wave climate from reef sheltering. A preliminary sediment budget suggests the majority (61%) of terrestrial sediment supplied to the shelf is stored locally. Sediment accumulating on the shelf is principally carbonate (85%) and is assumed to be marinederived. Terrestrial (12%) and LOI (3%) material represent considerably smaller, but significant constituents of the sediment stored. Collectively, data suggest terrestrial sedimentation is a lesser, but increasing sedimentary component of the La Parguera mixed siliciclastic-carbonate setting.