Amazon: Sediments also show flux reversal
In the Cretaceous period 145 to 65 million years ago, the Amazon actually flowed from east to west along its entire length and thus in the opposite direction to today. So far, this could only be proven for parts of the stream.
Russell Mapes of the University of North Carolina at Chapel Hill and his colleagues support the larger thesis with sediment samples from about eighty percent of the Amazon basin. Accordingly, parts of eastern South America - around the area of today's Guyana plateau - rose after the separation of the continent from Africa and were eroded by the Uramazonas. The material removed was transported westward and deposited, so that minerals such as zircon can still be found there today, the chemical signature of which suggests an eastern origin and an age of up to two billion years.
It was only during the Miocene, when the west of South America was increasingly rising due to the uplift of the Andes, that the flow direction of the Amazon reversed - but not completely: At the same time, the so-called Purus arch grew up in the center of the basin, a species Low mountain range that divided the course of the river. On its east side, the Amazon was already flowing towards the Atlantic, on its west side, waters coming from the Andes met the returning waters of the Purus Arc. In this inland basin in particular, the scientists unearthed sediments that were relatively young, at 500 million years old. It was not until the late Miocene that the dammed rivers had carved through the arch and joined the partial Amazon from the other side to now completely drain the Amazon Basin from west to east.
Previous knowledge about the changed flow direction of the Amazon was primarily based on biological knowledge. For example, in the west of the basin - around the Peruvian city of Iquitos - there are various species of fish such as sardines or rays, whose closest relatives live in the Pacific.
