Detrital zircon age signatures of the basal Cambrian sandstone unit in North China: implications for drainage divides during global Sauk transgression and separation from Gondwanaland

ABSTRACT The basal Cambrian sandstone unit in the North China craton (NCC) is an example of globally widespread siliciclastic succession that resides on the Great Unconformity and deposited on a hypothesized low-lying peneplain during the Cambrian global eustatic sea-level rise. Detrital zircon age signatures from this distinct sequence enable recognition of the ancient drainage system of the NCC in deep time and track its potential linkage with the Gondwana landmass. LA-ICP-MS U–Pb dating of the fossil-calibrated basal Cambrian (Series 2) detrital zircon samples from seven measured sections reveal marked spatial changes in their age signatures that can be divided into three distinct types. The first is generally characterized by the bimodal age populations with broad peaks at ~1.85 Ga and ~2.5 Ga that correlate with the Archean to Paleoproterozoic basement inboard of the NCC. The second is featured by multimodal distribution with diagnostic Neoproterozoic peaks that correspond to subregional magmatic record. The third also shows multiple-zircon age populations, but yields significant crystallization ages close to the early Cambrian age. Comparing our new data with existing age spectra for the Cambrian strata across the NCC and the northern Gondwana demonstrates that separate drainage systems did exist in the peneplained basement during global Cambrian transgression and the basal Cambrian unit in the NCC was not a part of the far-travelled sand sheet across the northern margin of Gondwana. The most suitable source for Cambrian-aged grains constrained by paleogeographic restoration is the arc terrane developed along the northern margin of the NCC as a result of subduction of the Paleo-Asian oceanic plate. Our new continental-scale detrital zircon provenance signatures in the basal Cambrian unit suggest that the NCC should be considered a discrete continental block separated by the Proto-Tethys Ocean in the Cambrian, rather than an integral part of the northern Gondwana. Graphical abstract


Introduction
Eustatic sea-level rise is commonly accompanied by a reduced sediment influx to the basin and reworking of previous deposited sediments that facilitate the formation of siliciclastic rocks with high maturity at the base of transgression sequence (Cattaneo and Steel 2003;Miall 2015). As one of the most dramatic global marine transgressions in earth history, the Sauk transgression of Sloss (1963) witnessed the globally widespread occurrence of a Cambrian sequence of quartzrich sandstone above the Great Unconformity on many paleocontinents, such as Laurentia (Lindsey and Gaylord 1992;Gehrels et al. 2011), Baltica (Isozaki et al. 2014;Lorentzen et al. 2018), Siberia (Sears and Price 2003) and Gondwana (Avigad et al. 2005;Bassis et al. 2016). Given the Great Unconformity has proven to be one of the most significant stratigraphic discontinuities on the earth and represents a time interval of significant crustal exhumation (Karlstrom and Timmons 2012;Peters and Gaines 2012), these basal Cambrian sandstone units provide a record of sediment routing and the development of drainage system on a very wide, peneplained Precambrian basement during a period of relative sealevel rise. In the case of quartz arenites, the lack of compositional variability in mature sediments makes traditional petrographic discrimination of provenance difficult. Therefore, many studies have investigated the provenance of these basal Cambrian sandstone units using the method of detrital zircon U-Pb geochronology (e.g. Kolodner et al. 2006;Gehrels et al. 2011;Lorentzen et al. 2018;Matthews et al. 2018), and explored the implications for paleogeographic correlations and tectonic evolution (e.g. McKenzie et al. 2011;Martin et al. 2015;Freiburg et al. 2020).
Among the eastern Asian continent, the North China craton (NCC) is a stable tectonic unit where the Great Unconformity and a comparable basal Cambrian sandstone unit developed (Chough et al. 2010;He et al. 2017;Meng et al. 1997;Wan et al. 2019;Li et al. 2020;Cho et al. 2021;Lee et al. 2021). The basal Cambrian nearshore quartz-rich sandstones exposed along the southern and western margin of the NCC, extending over ~3000 km from the present-day western part of Inner Mongolia (northwest China) to the Korean Peninsula. U-Pb dating of the basal Cambrian detrital zircon samples in the western margin yields double peaks at ca. 1.85 Ga and 2.50 Ga (Sun and Dong 2019;Zhang et al. 2020), similar to the age distribution of crystalline basement rocks inboard of the NCC (Darby and Gehrels 2006;Zhao and Zhai 2013;Myrow et al. 2015). Therefore, it has been argued that the sediments were not derived from other crustal blocks, but solely from the exposed parts of the NCC (Sun and Dong 2019;Zhang et al. 2020). This argument provides support for the long-held view that the NCC was a discrete continental block since the breakup of the Rodinia supercontinent (e.g. Sengör and Natal'in 1996;Stampfli et al. 2011;Wilhem et al. 2012;Cocks and Torsvik 2013;Zhao et al. 2020a). However, a growing number of the Pan-African-aged detrital zircons discovered from the basal Cambrian strata in the eastern part of the NCC have been generally considered to be sourced from Gondwana (McKenzie et al. 2011;Hu et al. 2013;He et al. 2017;Wan et al. 2019;Lee et al. 2021), implying its possible connection with the landmass of northern Gondwana.
The NCC is generally thought to have evolved into a relatively flat peneplain by early Cambrian time (Myrow et al. 2015;Meng et al. 1997;Cho et al. 2021). However, the observed nonuniformity in detrital zircon signature suggests that basal Cambrian sandstone unit across the NCC may be supplied by more diverse feeder systems than previously thought, thus undermining their implications without additional consideration for this spatial variability. In order to clarify sources of this distinct sequence, we report new detrital zircon U-Pb ages in the western and southern NCC and compare these with previously published zircon U-Pb data. The data both augment and confirm published age distributions and shed new light on the development of drainage divides on the peneplained NCC during global Cambrian transgression. These results demonstrate that the Basal Cambrian sandstone unit in the NCC should not be considered an integral part of the vast and fartravelled sand sheet across the northern margin of Gondwana, and provide further support for the development of a partially preserved arc associated with the convergent plate boundary of the northern NCC.

Geological setting
The NCC, also known as the Sino-Korean block, is one of major continental-scale cratonic masses in East Asia, which includes most of the North China and part of the Korean peninsula. With an area of ∼1.5 million km 2 , the NCC is separated from the South China block and Tibetan plateau to the south by the central orogenic belt of Qilian, Qinling-Dabie, and Sulu and bordered by the Central Asian accretionary orogen to the north ( Figure 1). Its basement was mainly formed in the Archean to middle Paleoproterozoic (Zhao and Zhai 2013;Cho et al. 2017), which has been thought to be related to its incorporation into the Columbia supercontinent during the period from 2.0 to 1.9 Ga (Kusky et al. 2007). Given the shared similarity of the Archean-Paleoproterozoic basement (Zhai and Santosh 2011) and ophiolitic suture has not yet been discovered, the triangle-shaped Alxa block is generally viewed as the westernmost part of the NCC. It has long been viewed that the Meso-to Neoproterozoic magmatism is rare in the NCC, but multiple Neoproterozoic magmatic events were recently recognized from several locations in the block, including ca. 853-835 Ma and ~740 Ma granitoid plutonism in the Helanshan region in the western NCC, and in the Korean Peninsula (Lee et al. 2003;Yang et al. 2019), and ca. 945-900, ca. 890-830 Ma and ca. 775 Ma intrusion and volcanism widespread in many subregions (Li et al. 2004;Liu et al. 2006Liu et al. , 2012Peng et al. 2010Peng et al. , 2011aPeng et al. , b, 2018Wang et al. 2011Wang et al. , 2012Kim et al. 2013b;Zhai et al. 2015;Zhang et al. 2016b;Su et al. 2021).
The sedimentary cover made of epeiric shallowmarine clastic and carbonate rocks of late Paleoproterozoic to Paleozoic ages. In contrast to the Neoproterozoic strata that are absent in most areas, the Cambrian sequence can be regionally found to rest unconformably on the Precambrian rocks of different ages, and the contact are well known as the Great Unconformity (He et al. 2017;Wan et al. 2019;Li et al. 2020;Lee et al. 2021;Liu and Zhang 2021). The Cambrian sedimentation in the NCC was initiated in the Cambrian Series 2, which is marked by a large-scale transgression that developed an epeiric sea across the continent (Chough et al. 2010;Myrow et al. 2015;He et al. 2017;Meng et al. 1997;Wan et al. 2019;Cho et al. 2021). The lowermost stratigraphic unit of the Cambrian, named as the Xinji Formation in the southern margin and the Suyukou Formation in the western margin, is characterized by marine phosphorus-bearing deposits. The basal Cambrian phosphorite deposits extend over ~1500 km along the western and southern margins of the NCC, and thus can be served as a time-parallel marker bed for regional stratigraphic correlation ( Figure 2). The age of the Xinji and Suyukou Formations has been well constrained to be ca. 520-514 Ma, because it contains trilobites and a diverse assemblage of small shelly fossils compatible with Series 2 of the Cambrian (Zhang et al. 1979;Yun et al. 2016;Li et al. 2016aLi et al. , 2021.

Sampling strategy and methodology
In this paper, we focus on seven well-studied regions along the southern and western margins of the NCC, including Suyukou and Qinglongshan sections in the west, and Shangzhangwan, Shuiyu, Yangpo and Xinji sections in the south (Figure 1). These sections were chosen on the basis of the quality of exposure of Ediacaran to Cambrian strata and existing biostratigraphic subdivision calibrated by Small Shelly Fossils (e.g. Yun et al. 2016;Li et al. 2016bLi et al. , 2021Pan et al. 2020). Given zircon is expected to be approximately one sand-grade finer than accompanying quartz grains in the case of equal hydraulic power (Komar 2007;Dickinson and Gehrels 2009), samples of medium-to coarse-grained quartz arenites were collected. Stratigraphic horizons of all samples for detrital zircon analysis are shown in Figure 2.
Zircon crystals were extracted from seven samples by standard density and magnetic separation techniques and then purified by hand-picking under a binocular microscope. All analyzed zircon grains were documented using cathodoluminescence images to select the spot with a diameter of 44 μm for dating. In situ zircon U-Pb analyses were conducted using laser-ablation multiple collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP MS) at the State Key Laboratory of Continental Dynamics at Northwest University. The detailed analytical methods of U-Pb dating of zircon by MC-ICP-MS are summarized in Yuan et al. (2004). In total, 777 analyses were obtained and 142 analyses that are more than 10% discordant (by comparison of 206 Pb-238 U and 206 Pb-207 Pb ages) are not considered or discussed further (628 dates were retained). We use

Detrital zircon results
Seven samples are conspicuously variable in detrital zircon U-Pb age signature. Among them, samples from the Qinglongshan, Longxian, Shangzhangwan, Shuiyu and Yangpo sections, labelled as QLS-3Z, CJW-1Z, SZW-1Z, 19NC-02 and YP-1Z, respectively, are predominated by the Archean and Paleoproterozoic ages, without any Meso-Neoproterozoic or Cambrian grouping ( Figure 3). In spite of obvious variations among these five samples, most zircons are clustered in age ranges of ca. 1750-1950 Ma and ca. 2400-2600 Ma, with two broad peaks at ~1.85 Ga and ~2.5 Ga (Figure 3). Here, the ~1.85 Ga peak is actually represented by one peak or multiple scattered peaks around 1.85 Ga. In contrast, samples from the Suyukou and Xinji sections, labelled as SYK-1Z and 20XJ-1, yield many younger dates. The Neoproterozoic grouping, with a peak at ca. 815 Ma, is the primary signal for sample SYK-1Z, whereas the sample 20XJ-1 yields a minor but significant peak close to the depositional age of the Cambrian Series 2 ( Figure 3). Therefore, the age spectra patterns allow three types of age signatures to be distinguished on the basis of diagnostic zircon age proportions. The first is characterized by all dates being Archean-Paleoproterozoic, while the second and third types exhibit unique Neoproterozoic and Cambrian ages, respectively (Figure 3).

Diverse feeder systems and drainage divides
Given the Great Unconformity has been recognized throughout the NCC (He et al. 2017;Wan et al. 2019;Li et al. 2020;Lee et al. 2021;Liu and Zhang 2021), it has long been accepted that the continent developed as a low-lying peneplain as a result of the prolonged phase of erosion and planation (Myrow et al. 2015;Meng et al. 1997;Cho et al. 2021). However, spatial nonuniformity of detrital zircon age signature preserved in the fossil-calibrated time-equivalent strata of the Cambrian Series 2 strongly suggests the sediment dispersal network developed on the NCC is more complicated than would be expected from a single continentalscale drainage system. This phenomenon is not only revealed by our new data, but also supported by existing dataset complied from published samples from the Cambrian strata across the continent. It is shown that the first type of age distribution is widely recognized, while the second type was restricted to the western and eastern margin, and the third type only occurred in the southern and eastern margins (Figure 4).
Evidence for diversity in the detrital zircon age signatures of the Cambrian sand sheet across the NCC reveals some previously unidentified complexities in drainage network and suggests the existence of drainage divides in the hypothetical low-lying peneplain of North China during global Cambrian transgression. It has been proven that the drainage system is largely controlled by topography related to tectonic deformation and mantle convection (Shephard et al. 2010;Wang et al. 2020b) and the drainage divides often lie along topographical ridges with high rock strength (e.g. resistant crystalline basement rocks; Bernard et al. 2019). The crystalline basement of the NCC is tectonically divisible in popular models into the eastern and western blocks (e.g. Zhao et al. 2005), which are separated by a central zone called the Trans-North China Orogen (Figure 5(a)). Presently, we cannot determine the location of elevated boundaries between different drainage areas in early Cambrian, but it seems that the spatial variation of detrital zircon provenance signatures in the lower Cambrian (Series 2) is more likely controlled by the granitegreenstone belts recognized by Zhai and Santosh (2011) (Figure 5(b)). During the middle Cambrian (Miaolingian), only two types of age distribution persisted, but they were more likely separated by a readily recognized drainage divide that approximately coincides with the western limit of Trans-North China Orogen ( Figure 5(c,d)).
Given it has long been recognized that drainage divides are not static through time but that they are mobile and can migrate laterally (Scherler and Schwanghart 2020), the possible migration of drainage divides, as well as the decrease of diversity of detrital zircon age signatures that from three types in the early Cambrian to two types in the middle Cambrian ( Figure 5), might be explained by continent-wide drainage reorganization, with the involvement of the incorporation of small-scale subregional sediment routing systems into continent-scale drainage networks. An alternative interpretation is that the source area yielding the distinctive Neoproterozoic ages might be submerged as a result of northward progressive marine transgression. In accord with the Sauk Sequence developed in North America (Sloss 1963;Meyers and Peters 2011;Peters and Gaines 2012), the Cambrian-aged sediments that overlie the Great Unconformity in the NCC are also time-transgressive, which is clearly shown by the reconstructed Cambrian paleogeography (Wang 1985;Zheng and Hu 2010) that the early Cambrian units occur on the margins of the continent and the middle Cambrian sediments overlie the Great Unconformity in continental interiors ( Figure 5).

Provenance interpretation
The three type signatures indicate the basal Cambrian nearshore deposits in the NCC were supplied by multiple sources. Among them, the widespread Archean-Palaeoproterozoic metamorphic basement in the NCC carry zircons with two dominate U-Pb age populations between ca. 1.75-1.95 Ga and ca. 2.40-2.60 Ga (Figure 6), of which the latter is considered to represent 80% of the Precambrian basement of the NCC (Zhao and Zhai 2013). Given nearly all detrital zircon samples in the NCC exhibit a consistent component of Archean and Early Proterozoic ages (e.g. Darby and Gehrels 2006;McKenzie et al. 2011;Myrow et al. 2015;Sun and Dong 2019;Zhang et al. 2020;Cho et al. 2021;Lee et al. 2021), the presence of these two populations with peaks at ~1.85 Ga and ~2.5 Ga is considered to be diagnostic detrital zircon age signature of the NCC (Yui et al. 2012;Kim et al. 2013b;Cho et al. 2021). Because age spectra for Meso-and Neoproterozoic sedimentary rocks in the NCC are also typified by the pattern with ca. 1.85 and 2.50 Ga peaks, we interpret the grains of Archean and Palaeoproterozoic age were either derived from basement rocks or recycled from the older sedimentary rocks.
It is generally assumed that Neoproterozoic magmatic rocks are poorly represented in present-day North China. However, this view was challenged by the recognition of ca. 853-835 Ma and ~740 Ma granitoid plutons in the western and eastern margins (Lee et al. 2003;Yang et al. 2019), and multiphase scattered mafic dike and acid volcanics, including ~925 Ma Dashigou dike swarm in the central North China (Peng et al. 2011a;Su et al. 2021), large voluminous ~900 Ma dike and sill complex in the south and in the east (Yang et al. 2004(Yang et al. , 2019Liu et al. 2006;Wang et al. 2011Wang et al. , 2012Peng et al. 2011b;Zhang et al. 2016b), and ca. 850-810 Ma dike swarms and volcanics in the west (Li et al. 2004;Peng et al. 2010Peng et al. , 2018Liu et al. 2012;Yang et al. 2019). In addition, abundant Neoproterozoic detrital zircons were discovered also in latest Ediacaran strata immediately below the Great Unconformity in the eastern and western margins Dong et al. 2017;He et al. 2017;Wan et al. 2019;Cho et al. 2021). In particular, the  1985;Zheng and Hu 2010;Hu et al. 2016) with spatial heterogeneity of detrital zircon provenance signature and two different reconstructions of pre-existing orogenic belts after Zhao et al. (2005) and Zhai and Santosh (2011). Dashed blue line represents the proposed drainage divide of the middle Cambrian drainage system. same ca. 815 Ma peak is also pronounced in an Ediacaran sample reported by Dong et al. (2017) in Helanshan area in the west, very close to our sample SYK-1Z classified as type 2. Taken together, grains of Neoproterozoic ages could have been either derived directly from matched magmatic rocks recently recognized in the NCC (Cho et al. 2017(Cho et al. , 2021 or recycled from the Ediacaran strata. The main reason of the orogens in Gondwana was assumed in previous provenance interpretations is that Cambrian magmatic rocks are poorly represented in present-day North China (McKenzie et al. 2011;Wang et al. 2016;Lee et al. 2016;Kim et al. 2013ba, 2019. However, the Gondwana is featured by presence of a series of internal collisional orogens that yield not only abundant Pan-African (ca. 680-530 Ma) aged zircons, but also significant Grenvillian (ca. 1250-900 Ma) grains, including the East African Orogen between eastern Africa and Indo-Antarctica (Stern 1994), the Kuunga-Pinjarra Orogen between Australia-Antarctica and Indo-Antarctica (Meert 2003;Collins and Pisarevsky 2005). Age distribution spectra for detrital zircons from Cambrian sandstone from the NCC stand in striking contrast to the existing Cambrian spectra from North Africa and Arabia (Avigad et al. 2005), Tethyan Himalaya (Myrow et al. 2009(Myrow et al. , 2010McQuarrie et al. 2013), West Australia (Markwitz et al. 2017), and many peri-Gondwanan terranes (Zhu et al. 2011;Zoleikhaei et al. 2021), which share a similar age distribution pattern dominated by two prominent population of ca. 650-550 Ma and ca. 1200-900 Ma (Squire et al. 2006; Figure 6). Therefore, the orogenic systems developed in Gondwana should be precluded as potential provenance for detrital zircons of Cambrian age recognized in the NCC.
An alternative interpretation that the proto-Japan arc developed along the eastern margin of the East Gondwana may serve as the source terrane for Cambrian zircons was proposed recently (Cho et al. 2021). Given the age of these grains is very close to the depositional age of the hosting strata, we agree with Cho et al. (2021) that Cambrian detrital zircons recognized in the NCC represent the first-cycle detritus and came directly from corresponding crystalline rocks, but we do not suggest that zircons of Cambrian age are necessarily directly related to the hypothesized proto-Japan arc. At first, although the discovery of Meso-to Neoproterozoic rocks and detrital zircons in (Cho et al. 2017) and ca. 1.85 Ga granitic gneiss in the Maizuru belt (Kimura et al. 2021) provide the supports for the linkage Figure 6. Comparison of distribution patterns of zircon ages from the basement (Nutman et al. 2011;Lv et al. 2012;Bai et al. 2014Bai et al. , 2015Bai et al. , 2019Zhang et al. 2015Sawaki et al. 2016;Li et al. 2016a;Liu et al. 2017b;Duan et al. 2019;Wang et al. 2019Wang et al. , 2019aWang et al. , 2019bZhao et al. 2020a;Dong et al. 2021;Liu and Zhang 2021;Xiao et al. 2021), Paleo-to Mesoproterozoic sediments Ying et al. 2011;Liu et al. 2014Liu et al. , 2017aZhang et al. 2014aZhang et al. , 2016bZhang et al. , 2020Zhong et al. 2015;Wang et al. 2020a), Neoproterozoic sediments Dong et al. 2017;Li et al. 2020;Zhang et al. 201), and the early-middle Cambrian sediments from the NCC (this study; Darby and Gehrels 2006;McKenzie et al. 2011;Hu et al. 2013;Kim et al. 2013bKim et al. , 2017Kim et al. , 2019Lee et al. 2016;Li et al. 2018a;He et al. 2017;Jang et al. 2018;Pang et al. 2018;Sun and Dong 2019;Wan et al. 2019;Zhang et al. 2020;Cho et al. 2021), and the Cambrian strata in the Northern Gondwana (Squire et al. 2006;Myrow et al. 2009Myrow et al. , 2010Wang et al. 2010;Zhu et al. 2011;McQuarrie et al. 2013;Markwitz et al. 2017;He et al. 2020;Zoleikhaei et al. 2021).
of the proto-Japan arc with the NCC, an alternative interpretation is that the proto-Japan arc was closely associated with the Cathaysian margin of South China during Paleozoic time (Aoki et al. 2015). Therefore, the paleogeographic affinity between NCC and the proto-Japan arc still remains highly hypothetical in the Cambrian. Second, wave-induced water motions, known as the longshore current and seaward-directed rip current, are the principal mechanisms of nearshore sediment transport and redistribution, the most coastal sediments are land-derived and initially supplied by rivers. The proto-Japan arc interpretation is inconsistent with the reconstructed Cambrian paleogeography showing the eastern margin of the NCC was generally submerged ( Figure 5).
Another alternative interpretation is that the North Qinling belt in the Qinling-Dabie orogen might serve as a potential source area for the Cambrian grains, because it carries a large volume of early Paleozoic granites with the ages between 500 Ma and 400 Ma . However, the linkage of the North Qinling belt with the NCC during the Cambrian remains questionable. It has proven that the North Qinling belt was separated from the NCC by the Proto-Tethys ocean in the Cambrian (Dong et al. 2018), and the amalgamation did not happen until the early Silurian . Therefore, the possibility of the North Qinling belt as the source area for the Cambrian detrital zircons recognized in the Cambrian of the NCC should be excluded.
Instead, the interpretation in accord with the existing paleogeographic reconstruction call for that the most likely source area for Cambrian zircons should be the Bainaimiao arc, an outboard arc complex developed along the northern margin of the NCC ( Figure 5). It has been proven that the NCC was high in the north and low in the south during the Ediacaran (Zhang and Zheng 2021). The lowermost strata overlying the Great Unconformity are time-progressive and show a younging trend toward north: series 2 in the southern margin and the Miaolingian in the interior ( Figure 5). Therefore, it is reasonable to claim that the NCC was still high in the north. The present-day Bainaimiao arc terrane consists mainly of Cambrian to Silurian magmatic and (meta)sedimentary rocks (Xiao et al. 2003;Zhang et al. 2014a). Abundant Ediacaran and Cambrian detrital zircons (ca. 600-500 Ma) were discovered also in early Paleozoic sandstones, including lithic arenites that consist of abundant volcanic fragment, in the Bainaimiao arc terrane (Zhang et al. 2014a;Zhou et al. 2018;Ma et al. 2019;Chen et al. 2020). Although the tectonic origin the Bainaimiao arc terrane is still highly debated and it is generally thought to be accreted to the northern margin of the NCC as a result of the closure of the South Bainaimiao ocean during the Late Silurian-Early Devonian time (Zhang et al. 2014a;Ma et al. 2019;Chen et al. 2020), details of the opening of this ocean have yet to be established and the Bainaimiao terrane may represent a continental arc along the northern margin of the NCC as a result of southward subduction of the Paleo-Asian Ocean before the opening of the South Bainaimiao ocean (Xiao et al. 2003;Xu et al. 2013;Chen et al. 2020).

Cambrian paleogeographic position of North China
In contrast to the well-established Cambrian paleogeographic configuration of core blocks of Gondwanaland (Africa, Antarctica, Australia, India, and South America), the position of the NCC during the period of Cambrian has been a matter of debate. The NCC was traditionally viewed as a separate and independent continent and was placed at some distance away from Gondwana (Sengör and Natal'in 1996;Stampfli et al. 2011;Cocks and Torsvik 2013). Some recent reconstructions have yielded a discordant paleogeographic model and placed the NCC as an integral part of Gondwana adjacent to India-Australia region of East Gondwana (McKenzie et al. 2011;Hu et al. 2013;He et al. 2017;Wan et al. 2019;Pan et al. 2019;Cho et al. 2021). Support for the Gondwanan affinity of the NCC is provided by the preservation of similar trilobites and small shelly fossils both in NCC and Gondwanan blocks (McKenzie et al. 2011;Álvaro et al. 2013;Yun et al. 2016;Li et al. 2016bLi et al. , 2021Pan et al. 2019) and the Pan-African detrital zircons recognized largely from the Cambrian strata in the NCC have been commonly interpreted to be derived from Gondwana (McKenzie et al. 2011;Hu et al. 2013;He et al. 2017;Wan et al. 2019;Lee et al. 2021).
Our provenance data support the long-held view that the NCC was a discrete continent separated from the north margin of East Gondwana (Figure 7), rather than some recent reconstructions suggesting the close association between the NCC and Gondwanaland. This is compatible with the regional geology that the southern margin of the NCC was passive through nearly the entire Cambrian (Meng et al. 1997), facing the Proto-Tethys Ocean (Figure 1), which had opened in Ediacaran or earlier (Liu et al. 2022). Given the paleomagnetic data permit placing the NCC in low-latitudinal regions (X. Zhao et al. 1992;Huang et al. 1999;Yang et al. 2002;H. Zhao et al. 2021) and the NCC, Australia, and the Himalaya were probably located in a largely similar faunal province in the Cambrian, the NCC should be considered a discrete continent separated by the Proto-Tethys Ocean (Figure 7), but not too distant from Gondwana (Cocks and Torsvik 2013;Metcalfe 2022). As seen by comparable early Paleozoic accretionary events along the northern margins of the NCC and Tarim craton (Han et al. 2016) and mutual tectonic relationships and deformational history revealed by tectonic reconstruction by removing the effects of younger tectonic distortion (Zuza and Yin 2017), we agree with Han et al. (2016) and Zuza and Yin (2017) that the NCC and Tarim were likely connected during the period from the Neoproterozoic to Cambrian as a continuous continental strip (Figure 7). The NCC and Tarim did not become part of Gondwanaland as the peri-Gondwanan blocks until the Silurian (Metcalfe 2022), when the Proto-Tethys Ocean against the present-day southern margins of the NCC and Tarim craton finally closed (Li et al. 2018b).

Conclusion
New detrital zircon provenance data obtained from the fossil-calibrated basal Cambrian (Series 2, ca. 520 Ma) both strengthened the Cambrian database of the NCC and shed new light on the development of diverse drainage systems on the peneplained NCC during global Cambrian transgression. The marked spatial nonuniformity in their age distribution patterns permits three distinctive types can be distinguished on the basis of diagnostic zircon age proportions. Type 1 is dominated by age populations of ca. 1750-1950 Ma and ca. 2400-2600 Ma, with two broad peaks at ~1.85 Ga and ~2.5 Ga that correlate with the Archean to Paleoproterozoic basement of the NCC; Type 2 carry abundant Neoproterozoic ages with peak at ca. 815 Ma that correspond to nearby magmatic record; and Type 3 is characterized by presence of first-cycle grains with unique Cambrian ages very close to the depositional age. Evidence for diversity in the age spectra from the Cambrian sand sheet across the NCC suggests the sediment dispersal network is more complicated than would be expected from a single continental-scale drainage system and the existence of drainage divides in the hypothesized low-lying peneplain of the NCC during global Cambrian transgression. Of importance, all three types stand in striking contrast to the existing Cambrian spectra from the northern Gondwana. The most likely source for Cambrian-aged grains constrained by Cambrian paleogeography of the NCC is the continental arc developed along the northern margin as a result of subduction of the Paleo-Asian oceanic plate, rather than the internal Pan-African orogens of Gondwana. Our provenance data do not support the close association between the NCC and Gondwanaland in the Cambrian suggested by some recent Si -Sibumasu; So -Somalia. Arrow denotes transport direction of detritus from the Grenvillian and Pan-African aged orogenic belts inboard of Gondwana feeding the peripheral super-fan system (compiled from Avigad et al. 2005Avigad et al. , 2017Duan et al. 2011Duan et al. , 2012, and sediment dispersal across North China sourced by the Neoproterozoic and Cambrian arc terrane as a result of subduction of the Paleo-Asian oceanic plate, respectively. Note the North China block is separated from Gondwanaland by the Proto-Tethys Ocean.
reconstructions, and confirm that the NCC was a discrete continent separated from the north margin of East Gondwana by the Proto-Tethys Ocean.