Facies patterns and depositional processes in two Frasnian mixed siliciclastic-carbonate systems in the Cantabrian Mountains, northwest Spain
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Date
2020-04
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Instytut Geologii UAM
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Abstract
Relative sea level fluctuations during the Frasnian generated two shallow-marine, mixed siliciclastic-carbonate successions
in the Devonian Asturo-Leonese Basin. Each system represents a third-order sequence-stratigraphical unit
deposited in the same basin during comparable extreme greenhouse conditions without nearby fluvial entry points.
Depositional control on the siliciclastic and carbonate distribution was driven by relative sea level fluctuations, basin
geometry, availability of sand and the way sediment was distributed by shelf currents. Early Variscan flexural bending
of the continental crust changed the basin shape from a shelf with a gradual profile and low dip (early Frasnian) towards
a shelf with a steep depositional dip (late Frasnian). Shelf distribution changed from along-shelf transport (early
Frasnian) towards offshore-directed gravity flows (late Frasnian). As a consequence, siliciclastic-carbonate distribution
changed from a predominance of skeletal carbonate in the proximal shoreface – foreshore area and siliciclastic predominance
distally (early Frasnian), to a distribution pattern with proximal shoreface skeletal carbonates, offshore muddy
carbonates and a siliciclastic zone in between where gravity flows distributed the siliciclastic sediment down dip (late
Frasnian).
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Keywords
mixed systems, sequence stratigraphy, depositional controls, Upper Devonian, Asturo-Leonese Basin
Citation
Geologos 26, 1 (2020): 1–23