Despite long-standing recognition of high-amplitude, high-frequency sea-level variation resulting from repeated glaciations of Gondwanaland, recorded as “cyclothems” in late Paleozoic strata worldwide, major questions remain concerning their precise timing and expression in the stratigraphic record. A deep meandering canyon in southern Utah cut by the San Juan River exposes cyclic Pennsylvanian (Moscovian) carbonate strata of the Paradox Formation of the Hermosa Group in three dimensions. These peritidally to subtidally deposited strata archive a long record of Pennsylvanian sea-level change that was important to the early development of sequence stratigraphy. Their interpretation with respect to sea level is complicated by lateral variations in sequence thickness and a lack, until recently, of precise geochronologic control. In this study, we use Structure from Motion photogrammetry (SfM) to quantify lateral stratigraphic variation in three dimensions (3D) in the inner gorge of the canyon, then integrate these data with published U-Pb geochronology and conodont biostratigraphy to assess magnitude and temporal significance of depositional cyclicity. 3D SfM models were used to precisely measure the thickness of sixteen depositional sequences in the Barker Creek and Akah intervals, which constitute the lower Paradox Formation. Bioherms ranging from 2–18 m in relief occur within five sequences, and are typically constructed by either microbialites, the sponge Chaetetes, or a mixture of both. On average, bioherms containing Chaetetes are steeper and thicker than those without them. Bioherm-generated bathymetric highs can influence overlying strata in several characteristic ways: 1) by serving as a nucleation site for bioherms in overlying sequences, 2) sequences often onlap bioherms, leading to local stratal truncations, and in some cases, 3) progradational geometries extend laterally outward from preexisting highs in underlying units. Sequence thickness can vary laterally by up to four times in areas with no obvious bioherms; sequences tend to be thickest in the vicinity of bioherms.To better understand the potential orbital significance and correlation of Paradox Formation cyclicity to an increasingly precise global record, we projected photogrammetry-generated average sequence thicknesses onto an age framework using conodont and fusulinid biostratigraphy and CA-TIMS U-Pb zircon ages for correlative strata in Eastern Europe. To mitigate the influence of local variability of accumulation rate, SfM-based average sequence thicknesses in the study area were used to construct a relative-sea-level history that can be compared to global records. While regional averaging cannot correct for the unknown durations of sequence-bounding unconformities, underfilled accommodation, or autocyclicity due to shoal migration, it does provide a more quantitative means to consider timescales of deposition and mechanisms responsible for cyclicity than is possible with a one-dimensional section or core. Paradox Formation cyclicity shares a broad similarity with the global record, suggesting coherent glacio-eustatic sea-level variation across several different tectonic regimes. If one explores a thickness to duration relationship in these sequences, it is plausible that eight thin (2–4 m) sequences in the investigated strata (S2.6–11; S3.5–6) have apparent durations ranging from 100 to 350 kyr, within the plausible range of short and long eccentricity. In contrast, four thicker (6–12 m) sequences in the middle Akah interval (S3.1–S3.4) contain deeper-water lithofacies and have apparent durations ranging from 500 to 1000 kyr, implying that they may be down-dip composites of multiple documented cyclothems in the North American Midcontinent, Urals–Donets, and South China Block successions.

中文翻译：

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美国犹他州 Paradox 组中序列和生物礁形态的摄影测量：宾夕法尼亚（莫斯科）冰川 - 海平面变化的一致性测试

尽管长期以来人们一直认识到冈瓦纳大陆反复冰川作用导致的高振幅、高频海平面变化，在全球晚古生代地层中被记录为“旋涡线”，但主要问题仍然在于它们在地层记录中的精确时间和表达。犹他州南部被圣胡安河切割的一条深蜿蜒的峡谷在三个维度上暴露了赫莫萨群悖论组的宾夕法尼亚（莫斯科）环状碳酸盐岩地层。这些沿潮间带沉积的地层存档了宾夕法尼亚海平面变化的长期记录，这对层序地层学的早期发展很重要。由于层序厚度的横向变化以及直到最近缺乏精确的地质年代控制，他们对海平面的解释变得复杂。在这项研究中，我们使用来自运动摄影测量 (SfM) 的结构来量化峡谷内峡谷中三个维度 (3D) 的横向地层变化，然后将这些数据与已发表的 U-Pb 地质年代学和牙形石生物地层学相结合，以评估沉积循环的幅度和时间意义. 3D SfM 模型用于精确测量 Barker Creek 和 Akah 层段中 16 个沉积层序的厚度，这些层序构成了较低的 Paradox 地层。浮雕范围为 2-18 m 的生物礁出现在五个序列中，通常由微生物群、海绵毛毛虫或两者的混合物构成。平均而言，含有毛毛藻的生物礁比没有毛毛藻的生物礁更陡、更厚。Bioherm 生成的测深高点可以通过几种特征方式影响上覆地层：1) 作为上覆层序中生物礁的成核位点，2) 层序经常与生物礁重叠，导致局部地层截断，并且在某些情况下，3) 前积几何形状从下伏单元中预先存在的高点横向向外延伸。在没有明显生物礁的区域，层序厚度可以横向变化多达四倍；序列往往在生物礁附近最厚。为了更好地理解悖论形成周期的潜在轨道意义和相关性与越来越精确的全球记录，我们使用牙形石和梭形生物地层学和 CA 将摄影测量生成的平均序列厚度投影到年龄框架上- 东欧相关地层的 TIMS U-Pb 锆石年龄。为了减轻积累率局部变异的影响，研究区基于 SfM 的平均层序厚度被用于构建可与全球记录进行比较的相对海平面历史。虽然区域平均不能纠正由于浅滩迁移导致的序列边界不整合、未填充容纳或自旋的未知持续时间，但它确实提供了一种比一维可能的方法更定量的方法来考虑沉积的时间尺度和造成周期性的机制部分或核心。悖论形成的周期性与全球记录具有广泛的相似性，表明在几个不同的构造体制中存在连贯的冰川 - 海平面变化。如果在这些层序中探索厚度与持续时间的关系，很可能在所研究的地层（S2.6-11；S3.5）中有八个薄（2-4 m）层序。5-6) 的明显持续时间在 100 到 350 kyr 之间，在短偏心和长偏心率的合理范围内。相比之下，中阿卡间隔 (S3.1-S3.4) 中的四个较厚 (6-12 m) 层序包含深水岩相，表观持续时间范围为 500 至 1000 kyr，这意味着它们可能是下倾的北美中部大陆、乌拉尔-顿涅茨和华南地块序列中多个有记载的环流的复合体。