Encrusting agglutinated foraminifera from the Agua de La Mula Member of the Agrio Formation (Neuquén Basin, Argentina)

CARATELLI, MARTINA; CITTON, PAOLO; ARCHUBY, FERNANDO M; PIGNATTI, JOHANNES

General Roca

Otro; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2023

Asociación Paleontológica Argentina

We report the first occurrence of Acruliammina longa from the upper Hauterivian marinesediments in the Neuquén Basin (Argentina) and from South America. Acruliamminalonga is an encrusting agglutinated foraminifer, first described as Placopsilina longa from the Grayson Formation (Albian) of the Washita Group (Texas). The known stratigraphicdistribution of A. longa ranges from the Valanginian to the lower Turonian?, as suggestedby occurrences in several key localities of Europe and North America. It has beenrecorded from the Valanginian and Hauterivian of the Bohemian Cretaceous Basin andSwitzerland, the lower Turonian of the Bohemian Massif (Czech Republic) and France,and the Cretaceous of Texas and Oklahoma. The studied material consists of agglutinatedforaminiferal tests encrusted on both valves of Ptychomya koeneni shells andindeterminate bivalve skeletal substrates forming macroids. The collected material wassampled from the upper Hauterivian Crioceratites diamantensis Zone in the Agua de laMula Member of the Agrio Formation, originating always from the base of highfrequency(6th-order) dilution hemisequences in the Agua de la Mula (AM) and Bajadadel Agrio (BA) sections. Encrusting foraminifera on Ptychomya koeneni shells weresampled throughout the first and second 3rd-order regressive systems tracts at the AMand BA sections, whereas foraminifera forming macroids were found along the third 3rdordertransgressive system tract in both sections. Energy dispersive spectroscopy wasused to perform chemical element mapping and obtaining X-ray spectra of the mainelements composing the agglutinated tests walls. X-ray computed microtomographyallowed us to evaluate the distribution of agglutinated foraminifera encrusting macroidswithout destroy them. Specimens identified as A. longa consist of a multi-chambered test,finely to coarsely agglutinated walls with quartz grains and quartzitic cementing material.The test is attached, at least initially in the enrolled early stage (planispirally coiled), lateruncoiled and rectilinear (uniserial) with cylindrical chambers wider than high. Theaperture is terminal, rounded, and cribrate. Up to 5 pore openings were observed on theapertural face. This study extend the paleogeographic distribution of A. longa, andinvestigate the paleoenvironmental and paleoecological significance of this species in themixed carbonate and siliciclastic depositional setting of the Neuquén Basin.Characterization of the encrusting foraminiferal tests and their position within the 3rdordersedimentary sequences allowed us to evaluate a possible relationship betweenpaleoenvironmental parameters during the late Hauterivian and behaviors of theencrusting foraminifera (feeding habit, life position, type of agglutinated material) thatmay have implications in paleoenvironmental reconstructions.