Sediments of the Quaternary
This category of glaciofluvial sediments includes all meltwater sands deposited above, within or below the Weichselian-era ground moraine. They were transported by the water melting off the glacier, and deposited in various forms and grain sizes.
The meltwater sands widely distributed across the ground moraine may contain a share of late Pleistocene to Holocene outwash mass. They may consist of a quite variegated spectrum of grain sizes, ranging from silty fine sand course sand, and can also be of variable thickness.
Locally, meltwater sands are widely distributed under the Weichselian ground moraine. Inside this area, glaciofluvial sands of fine to course size separate the upper, Weichselian-era ground moraine from the lower Saalian-era ground moraine.
Moreover, within the glacial till, interglacial sands occur, usually only locally, and generally only of minimal thickness. These sands cannot be distinguished petrographically from the glaciofluvial meltwater sands, so that the delimitation between the Weichselian and the Saalian-era tills is often difficult.
Due to their cohesionless nature, meltwater sands have a great water conductive capacity and are therefore good groundwater conductors.
Boulder clay, glacial till of the Weichselian Glaciation
The moraines of the Brandenburg Phase of the this Weichselian Glaciation, in some places covered by meltwater sands, forms a coherent horizon of glacial till of between five and 10 m in thickness, sometimes more. Petrographically, it consists mostly of weakly clayey, silty, calcium-containing sands with a low share of gravel and stones, and only rarely dropstones. On the surface, the till has been de-calcified by the effects of the weather and has turned into boulder clay.
Due to their share of clay and silt, the till and boulder clay constitute a binding sediment with a low level of water conductive capacity (an aquitard).
In the areas covered with sand and in the edge of the plateaus, the thickness of the ground moraine has generally been reduced by erosion.
The dropstones carried by the glacier or eroded out of the ground moraine can be seen all over the city.
Valley sands in the area of the glacial spillway and the ancillary valleys
As the Weichselian ice continued to melt, the Warsaw-Berlin Glacial Spillway was created. Its development occurred in a number of phases. Both the meltwater of the older period of the the Weichselian Glaciation (Frankfurt Phase) and of the younger period (the Pomeranian glacial edge) use the valley courses as drainage channels leading north-westward toward the Elbe and the North Sea.
In the Glacial Spillway, the valley sand is generally more than 10 m thick; below it are the sediments from the Saalian Glaciation. In the upper layers, the valley sand is fine to medium grained, in some cases silty; at greater depths, it becomes coarser, and more often includes gravelly admixtures. Both the Weichselian and the Saalian ground moraines have been largely eroded, so that the sand from the Weichselian Glaciation in most cases rests directly on older sand layers, sometimes as much as 50 m deep.
In the Panke Valley, an ancillary valley of the Glacial Spillway, this same sequence of sand can be seen, although its thickness is seldom greater than 10 m. Locally, glacial till deposits can be seen which are interpreted as erosion residues both of the Weichselian and the Saalian ground moraines.
Due to their cohesionless nature, the valley sand has a great water conductive capacity and is therefore a good groundwater conductor.