UPPER CRETACEOUS-PALEOCENE ECHINOIDS FROM NORTHERN PATAGONIA, ARGENTINA

ABSTRACT-

Echinoids are among the greatest in quantity conspicuous and diverse constituents of the Upper Cretaceous and Paleocene marine invertebrate fauna of Argentina. Nine species were mustered from localities exposing the Jag??el (Maastrichtian), Roca (Maastrichtian-Danian), Salamanca (Danian), Arroyo Barbudo (Danian), El Fuerte (Danian), and Arroyo Salado (Danian) Formations in northern Patagonia, Argentina. alone one of these taxa, Paraster joannisboehmi (Oppenheim in B?¶hm 1903) has been described previously from Argentina. Four taxa, Gauthieria menuthiae (Lambert and Savin in Lambert and Thi?©ry, 1911) Nucleopygus pullatus (Stoliczka, 1873) Diplodetus nutrix (Lambert in Boule 1899) and Hemiaster hawkinsi Lambert, 1933 have been described previously from Madagascar. single species, Micropsis desori (Cotteau in Leymerie and Cotteau, 1856) has been described previously from France. single taxon, Pygopistes parrasae is a novel species. Argentinian cassiduloids include the single two known Danian species of Nucleopygus and Pygopistes. The spatangoids were not powerfully affected by the K-T extinction circumstance Comparisons of the Patagonian echinoids with those of the Northern Hemisphere indicate that they were powerfully influenced by dispersal from Tethyan sources.

INTRODUCTION

ECHINOIDS ARE among the greatest in quantity conspicuous of marine invertebrate faunal uncompounded bodys of the Cretaceous-Paleogene boundary in southern southerly America. However, very few studies have been published upon this subject; some are brief mentions or descriptions, and greatest in quantity come from the early part of the twentieth hundred (Burckhardt, 1901; B?¶hm, 1903; Ameghino, 1906) greatest in quantity other references allude only to the nearness of this group of invertebrates in the Maastrichtian and Paleocene of Patagonia (Bertels, 1965; Camacho, 1970 1992; Reichler and Camacho, 1991; Parma, 1996a, 1996b) Studies by means of Bernasconi (1959) and Parma (1989) are exceptions in that they treated echinoids in more detail; however, they are now outdated.

Knowledge of the Maastrichtian-Danian echinoids from Argentina is in sharp contrast to that available for similar faunas elsewhere (Jagt et al., 1998 1999; Smith et al., 1999; Jagt, 1999a, 1999b 2000; Smith and Wright, 1999 2000; N?©raudeau et al., 2000; Smith and Jeffery 2000; Kroh 2001) In the at hand work, we study the Maastrichtian-Danian echinoids from northern Patagonia (Fig. 1) analyze their distribution from one side the Cretaceous-Paleogene boundary, and describe their paleobiogeographic relationships.

The genera Micropsis Cotteau in Leymerie and Cotteau, 1856 and Gauthieria Lambert, 1888 are recorded for the first time in Patagonia during the lower Danian (Fig. 2) At the same time, Gomphechinus Pomel 1883 is the single phymosomatoid found in the Maastrichtian of northern Patagonia. The Cassiduloida are exhibited in the lower Danian by the agency of Nucleopygus Agassiz, 1840 and Pygopistes Pomel 1883 while the Spatangoida, not powerfully affected by Cretaceous-Paleogene boundary facts are represented by Diplodetus Schl??ter 1900 Hemiaster Agassiz in Agassiz and Desor, 1847 Paraster Pomel 1869 and Proraster Arnaud in Grossouvre 1901

GEOLOGICAL SETTING

The Cretaceous-Paleogene boundary in southern southerly America is characterized by important relative sea horizontal changes. These are related primarily to subsidence of the Atlantic margin and were responsible for major transgressions. This subsidence may have been caused by means of lithospheric cooling and sediment loading (Uliana and Biddle, 1988) In northern Patagonia, this fact would have been contemporaneous with the unfolding of a foreland basin east of the Andes (Tunik, 2001) During the Maastrichtian-Danian interval, the southern tip of southerly America was reduced to an archipelago in which the emergent land was the central part of the Somuncur?? and the Deseado massifs (Yrigoyen, 1969; Uliana and Biddle, 1988; Riccardi, 1988; Urien et al., 1995; Malumi??n, 1999) Malumi??n and Caram?©s (1995) estimated the minimum area of without delay emergent Patagonia that was overlayed by the sea during the Danian to have been 507000 km^sup 2^ This large, inundationed surface was an important paleogeographic simple body in the continent and sure played a paramount role in the climatic and evolutionary circumstances recorded in Patagonia and the Antarctic Peninsula during that time. In the Neuqu?©n Basin, the sediments deposited by dint of this transgression are included in the Malargue assemblage that is well exposed in northern Patagonia.

Since the nineteenth hundred the Malarg??e Group has been studied by means of numerous authors (Camacho, 1992). A renewed interest in these stones has emerged in the past not many years, as they include the Cretaceous-Paleogene boundary in one as well as the other marine and continental facies (Parras and Casadio, 1999) Thus, they present an excellent opportunity to application of mind the modifications of ecosystems at the extremity of the Cretaceous in the Southern Hemisphere.

In the northwest of the Neuqu?©n Basin, the Malarg??e cluster is exposed in sections of above 400 m in thickness. From bottom to top it includes the Loncoche, Jag??el, Roca, and Pircala formations. In the southwest, the thickness recorded is les than 200 m and the units expos there are the Allen, Jag??el, Roca, and Carrizo formations.