Organic compounds at DSDP Hole 90-593@en

Corg and Norg contents in the acid insoluble mineral fraction were studied in sediments of Site 593. Both decrease systematically from Recent to early Miocene over 425 m of carbonate facies. C/N ratios (7-11) are typically marine and indicate that residual organic matter, bound to clay minerals, was originally scavenged from the marine habitat rather than being of terrigenous origin. Variations of Corg and Norg are almost entirely controlled by rates of sedimentation, which gradually increase from Recent to early Miocene. Preliminary results of carbohydrate distribution indicate that epigenetic and diagenetic processes alter both the concentrations and the ratios of individual monomers with depth. Total carbohydrate concentrations in the samples diminish from 91 µg/g sediment at 18 m sub-bottom depth to 49 µg/g at 335 m. In contrast, sugars in the acid insoluble residue increase with depth, suggesting release of structural polysaccharides and their subsequent association with clay minerals. Ratios of arabinose to fucose, which are about 6:1 in Recent carbonaceous sediments intercepted by sediment traps, vary from 1:1 in the youngest sample to 1:2.5 in the oldest.本研究针对593站位沉积物中的酸不溶矿物组分（acid insoluble mineral fraction）内的有机碳（Corg）与有机氮（Norg）含量开展了系统探究。在425米厚的碳酸盐岩相（carbonate facies）地层中，二者含量均从现代沉积向中新世早期呈系统性下降趋势。碳氮比（C/N ratios）介于7~11之间，整体呈现典型的海洋生源特征，表明结合于黏土矿物（clay minerals）的残余有机质最初来自海洋生境，而非陆源成因。有机碳与有机氮的含量变化几乎完全受控于沉积速率（sedimentation rates），该速率从现代沉积到中新世早期逐渐升高。碳水化合物分布（carbohydrate distribution）的初步研究结果显示，后生作用与成岩作用（epigenetic and diagenetic processes）会随深度改变各单糖单体的浓度及其比例。样品中的总碳水化合物浓度从海底以下18米处的91微克/克沉积物降至335米处的49微克/克。与之相反，酸不溶残渣（acid insoluble residue）中的糖类含量随深度增加而升高，这表明结构性多糖（structural polysaccharides）被释放后会与黏土矿物结合。沉积物捕获器（sediment traps）采集的现代含碳沉积物中，阿拉伯糖与岩藻糖（arabinose to fucose）的比值约为6:1；而本研究站位的该比值从最年轻样品中的1:1变化至最老样品中的1:2.5。