Foraminifera‐based estimates of paleobathymetry using Modern Analogue Technique, and the subsidence history of the early Miocene Waitemata Basin

Abstract

Cluster and Canonical Correspondence Analyses were used to group 52 early Miocene (Waitemata Group) benthic foraminiferal faunas into eight associations and relate them to proxies for paleobathymetry and bottomwater energy.Modern Analogue Technique (MAT) was used to estimate the paleodepth of each fossil fauna by comparing their generic composition with 371 modern New Zealand faunas. MAT estimates are mostly consistent with, but no more precise than, those inferred by conventional subjective means. MAT estimates could be improved by broadening the modern database. The less precise paleodepth estimates for outer shelf and bathyal faunas were improved using the known upper depth limits of several key bathyal taxa. The combined use of MAT and conventional methods is advocated to provide the most robust paleoenvironmental interpretations.The paleobathymetry estimates are consistent with previously inferred regional subsidence during formation of the Waitemata Basin. The faunas document the submergence of a land with up to 100 m of rolling relief, with initial creation of both sheltered bays (Elphidium and Melonis associations) and exposed coasts (Amphistegina and Cribrorotalia, Gaudryina, Cibicides associations). Dysoxic faunas (Nonionella dominated) provide evidence for the accumulation of fine sediment on the quiet floor of several sheltered, deeper water inlets (20-40 m). As subsidence continued, the former ridge crests became islands and finally disappeared, coincident with cessation of coarse terrigenous sediment supply. Paleobathymetry estimates imply that several coarse, shallow-water gravel or shell hash units slid down the submarine slopes of these small islands to be interbedded with mid-outer shelf sediment (with Bolivina and Cibicides dominated faunas). Aperiod of sediment starvation (hiatus or thin mudstone) ensued: in the south, it spanned an interval during which the basin subsided from c. 150 m down to >400-500 m; in the north, it lasted until the basin floor reached lower bathyal depths (c. >1700 m, OridorsalisNodosaria association), before sand turbidites flowed in from the northwest.

Paleoecology of an early Miocene, rapidly submerging rocky shore, Motuketekete Island, Hauraki Gulf, New Zealand

“…Our lithologic and macrofaunal data from Motuketekete Island are consistent with other studies (e.g., Hay ward & Brook 1984;Ricketts et al 1989;Hayward 2004) that have previously inferred regional subsidence during formation of the Waitemata Basin.…”

“…after their accumulation, Kawau Subgroup deposits were conformably overlain by deep-water Warkworth Subgroup sediments, which buried a topographically smoothed basin floor, filling it with turbidites (Hayward & Brook 1984). Kawau Subgroup strata in the central and northern Auckland region have long been known for their rich concentrations of macrofossils andbenthic foraminifera (e.g., Powell 1938Powell , 1976Squires 1962;Crabb 1971;Buckeridge 1975Buckeridge , 1983Hayward & Buzas 1979;Hayward 1986Hayward , 2004Eagle etal. 1994Eagle etal.…”

The Application of a Subtidal Foraminifera-Based Transfer Function to Reconstruct Holocene Paleobathymetry of the Po Delta, Northern Adriatic Sea

“…Although most ecological studies suggest that a combination of environmental factors control subtidal foraminifera, their spatial distribution patterns often correlate with water depth (Natland, 1933;Bandy and Chierici, 1966;Sen Gupta, 1977;Murray, 1991;Horton and others, 2007;Pascual and others, 2008). Many biotic and abiotic factors that control the distribution of foraminifera in shallow to deep marine waters vary with depth; thus, depth is simply a factor, along with latitude and longitude, in locating a sample in threedimensional space (e.g., Buzas, 1974;Boltovskoy and Wright, 1976;Sen Gupta, 1977;Murray, 1991;Hayward andothers, 1999, 2006;Morigi and others, 2005). Culver (1988) and Hayward (2004) have made quantitative estimates of paleowater depths from modern foraminiferal data.…”

“…Many biotic and abiotic factors that control the distribution of foraminifera in shallow to deep marine waters vary with depth; thus, depth is simply a factor, along with latitude and longitude, in locating a sample in threedimensional space (e.g., Buzas, 1974;Boltovskoy and Wright, 1976;Sen Gupta, 1977;Murray, 1991;Hayward andothers, 1999, 2006;Morigi and others, 2005). Culver (1988) and Hayward (2004) have made quantitative estimates of paleowater depths from modern foraminiferal data. More recently, Horton and others (2007) and Woodroffe (2009) used these contemporary relations in the central Great Barrier Reef to build a predictive transfer function capable of inferring the past water depth of a sediment sample from its foraminiferal content.…”

“…Following Imbrie and Kipp (1971), qualitative paleoenvironmental inferences have been replaced by quantitative reconstructions of specific physical parameters, such as sea surface temperature, organic carbon flux, salinity, and relative sea level (e.g., Gasse and others, 1995;Jones and Juggins, 1995;Wollenburg and Kuhnt, 2000;Charman, 2001;Horton and Edwards, 2006). Quantitative reconstructions of water depth have been made based upon well-developed and easily recognized depth-related foraminiferal distributions (Culver, 1988;Hayward, 2004;Horton and others, 2007;Woodroffe, 2009), although the bathymetric distribution of foraminiferal species will vary from basin to basin (e.g., Culver andBuzas, 1980, 1981), Hayward and others (1999) noted that depth zonations at inner to middle shelf depths are finer than those of the outer shelf and slope.…”