Kings Sequence and Calaveras Complex Rocks of the Southern Lake Kaweah Roof Pendant, Tulare County, California
Strongly deformed metasedimentary rocks of Paleozoic and Mesozoic age are found in the numerous roof pendants of the central and southwestern Sierra Nevada and, further north, in the Western Metamorphic Belt. Age, paleoenvironmental conditions, and geographic location at the time of deposition for these rocks provide essential input for reconstructions of the complex series of tectonic events that have produced the forearc basement and metamorphic framework for the Cretaceous Sierra Nevada arc. A dam spillway excavated through the southern end of the Lake Kaweah roof pendant, supplemented with nearby road cuts and natural outcrops, provides data regarding these three factors. Detrital zircon data provides a maximum depositional age constraint of ~165 Ma for rocks interpreted as Kings Sequence turbidites. The metaturbidites overlie metamorphosed ribbon chert and argillite beds (chert-argillite) interpreted as Calaveras Complex marine deposits. The latter also contains marble lenses similar to those in nearby pendants that have generally been interpreted as olistoliths, in part because chert-argillites devoid of carbonates are thought to form below the carbon compensation depth. The marble lenses found at this site are surrounded by calc-silicate rocks, and several calc-silicate layers of 5 to 15 m in thickness are found within the metachert unit. Well exposed contacts of these calc-silicate beds with the chert-argillite units display possible inconsistencies with an olistostrome interpretation. If the carbonates now found within the chert-argillite units were all originally deposited as sediment upon a marine basin floor, variations in environmental conditions such as a fluctuating carbon compensation depth may be represented at this location. Such changes could perhaps be produced, for example, by shifts in prevailing oceanic currents, seafloor uplift and subsidence, or a combination of these factors. Results of detrital zircon statistical analysis, petrological analysis, whole rock chemistry and field relations will be presented to help support the interpretations.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California