TY - JOUR

T1 - A joint study in geomorphology, pedology and sedimentology of a Mesoeuropean landscape in the Meseta and Atlas Foreland (NW Morocco)

T2 - A function of parent lithology, geodynamics and climate

AU - Dill, Harald G.

AU - Kaufhold, S.

AU - Techmer, A.

AU - Baritz, R.

AU - Moussadek, R.

PY - 2019/10

Y1 - 2019/10

N2 - The origin of the landscape spreading across NW Morocco (Meseta, Atlas Mts. Foreland) is geodynamically controlled by two collisional and one extensional regime, while climate changes had only a minor impact on the shaping the landscape. The existing landscape pertains to the series characterized by highly to partially eroded mountain blocks of Paleozoic and Early Mesozoic age which is represented at its best by the relics of the Variscan orogeny resultant in what is called “Mesoeurope”. The Mesoeuropean landscape in Morocco is described by four morphodynamic units. MD 1 (0.4–1.8 Ma/generation 3) has brought about landforms in a fluvial (-alluvial) depositional environment with a strong aeolian influence at its margins. Its drainage patterns feature a moderate to gentle dip of the palaeo-current with a predominantly meandering depositional regime. The major minerals are quartz, calcite, smectite, and smectite-illite mixed-layers (submature landscape). MD 2 (2.0–3.0 Ma/generation 2) involves coastal-marine processes of a microtidal environment. Only quartz warrants mentioning as major constituent (supermature landscape). MD 3 (Neogene/generation 1) is the core zone with extensive planation and chemical weathering which gave rise to amorphous silica and smectite-group minerals (mature landscape). MD 4 (Quaternary/generation 4) encompasses landforms typical of alluvial-fluvial environments evolving under a moderate to strong palaeo-current in the foothills of the Atlas Mts. Aside of quartz, calcite, chlorite, muscovite, illite, and feldspar, labile heavy minerals are as widespread as the calcitic carbocretes. Modern structural disturbances are accountable for the immature landforms and high preservation potential of labile mineral constituents. A morphodynamic comparison between the reference type of “Mesoeurope” and the current morphodynamic type under study in Morocco results into a binary classification scheme encompassing two phases, an older one called phase of planation and a younger one called phase of dissection, a sequence which reflects quiescence and relative stable geodynamic conditions succeeded by a period of tectonic mobility. There is one striking difference between the Moroccan landscape and the reference type in Mid-Europe; the reference type has no equivalent morphodynamic unit which was triggered by the opening of the Atlantic Ocean denoted by the lack of U/Pb data of supergene alteration minerals in the reference log. The most widespread soil types encountered in the Moroccan study sites are vertisols (MD 1, MD3), luvisols (MD 1, MD 2, MD 4) and cambisols. Second in abundance are planosols, which are confined to MD 2 and, locally, arenosol associated with plinthite (MD 1); kastanozem and chernozem (MD 3) are rare members of the topsoil. While the log activity of SiO2 varies in a narrow range, the pH of the meteoric water is considerable wide, from 4.2 to 9.4. The physical-chemical regime suggests a binary subdivision into a more acidic regime (MD1, MD2) in the N and an alkaline one (MD 3, MD4) in the S which goes along with the change in the redox ratios of organic matter (LER/HER) and the climate-zonation.

AB - The origin of the landscape spreading across NW Morocco (Meseta, Atlas Mts. Foreland) is geodynamically controlled by two collisional and one extensional regime, while climate changes had only a minor impact on the shaping the landscape. The existing landscape pertains to the series characterized by highly to partially eroded mountain blocks of Paleozoic and Early Mesozoic age which is represented at its best by the relics of the Variscan orogeny resultant in what is called “Mesoeurope”. The Mesoeuropean landscape in Morocco is described by four morphodynamic units. MD 1 (0.4–1.8 Ma/generation 3) has brought about landforms in a fluvial (-alluvial) depositional environment with a strong aeolian influence at its margins. Its drainage patterns feature a moderate to gentle dip of the palaeo-current with a predominantly meandering depositional regime. The major minerals are quartz, calcite, smectite, and smectite-illite mixed-layers (submature landscape). MD 2 (2.0–3.0 Ma/generation 2) involves coastal-marine processes of a microtidal environment. Only quartz warrants mentioning as major constituent (supermature landscape). MD 3 (Neogene/generation 1) is the core zone with extensive planation and chemical weathering which gave rise to amorphous silica and smectite-group minerals (mature landscape). MD 4 (Quaternary/generation 4) encompasses landforms typical of alluvial-fluvial environments evolving under a moderate to strong palaeo-current in the foothills of the Atlas Mts. Aside of quartz, calcite, chlorite, muscovite, illite, and feldspar, labile heavy minerals are as widespread as the calcitic carbocretes. Modern structural disturbances are accountable for the immature landforms and high preservation potential of labile mineral constituents. A morphodynamic comparison between the reference type of “Mesoeurope” and the current morphodynamic type under study in Morocco results into a binary classification scheme encompassing two phases, an older one called phase of planation and a younger one called phase of dissection, a sequence which reflects quiescence and relative stable geodynamic conditions succeeded by a period of tectonic mobility. There is one striking difference between the Moroccan landscape and the reference type in Mid-Europe; the reference type has no equivalent morphodynamic unit which was triggered by the opening of the Atlantic Ocean denoted by the lack of U/Pb data of supergene alteration minerals in the reference log. The most widespread soil types encountered in the Moroccan study sites are vertisols (MD 1, MD3), luvisols (MD 1, MD 2, MD 4) and cambisols. Second in abundance are planosols, which are confined to MD 2 and, locally, arenosol associated with plinthite (MD 1); kastanozem and chernozem (MD 3) are rare members of the topsoil. While the log activity of SiO2 varies in a narrow range, the pH of the meteoric water is considerable wide, from 4.2 to 9.4. The physical-chemical regime suggests a binary subdivision into a more acidic regime (MD1, MD2) in the N and an alkaline one (MD 3, MD4) in the S which goes along with the change in the redox ratios of organic matter (LER/HER) and the climate-zonation.

KW - Mesoeuropean landscape “plus”

KW - Morphodynamic classification scheme

KW - NW Morocco

KW - Physical-chemical regime

KW - Weathering

UR - http://www.scopus.com/inward/record.url?scp=85068253831&partnerID=8YFLogxK

U2 - 10.1016/j.jafrearsci.2019.103531

DO - 10.1016/j.jafrearsci.2019.103531

M3 - Article

AN - SCOPUS:85068253831

VL - 158

JO - Journal of African Earth Sciences

JF - Journal of African Earth Sciences

SN - 1464-343X

M1 - 103531

ER -