Several studies have reported Miocene shallow-marine incursions in the Pebas Megawetland system (Western Amazonia) based on paleontological and sedimentological evidence. Only a few publications restricted to Middle and Late Miocene fossils outcropping in the Iquitos (Peru), Benjamin Constant and Eirunepé (Brazil) areas have provided isotopic evidence to test these incursions. In this study, we present new carbon, oxygen, and strontium (⁸⁷Sr/⁸⁶Sr ratios) isotopic data of macrofossils (pacu and ray teeth, crab claws and oysters), and microfossils (ostracods and foraminifera) from reported lower to lower upper Miocene sedimentary rocks of Western and Eastern Amazonian (Peru and Brazil), mainly from shallow-marine deposits. It was also analyzed present-day organisms from distinct environments (beach, sea, riverine, and estuary) and compared these results with Miocene fossils. While C and O isotopic compositions indicate that Western Amazonia fossils display an isotopic composition similar to the present-day continental, limnic and riverine, environments (−17‰ to −5.61‰ for δ¹³C and − 10.14‰ to −1.92‰ for δ¹⁸O), Eastern Amazonia fossils display C and O isotopic compositions comparable to those from seawater environments (−2.53‰ to −0.72‰ for δ¹³C and − 4.85‰ to −1.76‰ for δ¹⁸O). We further used the ⁸⁷Sr/⁸⁶Sr isotopic composition of the fossils to estimate paleosalinity conditions. The ⁸⁷Sr/⁸⁶Sr isotopic compositions indicates that Eastern Amazonian water bodies of the Pirabas Formation (Marajó Basin) varied from mesohaline to marine conditions. In contrast, Early Miocene Western Amazonian water bodies of the Pebas Megawetland System (PMWS) are characterized by freshwater conditions. Nonetheless, in Middle and Early Late Miocene, oligohaline conditions are found in the Peruvian part of the PMWS. Paleosalinity estimates of the Brazilian part of the PMWS are less constrained and might indicate a salinity range between freshwater or oligohaline conditions. Our isotopic data suggest the PMWS was occasionally submitted to oligohaline conditions during Middle and Early Late Miocene shallow-marine incursions. We suggest that Miocene shallow-marine incursions in Western Amazonia at this time were characterized by transitional paleoenvironments, reconciling isotopic, sedimentological and paleontological evidences.

几项研究报告了基于古生物学和沉积学证据的中新世浅水侵入佩斯巴斯湿地系统（西亚马孙地区）。在伊基托斯（秘鲁），本杰明·康斯坦斯和巴西埃鲁涅佩（巴西）地区，只有少数中，晚期中新世化石露头的出版物提供了同位素证据来测试这些入侵。在这项研究中，我们提出了新的碳，氧和锶（⁸⁷ Sr / ⁸⁶西部和东部亚马逊（秘鲁和巴西）中新世下中下沉积岩的大化石（pac齿和齿，蟹爪和牡蛎）和微化石（真骨纲和有孔虫）的Sr比）同位素数据。海洋沉积物。还对来自不同环境（海滩，海洋，河流和河口）的当今生物进行了分析，并将这些结果与中新世化石进行了比较。虽然C和O同位素组成表明，西方亚马逊化石显示类似于当今大陆，湖沼和河流的同位素组成，环境（-17‰至-5.61‰为δ ¹³ C和- 10.14‰至-1.92‰，δ ^18岁O），东方亚马逊化石显示C和O同位素组成与那些从海水环境（-2.53‰至-0.72‰为δ ¹³ C和- 4.85‰至-1.76‰，δ ¹⁸ O）。我们进一步使用化石的⁸⁷ Sr / ⁸⁶ Sr同位素组成来估计古盐度条件。在⁸⁷ SR / ⁸⁶Sr同位素组成表明，Pirabas组（Marajó盆地）的东亚马逊水体从中卤到海洋条件各不相同。相比之下，佩巴斯超级湿地系统（PMWS）的中新世西部亚马逊河水体的特征是淡水条件。尽管如此，在中新世中期和早期，在PMWS的秘鲁部分发现了低盐条件。对PMWS巴西部分的古盐度估计的约束较少，可能表明淡水或少盐条件之间的盐度范围。我们的同位素数据表明，PMWS在中新世和晚中新世浅海入侵中偶尔会遇到寡盐环境。我们认为，此时西亚马逊地区的中新世浅海入侵具有过渡性的古环境特征，