assignments can be evaluated by comparison with radiochemical age assignments and late Pleistocene temperature histories inferred from one or more paleoclimatic records. The kinetic model ages can also be evaluated within the constraints of both eustatic sea-level and isotopic ice-volume records. Age assignments for many of the late Pleistocene localities investigated in this work are in the range of 100,000 to 140,000 years and these localities are correlated with the early part of Stage 5 of the marine isotopic record (Shackleton and Opdyke, 1973). These age assignments are, in all cases, consistent with the radiometric age assignments for" the calibration localities. Samples from high terraces on San Nicolas Island, Palos Verdes Hills, and San Joaquin Hills, and from the San Pedro Sand have kinetic model ages of between 350,000 and 550,000 years and appear correlative with all or part of Stages 9 and II of the marine isotopic record. Three low terrace localities in southern California have yielded samples with ages in the range 200,000 to 250,000 years (correlative with Stage 7 of the marine isotopic record), though previous interpretations of these localities had implied correlation with localities that are sho~~to be younger. Some of these older samples may have been reworked into younger deposits. Localities with late Stage 5 (80,000 to 100,000 yrs.) ages are found at Santa Cruz, California and on Point Loma, San Diego, California (the Bird Rock Terrace). Both radiometric and geologic information are consistent with these age assignments. Samples from Cape Blanco, Oregon, appear to be either lateor post-Stage 5 in age; samples from Goleta, California are definitely post-Stage 5 in age, and appear to be approximately 40,000 years in age. iii Several of these age assignments permit revisions in the interpretation of pre-existing paleoecologic data. In addition, long-term average uplift rates for each dated locality can be estimated: most of the Stage 5 localities reported herein have apparent uplift rates between .1 and .3 meters/lOOO yrs. Uplift rates of .15 to .75 meters/IOOO yrs. are inferred from the results for San Nicolas Island and the Palos Verdes Hills. Quite. rapid uplift rates of 1.5 to 2.75 meters/IOOO yrs. for Goleta and Cape Blanco are also inferred from our results.
The Santa Ana Mountains expose one of the most complete strati• graphic sections in coastal southern California, and much of the section contains distinctive rocks and diagnostic fossils. The section includes a basement complex of crystalline and semicrystalline rocks of Mesozoic age, unconformably overlain by as much as 5,200 m of Upper Cretaceous and Cenozoic clastic strata ranging in composition from organic shale to boulder conglomerate. The basement consists of the marine clastic Bedford Canyon Formation of Middle Jurassic age and is perhaps 5,500 m thick; the Upper Jurassic(?) and Lower(?) Cretaceous Santiago Peak Volcanics, 790 m thick; and extensive middle Cretaceous quartz plutonite bodies. The superjacent sedimentary deposits are mostly marine and of Late Cretaceous, Paleocene, Eocene, Miocene. Pliocene, and Pleistocene age. In addition, nonmarine units interfinger with marine, especially just above major unconformities. The northeastern, highest part of the Santa Ana Mountains is a sharply folded anticline, plunging northwest and having a downfaulted, narrow northeast limb and a similarly truncated nose. The downthrow to the north, on the Whittier fault zone, is variable, with an apparent stratigraphic separation of about 900 m. That to the northeast, on the Elsinore fault zone, may be slightly greater. The low western parts of the mountains are underlain by rocks that are only moderately folded, broken by numerous northwest-to north-trending normal faults. A complex, horstlike positive structure extends east-west along lower Santiago Creek. The broad Lorna Ridge syncline farther south underlies !lluch of the southern part of the mapped area. At the west edge of the mountains, the post-middle Miocene formations thicken slightly westward toward the subsiding Los Angeles basin, though both thickening and subsidence reverse directions in the subsurface anticlinal Anaheim nose, 5 or 6 km west of the mountains. The geologic map, structure sections, and supporting data show that the geologic record of the northern Santa Ana Mountains characterizes that of the northern Peninsular Ranges, including the San Joaquin Hills to the south and southwest, the Los Angles basin to the west, the Puente Hills to the north, and the Perris Block to the east. Thus, the mountains furnish evidence of regional significance: the boundary between basement and superjacent sedimentary rocks is of Early or middle Cretaceous age; northeastward transgression of Paleocene strata onto successively older units records an early Tertiary southwestward tilt of the mountain mass, and northward and eastward onlap of successively younger strata onto the basement surface is interptreted as additional evidence of an extensive, persistent early Tertiary peneplain; the tilting of the mountain mass and associated deformation continued to middle Miocene time, when relative depression of the Los Angeles basin began; and continuing deformation produced pronounced erosional unconformities in upper Miocene, Pliocene, and upper Pleistocene strata. TABLE ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.