The Co-Evolution of Paleoclimate, Paleoceanography, and Sedimentation in the Yanshan Basin, North China: Records from the Yangzhuang Formation of the Jixian Section

Abstract

The Yangzhuang Formation of the Mesoproterozoic Jixian System exhibits a well-developed carbonate sedimentary sequence. However, the carbonate cycles within the Yangzhuang Formation and their co-evolution with paleoclimate and paleoceanographic environment changes remain insufficiently studied. This study conducts a systematic investigation of the rhythmic layers of the Yangzhuang Formation within the Yanshan Basin, North China, through major and trace element analysis, rare earth element analysis, inorganic carbon isotope analysis, granulometric analysis, and time series analysis. The results show that the low content of terrigenous clastics (11.2%~32.6%), slow sedimentation rate (2.2–2.5 cm/ka), Mg/Ca molar ratio close to 1 (1.05–1.53), and small fluctuation of δ¹³C_carb (−0.37‰~−0.05‰) in Member 3 of the Yangzhuang Formation constitutes the processes of co-evolution, along with a mid-phase fluctuation. It indicates the stable evolution of the sedimentary environment and slow ocean expansion speed. However, there is a fluctuating characteristic affected by the breakup of the Colombian supercontinent. The chemical and granulometric analysis of the red and gray layers shows that the terrigenous materials are mainly derived from the eolian sediments, with differences in the wind carrying materials. The time series analysis of the dense samples displays the coupling between the rhythm of the red and gray layers, the inorganic carbon isotope cycle, and the 15 ka precessional cycle in the Mesoproterozoic. We conclude that the rhythm of layers is mainly affected by the monsoon change driven by low-latitude solar radiation at that time, and the age of the Yangzhuang Formation is limited to 1550~1520 ± 2 Ma. The study of the Mesoproterozoic sequence using geochemical data from carbonate deposits reveals the underlying mechanism of global co-evolution during this period, providing a basis for understanding the evolution of the Mesoproterozoic Earth system.

1. Introduction

The Yangzhuang Formation of the Mesoproterozoic Jixian System was formed in a nearshore oxidizing marine environment under arid and hot climatic conditions, characterized by typical carbonate sedimentation with a mass of terrigenous clastics [1]. The sedimentation of the Yangzhuang Formation exhibits features typical of low-latitude deposits during the “Icehouse” period and reflects cyclic variations in the paleoclimate [2]. This also resulted in sedimentation being significantly influenced by materials from both proximal and distal sources, as well as terrigenous clastics [3,4]. The paleoclimate and paleoceanographic conditions of the Jixian System during the Mesoproterozoic are a widely studied topic, with their records providing insights into the climate and oceanic changes during the breakup of the Columbia supercontinent in the Yanshan Basin [5,6]. The climate and shallow marine environment of the Jixian System exhibit multi-stage fluctuations. These fluctuations drove the rhythmic deposits of red and gray dolomite layers in the Yangzhuang Formation. However, the origin of this rhythmic alternation remains controversial [7,8,9].

Significant rhythmic dolomite lithofacies assemblages are key to studying paleoclimate changes and variations in the paleoceanographic chemical environment. These assemblages are crucial for understanding periodic geological events and the rapid cyclical fluctuations in relative sea level within the region [6]. Previous studies have primarily focused on paleomagnetism, paleontology, sequence stratigraphy, isotopic geochemistry, and tectonic settings. The stable and thick rhythmic dolomite of the Yangzhuang Formation provides a new perspective for identifying changes in source rock provenance, thereby shedding light on the changes in the Mesoproterozoic marine sedimentary environment in the Jixian System [10,11,12,13,14]. However, the relationship between the lithological changes in the thick rhythmic dolomite layers of the Yangzhuang Formation and the Mesoproterozoic climate, marine environmental cycles, and astronomical timescales remains unclear [15,16,17,18,19,20].

Through a comprehensive analysis of the geochemical characteristics and sedimentary records of the Yangzhuang Formation, as well as the co-evolution of sedimentary environments, climate, and marine conditions, we can gain a deeper understanding of the interplay between paleoclimatic, paleoceanography, sedimentation, and astronomical factors during the Mesoproterozoic era, against the backdrop of the breakup of the Columbia supercontinent. This allows us to elucidate how these factors collectively shaped the geological evolution of the North China region and the global geological history.

In this study, we propose a geochemical-based approach to reconstruct the sedimentary environment, sedimentation rate, and sea level changes and assess terrestrial material records. In addition, using granulometric analysis and time series analysis, we explore the correspondence between the rhythm of the red and gray dolomite layers, inorganic carbon isotope cycles, and the astronomical cycles of the Mesoproterozoic. Moreover, we explore the co-evolution of sedimentary environment, climate, and marine conditions while simultaneously determining the corresponding chronological spans of the Yangzhuang Formation. This study aims to provide a reference for understanding the evolution of the Mesoproterozoic Earth system.

2. Geological Setting

The Yanshan Basin has undergone a series of depositional phases, influenced by the breakup of the Columbia supercontinent, starting around 1800 Ma [21]. These phases include estuarine bays, restricted marine bays, and shallow marine stages, culminating in a shallow marine regression around 800 Ma. The Jixian section along the northern margin of the Yanshan Basin features a relatively continuous Mesoproterozoic sequence with global comparative significance [22]. The Yangzhuang Formation in the Jixian section is exposed at various localities in the Yanshan region of North China, including the Ming tombs area of Beijing [23], Pingquan of Hebei Province [9], and Jixian of Tianjin. In Jixian, the thickness of the formation reaches 707 m [24], located about 15 km north of the central urban area of Jizhou District (formerly known as Jixian) in Tianjin (Figure 1). The exposed area spans from 40°05′ N to 40°15′ N and from 117°40′ E to 117°50′ E.

The Yangzhuang Formation can be vertically divided into three members (Figure 2): The lower part of Member 1 consists of medium to thick bedded dark gray mudstone dolomite and purple-red mud-crystal dolomite, interbedded with siliceous dolomite and siliceous nodules. The upper part is dominated by siliceous dolomite and purple-red mud-crystal dolomite, with sedimentary structures, including stromatolites, ripple marks, feather-cross bedding, and bird’s-eye structures, indicating that the primary depositional environment was the intertidal zone. Member 2 is mainly composed of red, clastic-rich mud-crystal dolomite and siliceous dolomite, with sedimentary structures dominated by ripple marks, halite pseudomorphs, desiccation cracks, and gypsum, suggesting a predominant environment of the supratidal zone, with intertidal features also present. The lower part of Member 3 mainly consists of gray mudstone dolomite, while the upper part consists of interbedded purple-red and gray mud-crystal dolomite. The sedimentary structures are primarily stromatolites and ripple marks, indicating that the depositional environment was mainly between the supratidal and intertidal zones.

3. Samples and Methods

In this study, we collected a total of 64 rock samples of the Yangzhuang Formation, predominantly composed of dolomite. Among them, 35 micritic dolomite rock samples were collected with a relatively large spacing (Figure 2), including 5 samples each from Members 1 and 2 and 25 samples from Member 3 collected with an average spacing of 10 m within a length of 250 m. Additionally, 29 rock samples were densely sampled from a well-exposed, approximately 5-meter-thick rhythmic sedimentary sequence of red and gray dolomite layers in the upper-middle part of Member 3, based on changes in lithology and color, including 13 periodic rhythms. These included 13 samples of gray to gray–green mud-crystal dolomite, 3 samples of gray mudstone, and 13 samples of purple-red mud-crystal dolomite.

The isotope analysis of the samples was carried out at the State Key Laboratory of Biogeology and Environmental Geology at China University of Geosciences (Wuhan). Sample preparation involved collecting fresh specimens, followed by manual coarse crushing and machine fine grinding to produce powder (<200 mesh). After drying, 150–200 μg (60–100 mg for standards) was weighed on a high-precision balance and loaded into reaction tubes, inserting 2 standards per 10 samples. Testing utilized the Kiel IV system, and CO₂ gas was obtained by anhydrous orthophosphate method at a room temperature of 25 °C and a humidity of 40%. For dolomite-rich samples, reactions proceeded at 50 °C for 12 h to ensure completeness. Generated CO₂ was analyzed via a MAT253 mass spectrometer. Isotopic ratios (relative to PDB using GBW04416/04417 standards) were obtained with ±0.1‰ precision [28] (

Table 1. Selected geochemical proxies of rock samples.

	Depth (m)	${\mathsf{\delta }}^{13}{\mathbf{C}}_{\mathbf{c}\mathbf{a}\mathbf{r}\mathbf{b}}$ (‰)	${\mathbf{A}\mathbf{l}}_2{\mathbf{O}}_3$ (%)	$\mathbf{S}\mathbf{i}{\mathbf{O}}_2$ (%)	${\mathbf{N}\mathbf{a}}_2\mathbf{O}$ (%)	${\mathbf{K}}_2\mathbf{O}$ (%)	$\mathbf{T}\mathbf{i}{\mathbf{O}}_2$ (%)	$\mathbf{M}\mathbf{g}\mathbf{O}$ (%)		$\mathbf{C}\mathbf{a}\mathbf{O}$ (%)	$\mathbf{F}\mathbf{e}\mathbf{O}$ (%)	${\mathbf{F}\mathbf{e}}_2{\mathbf{O}}_3$ (%)	$\mathbf{M}\mathbf{n}\mathbf{O}$ (%)		Zr (ppm)	V (ppm)	Sc (ppm)	Sr (ppm)	Ba (ppm)
Yz1-1	45	−0.23	0.88	15.47	0.01	0.40	0.04	19.10		24.80	0.43	0.42	0.014		29.87	8.32	1.71	44.00	457
Yz1-2	95	−0.32
Yz1-3	145	−0.13	2.13	18.87	0.01	0.76	0.07	18.14		22.92	0.57	0.94	0.019		41.72	17.20	2.90	66.46	1612
Yz1-4	195	−0.14
Yz1-5	205	−0.11
Yz2-1	257	−1.30	4.18	29.13	0.05	2.40	0.13	16.28		17.91	0.43	1.45	0.022		84.91	22.28	4.64	102.23	2361
Yz2-2	285	−1.30
Yz2-3	320	−1.32
Yz2-4	373	−1.24	4.86	29.67	0.04	2.81	0.15	16.46		16.41	0.43	2.34	0.020		69.98	25.10	5.74	79.48	1225
Yz2-5	425	−1.28
Yz3-1	452	−0.22	5.15	26.88	0.01	2.75	0.18	16.99		17.58	0.86	1.74	0.016		82.69	22.42	7.69	47.62	603
Yz3-2	462	−0.12	2.55	24.57	0.04	1.32	0.08	17.39		21.77	0.57	0.95	0.016		43.94	17.48	3.30	70.97	1812
Yz3-3	472	−0.05	2.94	21.47	0.04	1.48	0.10	17.47		21.23	0.57	1.47	0.016		45.66	20.30	3.92	58.86	816
Yz3-4	482	−0.06	2.43	22.33	0.05	1.27	0.08	17.08		21.79	0.43	0.88	0.016		38.63	15.51	3.43	69.35	1782
Yz3-5	492	−0.14	2.85	23.40	0.05	1.49	0.09	16.85		20.79	0.57	1.25	0.016		51.84	16.07	3.77	66.18	1116
Yz3-6	502	−0.15	4.00	23.35	0.10	2.04	0.14	16.99		19.98	0.72	1.32	0.017		59.36	19.88	5.14	59.31	1103
Yz3-7	512	−0.18	2.82	21.65	0.09	1.45	0.08	17.15		21.77	0.72	0.96	0.016		48.63	17.34	3.50	63.57	907
Yz3-8	522	−0.18	3.06	23.23	0.10	1.54	0.11	16.74		20.60	0.57	1.45	0.017		52.82	17.62	4.08	65.96	719
Yz3-9	532	−0.21	5.17	27.65	0.00	2.96	0.17	16.54		17.23	0.86	1.62	0.016		64.92	21.99	5.88	42.95	358
Yz3-10	542	−0.07	3.03	21.17	0.02	1.79	0.09	17.43		21.68	0.57	0.96	0.017		55.66	17.48	4.90	68.65	910
Yz3-11	552	−0.10	3.24	22.88	0.01	1.81	0.10	17.48		20.73	0.66	1.29	0.016		64.42	19.60	4.95	80.84	1584
Yz3-12	562	−0.23	4.86	27.53	0.04	2.66	0.16	17.30		17.18	0.78	1.65	0.015		114.78	20.73	6.52	69.22	1185
Yz3-13	572	−0.24	5.39	30.78	0.03	2.83	0.18	16.77		15.28	0.86	2.26	0.015		133.91	26.08	6.59	96.20	2103
Yz3-14	582	−0.07	4.68	28.12	0.06	2.54	0.16	16.70		17.30	0.86	1.55	0.016		111.32	18.33	5.84	52.48	557
Yz3-15	592	−0.25	2.88	22.89	0.06	1.58	0.09	17.08		20.8	0.43	1.4	0.020		52.58	17.06	3.42	65.34	1120
Yz3-16	602	−0.11	2.12	22.11	0.07	0.71	0.06	17.75		22.04	0.43	0.8	0.022		44.06	20.73	2.47	90.34	4037
Yz3-17	612	−0.06	1.92	18.17	0.01	0.68	0.07	18.82		23.31	0.57	1.03	0.021		36.9	17.34	2.87	73.70	2456
Yz3-18	622	−0.1	2.47	19.14	0.01	1.42	0.08	17.87		22.56	0.57	0.88	0.020		40.73	14.95	3.43	53.53	469
Yz3-19	632	−0.15	2.96	21.23	0.01	1.69	0.09	17.55		21.28	0.57	1.29	0.018		46.78	20.02	4.06	68.92	1089
Yz3-20	642	−0.2	2.76	20.26	0.03	1.54	0.09	17.62		21.83	0.72	0.92	0.018		43.94	19.46	4.18	83.11	2040
Yz3-21	652	−0.2	2.58	19.84	0.03	1.42	0.08	17.52		22.34	0.57	1.17	0.018		50.11	21.15	4.49	84.53	1797
Yz3-22	662	−0.26	3.96	23.46	0.06	2.36	0.13	16.88		19.89	0.66	1.14	0.017		72.08	20.73	5.65	86.77	1696
Yz3-23	672	−0.35	2.21	18.94	0.06	1.07	0.08	17.57		23.19	0.57	0.94	0.020		36.53	18.47	3.19	74.09	1719
Yz3-24	682	−0.37	2.63	22.12	0.07	1.45	0.08	17.34		21.59	0.92	1.28	0.019		54.43	21.57	3.61	80.47	2178
Yz3-25	692	−0.32	5.06	36.94	0.01	3.11	0.19	14.04		15.05	0.86	1.36	0.018		91.95	29.33	5.49	134.24	3879
	La (ppm)	Ce (ppm)	Pr (ppm)	Nd (ppm)	Sm (ppm)	Eu (ppm)	Gd (ppm)	Tb (ppm)	Dy (ppm)	Ho (ppm)	Er (ppm)	Tm (ppm)	Yb (ppm)	Lu (ppm)	Y (ppm)	Rb (ppm)	U (ppm)	Th (ppm)	Cu (ppm)
Yz1-1	4.72	10.41	1.15	4.14	0.75	0.19	0.69	0.12	0.66	0.12	0.36	0.06	0.38	0.06	3.63	14.64	0.67	1.89	7.36
Yz1-3	4.96	12.32	1.49	5.72	1.05	0.24	0.89	0.15	0.82	0.16	0.46	0.08	0.51	0.08	4.55	27.47	1.54	2.80	5.11
Yz2-1	8.45	20.69	2.77	10.83	2.12	0.42	1.69	0.28	1.49	0.29	0.84	0.14	0.88	0.14	8.04	60.35	1.31	4.13	4.97
Yz2-4	13.93	28.71	3.49	13.04	2.35	0.47	1.94	0.31	1.75	0.34	0.96	0.16	0.98	0.15	9.29	79.14	1.63	5.02	5.72
Yz3-1	13.66	23.65	2.84	9.91	1.67	0.32	1.54	0.26	1.53	0.31	0.96	0.18	1.13	0.18	8.53	87.47	3.20	8.41	7.63
Yz3-2	7.51	16.15	2.05	7.60	1.40	0.26	1.18	0.20	1.06	0.21	0.57	0.10	0.64	0.11	5.80	38.53	1.52	2.94	8.98
Yz3-3	9.43	17.52	2.08	7.43	1.37	0.29	1.17	0.19	1.07	0.21	0.60	0.11	0.68	0.11	5.99	50.71	2.09	3.69	5.25
Yz3-4	5.36	13.11	1.68	6.45	1.20	0.26	1.07	0.18	0.95	0.18	0.54	0.10	0.60	0.09	5.30	39.33	1.47	2.86	7.25
Yz3-5	7.65	16.52	1.98	7.24	1.31	0.28	1.12	0.18	1.04	0.21	0.58	0.11	0.67	0.11	5.53	46.97	1.88	3.50	7.89
Yz3-6	9.07	17.41	2.09	7.45	1.33	0.29	1.19	0.20	1.13	0.23	0.67	0.12	0.77	0.13	6.29	65.60	2.39	4.51	4.95
Yz3-7	8.15	15.89	1.94	7.11	1.29	0.27	1.12	0.18	1.02	0.20	0.58	0.10	0.63	0.11	5.67	45.88	1.82	3.25	4.47
Yz3-8	9.66	18.47	2.24	8.41	1.56	0.31	1.30	0.21	1.20	0.23	0.69	0.12	0.75	0.12	6.45	50.40	2.07	4.06	4.67
Yz3-9	13.94	23.82	2.69	9.24	1.53	0.32	1.38	0.22	1.30	0.26	0.81	0.15	0.96	0.15	7.09	79.85	2.79	6.95	4.68
Yz3-10	9.40	19.17	2.34	8.65	1.55	0.31	1.32	0.22	1.22	0.23	0.69	0.12	0.72	0.12	6.49	50.64	1.85	4.51	4.76
Yz3-11	7.27	16.80	1.97	7.32	1.42	0.28	1.21	0.21	1.15	0.23	0.66	0.12	0.72	0.12	6.42	51.25	1.94	3.90	4.96
Yz3-12	13.24	25.30	2.97	10.51	1.95	0.38	1.85	0.35	2.17	0.45	1.36	0.23	1.47	0.23	11.84	69.30	3.37	6.74	6.83
Yz3-13	13.17	26.72	3.16	11.12	2.03	0.38	1.91	0.36	2.22	0.46	1.37	0.25	1.54	0.24	12.09	77.00	3.53	6.83	9.43
Yz3-14	15.49	27.20	3.15	11.22	2.04	0.39	1.95	0.37	2.18	0.45	1.35	0.24	1.49	0.23	11.70	69.64	3.35	8.08	4.78
Yz3-15	8.98	17.12	2.09	7.61	1.41	0.29	1.20	0.19	1.13	0.22	0.64	0.11	0.69	0.11	6.07	41.67	1.95	3.67	4.16
Yz3-16	2.68	8.54	1.11	4.54	0.94	0.21	0.78	0.13	0.74	0.14	0.42	0.07	0.45	0.08	4.06	24.21	1.22	2.52	3.68
Yz3-17	4.45	11.24	1.42	5.44	1.09	0.24	0.86	0.14	0.79	0.15	0.44	0.08	0.47	0.08	4.30	24.58	1.49	2.54	3.93
Yz3-18	8.86	15.85	1.85	6.59	1.15	0.24	1.04	0.16	0.89	0.17	0.51	0.10	0.59	0.10	5.09	41.71	1.73	3.32	4.27
Yz3-19	9.35	19.41	2.28	8.20	1.43	0.30	1.23	0.20	1.15	0.22	0.67	0.12	0.72	0.12	6.18	50.27	2.05	3.89	4.63
Yz3-20	6.15	15.44	1.97	7.35	1.34	0.25	1.06	0.18	1.04	0.20	0.60	0.11	0.69	0.11	5.72	46.82	1.82	3.43	7.40
Yz3-21	6.94	16.11	2.02	7.64	1.48	0.30	1.24	0.20	1.18	0.23	0.66	0.12	0.72	0.11	6.50	45.67	1.84	3.05	4.44
Yz3-22	10.58	21.72	2.59	9.25	1.68	0.33	1.44	0.25	1.46	0.30	0.89	0.16	1.02	0.16	8.03	63.70	2.64	5.36	4.86
Yz3-23	6.43	15.49	1.87	7.04	1.30	0.28	1.14	0.18	1.03	0.19	0.56	0.09	0.60	0.09	5.63	30.47	1.39	2.86	3.99
Yz3-24	6.30	14.28	1.69	6.35	1.21	0.25	1.03	0.18	1.00	0.20	0.57	0.10	0.67	0.11	5.68	41.99	2.03	2.72	4.45
Yz3-25	4.87	12.35	1.56	6.15	1.26	0.28	1.05	0.19	1.16	0.24	0.73	0.13	0.86	0.14	6.85	69.12	2.87	3.87	4.85

).

Sample preparation and whole-rock major and trace element analysis were completed at the Testing Center of the Eighth Geological and Mineral Exploration Institute of Shandong Province (Table 1).

The analysis of major elements was conducted using an Axios-type X-ray fluorescence spectrometer (PANalytical, Axios, Panaco, Netherlands)via the XRF method, according to the national standard GB/T 14506.28-2010 [29], with an error margin within 5%. Firstly, 1 g of the dried sample was accurately weighed, and the loss on ignition (LOI) through muffle furnace burning was determined. Subsequently, the sample was mixed with anhydrous lithium tetraborate in a mass ratio of 1:8 and melted into glass sheets at 1150–1125 °C (using a HMS-II-MZ high-frequency melting machine, Duolin, Chengdu, China). Finally, a calibration curve was established using standard material preparation samples, and the content of major elements in the sample was determined via X-ray fluorescence spectroscopy.

The analysis of trace elements and rare earth elements was performed using a NexION 2000 ICP-MS instrument (PerkinElmer Sciex, Waltham, MA, USA), with an error margin within 5%. Firstly, 25 mg of the sample was weighed, hydrofluoric acid was added, and it was heated to 120 °C. After the hydrofluoric acid evaporated, nitric acid and hydrofluoric acid were added for digestion in an oven. Then, after 48 h, it was removed, and the mixture was heated to evaporate the acid. Then, it was dissolved in nitric acid and evaporated again. Afterwards, perchloric acid was added, and it was steam dried again. Finally, it was dissolved in nitric acid, diluted to a specific volume, and shaken well for testing. After completion, it was tested using the ICP-MS instrument.

Micro-granulometric analysis can be performed using micrographs derived from petrographic thin sections of the collected samples [30]. Firstly, the microscopic plane-polarized light (PPL) images were preprocessed using software (Python 3.12) to enhance the visibility of granular features. The procedure involves converting images to grayscale format, adjusting brightness and contrast, applying threshold segmentation to filter out noise, and ultimately transforming them into black and white (B&W) images, thereby clearly enhancing the delineation of grain boundaries. Secondly, grains were automatically segmented via the software’s particle recognition function. However, manual intervention was required through two key procedures: (1) drawing white lines between linked grains to separate them for individual counting and measurement, and (2) redrawing blurred boundaries affected by defocusing artifacts or low contrast against the black background. Thirdly, to extract terrigenous grain size data, authigenic dolomite was excluded using optical characteristics from cross-polarized light (XPL) images (e.g., extinction behavior and birefringence differences). Additionally, particles with φ-values > 7 were omitted due to resolution constraints. Finally, the equivalent diameter of each grain was calculated via the software based on corrected segmentation boundaries.

In this study, time series analysis of the ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ data enables the recognition of astronomically forced sedimentary cycles at Member 3 of the Yangzhuang Formation, thus determining the estimation of sedimentation rate. The astrochronology is supported by spectral analysis on the geochemical data sets using the program Acycle. High-resolution astrochronology for the ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ data and statistical methods provide a chance to quantitatively analyze the matching of Milankovitch cycle signals with geochemical data cycles and evaluate sedimentation rates. These methods elucidate the links between orbital forcing and inorganic carbon isotope fluctuations.

4. Results

4.1. Lithology

The rock samples are predominantly composed of carbonate minerals, with a minor proportion of terrigenous clastics, with microcrystalline and blocky structures. The average composition of dolomite in these carbonate minerals is 11.0% silt-sized crystalline dolomite, 61.4% microcrystalline dolomite, and 21.2% micritic dolomite. The content of silt and fine sand varies between 1% and 6%, with an average of 4.3%, which mainly includes quartz, as well as trace feldspar and rock debris (carbonaceous mudstone, etc.). The rock samples are also contaminated with a small amount of cryptocrystalline mud (clay minerals and fine rock fragments), with a content of below 3% (Figure 3). Additionally, the rock samples contain trace amounts of rounded to ovoid coarse sand and medium-grained sand.

4.2. Post-Diagenetic Processes

The impact of post-diagenetic processes on the samples can be assessed via correlation analysis on the Ce anomaly (δCe), Eu anomaly (δEu), and ${\mathrm{D}\mathrm{y}}_{\mathrm{N}}/{\mathrm{S}\mathrm{m}}_{\mathrm{N}}$ ratio of the rare earth elements [31,32]. As shown in the figure, the correlation between the Ce anomaly and the Eu anomaly is weak, as is the correlation between the Ce anomaly and the ${\mathrm{D}\mathrm{y}}_{\mathrm{N}}/{\mathrm{S}\mathrm{m}}_{\mathrm{N}}$ ratio. This indicates that the Ce anomaly values of most samples reflect the original information and are minimally influenced by post-diagenetic alterations (Figure 4).

4.3. Paleoenvironments

Changes in paleosalinity of the Yangzhuang Formation can be assessed through the ratio of Calcium oxide and Iron (CaO/(Fe + CaO)) [33]. The measured values of the CaO/(Fe + CaO) ratio range from 0.87 to 0.98 (Figure 5), with an average value of 0.93. These values suggest relatively high water salinity during the sedimentary period, possibly corresponding to an epicontinental sea or lagoonal environment, which is consistent with the marine sedimentary environment of the Jixian System [34].

Paleo-redox conditions of the Yangzhuang Formation can be evaluated through various elemental ratios [35]. The ratio of uranium and thorium (U/Th) is a commonly used indicator for paleo-redox conditions; when the U/Th value is greater than 1.25, it indicates relative enrichment of U and hypoxic conditions. On the contrary, it indicates secondary oxidation or an oxidation environment. The U/Th ratio of the Yangzhuang Formation ranges from 0.32 to 0.75 (Figure 5), with an average value of 0.51, indicating that the sedimentary environment of this region was generally in an oxidizing to sub-oxidizing state. Correspondingly, the ratio of vanadium and scandium (V/Sc) also provides strong evidence that, under hypoxic conditions, the V/Sc ratio increases, which can help distinguish between a hypoxic environment (>9.1) and an oxidative environment (4.7–9.1). The V/Sc ratio of the Yangzhuang Formation ranges from 2.91 to 8.38, with an average value of 4.68, further supporting the conclusion that the environment was in an oxidizing to sub-oxidizing state. Compared to the Jixian System, which experienced multiple pulses of oxygenation under an overall hypoxic shallow marine background, the Yangzhuang Formation likely existed in a relatively oxygen-rich environment at that time [36].

Changes in paleodepth of the Yangzhuang Formation can be assessed through the ratio of strontium to barium (Sr/Ba). Strontium (Sr) has a higher mobility in deep-sea regions, while barium (Ba) tends to accumulate in nearshore and source areas, resulting in lower Sr content and a relatively lower Sr/Ba ratio in shallow marine regions [37]. Generally, the Sr/Ba ratio in marine sediments is greater than 1, whereas in terrestrial sediments, it is less than 1 [38]. According to the measurements from the Yangzhuang Formation, the Sr/Ba ratio ranges from 0.02 to 0.12 (Figure 5), with an average value of 0.06. Compared to the sedimentary environment of the Jixian Formation, the lower Sr/Ba ratio of the Yangzhuang Formation suggests that its sedimentary period predominantly occurred in a nearshore environment [39].

Comparison of paleosalinity and paleoredox indicators (Figure 5) suggests that during the deposition of Member 3 of the Yangzhuang Formation, there were certain fluctuations in the paleoceanographic environment.

4.4. Terrigenous Clastics

4.4.1. Stability of Terrigenous Clastics

Major element determinations of the Yangzhuang Formation samples reveal that, among the 25 samples from Member 3, the Al₂O₃ content ranges from 1.91% to 5.39%, with an average value of 3.35%, indicating generally low levels. The SiO₂ content ranges from 18.17% to 36.94%, with an average value of 23.6%. The FeO content ranges from 0.43% to 0.92%, with an average value of 0.66%. The Fe₂O₃ content ranges from 0.80% to 2.26%, with an average value of 1.26%. The Na₂O content ranges from 0.00% to 0.10%, with an average value of 0.04%. The K₂O content ranges from 0.68% to 3.11%, with an average value of 1.80%. These elements primarily originate from terrigenous clastics.

The total content of Al₂O₃, SiO₂, FeO, Fe₂O₃, Na₂O, and K₂O ranges from 22.37% to 47.35%, with an average value of 30.72%, indicating that the terrigenous clastics in Member 3 of the Yangzhuang Formation are relatively stable. Correlation analysis of the major elements in Member 3 of the Yangzhuang Formation reveals strong correlations between Al₂O₃, SiO₂, FeOt (FeO + Fe₂O₃), K₂O, and TiO₂ (

Table 2. Correlation analysis results of major elements.

	${\mathbf{A}\mathbf{l}}_2{\mathbf{O}}_3$ (%)	$\mathbf{S}\mathbf{i}{\mathbf{O}}_2$ (%)	$\mathbf{F}\mathbf{e}{\mathbf{O}}_{\mathbf{t}}$ (%)	${\mathbf{K}}_2\mathbf{O}$ (%)	$\mathbf{T}\mathbf{i}{\mathbf{O}}_2$ (%)
${\mathrm{A}\mathrm{l}}_2{\mathrm{O}}_3$ (%)	1
$\mathrm{S}\mathrm{i}{\mathrm{O}}_2$ (%)	0.84	1
$\mathrm{F}\mathrm{e}{\mathrm{O}}_{\mathrm{t}}$ (%)	0.87	0.70	1
${\mathrm{K}}_2\mathrm{O}$ (%)	0.98	0.84	0.81	1
$\mathrm{T}\mathrm{i}{\mathrm{O}}_2$ (%)	0.99	0.86	0.85	0.97	1

). Specifically, the stability of Al and Ti elements in fine-grained sedimentary rocks suggests minimal weathering influence, reflecting the abundance of terrigenous clastic material from sources such as rivers or aeolian processes [40], and the correlation coefficient of Al₂O₃ and TiO₂ is 0.99, indicating that the parent rock of the terrigenous clastics in the source area remains stable. The strong positive correlation between SiO₂ and the terrigenous elements (Al and Ti) further suggests that external influences are primarily from land-based sources [41]. The correlation coefficients of Al₂O₃ with other elements range from 0.84 to 0.99, indicating that Al₂O₃ is highly representative and can be used to measure changes in the abundance of terrigenous clastics.

4.4.2. Terrigenous Clastic Material

Due to the extremely low solubility of rare earth elements (REEs) in water, their short residence time, and the minor compositional changes during weathering, transportation, and diagenesis, they serve as reliable tracers for sediment analysis. In this study, carbonate rock samples exhibited high loss on ignition (LOI, mainly due to carbonate decomposition, Table 1). To account for this, the ΣREE content in terrigenous clastic material was normalized by removing the influence of carbonate components during calculation [42]. The La/Yb–ΣREE diagram (Figure 6a) shows that the samples fall within the mixing zone between granite and sedimentary rocks [43], while the Th/Sc–Zr/Sc diagram (Figure 6b) indicates that the samples align with the typical compositional evolution trend of igneous rocks, showing no evidence of sedimentary recycling [44]. These results suggest that although a mixed La/Yb–ΣREE signal is observed, the detrital material is more likely derived from internal mineral differentiation within granite rather than external sedimentary input. Therefore, the terrigenous detritus in the study area during the Yangzhuang Formation depositional period should predominantly originate from granite.

The Al₂O₃/TiO₂ ratios are sensitive to the composition of the sedimentary source rocks, and values ranging from 3 to 8, 8 to 21, and 21 to 70 reflect the composition of mafic, intermediate, and felsic igneous source rocks, respectively [41]. While the Al₂O₃/TiO₂ ratio is influenced by grain size variations, as both elements are strongly related to the clay fraction, Zr is generally expected to be concentrated in the coarse grain fraction. Consequently, debris sediments with larger grain sizes exhibit higher Zr/Al ratios [45]. The Zr/Al ratio in the samples of this study is concentrated between 23.7 and 46.9 with an average value of 34, intermediate between silt (Zr/Al ≈ 64) and clay (Zr/Al ≈ 13) [46], which is consistent with the component content in rock samples (Figure 3). It indicates that the source rock signal of Al₂O₃/TiO₂ is not significantly disturbed. Similarly, the TiO₂/Zr ratio ranges from 0 to 54, 54 to 194, and greater than 194, reflecting the composition of rhyolitic, intermediate, and mafic igneous rocks, respectively [47]. The combined phase diagrams of Al₂O₃–TiO₂ and TiO₂–Zr (Figure 6c,d) suggest that the terrigenous clastic material in the Yangzhuang Formation predominantly originates from felsic igneous source rocks with an acidic characteristic.

Member 3 of the Yangzhuang Formation profile primarily consists of interbedded red and gray mud-crystal dolomite. The red and gray mud-crystal dolomite was divided into two groups for comparative analysis. Based on the results of the major and trace element analysis, the difference between the red and gray dolomite layers indicates that the TiO₂/Zr ratio in the red layers is slightly higher than in the gray layers, with an average value of 20.0 for the red layers and 16.3 for the gray layers. This result suggests that the sedimentary source rocks of the terrigenous clastic material in the red layers are more closely associated with the characteristics of intermediate igneous rocks.

4.5. The Inorganic Carbon Isotopes Analysis

Previous studies of the early Mesoproterozoic inorganic carbon isotope ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ data have shown a gradual increase [18,48], reflecting a sustained oxygenation of seawater in this period [9]. However, in the carbonate rock records from the Yangzhuang Formation, a fluctuation in ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values were observed [15], suggesting a potential short-term environmental change during this period. In this study, we analyzed the inorganic carbon isotope ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ from both the 35 widely spaced samples and the 29 densely spaced samples from a 5-meter-thick sequence to explore the causes behind these fluctuations during this period (Figure 7).

The ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values of the Yangzhuang Formation samples exhibit distinct stratigraphic patterns. The ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values in Member 1 are relatively high, ranging from −0.32‰ to −0.11‰, with an average value of −0.19‰. The ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values in Member 2 are lower, ranging from −1.32‰ to −1.24‰, with an average value of −1.29‰. Samples from Member 2 of the Yangzhuang Formation reflect a negative shift event, characterized by lower overall values and a smaller range of variation. The ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values in Member 3 rise again, ranging from −0.37‰ to −0.05‰, with an initial value of −0.22‰, gradually increasing to −0.05‰ and then slowly decreasing to −0.21‰. After a minor fluctuation of about 0.18‰, the values ultimately decline slowly from −0.06‰ to −0.37‰ (Figure 7).

In addition to the Jixian section, the Yangzhuang Formation is also exposed in the Ming tombs section in Beijing [23,49,50] and the Pingquan section in Hebei Province [9]. However, these exposures are thinner, and the inorganic carbon isotope ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values are almost all negative, ranging from −2‰ to 0‰, which are similar to the characteristics of the Yangzhuang Formation in the Jixian section.

The inorganic carbon isotope ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values of the densely spaced 29 samples range from −0.39‰ to −0.05‰, with an average value of −0.13‰. The inorganic carbon isotope curve for the densely sampled section shows that, although the overall ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ variation is relatively small, it exhibits a certain regularity, which can be divided into several cycles. Each cycle has a fluctuation range of approximately 0.2–0.3‰, spanning around 4–5 red and gray dolomite layers.

Overall, the inorganic carbon isotope ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values of the Yangzhuang Formation show a negative shift event in Member 2, while the inorganic carbon isotope of Member 3 and the densely sampled section exhibit periodic cyclic characteristics.

4.6. Rare Earth Element Analysis

In the rare earth element analysis of the Yangzhuang Formation, the total rare earth element content (∑REE, ppm) of 25 dolomite samples from Member 3 ranges from 24.89 to 79.43, with an average value of 49.78. The light rare earth element content (∑LREE, ppm) ranges from 18.02 to 59.49, with an average value of 38.26; the heavy rare earth element content (∑HREE, ppm) ranges from 2.81 to 8.35, with an average value of 4.74. The average value of the ∑LREE/∑HREE ratio is 8.16, which falls between the respective ratios of NASC (7.30) and PAAS (9.50).

The rare earth element analysis also reveals significant differences between the red and gray dolomite samples. The average value of ∑REE in the red layers is 46.93 ppm, higher than that of the gray layers at 40.14 ppm, indicating that the content of terrigenous clastics was higher during the deposition of the red layers. The ∑LREE/∑HREE ratio of the red layers has an average value of 8.7, while in the gray layers it is 7.7. Additionally, the La/Yb ratio in the red layers has an average value of 12.1, compared to 9.8 in the gray layers. These results suggest systematic differences between the red and gray layers in these two indices, reflecting distinct differences in the provenance of terrigenous clastics during the deposition of the red and gray layers [51].

4.7. Granulometric Analysis of Red and Gray Layers

The sedimentation in this region primarily represents primary sedimentation, with the grain size distributions of terrigenous clastics significantly influencing its physical and chemical properties. The particle size composition is controlled by the provenance and transport dynamics, which in turn affect the granulometry, roundness, and sorting of the red and gray layers [52]. Both red and gray layer samples from the Yangzhuang Formation are primarily composed of mud-crystal dolomite, but the fine-grained content of the red layers is significantly higher than that of the gray layers, with similar roundness between the two (Figure 8).

Micro-granulometric analysis of the Yangzhuang Formation reveals that the gray layers primarily exhibit a bimodal distribution, with two modes at grain sizes of 4 and 6. In contrast, the red layers generally do not show a distinct bimodal grain size distribution, and a higher proportion of fine particles compared to medium-sized ones, most of which are larger than 6 (Figure 9).

The above structural characteristics show that the Yangzhuang Formation has wind-induced sedimentary characteristics, which may contain wind-borne sediments [3,53]. The particle size analysis shows that the red layers contain more wind-borne sediments than the gray layers [54]. The clastic particles and silt, and mud content in the matrix of the sediment are derived from volcanic ash [3,55]. Given the relatively low content of terrigenous material and its fine grain size, it can be inferred that the Jixian area was distant from the volcanic activity centers during the deposition of the Yangzhuang Formation.

Based on the differences in particle size distribution between the red and gray layers, as well as the systematic chemical composition variations in the terrigenous material, it is likely that the source regions of the terrigenous material in the red and gray layers of the Yangzhuang Formation exhibit structural differences. Additionally, the manner and distance of aeolian transportation may also differ.

According to the differences in the particle size analysis conclusions of the red and gray layers and the systematic differences in the chemical composition of land-based inputs, the terrestrial-source substances in the red and gray layers of the Yangzhuang Formation are mainly wind deposition, and there are certain differences in the transport method, distance and source area of wind carrier.

5. Discussion

Since the concept of sequence stratigraphy was proposed in the 20th century, it has attracted widespread attention from geologists. The development of sequences is controlled by multiple factors such as tectonic movements, eustatic fluctuation, provenance, and paleoclimate. The time span of first-order supersequences is greater than 50 Ma, second-order sequences are about 10–50 Ma, and third-order sequences are about 1–10 Ma. Below these time spans, there are also multiple meter-scale cyclic sequences reflecting the Milankovitch nature of stratigraphic records. The Jixian section is a typical representative of cyclic carbonate sedimentation, with the famous “Wumishan Cyclothem”.

5.1. Paleoceanographic Fluctuations

During the deposition of Member 3 of the Yangzhuang Formation, there were certain fluctuations in the paleoceanographic environment. These fluctuation features are also clearly reflected in terrigenous clastics and sedimentation rates. Since Al₂O₃ is mainly derived from terrigenous clastics and highly represents terrigenous clastics, the content of terrigenous clastics can be calculated by the ratio of the Al₂O₃ content of Member 3 of the Yangzhuang Formation to the average content of Al₂O₃ in the felsic granite from the Pre-Cambrian Yanshan region [56,57,58,59]. The contents of terrigenous clastics are calculated to be 11.2%~32.6%, with an average value of 20.2%.

Meanwhile, the strong correlation between the content of Mn in marine sediments and the sedimentation rate was found [60], and the calculation formula is as follows (Equation (1)).

$$\lg \left(\mathrm{v}\mathrm{s}\right)=0.2758-1.135\mathrm{l}\mathrm{g}({\displaystyle \frac{0.7745\mathrm{M}\mathrm{n}}{Ti}}-0.05)$$

(1)

The sedimentation rates of 25 samples from Member 3 of the Yangzhuang Formation are calculated to range from 7 m/Ma to 85 m/Ma, with an average value of 30 m/Ma, and most of them are distributed between 10 m/Ma and 40 m/Ma. The calculated sedimentation rate (vs) shows a strong correlation with the content of terrigenous clastics, indicating that this method for calculating terrigenous clastic content is reliable.

Fluctuations on a million-year scale (corresponding to third-order sequences) are believed to be influenced by tectonic movements, with oceanic spreading being the core process of tectonic activity. Marine chemistry is mainly influenced by factors such as seafloor expansion rate, hydrothermal circulation at mid-ocean ridges, and carbonate rock sedimentation cycle [61,62]. When the activity of the mid-ocean ridge increases, the input of hydrothermal fluids increases, which may lead to the consumption of magnesium in seawater, resulting in a decrease in the Mg/Ca ratio in seawater. Changes in the rate of seafloor expansion can also alter the volume of the ocean basin. As the expansion rate accelerates, the volume of the mid-ocean ridge increases, leading to shallower ocean basins and rising sea levels. The rise in sea level increases the pressure in deep-sea sedimentary areas, which may inhibit carbonate deposition, reduce calcium consumption, and thus lower the Mg/Ca ratio [63,64].

The CaO content in Member 3 of the Yangzhuang Formation ranges from 15.05% to 23.31%, with an average value of 20.35%. The MgO content ranges from 14.04% to 18.82%, with an average value of 17.16%. The Mg/Ca molar ratio ranges from 1.05 to 1.53, with an average value of 1.18, suggesting that the rate of oceanic expansion during this period was relatively slow. This corresponds to the slow rate of fragmentation of the Columbia supercontinent during a period of the intervals of near-static continental movement around 1500 Ma [65].

The ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values in marine carbonates can be influenced by multiple factors, including sea-level fluctuations, oceanic productivity, redox conditions, terrigenous input, and upwelling rate [66]. The formation of Mesoproterozoic stromatolitic reefs is closely linked to the periodic biological activities of microorganisms such as cyanobacteria. Through photosynthesis, these microbes elevated the ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values of dissolved inorganic carbon in the surrounding waters. Member 3 of the Yangzhuang Formation lacks well-developed stromatolites. The sampled intervals consist of micritic dolostone with an absence of biogenic reefs or microbial mat structures. Consequently, the inorganic carbon isotope values ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ are less influenced by biogenic reef activity and primarily reflect carbon cycling signatures of the shallow marine environment.

The ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values are also linked to hydrothermal activity. Hydrothermal fluids may carry mantle-derived inorganic carbon or light carbon produced by the oxidation of organic matter, leading to locally negative ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ values in carbonate rocks. Since europium (Eu) is scavenged in the seawater from a hydrothermal system [67], hydrothermal activity typically results in positive δEu. However, in Member 3 of the Yangzhuang Formation, δEu values range between 0.9 and 1.15, while only Member 1 exhibits significantly higher positive δEu. This suggests that only samples of Member 1 were likely influenced by hydrothermal activity associated with supercontinental rifting.

During the deposition of Member 3 of the Yangzhuang Formation, the North China Craton remained tectonically quiescent with limited volcanic activity, the depositional basin was distal to volcanic zones [57], and the section lacked upwelling influence. Thus, the ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ of inorganic carbon was likely governed by sea-level fluctuations, terrestrial inputs, redox conditions, and marine productivity, with organic matter production and decomposition ultimately modulating the isotopic signature [9]. Throughout this interval, carbonates were precipitated abundantly only in shallow marine environments [68]. A decline in sea level would enhance terrestrial clastic input, accelerate organic matter decomposition, and drive negative ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ excursions. Concurrently, the lowered sea level could depress the redox interface, where oxygenated waters might further promote organic degradation while stimulating surface organic productivity. These coupled fluctuations in organic production and decomposition ultimately modulated the isotopic composition of inorganic carbon.

In the early stage of Member 3 of the Yangzhuang Formation, terrestrial clastic input exhibited a strong negative correlation with ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$, suggesting that terrigenous material may have dominated as the primary control during this interval. By the late stage of Member 3, however, this correlation weakened significantly (Figure 10a). Concurrently, the redox proxy (U/Th) shifted from a positive correlation to a negative correlation with ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ (Figure 10b), implying a gradual decline in the predominance of surface organic matter decomposition. Integrating these phased correlation patterns, Member 3 likely underwent a gradual shift in marine environmental conditions, characterized by sea-level fluctuations coupled with variations in terrigenous clastic input. This preliminary interpretation requires further investigation to validate.

Sea-level fluctuations, acting as a nexus of multi-factor interactions, may serve as one of the primary drivers of ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ variability. Additionally, climatic and wind-driven processes could also influence ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ fluctuations, though these mechanisms warrant further investigation.

During the sedimentation period of Member 3 of the Yangzhuang Formation, the Mg/Ca ratio maintained a high correlation with the proportion of terrigenous clastics and the sedimentation rate corresponding to geochemistry. A significant mid-phase fluctuation was observed, characterized by slower mid-ocean ridge activity that coincided with an accelerated sedimentation rate during this interval, followed by resumption of previous depositional dynamics. The increased sedimentation rate during this phase corresponded to coeval paleoceanographic fluctuations, indicating hydrodynamic forcing driven by terrestrial input and marine environmental changes. These fluctuations were further modulated by factors such as seafloor spreading rates, mid-ocean ridge hydrothermal activity, and carbonate sedimentation cycles, collectively governing the coupled variations in global climate, marine environment, and marine chemistry [69]. When mid-ocean ridges experienced rapid spreading influenced by the rifting of the Columbia supercontinent, marine transgression prevailed with lower Mg/Ca ratios. The deepening seawater shifted depositional environments offshore, reducing terrigenous clastic input and slowing sedimentation rates. Conversely, decreased mid-ocean ridge spreading rates led to marine regression with elevated Mg/Ca ratios. Shallower waters moved depositional environments shoreward, where enhanced hydrodynamic forces increased material transport, resulting in greater terrigenous clastic supply and accelerated sedimentation rates.

5.2. Milankovitch Cycles

According to the Milankovitch theory, variations in summer solar radiation at high latitudes in the Northern Hemisphere are the primary drivers of the expansion and contraction of ice caps, as well as global climate changes on orbital timescales. This theory is supported by paleoceanographic records and has become a classical model for climate change [70]. Recent studies on the Xiamaling Formation in Jixian section show that the periodic changes in sediment chemistry are also controlled by Milankovitch cycles [71].

In the Milankovitch theory, the characteristic periodic changes in Earth’s orbital parameters include eccentricity, obliquity, and precession. During the Mesoproterozoic Yangzhuang Formation, these astronomical cycles differed significantly from those of the present, corresponding to approximately 90 ka, 24 ka, and 15 ka, respectively [72,73].

The densely spaced 29 samples obtained from a 5-meter-thick, well-exposed dolomite rhythmite within the carbonate shoal facies belt at the top of Member 3 of the Yangzhuang Formation exhibit chromatic rhythm characteristics that may be associated with a coupled interplay of biochemical processes, terrigenous input, climatic fluctuations, and aeolian dynamics. Through ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ analysis of these sequential samples, we aim to decipher the Milankovitch cycle signals recorded in this rhythmic sequence.

This study used a quasi-periodic sampling method based on the rhythmic characteristics of red and gray sedimentary cycles to acquire stratigraphic signals and the Fast Fourier Transform (FFT) method [74] to perform time series analysis of the detrended ${\mathsf{\delta }}^{13}{\mathrm{C}}_{\mathrm{c}\mathrm{a}\mathrm{r}\mathrm{b}}$ series. To satisfy the uniform sampling prerequisite for FFT, linear interpolation was applied at 1 cm intervals. In addition, we have increased the reliability of the interpolation scheme by synchronously using the Lomb–Scargle periodogram method, which is specifically designed to handle non-uniform sequences, while maintaining the original non-uniform sampling data for comparative verification [75]. The experimental results show that the spectral features obtained by the two methods are highly consistent in the main periodic components (Figure 11), which proves that the 1cm interpolation interval can effectively maintain the original sedimentary rhythm information and meet the requirements of FFT analysis for data uniformity.

Using the Fast Fourier Transform method, we find three cycles with periods of 2.2 m, 0.69 m, and 0.40 m (Figure 11), where the 0.40 m cycle is in close agreement with the average period of 0.37 m for the 13 red–gray interbedded rhythmic sequences. The statistical tuning of the correlation coefficient (COCO) method shows that optimal mean sedimentation rates are 2.2–2.5 cm/ka, and the significance level of the null hypothesis of no orbital forcing is less than 0.05 (Figure 11). Therefore, the 0.40 m, 0.69 m, and 2.2 m cycles represent 90 ka eccentricity, 24 ka obliquity, and 15 ka precession, respectively.

The average sedimentation rate after compaction, 2.2–2.5 cm/ka, corresponds to the sedimentation rate calculated by the formula of about 28 m/Ma (Figure 5). Considering that the total thickness of the Yangzhuang Formation in the Jixian section is 707 m, it thus estimated that the Yangzhuang Formation in Jixian spans about 30 ± 2 Ma. The weighted average age of magmatic zircon in the upper tuff in Member 3 of the Gaoyuzhuang Formation was measured in the Yanqing section in Beijing to be approximately 1560 Ma [26], suggesting that the sedimentation duration of the Gaoyuzhuang Formation may fall between 1600 Ma and 1550 Ma [27]. Therefore, the time span of the Yangzhuang Formation could be between 1550 Ma and 1520 ± 2 Ma.

The 0.69 m sedimentary period of intensively sampled in Member 3 of Yangzhuang Formation corresponds to the 24 ka cycle changes in the obliquity, which may lead to the periodic change in the climate system and marine productivity, ultimately reflected in the periodic changes in sedimentary material composition [76]. The 0.40 m sedimentary cycle corresponds to the 15 ka change in precession, which changes the Earth’s climate belt and geographical distribution, thus affecting the regional climate model and the source and transport process of sedimentary materials [77]. The rhythms of red and gray layers in the dense sampling area of the Yangzhuang Formation, the 0.40 m sedimentary cycle, and the 15 ka precessional cycle are highly consistent at that time. Lithofacies analysis shows that the terrigenous clastic materials of red and gray layers are mainly derived from aeolian deposits, and there are certain differences in the transport method, distance, and source area of the wind carrier.

Combined with the regional geological background, the North China Craton was located in the low-latitude area of the northern hemisphere on the edge of the Columbia supercontinent during the deposition period of the Yangzhuang Formation [10,14,78], and the surface aeolian process was much stronger than today. Based on the above evidence, the variation cycle of the material source of the red and gray layers in Member 3 of the Yangzhuang Formation shows that the monsoon cycle caused by the low-latitude solar radiation driven by precession is likely the main controlling factor.

6. Conclusions

During the sedimentation period of Member 3 of the Yangzhuang Formation, the seafloor exhibited a slow wave expansion state, with a mid-phase deceleration fluctuation. When the seafloor expansion decelerates, marine regression occurs, accompanied by an increase in terrigenous clastic input and an accelerated sedimentation rate. This fluctuation corresponds to a third-order sequence dominated by tectonic movements, suggesting that the breakup of the Columbia supercontinent was slow at that time, but with progressive characteristics, likely driven by episodic magmatic activity related to internal Earth processes.

The fluctuations in inorganic carbon isotopes from the rhythmically dense samples in Member 3 of the Yangzhuang Formation correspond to Milankovitch cycles. This allowed for the determination of the average sedimentation rate of the Yangzhuang Formation and a dating range for the formation between approximately 1550 Ma and 1520 ± 2 Ma.

During the sedimentation period of the Yangzhuang Formation, there were periodic changes in material composition and sedimentation rate, corresponding to the 24 ka obliquity cycle. These were likely caused by periodic changes in the climate system and marine productivity. The red–gray layers of the Yangzhuang Formation exhibit systematic differences in material provenance and distinct differences in grain size distribution. The rhythm of these layers corresponds to the 15 ka precessional cycle. The main controlling factor for the rhythmic sedimentation of the red–gray layers is likely the monsoon cycle driven by precession-induced variations in low-latitude solar radiation.