Abstract:
A detailed sedimentological analysis of the Palaeocene Lockhart Limestone has
been conducted to evaluate the depositional environment, diagenetic processes and
hydrocarbon potential of the eastern margin of the Upper Indus Basin. From bottom
to top, there are three microfacies recorded. The lower microfacies, composed of
fine-grained
micrite and some diagenetic dolomite, reflect the low energy and calm
palaeo-current
in the shallower section (1–2
m) of the inner shelf close to shore.
The middle microfacies contain algae that suggest 5–15
m of water depth, especially
along the inner-middle
shelf, but fractured and mixed bioclasts in micrite material
indicate calm to moderately active water close to the wave base. Progressing from
the lower microfacies to the middle microfacies, a gradual shift from orthochem
to allochem components is observed. The top microfacies is dominated by massive
benthic microfossils, indicating moderate energy-water
conditions with normal
salinity. However, the presence of limestone intraclasts surrounded by microspar,
miliolids and nummulites at the top indicates a high-energy
environment with
increasing salinity and water depths from 20 to 130 m. These findings show that the
Lockhart Limestone was deposited in a shallow shelf environment, spanning the
inner-mid
shelf. Diagenetic processes observed include micritisation, cementation,
dissolution, replacement, physical and chemical compaction, and fracture filling by calcite cement. The Lockhart Limestone represents a deepening upward
sequence deposited below the shelf margin system tract and highstand systems
tract in a regressive environment that could reflect good reservoir characteristics,
has the potential to serve as an excellent hydrocarbon reservoir rock, and could be
a primary target for future hydrocarbon exploration.
