PaleoBios, Volume 13, Number 50 PRELIMINARY REPORT ON A PALEONTOLOGIC INVESTIGATION OF THE LOWER AND MIDDLE MEMBERS, SESPE FORMATION, SIMI VALLEY LANDFILL, VENTURA COUNTY, CALIFORNIA Thomas S. Kelly1'2, E. Bruce Lander1'2, David P. Whistler1, Mark A. Roeder2, and Robert E. Reynolds3 ABSTRACT A paleontologic investigation employing wet screening and heavy liquid separation of rock samples from the lower and middle members of the continental Sespe Formation at the Simi Valley Landfill, Ventura County, California, is yielding large superposed samples of middle Eocene microvertebrates. This report documents the first records of identifiable mammals ("Peratherium" sp. undet, Sespedectes singularis, Simimys sp. undet.) from the lower member and the first records of Parasauromalus sp. undet; cf. Tinosaurus sp. indet; Paleoxantusia sp., cf. P. allisoni; melanosaurine anguids; cf. Batodonoides powayensis; Centetodon sp., cf. C. aztecus; "Namatomys" sp., cf. "N". fantastna; "Namatomys" n. sp.; Paradjidaumo n. sp.; Heliscomys n. sp.; Simimys n. sp.; Zapodidae?, n. gen. and sp.; Miacis sp. undet; Simimeryx n. sp.; and an indeterminate camelid from the middle member. A new local fauna, the Simi Valley Landfill Local Fauna of middle or late Duchesnean age, is recognized in the middle member, and lies stratigraphically higher than the Pearson Ranch Local Fauna. INTRODUCTION The northern side of Simi Valley, southern California, is well known for its vertebrate- bearing outcrops of the late middle Eocene to late Oligocene nonmarine Sespe Formation (Stock, 1932; Golz, 1976; Golz and Lillegraven, 1977; Lander, 1983; Mason, 1988; Kelly, 1990). During the early 1930's, investigators from the California Institute of Technology (CIT) discovered many fossil vertebrate localities in and near the unnamed canyon between Brea and Alamos Canyons. Since then, additional fossil localities have been recorded in this unnamed canyon by investigators from the Natural History Museum of Los Angeles County (LACM) and University of California Museum of Paleontology (UCMP) (Mason, 1988; Kelly, 1990). The CIT localities in this unnamed canyon are highly significant because they yielded the majority of specimens comprising the late middle Eocene Brea Canyon and Pearson Ranch Local Faunas and produced the type material for many land mammal genera and species (Lander, 1987a; Kelly, 1990). The Simi Valley Landfill now covers most of this unnamed canyon (Fig. 1) and most of the localities in this canyon, including CIT 150,150W, 150.5, 202, 202E, 202W, 207, and 218, have been destroyed by earth- moving activities associated with the landfill operation (Kelly, 1990). However, fossil- bearing beds still exist beyond the landfill excavation and remain productive. In 1987, the Simi Valley Landfill, which is owned by Waste Management of California, Inc., Vertebrate Paleontology Section, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, California 90007 Paleo Environmental Associates, Inc. 7734 Varna Ave., North Hollywood, California 91605 3 Division of Earth Science, San Bernardino County Museum, 2024 Orange Tree Lane, Redlands, California 92374 Page 2 Sespe Formation Kelly et al. Figure 1. Locations of Simi Valley Landfill, unnamed canyon between Brea and Alamos Canyons, and the Canada de la Brea (CDLB) and Strathern Faults. Base map: U.S. Geological Survey. 75 -minute, Simi, California Quadrangle (scale 1:24,000). proposed expanding the landfill to increase its capacity. Lander (1987a) inventoried and noted the importance of the paleontologic resources of the middle member of the Sespe Formation in a technical report in support of the draft environmental impact report prepared by the Ventura County Resource Management Agency (VCRMA, 1987) for the proposed landfill expansion. The report noted that the adverse environmental impacts of the pre-expansion phase of the landfill operation on the paleontological resources of the landfill site were not being mitigated. At the request of the VCRMA, Lander, then with Engineering- Science, Inc., of Pasadena, California, developed and directed an Interim Paleontologic Impact Mitigation Program to reduce these impacts, thereby ensuring compliance by the landfill operation with VCRMA environmental guidelines. This interim phase of the impact mitigation program was conducted at the landfill from August 1987 to June 1989, with Paleo Environmental Associates, Inc., also under the direction of Lander, assuming responsibility for the program in February 1989. The impact mitigation program for the expansion phase began in September 1989 and will run through December 1991. This report presents the results of the interim phase and of the current expansion phase of the impact mitigation program. METHODS Approximately 36 stratigraphically superposed beds, each comprised of sandstone below and claystone above, have been recognized in the middle member of the Sespe Formation at the Simi Valley Landfill (Emcon Associates, 1986; Kelly, 1990). Lander (1987a) noted that fossil remains had been recorded from a number of these beds at and immediately adjacent to the landfill. However, 17 of these beds were not known to have produced any remains. The initial task of the interim phase of the impact mitigation program included the collection of a 68 kg (150 lb) rock sample from each of the latter beds to process for microvertebrate remains. This task was conducted in November 1987 by Lander, Kelly, and Roeder. Processing of the samples and identification of recovered fossil remains were conducted by Whistler and Kelly. Beds found to be productive were sampled more intensively later in the program. The remainder of the interim phase of the program and the first 12 months of the expansion phase of the program consisted of sampling productive beds, including those identified as productive during the initial task of the interim phase, and beds in the lower member near the landfill entrance. Sampling consisted of collecting at least 68 kg (150 lb) of rock from a particular bed. However, samples as large as 21,491 kg (9,768 lb) were collected from beds in critical stratigraphic intervals. Collecting and wet screening of rock samples were conducted by Roeder and his assistants at the landfill. Final processing of most of these samples was conducted at the LACM; Reynolds processed some samples at the San Bernardino County Museum (SBCM). Each rock sample was broken down by soaking in water and then wet screened in water to remove the fine (clay) fraction. The remaining coarse fraction, a clean concentrate consisting of sand and small fossil remains, represented approximately a 97% reduction in Kelly et al. Sespe Formation Page 3 volume of the rock sample. At the LACM and SBCM, the fossil remains in the coarse fraction were further concentrated using a flotation process that employs a heavy liquid (sodium polytungstate or zinc bromide). The final concentrate, which represented another 90% reduction in volume, was then picked by hand under a 20-power microscope to remove identifiable bones and teeth. Identifiable remains were then curated and accessioned into the LACM and SBCM collections. As of June 30, 1990, 51,681 kg (113,698 lb) or rock had been collected during the impact mitigation program, of which, approximately 20,455 kg (45,000 lb) have been processed. In addition to screen washing rock samples to recover microvertebrate fossils, hand excavation of several cubic meters of rock in a small quarry (Kelly Quarry = LACM Loc. 5661) was conducted to allow the recovery of larger fossil land mammal remains. Stratigraphic sections were measured to the nearest 0.25 m with a Jacob's Staff. Correlation of beds within the landfill was accomplished by tracing beds, examining aerial photographs of the area before and after the landfill was developed, reviewing photographs taken during the CIT investigations, and using the geologic map prepared by Emcon Associates (1986). The contact between the lower and middle members of the Sespe Formation as defined by Taylor (1983) and Kelly (1990) is used herein. Definitions of terms used herein for taxa identifications are as follows: n. sp. indicates material is adequate for assignment to a new species; indet. (indeterminate) indicates material is inadequate for identification to generic and/or specific level; and undet. (undetermined) indicates material is adequate for identification to generic and/or specific level, but is in need of further study. ABBREVIATIONS CDLB - Canada de la Brea CIT - California Institute of Technology LACM - Natural History Museum of Los Angeles County LACM(CIT) - California Institute of Technology locality (collection and files now at LACM) loc. - locality NALMA - North American Land Mammal Age SBCM - San Bernardino County Museum UCMP - University of California Museum of Paleontology UCR - University of California Riverside VCRMA - Ventura County Resource Management Agency GEOLOGIC SETTING The Sespe Formation in the vicinity of the Simi Valley Landfill consists of 1656 m of sandstone, conglomerate, and mudstone that have been divided into three (lower, middle, upper) informal members (Stock, 1932; Taylor, 1983; Mason, 1988; Kelly, 1990). Within the landfill boundaries, only the lower and middle members are present. The lower member is exposed at the southern boundary of the landfill property and consists of nearly 320 m of interbedded sandstone, conglomerate, and minor claystone beds representing a sandy braided- river fades (Taylor, 1983). The middle member, highly variegated and weathering to a badlands topography (Kew, 1924), underlies virtually the entire landfill property and is exposed north of the landfill entrance. The middle member consists of over 600 m of interbedded structureless sandstone and claystone beds representing a meandering-river floodbasin facies (Taylor, 1983). Most beds consist of light gray to buff, coarse-grained sandstone overlain by red to green claystone. Conglomerate occurs at the base of some sandstones and occasionally channels are cut into the claystone at the top of the underlying bed. Figure 2 represents a generalized stratigraphic section of the middle member of the Sespe Formation at the Simi Valley Landfill. Most previously existing exposures of the middle member on the landfill property have been disturbed by excavation for cover material or buried by landfilling. Existing exposures continue to be affected by these activities, but continue to produce fossils. Excavation also creates new exposure, which can be sampled for fossil remains. Two north-dipping reverse faults, the Strathern and Canada de la Brea Faults, occur in the landfill property (Kimmel and others, 1983). Mason (1988) and Kelly (1990) have determined that offset has resulted in the absence of 46 to 55 m of strata along the Strathern Fault and approximately 262 m of strata being repeated above the Canada de la Brea Fault. Page 4 Sespe Formation Kelly et al. SIMI VALLEY LANDFILL SECTION LACM 5872 LACM 5871 LEGEND SANDSTONE m CLAYSTONE ¦ VERTICAL SCALE: SO METERS ¦ 2 LLI_1^ « o J UJ WLU LUX P So s LACM(CIT) 150, LACM 5875 LACM 5611. 5612. 5613, 5874 v| LACM 5614 LACM(CIT) 179, 218, LACM 5673 | LACMICIT) 128 STRATHERN FAULT (46 - 55 M OF SECTION MISSING) ¦¦¦I LACM 5633 LACM 5868, 5869, 5870 LACM 5666 LACM 5867 LACM 5865 LACM 5864 LACM 5863 LACM 5860. 5861. 5862 LACMICIT) 202. LACM 5616. 5660 LACMICIT) 207 LACM 5661 LACM 5859 LACM 5857, 5858 LACM 5656 LACM 5855 Z< < li. "-1 o< °-£