Abstract Ocean oxygenation during the Precambrian-Cambrian transition is thought to be one of the key factors for the rapid diversification of animals, known as the ‘Cambrian Explosion’. Siliceous sponges inhabiting continental slope settings were capable of shifting the respiratory oxygen demand in the water column to depth, resulting in an increase in oxygen levels of shallow water. To assess the global importance of the impact of ecosystem engineering by sponges, we evaluated the palaeo-environmental conditions that confine sponge expansion using multiple geochemical proxies including silicon and carbon stable isotopes as well as major- and trace elements in cherts and siliceous sedimentary rocks that were deposited in shallow water around the Precambrian-Cambrian transition. We investigated three lithosections in the Malyi Karatau Range in southern Kazakhstan. The lowermost chert samples of these sections are typically characterized by comparably low δ30Si values and exhibit molds of siliceous sponge spicules. Upsection the occurrence of cross-bedding structures and granular phosphorites document the shallowing of the depositional environment, where overall increasing δ30Si values and increasing Al/Si indicate less settlement of sponges and higher suspended particle loads. Corresponding carbon isotope records of the carbonate fraction decrease from near-zero to negative carbon isotope values averaging -5.9 ‰. The δ13Ccarb values overall coincide with Y/Ho, the redox indicator Ce/Ce*, and mass fractions of carbonate fluorapatite, suggesting that these ratios are predominantly controlled by the mineralization of organic matter in phosphatic sediment. The studied sections document the ecological requirements for sponge settlement and proliferation, such as the presence of a hard substrate and sufficiently low suspended particle concentrations and/or low wave energy. This work suggests that the widespread appearance of karsted surfaces around the Precambrian-Cambrian transition that were subsequently submerged during the Cambrian transgression would have created permissive habitats for sponges and large phosphate deposits. The capability of sponges to oxygenate shallow seawater and extensive phosphorous burial in epicontinental basins are thus feasible mechanisms for the seawater oxygenation around the Precambrian-Cambrian transition.

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前寒武纪-寒武纪过渡期间马里卡拉套山脉（哈萨克斯坦）浅水环境中的硅质海绵膨胀和磷生成

摘要 前寒武纪-寒武纪过渡期间的海洋氧化被认为是动物快速多样化的关键因素之一，被称为“寒武纪大爆发”。栖息在大陆斜坡环境中的硅质海绵能够将水体中的呼吸需氧量转移到深处，从而导致浅水的氧气含量增加。为了评估海绵对生态系统工程影响的全球重要性，我们使用多种地球化学替代物（包括硅和碳稳定同位素以及燧石和硅质沉积岩中的主要和微量元素）评估了限制海绵扩张的古环境条件。沉积在前寒武纪-寒武纪过渡附近的浅水中。我们调查了哈萨克斯坦南部 Malyi Karatau 山脉的三个岩层。这些剖面中最下面的燧石样品的典型特征是 δ30Si 值相对较低，并显示出硅质海绵针状体的模具。交叉层理结构和粒状磷矿的出现记录了沉积环境的变浅，其中 δ30Si 值总体增加和 Al/Si 增加表明海绵沉降较少和悬浮颗粒负载较高。碳酸盐部分的相应碳同位素记录从接近零减少到负碳同位素值，平均为 -5.9 ‰。δ13​​Ccarb 值总体上与 Y/Ho、氧化还原指示剂 Ce/Ce* 和碳酸盐氟磷灰石的质量分数一致，表明这些比率主要受磷酸盐沉积物中有机物的矿化控制。研究的部分记录了海绵沉降和增殖的生态要求，例如硬基质的存在和足够低的悬浮颗粒浓度和/或低波能。这项工作表明，前寒武纪-寒武纪过渡区周围广泛出现的岩溶表面，随后在寒武纪海侵期间被淹没，将为海绵和大型磷酸盐沉积物创造适宜的栖息地。因此，海绵对浅海海水的氧化能力和陆表盆地中广泛的磷埋藏是前寒武纪-寒武纪过渡期海水氧化的可行机制。研究的部分记录了海绵沉降和增殖的生态要求，例如硬基质的存在和足够低的悬浮颗粒浓度和/或低波能。这项工作表明，前寒武纪-寒武纪过渡区周围广泛出现的岩溶表面，随后在寒武纪海侵期间被淹没，将为海绵和大型磷酸盐沉积物创造适宜的栖息地。因此，海绵对浅海海水的氧化能力和陆表盆地中广泛的磷埋藏是前寒武纪-寒武纪过渡期海水氧化的可行机制。研究的部分记录了海绵沉降和增殖的生态要求，例如硬基质的存在和足够低的悬浮颗粒浓度和/或低波能。这项工作表明，前寒武纪-寒武纪过渡区周围广泛出现的岩溶表面，随后在寒武纪海侵期间被淹没，将为海绵和大型磷酸盐沉积物创造适宜的栖息地。因此，海绵对浅海海水的氧化能力和陆表盆地中广泛的磷埋藏是前寒武纪-寒武纪过渡期海水氧化的可行机制。例如存在硬质基材和足够低的悬浮颗粒浓度和/或低波能。这项工作表明，前寒武纪-寒武纪过渡区周围广泛出现的岩溶表面，随后在寒武纪海侵期间被淹没，将为海绵和大型磷酸盐沉积物创造适宜的栖息地。因此，海绵对浅海海水的氧化能力和陆表盆地中广泛的磷埋藏是前寒武纪-寒武纪过渡期海水氧化的可行机制。例如存在硬质基材和足够低的悬浮颗粒浓度和/或低波能。这项工作表明，前寒武纪-寒武纪过渡区周围广泛出现的岩溶表面，随后在寒武纪海侵期间被淹没，将为海绵和大型磷酸盐沉积物创造适宜的栖息地。因此，海绵对浅海海水的氧化能力和陆表盆地中广泛的磷埋藏是前寒武纪-寒武纪过渡期海水氧化的可行机制。这项工作表明，前寒武纪-寒武纪过渡区周围广泛出现的岩溶表面，随后在寒武纪海侵期间被淹没，将为海绵和大型磷酸盐沉积物创造适宜的栖息地。因此，海绵对浅海海水的氧化能力和陆表盆地中广泛的磷埋藏是前寒武纪-寒武纪过渡时期海水氧化的可行机制。这项工作表明，前寒武纪-寒武纪过渡区周围广泛出现的岩溶表面，随后在寒武纪海侵期间被淹没，将为海绵和大型磷酸盐沉积物创造适宜的栖息地。因此，海绵对浅海海水的氧化能力和陆表盆地中广泛的磷埋藏是前寒武纪-寒武纪过渡期海水氧化的可行机制。