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<p>The Abbottabad Formation in northern Pakistan contains early Cambrian dolomitic sequences with considerable varieties of microbialites (stromatolites), but the morphology, petrography, and depositional environments of stromatolites are not well studied. This research aims to fill this gap by analyzing these stromatolites, enhancing the understanding of early microbial carbonate systems and their paleoenvironmental significance in the Sub-Himalayan region. Additionally, it investigates the dolomite succession, highlighting its distinctive features, including the occurrence of both microbialite and dome-shaped stromatolites. A total of seventy dolomite samples were collected from the Muzaffarabad section, from which twenty-five thin sections were prepared and analyzed under a polarized microscope. The sedimentological and petrographic findings indicate that both thin laminated and massive dolomites are associated with stromatolite formation. Morphologically, the studied stromatolites can be categorized into four distinct forms: planar (microbialite), wavy (laterally linked hemispheroids; LLH), columnar, and spheroidal (stacked hemispheroids; SH) stromatolites. The first two forms are characterized by laminated structures (mat), while the latter two develop within thick dolomite beds. The Abbottabad Formation reveals a cycle of retrogradation and progradation, encompassing transgressive surfaces, maximum flooding surfaces, a subaerial unconformity, and minor hiatuses. This formation was deposited in a semi-enclosed carbonate platform environment, which transitioned into a low-energy lagoon. The laminated dolomite was formed in lagoons within subtidal settings, whereas the thicker dolomite deposits developed in supratidal environments.</p>

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Dolomitized stromatolites during regressive-transgressive cycles in the Cambrian Abbottabad Formation, Pakistan: depositional environment, sequence stratigraphic significance, and paleogeographic implications

  • 期刊论文

  • 发表日期：

    2025年10月7日

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  • Syed Kamran Ali,
  • George Kontakiotis,
  • Tariq Mahmood,
  • Muhammad Saleem Mughal,
  • Hammad Tariq Janjuhah,
  • Ahmer Bilal,
  • Evangelia Besiou,
  • Assimina Antonarakou

摘要

The Abbottabad Formation in northern Pakistan contains early Cambrian dolomitic sequences with considerable varieties of microbialites (stromatolites), but the morphology, petrography, and depositional environments of stromatolites are not well studied. This research aims to fill this gap by analyzing these stromatolites, enhancing the understanding of early microbial carbonate systems and their paleoenvironmental significance in the Sub-Himalayan region. Additionally, it investigates the dolomite succession, highlighting its distinctive features, including the occurrence of both microbialite and dome-shaped stromatolites. A total of seventy dolomite samples were collected from the Muzaffarabad section, from which twenty-five thin sections were prepared and analyzed under a polarized microscope. The sedimentological and petrographic findings indicate that both thin laminated and massive dolomites are associated with stromatolite formation. Morphologically, the studied stromatolites can be categorized into four distinct forms: planar (microbialite), wavy (laterally linked hemispheroids; LLH), columnar, and spheroidal (stacked hemispheroids; SH) stromatolites. The first two forms are characterized by laminated structures (mat), while the latter two develop within thick dolomite beds. The Abbottabad Formation reveals a cycle of retrogradation and progradation, encompassing transgressive surfaces, maximum flooding surfaces, a subaerial unconformity, and minor hiatuses. This formation was deposited in a semi-enclosed carbonate platform environment, which transitioned into a low-energy lagoon. The laminated dolomite was formed in lagoons within subtidal settings, whereas the thicker dolomite deposits developed in supratidal environments.