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

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

General Roca

Congreso; REUNIÓN DE COMUNICACIONES DE LA ASOCIACIÓN PALEONTOLÓGICA ARGENTINA; 2023

APA

We report the first occurrence of Acruliammina longa from the upper Hauterivian marine sediments in the Neuquén Basin (Argentina) and from South America. Acruliammina longa is an encrusting agglutinated foraminifer, first described as Placopsilina longa from the Grayson Formation (Albian) of the Washita Group (Texas). The known stratigraphic distribution of A. longa ranges from the Valanginian to the lower Turonian?, as suggested by occurrences in several key localities of Europe and North America. It has been recorded from the Valanginian and Hauterivian of the Bohemian Cretaceous Basin and Switzerland, the lower Turonian of the Bohemian Massif (Czech Republic) and France, and the Cretaceous of Texas and Oklahoma. The studied material consists of agglutinated foraminiferal tests encrusted on both valves of Ptychomya koeneni shells and indeterminate bivalve skeletal substrates forming macroids. The collected material was sampled from the upper Hauterivian Crioceratites diamantensis Zone in the Agua de la Mula Member of the Agrio Formation, originating always from the base of high-frequency (6th-order) dilution hemisequences in the Agua de la Mula (AM) and Bajada del Agrio (BA) sections. Encrusting foraminifera on Ptychomya koeneni shells were sampled throughout the first and second 3rd-order regressive systems tracts at the AM and BA sections, whereas foraminifera forming macroids were found along the third 3rd-order transgressive system tract in both sections. Energy dispersive spectroscopy was used to perform chemical element mapping and obtaining X-ray spectra of the main elements composing the agglutinated tests walls. X-ray computed microtomography allowed us to evaluate the distribution of agglutinated foraminifera encrusting macroids without 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), later uncoiled and rectilinear (uniserial) with cylindrical chambers wider than high. The aperture is terminal, rounded, and cribrate. Up to 5 pore openings were observed on the apertural face. This study extend the paleogeographic distribution of A. longa, and investigate the paleoenvironmental and paleoecological significance of this species in the mixed carbonate and siliciclastic depositional setting of the Neuquén Basin. Characterization of the encrusting foraminiferal tests and their position within the 3rd-order sedimentary sequences allowed us to evaluate a possible relationship between paleoenvironmental parameters during the late Hauterivian and behaviors of the encrusting foraminifera (feeding habit, life position, type of agglutinated material) that may have implications in paleoenvironmental reconstructions.