P. A. Lindberg | Geology Reports

USGS2008

Geologic map of the Prescott National Forest and the headwaters of the Verde River, Yavapai and Coconino Counties, Arizona

This 1:100,000-scale digital geologic map details the complex Early Proterozoic metavolcanic and plutonic basement of north-central Arizona; shows the mildly deformed cover of Paleozoic rocks; reveals where Laramide to mid-Tertiary plutonic rocks associated with base- and precious-metals deposits are exposed; subdivides the Tertiary volcanic rocks according to chemically named units; and maps the Pliocene to Miocene fill of major basins. Associated digital files include more than 1,300 geochemical analyses of all rock units; 1,750 logs of water wells deeper than 300 feet; and interpreted logs of 300 wells that define the depth to basement in major basins. Geophysically interpreted buried features include normal faults defining previous unknown basins, mid-Tertiary intrusive rocks, and half-grabens within shallow bains.

Arizona↗

USGS2007

Suboxic deep seawater in the late Paleoproterozoic: Evidence from hematitic chert and iron formation related to seafloor-hydrothermal sulfide deposits, central Arizona, USA

A current model for the evolution of Proterozoic deep seawater composition involves a change from anoxic sulfide-free to sulfidic conditions 1.8??Ga. In an earlier model the deep ocean became oxic at that time. Both models are based on the secular distribution of banded iron formation (BIF) in shallow marine sequences. We here present a new model based on rare earth elements, especially redox-sensitive Ce, in hydrothermal silica-iron oxide sediments from deeper-water, open-marine settings related to volcanogenic massive sulfide (VMS) deposits. In contrast to Archean, Paleozoic, and modern hydrothermal iron oxide sediments, 1.74 to 1.71??Ga hematitic chert (jasper) and iron formation in central Arizona, USA, show moderate positive to small negative Ce anomalies, suggesting that the redox state of the deep ocean then was at a transitional, suboxic state with low concentrations of dissolved O2 but no H2S. The presence of jasper and/or iron formation related to VMS deposits in other volcanosedimentary sequences ca. 1.79-1.69??Ga, 1.40??Ga, and 1.24??Ga also reflects oxygenated and not sulfidic deep ocean waters during these time periods. Suboxic conditions in the deep ocean are consistent with the lack of shallow-marine BIF ??? 1.8 to 0.8??Ga, and likely limited nutrient concentrations in seawater and, consequently, may have constrained biological evolution. ?? 2006 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗