Introduction
For the purposes of this report, recent sedimentation will include that occurring during Quaternary and Holocene times. The Quaternary period lasted from two million years ago, until about 12,000 years ago. Following the Pleistocene, the Holocene ranged from 12,000 years ago until 1950.
Throughout this time, sedimentation in Brittany, and all around the world, particularly the Northern Hemisphere, was dominantly controlled by glaciations and the sea level fluctuations they induced. At least four large-scale glacial events occurred in the Northern Hemisphere during the Quaternary Period. Figure 1 shows the 18O/16O isotopic ratios corresponding to glacial/interglacial periods over the past 900,000 years. The largest of these, the Anglian Glaciation, which lasted from 500,000 to 400,000 years ago, reached only as far south as London, England. However, these sea-level fluctuations have left their mark on the sedimentary history of Brittany.
The discussion of recent sedimentation of Brittany is divided into three sections. The first two of these cover sedimentation on continental margin. The first section covers the sedimentation occuring during regressive sea systems and the second covers transgressive sea deposits. As will be described below, many of the deposits focused on are eroded away each time the sea level falls during a glaciation. For this reason, the deposits discussed in these sections will all be from the last glacial cycle, beginning at the start of the Devensian Glaciation, approximtely 115,000 years ago, and continuing up through the current interglacial period. The third section will discuss sedimentation on land.

Regressive Seas
During times of sea regression, the primary sediment deposits occurred on the continental rise. During times of maximum glaciation, sea level dropped significantly. At 18,000 bp, during the last glacial maximum, global sea level was 120 meters lower than it is today. This drop in sea level exposed the area around the present day peninsula of Brittany, including the English Channel and the nothern part of the Bay of Biscay. Figure 2 shows the extent of the sea at 18,000 years bp, during the last glacial maximum. As these areas were subaerially exposed, they became subject to fluvial erosion, as water from further onshore now crossed the old continental shelf on its way to the sea. This water traveled in large rivers, as does water moving towards the seas on the modern day continents. During times of regressive or low still-stand seas, these rivers carved large incised valleys onto what is today the continental shelf. These incised valleys can be found in the Bay of Biscay, and on the Armorican Margin. Figure 3 shows the paleovalley network of the South Armorican margin. These valleys are believed to have been initially carved out during a lowstand sea prior to the Quaternary Period. The valleys would then have been infilled when the sea rose again. However, because these sediments are not compacted and lithified and are much younger than those which make up the rest of the shelf, they are more resistant to erosion. Thus, during the next glaciation and accompanying lowstand sea, rivers reformed in these sediments. These new rivers carved down through the sediments and cleared out the old valleys.
These sediments are carried away by the rivers, and eventually deposited as marine fans on the continental rise. Fans of this type can be seen today in the Western Approaches of the English Channel. There is one fan, deposited by a river running from the modern day Irish Sea, dated at seven thousand years. There are two more fans to the south, dated at twelve thousand years, which are believed to have originated from the Manche River, running through the modern day channel.
These fans, and the sea floor around them include a series of turbidite deposits. Dating of these deposits has shown an increasing number of turbidites towards the end of the last glacial maximum. This increase is representative of the increased terrigineous flux generated by the Manche River. The terrigineous flux increased due to the increased length of the river due to the low sea level, and also to the beginning of the melt-off of the glaciers.

Transgressive Seas
During times of sea transgression, the primary sediment deposits were on the continental shelf. Of particular interest was infilling of incised valleys. These valleys, as mentioned above, were carved out during regressive and low stillstand seas. They can be found on the South Armorican margin and in the Western Approaches. The sediments carried by rivers running though these valleys were deposited as the river opened to the sea, and water velocity fell. As sea level rose again at the end of each glaciation, the boundary between river and sea moved progressively nearer the mainland and these sediments were subsequently dropped nearer the mainland, progressively infilling the valleys.
This infilling progressed, as would be predicited, in a sequence of units representing depositional environments of increasing depth. The infilling of these incised valleys is shown in Figure 4 (from Menier, 2004). The bottom sediments in the valleys were laid down in a fluvial environment. These were deposited near the mouth of the river, where the channel widens, and water velocity starts to decrease. Above the fluvial deposits were estuarian deposits. These sediments were laid down in an estuary environment. At this time, the sea level had risen to just above the depositional area and the setting would be similar to marine estuaries found around the world today. Above the estuarian deposits are open marine deposits as sands. Once sea level rose high enough, the channel would be at the sea floor, as it is today. Above the sand shallow deposits, bay deposits (clay) have been found. These deposits fill in the top of the valleys and are continuous across the shelf surrounding the valleys. The progressive return to distal deposits suggests a complete transgressive sequence with a continuous increase in global sea level since the last glacial maximum, 18,000 years ago. In the English Channel and its western approaches, the infilling is made of muds deposits covered by progressive sands marine deposits. These deposits belong to the Little Sole formation (Pleistocene).
These depositional environments have been determined through careful study of both sediment cores and seismic surveys. Figure 5 shows a seismic survey through one of these infilled incised valleys of the South Armorican margin. The figure shows the original deep valley, and subsequent sedimentary units, which are remains of old infillings, which were only partially carved out during later lowstand sea periods.
Also found in the western approaches of the English Channel are a series of sand dunes (Melville formation.). Like the fans and turbidites, many believe these dunes to have been deposited during the last regressive system and are composed of sediments carried to the edge of the continental shelf by paleorivers, many flowing through the incised valleys discussed above. However, others claim that there is no clear unconfomity between these dunes and the infilled valleys, and thus the dunes were deposited during the transgressive system.

Land Deposits
Onland quaternary deposits rarely show succession of glacial cycles but they are consistent with the sea level fluctuations.
In general, glacial type deposits are peri-glacial one: eolian silts (loess) wich mainly come from the channel erosion. The eolian deposits are thinner from the north coast of brittany to the south and they are always on the northern slope of valleys (example of the Noth coast of Plougastel peninsula). Heads deposits are also related in many places and one of them was observed on Groix island (Figure 6). These deposits are intercalated with interglacial deposits wich show various changes of the global temperature and the sea-level fluctuations: beaches and sand dunes, podzols floors wich sometimes recover these dunes or peat deposits (lacustrines).

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Summary
The recent sedimentary evolution of Brittany has been heavily dependent on transgressive and regressive sea cycles corresponding to a series of Northern Hemisphere glaciations during the Quaternary Period. The last of these glaciations ended at the end of the Quaternary, and the whole of the Holocene was during a transgressive system associated with the beginning of the last interglacial time. The majority of recent continental margin deposits are no older than the last glacial maximum, 18,000 year ago. At this time, low sea levels allowed flowing rivers to erode away almost all sediment deposits from previous transgressions. Regressive seas led to deposits of submarine fans and turbidites on the continental rise. Transgressive seas led to infilling of incised valleys.
On land, the last 2 million years has been primarily an erosive time in Brittany, though some deposition has occurred such as eolian loess and peri-glacial head during glacial times and littoral sands dunes and lacustrine deposits during interglacial times.