Fluvial-aeolian interaction deposits: elements and clues for recognition

TRIPALDI, A.; SURIANO, J.; LIMARINO C.O.; ZÁRATE, M.A.

Ciudad de Mendoza, Argentina

Congreso; 18th International Sedimentological Congress; 2010

International Asociation of Sedimentologist

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} p.MsoTitle, li.MsoTitle, div.MsoTitle {mso-style-link:" Char Char"; margin:0cm; margin-bottom:.0001pt; text-align:center; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES-MX; font-weight:bold; mso-bidi-font-weight:normal; text-decoration:underline; text-underline:single;} span.CharChar {mso-style-name:" Char Char"; mso-style-locked:yes; mso-style-link:Title; mso-ansi-font-size:12.0pt; mso-ansi-language:ES-MX; mso-fareast-language:ES; mso-bidi-language:AR-SA; font-weight:bold; mso-bidi-font-weight:normal; text-decoration:underline; text-underline:single;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} p.MsoTitle, li.MsoTitle, div.MsoTitle {mso-style-link:" Char Char"; margin:0cm; margin-bottom:.0001pt; text-align:center; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES-MX; font-weight:bold; mso-bidi-font-weight:normal; text-decoration:underline; text-underline:single;} span.CharChar {mso-style-name:" Char Char"; mso-style-locked:yes; mso-style-link:Title; mso-ansi-font-size:12.0pt; mso-ansi-language:ES-MX; mso-fareast-language:ES; mso-bidi-language:AR-SA; font-weight:bold; mso-bidi-font-weight:normal; text-decoration:underline; text-underline:single;} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> In semiarid-arid continental settings the interplay between fluvial and aeolian processes produces a particular environment known as "fluvial-aeolian interaction system" (Langford, 1989). Although their deposits are common features in many desertic areas few examples from the sedimentary record have been described and studied (Langford and Chan, 1989; Newell, 2001; Veiga et al., 2002). Fluvial-eolian interaction environment has a complex regime where fluvial-deposited sediments are sporadically formed and afterward exposed to wind reworking. On the other way, remobilized aeolian deposits by subaqueous currents are deposited as fluvial units. Fluvial-aeolian interaction processes take place not only below arid-semiarid climatic conditions but also in more humid climates. However, most of fluvial-aeolian deposits occurs at the margin of dunefields and erg and associated with ephemeral alluvial systems. This work presents several features of fluvial-aeolian deposits, both modern and ancient, with examples from upper Quaternary and Tertiary units (La Rioja, San Juan and Mendoza provinces, Argentina). Modern cases correspond to the Guandacol river and to the Gualilán playa lake. The first is an ephemeral high-energy gravelly-sandy braidplain with aeolian landforms (Tripaldi & Limarino, 2008). Gualilán playa lake is an intramontane basin with climbing dunes and ripples associated to the piedmont (Suriano, 2010). Ancient examples were studied in the Vallecito and Vinchina formations, thick tertiary redbed successions of the Sierras Pampeanas and the Precordillera. These rocks represent interaction deposits included in erg sandstones and fluvial units. Other examples come from upper Quaternary succession (Tripaldi et al., 2010). In the studied deposits a very close interfingering of aeolian and fluvial levels was recognized. Remarkable features include: 1) inversely graded laminae (wind ripple); 2) sandy levels made up of unimodal, symmetrical or positive asymmetric, well to very well sorted sand; 3) open packing, high porosity and very low matrix percentage; 4) lack of muddy intraclasts, parting lineation and erosive surfaces in the aeolian beds; 5) massive or very poorly laminated beds of sand, silty sand or sandy silt (loessoid deposits) due to fluvially reworked aeolian beds; 6) high index ripple forms with coarsest grains at the crest, 7) bimodal, fine to very coarse-grained (occasionally granule) sandstones, with parallel to low angle cross-lamination and inversely graded laminae.