The stratigraphic record of Cenozoic uplift and denudation of the Himalayas is distributed across its peripheral foreland basins, as well as in the sediments of the Ganges–Brahmaputra Delta (GBD) and the Bengal–Nicobar Fan (BNF). Recent interrogation of Miocene–Quaternary sediments of the GBD and BNF advance our knowledge of Himalayan sediment dispersal and its relationship to regional tectonics and climate, but these studies are limited to IODP boreholes from the BNF (IODP 354 and 362, 2015-16) and Quaternary sediment cores from the GBD (NSF-PIRE: Life on a tectonically active delta, 2010-18). We examine a complementary yet understudied stratigraphic record of the Miocene–Pliocene ancestral Brahmaputra Delta in outcrops of the Indo-Burman Ranges fold–thrust belt (IBR) of eastern India. We present detailed lithofacies assemblages of Neogene delta plain (Tipam Group) and intertidal to upper-shelf (Surma Group) deposits of the IBR based on two ∼ 500 m stratigraphic sections. New detrital-apatite fission-track (dAFT) and (U-Th)/He (dAHe) dates from the Surma Group in the IBR help to constrain maximum depositional ages (MDA), thermal histories, and sediment accumulation rates. Three fluvial facies (F1–F3) and four shallow marine to intertidal facies (M1–M4) are delineated based on analog depositional environments of the Holocene–modern GBD. Unreset dAFT and dAHe ages constrain MDA to ∼ 9–11 Ma for the Surma Group, which is bracketed by intensification of turbidite deposition on the eastern BNF (∼ 13.5–6.8 Ma). Two dAHe samples yielded younger (∼ 3 Ma) reset ages that we interpret to record cooling from denudation following burial resetting due to a thicker (∼ 2.2–3.2 km) accumulation of sediments near the depocenter. Thermal modeling of the dAFT and dAHe results using QTQt and HeFTy suggest that late Miocene marginal marine sediment accumulation rates may have ranged from ∼ 0.9 to 1.1 mm/yr near the center of the paleodelta. Thermal modeling results imply postdepositional cooling beginning at ∼ 8–6.5 Ma, interpreted to record onset of exhumation associated with the advancing IBR fold belt. The timing of post-burial exhumation of the IBR strata is consistent with previously published constraints for the avulsion of the paleo-Brahmaputra to the west and a westward shift of turbidite deposition on the BNF that started at ∼ 6.8 Ma. Our results contextualize tectonic controls on basin history, creating a pathway for future investigations into autogenic and climatic drivers of behavior of fluvial systems that can be extracted from the stratigraphic record.

中文翻译：

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Brahmaputra三角洲祖先的新近纪浅海和河流沉积物的散布，埋葬和掘尸：印度-缅甸山脉

喜马拉雅山的新生代隆升剥蚀的地层记录分布在其周边前陆盆地，以及恒河-布拉马普特拉三角洲（GBD）和孟加拉-尼古巴扇（BNF）的沉积物中。最近对GBD和BNF的中新世-第四纪沉积物的询问提高了我们对喜马拉雅沉积物扩散及其与区域构造和气候的关系的了解，但这些研究仅限于来自BNF的IODP钻孔（IODP 354和362，2015-16）和GBD的第四纪沉积物核心（NSF-PIRE：构造活动三角洲的生命，2010-18年）。我们研究了印度东部印度－缅甸山脉褶皱-冲断带（IBR）露头中的中新世—上新世始祖布拉马普特拉三角洲的互补但未被充分研究的地层记录。我们基于两个〜500 m地层剖面，介绍了新近纪三角洲平原（蒂帕姆群）和潮间带至上层架（苏尔玛群）沉积的详细岩相组合。IBR中Surma组的新碎屑-磷灰石裂变径迹（dAFT）和（U-Th）/ He（dAHe）日期有助于限制最大沉积年龄（MDA），热史和沉积物堆积速率。根据全新世-现代GBD的模拟沉积环境，划定了三个河流相（F1-F3）和四个浅海相至潮间相（M1-M4）。未重置的dAFT和dAHe年龄将Surma组的MDA限制在约9-11 Ma，这是由于东部BNF的浊积体沉积加剧（约13.5-6.8 Ma）所致。两个dAHe样品产生了更年轻（〜3 Ma）的重置年龄，我们认为这是由于在沉积中心附近沉积物的堆积更厚（约2.2-3.2 km），从而使埋葬后从剥蚀中冷却下来。使用QTQt和HeFTy对dAFT和dAHe进行的热模拟表明，中新世晚期海相沉积物堆积速率在古三角洲中心附近可能在〜0.9至1.1 mm / yr的范围内。热模型结果表明沉积后的冷却始于约8–6.5 Ma，这被解释为记录了与前进的IBR折叠带相关的发掘尸体的开始。IBR岩层的埋葬后发掘的时间与先前公布的约束古布拉莫普特拉向西向西移动以及BNF上浊质沉积物向西移动的约束条件相一致（始于6.8 Ma）。