Patch reefs and their surrounding skeletal–peloidal–intraclast grainstone facies are very abundant on modern (sub-) tropical carbonate platforms. Compared to the barrier and fringing reef facies, the processes influencing composition, mineralogy, and stable-isotope record of peri-reefal sediment have received much less attention, despite a potentially significant volume of such sediment in many Phanerozoic carbonate platforms. To better understand the evolution and sedimentary record of patch-reef settings, this study investigates the patch-reef biota (scuba diving surveys) and composition (petrography), mineralogy (X-ray diffraction) and stable-isotope record (mass spectrometry) of peri-reefal sediments at East Beach on the northeastern, windward margin of San Salvador Island, the Bahamas. The macroalgae-dominated ecology is assessed, and a decadal decline in stony coral coverage with a shift to more opportunistic, stress-tolerant species is documented. The most common stony corals on these shallow-water (3–5 m) patch reefs are Diploria strigosa, Porites astreoides, and P. porites, and Halimeda lacrimosa dominates among green algae. Peri-reefal sediment is pure carbonate sand composed of roughly equal volumes of aragonite and high-Mg calcite (HMC), with mean MgCO3 content in HMC of 15.2%. The bulk-sediment isotope record shows very limited variation (δ13C between + 2.3‰ and + 3.2‰, and δ18O between − 0.8‰ and − 0.6‰) and this is consistent with similar modern settings. A lack of very fine particles and an abundance of intraclasts suggest that the environment is strongly influenced by bio- and physical erosion. Fast-growing algae have likely reached an abundance beyond the grazing capacity, which has drastically reduced the space for coral settlement and recruitment, and thus has compromised the patch-reef resilience in this part of the Bahamian Archipelago.

中文翻译：

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退化的迎风斑块礁和影响珊瑚礁周围沉积物组成、矿物学和稳定同位素记录的过程，圣萨尔瓦多岛，巴哈马

在现代（亚）热带碳酸盐台地上，斑块礁及其周围的骨架-球状-碎屑内颗粒岩相非常丰富。与屏障和边缘礁相相比，影响珊瑚礁周围沉积物的成分、矿物学和稳定同位素记录的过程受到的关注要少得多，尽管许多显生宙碳酸盐平台中可能存在大量此类沉积物。为了更好地了解斑块礁环境的演化和沉积记录，本研究调查斑块礁生物群（水肺潜水调查）和组成（岩相学）、矿物学（X 射线衍射）和稳定同位素记录（质谱）位于巴哈马圣萨尔瓦多岛东北向风边缘东海滩的珊瑚礁周围沉积物。评估以大型藻类为主的生态，并且记录了石珊瑚覆盖率的十年下降，并转向更具机会主义，耐压力的物种。这些浅水 (3-5 m) 斑块礁上最常见的石珊瑚是 Diploria strigosa、Porites asstreoides 和 P. porites，而 Halimeda lacrimosa 在绿藻中占主导地位。珊瑚礁周围沉积物是由大致相等体积的文石和高镁方解石 (HMC) 组成的纯碳酸盐砂，HMC 中的平均 MgCO3 含量为 15.2%。大块沉积物同位素记录显示的变化非常有限（δ13C 在 + 2.3‰ 和 + 3.2‰ 之间，δ18O 在 − 0.8‰ 和 − 0.6‰ 之间），这与类似的现代环境一致。缺乏非常细小的颗粒和大量的碎屑表明环境受到生物和物理侵蚀的强烈影响。