Journal of Paleontology, 91(5), 2017, p. 981–986 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.70
Palaxius floridanus n. isp., a new structured callianassid crustacean microcoprolite from the Pleistocene of south Florida
Eberhard Gischler,1 Joachim Blau,1 and Jörn Peckmann2
1Institut für Geowissenschaften, J.W. Goethe-Universität, Altenhöferallee 1, 60438 Frankfurt am Main, Germany ⟨
gischler@em.uni-frankfurt.de⟩ 2Institut für Geologie, Universität Hamburg, Bundesstraße 55, 20146 Hamburg, Germany ⟨
joern.peckmann@
uni-hamburg.de⟩
Abstract.—The crustacean microcoprolite Palaxius floridanus n. isp. is described from shallow-water carbonate platform deposits of Pleistocene limestones of south Florida. Palaxius floridanus n. isp. occurs in moderate-energy packstones and grainstones of the oolite facies of the Miami Limestone, and in skeletal packstones of the Key Largo Limestone, ranging in age from marine isotope stage (MIS) 11 to MIS 5a (ca. 400–80 kyr BP). The new ichnospecies resembles P. decemlunulatus, which has been described previously from Oligocene deposits. Late Jurassic and Late Cretaceous forms described as P. decemlunulatus belong to a new ichnogenus and new ichnospecies, respectively, yet to be described.
Introduction
Lithified fecal pellets of invertebrates may be very common locally and regionally in warm, shallow-water carbonate environments that form large sediment bodies, such as on the Bahamas and adjacent carbonate banks where peloidal facies cover several thousand square kilometers (Purdy, 1963; Enos, 1974). In addition to mollusks, callianassid and thalassinidean crustaceans are important producers of fecal pellets, and play a crucial role with respect to sedimentology, paleontology, and biology. They may bioturbate the sediment, modify sediment texture extensively down to one meter below the sea floor, and produce characteristic burrows and ichnofossils (Shinn, 1968; Pryor, 1975; Frey et al., 1978). These crustaceans may also redistribute organic matter and nutrients, increase the rate of organic decomposition, and increase the ventilation of the sediment column (Pinn et al., 1999, and references therein). Fleshy projections in the hindgut of thalassinidean and callianassid crustaceans may form complex systems of canals within fecal pellets that are taxonomically characteristic and have been encountered in thin-sections in sediment and microfacies studies (Moore, 1932; Brönnimann, 1972; Senowbari-Daryan, 1979; Blau and Grün, 2000, and references therein). The large majority of such studies have detailed crustacean microcoprolites fromthe Mesozoic. In thiswork, we describe a new, characteristic post-Paleogene microcoprolite that occurs in Pleistocene neritic carbonate deposits of south Florida.
Geological setting
Large parts of south Florida, including the island chain of the Florida Keys, are composed of late Pleistocene shallow-water limestone (Stanley, 1966; Hoffmeister et al., 1967; Hoffmeister and Multer, 1968; Perkins, 1977; Harrison and Coniglio, 1985). The reefal Key Largo Limestone crops out along the upper and central parts of the Florida Keys; the oolitic facies of the Miami
Limestone covers the southeastern part of the peninsula and the lower part of the Florida Keys (Fig. 1). These deposits were part of a large, shallow-water carbonate platform that formed during marine isotope stage (MIS) 5e, ca. 130–115 kyr BP (Multer et al., 2002; Muhs et al., 2011, and references therein). Outcrop and subsurface data have shown that the carbonate platform consists of six stacked platforms that were formed during Pleistocene sea-level highstands overlain by the Holocene Florida Reef Tract, and separated by subaerial exposure horizons that developed during Pleistocene sea-level lowstands (Perkins, 1977; Multer et al., 2002). During most of the Pleistocene platform stages, the margin was presumably char- acterized by a ramp-like morphology with predominantly mas- sive corals. The shallow bank-barrier reef margin with abundant acroporid corals and deeper water outlier reefs only developed in the latest Pleistocene MIS 5c (Lidz et al., 1991; Multer et al., 2002). Ooid shoals were abundant along the southeastern and southern parts of the platformmargin during MIS 5e (Hoffmeister et al., 1967; Halley et al., 1977; Halley and Evans, 1983).
Methods
Descriptions of the microcoprolites were made based on thin- section observations using a Leica DM 2500M petrographic microscope with attached digital camera. Microcoprolites were compared to existing descriptions in the literature, taking into account the general comments by Brönnimann (1972). After the specimens analyzed here had been found, >200 existing thin- sections of the study by Multer et al. (2002) were searched for structured crustacean microcoprolites, along with 20 thin- sections from outcrops in Coral Gables and the Everglades, south Florida. In addition, 120 thin-sections from the Pleistocene shallow-water limestones of Belize (Gischler, 2007; Gischler, et al., 2010) were searched for structured crustacean micro- coprolites, albeit, without success.
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