Journal of Paleontology, 85(3), 2011, p. 524–536 Copyright ’ 2011, The Paleontological Society 0022-3360/11/0085-0524$03.00 EPIZOIC STRAMENTID CIRRIPEDES ON AMMONITES FROM LATE CRETACEOUS PLATY LIMESTONES IN MEXICO CHRISTINA IFRIM,1 FRANCISCO J. VEGA,2 AND WOLFGANG STINNESBECK1 1Institut fu¨r Geowissenschaften, Ruprecht-Karls-Universita¨t, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany, ,[email protected].; and 2Instituto de Geologı´a, Universidad Nacional Auto´noma de Me´xico, Ciudad Universitaria, Coyoaca´n, 04510 Me´xico, D.F., Mexico ABSTRACT—The discovery of platy limestone deposits in northeastern Mexico has led to the collection of well- preserved stramentids of early Turonian age from Vallecillo, state of Nuevo Leo´n, and of early Coniacian age from El Carranza, state of Coahuila. Stramentum (Stramentum) pulchellum (Sowerby, 1843) colonized the ammonite shells during the lifetime of the animals, occasionally in two subsequent generations. Colonization of the ammonite shell by Stramentum (S.) pulchellum was hindered by strong ornamentation only. The ammonites did not interfere with their epizoans. Colonization during lifetime shows that these ammonites dwelled in well-oxygenated water levels near the surface, and most stramentids were embedded alive. The known paleobiogeographic occurrence of Stramentum (S.) pulchellum and its long stratigraphic occurrence are considerably enlarged by our findings. The pseudoplanktonic mode of life of Stramentum, and attachment to ammonite shells, may have been a response of a once benthic organism to repeated oxygen-deficient conditions on the seafloor of mid-Cretaceous oceans, i.e., to oceanic anoxic events (OAEs). INTRODUCTION matter are preserved as black stains. The sediment was thus HE THORACIC crustacean Stramentum sp. is widespread in originally black, rich in organic matter, which is typical for T sediments of Cenomanian-Coniacian age. Most reports fine-grained sediment with good fossil preservation (Martill, for Stramentum sp. are from Europe and North America, as 1987; Allison, 1988; Seilacher, 1990; Hemleben and Swin- summarized by Hauschke (1994) and Hattin and Hirt (1991). burne, 1991). Few reports exist from South America (Royo y Go´mez, 1941; The platy limestone is laminated below millimeter scale. It Villamil and Arango, 1998). Nomura et al. (2009) provided the splits perfectly parallel to lamination when dry, and preferably most recent summary, although the specimen reported from through fossils contained in the sediment. Japan is incomplete. During recent years, the discovery of The platy limestones are best described as mud- to several new localities with platy limestone deposition, namely wackestones (Dunham, 1962) and indicate a pelagic environ- the early Turonian Platy Limestone at Vallecillo, Nuevo Leo´n, ment, consistent with the paleogeographic position of and the early Coniacian Yellow Platy Limestone Member at Vallecillo on the outer shelf. Clastic components reach Rosario and Carranza to the northwest of Muzquiz, led to the between 10 percent and 25 percent of the sediment and were collection of well-preserved stramentids from the early Late supplied to the Vallecillo region by aeolian transport. The Cretaceous of northeastern Mexico. The stramentid specimens calcite component is biogenic in origin, whereas the Fe-oxides known from these localities grew on ammonite shells and were result from precipitation of sulfides on the Vallecillo seafloor previously only superficially figured (Stinnesbeck et al., 2005; in a very hostile, low-oxygen environment (Ifrim, 2006). Ifrim and Stinnesbeck, 2007; Vega et al., 2007). The present Fossils are found throughout the section. Ammonites are paper aims for a detailed description and interpretation of preserved as flattened impressions. Some body chambers are Stramentum Logan, 1897 from these localities. They allow us filled with sediment and preserved as flat internal molds. to draw conclusions on the paleoecology of their hosts. Phragmocones are less well preserved, because the empty The early Turonian Vallecillo Platy Limestone Member.— shells broke under lithologic overburden, and septae crushed Vallecillo is located 100 km north of Monterrey, Nuevo Leo´n, irregularly. in northeastern Mexico, and has been known since the The abundant and diverse assemblage of ammonites and 1990s for well-preserved fossil fishes, ammonites and marine inoceramid bivalves, and also the planktic foraminifers reptiles. The most complete section is exposed in a quarry at preserved in the sediment, allow for a detailed biostratigraphic N26u39.329 and W 100u00.829 (Fig. 1). zonation of the Vallecillo section (Ifrim and Stinnesbeck, 2007, The sedimentology, microfacies, age, preservation of fossils, 2008). The base of the Turonian stage is present in the lowest and composition of the fossil assemblage were described in part of the section at the 0.21 m-level (Watinoceras- and detail by Ifrim et al. (2005), Ifrim (2006), Ifrim et al. (2007; Mytiloides puebloensis zones), followed by 5.5 m sediments of 2008), and Ifrim and Stinnesbeck (2007; 2008), so only a short the early Turonian (Pseudaspidoceras flexuosum to Mammites summary is provided here. nodosoides Zone, and Mytiloides kossmati Zone), and by the The composite section of platy limestone exposed at middle Turonian above the 5.70 m-level (Collignoniceras Vallecillo is approximately 8 m thick and consists of pink to woollgari and Mytiloides mytiloides zones). All stramentid yellow marly limestone beds between 8 and 40 cm thick, crustaceans known from Vallecillo are therefore of early- intercalated by white or grey mudstone beds with thicknesses middle Turonian age (Fig. 2). between 1 and 30 cm (Fig. 2). The mudstone beds occasionally The planktonic foraminifers, the most abundant bioclasts, contain crusts of goethite and/or hematite, in part with are rare in the lower section, and the specimens are goethite concretions with cubic pseudomorphs, probably after small. They represent the Whiteinella archaeocretacea Zone. pyrite. In the most carbonaceous beds, traces of organic Upsection, in the Helvetoglobotruncana helvetica Zone, the 524 IFRIM ET AL.—EPIZOIC STRAMENTID CIRRIPEDES ON LATE CRETACEOUS AMMONITES, MEXICO 525 The early Coniacian Yellow Limestone Member, Mu´zquiz.— Platy limestone is also known from northern Coahuila (Fig. 1) from two commercial quarries northwest of Mu´zquiz. The El Rosario quarry is located approximately 100 km northwest of the town, at N 28u52.5869, W 102u24.2229 and was document- ed by Stinnesbeck et al. (2005). Our material is from Carranza, 30 km north of Rosario, at N 29u10.7759, W 102u27.1939.In this quarry, the limestones are extracted along a 10 km outcrop of a single bed corresponding to beds R40–42 of El Rosario. Other layers occasionally exposed are correlated to layers R38–46, i.e., to the middle Yellow Limestone Member at Rosario (Fig. 3) by their similar lithology, thickness and fossil content. The abundant presence of the inoceramid Cremnoceramus deformis erectus (Meek, 1877) permits assign- ment of an early Coniacian age (Walaszczyk and Wood, 1998; Gradstein et al., 2004) to all layers exposed at Carranza (Fig. 3). The colonized specimen of Peroniceras tridorsatum de Grossouvre, 1894 studied here was collected from the Carranza quarry and erroneously included into the Rosario assemblage (Stinnesbeck et al., 2005; Ifrim et al., 2007) due to the similarity of lithology. Platy limestones at Carranza and Rosario are mud- to wackestones (Dunham, 1962), with planktonic foraminifers, and less frequently calcispheres and recrystallized radiolarians. This microfossil content, particularly the keeled planktonic foraminifers Dicarinella Porthault, 1970 and Marginotruncana Hofker, 1956, indicates a pelagic environment with water depths .50 m (Leary et al., 1989; Leckie et al., 1998). The cirriped Stramentum (S.) pulchellum is represented by fifty specimens attached to a shell of the ammonite Peroniceras tridorsatum (Fig. 4), and some more attached to a Forresteria Reeside, 1932 (Vega et al., 2007), possibly also from Carranza. Only nektic forms have been recognized in the crustacean assemblage of the Yellow Limestone Member. The Yellow Limestone Member is another example of formation of platy limestone in the open sea, comparable to the Vallecillo platy limestone (Ifrim et al., 2007). During deposition, the North American coastline was located at least 200–300 km to the west of Carranza (e.g., Young, 1963; Corbett et al., 1987; Kennedy and Cobban, 1991; Gold- hammer and Johnson, 2001) or 500 km to the North FIGURE 1—Map of Mexico with inset of northeastern Mexico. Fossil (Salvador, 1991). The deep water may have been stagnant localities are marked with an asterisk. due to the location in the Rio Grande Embayment, where only the surface waters may have been connected to major currents; assemblages become gradually more diverse, more abundant, even though, the presence of occasional benthic foraminifers and individuals are larger. These changes in the planktonic and trace fossils at Rosario suggest a less hostile environment foraminiferal assemblages appear to be related to the recovery than at Vallecillo. of the marine ecosystem from Oceanic Anoxic Event 2, a black shale event of global scale during the latest Cenomanian. OAE SYSTEMATIC PALEONTOLOGY 2 persisted into the early Turonian and affected deep-dwelling, The systematics of ammonites follows the Treatise of large, keeled planktonic foraminifers by an expanded oxygen Invertebrate