Abstract Sinusichnus Gibert 1996 is recorded for the first time in the Oligocene-Miocene Pirabas Formation of Northern Brazil. In these Oligocene-Miocene carbonate deposits, Sinusichnus sinuosus is characterized by horizontal, highly regular sinusoidal burrow systems with T- and H-shaped branching points. The main difference between the S. sinuosus described herein and other occurrences worldwide is the anomalous diameter of the burrows (4 to 10 cm). These trace fossils occur in organic matter-rich, wackestone/packstone and laminated mudstones interbedded with boundstones deposited in an inner carbonate platform paleoenvironment. The exceptional size of the studied S. sinuosus could have been associated to the producer’s size, which may be attributed to construction by large crustaceans, similar to fossils found within the Pirabas Formation. Also, the sinusoidal morphology and retrusive spreiten could be a result of the fodinichnial/domichnial behavior.

中文翻译：

---

甲壳类动物从亚马逊东部渐新世-中新世碳酸盐矿床中挖洞 Sinusichnus sinuosus

摘要 Sinusichnus Gibert 1996首次在巴西北部渐新世-中新世Pirabas组记录。在这些渐新世-中新世碳酸盐矿床中，Sinusichnus sinuosus 的特征是水平的、高度规则的正弦洞穴系统，具有 T 形和 H 形分支点。此处描述的 S. sinuosus 与世界范围内的其他物种之间的主要区别在于洞穴的异常直径（4 至 10 厘米）。这些痕量化石出现在富含有机质的碎屑岩/灰岩和层状泥岩中，夹层泥岩与沉积在内部碳酸盐台地古环境中的边界岩互层。所研究的 S. sinuosus 的异常大小可能与生产者的大小有关，这可能归因于大型甲壳类动物的构造，类似于在 Pirabas 组中发现的化石。还，