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Keimedy, 1996), unpublished paleontological reports (Demdrd and Walsh, 1993), and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).
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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.