Palaeogeography, Palaeoclimatology, Palaeoecology, 78 (1990): 135 148 135 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands Paleolatitude distribution of Phanerozoic marine ooids and cements BRADLEY N. OPDYKE and BRUCE H. WILKINSON Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109-1063 (U.S.A.) (Received June 5, 1989; revised and accepted October 31, 1989) Abstract Opdyke, B. N. and Wilkinson, B. H., 1990. Paleolatitude distribution of Phanerozoic marine ooids and cements. Palaeogeogr., Palaeoclimatol., Palaeoecol., 78: 135-148. Data on 493 Phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric CO2 and/or oceanic temperature gradient. Holocene ooid and cement precipitation occurs over similar latitudes, with means centered around 24° and 28°, respectively. Aragonite and calcite also display roughly comparable distributions, with average occurrences between 25° and 28°. Surface seawater saturation values requisite for ooid-cement carbonate precipitation are at least 3.8 (~,rs) for aragonite and 3.4 (~a,s) for calcite. Ancient ooid-cement occurrences vary in space and time, with depositional zones generally closer to the equator during continental emergence; greatest extent correlates with periods of maximum transgression. Aragonite formation is favored in more equatorial localities than calcite when cement-ooid distributions are narrow and continents are emergent. Similarity of latitude distribution of marine ooids, cement, and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in Phanerozoic seas than biological processes related to net productivity of various carbonate platform communities. Continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time. Introduction 1964). Occurrences of Paleozoic tillite are still widely used to calibrate apparent polar wander Geologists have long used the distribution of paths (e.g. Van der Voo, 1988; Scotese and different rock types or floral/faunal assem- Barrett, 1989), and temperature indicators blages to interpret ancient climates. Even such as fossil fauna and flora remain the before general acceptance of plate tectonics, principal evidence that Cretaceous and Eocene continental mobility was inferred from anom- climates were generally warmer than at pre- alous lithologic occurrences such as evaporite sent (e.g. Bailey and Sinnott, 1915; Smiley, and/or carbonate sequences at high latitudes 1967; Douglas and Williams, 1982; Wolfe and (e.g. Wegener, 1915; Koeppen and Wegener, Upchurch, 1987). 1924; DuToit, 1939). Early paleomagnetic Limestone-dolostone sequences are particu- studies also relied heavily on the coincidence larly notable in this regard in that carbonate of specific facies within projected paleolati- accumulation is generally thought to be tudes as support of continental reconstruc- favored in warm shallow seas that are far tions (e.g. Opdyke, 1959, 1962; Blackett, 1961; removed from sources of terrigenous clastic Irving and Briden, 1962; Briden and Irving, sediment (e.g. Milliman, 1974; Wilson, 1975; 0031-0182/90/$03.50 © 1990 Elsevier Science Publishers B.V. 136 B.N. OPDYKE AND B. H. WILKINSON Leeder, 1982; Tucker, 1985). Modern platforms Late Cretaceous, a time period characterized occur preferentially on tropical to subtropical by continental submergence, elevated CO2, shelves (Emery, 1968; Lees, 1975) where warmer climate, and possibly greater poleward seawater reaches its highest saturation (Morse extent of carbonate-saturated seawater. Briden et al., 1980), and available data suggest that and Irving (1964) and Ziegler et al. (1984), on paleoplatforms exhibit a similar distribution the other hand, concluded that areas of carbon- (e.g. Briden and Irving, 1964; Parrish, 1982; ate deposition do not expand poleward during Ziegler, 1984); Mesozoic-Cenozoic limestones warmer time intervals, and suggested that occupy a range concentrated about the equa- limits of carbonate generation are primarily tor, but exhibit a skewed distribution that controlled by biologic factors such as the suggests primary accumulation at about 20 ° interdependence between latitude, degree of (Fig.l). light penetration, and the direct or indirect Given this relatively narrow range, the fixation of calcium carbonate by algae in paleolatitude distribution of cratonic lime- shallow platform settings. stone sequences should serve as a sensitive Clearly, a number of interrelated processes record of changes in those parameters that act to determine areas of carbonate generation control seawater saturation, including temper- in shallow marine environments. At the coars- ature, atmospheric CO2 (e.g. Mackenzie and est scale, rates of limestone accumulation must Pigott, 1981; Berner et al., 1983), and climate reflect rates of delivery of Ca and CO~- ions (e.g. Fisher, 1981, 1984; Sandberg, 1983, 1985; to global oceans which, in turn, depend on Worsley et al., 1986). Previous studies of areas of exposed crust, rates of weathering, carbonate accumulation, however, have ar- and amounts of hydrothermal alteration at rived at different conclusions concerning oceanic ridges. In addition, finite ion source specific details of the reliability of this record. fluxes are partially controlled by dissolution Opdyke and Wilkinson (1989), for example, processes in the ocean and are ultimately suggested that maximum expansion of shallow partitioned between deep marine and shallow carbonate environments occurred during the platform depositional settings, depending on those factors that control net carbonate prod- uctivity of planktic and benthic marine com- 80 munities. Given that planktic calcifiers only arose and diversified since the Triassic, and 6o that a variety of taxa have dominated benthic cnnit communities over the past 590 m.y., secular change in the distribution of platform carbon- 4o O ate might indeed reflect a complex of biologic factors largely independent of variables such 20 as temperature and salinity that determine levels of carbonate saturation in shallow marine settings. -70 -50 -30 -10 10 30 50 70 In short, patterns of cratonic carbonate DEGREES LATITUDE accumulation probably record diverse rela- Fig.1. Paleolatitude distribution of Mesozoic-Cenozoic tions between biological and physicochemical shallow water carbonate sequence localities, modified from Zielger et al. (1984). Bars represent actual data whereas the processes that preclude simple correlation shaded curve represents the likely sum of northern and between limits of biogenic carbonate produc- southern hemisphere occurrences. To eliminate bias intro- tion, ambient seawater saturation, and cli- duced by the dominance of Mesozoic-Cenozoic shallow mate. In order to examine these relations and marine basins in the northern hemisphere, the southern hemisphere is inferred to have a similar potential for the to evaluate the appropriateness of carbonate distribution of carbonates. sediment distribution as a record of paleo- PALEOLATITUDE DISTRIBUTION OF PHANEROZOIC MARINE OOIDS AND CEMENTS 137 climate, while striving to avoid many of the al., 1980; Mucci, 1983; Cooke and Kepkay, 1984; factors that influence the distribution of differ- Feely et al., 1984). but, given that calcium/ ent biotic communities, we have evaluated salinity ratios of modern seawater vary by Phanerozoic limits of inorganic calcium no more than about 1.5% (Culkin and Cox, carbonate precipitation through tabulation of 1966), seawater saturation variation is largely occurrences of marine ooids and cement. Such controlled by differences in carbonate ion an approach may yield a better measure of concentration. Because alkalinity values are physicochemical variation in the marine realm relatively constant in surface oceans, change because these are largely abiotic precipitates, in temperature is therefore the most important the distribution and mineralogy of which may factor in controlling carbonate saturation respond to changes in physical and chemical levels (e.g. Takahashi et al., 1982) and, hence, parameters of surface seawater throughout where ooids and cement originate, (Fig.2). As a geologic time. result, greater carbonate saturation is found in equatorial regions as CO 2 is released to the Abiotic carbonate precipitates atmosphere, while in polar regions atmo- spheric CO 2 is absorbed by the colder waters. The inorganic precipitation of calcium Because of the strong dependence of carbonate carbonate from marine fluids results either in saturation on temperature and hence latitude, the formation of layers of pore-lining cement or massive carbonate precipitation from marine their centripetal counterpart as cortical lami- fluids is generally restricted to tropical seas. nae on ooids and other coated grains. While Regional deviation from this pattern, how- these forms of calcium carbonate generally ever, may give rise to variation in ooid-cement record the accumulation of limestone in distribution. Western boundary currents, for shallow tropical settings, variation in their example, carry warmer water to temperature abundance as sediment components, and the latitudes, somewhat expanding depositional dominance of different calcium carbonate poly- range along