Grain size distribution, carbon content and wet bulk density of sediment cores in the equatorial Atlantic and the Norwegian Sea

Near-surface sediments from the equatorial east Atlantic and the Norwegian Sea exhibit pronounced shear strength maxima in profiles from the peak Holocene and Pleistocene. These semi-indurated layers start to occur at 8-102 cm below the sediment surface and can be explained neither by the modal composition nor by the effective overburden pressure of the sediments. However, scanning electron microscope and microprobe data exhibit micritic crusts and crystal carpets, which are clearly restricted to (undisturbed) samples from indurated layers and form a manifest explanation for their origin. The minerals precipitated comprise calcite, aragonite, and in samples more proximal to the African continent SiO2 needles, and needles of as yet unidentified K-Mg-Fe-Al silicates, crusts of which dominate the indurated layers in the Norwegian Sea. By their stratigraphic position in deep-sea sediments the carbonate-based shear strength maxima are tentatively ascribed to dissolved adjacent pteropod layers from the early Holocene and hence to short-lived no-analogue events of early diagenesis. Possibly, they have been controlled by a reduced organic carbon flux, leading to increased aragonite preservation in the deep sea.

赤道东大西洋和挪威海的近地表沉积物在全新世高峰期及更新世的剖面中呈现出显著的剪切强度最大值（shear strength maxima）。这些半固结层（semi-indurated layers）始于沉积物表面以下8-102厘米处，既无法通过沉积物的模态组成，也不能用有效上覆压力来解释。然而，扫描电子显微镜与微探针数据显示，微晶壳（micritic crusts）和晶体毯（crystal carpets）明显局限于（未受扰动的）固结层样本中，为其成因提供了明确解释。沉淀的矿物包括方解石、文石，以及在更靠近非洲大陆的样本中的SiO₂针状物，还有尚未鉴定的K-Mg-Fe-Al硅酸盐针状物；其中，微晶壳在挪威海的固结层中占主导地位。基于这些层在深海沉积物中的地层位置，碳酸盐主导的剪切强度最大值暂被归因于早全新世相邻翼足类层的溶解，因此属于早期成岩作用的短期非类似事件。它们可能受有机碳通量减少的控制，进而导致深海中文石保存率上升。