Late Pliocene Megafossils of the Pico Formation, Newhall Area, Los Angeles County, Southern California
Late Pliocene Megafossils of the Pico Formation, Newhall Area, Los Angeles County, Southern California
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上新世晚期皮科地层巨型化石，南加州洛杉矶县纽霍尔地区
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发表时间：
2012
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通讯作者：
R. Squires
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作者：
R. Squires
详细描述了南加州北方洛杉矶县纽荷尔以南皮科组中巨化石的分类组成和地层分布。83个分类群，从15个地方，被发现：一个腕足类，36双壳类，40腹足类，一个舟足类，一个螃蟹，一个藤壶，一个海胆，一个鲨鱼，和一个陆地植物。所有这些都在这里说明。本文报道了栉孔扇贝Argopecten invalidus（Hanna，1924）与A. subdolus（Hertlein，1925）和A. callidus（Hertlein，1925）.稀有的腹足类Calliostoma和Ocinebrina可能是新种。软体动物，这是上新世晚期的指示年龄，生活在沃茨的内部亚滨海深度和正常的海洋盐度。41个现存物种中的大多数表明暖温带沃茨类似于今天发生的邻近海岸，虽然少数物种，无论是现存的还是灭绝的，表明南部温暖的水组成部分。动物群主要生活在软砂中或软砂上，但也有少数生活在其他贝壳上或可能生活在大型岩石碎屑上。作为本研究的一部分进行的地质野外绘图显示，纽霍尔以南的皮科组沉积在辫状河进入海洋环境的地点（即，辫状三角洲）。最初，在地层的下部和中部，河流砾石和粗砂与相对较深的近海淤泥相互交错，缺乏巨型动物。最后，三角洲形成了，形成的上部变浅条件有利于巨型动物生活在三角洲滨面细沙中或紧邻其处。风暴波浪横扫三角洲，将巨型动物的外壳与火成岩和变质基底岩石的鹅卵石一起沿着集中在通道化的沉积物中。死后的运输距离很短，证明了许多双瓣双壳类贝壳。
Taxonomic composition and stratigraphic distribution of megafossils in the Pico Formation south of Newhall, northern Los Angeles County, Southern California, are described in detail. Eighty-three taxa, from 15 localities, were found: one brachiopod, 36 bivalves, 40 gastropods, one scaphopod, one crab, one barnacle, one sea urchin, one shark, and one land plant. All are illustrated here. The pectinid bivalve Argopecten invalidus (Hanna, 1924) is put into synonymy with A. subdolus (Hertlein, 1925) and A. callidus (Hertlein, 1925). Rare specimens of the gastropods Calliostoma and Ocinebrina might be new species. The mollusks, which are indicative of a late Pliocene age, lived in waters of inner sublittoral depths and normal marine salinity. Most of the 41 extant species indicate warm-temperate waters similar to those occurring today off the adjacent coast, although a few species, both extant and extinct, indicate a southerly warmer water component. The fauna lived predominantly in, or on, soft sands, but a few lived on other shells or possibly on large rock clasts. Geologic field mapping done as part of this present study revealed that the Pico Formation south of Newhall was deposited at the site where a braided river entered the marine environment (i.e., braid delta). Initially, the river gravel and coarse sand interfingered with relatively deep offshore silts, barren of megafauna, in the lower and middle parts of the formation. Eventually, the delta built up, and the resulting shoaling conditions in the upper part of the formation were conducive for the megafauna to live in, or immediately adjacent to, the deltaic shoreface fine sands. Storm waves raked the delta and concentrated the shells of the megafauna, along with cobbles of igneous and metamorphic basement rocks, into channelized deposits. Postmortem transport distance was short, as evidenced by many paired-valved bivalve shells.