TY - JOUR

T1 - Sedimentary structure of inferred cyclic-step bedforms in submarine volcaniclastic slope deposits, Cuatro Calas, south-east Spain

AU - van den Berg, Jan H.

AU - Lang, Jörg

PY - 2021/5/24

Y1 - 2021/5/24

N2 - Cyclic steps are widespread on submarine slopes of many modern insular volcanoes. This paper provides the first detailed description and interpretation of the sedimentary structures and depositional architecture of cyclic-step deposits of such bedforms formed on the submarine slope of an ancient volcano. The partially depositional cyclic steps are preserved in a 67 m thick coset of 1 to 12 m thick cobble-based units of middle Miocene submarine volcaniclastics, exposed along a cliff outcrop in south-east Spain. The main structure in the units is unidirectional crude low-angle cross-bedding passing upward to centimetre to decimetre-scale diffuse stratification more or less parallel to the unit bounding surfaces. The depositional architecture produced by inferred sinuous to straight-crested cyclic steps is compared with deposits of crescent-shaped cyclic steps formed in confined settings. With a novel method, a maximum cyclic step height and length of 22 m and 460 m, respectively, have been calculated. The architecture of some of the thicker cyclic-step units is complicated by structures that were formed as cyclic-step trough-fills, by superimposed cyclic steps or downstream migrating antidunes. These structures possibly reflect adaptation processes of the bedform morphology to a lower strength of the hydraulic jumps and related density flows. In the upper, less well-exposed part of the succession more steeply inclined gravel backsets that probably represent deposits of crescent-shaped cyclic steps accreted in a more energetic, confined setting proximal to the coastal source of the density flows. A facies model of straight-crested cyclic steps is presented that may aid in the identification of similar bedforms in submarine volcaniclastic environments and comparable non-volcanic settings.

AB - Cyclic steps are widespread on submarine slopes of many modern insular volcanoes. This paper provides the first detailed description and interpretation of the sedimentary structures and depositional architecture of cyclic-step deposits of such bedforms formed on the submarine slope of an ancient volcano. The partially depositional cyclic steps are preserved in a 67 m thick coset of 1 to 12 m thick cobble-based units of middle Miocene submarine volcaniclastics, exposed along a cliff outcrop in south-east Spain. The main structure in the units is unidirectional crude low-angle cross-bedding passing upward to centimetre to decimetre-scale diffuse stratification more or less parallel to the unit bounding surfaces. The depositional architecture produced by inferred sinuous to straight-crested cyclic steps is compared with deposits of crescent-shaped cyclic steps formed in confined settings. With a novel method, a maximum cyclic step height and length of 22 m and 460 m, respectively, have been calculated. The architecture of some of the thicker cyclic-step units is complicated by structures that were formed as cyclic-step trough-fills, by superimposed cyclic steps or downstream migrating antidunes. These structures possibly reflect adaptation processes of the bedform morphology to a lower strength of the hydraulic jumps and related density flows. In the upper, less well-exposed part of the succession more steeply inclined gravel backsets that probably represent deposits of crescent-shaped cyclic steps accreted in a more energetic, confined setting proximal to the coastal source of the density flows. A facies model of straight-crested cyclic steps is presented that may aid in the identification of similar bedforms in submarine volcaniclastic environments and comparable non-volcanic settings.

KW - Backsets

KW - cyclic steps

KW - high-density turbidity current

KW - submarine volcaniclastics

KW - supercritical flow

UR - http://www.scopus.com/inward/record.url?scp=85100094897&partnerID=8YFLogxK

U2 - 10.1111/sed.12833

DO - 10.1111/sed.12833

M3 - Article

AN - SCOPUS:85100094897

VL - 68

SP - 1439

EP - 1464

JO - SEDIMENTOLOGY

JF - SEDIMENTOLOGY

SN - 0037-0746

IS - 4

ER -