Search for: All records

Miocene strata of the Claremont, Orinda, and Moraga formations of the Berkeley Hills (California Coast Ranges, USA) record sedimentation and volcanism during the passage of the Mendocino triple junction and early evolution of the San Andreas fault system. Detrital zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) age spectra indicate a change in sedimentary provenance between the marine Claremont formation (Monterey Group) and the terrestrial Orinda and Moraga Formations associated with uplift of Franciscan Complex lithologies. A sandstone from the Claremont formation produced a detrital zircon chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) maximum depositional age of 13.298 ± 0.046 Ma, indicating younger Claremont deposition than previously interpreted. A trachydacite tuff clast within the uppermost Orinda Formation yielded a CA-ID-TIMS U-Pb zircon date of 10.094 ± 0.018 Ma, and a dacitic tuff within the Moraga Formation produced a CA-ID-TIMS U-Pb zircon date of 9.974 ± 0.014 Ma. These results indicate rapid progression from subsidence in which deep-water siliceous sediments of the Claremont formation were deposited to uplift that was followed by subsidence during deposition of terrestrial sediments of the Orinda Formation and subsequent eruption of the Moraga Formation volcanics. We associate the Orinda tuff clast and Moraga volcanics with slab-gap volcanism that followed the passage of the Mendocino triple junction. Given the necessary time lag between triple junction passage and the removal of the slab that led to this volcanism, subsidence associated with ca. 13 Ma Claremont sedimentation and subsequent Orinda to Moraga deposition can be attributed to basin formation along the newly arrived transform boundary. 

This repository has code and data associated with research on the Miocene stratigraphy of the Berkeley Hills associated with the manuscript: Chronostratigraphy of Miocene strata in the Berkeley Hills (California Coast Range, USA) and the arrival of the San Andreas transform boundary Stacey H. Gerasimov, Eben B. Hodgin, James L. Crowley, Nicholas L. Swanson-Hysell The code folder contains Jupyter notebooks that utilize a Python kernel to visualize and analyze the data. TAS_plot.ipynb: plots the total alkali vs silica composition of samples composite_pystrat.ipynb: generates the composite stratigraphic column thicknesses date_bar_plots.ipynb: makes the date bar plots of CA-ID-TIMS U-Pb dates detrital_zircon_analysis.ipynb: conducts statistical analyses and generates visualizations of detrital zircon data from this study and others that are integrated for comparison