Molar-tooth structures (MTS) are enigmatic, micro-crystalline calcite-filled fissures, confined in Proterozoic carbonates. Here we present petrography, carbon isotope, total organic carbon (TOC) and morphological attributes in the context of interpreted palaeoenvironment to understand its development in the Mesoproterozoic carbonates of Lesser Himalaya. Lack of any detrital infill, uniform crystal size and gradational contact with host limestone indicate rapid calcite precipitation in fluid-filled cracks. Reworking of MT as intraclast, folding and offset of MT ribbons supports for early formation before significant lithification. Moderate TOC (0.1–0.9) is possibly due to organic matter preservation under sub-oxic to slightly anoxic/dysoxic conditions. Storm generated bedforms indicate deposition in between fair weather- and storm wave base. Average 1.4‰ depletion of δ¹³C in MT relative to host limestone, presence of relict microbial laminae along the margin of the MT cracks and storm generated bedforms at outcrop scale indicates that the cracks might have formed by the combined effect of degassing of CO₂ generated during the microbial oxidation of organic matter and wave loading by storm. Precipitation of microcrystalline calcite within the cracks may have been triggered by alkalinity generated by the mixing of the outflowing CO₂ with seawater.

1. 1.

   Molar-tooth structures from Mesoproterozoic carbonates, lesser Himalaya.

2. 2.

   Carbon and oxygen isotopic study from the molar-tooth structures.

3. 3.

   Depletion in carbon isotope value in molar-tooth compared to host limestone.

4. 4.

   CO₂ degassing combined with wave loading generated cracks.

5. 5.

   Increased alkalinity due to outflow and mixing promoted precipitation.

臼齿结构（MTS）是密闭的，微晶方解石填充的裂隙，仅局限在元古代碳酸盐中。在这里，我们介绍了解释的古环境背景下的岩相学，碳同位素，总有机碳（TOC）和形态属性，以了解其在小喜马拉雅中元古代碳酸盐岩中的发展。缺少任何碎屑填充物，均匀的晶体尺寸以及与主体石灰石的渐变接触表明在充满流体的裂缝中方解石迅速沉淀。MT的重新加工，如MT的内部破损，折叠和偏移，有助于在明显石化之前及早形成。中等的TOC（0.1-0.9）可能是由于有机物在低氧至轻度缺氧/低氧的条件下保存所致。暴风雨产生的床形表明天气和风暴波基之间存在沉积。δ ¹³在相对于主机石灰石，沿MT裂纹和风暴产生的底形在露头规模的边缘遗微生物薄层的存在MT C表示的是，裂纹可能由CO的脱气的组合效果已形成₂的微生物氧化过程中产生的物质和风暴带来的海浪负荷。裂缝中微晶方解石的沉淀可能是由于流出的CO ₂与海水混合而产生的碱度引起的。

1. 1。

   中小生代碳酸盐碳酸盐的磨牙齿结构。

2. 2。

   从臼齿结构研究碳和氧同位素。

3. 3。

   与主体石灰石相比，臼齿中碳同位素值的减少。

4. 4，

   CO ₂脱气与波浪载荷相结合会产生裂纹。

5. 5，

   由于流出而增加的碱度和混合促进了沉淀。