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HomeMy WebLinkAboutCT 06-16; CARLSBAD BOAT CLUB AND RESORT; TECHNICAL REPORT PALEONTOLOGICAL RESOURCE ASSESSMENT; 2007-03-20TECHNICAL REPORT PALEONTOLOGICAL RESOURCE ASSESSMENT CARLSBAD BOAT CLUB & RESORT CITY OF CARLSBAD SAN DIEGO COUNlY, CALIFORNIA DTTRODUCTION V.I.P. Partners proposes to construct a condominium project at the old Whitney's Landing site (4509 Adams Street) located on the northeastem shore of Aqua Hedionda Lagoon, in the City of Carlshad, San Diego County, Cahfomia (Figure 1). This project wUl require demolition of existing buildings, excavations into the hillside, and construction of a four story condominium building This technical report provides an assessment of issues related to paleontological resources within the project Area of Potential Effect (APE). The purpose of this report is to assist V.I.P. Partners in planning and design efforts for the purposed project as related to paleontological re^tirce issues. Specifically, this report is intended to summarize existing paleontological resource data m the project area and vicinity; assess potential impacts to paleontological resources fix)m construction of the project; and identify mitigation measures to avoid or reduce project-related impacts wherever feasible. Additional discussion of report methodology is provided below. This report was prepared by Thomas A. Demdrd of the Department of PaleoServices at the San Diego Natural History Museum (SDNHM), San Diego, California. As defined here, paleontological resources (i.e., fossils) are the remains and/or traces of prehistoric (i.e., 10,000 years or older) plant and animal life excliasive of humans. Fossil remains such as hones, teeth, shells, leaves, and wood are fPund in the geologic deposits (rock formations) within which they were originaUy buried. For the purposes of this report, paleontological resources can he thought of as including not only the actual fossil remains but also the collecting locahties and the geologic formations containing those localities. METHODOLOGY A review was conducted of relevant published geologic reports (Wilson, 1972; Tan and Keimedy, 1996), unpublished paleontological reports (Demdrd and Walsh, 1993), and miiseum paleontological locality data (SDNHM, Department of Paleontology; University of California, Museum of Paleontology). This ^jproach was followed in recognition of the direct relationship between paleontological resources and the geologic formations within which they are entombed. Knowing the geology of a particular area and the fossil productivity of formations that occur in that area, it is possible to predict where fossils will, or will not, he encountered. RECEIVEO MAR 2 0 20O7 ' CITY OF CARLSBAD PLANNING DEPT A walkover field survey of the project APE and immediately surrounding areas was conducted on 8 February 2007 by SDNHM personnel to determine the paleontological resource sensitivity of the geologic units that will be affected by the proposed improvements. This work involved inspection of the site for bedrock outcrops, geologic contacts, and the presence of paleontological resources (i.e., fossils). ■■on Project site eservoir y • ^Vl — ^_SubSla Tanks \y^ .-65Watc Tan SOOm lOOOtn Figure 1, Index map showing location of the Carlsbad Boat Club and Resort project site. Base map; San Luis Rey, CA 7.5' USGS topographic quadrangle. EXISTING CONPITIONS PHYSICAL GEOLOGICAL SETTING The project APE is underlain by geologic deposits mapped as the Eocene-age Santiago Formation by Wilson (1972) and Tan and Kennedy (1996). In addition, during the field survey geologic deposits referable to a Pleistocene-age marine terrace (probably Bay Point Formation) were observed on an adjacent lot to the west of the project site. The depositional contact between the Pleistocene and Eocene age deposits occurs at approximately elevation 27 feet and it is hkely that the Pleistocene deposits extend onto the project site. PALEONTOLOGICAL RESOURCE ASSESSMENT The following section provides a general overview of the types of geologic deposits located within or immediately adjacent to the project APE. Pleistocene marine terrace deposits Introduction: The upper portions of the project area (above approximately elevation 27 feet) are underlain by red-brown, poorly sorted, medium- to very coarse-grained, compact sandstone with local stringers and thin beds of pebble to cobble conglomerate. These strata closely resemble Pleistocene marine terrace deposits mapped by Tan and Kennedy (1996) on the south side of Aqua Hedionda Lagoon. As discussed by Eisenberg (1985) the Pleistocene marine terrace deposits in the Carlsbad and Oceanside area accumulated on a stair step series of elevated marine abrasion platforms (i.e., sea floors) which formed as a result of past periods of sea level fluctuation caused by episodes of global warming and cooHng. Paleontology: Fossils locally occur in the Pleistocene marine terrace deposits exposed in Carlsbad and Oceanside and consist primarily of weU-preserved shells and tests of nearshore marine invertebrates (e.g., clams, oysters, scallops, snails, crabs, sea urchins, and sand dollars). Sparse remains of marine vertebrates (e.g., sharks, rays, and bony fish) have also been recovered fiem these deposits. These fossils are significant and serve to document the location and faunal composition of Pleistocene marine paleoenvironments in northem San Diego County. The geologic age of these deposits ranges fiem approximately 120,000 to 300,000 years old. Site Specific Assessment: There are no previous records of fossil localities occurring within the Pleistocene marine terrace deposits in this area of Carlsbad. However, there are recorded paleontologjcal collecting sites in correlative deposits as exposed to the north and south of the project area. Because of these previoiis records, and following the paleontological guidelines developed by the County of San Diego, these marine terrace deposits are assigned a moderate paleontological resource sensitivity rating. Santiago Formation Introduction: The Santiago Formation was named by Woodring and Popenoe (1945) for a sequence of Eocene strata exjposed in the Santa Ana Mountains of Orange County. The Eocene strata of northwestem San Diego County have generally been assigned to the Santiago Formation (Wilson, 1972) rather than to the La JoUa or Poway groups of southwestern San Diego County because the sequence of distinctive conglomerates that serves to divide and define formations of these latter groups does not occur in northwestem San Diego County. As recognized here, the Santiago Formation is broadly correlative with almost the entire middle Eocene stratigraphie sequence at San Diego (Ardath Shale through Pomerado Conglomerate), approximately 40-49 Ma. Wilson (1972) recognized three members of the Santiago Formation in the Encinitas-Carlsbad area, referring to them as members "A", "B", and "C" in ascending order. Member "C" is composed predominantly of fine- to very coarse-grained, white to gray-vriiite, fiiable, eross-bedded, arkosic sandstone with interbeds of green to green-brown siltstone, silty mudstone, and clayston6" (Wilson, 1972). Member "B" consists largely of green and gray, very fine- to medium-grained, arkosic sandstone, with common calcite-cemented concretions and firequent interbeds of multicolored clayey sandstone and claystone (Wilson, 1972). Member "A" generally consists of green, unfossUiferous, massive mudstone (Wilson, 1972). The Eocene sedimentary rocks exposed in the project area are assigned to Member "C" of the Santiago Formation based on their coarse-grained, arkosic lithology. Paleontology: Member "C" of the Santiago Formation has produced abundant vertebrate fossils fi^m several districts including Carlsbad, Oceanside, and Camp Pendleton Marine Corps Base (Golz and LiUegraven, 1977; Walsh, 1991). Fossils collected firom this upper unit include well-preserved remains of turtles, snakes, lizards, crocodiles, birds, and mammals (e.g., opossums, insectivores, primates, rodents, brontotheres, tapirs, protoreodonts, and other early artiodactyls). The mammal assemblages are especially significant because of their great feunal diversity and excellent specimen preservatioiL These fossils, together with contemporaneous mammal fossils fi-om the Poway Groiip make the Eocene deposits of San Diego County among the most significant in North America. Also recovered fix)m Member "C" deposits are remains of various types of marine organisms including calcareous nannoplankton (Bukry, 1991) and moUusks (Dem&d and Boettcher, 1985; Wilson, 1972). Member "B" has produced well-preserved vertebrate fossils fixjm several localities in Carlsbad and Oceanside (Walsh, 1991). Fossils collected fi:om this member include remains of opossums, insectivores, primates, rodents, brontothere, rhinoceros, and uintathere. Also recovered fix)m Member "B" deposits are remains of various types of marine and estuarine molluscs (Wilson, 1972). Member "A" has yet to produce any fossils, but the discovery of any diagnostic fossils in this rock unit would be of great importance in resolving the age and stratigr^hic relations of the Santiago Formation. Site Specific Assessment: There are numerous recorded fossil collecting sites fix)m the Santiago Formation located east and northeast of the projeet site. These sites were collected diiring the early 1970s by paleontologists and students from University of California campuses at Berkeley and Riverside. The collecting sites were exposed by mass grading operations for the Laguna Riviera residential development and produced very significant and well-preserved remains of terrestrial reptiles and mammals. Because of these previous records, and foUowing the paleontological guidelines developed by the County of San Diego, the Santiago Formation is assigned a high paleontological resource sensitivity rating. IMPACT ANALYSIS INTRODUCTION Direct impacts to paleontological resources occur when earthwork activities, such as mass grading operations, cut into the geological deposits (formations) within which fossils are buried. These direct impacts are in the form of physical destruction of fossil remains. Since fossils are the remains of prehistoric animal and plant life they are considered to be nonrenewable. Such impacts can be significant and, under CEQA guidelines, reqiiire mitigation. Impacts to paleontological resources are typically rated from high to zero dependingupon the resource sensitivity of impacted formations. High significance Impacts to high sensitivity formations (Santiago Formation). Moderate significance Impacts to moderate sensitivity formations (marine terrace deposits). Low significance Impacts to low sensitivity formations. Zero significance Impacts to formations with no fossil potential. SITE SPECIFIC IMPACTS Pleistocene marine terrace deposits Construction drawings for the proposed project indicate an extensive excavation into the eidsting slope. This excavation will almost certainly impact potentially fossil-bearing strata of the Pleistocene marine terrace deposits. These potential negative impacts to paleontological resources can be reduced to below the level of significance through implementation of the mitigation plan as outlined below. Santiago Formation Construction plans for the proposed project indicate an extensive excavation into the existing slope. This excavation will almost certainly impact potentially fossil-bearing strata of the Santiago Formation. These potential negative impacts to paleontological resources can be reduced to below the level of significance through implementation of the mitigation plan as outlined below. MITIGATION MEASURES 1. A qualified paleontologist should attend the pre-construction meeting to consult with the grading and excavation contractors concerning excavation schedules, paleontological field techniques, and safety issues. (A qualified paleontologist is defined as an individual with a MS or Ph.D. in paleontology or geology that is familiar with paleontological procedures and techniques, who is knowledgeable in the geology and paleontology of San Diego County, and who has worked as a paleontological mitigation project supervisor in the coimty for at least one year.) 2. A paleontological monitor should be on-site on a fuU-time basis during the original cutting of previously undisturbed deposits of high paleontological resource potential (Santiago Formation) to inspect exposures for contained fossils. Grading activities in previously undisturbed deposits of moderate paleontological resource potential (Pleistocene marine terrace deposits) should be monitored on a part-time basis. (A paleontological monitor is defined as an individual who has experience in the collection and salvage of fossil materials. The paleontological monitor should work under the direction of a qualified paleontologist) 3. When fossils are discovered, the paleontologist (or paleontological monitor) should recover them. In most cases this fossil salvage can be completed in a short period of time- However, some fossil specimens (such as a complete large mammal skeleton) may require an extended salvage period. In these instances the paleontologist (or paleontological monitor) should be allowed to temporarily direct, divert, or halt grading to allow recovery of fossil remains iu a timely manner. Because of the potential for the recovering of small fossil remains, such as isolated mammal teeth, it may be necessary to set up a screen-washing operation on the site. 4. Fossil remains collected during monitoring and salvage should be cleaned, repaired, sorted, and cataloged as part of the mitigation program. 5. Prepared fossils, along with copies of aU pertinent field notes, photos, and m^s, should be deposited (as a donation) in a scientific institution with permanent paleontological collections such as the San Diego Natural History Museum. Donation of the fossils should be accompanied by financial support for initial specimen storage. 6. A jSnal summary report should be completed that outlines the results of the mitigation program. This report should include discussions of the methods used, stratigraphic section(s) exposed, fossils collected, and significance of recovered fossils. REFERENCES Bukry, D. 1991. Transoceanic correlation of Middle Eocene coccoUth Subzone CP 14a at Batiquitos Lagoon, San Diego Comty. ^ P.L. Abbott and J.A. May (eds.). Eocene Geologic History, San Diego Region. Society of Economic Paleontologists and Mineralogists, Pacific Section 68:189-194. Demdrd, T.A., and R.S. Boettcher. 1985. Paleontology and biostratigraphy of middle Eocene nearshore marine sedimentary rocks, Leucadia, San Diego Coimty, Cahfomia. P.L. Abbott (ed.). On the Manner of Deposition of the Eocene Strata in Northern San Diego County. San Diego Association of Geologists, fieldtrip guidebook, pp. 49-53. Demdrd, T. A. and S. L. Walsh, 1993. Paleontological Resources, Coimty of San Diego. Prepared for the San Diego Planning Commission, pp. 1-68. Eisenberg, L.I. 1985. Pleistocene faults and marine terraces, northern San Diego County. Tn, P.L. Abbott (ed.). On the Manner of Deposition of the Eocene Strata in Northem San Diego County. San Diego Association of Geologists, fieldtrip guidebook, pp. 87-91. Golz, D.J., and J.A. LiUegraven. 1977. Summary of known occurrences of terrestrial vertebrates from Eocene strata of southern California University of Wyoming, Contributions to Geology 15:43-65. Tan, S.S., and Kennedy, M.P., 1996. Geologic m^s of the northwestern part of San Diego, California California Division of Mines and Geology Open-File Report 96-02,2 sheets (scale 1:24,000). Walsh, S.L. 1991b. Eocene mammal faunas of San Diego County. In, P.L. Abbott and J.A. May (eds.). Eocene Geologic History San Diego Region. Society of Economic Mineralogists and Paleontologists, Pacific Section 68:161-178. Wilson, K.L. 1972. Eocene and related geology of a portion of the San Luis Rey and Encinitas quadrangles, San Diego County, California Unpubhshed M.A. thesis. University of California, Riverside, 135 p. Woodring, W.P., and Popenoe, W.P. 1945. Paleocene and Eocene stratigr^hy of northwestern Santa Ana Mountains, Orange County, California U. S. Geological Survey Oil and Gas Investigations Preliminary Chart 12.