The Paleocene–Eocene thermal maximum (PETM; ca. 56 Ma) geological interval records a marked decline in calcium carbonate (CaCO3) in seafloor sediments, potentially reflecting an episode of deep- and possibly shallow-water ocean acidification. However, because CaCO3 is susceptible to postburial dissolution, the extent to which this process has influenced the PETM geological record remains uncertain. Here, we tested for evidence of postburial dissolution by searching for imprint fossils of nannoplankton preserved on organic matter. We studied a PETM succession from the South Dover Bridge (SDB) core, Maryland, eastern United States, and compared our imprint record with previously published data from traditionally sampled CaCO3-preserved nannoplankton body fossils. Abundant imprints through intervals devoid of CaCO3 would signify that postburial dissolution removed much of the CaCO3 from the rock record. Imprints were recorded from most samples but were rare and of low diversity. Body fossils were substantially more numerous and diverse, capturing a more complete record of the living nannoplankton communities through the PETM. The SDB succession records a dissolution zone/low-carbonate interval at the onset of the PETM, through which nannoplankton body fossils are rare. No nannoplankton imprints were found from this interval, suggesting that the rarity of body fossils is unlikely to have been the result of postburial dissolution. Instead, our findings suggest that declines in CaCO3 through the PETM at the SDB location were the result of: (1) biotic responses to changes that were happening during this event, and/or (2) CaCO3 dissolution that occurred before lithification (i.e., in the water column or at the seafloor).The Paleocene–Eocene thermal maximum (PETM; ca. 56 Ma) was a geologically rapid global warming event, lasting ~200,000 yr, throughout which global temperatures increased by ~5–8 °C (McInerney and Wing, 2011, and references therein). The event was likely caused by a massive injection of isotopically light carbon into the ocean-atmosphere system over several thousands of years (McInerney and Wing, 2011; Turner, 2018), although the carbon sources and ultimate trigger of the PETM are still debated (e.g., McInerney and Wing, 2011; Kender et al., 2021). In the geological record, marine PETM successions are generally characterized by major declines in calcium carbonate (CaCO3; Zachos et al., 2005) alongside marked changes in micro- and nannofossil assemblages, including benthic foraminiferal extinctions (Thomas 1989, 2003, 2007), calcareous nannoplankton species turnover (Gibbs et al., 2006), and reduced nannoplankton calcification rates (O’Dea et al., 2014). Together with boron-based proxy evidence (Penman et al., 2014; Babila et al., 2018, 2022), such signals are commonly associated with deep-water, and possibly shallow-water, ocean acidification (OA; Zachos et al., 2005; Kump et al., 2009; Gibbs et al., 2010; Bralower et al., 2018; Babila et al., 2022), and/or other environmental changes, such as elevated sea-surface temperatures (Aze et al., 2014). However, the extent to which postburial CaCO3 dissolution, also termed chemical erosion (Bralower et al., 2014), has affected these records is difficult to determine, and where severe dissolution has likely taken place, its timing generally remains unclear.Imprint fossils of nannoplankton preserved on organic matter provide a tool with which to test the degree and timing of CaCO3 dissolution throughout intervals where CaCO3 preservation is poor (Slater et al., 2022). Although other approaches have been applied to PETM strata to understand the impact of dissolution, such as foraminiferal fragmentation and dissolution of nannofossil rims and central areas (Bralower et al., 2014), these methods rely on the preservation of CaCO3 and are not necessarily indicative of the timing of dissolution. For example, dissolution of nannofossils could occur at any point after their formation—in the water column, at the seafloor, or after deposition and lithification. Nannofossil imprints, however, can be preserved in sediments devoid of CaCO3, and where this is the case, they can reveal that CaCO3 has been removed from the rock record after deposition (Slater et al., 2022).Here, we searched for nannofossil imprints through a PETM succession from the South Dover Bridge (SDB) core, southern Maryland, eastern United States (38°44′49.34″N, 76°00′25.09″W; Fig. 1; drilled by the U.S. Geological Survey), with the aim to determine the timing of potential CaCO3 dissolution. The SDB section was chosen because it represents a relatively shallow-water marine environment (~120–150 m depth; Self-Trail et al., 2012; Robinson and Spivey, 2019) that preserves organic matter (Alemán González et al., 2012; Edwards, 2012), which is required for imprint preservation (Batten, 1985; Slater et al., 2022). Furthermore, the succession appears to record a spectrum of dissolution conditions through the PETM interval, from little to no dissolution below and above the carbon isotope excursion (CIE) to pervasive dissolution at the base of the CIE. The calcareous nannoplankton “body” fossils (i.e., the calcite fossil remains of nannoplankton cell-wall coverings) from this succession have previously been studied in detail, with diverse and abundant assemblages spanning the PETM described by Self-Trail (2011), Alemán González et al. (2012), and Self-Trail et al. (2012). A notable ~2-m-thick dissolution zone has been recognized near the base of the CIE, through which nannoplankton body fossils are extremely sparse (Self-Trail, 2011; Self-Trail et al., 2012). Bralower et al. (2018) described a low-carbonate interval (LCI), representing a slightly amended version of the dissolution zone, from several PETM sections across Maryland and New Jersey, including the SDB core. Bralower et al. (2018) discussed numerous possible causes for the LCI, hypothesizing that this was likely due to shoaling of the lysocline and calcite compensation depth (CCD), but that eutrophication and microbial activity potentially exacerbated the impact of acidification. Further proxy-based reconstructions of seawater pH from the SDB core have inferred that OA started prior to the main CIE, during a pre-onset excursion (Babila et al., 2022). Indeed, these studies point to relatively shallow-water OA. However, rich and abundant nannofossil imprints preserved within the sediments low in CaCO3 could reveal that CaCO3 was removed by diagenetic dissolution rather than in situ water-column OA or changes to the CCD or lysocline depth that affected seafloor carbonate. Such results would not necessarily discount the interpretation that changes to seawater chemistry influenced CaCO3 PETM records, but they could provide an indication of the extent of diagenetic CaCO3 dissolution.Postdrilling dissolution of carbonate is common in organic-rich sediments of the Atlantic Coastal Plain, likely due to pyrite oxidation, and so sampling for body fossils needs to occur as soon as possible after coring (Self-Trail and Seefelt, 2005; Self-Trail, 2011). This is likely why the sediments of the Marlboro Clay in the SDB core record abundant body fossils, whereas their outcrop counterparts and older cores are generally barren or yield very sparse nannofossils (Bybell and Gibson, 1994; Gibson and Bybell, 1994; Self-Trail, 2011). As the SDB core was recovered in 2007, it is probable that at least some postdrilling dissolution of CaCO3 has taken place; a secondary goal of this study was therefore to examine the nannofossil assemblages using an approach that may be immune to the modifying effects of diagenetic and postdrilling dissolution, by studying nannofossil imprints.We examined 12 samples spanning the PETM of the SDB core (Fig. 2). Rock samples were dissolved in HCl and HF, and resultant residues were sieved at 5 µm to isolate organic matter. Processing was conducted at Global Geolab Limited, Medicine Hat, Alberta, Canada. Final residues were studied using light microscopy (LM) with an Olympus BX53 and scanning electron microscopy (SEM) using an ESEM FEI Quanta FEG 650 scanning electron microscope at the Swedish Museum of Natural History.For LM, residues were strewn across cover slips and mounted onto glass slides with epoxy resin. To assess the composition of organic matter, palynofacies analysis was conducted, where a minimum of 300 organic particles were counted per sample (see Table S1 in the Supplemental Material1 for palynofacies categories).For SEM, residues were strewn across SEM stubs, dried, and coated with gold. Organic matter on SEM stubs was observed in systematic traverses for 2 h per sample at ×10,000 magnification, followed by 30 min at ×5000 magnification, during which all potential imprints were photographed; this procedure was followed by 30 min at ×5000 magnification to search for well-preserved specimens. Unprocessed rock material from two samples (PJ-SDB13-003 and PJ-SDB13-004) was also examined for imprints and body fossils. For this approach, freshly cleaved rock was mounted onto SEM stubs, coated with gold, and examined for 2 h per sample at ×10,000 magnification.We found imprints in nine of the 12 investigated samples (Fig. 2; Table S1). Including indeterminate coccoliths, eight taxa were recorded (Fig. 2). Preservation was variable, with a mixture of well-preserved (Figs. 2B and 2C) and poorly preserved (Fig. 2G) specimens.Imprint assemblages were considerably less rich than previously sampled body fossils, demonstrating that body fossils capture a more complete record of nannoplankton through the PETM in the SDB core (Fig. 3). Previous studies have shown that body fossils are extremely sparse through the dissolution zone/LCI (Fig. 3; Self-Trail, 2011; Self-Trail et al., 2012; Bralower et al., 2018). Observations of rock surfaces and organic residues from the sample taken from the dissolution zone/LCI here (PJ-SDB13-003) revealed similar findings; one taxon, either Braarudosphaera sp. or Micrantholithus sp. (a more definitive identification was difficult since only side-views were visible), was recorded on rock surfaces (Fig. S1), and no imprints were found in organic residues. For sample PJ-SDB13-004, which yielded the richest imprint assemblage, body fossils on rock surfaces were common and well preserved (Fig. S1).Palynofacies assemblages were codominated by phytoclasts, amorphous organic matter (AOM), and marine palynomorphs. The dinoflagellate Apectodinium was present through the PETM, recording the acme interval associated with this event (Bujak and Brinkhuis, 1998; Crouch et al., 2001; Sluijs et al., 2007). AOM increased in relative abundance around the onset of the CIE, within the dissolution zone/LCI, reflecting a relative increase in organic matter deposition and a corresponding decline in CaCO3 preservation associated with the PETM (Zachos et al., 2005; Schneider-Mor and Bowen, 2013).The rarity of nannofossil imprints across the PETM suggests that the taphonomic conditions required for their preservation were suboptimal compared to body fossils (Fig. 3; Self-Trail, 2011; Self-Trail et al., 2012). Imprints were only recorded from strata that also yielded body fossils (Fig. 3), and no imprints were found on unprocessed rock surfaces. Hence, rather than representing “ghost” nannofossils, i.e., imprints found in rocks that are barren of body fossils (Slater et al., 2022), the imprints here are likely the molds of body fossils that were dissolved during acid digestion in the laboratory.Although only one sample was examined from the dissolution zone/LCI here, both the absence of imprints and the rarity of body fossils in this sample suggest that: (1) nannoplankton production declined through the early stages of the PETM, and/or (2) dissolution of CaCO3 occurred before lithification, in the water column, at the seafloor, or during the earliest stages of diagenesis. If dissolution occurred after lithification, we would expect to find imprints, as overburden would have likely facilitated their formation. At this stage, our data alone cannot discount interpretations 1 or 2, but previously studied nannoplankton counts with taxon-specific Sr/Ca data from other localities support the hypothesis that the decrease in CaCO3 through the PETM was primarily driven by an increase in seafloor dissolution rather than a decrease in production in surface waters (Gibbs et al., 2010). The scarcity of imprints suggests that the timing of potential CaCO3 dissolution was unlikely to have been postlithification, and our findings therefore support the hypothesis that shelf acidification linked to shoaling of the lysocline and CCD contributed to the decline in CaCO3 preservation at the onset of the PETM in the SDB region (Bralower et al., 2018).Nannofossil imprint assemblages from Mesozoic oceanic anoxic events (OAEs), and especially the Toarcian OAE, are generally richer, more numerous, and better preserved than those documented here (Slater et al., 2022). In addition to variations in seawater chemistry, these discrepancies likely also relate to the amount and type of organic matter—and, in particular, the quantity of AOM, since this is a good substrate for imprinting (Slater et al., 2022)—preserved through these different events and localities. Given that organic matter appears to be necessary for imprinting, the rarity of imprints through the PETM compared to the OAEs is likely a product of the lower relative abundances of AOM and the generally lower total organic carbon values (Bralower et al., 2018) compared to the OAEs (e.g., McArthur et al., 2008). Furthermore, the preservation of AOM as larger fragments through the OAEs (Slater et al., 2022) appears to be important, because imprints are less distinct on the smaller, highly fragmented pieces that are typical of the PETM in the SDB core. Although imprints are generally most common on AOM compared to other types of organic matter, they can also be preserved on dinoflagellates (Downie, 1956), prasinophyte algae, and pollen (Slater et al., 2022). The lack of imprints on the dinoflagellate Apectodinium, which is abundant through the PETM in the SDB core, suggests that the surface of this cyst was a poor substrate for imprinting.Comparisons of imprint and body nannofossil records through the Mesozoic OAEs revealed marked differences in abundance and diversity patterns between these fossil records. In numerous OAE samples, imprint assemblages were substantially more diverse than body fossil records, and in many cases, rich imprint records were found in samples barren of body fossils (Slater et al., 2022). This is not the case for the PETM in the SDB core. Although the sampling resolution of imprints here was lower than body fossil records (Self-Trail, 2011; Self-Trail et al., 2012), the pattern of lower imprint richness through the studied succession was consistent. More generally, the abundance of body fossils and the scarcity of imprints throughout most of the PETM in the SDB core indicate that postburial CaCO3 dissolution was less pervasive compared to the OAE records. These observations bolster confidence that traditionally sampled body fossil records (Self-Trail, 2011; Self-Trail et al., 2012) have not been extensively modified by postburial dissolution and thus provide a relatively good representative signal of the buried CaCO3 in the Atlantic Coastal Plain region.Imprint fossils of nannoplankton represent a relatively novel tool with which to test the extent and timing of CaCO3 dissolution through geological intervals where CaCO3 preservation is poor. In the case of the PETM, the scarcity of these fossils through intervals of low CaCO3 preservation suggests that any dissolution took place before lithification, in the water column or at the seafloor, supporting hypotheses of seafloor and/or potentially shallower-water CaCO3 dissolution. Future studies testing for the presence and abundance of nannofossil imprints through the PETM at higher resolution, and in deep-water successions elsewhere, will potentially shed more light on the timing of dissolution through this important geological interval.The Swedish Research Council (2019-04524 [Slater], 2023-03330 [Slater]), Formas (Swedish Research Council for Sustainable Development; 2023-00984 [Slater]), the Royal Swedish Academy of Sciences (GS2021-0018 [Slater]), the Palaeontological Association (Sylvester-Bradley award [Jardine]), and the German Research Foundation (443701866 [Jardine]) funded this research. We thank Lucy Edwards for help with sample collection; Andreas Karlsson for assistance with SEM photography; and Jean Self-Trail, Timothy Bralower, and an anonymous reviewer for their helpful reviews.

中文翻译：

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超微化石在古新世-始新世最热时期留下了印记

古新世-始新世最热期（PETM；约 56 Ma）地质区间记录了海底沉积物中碳酸钙 (CaCO3) 的显着下降，这可能反映了深水和浅水海洋酸化的发生。然而，由于 CaCO3 很容易受到埋后溶解的影响，因此该过程对 PETM 地质记录的影响程度仍不确定。在这里，我们通过寻找有机物上保存的超微浮游生物的印记化石来测试埋后溶解的证据。我们研究了来自美国东部马里兰州南多佛桥 (SDB) 核心的 PETM 序列，并将我们的印记记录与之前发布的传统 CaCO3 保存的纳米浮游生物体化石样本数据进行了比较。没有 CaCO3 的层段中的大量印记表明埋后溶解从岩石记录中去除了大部分 CaCO3。大多数样本都记录有印记，但数量很少且多样性较低。尸体化石的数量和多样性显着增加，通过 PETM 捕获了现存超小型浮游生物群落的更完整记录。 SDB序列记录了PETM开始时的溶解带/低碳酸盐层段，在此期间超小型浮游生物体化石很少见。在此期间没有发现微浮游生物印记，这表明尸体化石的稀有不太可能是埋后溶解的结果。相反，我们的研究结果表明，SDB 位置处通过 PETM 的 CaCO3 下降是由于：(1) 对该事件期间发生的变化的生物反应，和/或 (2) 在石化之前发生的 CaCO3 溶解（即，古新世-始新世最热期（PETM；约 56 Ma）是地质学上快速的全球变暖事件，持续约 200,000 年，在此期间全球温度上升了约 5-8 °C（ McInerney 和 Wing，2011 年以及其中的参考文献）。该事件很可能是由数千年来向海洋-大气系统中大量同位素轻碳注入引起的（McInerney 和 Wing，2011；Turner，2018），尽管 PETM 的碳源和最终触发因素仍然存在争议（例如，McInerney 和 Wing，2011 年；Kender 等人，2021 年）。在地质记录中，海洋 PETM 演替的一般特征是碳酸钙（CaCO3；Zachos 等，2005）大幅下降，同时微型和超微化石组合发生显着变化，包括底栖有孔虫灭绝（Thomas 1989、2003、2007），钙质微浮游生物物种更替（Gibbs 等，2006），并降低微浮游生物钙化率（O'Dea 等，2014）。连同基于硼的代理证据（Penman 等人，2014 年；Babila 等人，2018 年、2022 年），此类信号通常与深水和可能浅水的海洋酸化有关（OA；Zachos 等人，2022 年）。 ，2005 年；Kump 等人，2009 年；Gibbs 等人，2010 年；Bralower 等人，2018； Babila 等人，2022）和/或其他环境变化，例如海面温度升高（Aze 等人，2014）。然而，埋藏后 CaCO3 溶解（也称为化学侵蚀（Bralower 等，2014））对这些记录的影响程度很难确定，并且在可能发生严重溶解的地方，其时间通常仍不清楚。保存在有机物上的微浮游生物提供了一种工具，可用于测试 CaCO3 保存较差的整个区间内 CaCO3 溶解的程度和时间（Slater 等人，2022）。尽管其他方法已应用于 PETM 地层以了解溶解的影响，例如有孔虫破碎和超微化石边缘和中心区域的溶解（Bralower 等，2014），但这些方法依赖于 CaCO3 的保存，并不一定具有指示性。解散的时间。例如，超微化石的溶解可能发生在其形成后的任何时刻——在水柱中、在海底、或在沉积和岩化之后。然而，超微化石印记可以保存在不含 CaCO3 的沉积物中，在这种情况下，它们可以揭示 CaCO3 在沉积后已从岩石记录中去除（Slater 等人，2022）。在这里，我们寻找超微化石来自美国东部马里兰州南部的南多佛桥 (SDB) 核心的 PETM 序列印记（38°44′49.34″N，76°00′25.09″W；图 1；由美国地质调查局钻探），目的是确定潜在 CaCO3 溶解的时间。选择 SDB 剖面是因为它代表了相对浅水的海洋环境（~120-150 m 深度；Self-Trail 等人，2012 年；Robinson 和 Spivey，2019 年），可以保存有机物（Alemán González 等人，2012 年） ；Edwards，2012），这是印记保存所必需的（Batten，1985；Slater 等人，2022）。此外，序列似乎记录了整个 PETM 区间的一系列溶解条件，从低于和高于碳同位素偏移 (CIE) 的溶解很少到没有溶解，到 CIE 底部的普遍溶解。这一演替过程中的钙质超微浮游生物“身体”化石（即超微浮游生物细胞壁覆盖物的方解石化石残骸）此前已被详细研究过，Self-Trail (2011) Alemán González 描述的跨越 PETM 的多样且丰富的组合等人。 (2012) 和 Self-Trail 等人。 （2012）。在 CIE 底部附近发现了一个约 2 米厚的显着溶蚀带，其中微浮游生物化石极其稀疏（Self-Trail，2011；Self-Trail 等，2012）。布拉洛尔等人。 （2018）描述了一个低碳酸盐区间（LCI），代表了溶解区的稍微修改版本，来自马里兰州和新泽西州的几个 PETM 部分，包括 SDB 核心。布拉洛尔等人。 (2018) 讨论了 LCI 的多种可能原因，假设这可能是由于溶斜层和方解石补偿深度（CCD）的浅化造成的，但富营养化和微生物活动可能加剧了酸化的影响。对来自 SDB 核心的海水 pH 值进行进一步基于代理的重建推断，OA 在主要 CIE 之前开始，在发作前的偏移期间开始（Babila 等人，2022）。事实上，这些研究指出了相对浅水的OA。然而，在 CaCO3 含量低的沉积物中保存的丰富而丰富的超微化石印记可以表明，CaCO3 是通过成岩溶解而不是原位水柱 OA 或影响海底碳酸盐的 CCD 或溶斜层深度的变化而被去除的。这些结果不一定会否定海水化学变化影响 CaCO3 PETM 记录的解释，但它们可以提供成岩 CaCO3 溶解程度的指示。碳酸盐的钻后溶解在大西洋沿海平原富含有机物的沉积物中很常见，很可能由于黄铁矿氧化，因此取芯后需要尽快对尸体化石进行取样（Self-Trail 和 Seefelt，2005 年；Self-Trail，2011 年）。这可能就是为什么 SDB 核心中的万宝路粘土沉积物记录了丰富的人体化石，而其露头对应物和较古老的核心通常是贫瘠的或产生非常稀疏的超微化石（Bybell 和 Gibson，1994；Gibson 和 Bybell，1994；Self-Trail） ，2011）。由于 SDB 岩心于 2007 年回收，因此可能至少发生了一些 CaCO3 的钻后溶解；因此，本研究的第二个目标是通过研究超微化石印记，采用一种可能不受成岩作用和钻后溶解改变影响的方法来检查超微化石组合。我们检查了跨越 SDB 岩心 PETM 的 12 个样本（图 2） ）。将岩石样品溶解在 HCl 和 HF 中，并将所得残留物过 5 µm 筛分以分离有机物。处理是在加拿大艾伯塔省梅迪辛哈特的 Global Geolab Limited 进行的。在瑞典自然历史博物馆，使用配备奥林巴斯 BX53 的光学显微镜 (LM) 和使用 ESEM FEI Quanta FEG 650 扫描电子显微镜的扫描电子显微镜 (SEM) 对最终残留物进行研究。对于 LM，将残留物撒在盖玻片上并封固到带有环氧树脂的载玻片上。为了评估有机质的组成，进行了孢粉相分析，每个样品至少计数了 300 个有机颗粒（有关孢粉相类别，请参阅补充材料 1 中的表 S1）。对于 SEM，将残留物散布在 SEM 存根上，干燥并收集。涂有金色。在 10,000 倍放大倍率下系统地横移 2 小时，观察 SEM 存根上的有机物，然后在 5000 倍放大倍率下系统横移 30 分钟，在此期间对所有潜在的印记进行拍照；该程序随后在 5000 倍放大倍数下进行 30 分钟，以寻找保存完好的标本。还检查了两个样品（PJ-SDB13-003 和 PJ-SDB13-004）中未加工的岩石材料的印记和身体化石。对于这种方法，将新劈裂的岩石安装在 SEM 短棒上，涂上金，并在 10,000 倍放大倍数下检查每个样品 2 小时。我们在 12 个研究样品中的 9 个中发现了印记（图 2；表 S1）。包括不确定的颗石岩在内，共记录了八个类群（图2）。保存情况各不相同，既有保存完好的标本（图 2B 和 2C），也有保存较差的标本（图 2G）。印记组合的丰富程度远低于以前采样的尸体化石，这表明尸体化石捕获了更完整的记录。微浮游生物通过 SDB 核心的 PETM（图 3）。先前的研究表明，穿过溶解带/LCI的尸体化石极其稀疏（图3；Self-Trail，2011；Self-Trail等人，2012；Bralower等人，2018）。对岩石表面和取自溶解区/LCI (PJ-SDB13-003) 的样品的有机残留物的观察也揭示了类似的发现；一个分类单元，Braarudosphaera sp。或微花石属 sp。 （更明确的识别很困难，因为只能看到侧视图），在岩石表面上记录（图S1），并且在有机残留物中没有发现印记。对于印记组合最丰富的样品PJ-SDB13-004来说，岩石表面的尸体化石常见且保存完好（图S1）。孢粉相组合以植物碎屑、无定形有机质（AOM）和海洋孢粉型为主。甲藻 Apetodinium 通过 PETM 出现，记录与该事件相关的 acme 间隔（Bujak 和 Brinkhuis，1998；Crouch 等人，2001；Sluijs 等人，2007）。在 CIE 开始前后，在溶解带/LCI 内，AOM 的相对丰度增加，反映出有机物沉积的相对增加以及与 PETM 相关的 CaCO3 保存的相应下降（Zachos 等，2005；Schneider-Mor 和Bowen, 2013）。PETM 中超微化石印记的稀有性表明，与尸体化石相比，其保存所需的埋藏条件并不理想（图 3；Self-Trail，2011；Self-Trail 等人，2012）。仅在也产生人体化石的地层中记录了印记（图3），在未加工的岩石表面上未发现印记。因此，这里的印记并不是代表“幽灵”超微化石，即在没有人体化石的岩石中发现的印记（Slater 等，2022），而是很可能是在实验室酸消化过程中溶解的人体化石的模具。虽然这里只检查了溶解带/LCI 的一个样本，但该样本中没有印记和尸体化石的稀有表明：（1）超小型浮游生物产量在 PETM 早期阶段下降，和/或（ 2) CaCO3的溶解发生在岩化之前、在水体中、在海底、或在成岩作用的最早阶段。如果溶解发生在岩化之后，我们预计会发现印记，因为覆盖层可能会促进它们的形成。在这个阶段，我们的数据本身不能否定解释 1 或 2，但之前使用来自其他地区的分类群特异性 Sr/Ca 数据研究的超微浮游生物计数支持这样的假设：通过 PETM 的 CaCO3 减少主要是由海底溶解增加驱动的。而不是地表水产量的减少（Gibbs 等，2010）。印记的稀缺表明，潜在的 CaCO3 溶解时间不太可能是在石化后，因此我们的研究结果支持这样的假设：与溶斜层和 CCD 浅滩相关的陆架酸化导致了 PETM 开始时 CaCO3 保存的下降。位于 SDB 地区（Bralower 等，2018）。中生代海洋缺氧事件（OAE），特别是托阿尔纪 OAE 中的超微化石印记组合通常比此处记录的更丰富、数量更多且保存得更好（Slater 等，2018）。 ，2022）。除了海水化学的变化之外，这些差异可能还与有机物的数量和类型有关，特别是 AOM 的数量，因为这是一种良好的印迹基质（Slater 等人，2022 年）。通过这些不同的事件和地点。鉴于有机物似乎是印记所必需的，与 OAE 相比，通过 PETM 的印记的稀有性可能是 AOM 相对丰度较低和总有机碳值普遍较低的产物（Bralower 等人，2018）。给 OAE（例如，McArthur 等，2008）。此外，通过 OAE 将 AOM 作为较大碎片保存似乎很重要（Slater 等人，2022），因为在 SDB 核心中典型的 PETM 较小、高度碎片化的碎片上，印记不太明显。尽管与其他类型的有机物相比，AOM 上的印记通常最常见，但它们也可以保留在甲藻 (Downie, 1956)、绿藻和花粉上 (Slater 等，2022)。甲藻Apertodinium 上缺乏印记，而SDB 核心中的PETM 丰富了甲藻的印记，这表明该囊肿的表面是印记的不良基底。中生代OAE 的印记和身体超微化石记录的比较揭示了丰度的显着差异。以及这些化石记录之间的多样性模式。在许多 OAE 样本中，印记组合比身体化石记录更加多样化，并且在许多情况下，在没有身体化石的样本中发现了丰富的印记记录（Slater 等，2022）。 SDB 核心中的 PETM 并非如此。虽然这里的印记采样分辨率低于人体化石记录（Self-Trail，2011；Self-Trail et al.，2012），在所研究的演替过程中印记丰富度较低的模式是一致的。更一般地说，SDB 核心中大部分 PETM 中丰富的尸体化石和印记的稀缺表明，与 OAE 记录相比，埋藏后 CaCO3 溶解不太普遍。这些观察结果增强了人们的信心，即传统采样的尸体化石记录（Self-Trail，2011；Self-Trail 等人，2012）并未因埋后溶解而被广泛修改，从而为大西洋沿岸埋藏的 CaCO3 提供了相对较好的代表性信号。平原地区。超小型浮游生物的印记化石代表了一种相对新颖的工具，可以通过 CaCO3 保存较差的地质区间来测试 CaCO3 溶解的程度和时间。就 PETM 而言，由于 CaCO3 保存水平较低，这些化石的稀缺性表明，任何溶解都发生在岩化之前，在水柱或海底，支持了海底和/或潜在的浅水 CaCO3 溶解的假设。未来的研究将通过 PETM 以更高分辨率测试超微化石印记的存在和丰度，并在其他地方的深水序列中进行测试，这将有可能为这一重要地质区间的溶解时间提供更多线索。瑞典研究委员会 (2019-04524) [Slater], 2023-03330 [Slater])、Formas（瑞典可持续发展研究理事会；2023-00984 [Slater]）、瑞典皇家科学院 (GS2021-0018 [Slater])、古生物学协会 (Sylvester-布拉德利奖 [Jardine]）和德国研究基金会（443701866 [Jardine]）资助了这项研究。我们感谢露西·爱德华兹 (Lucy Edwards) 在样本收集方面提供的帮助； Andreas Karlsson 提供 SEM 摄影协助；以及 Jean Self-Trail、Timothy Bralower 和一位匿名审稿人的有益评论。未来的研究将通过 PETM 以更高分辨率测试超微化石印记的存在和丰度，并在其他地方的深水序列中进行测试，这将有可能为这一重要地质区间的溶解时间提供更多线索。瑞典研究委员会 (2019-04524) [Slater], 2023-03330 [Slater])、Formas（瑞典可持续发展研究理事会；2023-00984 [Slater]）、瑞典皇家科学院 (GS2021-0018 [Slater])、古生物学协会 (Sylvester-布拉德利奖 [Jardine]）和德国研究基金会（443701866 [Jardine]）资助了这项研究。我们感谢露西·爱德华兹 (Lucy Edwards) 在样本收集方面提供的帮助； Andreas Karlsson 提供 SEM 摄影协助；以及 Jean Self-Trail、Timothy Bralower 和一位匿名审稿人的有益评论。未来的研究将通过 PETM 以更高分辨率测试超微化石印记的存在和丰度，并在其他地方的深水序列中进行测试，这将有可能为这一重要地质区间的溶解时间提供更多线索。瑞典研究委员会 (2019-04524) [Slater], 2023-03330 [Slater])、Formas（瑞典可持续发展研究理事会；2023-00984 [Slater]）、瑞典皇家科学院 (GS2021-0018 [Slater])、古生物学协会 (Sylvester-布拉德利奖 [Jardine]）和德国研究基金会（443701866 [Jardine]）资助了这项研究。我们感谢露西·爱德华兹 (Lucy Edwards) 在样本收集方面提供的帮助； Andreas Karlsson 提供 SEM 摄影协助；以及 Jean Self-Trail、Timothy Bralower 和一位匿名审稿人的有益评论。