Development of the early Carnian deepening upward sequence of the Huglu Unit within the tectonic slices/blocks of the Mersin Mélange, southern Turkey: Biochronologies, geochemistry of volcaniclastics and palaeogeographic implications

Abstract

The Mersin Ophiolitic Complex in southern Turkey includes two different units; the Mersin Mélange (MM) and Mersin Ophiolite with a metamorphic sole. Within the MM the Tavuscayiri megablock exposes in the Kilin section the Carnian Tavuscaryiri Formation with an alternation of conglomerates and sandstones at the base, followed by sandy limestones and thick-bedded to massive limestones overlain by volcanoclastics of the Huglu Tuffites. This succession is interpreted as a deepening upward sequence from fluvial to pelagic marine conditions. We present a new interdisciplinary study with focus on biochronology and geochemistry in order to elucidate the stratigraphy and palaeogeographic history of this succession. We discuss the potential impact of the Huglu volcanism on the Late Triassic climate shift, the Carnian Pluvial Event (CPE). The biochronology based on palynomorphs, ammonoids, conodonts, radiolaria and ostracods indicate that the drowning of the platform took place within <2 Ma of the Early Carnian. The Huglu Tuffites include subalkaline felsic vitric tuffs and tuffites. These volcaniclastics are highly rich in Th and display prominent negative anomalies. These features suggest their subduction-related origin. Our data suggest that the oceanic Sorgun Arc and the northern margin of the Gondwanan Tauride-Anatolide Platform (TAP) were under extension owing to back-arc rifting in the Late Triassic. The Huglu Tuffites were deposited in prograding deepening rifted back-arc basin nearby the oceanic-continent transition. While the subduction-related basalts with depleted geochemical signatures were erupted in the rifted Sorgun Arc, the continuum of these back-arc rifting at the northern edge of the TAP culminated in the voluminous volcanic activity of the Huglu Tuffites during the late Early to Late Carnian. The new biochronological findings show that the main volcanic activity correlates with the beginning of the CPE and therefore may represent an important trigger for this climate event. © 2023