Fenton, C.R.

Fink, D.

Hughes, C.

English

Glacial geomorphological mapping, 10Be cosmogenic exposure ages of 30 erratics from 3 valley systems and palaeoglacier-climate modelling in the highest peaks of the Atlas Mountains, Morocco (31.1°N, 7.9°W), provides new and novel insights as to the history and evolution of the largest desert region on Earth. The Atlas Mountains display evidence of extensive and multiple late Pleistocene glaciations whose extent is significantly larger than that recognised by previous workers. The largest ice field and valley glaciers formed in the Toubkal massif and here we find 3 distinct phases of glacial advances within the Last glacial cycle. The oldest moraines occurring at the lowest elevations have yielded 10Be ages from 30.5 to 87.3 ka. Five of seven samples from moraines at intermediate elevations gave ages of 13.8 to 24.2 ka (2 outliers) which correlates well with the global Last Glacial Maximum (ca. 22-19 ka) and the last termination. Five erratics from the youngest and most elevated moraines yielded a suite of well peaked exposure ages from 11.1 to 12.9 ka which unequivocally falls within the northern hemisphere Younger Dryas (12.9-11.7 ka) chronosequence. The glacial record of the High Atlas effectively reflects moisture supply to the north-western Sahara Desert and can provide an indication of shifts between arid and pluvial conditions. The low altitude range from 2000-2500 m of the glaciations in all three glacial episodes recorded in the High Atlas indicate that climate was not only significantly cooler than today, but also very much wetter. The new evidence on the extent, timing and palaeoclimatic significance of glaciations in this region has major implications for understanding moisture transfer between the North Atlantic Ocean and the Sahara Desert during Pleistocene cold stages. Glacier advance in the High Atlas during this interval provides insight into the seasonal distribution of precipitation and provides valuable insight into the respective roles of moisture supply from the North Atlantic depressions and the West African Monsoon. This in turn then has important bearing on the strengths of meridional vs. zonal circulation at mid-latitudes during pluvial phases

The University of Manchester - Institutional Repository

The University of Manchester ResearchExtent, timing and palaeoclimatic significance of LatePleistocene glaciation in the High Atlas, MoroccoLink to publication record in Manchester Research ExplorerCitation for published version (APA):Hughes, C., Fink, D., & Fenton, C. R. (2012). Extent, timing and palaeoclimatic significance of Late Pleistoceneglaciation in the High Atlas, Morocco. Poster session presented at 21st International Radiocarbon Conference,UNESCO Headquarters.Citing this paperPlease note that where the full-text provided on Manchester Research Explorer is the Author Accepted Manuscriptor Proof version this may differ from the final Published version. If citing, it is advised that you check and use thepublisher's definitive version.General rightsCopyright and moral rights for the publications made accessible in the Research Explorer are retained by theauthors and/or other copyright owners and it is a condition of accessing publications that users recognise andabide by the legal requirements associated with these rights.Takedown policyIf you believe that this document breaches copyright please refer to the University of Manchester’s TakedownProcedures [http://man.ac.uk/04Y6Bo] or contact uml.scholarlycommunications@manchester.ac.uk providingrelevant details, so we can investigate your claim.Download date:09. Jun. 2022Extent, timing and palaeoclimatic significance of Late Pleistocene and Holocene glaciation in the High Atlas, Morocco  David Fink1 , Philip  Hughes2  and  Cassie Fenton3  1 Australian Nuclear Science and Technology Organisation, Sydney Australia, 2   School of Environment and Development , University of Manchester, Manchester, UK., 3  Helmholtz-Zentrum Potsdam, D-14473 Potsdam, Germany Samples were processed and measured at SUERC and ANSTO. All 10Be exposure ages based on 10Be/9Be ratios normalised to NIST-SRM-4325 with 10Be/Be = 27, 900x10-15 and a production rate of 4.60 at/g/y using Stone scaling. Fig 3 Fig 4 #8      Likemt-8 #9    Likemt-7  DISCUSSION: The glacial record of the High Atlas reflects moisture supply to the north-western Sahara Desert indicating  shifts between arid and pluvial conditions. The low ELA moraine elevations of  2000-2500 m for the MIS 2-4  glacial advances  indicates significantly cooler and wetter climates than today. The new evidence on glacial timing and ELAs in the High Atlas has major implications for moisture transfer between North Atlantic depressions and the West African Monsoon during Pleistocene cold stages. This in turn has important bearing on the strengths of meridional vs. zonal circulation at mid-latitudes during pluvial phases. Fig 2 Fig 1 View from below Likemt right lateral  to cirque moraine. 14 15 9 8 7 View from Likemt right lateral  to Tacheddirt village. 7 8 3,4 Tacheddirt village LATE  PLEISTOCENE  GLACIERS   INTRODUCTION: To the west of Mt Akousal and its Pleistocene glacial record  near the village of Arrmoud, geomorphic mapping of n’Imserdane valley has identified massive landslide debris intermixed with glacial moraine ridges. The slope derived rock avalanche debris consists of two lobes – unit A at lower valley elevations (~2100) underlying Arrmoud village (~1700), and a smaller cross valley lobe, unit-B, at ~2300-2400 m. Three apparent glacial units are defined - #1 on the northern flank, #2 , adjacent to avalanche unit-B and #3 at ~2500 above avalanche unit-B (Figs 5 & 6).    RESULTS: Within the analytical age errors per sample (~0.1 to 0.4 ka) and inherent geologic variability per unit, timing of rock wall collapse and glacial advances are coeval. All 7 (of 9) moraine  boulder ages and 6 avalanche ages peak between 3.1  to 4.5 ka.   HOLOCENE   GLACIERS  &  ROCK- SLOPE   FAILURE     DISCUSSION: Glacial units (#1,2,3) show distinct moraine morphology. Moraine ages, ~ 4ka, appear to be unequivocally mid-late Holocene. However to date, Holocene moraines ages are not observed elsewhere in Toubkal. Absence of Pleistocene age on glacial units may be the result of their modification and/or destruction by repetitive rock-wall failure events from over-steepened flanks following major glacial retreat (10-20ka). The most recent avalanche,~4 ka, is likely due to seismic activity (Tizi n’Test fault,1 km distant and a major fault of Toubkal Massif). Either rock-fall events have altered all the glacial record, or specific local parameters enable preservation of Holocene glaciers. The relationship between avalanches and moraine assemblages is complex and the subject of ongoing research. Fig 5 Fig 6 INTRODUCTION: The Atlas Mountains,  Morocco (31.1 N, 7.9 W, Fig 1), display extensive and multiple late Pleistocene glaciations. Their extent is significantly larger than that recognised by previous workers.  Glacial geomorphological mapping coupled with 10Be cosmogenic exposure ages of ~20 erratics from 3 valley systems in the highest peaks of the Atlas Mountains, provide new insights on the history and evolution of the largest desert region on Earth.     RESULTS: The largest ice field and valley glaciers formed in the Toubkal massif (yellow circle Fig 2). The regions studied are outlet glacial valleys of Mt Aksoual (3912 m) (Fig 3) and northern slopes of Adrar Adj Mt (3129 m) at Azib Mzik (Fig 4). Three  distinct phases of glacial advances are evident within the Last Glacial Cycle.   1.Pre-LGM:  the oldest moraines occur at the lowest elevations (~2300 m) with 5 10Be erratics giving ages ~ 30 to 88 ka (1 outlier)  2.LGM: moraines at intermediate elevations (~2500m) with 5 ages ~15.5 to 24.0 ka (2 outliers) associated to the global LGM (~ 22-20 ka) and Termination-1.   3.Late Younger Dryas: youngest and most elevated moraines (~2900m) with 5 ages peaked from 10.1 to 11.9 ka. Typical sequence (Fig3) varies in elevation range due to strong local topo-climatic controls. 

Extent, timing and palaeoclimatic significance of Late Pleistocene glaciation in the High Atlas, Morocco

https://pure.manchester.ac.uk/ws/files/33527476/FULL_TEXT.PDF

Extent, timing and palaeoclimatic significance of Late Pleistocene glaciation in the High Atlas, Morocco

Abstract

Similar works

Full text

Available Versions

The University of Manchester - Institutional Repository