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Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses
Quaternary Geochronology ( IF 1.7 ) Pub Date : 2022-05-19 , DOI: 10.1016/j.quageo.2022.101336
Teena Chauhan , Hans Petter Sejrup , Berit Oline Hjelstuen , Darrell S. Kaufman , Irfan Baig , Benedict T.I. Reinardy

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.

Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.



中文翻译:

北海北部早至中更新世沉积物的年代学:来自氨基酸和锶同位素分析的新证据

在北海早至中更新世的冰期-间冰期循环期间沉积的沉积物在时间上受到的限制很差。为了对这些单位的年代学做出贡献,已经对北海北部一个横断面沿线的四个浅钻孔和一个油井的样品进行了氨基酸消旋化 (AAR) 和锶 (Sr) 同位素分析。通过反相液相色谱法在底栖有孔虫物种Elphidium excavatum中获得的 D/L Asp(天冬氨酸)值由于一致的结果和这种底栖物种的良好地层分布而受到关注。对于早更新世,基于 Sr 年龄的北海北部中部 16/1-8 井的年龄模型允许对填充前第四纪中央盆地的前进楔进行测年。使用已发表的放射性碳测年样品的年龄和与先前确定的 Bruhnes/Matuyama (B/M) 古地磁边界相关的样品和本研究的 Sr 年龄,绘制了Elphidium excavatum中 Asp 消旋化的区域校准曲线。基于所有可用的地质年代学证据,样品被分配到海洋氧同位素阶段(MIS),不确定性约为 10-70 ka。

Sr 年龄表明小于 200 万年 (Ma) 的中断可能是由于 Utsira 组(上新世)和早更新世之间的非沉积或低沉积。沉积速率增加约 1.5 ± 0.07 Ma (~MIS 51) 可能部分是由于来自东南部河流的沉积物供应,部分原因是冰盖从挪威海岸向中部延伸了约 1.36 ± 0.07 Ma北海。可能在 1.1 Ma (~ MIS 32) 左右发生了盆地范围的冰川作用(本研究中的上部区域不整合/ Q4 单元顶部),导致侵蚀和区域不整合。挪威海峡的两个间冰期已被确定日期:Radøy 间冰期为 1.07 ± 0.01 Ma(可能是 MIS 31,“超级间冰期”),挪威海沟间冰期为 0.50 ± 0.02 Ma(可能是 MIS 13)。在所有浅钻孔中在同一地层​​水平上识别出的一个巨大的直到单元可能部分代表一个广泛的 MIS 12 冰川作用。本研究表明,结合使用氨基酸消旋数据和 Sr 同位素年代学可以细化与冰川过程影响部分相关的第四纪北海沉积物的年代学模糊性。

更新日期:2022-05-19
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