The Belize Basin in southern Belize, Central America, contains numerous seepage oils derived from marly and carbonate source rocks, but since no definitive source rocks have been identified the source remains uncertain. This study examines by pyrolysis and organic petrography the source rock quality and maturity of 66 samples collected from three newly exposed carbonate sections in the southeastern Belize Basin together with organic geochemical analysis of five new occurrences of seepage oils from the southern Belize Basin. Combined ammonite and aptychi biostratigraphy suggest a Berriasian to Hauterivian age of the source rock samples. Low T values show the samples are thermally immature. Numerous samples are oil-prone and have Hydrogen Index values >300–400 mg HC/g TOC, reaching a maximum of 768 mg HC/g TOC. The samples with source rock potential contain from 32 to 64% pyrolysable organic carbon and contains liptinite-rich Type II kerogen consisting of alginite, bituminite, and liptodetrinite. The calculated Ultimate Expulsion Potential (UEP) of a 22.5 m thick section amounts to ∼2.5 mmboe/km. This generation capacity is volumetrically relatively small, but it could be compensated for by a thicker source rock section. However, the identified source rocks could account for the seepage oils in the Belize Basin, and they are thus the first documentation of Lower Cretaceous source rocks in Belize. A plausible explanation for the widespread occurrence of seepage oils in the Belize Basin could be generation from organic-rich layers with bituminite and alginite. In line with this and previously examined seepage oils, the new variably degraded oils were sourced from carbonate source rock facies.

中文翻译：

---

中美洲伯利兹南部伯利兹盆地下白垩统碳酸盐岩烃源岩和渗流油的质量和成分

中美洲伯利兹南部的伯利兹盆地含有大量来自泥灰岩和碳酸盐烃源岩的渗漏油，但由于尚未确定明确的烃源岩，其来源仍然不确定。本研究通过热解和有机岩相学检查了从伯利兹盆地东南部三个新暴露的碳酸盐岩剖面采集的 66 个样品的烃源岩质量和成熟度，并对伯利兹盆地南部五个新出现的渗漏油进行了有机地球化学分析。组合菊石和阿普蒂奇生物地层学表明烃源岩样本的年龄为贝里亚纪至欧特里夫纪。低 T 值表明样品热不成熟。许多样品都含有石油，氢指数值 >300–400 mg HC/g TOC，最高可达 768 mg HC/g TOC。具有烃源岩潜力的样品含有 32% 至 64% 的可热解有机碳，并含有富含脂褐质的 II 型干酪根，由褐藻岩、烟煤和脂质岩组成。计算得出的 22.5 m 厚截面的极限排出潜力 (UEP) 相当于 ∼2.5 mmboe/km。这种发电能力在体积上相对较小，但可以通过较厚的烃源岩部分来补偿。然而，已确定的烃源岩可以解释伯利兹盆地的渗流石油，因此它们是伯利兹下白垩统烃源岩的第一份记录。伯利兹盆地渗油广泛存在的一个合理解释可能是由含有烟煤和藻岩的富含有机物层产生。与此一致以及之前检查的渗漏油，新的不同降解的油来自碳酸盐源岩相。