Geo-Marine Letters ( IF 1.4 ) Pub Date : 2021-07-21 , DOI: 10.1007/s00367-021-00710-x Amila Sandaruwan Ratnayake 1
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The geology of Sri Lanka captures one of the longest and most complete records of Jurassic to Miocene tectonic evolutions from the mid-latitudes of the southern hemisphere to the equatorial northern hemisphere. Sedimentary basins in Sri Lanka provide a natural laboratory with which to reconstruct paleoclimate during the island’s northward voyage from Gondwana to Asia. Here, drill core cuttings were obtained from the Barracuda hydrocarbon exploration well in the offshore Mannar Basin, Sri Lanka. CHNS elemental analysis, gas chromatography-mass spectrometry, and stable C and N isotopic analyses were performed. The results suggest the deposition of organic carbon depleted (average total organic carbon (TOC) = 0.97%) sediments under the arid climate of the Early Campanian. Separation of the Laxmi Ridge-Seychelles and Seychelles from the Indian plate and sea-level regression may have enhanced the deposition of organic carbon–rich (average TOC = 1.34%) and terrestrial organic matter (OM)–rich (average C/N ratio = 20.36) sediments during the Late Campanian to Late Maastrichtian. CaCO3-rich (average = 32.5%) Upper Cretaceous sediments then show a period of high productivity under a warm climate. The Deccan-Reunion basalt likely acted as a major contributor to the mass extinction of coccolithophores/foraminifera at the Late Maastrichtian followed by a reduction of CaCO3 and organic carbon content. The Early-Late Paleocene was characterized by the deposition of algal-derived OM with a terrestrial contribution (average C/N ratio = 15.75) under oxic depositional conditions (average C/S ratio = 16.21). However, the depositional environment changed drastically to one of oxygen-poor marine conditions (average C/S ratio = 6.83) during the Late Paleocene to the Early Oligocene due to weak oceanic circulation under a greenhouse climate. In contrast, the deposition of CaCO3-rich sediments since the Late Paleocene (average = 40.2%) is linked to the movement of the Indian plate into northern, warmer tropical latitudes. The Middle Oligocene to Miocene sedimentary succession was characterized by terrestrial OM-rich (average TOC = 2.51% and C/N = 23.45) sediments. The Middle-Upper Miocene sedimentary succession contains lamination and back carbon (charcoal fragments) suggesting the development of the present-day South Asian monsoon system. This record from Sri Lanka provides important new insights into Jurassic-Miocene geological and climatic evolution in this tropical part of the world for the first time.
Graphical abstract
中文翻译：
印度洋晚白垩世至中新世古气候变化：来自斯里兰卡深水马纳尔盆地的见解
斯里兰卡的地质记录了从南半球中纬度到赤道北半球的侏罗纪到中新世构造演化的最长和最完整的记录之一。斯里兰卡的沉积盆地提供了一个天然实验室，可以在该岛从冈瓦纳大陆向北航行到亚洲期间重建古气候。在这里，钻屑取自斯里兰卡近海马纳尔盆地的 Barracuda 油气勘探井。进行了 CHNS 元素分析、气相色谱-质谱和稳定 C 和 N 同位素分析。结果表明，在早坎帕阶干旱气候下，有机碳耗尽（平均总有机碳 (TOC) = 0.97%）沉积物的沉积。Laxmi Ridge-Seychelles 和 Seychelles 与印度板块的分离和海平面回归可能增强了富含有机碳（平均 TOC = 1.34%）和富含陆地有机质（OM）（平均 C/N 比）的沉积= 20.36) 晚坎帕阶到晚马斯特里赫特的沉积物。碳酸钙3丰富（平均 = 32.5%）上白垩统沉积物随后在温暖气候下显示出高生产力时期。德干-留尼汪玄武岩可能是马斯特里赫特晚期球石藻/有孔虫大规模灭绝的主要原因，随后 CaCO 3和有机碳含量减少。早晚古新世的特征是在含氧沉积条件下（平均 C/S 比 = 16.21），藻类来源的 OM 沉积具有陆地贡献（平均 C/N 比 = 15.75）。然而，由于温室气候下海洋环流较弱，在晚古新世至早渐新世期间，沉积环境急剧变化为缺氧海洋条件之一（平均 C/S 比 = 6.83）。相比之下，CaCO 3的沉积自晚古新世以来的丰富沉积物（平均值 = 40.2%）与印度板块向北部、温暖的热带纬度的运动有关。中渐新世至中新世沉积序列的特征是陆相富含 OM（平均 TOC = 2.51% 和 C/N = 23.45）沉积物。中上中新世沉积序列包含层理和背碳（木炭碎片），表明当今南亚季风系统的发展。斯里兰卡的这项记录首次为世界这个热带地区的侏罗纪-中新世地质和气候演化提供了重要的新见解。
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