--> Timing and duration of the Late Ordovician glaciation using the Ely Springs Dolomite of east-central California

AAPG Pacific Section Convention, 2020 Vision: Producing the Future:

Datapages, Inc.Print this page

Timing and duration of the Late Ordovician glaciation using the Ely Springs Dolomite of east-central California

Abstract

The Late Ordovician is characterized by an anomalous glacial episode that caused profound changes in global climate and oceanic circulation, and led to a mass extinction. Although the Late Ordovician glaciation is well recognized, the timing/extent of glaciation is poorly understood, with two competing hypotheses: 1) the Late-Ordovician glaciation was short-lived (<1 myr) and limited to the Hirnantian (e.g., Brenchly et. al., 1994); or, 2) the Late Ordovician glaciation was long-lived (up to 17 myr) and began perhaps as early as the Sandbian (early Late Ordovician) (e.g., Saltzman and Young, 2005). The goal of this study is to constrain the duration of the Late Ordovician glaciation by examining the Upper Ordovician - Lower Silurian Ely Springs Dolomite at 2 localities from east-central California: the Nopah Range and the Hard Scramble Nose (Talc City Hills). Overall, sequence stratigraphic and petrographic evidence points to a short-lived glaciation, based on the presence of small scale (1 m -10 m), high frequency, autocyclic sea level fluctuations prior to and after the Hirnantian glaciation, along with the presence of photozoan (warm water) carbonate assemblages throughout the lower and upper members of the Ely Springs Dolomite. Carbon isotope data and paleokarst reveal that the middle member of the Ely Springs Dolomite is absent from both localities, which reflects extensive drawdown of sea levels (10 m - 50 m) during the glaciation, which is constrained to the Hirnantian. Increasing Ba levels across the lower member reflect heightened levels of upwelling – driven productivity as expanding Gondwanan ice sheets invigorated ocean circulation.