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Please join us for a grad student seminar this Friday Sept 22 at 3:30 pm in rm 155 Geology presented by Lindsey Wesolowski, MSc candidate

Posted on 2017-09-18 in Events
Sep 22, 2017

Please join us for a grad student seminar this Friday Sept 22 at 3:30 pm in rm 155 Geology presented by Lindsey Wesolowski, MSc candidate:

TRACE FOSSILS, SEDIMENTARY FACIES AND PARASEQUENCE ARCHITECTURE FROM THE LOWER CRETACEOUS MULICHINCO FORMATION OF ARGENTINA: THE ROLE OF FAIR-WEATHER WAVES IN SHOREFACE DEPOSITS

Wesolowski, L.J. a, Buatois, L.A. a, Mángano, M.G. a, Ponce, J.J. b, and N.B. Carmona b

a Department of Geological Sciences, University of Saskatchewan, Saskatoon, Canada S7N 5E2

b CONICET, Instituto de Investigación en Paleobiología y Geología, Universidad Nacional de Rio Negro, General Roca. 8332, Rio Negro, Argentina

ABSTRACT

Shorefaces can display strong facies variability and integration of sedimentology and ichnology provides a high-resolution model to identify variations among storm-dominated, storm-influenced and weakly storm-affected deposits. In addition, ichnology can be used to help delineate parasequences as trace-fossil associations are excellent indicators of environmental conditions that typically change along the depositional profile. Shallow-marine deposits and associated ichnofaunas from the Mulichinco Formation (Valanginian, Lower Cretaceous) in Puerta Curaco within the Neuquén Basin of western Argentina, were analyzed to evaluate stress factors on shoreface benthos and parasequence architecture.

Four distinct types of parasequences were recognized; storm-dominated, weakly storm-affected, and storm-influenced 1 and 2, categorized based on parasequence architectural variability derived from varying degrees of storm influence within the offshore transition and lower shoreface. During storm-dominated conditions, the Skolithos Ichnofacies prevails within the offshore transition and lower shoreface represented by an ichnoassemblage dominated by Thalassinoides isp., and Ophiomorpha annulata. Under weakly storm-affected conditions, the Cruziana Ichnofacies is recognized, characterized by an ichnoassemblage dominated by Thalassinoides isp. and Gyrochorte comosa in the offshore transition, and by Gyrochorte comosa within the lower shoreface. Storm-influenced conditions yield a wider ichnologic variability, showing elements of both ichnofacies, underscoring the importance of fair-weather waves.

Storm influence on sedimentation is affected by both allogenic (e.g. tectonic subsidence, sea-level, and sediment influx) and autogenic (e.g. hydrodynamic) controls at both parasequence and intra-parasequence scales. Autogenically induced deltaic lobe switching facilitated reworking by wave and longshore currents, resulting in weakly storm-affected shorefaces sheltered by the alongshore barriers. This type of shoreface, commonly overlooked in past literature, expands our understanding of the sedimentary dynamics and stratigraphic architecture in a shoreface highly prone to various parasequence and intra-parasequence scale degrees of storm influence.

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