Abstract

The upper Turonian–Maastrichtian Kawagarh Formation represents a thick sequence of carbonates in the Kalachitta Range, Pakistan and it is the only stratigraphic record of Late Cretaceous sedimentation in northwestern Lesser Himalayas. Global sea-level marks a gradual fall of ∼40 to 50 m during the deposition of the Kawagarh Formation. This study is based on detailed outcrop and petrographic investigations of six stratigraphic sections exposed in Kalachitta Range. Carbonate grains are dominantly composed of pelecypods, oysters, trigonia and plankton distributed in a micritic groundmass. Five microfacies, (1) Planktonic Mudstone, Wackestone and Packstone Microfacies, (2) Pelecypodic Planktonic Mudstone and Wackestone Microfacies, (3) Pelecypodic Wackestone and Packstone Microfacies, (4) Marl Microfacies and (5) Dolostone Microfacies, were identified using distribution of faunal types and matrix. Based on faunal paleoecology, microfacies analysis and sedimentary structures, a shallow open-marine, northward-dipping ramp model has been proposed for the deposition of the Kawagarh Formation beginning with a transgressive cycle, which also corresponds to global sea-level rise, and possibly terminated by uplift owing to initial collision of the Indian Plate with the Kohistan-Ladakh Arc at the end of the Cretaceous.

1. KEYPOINTS

2. Paleontological and paleoecological evidence is used to develop a shallow, open-marine ramp deposition model for the Kawagarh Formation.

3. The initiation of Kawagarh sedimentation with transgression in the late Turonian synchronise with global sea-level curve. Sedimentation was terminated by initial collision of the Indian Plate with the Kohistan-Ladakh Arc.

摘要

上Turonian-Maastrichtian Kawagarh组代表了巴基斯坦Kalachitta山脉的一个厚碳酸盐层序，它是小喜马拉雅山西北部晚白垩世沉积的唯一地层记录。在 Kawagarh 组沉积期间，全球海平面标志着约 40 至 50 m 的逐渐下降。本研究基于对卡拉奇塔山脉出露的六个地层剖面的详细露头和岩石学调查。碳酸盐颗粒主要由分布在泥晶基质中的鳞足类、牡蛎、三角藻和浮游生物组成。五种微相，(1) 浮游泥岩、泥灰岩和泥灰岩微相，(2) 远足浮游泥岩和泥灰岩微相，(3) 远足泥岩和泥灰岩微相，(4) 泥灰岩微相和 (5) 白云岩微相，使用动物群类型和矩阵的分布来识别。基于动物群古生态学、微相分析和沉积结构，提出了一个浅海、北倾斜坡模型，用于以海进旋回开始的 Kawagarh 组沉积，这也对应于全球海平面上升，并可能由于白垩纪末印度板块与科希斯坦-拉达克弧的初始碰撞而被隆起终止。

1. 关键点

2. 古生物学和古生态学证据用于为 Kawagarh 组开发浅层、开阔的海洋斜坡沉积模型。

3. 土伦晚期 Kawagarh 沉积与海侵的开始与全球海平面曲线同步。沉积因印度板块与科希斯坦-拉达克弧的最初碰撞而终止。