Upcoming Meetings
Future Meetings
- May 23, 2026 Hike & Brew @ Clark Regional Park and Fullerton Brew Co.
- June 6, 2026 Geology Hike @ Little Corona del Mar Beach with Dr. Rick Behl and LABGS, Newport Beach
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June 10, 2026 @ Joint meeting with SDAG at El Adobe restaurant in San Juan Capistrano
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July 6, 2026 @ Online
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Aug 3, 2026 @ Orange Coast College Costa Mesa, CA
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Aug 31, 2026 @ Dave & Busters, Orange, CA 92868
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Nov 2, 2026 @ Dave & Busters, Orange, CA 92868
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Dec 1, 2026 @ TBA
SCGS September Meeting
Monday, November 2 at 6:00 PM
South Coast Geological Society invites you to attend our November 2026 meeting and lecture!
Dave & Busters
20 City Blvd W, Orange, CA 92868
Eleanora (Norrie) Robbins, PhD., will present her project: Origin of San Diego Terrace Redbeds–Pigmentation by Chembiotic Oxidation of Detrital Magnetite in Red Brown Pleistocene Terrace Sandstones, Southern Calif
Abstract: Along the coastline of San Diego County are 20 named Pleistocene marine terraces. Red brown Pleistocene sandstone overlies them all. These colorful uplifted sandstones are mapped as “paralic,” being former beaches. Analyzed microscopically for this research were the accessible red brown terrace sandstones, and for comparison, sediments from modern beaches and rivers. Soil concretions were collected and analyzed from 10 terraces including that at Crystal Cove. And the weathering of magnetite-bearing rocks in the modern watersheds was addressed.
All of these Pleistocene sandstones and modern sediments contained magnetite, ilmenite, quartz, and other accessory minerals. Transmitted and reflected light microscopy revealed that most magnetite grains in the sandstones were coated with the iron oxide minerals goethite and lepidocrocite. Ilmenite grains were often coated with leucoxene. Quartz grains were coated with goethite, ferrihydrite, and Mn oxide minerals; crystalline hematite was present but rare.
My geomicrobiology study focused primarily on the microbial communities colonizing the quartz grains and catalyzing the precipitation of the Fe- and Mn-oxide minerals. Some of the bacteria that create these oxide biofilms are quite distinct microscopically (Leptothrix discophora holdfasts, Siderocapsa-like capsules). Others are iron-oxide coated undistinguished rods, coccobacilli, and cocci.
The sequence, timing, and post depositional environments that produced these pigmenting minerals are not obvious and need study. Weathering/oxidation was needed to produce the minerals coating magnetite; reduction and then oxidation were needed for the bacteria producing biofilms on quartz; and dehydration with salinity or burial was needed to from hematite.
Miller and Folk (my hero!) reported in 1955 that all redbeds contain detrital magnetite and ilmenite. My study shows that they were spot on for the Pleistocene redbeds in San Diego County
Speaker Information:
Eleanora (Norrie) Robbins is an economic geologist, palynologist (fossil pollen grains), and geomicrobiologist. Her degrees are from Ohio State, Univ. Arizona, and Penn State. Her work life included two years with the Geological Survey of Tanzania as a Peace Corps Volunteer in Dodoma, 34 years with the USGS (DC, Denver, and Reston), and 15 years as adjunct faculty at SDSU in the Dept. of Geological Sciences. Now she is retired in Irvine and trying to learn the local geology.
Please Register by November 2 at 5 PM