Distinguishing glacial diamictons and landforms using till macrofabric and grain size analysis: Serra da Cabreira Mountains, NW Portugal

ABSTRACT

Information on the nature of processes occurring in modern glaciers can be obtained through the study of diamictons and landforms that are the product of past glaciations. Macrofabric and grain size analysis of late Quaternary glacial diamictons and moraines present in several valleys of the Serra da Cabreira Mountains in northwest Portugal revealed the presence of two types of diamictons deposited in different stages and were used to re-construct the glacial paleo process history of this mountainous region. Supraglacial melt-out tills and paraglacially reworked tills by debris flows are dominant in this range. Supraglacial melt-out tills, representative of periods of glacial stability followed by recession, present girdle to transitional fabrics and coarser to medium, poorly sorted sediments. Paraglacially reworked tills by debris flows, representative of postglacial mass wasting activity, present girdle fabrics and coarser, poorly sorted sediments. These diamictons and landforms are of particular importance in the reconstruction of the glacial dynamics and history of the Serra da Cabreira Mountains due to a scarcity of chronological data based on absolute dating methods. These Atlantic mountains are also the lowest glaciated range in the Iberian Peninsula, which makes them a compelling area to investigate mountain glacial dynamics in low-elevation Atlantic ranges.

KEYWORDS:

• Glacial geomorphology
• till macrofabric
• grain size
• Serra da cabreira mountains
• NW Portugal

Acknowledgments

We thank the Department of Geology at San Jose State University and Ryan Portner, Director of the Sedimentology Lab, for supporting the grain size analysis work. We also thank Alberto Gomes, Edgar Figueira, and Jorge Costa from the Department of Geography at the University of Porto, Portugal for fieldwork assistance. A special thank you to Helder Santos for some of the photographic work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, Joao Santos, upon reasonable request.