Biostratigraphy and paleoenvironmental reconstruction of the marine lower Miocene Chechiș Formation in the Transylvanian Basin based on foraminiferal assemblages

Abstract

Planktonic and benthic foraminiferal assemblages were used for biostratigraphy and paleoenvironmental reconstruction of the marine lower Miocene Chechiș Formation from the Gălpâia section (Sălaj county, Romania) in the northwestern Transylvanian Basin. Planktonic foraminifera suggest an Eggenburgian (Burdigalian) age for the deposits studied and reveal episodes of high primary productivity and mostly cool surface waters. Benthic foraminiferal assemblages indicate paleoenvironmental deepening from outer shelf to upper bathyal settings. Deltaic influences may be observed at the base of the studied section in outer shelf (possibly upper bathyal) environments with oxygenated bottom water and episodic high primary productivity, as a consequence of nutrient input from the land. Changes in paleobathymetry resulted in reduction of primary productivity. The benthic assemblages from the uppermost part of the section are dominated by tubular agglutinated foraminifera and indicate an upper bathyal setting with low organic flux to the sea floor. The sediments of the studied section were deposited during the late stage of the first early Miocene relative sea-level rise in the Transylvanian Basin.