ELSEVIER Sedimentary Geology 105 (1996) 63-90 SEDIMENTARY GEOLOGY Shallow marine event sedimentation in a volcanic arc-related setting: the Ordovician Suri Formation, Famatina Range, northwest Argentina Marfa Gabriela Mfingano ~, Luis Alberto Buatois 1 CONICET, Facultad de Ciencias Naturales, Universidad Nacional de Tucurndn, Casilla de correo l (correo central), 4000 San Miguel de Tucurndn, Argentina Received 2 August 1994; revised version accepted 6 October 1995 Abstract The Loma del Kil6metro Member of the Lower Ordovician Suri Formation records arc-related shelf sedimentation in the Famatina Basin of northwest Argentina. Nine facies, grouped into three facies assemblages, are recognized. Facies assemblage 1 [massive and parallel-laminated mudstones (facies A) locally punctuated by normally graded or parallel- laminated silty sandstones (facies B] records deposition from suspension fall-out and episodic storm-induced turbidity currents in an outer shelf setting. Facies assemblage 2 [massive and parallel-laminated mudstones (facies A) interbedded with rippled-top very fine-grained sandstones (facies D)] is interpreted as the product of background sedimentation alternating with distal storm events in a middle shelf environment. Facies assemblage 3 [normally graded coarse to fine-grained sandstones (facies C); parallel-laminated to low angle cross-stratified sandstones (facies E); hummocky cross-stratified sandstones and siltstones (facies F); interstratified fine-grained sandstones and mudstones (facies G); massive muddy siltstones and sandstones (facies H); tuffaceous sandstones (facies I); and interbedded thin units of massive and parallel-laminated mudstones (facies A)] is thought to represent volcaniclastic mass flow and storm deposition coupled with subordinated suspension fall-out in an inner-shelf to lower-shoreface setting. The Loma del Kil6metro Member records regressive-transgressive sedimentation in a storm- and mass flow-dominated high-gradient shell Volcano-tectonic activity was the important control on shelf morphology, while relative sea-level change influenced sedimentation. The lower part of the succession is attributed to mud blanketing during high stand and volcanic quiescence. Progradation of the inner shelf to lower shoreface facies assemblage in the middle part represents an abrupt basinward shoreline migration. An erosive-based, non-volcaniclastic, turbidite unit at the base of this package suggests a sea level fall. Pyroclastic detritus, andesites, and a non-volcanic terrain were eroded and their detritus was transported basinward and redeposited by sediment gravity flows during the low stand. The local coexistence of juvenile pyroclastic detritus and I Present address: Kansas Geological Survey, 1930 Constant Ave., The University of Kansas, Campus West, 66047 Lawrence, KS, USA. 0037-0738/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSD1 0037-0738(95)00134-4