2011-11-21

Geological impressions

Archaeological stone tool finds from the Maas river gravels  are related to the terraces where they were found on. In a way, this sometimes a more reliable manner of dating artifacts compared to absolute dating techniques like C14,  TL or OLS. The Kempen Plateau terrace (B) has an estimated age of 600.000 years, the St. Pietersberg terrace ( at Bemelen NL) is about 800.000-900.000 years old.
The locations , mentioned in the text


Some images ( compilations) from the large Kempen fan gravels depositions of the Maas river during the Cromerian periods ( ca 850.000 BP - 420.000 BP). Up to 20 meters of gravels, loam, coarse sands have build  the west- upper terrace of the Maas -river, visible here in  the  S.B.S. pit [ community of Maasmechelen, Belgium] (click to enlarge)
Notice the upper red horizons being the lower part of the integrated As paleosol with an assumed Holsteinian date, ( between 420.000 BP - 360.000 BP ) the top horizons are already dug out.
After the Elsterian glacial the Maas river cut itself in the landscape, in the same period, the Kempen Plateau was  'created' by "inverted topography" as the soft Miocene sands were eroding. leaving the gravel plateau up to 50 meters in the surrounding landscape.


Soil profiles showing the stratigraphy of different gravel depositions ( mainly iron  oxidated, in red, clay horizons ( light brown- blueish,) coarse sands ( light colored) and manganese dioxide ( black)


 Black oxidation horizon weathering, indicating a different climate type, with much higher temperatures ( up to 1-2 degrees Celsius average  ) and large average precipitation levels . The oxidation is influenced  by clay minerals and reactions in the bedrock material. An important climate related subject in the producing of manganese oxide horizons is the amount of litter , in combination with low differences in surface levels, supposing the Kempen area would have been a relative "flat:" area during horizon genese.At MA6, location of the  former riverbank of the Maas river, it's obvious the manganese oxide horizon has been cut in by the river, thus exposing these horizons on the present slopes.(photo: S.B.S. pit, Maasmechelen, Belgium)

Image above  taken at Geological wall, community of As 
(Below:)Different horizons showing  different depositions of  subangular Maas- river gravels. Coarse aggrading gravels are changed by high energy transport deposits during more glacial conditions. Below the black oxidation horizon, I found in the red horizon an iron oxidation - breccia ( see image below, ( ASAC collections sample)).(Image above  taken at Geological wall, community of As)


Below: Clay layers are formed by the river, during interglacial conditions. Such layers are impermeable and could cause chemical reactions in the bedrock during sub- tropical conditions, thus weathering the soil and producing iron -, aluminum-  and manganese- oxidations.( Image: ASAC collections sample) This is a non stained, non- oxidated example from the SIBELCO pit at Maasmechelen.


 (Below:)The iron oxide creates intense red colors in the clay/ loam (below)Image: ASAC collections sample






 Above: Two different black dioxide horizons are visible , one left top, right below the As-Paleosol, the other in the lowest visible undisturbed horizon.


 (Above) Small geological  insight  of the Pleistocene Maas river at Bemelen (NL). Top -horizons show eroded loess, leached loess and gravel layers. The direction ( southeast -  northwest) of the pebbles during deposition in the early Pleistocene is suggesting the Maas river made a large bend towards the east, ( eroding bank) , leaving the city of Maastricht at the depositional riverside.

During the formation of the river terrace heavy weathering took place , causing heavily cemented integrated layers. Gravel horizons are different in composition ( size, origin of pebbles), and deposition patterns; in this way gravel containing horizons where possible artifacts may occur can be traced.

Variable stratigraphy 
The Kikbeek -pit near the village of Opgrimbie is a grateful geological monument, showing in present times  Pleistocene processes of gully- forming on eroding surfaces
Exposed surfaces without any vegetation are the beginning of the development of surface drainage systems such as gully's , caused by heavy erosional processes. 
When we regard the local Kempen plateau stratigraphy, it seems there are many differences within local stratigraphies.
The top horizons, like for example in the former Kikbeek- pit, show large differences in Pleistocene geological elements , depending on local circumstances. The three pictures below were taken from the same local stratigraphy, over a distance of ca 15 meters.

(1) Developed oxidation horizons alternating with coarse sands 
(2) west Manganese oxidation (in black) between sand - horizons
(3 ) west Unsorted gravels below a bleached top horizon
Prehistoric man most probably never saw the lignite ( black)  and Micocene sand-covers (white)  that are exposed here at the shore of an artificial lake in the former Kikbeek- pit near Opgrimbie (B)


For more geological information see the website on regional geology  of ASAC
AGC (argeocol.hpage.com); website is under construction

Bibliography /internet

Michael A. Summerfield  Global geomorphology , an introduction to the study of landforms Longman | april 1991

Judson Kauffman Leet Physical geology; Prentice-Hall 1987

River Systems: Process and Form Compiled by Jeff Crabaugh at Carleton College (SERC) and the University of Wyoming:    sediment transport movies

ENFIA Natural History Geoarchaeology  ( The Eldorado National Forest Interpretive Association)

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