Research Paper THEMED ISSUE: Results of IODP Expedition 313: The History and Impact of Sea-Level Change Offshore New Jersey GEOSPHERE Miocene relative sea level on the New Jersey shallow continental shelf and coastal plain derived from one-dimensional GEOSPHERE; v. 12, no. 5 backstripping: A case for both eustasy and epeirogeny doi:10.1130/GES01241.1 M.A. Kominz1, K.G. Miller2, J.V. Browning3, M.E. Katz4, and G.S. Mountain2 8 figures; 3 tables; 5 supplemental files 1Department of Geosciences, Western Michigan University, 1186 Rood Hall, 1903 West Michigan Avenue, Kalamazoo, Michigan 49008, USA 2Department of Earth and Planetary Sciences, and the Institute of Earth, Oceans, and Atmospheric Sciences, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8066, USA CORRESPONDENCE: michelle .kominz@ wmich .edu 3Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8066, USA 4Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180, USA CITATION: Kominz, M.A., Miller, K.G., Browning, J.V., Katz, M.E., and Mountain, G.S., 2016, Miocene relative sea level on the New Jersey shallow conti­ nental shelf and coastal plain derived from one-­ ABSTRACT et al., 1988). We use the term relative sea-level change to include changes in dimensional backstripping: A case for both eustasy eustasy coupled with epeirogenic (broad regional uplift; Grabau, 1936) and and epeirogeny: Geosphere, v. 12, no. 5, p. 1– 20, doi:10.1130/GES01241.1. Onshore drilling by Ocean Drilling Program (ODP) Legs 150X and 174AX local changes in the height of lithosphere relative to the center of the Earth. and offshore drilling by Integrated Ocean Drilling Program (IODP) Expedition That is, relative sea-level change is measured relative to a fixed point on the Received 31 July 2015 313 provides continuous cores and logs of seismically imaged Lower to Middle crust (Posamentier et al., 1988). Eustasy is of particular importance because Revision received 9 May 2016 Miocene sequences. We input ages and paleodepths of these sequences into it serves as the datum against which Earth’s tectonic and climate history can Accepted 3 August 2016 one-dimensional backstripping equations, progressively accounting for the be measured (e.g., Miller et al., 2005). In this paper, we attempt to untangle effects of compaction, Airy loading, and thermal subsidence. The resulting thermal subsidence and epeirogeny from eustasy. difference between observed subsidence and theoretical thermal subsidence The timing and magnitude of relative sea level has been studied in detail provide relative sea-level curves that reflect both global average sea level and at the Late Cretaceous to Miocene of the New Jersey margin. Onshore New non-thermal subsidence. In contrast with expectations, backstripping sug- Jersey drilling by Ocean Drilling Program (ODP) Legs 150X and 174AX in con- gests that the relative sea-level maxima in proximal onshore sites were lower cert with Legs 150 and 174A outer shelf and continental slope drilling (Fig. 1; than correlative maxima on the shelf. This requires that the onshore New Jer- e.g., Miller et al., 1997, 1998a; Mountain et al., 2010) has shown that the timing sey coastal plain has subsided relative to the shelf, which is consistent with of sequence boundaries (erosional surfaces recognized in cores and seismic models of relative epeirogeny due to subduction of the Farallon plate. These profiles), is consistent withd 18O increases from deep-sea records (Miller et al., models predict subsidence of the coastal plain relative to the shelf. Although 1991, 1996a, 2005, 2011; Browning et al., 2008). This suggests that relative sea- onshore and offshore sea-level estimates are offset by epeirogeny, the ampli- level changes observed on the New Jersey margin were caused, at least in tude of million-year–scale Early to Middle Miocene sea-level changes seen at part, by eustatic variations due to ice growth and decay. the New Jersey margin is generally 5–20 m and occasionally as great as 50 m. Backstripping is a modeling technique that accounts for the effects of sedi- These events are interpreted to represent eustatic variations, because they oc- ment compaction, sediment loading, and, in this case, thermal subsidence. cur on a shorter time frame than epeirogenic influences. Correction for epeiro- Applied to the onshore coreholes, backstripping provides a relative sea-level genic effects largely reconciles differences between onshore and offshore rela- record for the New Jersey margin that in the absence of other tectonic effects tive sea-level estimates and suggests that backstripping provides a testable yields a testable estimate of eustatic change (Miller et al., 2005; Kominz et al., eustatic model for the Early to Middle Miocene. 2008). However, mantle tomographic studies coupled with models of litho- spheric epeirogeny suggest that the New Jersey margin has undergone broad tectonic subsidence over the past 50 million years (e.g., Conrad et al., 2004; INTRODUCTION Moucha et al., 2008; Spasojević et al., 2008). Thus, more work is required to separate eustatic and epeirogenic effects in this region. One of the outstanding challenges in studying Earth history is document- Several processes must be accounted for to untangle eustasy from epeirog- ing the timing and magnitude of global sea-level change (e.g., Haq et al., 1987, eny. Most backstripping estimates of the magnitude of sea-level change in this For permission to copy, contact Copyright 1988; Miller et al., 2005). Here we use eustasy to mean the global change in region have used a one-dimensional approach that assumes an Airy response Permissions, GSA, or [email protected]. sea level relative to a fixed point, e.g., the center of the Earth (Posamentier to sediment loads (Kominz et al., 1998; Miller et al., 1998a, 2005; Van Sickel © 2016 Geological Society of America GEOSPHERE | Volume 12 | Number 5 Kominz et al. | Miocene relative sea level: IODP 313 New Jersey Margin 1 Research Paper –75° –74° –73° –72° P L F O H E R S C A L T N T U N E O T I N C S O I U C O O Z E C E O A N Sea Figure 1. Location map. Sites used in this E T E L E C Girt work are indicated as large red circles for A R O P C I 40° M M27 Integrated Ocean Drilling Program (IODP) M28 Expedition 313 sites and as large green cir- Island M29 Beach cles for the onshore coreholes with lower Ancora to middle Miocene strata. Seismic profiles Ft. Mott Bass River 1071 are from three different data acquisition New cruises (R/V Ewing cruise Ew9009, R/V Jersey Atlantic 1072 1073 Oceanus cruise Oc270, and R/V Cape Hatteras cruise CH0698; Monteverde et al., City Millville 2008; Mountain et al., 2010; Miller et al., Ocean View 2013a). The seismic section Oc270 line Cape 529 (red line passing through Exp 313 drill May sites) is shown in Figure 2. The Anchor Zoo Anchor 906 Dickinson well (gray filled dot; Poag, 1985; 00 39° Dickinson * 20 well Seismic Profiles Sugarman et al., 2011) was drilled as a gas a Cape 902 exploration well between the Cape May CH0698 Oc270 903 May 0 904 and Cape May Zoo sites. AMCOR—Atlan- ula 10 0 Ew9009 Figure 2 0 10 tic Margin Coring Project; DSDP—Deep Sea Drilling Program. DrillDrillsites Sites 905 Bethany Beach IODP Expedition 313 offshore ODP onshore ODP 200 DSDP AMCOR 00 N oil exploration 30 et al., 2004; Kominz et al., 2008). Only one model, of Upper Eocene to lower- ing of glaciers (glacial isostatic adjustment [GIA]) has been shown to vary most Miocene strata, used a two-dimensional backstripping approach that in- globally (e.g., Peltier, 1998) with impact in this region (e.g., Raymo et al., 2011). corporates flexural rigidity of the lithosphere to account for subsidence caused This effect is most pronounced during the large Northern Hemisphere ice ages by sediment loads at a distance (Kominz and Pekar, 2001). There are several of the past 2.7 m.y., but GIA influences the reference frame of older records as complications inherent in estimates of New Jersey margin relative sea level. well (e.g., Raymo et al., 2011). One issue is the fact that coastal plain sediments rarely contain a complete Drilling data provided by IODP Expedition 313 (hereafter “Exp 313”) on record of sea-level change. They generally preserve only the transgressive the New Jersey shallow continental shelf focused on Lower to Middle Mio- and highstand systems tracts, leaving lowstand sediments farther seaward cene strata (Mountain et al., 2010). This data set presents an opportunity to beneath what is now the continental shelf (Miller et al., 1998a). As discussed estimate amplitudes of offshore relative sea-level change based on cores, above, other tectonic effects have been postulated in this region so that tec- logs, and seismic profiles that can be compared to the onshore results. By tonic subsidence may not be entirely thermal. In particular, the arrival of the providing estimates of the magnitude of relative sea-level change, we can Farallon slab beneath the North American east coast ca. 75 Ma requires that begin to address the magnitude and timing of both eustasy and more regional New Jersey subsided beyond the predicted thermal subsidence (Conrad et al., epeirogeny. 2004; Kominz et al., 2008; Moucha et al., 2008; Müller et al., 2008; Spasojević Exp 313 drilled three coreholes (sites M27, M28, and M29; Fig. 1) in ~30 m et al., 2008). This means that the stratigraphic succession in this region has of water, targeting Miocene sequences that also were cored in multiple loca- been imprinted by eustatic, thermal, and epeirogenic processes.