EGQSJE&G Quaternary Science JournalEGQSJE&G Quaternary Sci. J.2199-9090Copernicus PublicationsGöttingen, Germany10.5194/egqsj-68-1-2019Quaternary fluvial environments in NE Morocco inferred from
geochronological and sedimentological investigationsQuaternary fluvial environments in NE MoroccoBartzMelaniem.bartz@uni-koeln.deInstitute of Geography, University of Cologne, Cologne, GermanyMelanie Bartz (m.bartz@uni-koeln.de)25January201968114This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/This article is available from https://egqsj.copernicus.org/articles/68/1/2019/egqsj-68-1-2019.htmlThe full text article is available as a PDF file from https://egqsj.copernicus.org/articles/68/1/2019/egqsj-68-1-2019.pdfcitationstatementBartz, M.: Quaternary fluvial environments in NE Morocco inferred from
geochronological and sedimentological investigations, E&G Quaternary Sci. J., 68, 1–4, https://doi.org/10.5194/egqsj-68-1-2019, 2019.
Supervisors: Helmut Brückner, Olaf Bubenzer
and Gilles Rixhon
The investigation of
fluvial archives in NE Morocco is of high interest for unravelling
palaeoenvironmental changes linked to Quaternary climate fluctuations,
long-term tectonic activity and/or human influence in NW Africa. The
prehistoric site of Ifri n'Ammar is situated in NE Morocco (Fig. 1) and
represents a key location for deciphering the history of anatomically modern
humans (AMHs) in northern Africa because it reveals Middle and Late Palaeolithic occupation phases since ∼170 ka (Moser, 2003; Nami and Moser, 2010, Richter et al., 2010; Klasen et
al., 2018; Fig. 2). This study uses two fluvial systems of different nature
– the ephemeral stream Wadi Selloum and the perennial Moulouya River
(Fig. 1) – in order to reconstruct the varying environmental conditions for
the last ∼170 kyr, the time when AMH started to disperse into the
region.
Relief map (based on ASTER Global DEM) of the lower Moulouya
catchment including the two study areas (greyish rectangles) of the Wadi
Selloum and the ∼20 km long investigated river reach of the
Moulouya River. The red star denotes the prehistoric site of Ifri n'Ammar.
(a–c) Images of the study areas. (a) Ephemeral stream Wadi
Selloum in the direct vicinity of Ifri n'Ammar with up to 5 m high Holocene
overbank fines (view towards the SE). (b) Footwall reach of the
thrust zone showing stacked fluvial terraces of the Moulouya with Early
Pleistocene gravel deposits and Holocene overbank fines (view towards N).
(c) Hanging wall reach characterised by a well-preserved staircase
of up to three Pleistocene Moulouya terraces above Holocene overbank fines
and the modern floodplain. A clear unconformity (dashed line) between Neogene
marls and Pleistocene river gravel is illustrated. Person for scale (ellipse)
(view towards the NE).
Both fluvial systems provide valuable insights into the geomorphic evolution
of the region. It could be demonstrated that both responded to different
environmental triggers: the small catchment of the Wadi Selloum (∼290 km2) is highly affected by the sensitive ecosystem of the
Mediterranean region. This ephemeral stream is characterised by a
discontinuous and heterogeneous sediment record (Fig. 1a) caused by
short-term climatic shifts and human influence (Bartz et al., 2015, 2017). In
contrast, the terrace record of the lower Moulouya was considerably affected
by tectonic processes related to the collision between the African and
Eurasian plates. A W–E-striking thrust fault,
associated with N–S compressive shortening in this region, could be
identified; it strongly deformed the late Neogene sedimentary sequence of the
lowermost basin drained by the Moulouya (Fig. 1) (Rixhon et al., 2017). While long-lasting
aggradation led to the formation of composite fill terraces several tens of
metres thick in the footwall reach (Triffa plain; Fig. 1b), a terrace
staircase with at least three distinct terrace levels characterises the
hanging wall reach (Ouled Mansour plateau; Fig. 1c). Tectonic activity
appears thus to be the main driver for the evolution of the lower Moulouya
terraces (Rixhon et al., 2017; Bartz et al., 2018).
Chronological correlation between the on-site archive
(occupation phases of the rock shelter Ifri n'Ammar) and the off-site
archives (ephemeral stream deposits of Wadi Selloum and fluvial terrace
deposits of the lower Moulouya). Chronological data of the two fluvial
systems are based on optically stimulated luminescence (OSL),
thermoluminescence (TL) (see Bartz et al., 2015), thermally transferred OSL
(TT OSL) (see Bartz et al., 2019),
post-infrared infrared stimulated luminescence and electron spin resonance
(ESR) dating (see Bartz et al., 2017, 2018). From these results, phases of
morphodynamic activity and stability can be deduced. The chronological
framework of the prehistoric site of Ifri n'Ammar is based on radiocarbon
(Moser, 2003) and luminescence dating (Richter et al., 2010; Klasen et al.,
2018).
Establishing chronostratigraphies of river sedimentary sequences always
remains challenging. However, fluvial deposits of the Wadi Selloum could be
well dated via optically stimulated luminescence (OSL) of quartz and
post-infrared infrared stimulated luminescence of K feldspar. Although an
independent age control was not possible, inter-method comparisons with
thermoluminescence (TL) dating of a pottery shard (Bartz et al., 2015) and
OSL and post-infrared infrared dating of two samples from the same sedimentary
unit (Bartz et al., 2017) allowed the establishment of robust chronologies of
the ephemeral stream deposits. The ages range between 102±8 and 1.3±0.2 kyr; they highlight the discontinuous fluvial deposition between MIS 5c
and the Holocene (Fig. 2).
Due to the expected Early to Middle Pleistocene age of the fluvial terraces
of the lower Moulouya it was challenging to establish luminescence
chronologies. Quartz and K feldspar
luminescence signals of the studied deposits had reached saturation,
suggesting fluvial deposition at least as early as the Middle Pleistocene
(Bartz et al., 2018; Fig. 2). However, electron spin resonance (ESR) dating
offered a useful alternative way to gain further chronological information.
Based on the multiple-centre approach in fluvial environments (Duval et al.,
2015), aluminium (Al) and titanium (Ti) centres were measured in quartz; this
was cross-checked with palaeomagnetic analyses (Bartz et al., 2018). Thus, a
robust geochronological framework was established for the fluvial terraces,
with numerical ages dating back to the Early Pleistocene and ranging between
∼1.5 and ∼1.1 Ma (Bartz et al., 2018) (Fig. 2). Recently, Bartz
et al. (2019) additionally applied thermally transferred (TT) OSL on the same
strata. The single-grain TT OSL results matched well with the newly
established ESR chronology and proved the lower Quaternary (Calabrian) age of
the fluvial terraces (Bartz et al., 2018, 2019).
Bearing in mind that chronostratigraphies of the ephemeral stream deposits
and of the pre-Holocene Moulouya fluvial terraces
do not yet exist, the application of different trapped
charge dating techniques in combination with palaeomagnetic research served
as a valuable tool to obtain
chronological information about the deposition in the different fluvial
systems.
In addition to using numerical and relative dating techniques,
sedimentological, geochemical, mineralogical and micromorphological analyses
have been carried out to distinguish periods of enhanced
flooding–aggradation from periods of
relative stability favourable for pedogenesis. The Wadi Selloum gives
information about morphodynamic phases in the time of the settling of AMH
(Fig. 2): periods of enhanced aggradation occurred around ∼100, ∼75 and ∼55 ka, after the Last Glacial Maximum, and during the
Holocene, whilst sedimentation ended after ∼1.3 ka. Pedogenesis may be
used as an environmental indicator for more humid climate conditions during
MIS 3 (palaeo-Calcisol), the early Holocene (Calcisol) and the late Holocene
(Fluvisol) (Fig. 2).
Although palaeoenvironmental implications should be taken with caution due
to the discontinuity of the ephemeral stream system, it appears that more
humid and warmer climate conditions may have favoured human settling in this
area. This study thus provides the first insights into the palaeoenvironmental
changes around the prehistoric site of Ifri n'Ammar during the last
glacial–interglacial cycle. In contrast, the absence of Middle and Late
Pleistocene deposits in the sedimentary record (Fig. 2) of the lower
Moulouya seems to rule out climate as the main driver for long-term fluvial
evolution in that region at least during the lower Quaternary. However, it
provides valuable information on the regional tectonic history in NE Morocco
(Bartz et al., 2018).
The data are not deposited in data repositories, but are published in
the articles Bartz et al. (2015), (2017), (2018) and (2019).
Acknowledgements
This research is affiliated with the CRC 806 “Our way to Europe”, which is
funded by the German Research Foundation (DFG; grant no. SFB 806/2). The
support from the “Institut National des Sciences de l'Archéologie et du
Patrimoine du Maroc” (INSAP), especially Abdeslam Mikdad at Rabat, and by the
“Commission for Archaeology of Non-European Cultures” (KAAK), especially
Josef Eiwanger, of the German Archaeological Institute (DAI) is gratefully
acknowledged. Furthermore, my sincere thanks go to Mathieu Duval (Griffith
University, Australia, and CENIEH, Spain), without whose support this
research could not have been successfully completed.
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