Climate controls on tufa deposition over the last 5000 years: A case study from Northwest Africa

Abstract

The occurrence and rate of tufa deposition are controlled by a large number of external and internal factors, including climate which often represents the main allocyclic factor. In this study, the first of its kind in the Middle Atlas (Northern Morocco), we test the dependency between climate factor and Holocene tufa deposits in basin-like settings that involve enlarged barrage and extensive dammed area using sedimentologic and stratigraphic analyses complemented with a paleoclimate multi-proxy approach and radiocarbon dating. The sedimentologic and stratigraphic analyses revealed a remarkable change in the vertical stacking pattern within the main barrage-cascade: higher (lower) Aggradation/Progradation ratio between ca. 4 and ca. 2.7 cal kyr B.P. (between ca. 2.7 and ca. 0.35 cal kyr B.P.), which would have conditioned a transgressive (highstand) interval “basinward”. This shift is modulated by changes in precipitation and summer insolation, which is consistent with the petrographic analysis of the laminated microbialites (oncoids and stromatolites). The previously reported arid and cold period of the Mid-Holocene Transition (between 6 and 5 cal kyr B.P.) is recorded in the sedimentary deposits and demonstrates landscape instability. The North Atlantic high-latitude cooling events between 4.6 and 2.7 cal kyr B.P. (Bond events 2 and 3) resulted in the interruption of (bio-)calcification and the development of fen and sapropel (organic-rich facies) layers, respectively. The 4.2 ka event, might have coincided herein with a fifth-order bounding surface delineating the two depositional sequences recognized on the “basin-scale”. A multi-centennial timescale period with climate optimum conditions coinciding with enhanced calcite precipitation at the downstream-facing of the main barrage (buttress development), and centred at ca. 2 cal kyr B.P. may coincide with the Roman-Iberian Climate Optimum. A recurrent occurrence with a high frequency of sub-humid marshy conditions underscored the upper part of the highstand interval which may reflect solar imprints, as already reported in previous studies in the region. • Tufa is a promising paleoclimate archive for millennial and multicentennial variability. • Climate is the main allocyclic control on the stacking pattern at barrage-cascade settings. • Higher (lower) summer temperature enhanced (reduced) vertical accretion at the barrage sill. • Bond events 4.6 and 2.7 ka coincided with fen and sapropel development, respectively. • Tufa is likely to record solar imprints in basin-like settings.