Neogene shallow-marine and fluvial sediment dispersal, burial, and exhumation in the ancestral Brahmaputra delta: Indo-Burman Ranges, India
Neogene shallow-marine and fluvial sediment dispersal, burial, and exhumation in the ancestral Brahmaputra delta: Indo-Burman Ranges, India
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DOI：
10.2110/jsr.2020.60
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发表时间：
2020-10
影响因子：
2
通讯作者：
R. Sincavage;P. Betka;S. Thomson;L. Seeber;M. Steckler;C. Zoramthara
中科院分区：
文献类型：
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作者：
R. Sincavage;P. Betka;S. Thomson;L. Seeber;M. Steckler;C. Zoramthara
喜马拉雅山脉新生代隆起和剥蚀的地层记录分布在其周边的前陆盆地，以及恒河-雅鲁藏布江三角洲（GBD）和孟加拉-尼科巴扇（BNF）的沉积物中。最近对GBD和BNF的中新世-第四纪沉积物的调查推进了我们对喜马拉雅沉积物分散及其与区域构造和气候关系的认识，但这些研究仅限于BNF的IODP钻孔（IODP 354和362，2015 - 16）和GBD的第四纪沉积物岩心（NSF-PIRE：构造活动三角洲上的生命，2010 - 18）。我们研究了印度东部印缅山脉褶皱冲断带（IBR）露头中的中新世-上新世祖先雅鲁藏布江三角洲的一个补充但研究不足的地层记录。我们提出了详细的岩相组合的上第三系三角洲平原（Tipam组）和潮间带的上层架（Surma组）沉积的IBR的基础上两个500米的地层剖面。新的碎屑-磷灰石裂变径迹（dAFT）和（U-Th）/He（dAHe）的日期从苏尔玛组在IBR有助于限制最大沉积年龄（MDA），热历史，沉积物的积累速率。通过对全新世-现代GBD沉积环境的模拟，划分出3个河流相（F1-F3）和4个浅海-潮间相（M1-M4）。未重置的dAFT和dAHe年龄将苏尔马群的MDA限制在13.9 - 11 Ma，这与东部BNF（13.5 - 6.8 Ma）上浊流沉积的加剧有关。两个dAHe样品产生了年轻的（103Ma）复位年龄，我们解释记录冷却剥蚀后埋藏复位由于沉积中心附近的沉积物积累较厚（102.2 - 3.2公里）。热模拟的dAFT和dAHe的结果，使用QTQt和HeFTy表明，晚中新世边缘海洋沉积物的积累率可能已经从0.9至1.1毫米/年的中心附近的古三角洲。热模拟结果表明，沉积后冷却开始于2008 - 6.5 Ma，解释为记录与前进的IBR褶皱带相关的折返开始。IBR地层的埋藏后折返的时间是一致的，与先前公布的约束的古雅鲁藏布江的撕拉向西和浊流沉积的BNF，开始在6.8Ma的西移。我们的研究结果的背景下构造控制盆地的历史，创造了一个途径，为未来的调查自生和气候的河流系统的行为，可以从地层记录中提取的驱动程序。
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.