Annually-resolved Sedimentation of the Middle Miocene Clarkia Lake Deposit (USA)

Abstract

Lacustrine varved sediments are high-resolution paleoenvironmental archives, in which their layers function as temporal markers of seasonality. The temporal framework of such records is required to improve benchmark climate models because they offer snapshots of past climate systems within annual to millennial timescales. The middle Miocene Clarkia Lake Deposit (Idado, USA) is a plant fossil Lagerstätte containing varve-like sediments deposited during the Miocene Climate Optimum, a phase of global warming and carbon cycle perturbation at ca. 16 million years ago. Despite being extensively studied in the past decades, its absolute age and temporal relationship with the Columbia River Flood Basalt, and the causes of the varves remained elusive. This study presents the first tephra- derived U-Pb zircon ages for the Clarkia Lake Deposit and an age model based on spectral analysis of elemental and color distribution of the sediments obtained via micro X-Ray fluorescence. The results show that the Clarkia Lake Deposit (1) is dated at 15.78 ± 0.03 Ma, after the most intense eruption phases of the Columbia River Flood Basalt Group; and (2) represents ~840 varve-years. These stratigraphic relationships highlight the Clarkia Lake Deposit as a high-resolution archive of the Miocene Climate Optimum, in a greenhouse world that may be employed as an analog for modeling future Earth’s climate.