Hạ Long Bay – Wikipedia

DateGeologic periodEvents570,000,000–500,000,000 BCbeginning of the Cambrian PeriodThe area, which now forms Ha Long Bay, was basically mainland, subject to a process of rain erosion.end of the Cambrian PeriodThe area was flooded, commencing the existence of Ha Long Bay.500,000,000–400,000,000 BCOrdovician and Silurian periodsThe area of north-east Vietnam was almost like a deep sea, submitted to the constant activity of tectonic plates.end of the Silurian PeriodIt underwent a phase of inverse-motion that created mountains deep under the water.420,000,000–340,000,000 BCend of the Silurian Period and throughout the whole Devonian PeriodThe area was subjected to powerful forces of erosion from the hot and dry climate. At this point, Ha Long was part of a wide mainland that comprised most of today’s South China Sea and Chinese continental shelf.end of the Devonian PeriodDue to tectonic activity, the Ha Long area and the entire north-east region were raised from the depths340,000,000–240,000,000 BClater Carboniferous and Permian periodsThe formation of the limestone layer more than 1,000 m thick. A shallow and warm sea reformed, which existed for approximately 100 million years. It created two kinds of limestone: the Cát Bà layer of the early Carboniferous period (450 m thick); and the Quang Hanh layer of the middle Carboniferous and the early Permian period (750 m thick). These two layers constitute the majority of the islands of the Bay.67,000,000 BCend of the Cretaceous PeriodHạ Long Bay existed in the environment of a high mountainous mainland due to the influence of strong mountain-forming phases.middle of the Paleogene PeriodThese motions remain continuous and stable, while strong processes of erosion began, and after millions of years, a form of semi-highland topography took shape. The continuation of this erosion has progressively cut the highlands into blocks with altitudes similar to today’s mountains26,000,000–10,000,000 BCNeogene PeriodThe development of the Ha Long depression2,000,000–9000 BCPleistocene epoch of the Quaternary periodThe process of erosion began dissolving the limestone-rich region of Ha Long, after that, forming the limestone plain was most active68,000–9000 BCmiddle and late Pleistocene EpochPeriod when the caves and grottoes of the area formed.early Holocene EpochThe islands of today’s Ha Long Bay are basically remnants of these mountains, flooded. Rainwater flowed into crevices in the limestone that had formed from tectonic activity. This steady erosion constantly widened the cracks, eventually creating today’s formations.9000–5000 BCHolocene EpochThis period is notable for the advance of the sea.5000–2000 BCThe movement of the sea reached its peak and forming today’s Ha Long Bay.2000–1000 BCWith the sea in a steady process of recession, Ha Long culture began to develop.beginning of the late Holocene EpochThe level of the water once again increased, forming a marshy floor of canals and streams, and creating the water marks that can be seen on the stone cliffs of today.