Dating the Northwest Shelf of Australia Since the Pliocene

Accurate dating of marine sediments is essential to reconstruct past changes in oceanography and climate. Benthic foraminiferal oxygen isotope series from such sediments record long‐term changes in global ice volume and deep‐water temperature. They are commonly used in the Plio‐Pleistocene to correlate deep ocean records and to construct age models. However, continental margin settings often display much higher sedimentation rates due to variations in regional depositional setting and local input of sediment. Here, it is necessary to create a regional multi‐site framework to allow precise dating of strata. We create such a high‐resolution regional framework to determine the ages of events for the Northwest Shelf (NWS) of Australia, which was cored by International Ocean Discovery Program (IODP) Expedition 356. We employ benthic foraminiferal oxygen and carbon isotopes to construct an astronomically‐tuned age model for IODP Site U1463 (5.16–1.69 Ma). The age model is applied to the IODP Site U1463 downhole‐logging natural gamma radiation (NGR) depth‐series, which was then correlated to NGR depth‐series of several IODP sites and industry wells in the area. This approach allows assigning ages to regional seismic reflectors and the timing of key climate‐related siliciclastic phases in a predominantly carbonate‐rich sequence, like the late Miocene‐Pliocene Bare Formation. This age model is also used to chronologically calibrate planktonic foraminiferal biostratigraphic datums showing that the Indonesian Throughflow (ITF) had shoaled enough in the early Pliocene to act as biogeographical barrier between the Pacific and Indian Ocean.

stack are not possible. Additionally, local or regional climate events may have a big impact on the sediment signal preventing the correlation to a global stack. Under such circumstances it becomes necessary to create a regional framework to allow the accurate construction of age models in that particular area.
Analyses of industry seismic and downhole log datasets/samples have contributed significantly to our knowledge of the Cenozoic evolution of the NWS. However, until IODP Expedition 356 (Gallagher et al., 2017), the only samples of the upper Cenozoic strata of the region were cuttings, sidewall cores (Gallagher et al., 2009;Moss et al., 2004;Rosleff-Soerensen et al., 2012;Wallace et al., 2003), limited engineering cores of the upper 80 m (Collins, 2002;Gallagher et al., 2014) and samples of the modern sedimentary veneer (James et al., 2004;Jones, 1973).
IODP Expedition 356 continuously cored up to 1 km of Miocene to Recent strata in four sites from the Northern Carnarvon and Roebuck basins to document Indonesian Throughflow (ITF) evolution, long-term variations in Australian monsoon precipitation, and the establishment of continental aridity (Gallagher et al., 2017). A suite of downhole logs was obtained from each site including seismic velocity data. These wireline logs are directly comparable to similar data from industry wells (Gallagher et al., 2014) and can be used to correlate subsurface reflectors in 2D seismic data (cf. McCaffrey et al., 2020).
In this work, we construct an astronomically tuned, and, therefore, independent, age model for IODP Site U1463 based on benthic foraminiferal δ 18 O and δ 13 C records improving the accuracy and temporal resolution of previous age models for this site (Auer et al., 2019;Christensen et al., 2017;De Vleeschouwer et al., 2018;Karatsolis et al., 2020). We then extrapolate the IODP Site U1463 age model to other IODP Expedition 356 sites, as well as to regional industry wells and to 2D seismic data. This approach ultimately results in a consistent age model for late Neogene strata on the NWS of Australia. The correlation of Neogene stratigraphy among industry wells and IODP Expedition 356 sites is achieved by using natural gamma radiation (NGR) wireline logs. Distinct marker beds and their geological ages are then mapped throughout regional 2D seismic lines along the NWS. The independent age model is also used to establish a high-resolution planktonic foraminiferal biostratigraphy allowing comparison with published biohorizons from the latest Miocene into the Pleistocene. These updated, calibrated biohorizons will help to disentangle planktonic foraminiferal paleobiogeographic patterns related to the Indonesian Throughflow by comparison with sites located in the western Pacific and the rest of the Indian Ocean for the Neogene.

Site Selection
We selected a series of IODP sites and industry wells to establish a consistent framework for dating the NWS (Figure 1; Table 1). IODP Site U1463 in the Northern Carnarvon Basin was selected as reference site for the NWS of Australia as this site contains a continuous, high-resolution record of deeper water sediments from the Mio-Pliocene transition into the Pleistocene (Gallagher et al., 2017). A high-resolution benthic stable oxygen and carbon isotope record was established for this site and astronomical tuning was performed to provide an independent age model for the NWS. The NGR record was then used for correlation to the other IODP sites and the industry wells. Additionally, this age model was used to determine the timing for important biostratigraphic datums for planktonic foraminifera for this section of the Indian Ocean.
IODP Site U1462 in the Northern Carnarvon Basin and IODP Site U1464 in the Roebuck Basin are included as part of a parallel section along the NWS (Figure 1). For all these sites NGR records are available and can therefore be correlated to the reference NGR record of IODP Site U1463 (Gallagher et al., 2017). Additionally, we included a series of industry wells on the NWS to expand the coverage on the NWS (Figure 1; Table 1). The wells were selected based on their previous use in paleoceanographic reconstructions, and for having representative NGR records to allow correlation with the IODP sites (Gallagher et al., 2014

Benthic Stable Oxygen and Carbon Isotopes
The shipboard biostratigraphy Gallagher et al., 2017) provided the necessary time markers to inform a sampling strategy that allows for the construction of an astronomically-tuned age model (30-40 cm sampling resolution, corresponding to ∼6 kyr temporal resolution; Figure 2). Samples were freeze-dried, subsequently washed over a 63 µm mesh sieve and oven-dried. As preservation was occasionally poor and abundance low we selected Uvigerina spp. instead of one species of Uvigerina for performing stable oxygen and carbon isotopes (Figures 2 and 3). Up to 20 specimens were picked from the 250-400 µm size fraction, which was extended to 150-250 µm when not enough specimens were present. Stable isotope analyses were performed on a Finnigan MAT 251 gas isotope ratio mass spectrometer equipped with an automated carbonate preparation device at MARUM, University of Bremen. Isotopic results were calibrated GROENEVELD ET AL.
10.1029/2020GC009418 4 of 20  . Black crosses indicate shipboard calcareous nannofossil and planktonic foraminiferal biostratigraphic age markers (Gallagher et al., 2017); (c) Correlation of the TEX 86 record (Smith et al., 2020) in the depth domain with the benthic δ 18 O-stack LR04 (Lisiecki & Raymo, 2005); (d) Correlation of the benthic δ 18 O in the depth domain with the benthic δ 18 O-stack LR04 (Lisiecki & Raymo, 2005). Gray, vertical lines between the records in panels b-d indicate tie-points; dark gray lines indicate tie-points based on the proxy in that particular panel. IODP, International Ocean Discovery Program. (a) relative to the Vienna Pee Dee belemnite (VPDB) using the NBS19 standard. The standard deviation of the house standard (Solnhofen limestone) was 0.03‰ for δ 13 C and 0.04% for δ 18 O during the measuring period.

Spectral Analyses
Spectral analyses were carried out using the multi-taper method with three 2π−tapers (Thomson, 1982) and LOWSPEC background estimation (Meyers, 2012), as implemented in the R-package "astrochron" (Meyers, 2014). The confidence levels were calculated applying the LOWESS-based procedure (Cleveland, 1979;Ruckstuhl et al., 2001). Depth-to-time conversion and bandpass filtering were carried out using the functions GROENEVELD ET AL.  (Smith et al., 2020) in comparison with the global benthic LR04 δ 18 O-stack (black) (Lisiecki & Raymo, 2005). IODP, International Ocean Discovery Program. (a) "tune" and "bandpass" from the same R-package. The astronomical solution of Laskar et al. (2004) was used as reference ( Figure 2). Generally, this study adheres to the guidelines for an effective cyclostratigraphic study described in Sinnesael et al. (2019).

Biostratigraphy
Dried samples were sieved at 150 µm mesh before identification of specific marker species. A total of 121 samples of IODP Site U1463 (section 356-U1463-C-20-H4 (188.05 m CCSF) to section 356-U1463-C-56-F3 (401.78 m CCSF)) were investigated for specific species of planktonic foraminifera to determine if biostratigraphic first and/or last occurrences agree with published datums for the Atlantic and Pacific. Planktonic foraminifera were identified following the taxonomy of Kennett and Srinivasan (1983), Bolli and Saunders (1985), Schiebel et al. (2017), Wade et al. (2018), and Lam and Leckie (2020a). Published ages for bio-events are from Wade et al. (2011) and King et al. (2020). Individual foraminifera were recorded in qualitative terms based on an assessment of all grains from the 150 to 250 µm, 250 to 400 µm, and >400 µm size fractions loosely covering a picking tray. The relative abundance of specific foraminiferal species within the assemblage was classified as common, possibly present, or in absolute numbers to determine ratios (e.g., sinistral vs. dextral for Pulleniatina spp.). Due to the occasional poor preservation of the sample material, it was not always possible to determine if a certain species was present in a particular sample (Gallagher et al., 2017). Preservation was classified from very poor via poor, medium, and good to very good.

Dynamic Time Warping of Natural Gamma Radiation Records
Downhole logging formed an indispensable part of scientific data acquisition during IODP Expedition 356, with downhole logging performed at five out of a total of seven sites (Gallagher et al., 2017). In this paper, we incorporate downhole logging records from IODP sites U1462, U1463 (Northern Carnarvon Basin) and U1464 (Roebuck Basin). The natural gamma radiation (NGR) logs of the latter two sites have been used for paleoclimate studies in Christensen et al. (2017) and Groeneveld et al. (2017) respectively, and a detailed description of the NGR downhole logging methodology during IODP Expedition 356 can be found in these two studies.
We complement the IODP NGR downhole logs with wireline log data from the latest Miocene to Pleistocene sections of four industry wells from the Northern Carnarvon Basin (Figures 1 and 4; Table 1). From east to west, these industry wells are Finucane-1, Angel-2, Goodwyn-6, and Goodwyn-2; their well logs can be sourced from the Geoscience Australia online NOPIMS database (http://www.ga.gov.au/nopims; last access May 21, 2020). We interpreted the approximate stratigraphic position of the latest Miocene in the industry wells by using previously-published biostratigraphic data from cuttings by Gallagher et al. (2009Gallagher et al. ( , 2014 and by extrapolating from the detailed IODP age-depth models in the Carnarvon Basin. We established a detailed correlation between the three IODP and four industry NGR downhole logs by applying a dynamic time warping approach. Dynamic time warping (DTW) is a technique to compare depthor time-series with each other ( Figure 5; supporting information). The objective of DTW is, given two complementary series, to stretch or compress them locally in order to make one resemble the other as much as possible. Hence, the warping refers to the optimal deformation of the depth-or time-scale of one of the two input series to match the other. It is important to note that DTW results in a continuous transfer function between the warped and the reference record. It thus does not provide specific tie-points linking the analyzed records. In a geologic context, DTW can be useful, as the technique can incorporate constraints on stratigraphic ages and realistic sedimentation rates (Kotov & Pälike, 2017;Lisiecki & Herbert, 2007;Lisiecki & Lisiecki, 2002). In this study, we compute dynamic time warps and optimal alignments between NGRlogs by using the open-source R package dtw by Giorgino (2009) on the R platform for statistical computing (R Core Team, 2014). Thereby, we always use the IODP Site U1463 computed gamma ray emission (HCGR) measured in American Petroleum Institute units (gAPI) as the reference. The depth-scales of the two other IODP sites and four other industry wells are thus warped to display an optimal NGR-series fit with IODP Site U1463 (Figures 4 and 5; supporting information). During DTW, we use the slope-constrained step patterns from Sakoe and Chiba (1978) to place bounds on the local slope of the warping curve. Therefore, we avoid the situation where local sedimentation rates exhibit unrealistic deviations from the mean sedimentation  rate. After DTW, we tested whether the generated mapping function between the depth-series under investigation and IODP Site U1463 fulfills biostratigraphic and lithostratigraphic scrutiny. When this was not the case, we reiterated DTW with adjusted settings, for example by tightening or relaxing sedimentation rate constraints or by adjusting the presumed stratigraphic position of the latest Miocene in the industry wells.

Definition of Different Depth Scales
The measurement of depth is an essential obstacle in sub-surface marine geology. Next to the two-way travel time in seismic images, this study uses several different depth-scales for isotopic and NGR depth-series following commonly used routines for the respective data sources. Industry wireline NGR logs are reported along a depth-scale in meters below rotary table (mbrt) from which the well was drilled. This depth scale GROENEVELD ET AL.

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8 of 20 thus also includes the full depth-range of the water column and the height of the rotary table above mean sea-level. Sources of error in this depth-scale are related to uncompensated heave in case of floating rigs, stretching of the wireline cable and stick and slip of the downhole tool.
IODP wireline NGR logs are reported using a Wireline log Matched depth below Sea Floor (WMSF) depth scale. Water depth and rig height are excluded by identifying the sea floor by means of a stepwise increase in the NGR signal at the sea bed. The uncertainty on this determination adds to the above-mentioned sources of error.
Core-based data from the IODP sites, like the biostratigraphic horizons, are reported in cored meters below seafloor (CSF-A). Each hole of a particular site has its own CSF-A depth scale. Additionally to the wireline downhole logging to acquire the NGR, discrete analyses for NGR were also performed on the recovered core material Gallagher et al., 2017). This allowed to correlate between the CSF-A depth scale (discrete NGR analyses) and the WMSF depth scale of the downhole logging . The resulting tie-points were used to linearly extrapolate from the CSF-A depth scale to the WMSF depth scale.
We report benthic isotope data, measured on IODP core samples, along the Core Composite depth below Sea Floor (CCSF) depth scale. This depth scale considers adjusted depths constructed to resolve gaps in the core recovery and depth inconsistencies between the different holes and their respective CSF-A depth scales. Typically, a CCSF scale is constructed onboard a research vessel like R/V JOIDES Resolution by shifting cores vertically based on the correlation of high-resolution core logging data from multiple, adjacent holes. In this instance, for IODP Site U1463, we use the shipboard splice (Gallagher et al., 2017), with the slight revision in the Pliocene, as reported in De Vleeschouwer et al. (2018). At IODP Site U1463, the WMSF depth is consistently shallower than the CCSF scale: The offset between wireline and coring depth varies from 15 to 38 m and may be explained by sediment expansion in the drilling process.

Seismic Correlation and Age Determination
Extensive publicly released petroleum exploration multichannel seismic surveys are available for the NWS for our 2D seismic analyses (Longley et al., 2002), which have been provided by Geoscience Australia (https://nopims.dmp.wa.gov.au/nopims; latest access June, 7 2020). These industry seismic data have been extensively used in previous studies to document the Paleogene to Neogene evolution of the carbonates and siliciclastics along this margin (e.g. Belde et al., 2017;McCaffrey et al., 2020;Rosleff-Soerensen et al., 2012). Key seismic reflectors in these datasets were previously assigned ages based on either biostratigraphy (Belde et al., 2017;Gallagher et al., 2014;McCaffrey et al., 2020) or Sr-isotope ages (Rosleff-Soerensen et al., 2012). In this study we use the ages determined by the orbitally-tuned benthic foraminiferal isotope age model.
We constructed two composite seismic profiles; one parallel along the NWS connecting the different IODP sites and industry wells, and one perpendicular to IODP Site U1463 to show the 3D-presence of the main features on the NWS (Figures 6 and 7). The WMSF depth scale was converted to a two-way travel time (TWT) scale using downhole velocity (check-shot) data to allow the ages to be plotted on seismic profiles. In the absence of check-shot velocity data, correlation to the TWT scale is calculated by cumulatively adding sonic travel times between each downhole P-wave velocity measurement. Industry well depths were correlated to the TWT scale using the calibrated check-shot data and Vertical Seismic Profiles (VSP) from Industry well completion reports. Seismic correlation and identification of characteristic features were performed using the IHS Markit Kingdom software using standard criteria for identification (Mitchum Jr. et al., 1977). The characteristic horizons H5 (Tortonian), H6 (Base Pliocene), and H7 (Base Pleistocene) were used as baseline to correlate the different seismic profiles (Belde et al., 2017;McCaffrey et al., 2020).

Orbitally Tuned Age Model Based on Benthic Stable Isotopes
The initial age model for IODP Site U1463 was based on shipboard data, specifically the biostratigraphy using nannofossils and planktonic foraminifera Gallagher et al., 2017). This showed that a complete latest Miocene to Pleistocene sediment sequence is present at IODP Site U1463. Stable oxygen and carbon isotopes using the planktonic foraminifer Trilobatus sacculifer showed that the δ 13 C record exhibited the 405 kyr eccentricity cyclicity that could be correlated to the astronomical solution Laskar et al., 2004). The completeness of the IODP Site U1463 sediment archive and its clear link to global insolation patterns means it can be used to construct a reference age model for the NWS of Australia.
Benthic stable oxygen isotope data are commonly used to construct Plio-Pleistocene age models as they contain the global signature of climatic and oceanographic change through time (Lisiecki & Raymo, 2005). The main premise of these type of data is that the benthic foraminifera live at water depths where local changes in water mass characteristics are only minor, and thus the global signal is the main control on this proxy. Paleo-water depths for IODP Site U1463 during the Pliocene and early Pleistocene, however, were never deeper than ∼600 m, which means that bottom waters may have experienced significant changes in temperature and salinity affecting the δ 18 O-signature of benthic foraminifera (Gallagher et al., 2017;Gurnis et al., 2020). Additionally, ice volume changes during the early Pliocene, and thus variations in benthic δ 18 O, were not very pronounced (Lisiecki & Raymo, 2005). Spectral analysis of the Uvigerina spp. δ 13 C record in the depth domain shows the presence of significant cycles of ∼2.2 m and ∼24 m, respectively ( Figure 2). Taking into account bio-and magnetostratigraphic constraints, these cycles likely correspond to the imprint of 41-kyr obliquity and 405-kyr eccentricity. The latter cycles are particularly useful for age-depth model GROENEVELD ET AL.

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10 of 20 construction, as the bio-and magnetostratigraphy unambiguously assigns them to the fifth-twelfth 405-kyr eccentricity cycles counting back from the present (Figure 2; Laskar et al., 2004). In this first step, we thus applied the 405-kyr astrochronozones as proposed by Hilgen et al. (2020). In a second step, we correlated the benthic δ 18 O record at IODP Site U1463 to the LR04 benthic oxygen isotope stack for pinpointing the more pronounced glacial cycles (Figure 3; Lisiecki & Raymo, 2005). In the younger part of the age model, that is after the onset of Northern Hemisphere Glaciation (<2.7 Ma), we additionally used the strong expression of glacial-interglacial oscillations in the TEX 86 sea water temperature record of IODP Site U1463 to fine-tune the age model (Smith et al., 2020). The 29 tie-points between depth and time define the age-depth model of IODP Site U1463 and imply sedimentation rates between 4 and 8 cm/kyr throughout the studied interval with increasing sedimentation rates up to 16 cm/kyr in the youngest part of the record ( Table 2). The age model in this study is similar yet temporally more extensive (∼3.5 Myr vs. < 1 Myr) than the previous IODP Site U1463 age models presented in De Vleeschouwer et al. (2018) and Auer et al. (2019).

Planktonic Foraminiferal Biostratigraphy
Biostratigraphy using planktonic foraminifera is important not only for paleoceanographic reconstructions but also commonly used in the industry for age dating of petroliferous strata. The first and last appearances of different species, known as biohorizons, can be linked to paleomagnetic timescales and orbitally tuned using benthic foraminiferal δ 18 O records to create highly precise age models (Gradstein et al., 2012;Wade et al., 2011). The initial age models for IODP Site U1463 and the nearby IODP sites were only based on the biostratigraphy, as the nature of the carbonate-rich sediments present prevented reliable paleomagnetic analyses (Gallagher et al., 2017  barriers often lead to diachroneity of biozonal datums compared to apparently global events. One of the better known and more-recent of these regional bio-events is the disappearance of Globigerinoides ruber (pink) in the Indo-Pacific realm 120 kyr ago (Thompson et al., 1979), whereas this taxon still lives today in the Atlantic.
Pliocene planktonic foraminiferal biohorizons are mainly calibrated using Pacific or Atlantic studies (Gradstein et al., 2012, King et al., 2020Wade et al., 2011) and often with differences of up to several 100 kyr (Table 3; Gradstein et al., 2012). These variations hamper the reconstruction of high-resolution paleoceanographic records for the Indian Ocean as it is still unclear which of these biohorizons are applicable to this ocean basin. In addition, existing older biostratigraphic studies for the Indian Ocean (e.g. Srinivasan & Chaturvedi, 1992;Srinivasan & Sinha, 1998;Zachariasse, 1992) are often based on out-of-date age models.
We document 24 early Pliocene to early Pleistocene biostratigraphic datums at IODP Site U1463 that were determined with an average time resolution of ∼28 kyr per sample. New ages for the respective biostratigraphic datums are based on the independently, orbitally-tuned benthic isotope age model for IODP Site U1463 (Table 3). The biostratigraphy at IODP Site U1463 can be closely tied to Ocean Drilling Program (ODP) Site 763 further offshore western Australia (Figure 1; Sinha & Singh, 2008). With a few exceptions, the bio-events are very similar at both locations ( Table 3). For example, the final occurrence of Globoturborotalita nepenthes (4.18 Ma) is ∼760 kyr earlier than at ODP Site 763, yet close to the commonly published age (4.38 Ma; King et al., 2020). As G. nepenthes is quite rare at IODP Site U1463, its earlier disappearance may be due to specific local oceanographic conditions. Similarly, Globoconella inflata appears 670 kyr later at IODP Site U1463 than at ODP Site 763. This species is commonly present in temperate water masses. Accordingly, as G. inflata appeared much earlier at ODP Site 763, it implies that this site may have been affected earlier by the north-flowing West Australian Current than the more proximal IODP Site U1463, as was also suggested by previous reconstructions (Auer et al., 2019;De Vleeschouwer et al., 2018;Karas et al., 2011). Some of our Indian Ocean biozonal datums at IODP Site U1463 differ from previous foraminiferal bio-horizons (  (Gradstein et al., 2012;Wade et al., 2011). However, in several locations in the Pacific and Atlantic it was found to have persisted until 3.11-3.13 Ma (Chaisson and Pearson, 1997;Lourens et al., 2004;Shackleton et al., 1995), and perhaps more commonly into younger strata (Boltovskoy, 1974;Chaisson & Leckie, 1993;Jenkins & Srinivasan, 1986;Lam & Leckie, 2020b;Norris et al., 1998;Shackleton et al., 1995).
Changes in the coiling direction of certain planktonic species such as the genus Pulleniatina spp. may be used as biostratigraphic markers (Saito et al., 1976). The most commonly used datum is the L9-event GROENEVELD ET AL.  Karatsolis et al. (2020).

Table 2 Tie-points of Reconstructed Age versus Sediment Depth and Sedimentation Rates Based on Benthic Stable Oxygen and Carbon Isotopes, TEX 86
Temperatures (Smith et al., 2020), and K (%) Karatsolis et al., 2020)   (100%-sinistral to 100%-dextral) reported at 4.08 Ma (Gallagher et al., 2017;Saito, 1976;Wade et al., 2011). At Site U1463, the first dextral specimens appear at 4.20 Ma and the last sinistral specimens were present at 3.95 Ma, a total time span of ∼250 kyr for the full change in coiling direction (Table 3) (see data in Pangaea). After this change Pulleniatina disappears from the Atlantic until 2.26 Ma, yet predominantly dextral forms are still present in the Indian Ocean. At IODP Site U1463 sinistral specimens become common and occasionally dominant again after 2.49 Ma and after 1.76 Ma constitute 100% of the specimens equivalent to Saito's events L4-L8.
The Indonesian Throughflow (ITF) is a major influence on the biostratigraphy in the Indian Ocean as it supplies warm waters from the equatorial Pacific. As the ITF is a relatively shallow current system, sub-surface foraminiferal species are living in water masses, which may originate from the sub-Antarctic or even Atlantic rather than from the Pacific. Srinivasan and Sinha (1998) showed that Pulleniatina spectabilis, a commonly occurring Pliocene thermocline species in the equatorial Pacific, never migrated into the Indian Ocean during the Pliocene suggesting that the ITF was already restricted to such an extent that only shallower waters may have passed through it. Indeed, P. spectabilis is also not present at IODP Site U1463. However, there is no consistent pattern in offsets between biodatums for other deeper-dwelling species, especially Globorotalia spp. at IODP Site U1463 with those in the Atlantic or the Pacific. Some taxa have ages very similar to Atlantic datums, for example, Globorotalia exilis, while others are more similar to Pacific age datums, for example, Globorotalia pseudomiocenica, or somewhere in-between, for example Globorotalia limbata (Table 3). Although a major switch in the restriction of the ITF occurred 3.5-3.0 Ma when the source waters for the ITF changed from the south Pacific to the north Pacific due to the northward movement of the Australian plate (Cane & Molnar, 2001;Karas et al., 2009), P. spectabilis occurred ∼5.20-4.20 Ma (Berggren et al., 1995). The lack of a consistent pattern in the biohorizons of deeper-dwelling species during the Pliocene implies that a biogeographical barrier existed prior to the early Pliocene.
One particular biohorizon that may have been established via a different pathway from the Pacific than the ITF is the first occurrence of Globorotalia truncatulinoides. This datum is generally placed at 1.93 Ma (Wade et al., 2011), however, in the southwest Pacific this species had already appeared at ∼2.8 Ma (Dowsett, 1989;Lazarus et al., 1995;Spencer-Cervato & Thierstein, 1997). At IODP Site U1463, it appears at 2.17 Ma; this may be due to its migration from the southwest Pacific via the Tasman Leakage (Speich et al., 2002;van Sebille et al., 2012).

Correlation of NGR Between IODP Sites and Industry Wells
Time warping the NGR records of the other Exp. 356 IODP sites and industry wells demonstrates that these sequences have similar downhole gamma ray signatures, compared to IODP Site U1463 (Figure 4; Christensen GROENEVELD ET AL.  (Wade et al., 2011 -Pacific); 3.05 Ma (Shackleton et al., 1995 -Pacific); 3.11 Ma (Wade et al., 2011 -Atlantic). g A similar occurrence was found at IODP Site U1482 (Rosenthal et al., 2018). h This is the next sample after %-sinistral specimens was zero for the first time. See text for further discussion.  , 2017). Around the Miocene-Pliocene transition (∼5.3 Ma; ∼380 m WMSF) an increase in NGR was interpreted by these authors to be related to the onset of a wetter climate in northwestern Australia resulting in an increase in river-brought sediments to the NWS due to increasing precipitation. Although a similar increase is seen at most sites investigated, a recent study suggests that this steep increase may not be solely climate related, but rather a tectonic deepening event that did not occur simultaneously in different basins, although this nevertheless created the accommodation space needed to deposit climate-related cyclic sedimentation (Karatsolis et al., 2020). At IODP Site U1464 located in the Roebuck Basin the onset occurs rather abruptly at ∼6.0 Ma (∼320 m WMSF), while at Site U1463 in the Northern Carnarvon Basin the onset is later around 5.3 Ma (∼380 m WMSF). In addition, all major patterns may be correlated in these different NGR records suggesting a common age history. The uppermost part of the NGR records, that is, above ∼80 m, does not show much structure as this part in the NGR signal of the drilling holes is usually impeded by hole casing (Figure 4).
In a final step we projected the biostratigraphic datums determined at IODP Site U1463 onto the other sites following the DTW correlations performed using the NGR. As these correlations are based on U1463 GROENEVELD ET AL.  wireline depth below the seafloor (WMSF) and the biostratigraphic datums are reported in U1463 cored depth (CSF-A), this projection involved a conversion of the U1463 depth scale from cored to wireline depth (WMSF). After this conversion, the U1463 biostratigraphic datums were projected along our DTW correlations determining approximate positions of the respective biostratigraphic datums at each site (Table 4). We emphasize that this projection does not classify as a new age model for the other sites but rather predicts the expected position of different biostratigraphic datums.

Seismic Stratigraphic Analyses
A series of 2D multi-channel seismic profiles were combined to produce a regional composite profile across the NWS connecting several IODP 356 sites (Site U1462 to Site U1464) and industry wells over a distance of ∼400 km ( Figure 6). Tracing of seismic reflectors across large distances such as these often encounters many challenges (e.g. condensed surfaces or erosional truncations) when attempted in isolation. However, integration of seismic data with correlated NGR and biostratigraphical data provides regularly distributed control points that allow for accurate tracing of these horizons, even across uncertain sections. This integration between the NGR, biostratigraphy and seismic data increased the accuracy and absolute age determination of previously published seismic horizons (H6 and H7; Belde et al., 2017;McCaffrey et al., 2020) across the shelf between IODP 356 sites U1462 and U1464. The transition from the Miocene into the Pliocene is represented across the majority of the shelf between IODP sites U1462 and U1464 by the distinct shift in reflector geometry. This transition, from sets of strong reflectors surrounded by discontinuous zones of disrupted reflectors below the H6 horizon (∼6.2 Ma, Figure 6), to low amplitude parallel reflectors above, is observed in the well data as a shift in lithology from shallow water carbonate/reefal dominated, to deeper water fine grained sediments. Toward the southern end of the section, the seismic architecture becomes increasingly complex as these sediments are interbedded with the mixed siliciclastic and carbonate Bare Formation ( Figure 6). This unit developed as a fluvial to fluvio-deltaic deposit on a mainly carbonate-dominated shelf (Cathro et al., 2003;Sanchez et al., 2012;Tagliaro et al., 2018;Wallace et al., 2003). Siliciclastic input became especially intense from the Pliocene onwards when climate became wetter . Between IODP Site U1462 and Angel-2 the Plio-Pleistocene sediments are observed to be underlain by the Bare Formation, placing the top of the Bare Formation at 5.59 Ma at IODP Site U1462. Further north however, between Angel-2 and Finucane-1, a thick siliciclastic package ending at ∼2.38 Ma is observed to be interbedded with the surrounding Plio-Pleistocene sediments, showing that this formation is non-synchronously deposited along the NWS ( Figure 6). Tagliaro et al. (2018) even identified Bare-like sediments within the overlying carbonates at the nearby industry well Bounty-1 with an age of 1.63 Ma, although the sand layers were minor in comparison with the limestone surrounding them.
Further toward the northeast the Cenozoic sediment sequence of predominantly carbonates continues further back in time until the early Cenozoic, although IODP sites U1463 and U1464 only drilled to the early Miocene (Gallagher et al., 2017;Groeneveld et al., 2017). The depositional setting during the Miocene is generally very shallow with likely subaerial exposure during certain times such that hiatuses may be present Petrick et al., 2019).
Additionally, a dip profile crossing the Northern Carnarvon Basin at the location of IODP Site U1463 was constructed showing the general downslope geometry of the shelf (Figure 7). This profile also shows reef developments during the Miocene, and the presence of a newly identified mass transport deposit on top of the regular sedimentary sequence, called the Picard-slide (Gallagher et al., 2017; Figure 7) with an estimated age range between 910 and 610 ka.

Implications for Dating the History of the NWS
The creation of a consistent age model for the late Neogene strata on the NWS and its relationship to other subsurface downhole and seismic datasets has allowed us to produce a consistent framework to investigate the evolution of various laterally discontinuous carbonate (tropical reefs) and siliciclastic (the Bare Formation) units that are widespread in this region. After large areas of the NWS were sub-aerially exposed during the late Miocene Petrick et al., 2019;Tagliaro et al., 2018), tectonic subsidence during the latest Miocene created sufficient accommodation space to deposit a thick sequence of sediments during the Pliocene and early Pleistocene (Gallagher et al., 2017;Gurnis et al., 2020). This tectonic subsidence is also thought to play a role in the transition of the NWS reef system from primarily barrier reef morphologies in the middle Miocene to pinnacle and atoll formations in the Pliocene (McCaffrey et al., 2020).
Our new age framework suggests that deposition of the siliciclastic Bare Formation occurred during the late Miocene and early Pliocene. The Bare Formation is a laterally discontinuous progradational sand-dominated unit that reached IODP Site U1462 by the earliest Pliocene (Tagliaro et al., 2018). Deposition of the Bare Formation expanded and prograded with the onset of wet climate in northwestern Australia near the base of the Pliocene (5.3 Ma), and deposition continued until climate switched again to dry conditions by the early Pleistocene (2.39-1.93 Ma; Christensen et al., 2017;Tagliaro et al., 2018). Our new age framework constrains the age of the termination of this siliciclastic pulse to 2.38 Ma (222 m WMSF in U1463) near Angel-2 ( Figure 6), with remnant siliciclastic deposition continuing until as young as 1.63 Ma at the nearby industry well Bounty-1 (Tagliaro et al., 2018).
Our age constrained seismic stratigraphic framework may be applied to most of continental shelf and slope regions of the NWS over an area of ∼150,000 km 2 . Paleoceanographic drilling has been performed for example on the Wombat Plateau located north of the NWS providing reconstructions going back to the early Cenozoic, but also including detailed studies on the Pliocene and Pleistocene (Exon et al., 1992;Holbourn et al., 2004;Karas et al., 2011). More recently IODP Expedition 363 drilled sites U1482 and U1483 off the northwestern slope of the NWS in the direct outflow of the Indonesian Gateway (Rosenthal et al., 2018). However, linking these dated reflectors to deep ocean archive is not straightforward as deep ocean to continental margin linking seismic data are rare. Nevertheless, the NGR and benthic isotope records of the NWS can be correlated allowing a direct link between pelagic paleoceanographic reconstructions and the terrestrial input from Australia to the more proximal locations.

Conclusions
In this study, we have created a high-resolution regional framework to precisely determine the ages of sediments and events on the northwest shelf (NWS) of Australia. This area is ideally located to record changes in the outflow of the Indonesian Throughflow (ITF) as well as to monitor how monsoonal precipitation and aridity change over Australia.
We reconstructed an independent, astronomically tuned age model based on benthic foraminiferal oxygen and carbon isotopes for International Ocean Discovery Program (IODP) Site U1463. The NGR record for IODP Site U1463 was then correlated to the NGR records of several other IODP sites and industry wells on the NWS. Additionally, these sites were linked to each other using a composite seismic profile along the NWS connecting the main reflectors in the region.
This independently dated and consistent age framework for the NWS allowed us to update existing biostratigraphic datums on planktonic foraminifera, and to fine-tune the ages of the main seismic reflectors and major sedimentary events, for example, top of the Bare Formation at 2.38 Ma, on the NWS. Biostratigraphic datums of deeper-dwelling planktonic foraminifera show that the ITF shoaled sufficiently near the start of the Pliocene to act as biogeographical barrier. Comparison with regional (ODP Site 763A and IODP Site U1482) and global biostratigraphic events suggests that this area may have provided specific conditions such that some species, that is, D. altispira, Sphaeroidinellopsis kochi, and Globorotalia margaritae, survived several 100 kyr longer than their published last occurrences in the tropical to subtropical biozonation scheme (King et al., 2020;Wade et al., 2011).
We showed how the combination between an independent orbitally-tuned benthic isotope record, downhole records of physical properties and an extensive seismic network, a framework can be created that provides a consistent age model for a specific region. This regional and seismically tied Neogene age model can be used to improve age constraints on subsurface reef and carbonate platform development (e.g., McCaffrey et al., 2020), mass transport deposit generation and periodicity, and the evolution of major siliciclastic pulses (e.g. the Bare Formation; Tagliaro et al., 2018) related to regional (and global) climate and oceanic events.